Compartment dehumidification at low ambient temperature

Abstract

A method of operating a heating, ventilation and air conditioning (HVAC) system of a vehicle includes operating the HVAC system in a heating mode to heat a supply airflow and direct the heated supply airflow into a passenger compartment of the vehicle; and selectively directing a refrigerant flow through an evaporator of the HVAC system to reduce the relative humidity of the supply airflow by condensing excess moisture out of the supply airflow at the evaporator.

Description

Technical Field

[0001] The present disclosure relates to vehicle heating, ventilation and air conditioning (HVAC) systems, and in particular to the operation of such systems at low ambient temperatures (eg, ambient temperatures below 40 degrees Fahrenheit). Background Art

[0002] In cold conditions, heating the cabin using the recirculated air mode of the HVAC system is generally more efficient than heating the cabin using the fresh air mode. This increase in efficiency improves vehicle mileage, especially the mileage of electric vehicles. In a typical recirculated air mode, the air in the cabin is indefinitely filtered and recirculated through the cabin. As moisture from passengers and other items (such as food and beverages) accumulates in the cabin, this tends to increase the relative humidity of the air in the cabin. This increase in relative humidity also increases the occurrence of fogging on the interior surfaces of the windows. Summary of the invention

[0003] In one exemplary embodiment, a method of operating a heating, ventilation and air conditioning (HVAC) system of a vehicle includes: operating the HVAC system in a heating mode to heat a supply airflow and directing the heated supply airflow into a passenger compartment of the vehicle; and optionally directing a refrigerant flow through an evaporator of the HVAC system to reduce the relative humidity of the supply airflow by condensing excess moisture out of the supply airflow at the evaporator.

[0004] In addition to one or more features described herein, the supply airflow is a recirculated airflow from the passenger cabin.

[0005] In addition to one or more features described herein, accumulated moisture is removed from the evaporator by opening a fresh air duct to allow ambient air to enter as part of the supply air flow and stopping the flow of refrigerant through the evaporator.

[0006] In addition to one or more features described herein, operation of the evaporator is controlled to maintain an evaporator superheat greater than zero.

[0007] In addition to one or more features described herein, relative humidity and passenger cabin temperature are monitored via a humidity sensor.

[0008] In addition to one or more features described herein, flow of refrigerant through the evaporator is stopped when the relative humidity is below a selected threshold.

[0009] In addition to one or more features described herein, the ambient temperature outside the vehicle is less than 40 degrees Fahrenheit.

[0010] In addition to one or more features described herein, the dew point of the supply gas stream is greater than zero degrees Celsius.

[0011] In another exemplary embodiment, a heating, ventilation and air conditioning (HVAC) system of a vehicle includes a refrigerant circuit, a condenser heater, and an evaporator, the refrigerant circuit including a compressor for causing a refrigerant to flow through the refrigerant circuit. One or more supply air flow inlets are configured to direct the supply air flow through one or more of the condenser heater and the evaporator, and one or more outlet ducts are configured to direct the supply air flow to a passenger compartment of the vehicle. The HVAC system controller is configured to operate the HVAC system in a heating mode to heat the supply air flow by directing the supply air flow through the condenser heater, and direct the heated supply air flow into the passenger compartment of the vehicle. The refrigerant flow is selectively directed through the evaporator to reduce the relative humidity of the supply air flow by condensing excess moisture out of the supply air flow at the evaporator.

[0012] In addition to one or more features described herein, the supply airflow is a recirculated airflow from the passenger cabin.

[0013] In addition to one or more of the features described herein, the HVAC system controller is configured to open the fresh air duct to allow ambient air to enter as part of the supply air flow to remove accumulated moisture from the evaporator.

[0014] In addition to one or more of the features described herein, the HVAC system controller is further configured to control operation of the evaporator to maintain an evaporator superheat greater than zero.

[0015] In addition to one or more of the features described herein, the HVAC system controller is further configured to cease directing the refrigerant flow through the evaporator when the relative humidity is below a selected threshold.

[0016] In addition to one or more features described herein, the blower is configured to cause a supply air flow through the HVAC system.

[0017] In addition to one or more features described herein, the coolant circuit has a coolant flow therethrough and is thermally coupled to the refrigerant circuit via a chiller.

[0018] In addition to one or more features described herein, the coolant flow is configured to cool a rechargeable energy storage system of a vehicle.

