System and method for monitoring performance of air filter

Abstract

A system includes a device including a substrate, a resistor disposed on the substrate, and a thermistor disposed on the substrate and thermally coupled to the resistor. The system further includes a control unit including a power source and a controller. The controller is communicably coupled to the resistor and the power source. The controller is configured to: supply, via the power source, electrical power to the resistor for a time period extending from a first time instance to a second time instance; determine, via the thermistor, a variation of the temperature of the resistor during the time period; and determine an airflow speed based on the variation of the temperature of the resistor in the time period. The system may further include an air filter proximal to which the device may be disposed. The controller may be further configured to determine a filter parameter based on the airflow speed.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to a system and a method for monitoring a performance of an air filter.BACKGROUND

[0002] Various applications may require measurement and monitoring of an airflow speed. For example, a smart heating, ventilation, and air conditioning (HVAC) system may monitor an airflow speed through an air filter to predict or estimate the remaining life of the air filter. However, conventional systems and methods for measuring the airflow speed may be complex, non-versatile, energy inefficient, and inaccurate under a variety of operational conditions. Further, conventional systems and methods for monitoring a performance of an air filter may be unreliable.SUMMARY

[0003] In a first aspect, the present disclosure provides a system for monitoring a performance of an air filter. The system includes a device. The device includes a substrate. The device further includes at least one resistor disposed on the substrate. The device further includes at least one thermistor disposed on the substrate and thermally coupled to the at least one resistor. The system further includes a control unit. The control unit includes a power source electrically connected to the at least one resistor and configured to supply electrical power to the at least one resistor. The control unit further includes a controller communicably coupled to the at least one thermistor and the power source. The controller is configured to supply, via the power source, the electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance. The controller is further configured to determine, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period. The controller is further configured to determine an airflow speed based on the variation of the temperature of the at least one resistor in the time period.

[0004] In a second aspect, the present disclosure provides a method for monitoring a performance of an air filter. The method includes providing a device. The device includes a substrate. The device further includes at least one resistor disposed on the substrate. The device further includes at least one thermistor disposed on the substrate and thermally coupled to the at least one resistor. The method further includes supplying, via a power source, electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance. The method further includes determining, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period. The method further includes a determining an airflow speed based on the variation of the temperature of the at least one resistor in the time period.

[0005] The details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Exemplary embodiments disclosed herein may be more completely understood in consideration of the following detailed description in connection with the following figures. The figures are not necessarily drawn to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

[0007] FIG. 1 is a schematic diagram of a system for monitoring a performance of an air filter according to an embodiment of the present disclosure;

[0008] FIG. 2 is a graph depicting a variation of a temperature of a resistor with respect to time according to an embodiment of the present disclosure;

[0009] FIG. 3 is a schematic circuit diagram of the system according to an embodiment of the present disclosure;

[0010] FIG. 4 is a schematic perspective view of a fixture according to an embodiment of the present disclosure;

[0011] FIG. 5A is a schematic rear perspective view of the system according to an embodiment of the present disclosure;

[0012] FIG. 5B is a schematic front perspective view of the system of FIG. 5A according to an embodiment of the present disclosure;

[0013] FIG. 6 is a schematic perspective view of the system according to another embodiment of the present disclosure;

[0014] FIG. 7 is a flowchart depicting various steps of a method for monitoring a performance of an air filter according to an embodiment of the present disclosure;

[0015] FIG. 8 is a graph depicting variations of a temperature of a resistor and a voltage supplied across the resistor with respect to time; and

[0016] FIG. 9 is a graph depicting a variation of temperature differential of the resistor with respect to an airflow speed.DETAILED DESCRIPTION

[0017] In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

[0018] In the following disclosure, the following definitions are adopted.

[0019] As recited herein, all numbers should be considered modified by the term “about.” As used herein, “a,”“an,”“the,”“at least one,” and “one or more” are used interchangeably.

[0020] As used herein as a modifier to a property or attribute, the term “generally,” unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within + / −20% for quantifiable properties).

[0021] The term “substantially,” unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / −10% for quantifiable properties) but again without requiring absolute precision or a perfect match.

[0022] The term “about,” unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / −5% for quantifiable properties) but again without requiring absolute precision or a perfect match.

[0023] Terms such as same, equal, uniform, constant, strictly, and the like, are understood to be within the usual tolerances or measuring error applicable to the particular circumstance rather than requiring absolute precision or a perfect match.

[0024] As used herein, the terms “first” and “second” are used as identifiers. Therefore, such terms should not be construed as limiting of this disclosure. The terms “first” and “second” when used in conjunction with a feature or an element can be interchanged throughout the embodiments of this disclosure.

[0025] As used herein, when a first material is termed as “similar” to a second material, at least 90 weight % of the first and second materials are identical and any variation between the first and second materials includes less than about 10 weight % of each of the first and second materials.

[0026] As used herein, “at least one of A and B” should be understood to mean “only A, only B, or both A and B.”

[0027] Unless specified or limited otherwise, the terms “attached,”“connected,”“coupled,” and variations thereof, are used broadly and encompass both direct and indirect attachments, connections, and couplings.

[0028] As used herein, the term “configured to” is at least as restrictive as the term “adapted to” and requires actual design intention to perform the specified function rather than mere physical capability of performing such a function.

[0029] As used herein, the term “battery” refers to a device including one or more electrochemical cells that convert stored chemical energy into electrical energy. Examples of battery include primary batteries (non-rechargeable) and secondary batteries (rechargeable), such as Lithium-ion (Li-ion), Nickel Cadmium (Ni—Cd), Nickel-Metal Hydride (Ni-MH), and Lead-Acid. Batteries may have any shape, such as a coin, a button, a sheet, a cylinder, a prism, and so forth.

[0030] The present disclosure relates to a system for monitoring a performance of an air filter. The system includes a device. The device includes a substrate. The device further includes at least one resistor disposed on the substrate. The device further includes at least one thermistor disposed on the substrate and thermally coupled to the at least one resistor. The system further includes a control unit. The control unit includes a power source electrically connected to the at least one resistor and configured to supply electrical power to the at least one resistor. The control unit further includes a controller communicably coupled to the at least one thermistor and the power source. The controller is configured to supply, via the power source, the electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance. The controller is further configured to determine, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period. The controller is further configured to determine an airflow speed based on the variation of the temperature of the at least one resistor in the time period.

[0031] The system may function as a compact, low-cost, low-power consuming, and physically robust airflow sensor which may be sufficiently accurate under a variety of operational conditions. For example, the system may be suitable for operation over a temperature range of from 0 degrees Celsius (° C.) to 60° C. The device of the system may have low thermal loss via natural convection, thermal conduction, and radiation, while having high thermal loss via forced convection (e.g., airflow) to improve measurement of the airflow speed. The device may be positioned in a path of an airflow to measure the airflow speed using the system.

[0032] In some examples, the system may further include an electrical circuit connected with the controller for improving the accuracy of measurement of a resistance of the thermistor. Specifically, the system may utilize switches and a resistor network for improving the accuracy of measurement of a resistance of the thermistor over a wide range of temperatures.

[0033] The system may be suitable for implementation in heating, ventilation, and air conditioning (HVAC) systems. In some examples, the system may be used to determine a clogging level of an air filter of the HVAC systems. In other words, the system may be used to determine the remaining life of the air filter. Specifically, the system may monitor the performance of the air filter by determining a filter parameter (e.g., the clogging level or loading level) associated with the air filter based at least on the airflow speed. In some examples, the system may employ additional pressure and temperature sensors to determine the filter parameter associated with the air filter.

[0034] The system may facilitate timely maintenance and replacement of the air filter based on the filter parameter rather than predetermined schedules. The system may also aid in preventing premature disposal of the air filter (i.e., when the air filter is capable of effectively filtering air). This may reduce operational costs.

[0035] Referring now to the figures, FIG. 1 illustrates a schematic diagram of a system 100 for monitoring a performance of an air filter according to an embodiment of the present disclosure.

[0036] The system 100 includes a device 110. The device 110 is partially shown in FIG. 1. The device 110 includes a substrate 112. The device 110 further includes at least one resistor 114 (hereinafter also referred to as “the resistor 114”) disposed on the substrate 112. The device 110 further includes at least one thermistor 122 (hereinafter also referred to as “the thermistor 122”) disposed on the substrate 112. The thermistor 122 is thermally coupled to the resistor 114.

[0037] The resistor 114 may function as a heating element. Specifically, the resistor 114 may heat up in response to being subjected to electrical power. The resistor 114 may be selected based on desired application attributes. As an example, the resistor 114 may have a resistance of 1 kiloohm. It may be noted that the resistance of the resistor 114 may vary upon desired application attributes.

[0038] The thermistor 122 may function as a temperature sensor that senses a temperature of the resistor 114. The thermistor 122 may be thermally coupled to the resistor 114 using any suitable technique, such that the thermistor 122 is able to sense the temperature of the resistor 114. For example, the thermistor 122 may be thermally coupled to the resistor 114 via a thermally conductive material. The thermistor 122 may be selected based on desired application attributes. The temperature of the resistor 114 may be determined based on a change in a resistance of the thermistor 122. In some embodiments, the thermistor 122 includes a negative temperature coefficient thermistor. In such embodiments, the resistance of the thermistor 122 may decrease with an increase in the temperature of the resistor 114.

[0039] The substrate 112 may extend along a longitudinal axis 113 and have a length along the longitudinal axis 113. The substrate 112 may have a width 112W perpendicular to the longitudinal axis 113. The width 112W may be less than the length of the substrate 112. In some embodiments, the length of the substrate 112 may be greater than 1 centimeter (cm) and less than 20 cm. In some embodiments, the width 112W of the substrate 112 may be less than 5 cm, less than 4 cm, less than 3 cm, or less than 2 cm.

[0040] The substrate 112 may be configured to reduce or minimize absorption of heat from the resistor 114. Specifically, the substrate 112 may have a low thermal conductivity, or in other words, a high thermal resistance. Accordingly, the substrate 112 may be made from any suitable material having a high thermal resistance. For example, the substrate 112 may be made from polyimide.

[0041] In some embodiments, the substrate 112 may be flexible. In such embodiments, the device 110 may be configured as a flex circuit. The thermistor 122 and the resistor 114 may be thermally coupled to each other via an interconnecting trace 115 with associated solder fillets. In some embodiments, the substrate 112 may include polyimide. The substrate 112 including polyimide may have high flexibility and high thermal resistance. In some embodiments, the device 110 may further include a plurality of resistor electrical traces 116 disposed on the substrate 112. The plurality of resistor electrical traces 116 may be electrically connected to the resistor 114. The device 110 may further include a plurality of thermistor electrical traces 124 disposed on the substrate 112. The plurality of thermistor electrical traces 124 may be electrically connected to the thermistor 122. The plurality of resistor electrical traces 116 and the plurality of thermistor electrical traces 124 may be made from copper, for example.

[0042] The device 110 may have a simple, compact, physically robust, and low-cost construction. The device 110 may have low thermal loss via natural convection, thermal conduction, and radiation, while having high thermal loss via forced convection (e.g., airflow) to improve measurement of the airflow speed.

[0043] The system 100 further includes a control unit 130. The control unit 130 includes a power source 132 and a controller 134. The power source132 is electrically connected to the resistor 114. The power source 132 is configured to supply electrical power to the resistor 114. In some embodiments, the power source 132 may include a battery. The battery may be of any suitable type, such as a button battery, for example.

[0044] The controller 134 is communicably coupled to the thermistor 122 and the power source 132. The controller 134 may include one or more integrated circuits, which can be programmed to perform various functions, as will be described in detail below. The controller 134 may include one or more microcomputers, processors, application-specific integrated circuits, or any other suitable programmable circuit or combination of circuits. The controller 134 may include both hardware and software components, and the term “controller” is meant to broadly encompass the combination of such components. In some examples, the processor of the controller 134 may be remote from the device 110 (e.g., on a remote server, a cloud server, a hub, etc.) and communicably coupled to other components of the controller 134 via a wireless connection.

[0045] FIG. 2 illustrates a graph 30 depicting a variation of the temperature of the resistor 114 with respect to time according to an embodiment of the present disclosure. The graph 30 includes a temperature curve 32 representing the variation of the temperature of the resistor 114 with respect to time.

[0046] Referring to FIGS. 1 and 2, the controller 134 is configured to supply, via the power source 132, the electrical power to the resistor 114 for a time period TP extending from a first time instance T1 to a second time instance T2, such that the temperature of the resistor 114 at the second time instance T2 is greater than the temperature of the resistor 114 at the first time instance T1.

[0047] In other words, the electrical power supplied to the resistor 114 during the time period TP may raise the temperature of the resistor 114. As depicted by the temperature curve 32, the temperature of the resistor 114 may rise from a first temperature TM1 at the first time instance T1 to a second temperature TM2 at the second time instance T2. The second temperature TM2 is greater than the first temperature TM1. In some cases, the first temperature TM1 may correspond to an ambient temperature.

[0048] The time period TP may be selected depending upon desired accuracy and power consumption of the system 100. The time period TP being longer may increase the accuracy of determining the airflow speed while increasing the power consumption from the power source 132. In some embodiments, the time period TP is from 1 second to 10 seconds. In some embodiments, the time period TP may be from 3 seconds to 8 seconds. In some embodiments, the time period TP may be about 5 seconds. The time period TP being from 1 second to 10 seconds may provide a good balance between the accuracy of determining the airflow speed and the power consumption.

[0049] In some embodiments, supplying the electrical power to the resistor 114 via the power source 132 includes applying a constant voltage across the resistor 114. As an example, the controller 134 may be configured to supply, via the power source 132, a constant voltage (e.g., 3 volts) across the resistor 114 during the time period TP.

[0050] The controller 134 is further configured to determine, via the thermistor 122, the variation of the temperature of the resistor 114 during the time period TP. In some embodiments, the variation of the temperature of the resistor 114 during the time period TP may correspond to a temperature differential between the first temperature TM1 and the second temperature TM2 or the temperature curve 32.

[0051] The controller 134 is further configured to determine the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP. In other words, the controller 134 may determine the airflow speed based on a rise in the temperature of the resistor 114 during the time period TP. Assuming the first temperature TM1 as constant, a higher airflow speed may correspond to a smaller rise in the temperature of the resistor 114.

[0052] As discussed above, the processor of the controller 134 may be remote from the device 110. In some embodiments, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP may be performed remotely from the device 110. For example, the processor of the controller 134 may perform remote calculations (e.g., in the cloud) from the raw data collected from the various components of the device by the controller 134.

[0053] The system 100 may function as a compact, low-cost, low-power consuming, and physically robust airflow sensor which may be sufficiently accurate under a variety of operational conditions. For example, the system 100 may be suitable for operation over a temperature range of from 0 degrees Celsius (° C.) to 60° C.

[0054] The device 110 may be positioned in a path of the airflow to measure the airflow speed using the system 100. Specifically, the device 110 may be positioned in the path of the airflow, such that the resistor 114 receives the airflow. The system 100 may be suitable for implementation in heating, ventilation, and air conditioning (HVAC) systems. In some examples, the system 100 may be used to determine a clogging level of an air filter of the HVAC systems. In other words, the system 100 may be used to determine the remaining life of the air filter.

[0055] In some embodiments, determining the variation of the temperature of the resistor 114 during the time period TP via the thermistor 122 includes determining, via the thermistor 122, the first temperature TM1 of the resistor 114 at the first time instance TM1. In some embodiments, determining the variation of the temperature of the resistor 114 during the time period TP via the thermistor 122 further includes determining, via the thermistor 122, the second temperature TM2 of the resistor 114 at the second time instance T2. In some embodiments, determining the variation of the temperature of the resistor 114 during the time period TP via the thermistor 122 further includes determining a temperature differential TD between the first temperature TM1 and the second temperature TM2. The temperature differential TD may be defined as a difference between the second temperature TM2 and the first temperature TM1. In some embodiments, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP includes determining the airflow speed based on the temperature differential TD. For example, the system 100 may utilize a set of temperature differential vs. airflow speed curves to determine the airflow speed based on the temperature differential TD.

[0056] In some other embodiments, determining the variation of the temperature of the resistor 114 during the time period TP via the thermistor 122 includes determining, via the thermistor 122, the temperature curve 32 representing the variation of the temperature of the resistor 114 during the time period TM. In some embodiments, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP includes determining the airflow speed based on the temperature curve 32. In such embodiments, the controller 134 may determine the airflow speed based on a plurality of temperatures points of the temperature curve 32. This may further improve the accuracy of measurement of the airflow speed.

[0057] FIG. 3 illustrates a schematic circuit diagram of the system 100 according to an embodiment of the present disclosure.

[0058] The controller 134 may include a first input port 136 configured to receive a first signal and a second input port 137 configured to receive a second signal. Each of the first signal and the second signal may be an analog signal. The controller 134 may be configured to measure a voltage difference between the first signal and the second signal. The controller 134 may further include an output port 138 configured to be connected to the resistor 114. The controller 134 may be configured to apply a voltage across the resistor 114 through the output port 138.

[0059] The system 100 may further include an electrical circuit 10. The electrical circuit 10 may include the resistor 114 and the thermistor 122. The thermistor 122 may be connected in parallel with the resistor 114. The electrical circuit 10 may further include at least one first circuit resistor 12 (hereinafter also referred to as “the first circuit resistor 12”) connected in series with the thermistor 122. The electrical circuit 10 may further include a first circuit node 22 disposed between the thermistor 122 and the first circuit resistor 12. The first circuit node 22 may be configured to be connected to the first input port 136 of the controller 134.

[0060] The electrical circuit 10 may further include at least one second circuit resistor 14 (hereinafter also referred to as “the second circuit resistor 14”) connected in parallel with the thermistor 122 and the first circuit resistor 12. The electrical circuit 10 may further include at least one third circuit resistor 16 (hereinafter also referred to as “the third circuit resistor 16”) connected in series with the second circuit resistor 14. The electrical circuit 10 may further include a second circuit node 24 disposed between the second circuit resistor 14 and the third circuit resistor 16. The second circuit node 24 may be configured to be connected to the second input port 137 of the controller 134.

[0061] The electrical circuit 10 may further include a first connection node 26 and a second connection node 28. The second circuit resistor 14 may be disposed between the second circuit node 24 and the first connection node 26. Further, the third circuit resistor 16 may be disposed between the second circuit node 24 and the second connection node 28.

[0062] The controller 134 may further include at least one first controller resistor 142 (hereinafter also referred to as “the first controller resistor 142”) and at least one second controller resistor 144 (hereinafter also referred to as “the second controller resistor 144”) connected in series with the first controller resistor 142. The controller 134 may further include a controller node 146 disposed between the first controller resistor 142 and the second controller resistor 144. The controller node 146 may be configured to be connected to the second circuit node 24.

[0063] The controller 134 may further include a first switch 148 connected in series with the first controller resistor 142. The first switch 148 may be configured to be connected between the controller node 146 and the first connection node 26. The controller 134 may further include a second switch 152 connected in series with the second controller resistor 144. The second switch 152 may be configured to be connected between the controller node 146 and the second connection node 28. The controller 134 may be further configured to selectively operate each of the first switch 148 and the second switch 152. This may allow the controller 134 to control the voltage of the second signal in response to changes in the ambient temperature.

[0064] For example, in operation, the controller 134 may apply a voltage VDD across the resistor 114 through the output port 138 for the time period TP (shown in FIG. 2). The controller 134 may receive the first signal from the first circuit node 22 and the second signal from the second circuit node 24 to measure the resistance of the thermistor 122. The first circuit resistor 12 and the second circuit resistor 14 may each have a resistance approximately equal to that of the thermistor 122 under normal ambient temperatures (e.g., 25° C.). The controller 134 may open the first switch 148 and the second switch 152, thereby bypassing the first controller resistor 142 and the second controller resistor 144. This may form a voltage divider that gives a value of the voltage at the second circuit node 24 equal to VDD / 2. Small changes to the value of the resistance of the thermistor 122 may be measured when the voltage at the first circuit node 22 is near VDD / 2 (i.e., the value of the resistance of the thermistor 122 is near that of the first circuit resistor 12). However, in instances where an increase in the temperature of the resistor 114 causes the value of the resistance of the thermistor 122 to become less than that of the first circuit resistor 12, or a decrease in the temperature of the resistor 114 causes the value of the resistance of the thermistor 122 to become greater than that of the first circuit resistor 12, the first switch 148 and / or the second switch 152 may be closed, which in turn may form a voltage divider including the second circuit resistor 14, the third circuit resistor 16, the first controller resistor 142, and the second controller resistor 144. This may enable the ability to shift the voltage at the second circuit node 24 down or up, as needed.

[0065] In some embodiments, the electrical circuit 10 may further include the power source 132 and a voltage regulator 135. In some other embodiments, the controller 134 may include the voltage regulator 135. In other words, the voltage regulator 135 may be a built-in regulator of the controller 134. In such embodiments, the power source 132 may be connected directly to the controller 134.

[0066] FIG. 4 illustrates a schematic perspective view of a fixture 160 according to an embodiment of the present disclosure.

[0067] In some embodiments, the system 100 (shown in FIG. 1) may further include the fixture 160. The fixture 160 may be configured to support the device 110. The fixture 160 may provide physical protection to the device 110.

[0068] The fixture 160 may include a through aperture 168. The resistor 114 may be positioned at the through aperture 168. During use, the fixture 160 supporting the device 110 may be positioned in a path of the airflow to measure the airflow speed, such that the resistor 114 is exposed to or receives the airflow.

[0069] In some embodiments, the through aperture 168 may be circular. The through aperture 168 may have a diameter 168D. The diameter 168D may be at least three times greater than the width 112W (shown in FIG. 1) of the substrate 112. This may allow efficient thermal interaction of the airflow with the resistor 114.

[0070] In the illustrated embodiment of FIG. 4, the fixture 160 further includes a base 162 and an elongate member 164 extending from the base 162. The fixture 160 further includes a head 166 connected to the elongate member 164 and spaced apart from the base 162. The through aperture 168 is disposed on the head 166.

[0071] FIGS. 6A and 6B illustrate perspective views of the system 100 according to an embodiment of the present disclosure.

[0072] The system 100 may further include a printed circuit board 170. The control unit 130 may be disposed on the printed circuit board 170. Specifically, the power source 132 and the controller 134 may be disposed on the printed circuit board 170.

[0073] The printed circuit board 170 may form the fixture 160. Specifically, the printed circuit board 170 may include the aperture 168 and support the device 110. The printed circuit board 170 may further include an interface 175. The interface 175 may be configured to physically support the device 110 and electrically connect various components of the device 110 to the control unit 130. The resistor 114 may be electrically coupled to the power source 132 via the interface 175. Further, the thermistor 122 may be communicably coupled to the controller 134 via the interface 175. The interface 175 may support the device 110 such that the resistor 114 is positioned at the through aperture 168.

[0074] FIG. 6 illustrates a perspective view of the system 100 according to another embodiment of the present disclosure.

[0075] The system 100 may further include an air filter 70. As used herein, the term “air filter” refers to filter media configured to filter air. Filter media may be of any suitable type, for example, pleated or unpleated. The air filter 70 defines an upstream side and a downstream side. The downstream side refers to the side of the air filter 70 to which air flows. That is, the downstream side receives filtered air through the air filter 70. The upstream side is opposite to the downstream side and refers to the side of the air filter 70 from which air flows.

[0076] In some embodiments, the system 100 may further include a filter frame 80 that houses the air filter 70. In some embodiments, the air filter 70 may be replaceable and the filter frame 80 may allow replacement of the air filter 70.

[0077] The device 110 may be disposed proximal to the air filter 70. In some embodiments, the device 110 may be disposed upstream of the air filter 70. In some embodiments, the device 110 may be disposed downstream of the air filter 70. In some embodiments, the device 110 may be disposed on the air filter 70. In some embodiments, the device 110 may be disposed on the filter frame 80.

[0078] The controller 134 may be further configured to determine a filter parameter associated with the air filter 70 based at least on the airflow speed. In some embodiments, the filter parameter includes a clogging level of the air filter 70. The clogging level of the air filter 70 may also be referred to as a “loading level” of the air filter 70.

[0079] In some embodiments, the system 100 may further include a pressure sensor 180 disposed proximal to the air filter 70 and communicably coupled to the controller 134. In some embodiments, the pressure sensor 180 may be disposed upstream of the air filter 70. In some embodiments, the pressure sensor 180 may be disposed downstream of the air filter 70. In some embodiments, the pressure sensor 180 may be disposed on the air filter 70. In some embodiments, the pressure sensor 180 may be disposed on the filter frame 80. In some embodiments, the pressure sensor 180 may be an absolute pressure sensor.

[0080] The controller 134 may be further configured to determine, via the pressure sensor 180, a pressure. The filter parameter associated with the air filter 70 may be determined further based on the pressure. Specifically, in some embodiments, the controller 134 may be configured to determine the filter parameter associated with the air filter 70 based on the airflow speed and the pressure. The filter parameter determined based on the airflow speed and the pressure may be more accurate than the filter parameter determined solely based on the airflow speed.

[0081] In some embodiments, the system 100 may further include a temperature sensor 190 disposed proximal to the air filter 70 and communicably coupled to the controller 134. In some embodiments, the temperature sensor 190 may be disposed upstream of the air filter 70. In some embodiments, the temperature sensor 190 may be disposed downstream of the air filter 70. In some embodiments, the temperature sensor 190 may be disposed on the air filter 70. In some embodiments, the temperature sensor 190 may be disposed on the filter frame 80.

[0082] The controller 134 may be further configured to determine, via the temperature sensor 190, a temperature. The filter parameter associated with the air filter 70 may be determined further based on the temperature. Specifically, in some embodiments, the controller 134 may be configured to determine the filter parameter associated with the air filter 70 based on the airflow speed, the pressure, and the temperature.

[0083] In some embodiments, the device 110, the pressure sensor 180, and the temperature sensor 190 may be positioned downstream of the air filter 70 on a face of the air filter 70 or at least partially inside a valley defined between two adjacent pleats of the air filter 70. Alternatively, the device 110, the pressure sensor 180, and the temperature sensor 190 may be disposed on the filter frame 80. In some embodiments, the system 100 may further include a sensor housing 85 configured to be mounted to the filter frame 80. In some embodiments, the sensor housing 85 may be mounted to the filter frame 80 downstream of the air filter 70. In some embodiments, the filter frame 80 may include one or more mounting features 82 that allow mounting of the sensor housing 85 to the filter frame 80. The device 110, the pressure sensor 180, and the temperature sensor 190 may be coupled to the sensor housing 85. In some embodiments, the control unit 130 may be coupled to the sensor housing 85. In some embodiments, the pressure sensor 180 and the temperature sensor 190 may be powered by the power source 132.

[0084] In some embodiments, the controller 134 may be configured to monitor a change in the airflow speed to determine the filter parameter associated with the air filter 70. It may be noted that airflow speed determined by the controller 134 may or may not directly match, for example, a bulk velocity in the center of an HVAC duct, as the airflow speed determined using the device 110 may be influenced based on its arrangement relative to the filter frame 80, the air filter 70, and various other structures associated with the device 110. However, the airflow speed associated with the air filter 70 determined via the device 110 may be sufficient for determining the filter parameter (e.g., the clogging level associated with the air filter 70).

[0085] In some embodiments, the controller 134 may be configured to monitor a change in the airflow speed and the pressure to determine the filter parameter associated with the air filter 70. In some embodiments, the controller 134 may be configured to monitor a change in the airflow speed, the pressure, and the temperature to determine the filter parameter associated with the air filter 70. The controller 134 may combine the airflow speed with at least one of the pressure and the temperature to determine the filter parameter associated with the air filter 70.

[0086] In some embodiments, the controller 134 may be further configured to be communicably coupled to a terminal device 195. The controller 134 may be further configured to communicate the filter parameter associated with the air filter 70 to the terminal device 195.

[0087] As used herein, the term “terminal device” refers to any terminal device capable of wireless communications (e.g., with each other, with a controller, or with a remote server). The communications may involve transmitting and / or receiving wireless signals using electromagnetic signals, radio waves, infrared signals, and / or other types of signals suitable for conveying information over air.

[0088] In some embodiments, the terminal device 195 may be a mobile terminal. As used herein, the term “mobile terminal” may include a cellular or mobile telephone; a smart phone which may combine a cellular telephone with data processing capabilities, Internet / Intranet access, Web browser, organizer, calendar and / or a global positioning system (GPS) receiver; a consumer electronics device or other appliance that includes telephone transceiver (e.g., VOIP) capabilities; or another type of hand-held computational or communication device.

[0089] In some embodiments, the controller 134 may employ at least one of Bluetooth communication and Wi-Fi communication to directly communicate the filter parameter associated with the air filter 70 to the terminal device 195. In some other embodiments, the controller 134 may be configured to indirectly communicate (such as through web servers, etc.) the filter parameter associated with the air filter 70 to the terminal device 195. A user may conveniently inspect the filter parameter via the terminal device 195.

[0090] The system 100 may facilitate timely maintenance and replacement of the air filter 70 based on the filter parameter rather than predetermined schedules. The system 100 may also aid in preventing premature disposal of the air filter 70 (i.e., when the air filter 70 is capable of effectively filtering air). This may reduce operational costs.

[0091] In some embodiments, the system 100 may further include additional sensors to monitor the air quality through the air filter 70, such as, for example, humidity sensors, carbon dioxide sensors, gaseous species and / or contaminant sensors, and particulate sensors. The system 100 may also include various other sensors, such as, for example, vibration sensors and accelerometers.

[0092] FIG. 7 illustrates a flowchart depicting various steps of a method 200 for monitoring a performance of an air filter according to an embodiment of the present disclosure. One or more steps of the method 200 may be carried out, for example, by the system 100 of FIGS. 1 and 6.

[0093] At step 202, the method 200 includes providing a device. The device includes a substrate. The device further includes at least one resistor disposed on the substrate. The device further includes at least one thermistor disposed on the substrate and thermally coupled to the at least one resistor. Referring to FIG. 1, for example, the method 200 may include providing the device 110.

[0094] At step 204, the method 200 further includes supplying, via a power source, electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance. Referring to FIGS. 1 and 2, for example, the method 200 may include supplying, via the power source 132, the electrical power to the resistor 114 for the time period extending from the first time instance T1 to the second time instance T2, such that the temperature of the resistor 114 at the second time instance T2 (i.e., the second temperature TM2) is greater than the temperature of the resistor 114 at the first time instance T1 (i.e., the first temperature TM1).

[0095] At step 206, the method 200 further includes determining, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period. Referring to FIGS. 1 and 2, for example, the method 200 may include determining, via the thermistor 122, the variation of the temperature of the resistor 114 during the time period TP.

[0096] At step 208, the method 200 further includes determining an airflow speed based on the variation of the temperature of the at least one resistor in the time period. Referring to FIGS. 1 and 2, for example, the method 200 may include determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP.

[0097] In some embodiments, determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor includes determining, via the at least one thermistor, a first temperature of the at least one resistor at the first time instance. Determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor further includes determining, via the at least one thermistor, a second temperature of the at least one resistor at the second time instance. Determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor further includes determining a temperature differential between the first temperature and the resistor temperature. Further, determining the airflow speed based on the variation of the temperature of the at least one resistor in the time period includes determining the airflow speed based on the temperature differential.

[0098] Referring to FIGS. 1 and 2, for example, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP via the thermistor 122 may include: determining, via the thermistor 122, the first temperature TM1 of the resistor 114 at the first time instance T1; determining, via the thermistor 122, the second temperature TM2 of the resistor 114 at the second time instance T2; and determining the temperature differential TD between the first temperature TM1 and the second temperature TM2. Further, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP may include determining the airflow speed based on the temperature differential TD.

[0099] In some embodiments, determining the airflow speed based on the variation of the temperature of the at least one resistor in the time period via the at least one thermistor includes determining, via the at least one thermistor, a temperature curve representing the variation of the temperature of the at least one resistor during the time period. Further, determining the airflow speed based on the variation of the temperature of the at least one resistor in the time period includes determining the airflow speed based on the temperature curve.

[0100] Referring to FIGS. 1 and 2, for example, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP via the thermistor 122 may include determining, via the thermistor 122, the temperature curve 32 representing the variation of the temperature of the resistor 114 during the time period TP. Further, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP may include determining the airflow speed based on the temperature curve 32.

[0101] In some embodiments, the method 200 further includes disposing the device proximal to an air filter. The method 200 further includes determining a filter parameter associated with the air filter based at least on the airflow speed. Referring to FIG. 6, for example, the method 200 may include disposing the device 110 proximal to the air filter 70 and determining the filter parameter associated with the air filter 70 based at least on the airflow speed.

[0102] In some embodiments, the method 200 further includes disposing a pressure sensor proximal to the air filter. The method 200 further includes determining, via the pressure sensor, a pressure. The filter parameter associated with the air filter is determined further based on the pressure. Referring to FIG. 6, for example, the method 200 may include disposing the pressure sensor 180 proximal to the air filter 70 and determining, via the pressure sensor 180, the pressure. The filter parameter associated with the air filter 70 may be determined further based on the pressure. For example, the filter parameter associated with the air filter 70 may be determined based on the airflow speed and the pressure.

[0103] In some embodiments, the filter parameter includes a clogging level of the air filter. Referring to FIG. 6, for example, the filter parameter may include the clogging level of the air filter 70.

[0104] In some embodiments, the method 200 further includes disposing a temperature sensor proximal to the air filter. The method 200 further includes determining, via the temperature sensor, a temperature. The filter parameter associated with the air filter is determined further based on the temperature. Referring to FIG. 6, for example, the method 200 may include disposing the temperature sensor 190 proximal to the air filter 70 and determining, via the temperature sensor 190, the temperature. The filter parameter associated with the air filter 70 may be determined further based on the temperature. For example, the filter parameter associated with the air filter 70 may be determined based on the airflow speed, the pressure, and the temperature.

[0105] In some embodiments, the method 200 further includes communicating the filter parameter associated with the air filter to a terminal device. Referring to FIG. 6, for example, the method 200 may include communicating the filter parameter associated with the air filter 70 to the terminal device 195.Experimental Results

[0106] The experimental results are described with reference to FIGS. 1, 2, 8, and 9. The system 100 was used to determine the speed of an airflow produced by a fan through a baffle. The baffle was designed to simulate the environment of an HVAC system. Specifically, the baffle was designed to reduce a turbulence of the airflow to produce a near-laminar airflow at an exit end of the baffle.

[0107] The device 110 was positioned at the exit end, such that the resistor 114 received the airflow produced by the fan through the baffle. The speed of the fan (or fan speed) was varied to analyze the performance of the system 100. Specifically, the speed of the fan was varied to produce an airflow having an airflow speed between 0 feet per minute (ft / min) and 550 ft / min (tested using an anemometer). The experiment was repeated for different fan speeds. The results of the experiment were determined and plotted.

[0108] FIG. 8 illustrates a graph 40 depicting a variation of the temperature of the resistor 114 with respect to time for the different fan speeds and the voltage supplied across the resistor 114 with respect to time. Time is expressed in seconds in the abscissa (X-axis), temperature is expressed in degrees Celsius (° C.) in the left ordinate (left Y-axis), and the voltage across the resistor 114 is expressed in volts in the right ordinate (right Y-axis).

[0109] The graph 40 includes a first temperature curve 42 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 0 ft / min. The graph 40 further includes a second temperature curve 44 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 140 ft / min. The graph 40 further includes a third temperature curve 46 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 275 ft / min. The graph 40 includes a fourth temperature curve 48 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 415 ft / min. The graph 40 further includes a fifth temperature curve 50 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 550 ft / min. The graph 40 further includes a voltage curve 52 depicting the variation in voltage supplied across the resistor 114. As depicted by the voltage curve 52, a voltage pulse of 3 volts was applied to the resistor 114 for a time period TP1 of 5 seconds (from 0 seconds to 5 seconds).

[0110] As depicted by the graph 40, the initial temperature of the resistor 114 was kept constant (24° C.) for each different fan speed. It was noted that the temperature at the end of the time period TP1 was distinctly identifiable. It was concluded that the system 100 could be used to determine the airflow speed based on the rise in the temperature of the resistor 114 due to the voltage pulse. The temperature differential for the different fan speeds observed during the time period TP1 was determined and plotted against normalized airflow speed.

[0111] FIG. 9 illustrates a graph 60 depicting a variation of the temperature differential of the resistor 114 with respect to normalized airflow speed (where 0 represents airflow speed of 0 ft / min and 1 represents airflow speed of 550 ft / min). The normalized airflow speed is expressed in the abscissa (X-axis) and the temperature differential is expressed in degrees Celsius (C) in the ordinate (Y-axis).

[0112] The graph 60 includes a plurality of temperature points 62 representing the temperatures of the resistor 114 with respect to normalized airspeed. The graph 60 further includes an exponential curve 64 that best fits the plurality of temperature points 62. The exponential curve 64 could be used to determine the airflow speed for any given temperature differential for any given ambient temperature using the system 100. It was noted that the initial ambient temperature may have some effect on the temperature differential for any given airflow speed, which may need to be corrected via a more complex exponential equation or a set of exponential equations for different temperature bands, depending on desired accuracy. Alternatively, a lookup table could be created by empirically measuring the temperature differential versus airflow speed, which could be used to determine the airflow speed using the system 100.

[0113] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0114] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Examples

Embodiment Construction

[0017]In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

[0018]In the following disclosure, the following definitions are adopted.

[0019]As recited herein, all numbers should be considered modified by the term “about.” As used herein, “a,”“an,”“the,”“at least one,” and “one or more” are used interchangeably.

[0020]As used herein as a modifier to a property or attribute, the term “generally,” unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within + / −20% for quantifiable properties).

[0021]...

TECHNICAL FIELD

[0001] The present disclosure relates generally to a system and a method for monitoring a performance of an air filter.BACKGROUND

[0002] Various applications may require measurement and monitoring of an airflow speed. For example, a smart heating, ventilation, and air conditioning (HVAC) system may monitor an airflow speed through an air filter to predict or estimate the remaining life of the air filter. However, conventional systems and methods for measuring the airflow speed may be complex, non-versatile, energy inefficient, and inaccurate under a variety of operational conditions. Further, conventional systems and methods for monitoring a performance of an air filter may be unreliable.SUMMARY

[0003] In a first aspect, the present disclosure provides a system for monitoring a performance of an air filter. The system includes a device. The device includes a substrate. The device further includes at least one resistor disposed on the substrate. The device further includes at least one thermistor disposed on the substrate and thermally coupled to the at least one resistor. The system further includes a control unit. The control unit includes a power source electrically connected to the at least one resistor and configured to supply electrical power to the at least one resistor. The control unit further includes a controller communicably coupled to the at least one thermistor and the power source. The controller is configured to supply, via the power source, the electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance. The controller is further configured to determine, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period. The controller is further configured to determine an airflow speed based on the variation of the temperature of the at least one resistor in the time period.

[0004] In a second aspect, the present disclosure provides a method for monitoring a performance of an air filter. The method includes providing a device. The device includes a substrate. The device further includes at least one resistor disposed on the substrate. The device further includes at least one thermistor disposed on the substrate and thermally coupled to the at least one resistor. The method further includes supplying, via a power source, electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance. The method further includes determining, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period. The method further includes a determining an airflow speed based on the variation of the temperature of the at least one resistor in the time period.

[0005] The details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Exemplary embodiments disclosed herein may be more completely understood in consideration of the following detailed description in connection with the following figures. The figures are not necessarily drawn to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

[0007] FIG. 1 is a schematic diagram of a system for monitoring a performance of an air filter according to an embodiment of the present disclosure;

[0008] FIG. 2 is a graph depicting a variation of a temperature of a resistor with respect to time according to an embodiment of the present disclosure;

[0009] FIG. 3 is a schematic circuit diagram of the system according to an embodiment of the present disclosure;

[0010] FIG. 4 is a schematic perspective view of a fixture according to an embodiment of the present disclosure;

[0011] FIG. 5A is a schematic rear perspective view of the system according to an embodiment of the present disclosure;

[0012] FIG. 5B is a schematic front perspective view of the system of FIG. 5A according to an embodiment of the present disclosure;

[0013] FIG. 6 is a schematic perspective view of the system according to another embodiment of the present disclosure;

[0014] FIG. 7 is a flowchart depicting various steps of a method for monitoring a performance of an air filter according to an embodiment of the present disclosure;

[0015] FIG. 8 is a graph depicting variations of a temperature of a resistor and a voltage supplied across the resistor with respect to time; and

[0016] FIG. 9 is a graph depicting a variation of temperature differential of the resistor with respect to an airflow speed.DETAILED DESCRIPTION

[0017] In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

[0018] In the following disclosure, the following definitions are adopted.

[0019] As recited herein, all numbers should be considered modified by the term “about.” As used herein, “a,”“an,”“the,”“at least one,” and “one or more” are used interchangeably.

[0020] As used herein as a modifier to a property or attribute, the term “generally,” unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within + / −20% for quantifiable properties).

[0021] The term “substantially,” unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / −10% for quantifiable properties) but again without requiring absolute precision or a perfect match.

[0022] The term “about,” unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / −5% for quantifiable properties) but again without requiring absolute precision or a perfect match.

[0023] Terms such as same, equal, uniform, constant, strictly, and the like, are understood to be within the usual tolerances or measuring error applicable to the particular circumstance rather than requiring absolute precision or a perfect match.

[0024] As used herein, the terms “first” and “second” are used as identifiers. Therefore, such terms should not be construed as limiting of this disclosure. The terms “first” and “second” when used in conjunction with a feature or an element can be interchanged throughout the embodiments of this disclosure.

[0025] As used herein, when a first material is termed as “similar” to a second material, at least 90 weight % of the first and second materials are identical and any variation between the first and second materials includes less than about 10 weight % of each of the first and second materials.

[0026] As used herein, “at least one of A and B” should be understood to mean “only A, only B, or both A and B.”

[0027] Unless specified or limited otherwise, the terms “attached,”“connected,”“coupled,” and variations thereof, are used broadly and encompass both direct and indirect attachments, connections, and couplings.

[0028] As used herein, the term “configured to” is at least as restrictive as the term “adapted to” and requires actual design intention to perform the specified function rather than mere physical capability of performing such a function.

[0029] As used herein, the term “battery” refers to a device including one or more electrochemical cells that convert stored chemical energy into electrical energy. Examples of battery include primary batteries (non-rechargeable) and secondary batteries (rechargeable), such as Lithium-ion (Li-ion), Nickel Cadmium (Ni—Cd), Nickel-Metal Hydride (Ni-MH), and Lead-Acid. Batteries may have any shape, such as a coin, a button, a sheet, a cylinder, a prism, and so forth.

[0030] The present disclosure relates to a system for monitoring a performance of an air filter. The system includes a device. The device includes a substrate. The device further includes at least one resistor disposed on the substrate. The device further includes at least one thermistor disposed on the substrate and thermally coupled to the at least one resistor. The system further includes a control unit. The control unit includes a power source electrically connected to the at least one resistor and configured to supply electrical power to the at least one resistor. The control unit further includes a controller communicably coupled to the at least one thermistor and the power source. The controller is configured to supply, via the power source, the electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance. The controller is further configured to determine, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period. The controller is further configured to determine an airflow speed based on the variation of the temperature of the at least one resistor in the time period.

[0031] The system may function as a compact, low-cost, low-power consuming, and physically robust airflow sensor which may be sufficiently accurate under a variety of operational conditions. For example, the system may be suitable for operation over a temperature range of from 0 degrees Celsius (° C.) to 60° C. The device of the system may have low thermal loss via natural convection, thermal conduction, and radiation, while having high thermal loss via forced convection (e.g., airflow) to improve measurement of the airflow speed. The device may be positioned in a path of an airflow to measure the airflow speed using the system.

[0032] In some examples, the system may further include an electrical circuit connected with the controller for improving the accuracy of measurement of a resistance of the thermistor. Specifically, the system may utilize switches and a resistor network for improving the accuracy of measurement of a resistance of the thermistor over a wide range of temperatures.

[0033] The system may be suitable for implementation in heating, ventilation, and air conditioning (HVAC) systems. In some examples, the system may be used to determine a clogging level of an air filter of the HVAC systems. In other words, the system may be used to determine the remaining life of the air filter. Specifically, the system may monitor the performance of the air filter by determining a filter parameter (e.g., the clogging level or loading level) associated with the air filter based at least on the airflow speed. In some examples, the system may employ additional pressure and temperature sensors to determine the filter parameter associated with the air filter.

[0034] The system may facilitate timely maintenance and replacement of the air filter based on the filter parameter rather than predetermined schedules. The system may also aid in preventing premature disposal of the air filter (i.e., when the air filter is capable of effectively filtering air). This may reduce operational costs.

[0035] Referring now to the figures, FIG. 1 illustrates a schematic diagram of a system 100 for monitoring a performance of an air filter according to an embodiment of the present disclosure.

[0036] The system 100 includes a device 110. The device 110 is partially shown in FIG. 1. The device 110 includes a substrate 112. The device 110 further includes at least one resistor 114 (hereinafter also referred to as “the resistor 114”) disposed on the substrate 112. The device 110 further includes at least one thermistor 122 (hereinafter also referred to as “the thermistor 122”) disposed on the substrate 112. The thermistor 122 is thermally coupled to the resistor 114.

[0037] The resistor 114 may function as a heating element. Specifically, the resistor 114 may heat up in response to being subjected to electrical power. The resistor 114 may be selected based on desired application attributes. As an example, the resistor 114 may have a resistance of 1 kiloohm. It may be noted that the resistance of the resistor 114 may vary upon desired application attributes.

[0038] The thermistor 122 may function as a temperature sensor that senses a temperature of the resistor 114. The thermistor 122 may be thermally coupled to the resistor 114 using any suitable technique, such that the thermistor 122 is able to sense the temperature of the resistor 114. For example, the thermistor 122 may be thermally coupled to the resistor 114 via a thermally conductive material. The thermistor 122 may be selected based on desired application attributes. The temperature of the resistor 114 may be determined based on a change in a resistance of the thermistor 122. In some embodiments, the thermistor 122 includes a negative temperature coefficient thermistor. In such embodiments, the resistance of the thermistor 122 may decrease with an increase in the temperature of the resistor 114.

[0039] The substrate 112 may extend along a longitudinal axis 113 and have a length along the longitudinal axis 113. The substrate 112 may have a width 112W perpendicular to the longitudinal axis 113. The width 112W may be less than the length of the substrate 112. In some embodiments, the length of the substrate 112 may be greater than 1 centimeter (cm) and less than 20 cm. In some embodiments, the width 112W of the substrate 112 may be less than 5 cm, less than 4 cm, less than 3 cm, or less than 2 cm.

[0040] The substrate 112 may be configured to reduce or minimize absorption of heat from the resistor 114. Specifically, the substrate 112 may have a low thermal conductivity, or in other words, a high thermal resistance. Accordingly, the substrate 112 may be made from any suitable material having a high thermal resistance. For example, the substrate 112 may be made from polyimide.

[0041] In some embodiments, the substrate 112 may be flexible. In such embodiments, the device 110 may be configured as a flex circuit. The thermistor 122 and the resistor 114 may be thermally coupled to each other via an interconnecting trace 115 with associated solder fillets. In some embodiments, the substrate 112 may include polyimide. The substrate 112 including polyimide may have high flexibility and high thermal resistance. In some embodiments, the device 110 may further include a plurality of resistor electrical traces 116 disposed on the substrate 112. The plurality of resistor electrical traces 116 may be electrically connected to the resistor 114. The device 110 may further include a plurality of thermistor electrical traces 124 disposed on the substrate 112. The plurality of thermistor electrical traces 124 may be electrically connected to the thermistor 122. The plurality of resistor electrical traces 116 and the plurality of thermistor electrical traces 124 may be made from copper, for example.

[0042] The device 110 may have a simple, compact, physically robust, and low-cost construction. The device 110 may have low thermal loss via natural convection, thermal conduction, and radiation, while having high thermal loss via forced convection (e.g., airflow) to improve measurement of the airflow speed.

[0043] The system 100 further includes a control unit 130. The control unit 130 includes a power source 132 and a controller 134. The power source132 is electrically connected to the resistor 114. The power source 132 is configured to supply electrical power to the resistor 114. In some embodiments, the power source 132 may include a battery. The battery may be of any suitable type, such as a button battery, for example.

[0044] The controller 134 is communicably coupled to the thermistor 122 and the power source 132. The controller 134 may include one or more integrated circuits, which can be programmed to perform various functions, as will be described in detail below. The controller 134 may include one or more microcomputers, processors, application-specific integrated circuits, or any other suitable programmable circuit or combination of circuits. The controller 134 may include both hardware and software components, and the term “controller” is meant to broadly encompass the combination of such components. In some examples, the processor of the controller 134 may be remote from the device 110 (e.g., on a remote server, a cloud server, a hub, etc.) and communicably coupled to other components of the controller 134 via a wireless connection.

[0045] FIG. 2 illustrates a graph 30 depicting a variation of the temperature of the resistor 114 with respect to time according to an embodiment of the present disclosure. The graph 30 includes a temperature curve 32 representing the variation of the temperature of the resistor 114 with respect to time.

[0046] Referring to FIGS. 1 and 2, the controller 134 is configured to supply, via the power source 132, the electrical power to the resistor 114 for a time period TP extending from a first time instance T1 to a second time instance T2, such that the temperature of the resistor 114 at the second time instance T2 is greater than the temperature of the resistor 114 at the first time instance T1.

[0047] In other words, the electrical power supplied to the resistor 114 during the time period TP may raise the temperature of the resistor 114. As depicted by the temperature curve 32, the temperature of the resistor 114 may rise from a first temperature TM1 at the first time instance T1 to a second temperature TM2 at the second time instance T2. The second temperature TM2 is greater than the first temperature TM1. In some cases, the first temperature TM1 may correspond to an ambient temperature.

[0048] The time period TP may be selected depending upon desired accuracy and power consumption of the system 100. The time period TP being longer may increase the accuracy of determining the airflow speed while increasing the power consumption from the power source 132. In some embodiments, the time period TP is from 1 second to 10 seconds. In some embodiments, the time period TP may be from 3 seconds to 8 seconds. In some embodiments, the time period TP may be about 5 seconds. The time period TP being from 1 second to 10 seconds may provide a good balance between the accuracy of determining the airflow speed and the power consumption.

[0049] In some embodiments, supplying the electrical power to the resistor 114 via the power source 132 includes applying a constant voltage across the resistor 114. As an example, the controller 134 may be configured to supply, via the power source 132, a constant voltage (e.g., 3 volts) across the resistor 114 during the time period TP.

[0050] The controller 134 is further configured to determine, via the thermistor 122, the variation of the temperature of the resistor 114 during the time period TP. In some embodiments, the variation of the temperature of the resistor 114 during the time period TP may correspond to a temperature differential between the first temperature TM1 and the second temperature TM2 or the temperature curve 32.

[0051] The controller 134 is further configured to determine the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP. In other words, the controller 134 may determine the airflow speed based on a rise in the temperature of the resistor 114 during the time period TP. Assuming the first temperature TM1 as constant, a higher airflow speed may correspond to a smaller rise in the temperature of the resistor 114.

[0052] As discussed above, the processor of the controller 134 may be remote from the device 110. In some embodiments, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP may be performed remotely from the device 110. For example, the processor of the controller 134 may perform remote calculations (e.g., in the cloud) from the raw data collected from the various components of the device by the controller 134.

[0053] The system 100 may function as a compact, low-cost, low-power consuming, and physically robust airflow sensor which may be sufficiently accurate under a variety of operational conditions. For example, the system 100 may be suitable for operation over a temperature range of from 0 degrees Celsius (° C.) to 60° C.

[0054] The device 110 may be positioned in a path of the airflow to measure the airflow speed using the system 100. Specifically, the device 110 may be positioned in the path of the airflow, such that the resistor 114 receives the airflow. The system 100 may be suitable for implementation in heating, ventilation, and air conditioning (HVAC) systems. In some examples, the system 100 may be used to determine a clogging level of an air filter of the HVAC systems. In other words, the system 100 may be used to determine the remaining life of the air filter.

[0055] In some embodiments, determining the variation of the temperature of the resistor 114 during the time period TP via the thermistor 122 includes determining, via the thermistor 122, the first temperature TM1 of the resistor 114 at the first time instance TM1. In some embodiments, determining the variation of the temperature of the resistor 114 during the time period TP via the thermistor 122 further includes determining, via the thermistor 122, the second temperature TM2 of the resistor 114 at the second time instance T2. In some embodiments, determining the variation of the temperature of the resistor 114 during the time period TP via the thermistor 122 further includes determining a temperature differential TD between the first temperature TM1 and the second temperature TM2. The temperature differential TD may be defined as a difference between the second temperature TM2 and the first temperature TM1. In some embodiments, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP includes determining the airflow speed based on the temperature differential TD. For example, the system 100 may utilize a set of temperature differential vs. airflow speed curves to determine the airflow speed based on the temperature differential TD.

[0056] In some other embodiments, determining the variation of the temperature of the resistor 114 during the time period TP via the thermistor 122 includes determining, via the thermistor 122, the temperature curve 32 representing the variation of the temperature of the resistor 114 during the time period TM. In some embodiments, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP includes determining the airflow speed based on the temperature curve 32. In such embodiments, the controller 134 may determine the airflow speed based on a plurality of temperatures points of the temperature curve 32. This may further improve the accuracy of measurement of the airflow speed.

[0057] FIG. 3 illustrates a schematic circuit diagram of the system 100 according to an embodiment of the present disclosure.

[0058] The controller 134 may include a first input port 136 configured to receive a first signal and a second input port 137 configured to receive a second signal. Each of the first signal and the second signal may be an analog signal. The controller 134 may be configured to measure a voltage difference between the first signal and the second signal. The controller 134 may further include an output port 138 configured to be connected to the resistor 114. The controller 134 may be configured to apply a voltage across the resistor 114 through the output port 138.

[0059] The system 100 may further include an electrical circuit 10. The electrical circuit 10 may include the resistor 114 and the thermistor 122. The thermistor 122 may be connected in parallel with the resistor 114. The electrical circuit 10 may further include at least one first circuit resistor 12 (hereinafter also referred to as “the first circuit resistor 12”) connected in series with the thermistor 122. The electrical circuit 10 may further include a first circuit node 22 disposed between the thermistor 122 and the first circuit resistor 12. The first circuit node 22 may be configured to be connected to the first input port 136 of the controller 134.

[0060] The electrical circuit 10 may further include at least one second circuit resistor 14 (hereinafter also referred to as “the second circuit resistor 14”) connected in parallel with the thermistor 122 and the first circuit resistor 12. The electrical circuit 10 may further include at least one third circuit resistor 16 (hereinafter also referred to as “the third circuit resistor 16”) connected in series with the second circuit resistor 14. The electrical circuit 10 may further include a second circuit node 24 disposed between the second circuit resistor 14 and the third circuit resistor 16. The second circuit node 24 may be configured to be connected to the second input port 137 of the controller 134.

[0061] The electrical circuit 10 may further include a first connection node 26 and a second connection node 28. The second circuit resistor 14 may be disposed between the second circuit node 24 and the first connection node 26. Further, the third circuit resistor 16 may be disposed between the second circuit node 24 and the second connection node 28.

[0062] The controller 134 may further include at least one first controller resistor 142 (hereinafter also referred to as “the first controller resistor 142”) and at least one second controller resistor 144 (hereinafter also referred to as “the second controller resistor 144”) connected in series with the first controller resistor 142. The controller 134 may further include a controller node 146 disposed between the first controller resistor 142 and the second controller resistor 144. The controller node 146 may be configured to be connected to the second circuit node 24.

[0063] The controller 134 may further include a first switch 148 connected in series with the first controller resistor 142. The first switch 148 may be configured to be connected between the controller node 146 and the first connection node 26. The controller 134 may further include a second switch 152 connected in series with the second controller resistor 144. The second switch 152 may be configured to be connected between the controller node 146 and the second connection node 28. The controller 134 may be further configured to selectively operate each of the first switch 148 and the second switch 152. This may allow the controller 134 to control the voltage of the second signal in response to changes in the ambient temperature.

[0064] For example, in operation, the controller 134 may apply a voltage VDD across the resistor 114 through the output port 138 for the time period TP (shown in FIG. 2). The controller 134 may receive the first signal from the first circuit node 22 and the second signal from the second circuit node 24 to measure the resistance of the thermistor 122. The first circuit resistor 12 and the second circuit resistor 14 may each have a resistance approximately equal to that of the thermistor 122 under normal ambient temperatures (e.g., 25° C.). The controller 134 may open the first switch 148 and the second switch 152, thereby bypassing the first controller resistor 142 and the second controller resistor 144. This may form a voltage divider that gives a value of the voltage at the second circuit node 24 equal to VDD / 2. Small changes to the value of the resistance of the thermistor 122 may be measured when the voltage at the first circuit node 22 is near VDD / 2 (i.e., the value of the resistance of the thermistor 122 is near that of the first circuit resistor 12). However, in instances where an increase in the temperature of the resistor 114 causes the value of the resistance of the thermistor 122 to become less than that of the first circuit resistor 12, or a decrease in the temperature of the resistor 114 causes the value of the resistance of the thermistor 122 to become greater than that of the first circuit resistor 12, the first switch 148 and / or the second switch 152 may be closed, which in turn may form a voltage divider including the second circuit resistor 14, the third circuit resistor 16, the first controller resistor 142, and the second controller resistor 144. This may enable the ability to shift the voltage at the second circuit node 24 down or up, as needed.

[0065] In some embodiments, the electrical circuit 10 may further include the power source 132 and a voltage regulator 135. In some other embodiments, the controller 134 may include the voltage regulator 135. In other words, the voltage regulator 135 may be a built-in regulator of the controller 134. In such embodiments, the power source 132 may be connected directly to the controller 134.

[0066] FIG. 4 illustrates a schematic perspective view of a fixture 160 according to an embodiment of the present disclosure.

[0067] In some embodiments, the system 100 (shown in FIG. 1) may further include the fixture 160. The fixture 160 may be configured to support the device 110. The fixture 160 may provide physical protection to the device 110.

[0068] The fixture 160 may include a through aperture 168. The resistor 114 may be positioned at the through aperture 168. During use, the fixture 160 supporting the device 110 may be positioned in a path of the airflow to measure the airflow speed, such that the resistor 114 is exposed to or receives the airflow.

[0069] In some embodiments, the through aperture 168 may be circular. The through aperture 168 may have a diameter 168D. The diameter 168D may be at least three times greater than the width 112W (shown in FIG. 1) of the substrate 112. This may allow efficient thermal interaction of the airflow with the resistor 114.

[0070] In the illustrated embodiment of FIG. 4, the fixture 160 further includes a base 162 and an elongate member 164 extending from the base 162. The fixture 160 further includes a head 166 connected to the elongate member 164 and spaced apart from the base 162. The through aperture 168 is disposed on the head 166.

[0071] FIGS. 6A and 6B illustrate perspective views of the system 100 according to an embodiment of the present disclosure.

[0072] The system 100 may further include a printed circuit board 170. The control unit 130 may be disposed on the printed circuit board 170. Specifically, the power source 132 and the controller 134 may be disposed on the printed circuit board 170.

[0073] The printed circuit board 170 may form the fixture 160. Specifically, the printed circuit board 170 may include the aperture 168 and support the device 110. The printed circuit board 170 may further include an interface 175. The interface 175 may be configured to physically support the device 110 and electrically connect various components of the device 110 to the control unit 130. The resistor 114 may be electrically coupled to the power source 132 via the interface 175. Further, the thermistor 122 may be communicably coupled to the controller 134 via the interface 175. The interface 175 may support the device 110 such that the resistor 114 is positioned at the through aperture 168.

[0074] FIG. 6 illustrates a perspective view of the system 100 according to another embodiment of the present disclosure.

[0075] The system 100 may further include an air filter 70. As used herein, the term “air filter” refers to filter media configured to filter air. Filter media may be of any suitable type, for example, pleated or unpleated. The air filter 70 defines an upstream side and a downstream side. The downstream side refers to the side of the air filter 70 to which air flows. That is, the downstream side receives filtered air through the air filter 70. The upstream side is opposite to the downstream side and refers to the side of the air filter 70 from which air flows.

[0076] In some embodiments, the system 100 may further include a filter frame 80 that houses the air filter 70. In some embodiments, the air filter 70 may be replaceable and the filter frame 80 may allow replacement of the air filter 70.

[0077] The device 110 may be disposed proximal to the air filter 70. In some embodiments, the device 110 may be disposed upstream of the air filter 70. In some embodiments, the device 110 may be disposed downstream of the air filter 70. In some embodiments, the device 110 may be disposed on the air filter 70. In some embodiments, the device 110 may be disposed on the filter frame 80.

[0078] The controller 134 may be further configured to determine a filter parameter associated with the air filter 70 based at least on the airflow speed. In some embodiments, the filter parameter includes a clogging level of the air filter 70. The clogging level of the air filter 70 may also be referred to as a “loading level” of the air filter 70.

[0079] In some embodiments, the system 100 may further include a pressure sensor 180 disposed proximal to the air filter 70 and communicably coupled to the controller 134. In some embodiments, the pressure sensor 180 may be disposed upstream of the air filter 70. In some embodiments, the pressure sensor 180 may be disposed downstream of the air filter 70. In some embodiments, the pressure sensor 180 may be disposed on the air filter 70. In some embodiments, the pressure sensor 180 may be disposed on the filter frame 80. In some embodiments, the pressure sensor 180 may be an absolute pressure sensor.

[0080] The controller 134 may be further configured to determine, via the pressure sensor 180, a pressure. The filter parameter associated with the air filter 70 may be determined further based on the pressure. Specifically, in some embodiments, the controller 134 may be configured to determine the filter parameter associated with the air filter 70 based on the airflow speed and the pressure. The filter parameter determined based on the airflow speed and the pressure may be more accurate than the filter parameter determined solely based on the airflow speed.

[0081] In some embodiments, the system 100 may further include a temperature sensor 190 disposed proximal to the air filter 70 and communicably coupled to the controller 134. In some embodiments, the temperature sensor 190 may be disposed upstream of the air filter 70. In some embodiments, the temperature sensor 190 may be disposed downstream of the air filter 70. In some embodiments, the temperature sensor 190 may be disposed on the air filter 70. In some embodiments, the temperature sensor 190 may be disposed on the filter frame 80.

[0082] The controller 134 may be further configured to determine, via the temperature sensor 190, a temperature. The filter parameter associated with the air filter 70 may be determined further based on the temperature. Specifically, in some embodiments, the controller 134 may be configured to determine the filter parameter associated with the air filter 70 based on the airflow speed, the pressure, and the temperature.

[0083] In some embodiments, the device 110, the pressure sensor 180, and the temperature sensor 190 may be positioned downstream of the air filter 70 on a face of the air filter 70 or at least partially inside a valley defined between two adjacent pleats of the air filter 70. Alternatively, the device 110, the pressure sensor 180, and the temperature sensor 190 may be disposed on the filter frame 80. In some embodiments, the system 100 may further include a sensor housing 85 configured to be mounted to the filter frame 80. In some embodiments, the sensor housing 85 may be mounted to the filter frame 80 downstream of the air filter 70. In some embodiments, the filter frame 80 may include one or more mounting features 82 that allow mounting of the sensor housing 85 to the filter frame 80. The device 110, the pressure sensor 180, and the temperature sensor 190 may be coupled to the sensor housing 85. In some embodiments, the control unit 130 may be coupled to the sensor housing 85. In some embodiments, the pressure sensor 180 and the temperature sensor 190 may be powered by the power source 132.

[0084] In some embodiments, the controller 134 may be configured to monitor a change in the airflow speed to determine the filter parameter associated with the air filter 70. It may be noted that airflow speed determined by the controller 134 may or may not directly match, for example, a bulk velocity in the center of an HVAC duct, as the airflow speed determined using the device 110 may be influenced based on its arrangement relative to the filter frame 80, the air filter 70, and various other structures associated with the device 110. However, the airflow speed associated with the air filter 70 determined via the device 110 may be sufficient for determining the filter parameter (e.g., the clogging level associated with the air filter 70).

[0085] In some embodiments, the controller 134 may be configured to monitor a change in the airflow speed and the pressure to determine the filter parameter associated with the air filter 70. In some embodiments, the controller 134 may be configured to monitor a change in the airflow speed, the pressure, and the temperature to determine the filter parameter associated with the air filter 70. The controller 134 may combine the airflow speed with at least one of the pressure and the temperature to determine the filter parameter associated with the air filter 70.

[0086] In some embodiments, the controller 134 may be further configured to be communicably coupled to a terminal device 195. The controller 134 may be further configured to communicate the filter parameter associated with the air filter 70 to the terminal device 195.

[0087] As used herein, the term “terminal device” refers to any terminal device capable of wireless communications (e.g., with each other, with a controller, or with a remote server). The communications may involve transmitting and / or receiving wireless signals using electromagnetic signals, radio waves, infrared signals, and / or other types of signals suitable for conveying information over air.

[0088] In some embodiments, the terminal device 195 may be a mobile terminal. As used herein, the term “mobile terminal” may include a cellular or mobile telephone; a smart phone which may combine a cellular telephone with data processing capabilities, Internet / Intranet access, Web browser, organizer, calendar and / or a global positioning system (GPS) receiver; a consumer electronics device or other appliance that includes telephone transceiver (e.g., VOIP) capabilities; or another type of hand-held computational or communication device.

[0089] In some embodiments, the controller 134 may employ at least one of Bluetooth communication and Wi-Fi communication to directly communicate the filter parameter associated with the air filter 70 to the terminal device 195. In some other embodiments, the controller 134 may be configured to indirectly communicate (such as through web servers, etc.) the filter parameter associated with the air filter 70 to the terminal device 195. A user may conveniently inspect the filter parameter via the terminal device 195.

[0090] The system 100 may facilitate timely maintenance and replacement of the air filter 70 based on the filter parameter rather than predetermined schedules. The system 100 may also aid in preventing premature disposal of the air filter 70 (i.e., when the air filter 70 is capable of effectively filtering air). This may reduce operational costs.

[0091] In some embodiments, the system 100 may further include additional sensors to monitor the air quality through the air filter 70, such as, for example, humidity sensors, carbon dioxide sensors, gaseous species and / or contaminant sensors, and particulate sensors. The system 100 may also include various other sensors, such as, for example, vibration sensors and accelerometers.

[0092] FIG. 7 illustrates a flowchart depicting various steps of a method 200 for monitoring a performance of an air filter according to an embodiment of the present disclosure. One or more steps of the method 200 may be carried out, for example, by the system 100 of FIGS. 1 and 6.

[0093] At step 202, the method 200 includes providing a device. The device includes a substrate. The device further includes at least one resistor disposed on the substrate. The device further includes at least one thermistor disposed on the substrate and thermally coupled to the at least one resistor. Referring to FIG. 1, for example, the method 200 may include providing the device 110.

[0094] At step 204, the method 200 further includes supplying, via a power source, electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance. Referring to FIGS. 1 and 2, for example, the method 200 may include supplying, via the power source 132, the electrical power to the resistor 114 for the time period extending from the first time instance T1 to the second time instance T2, such that the temperature of the resistor 114 at the second time instance T2 (i.e., the second temperature TM2) is greater than the temperature of the resistor 114 at the first time instance T1 (i.e., the first temperature TM1).

[0095] At step 206, the method 200 further includes determining, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period. Referring to FIGS. 1 and 2, for example, the method 200 may include determining, via the thermistor 122, the variation of the temperature of the resistor 114 during the time period TP.

[0096] At step 208, the method 200 further includes determining an airflow speed based on the variation of the temperature of the at least one resistor in the time period. Referring to FIGS. 1 and 2, for example, the method 200 may include determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP.

[0097] In some embodiments, determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor includes determining, via the at least one thermistor, a first temperature of the at least one resistor at the first time instance. Determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor further includes determining, via the at least one thermistor, a second temperature of the at least one resistor at the second time instance. Determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor further includes determining a temperature differential between the first temperature and the resistor temperature. Further, determining the airflow speed based on the variation of the temperature of the at least one resistor in the time period includes determining the airflow speed based on the temperature differential.

[0098] Referring to FIGS. 1 and 2, for example, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP via the thermistor 122 may include: determining, via the thermistor 122, the first temperature TM1 of the resistor 114 at the first time instance T1; determining, via the thermistor 122, the second temperature TM2 of the resistor 114 at the second time instance T2; and determining the temperature differential TD between the first temperature TM1 and the second temperature TM2. Further, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP may include determining the airflow speed based on the temperature differential TD.

[0099] In some embodiments, determining the airflow speed based on the variation of the temperature of the at least one resistor in the time period via the at least one thermistor includes determining, via the at least one thermistor, a temperature curve representing the variation of the temperature of the at least one resistor during the time period. Further, determining the airflow speed based on the variation of the temperature of the at least one resistor in the time period includes determining the airflow speed based on the temperature curve.

[0100] Referring to FIGS. 1 and 2, for example, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP via the thermistor 122 may include determining, via the thermistor 122, the temperature curve 32 representing the variation of the temperature of the resistor 114 during the time period TP. Further, determining the airflow speed based on the variation of the temperature of the resistor 114 in the time period TP may include determining the airflow speed based on the temperature curve 32.

[0101] In some embodiments, the method 200 further includes disposing the device proximal to an air filter. The method 200 further includes determining a filter parameter associated with the air filter based at least on the airflow speed. Referring to FIG. 6, for example, the method 200 may include disposing the device 110 proximal to the air filter 70 and determining the filter parameter associated with the air filter 70 based at least on the airflow speed.

[0102] In some embodiments, the method 200 further includes disposing a pressure sensor proximal to the air filter. The method 200 further includes determining, via the pressure sensor, a pressure. The filter parameter associated with the air filter is determined further based on the pressure. Referring to FIG. 6, for example, the method 200 may include disposing the pressure sensor 180 proximal to the air filter 70 and determining, via the pressure sensor 180, the pressure. The filter parameter associated with the air filter 70 may be determined further based on the pressure. For example, the filter parameter associated with the air filter 70 may be determined based on the airflow speed and the pressure.

[0103] In some embodiments, the filter parameter includes a clogging level of the air filter. Referring to FIG. 6, for example, the filter parameter may include the clogging level of the air filter 70.

[0104] In some embodiments, the method 200 further includes disposing a temperature sensor proximal to the air filter. The method 200 further includes determining, via the temperature sensor, a temperature. The filter parameter associated with the air filter is determined further based on the temperature. Referring to FIG. 6, for example, the method 200 may include disposing the temperature sensor 190 proximal to the air filter 70 and determining, via the temperature sensor 190, the temperature. The filter parameter associated with the air filter 70 may be determined further based on the temperature. For example, the filter parameter associated with the air filter 70 may be determined based on the airflow speed, the pressure, and the temperature.

[0105] In some embodiments, the method 200 further includes communicating the filter parameter associated with the air filter to a terminal device. Referring to FIG. 6, for example, the method 200 may include communicating the filter parameter associated with the air filter 70 to the terminal device 195.Experimental Results

[0106] The experimental results are described with reference to FIGS. 1, 2, 8, and 9. The system 100 was used to determine the speed of an airflow produced by a fan through a baffle. The baffle was designed to simulate the environment of an HVAC system. Specifically, the baffle was designed to reduce a turbulence of the airflow to produce a near-laminar airflow at an exit end of the baffle.

[0107] The device 110 was positioned at the exit end, such that the resistor 114 received the airflow produced by the fan through the baffle. The speed of the fan (or fan speed) was varied to analyze the performance of the system 100. Specifically, the speed of the fan was varied to produce an airflow having an airflow speed between 0 feet per minute (ft / min) and 550 ft / min (tested using an anemometer). The experiment was repeated for different fan speeds. The results of the experiment were determined and plotted.

[0108] FIG. 8 illustrates a graph 40 depicting a variation of the temperature of the resistor 114 with respect to time for the different fan speeds and the voltage supplied across the resistor 114 with respect to time. Time is expressed in seconds in the abscissa (X-axis), temperature is expressed in degrees Celsius (° C.) in the left ordinate (left Y-axis), and the voltage across the resistor 114 is expressed in volts in the right ordinate (right Y-axis).

[0109] The graph 40 includes a first temperature curve 42 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 0 ft / min. The graph 40 further includes a second temperature curve 44 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 140 ft / min. The graph 40 further includes a third temperature curve 46 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 275 ft / min. The graph 40 includes a fourth temperature curve 48 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 415 ft / min. The graph 40 further includes a fifth temperature curve 50 representing the variation of the temperature of the resistor 114 with respect to time for the airflow speed of 550 ft / min. The graph 40 further includes a voltage curve 52 depicting the variation in voltage supplied across the resistor 114. As depicted by the voltage curve 52, a voltage pulse of 3 volts was applied to the resistor 114 for a time period TP1 of 5 seconds (from 0 seconds to 5 seconds).

[0110] As depicted by the graph 40, the initial temperature of the resistor 114 was kept constant (24° C.) for each different fan speed. It was noted that the temperature at the end of the time period TP1 was distinctly identifiable. It was concluded that the system 100 could be used to determine the airflow speed based on the rise in the temperature of the resistor 114 due to the voltage pulse. The temperature differential for the different fan speeds observed during the time period TP1 was determined and plotted against normalized airflow speed.

[0111] FIG. 9 illustrates a graph 60 depicting a variation of the temperature differential of the resistor 114 with respect to normalized airflow speed (where 0 represents airflow speed of 0 ft / min and 1 represents airflow speed of 550 ft / min). The normalized airflow speed is expressed in the abscissa (X-axis) and the temperature differential is expressed in degrees Celsius (C) in the ordinate (Y-axis).

[0112] The graph 60 includes a plurality of temperature points 62 representing the temperatures of the resistor 114 with respect to normalized airspeed. The graph 60 further includes an exponential curve 64 that best fits the plurality of temperature points 62. The exponential curve 64 could be used to determine the airflow speed for any given temperature differential for any given ambient temperature using the system 100. It was noted that the initial ambient temperature may have some effect on the temperature differential for any given airflow speed, which may need to be corrected via a more complex exponential equation or a set of exponential equations for different temperature bands, depending on desired accuracy. Alternatively, a lookup table could be created by empirically measuring the temperature differential versus airflow speed, which could be used to determine the airflow speed using the system 100.

[0113] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0114] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Examples

Embodiment Construction

[0017]In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

[0018]In the following disclosure, the following definitions are adopted.

[0019]As recited herein, all numbers should be considered modified by the term “about.” As used herein, “a,”“an,”“the,”“at least one,” and “one or more” are used interchangeably.

[0020]As used herein as a modifier to a property or attribute, the term “generally,” unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within + / −20% for quantifiable properties).

[0021]...

Claims

1. A system for monitoring a performance of an air filter, the system comprising:a device comprising:a substrate;at least one resistor disposed on the substrate; andat least one thermistor disposed on the substrate and thermally coupled to the at least one resistor; anda control unit comprising:a power source electrically connected to the at least one resistor and configured to supply electrical power to the at least one resistor; anda controller communicably coupled to the at least one thermistor and the power source, wherein the controller is configured to:supply, via the power source, the electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance;determine, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period; anddetermine an airflow speed based on the variation of the temperature of the at least one resistor in the time period.

2. The system of claim 1, wherein the substrate comprises polyimide.

3. The system of claim 1, wherein supplying the electrical power to the at least one resistor via the power source comprises applying a constant voltage across the at least one resistor.

4. The system of claim 1, wherein:determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor comprises determining, via the at least one thermistor, a temperature curve representing the variation of the temperature of the at least one resistor during the time period; anddetermining the airflow speed based on the variation of the temperature of the at least one resistor in the time period comprises determining the airflow speed based on the temperature curve.

5. The system of claim 1, wherein:determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor comprises:determining, via the at least one thermistor, a first temperature of the at least one resistor at the first time instance;determining, via the at least one thermistor, a second temperature of the at least one resistor at the second time instance; anddetermining a temperature differential between the first temperature and the second temperature; anddetermining the airflow speed based on the variation of the temperature of the at least one resistor in the time period comprises determining the airflow speed based on the temperature differential.

6. The system of claim 1, wherein the at least one thermistor is a negative temperature coefficient thermistor.

7. The system of claim 1, further comprising a fixture configured to support the device, wherein the fixture comprises a through aperture, and wherein the at least one resistor is positioned at the through aperture.

8. The system of claim 1, wherein the device further comprises:a plurality of resistor electrical traces disposed on the substrate and electrically connected to the at least one resistor; anda plurality of thermistor electrical traces disposed on the substrate and electrically connected to the at least one thermistor.

9. The system of claim 1, wherein the controller comprises:a first input port configured to receive a first signal;a second input port configured to receive a second signal, wherein the controller is configured to measure a voltage difference between the first signal and the second signal; andan output port configured to be connected to the at least one resistor, wherein the controller is configured to apply a voltage across the at least one resistor through the output port.

10. The system of claim 9, further comprising an electrical circuit, the electrical circuit comprising:the at least one resistor;the at least one thermistor connected in parallel with the at least one resistor;at least one first circuit resistor connected in series with the at least one thermistor;a first circuit node disposed between the at least one thermistor and the at least one first circuit resistor, wherein the first circuit node is configured to be connected to the first input port of the controller;at least one second circuit resistor connected in parallel with the at least one thermistor and the at least one first circuit resistor;at least one third circuit resistor connected in series with the at least one second circuit resistor; anda second circuit node disposed between the at least one second circuit resistor and the at least one third circuit resistor, wherein the second circuit node is configured to be connected to the second input port of the controller.

11. The system of claim 10, wherein:the electrical circuit further comprises:a first connection node, wherein the at least one second circuit resistor is disposed between the second circuit node and the first connection node; anda second connection node, wherein the at least one third circuit resistor is disposed between the second circuit node and the second connection node;the controller further comprises:at least one first controller resistor;at least one second controller resistor connected in series with the at least one first controller resistor;a controller node disposed between the at least one first controller resistor and the at least one second controller resistor, wherein the controller node is configured to be connected to the second circuit node;a first switch connected in series with the at least one first controller resistor, wherein the first switch is configured to be connected between the controller node and the first connection node; anda second switch connected in series with the at least one second controller resistor, wherein the second switch is configured to be connected between the controller node and the second connection node; andthe controller is further configured to selectively operate each of the first switch and the second switch.

12. The system of claim 1, further comprising an air filter, wherein the device is disposed proximal to the air filter, and wherein the controller is further configured to determine a filter parameter associated with the air filter based at least on the airflow speed.

13. The system of claim 12, wherein the filter parameter comprises a clogging level of the air filter.

14. The system of claim 12, further comprising a pressure sensor disposed proximal to the air filter and communicably coupled to the controller, wherein the controller is further configured to determine, via the pressure sensor, a pressure, and wherein the filter parameter is determined further based on the pressure.

15. The system of claim 14, further comprising a temperature sensor disposed proximal to the air filter and communicably coupled to the controller, wherein the controller is further configured to determine, via the temperature sensor, a temperature, and wherein the filter parameter is determined further based on the temperature.

16. The system of claim 12, wherein the controller is configured to be communicably coupled to a terminal device, and wherein the controller is further configured to communicate the filter parameter to the terminal device.

17. A method for monitoring a performance of an air filter, the method comprising:providing a device comprising:a substrate;at least one resistor disposed on the substrate; andat least one thermistor disposed on the substrate and thermally coupled to the at least one resistor;supplying, via a power source, electrical power to the at least one resistor for a time period extending from a first time instance to a second time instance, such that a temperature of the at least one resistor at the second time instance is greater than the temperature of the at least one resistor at the first time instance;determining, via the at least one thermistor, a variation of the temperature of the at least one resistor during the time period; anddetermining an airflow speed based on the variation of the temperature of the at least one resistor in the time period.

18. The method of claim 17, wherein:determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor comprises determining, via the at least one thermistor, a temperature curve representing the variation of the temperature of the at least one resistor during the time period; anddetermining the airflow speed based on the variation of the temperature of the at least one resistor in the time period comprises determining the airflow speed based on the temperature curve.

19. The method of claim 17, wherein:determining the variation of the temperature of the at least one resistor during the time period via the at least one thermistor comprises:determining, via the at least one thermistor, a first temperature of the at least one resistor at the first time instance;determining, via the at least one thermistor, a second temperature of the at least one resistor at the second time instance; anddetermining a temperature differential between the first temperature and the second temperature; anddetermining the airflow speed based on the variation of the temperature of the at least one resistor in the time period comprises determining the airflow speed based on the temperature differential.

20. The method of claim 17, further comprising:disposing the device proximal to an air filter; anddetermining a filter parameter associated with the air filter based at least on the airflow speed.

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