[0019] In another exemplary embodiment, a vehicle includes a vehicle body defining a passenger compartment, and a heating, ventilation and air conditioning (HVAC) system configured to provide heating and / or cooling to the passenger compartment. The HVAC system includes a refrigerant circuit, a condenser heater, and an evaporator, the refrigerant circuit including a compressor for causing a refrigerant to flow through the refrigerant circuit. One or more supply air flow inlets are configured to direct the supply air flow through one or more of the condenser heater and the evaporator, and one or more outlet ducts are configured to direct the supply air flow to the passenger compartment. The HVAC system controller is configured to operate the HVAC system in a heating mode to heat the supply air flow by directing the supply air flow through the condenser heater, and direct the heated supply air flow into the passenger compartment of the vehicle, and optionally direct the refrigerant flow through the evaporator to reduce the relative humidity of the supply air flow by condensing excess moisture out of the supply air flow at the evaporator.

[0020] In addition to one or more features described herein, the supply airflow is a recirculated airflow from the passenger cabin.

[0021] In addition to one or more of the features described herein, the HVAC system controller is configured to open the fresh air duct to allow ambient air to enter as part of the supply air flow to remove accumulated moisture from the evaporator.

[0022] In addition to one or more of the features described herein, the HVAC system controller is further configured to control operation of the evaporator to maintain an evaporator superheat greater than zero.

[0023] The above features and advantages and other features and advantages of the present disclosure are apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other features, advantages and details appear, by way of example only, from the following detailed description, which refers to the accompanying drawings, in which:

[0025] Figure 1 is a schematic diagram of an embodiment of a vehicle;

[0026] Figure 2 is a schematic diagram of an embodiment of a heating, ventilation and air conditioning (HVAC) system of a vehicle;

[0027] Figure 3 is a schematic diagram of an embodiment of an HVAC system operating in a fresh air mode;

[0028] Figure 4 is a schematic diagram of an embodiment of an HVAC system operating in a recirculated air mode; and

[0029] Figure 5is a schematic diagram of a method of operating an HVAC system of a vehicle. DETAILED DESCRIPTION

[0030] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate the same or corresponding parts and features.

[0031] According to an exemplary embodiment, a vehicle according to a non-limiting example is Figure 1 10. The vehicle 10 includes a body 12 supported on a plurality of wheels 16. In a non-limiting example, two of the plurality of wheels 16 are steerable. That is, changing the position of two of the plurality of wheels 16 relative to the body 12 will cause the vehicle 10 to change direction. The body 12 partially defines a passenger compartment 20 having a seat 22 positioned behind an instrument panel 26. A steering controller 30 is disposed between the seat 22 and the instrument panel 26. The steering controller 30 is operated to control the orientation of the steerable wheels. The vehicle 10 includes an electric motor 34 that provides power to one or more of the plurality of wheels 16. A rechargeable energy storage system (RESS) 38 or battery assembly provides power to the electric motor 34.

[0032] Reference now Figure 2 , a heating, ventilation and air conditioning (HVAC) system 40 is operably connected to the RESS 38 for thermal management of the RESS 38 and thermal management of the passenger compartment 20. The HVAC system 40 includes a refrigerant circuit 42 and a coolant circuit 44, which are configured to exchange thermal energy between the refrigerant circuit 42 and the coolant circuit 44, and condition the passenger compartment 20 and also cool the RESS 38. The refrigerant circuit 42 includes a refrigerant flow 46 circulating therethrough. The circulation of the refrigerant flow 46 is driven by a compressor 48, wherein the refrigerant circuit 42 also includes an external condenser 50, a condenser heater 52 arranged in a fluid parallel relationship, and an evaporator 54 and a cooler 56 arranged in a fluid parallel relationship with each other. A condenser heater valve 58 and an external condenser valve 60 are positioned along the refrigerant circuit 42 to selectively direct the refrigerant 46 to flow through the condenser heater 52 and / or the external condenser 50. Similarly, the cooler valve 62 and the evaporator expansion valve 64 are positioned along the refrigerant circuit 44 to selectively direct the refrigerant 46 to flow through the cooler 56 and / or the evaporator 54. The condenser heater 52 and the evaporator 54 selectively provide cooling airflow to the passenger compartment 20 via the evaporator 54 or provide heating airflow to the passenger compartment 20 via the condenser heater 52 through the air door 66. To provide cooling airflow or heating airflow, the supply airflow 68 is forced by the blower 70 through the evaporator 54 and / or the condenser heater 52 and into the passenger compartment 20 through the air door 66.

[0033] The coolant circuit 44 includes a coolant pump 72 to direct a coolant flow 74 through the chiller 56, wherein the coolant flow 74 exchanges heat energy with the refrigerant flow 46 to cool the coolant flow 74. The coolant flow 74 is directed to the RESS 38 to condition the RESS 38.

[0034] refer to Figure 3 and 4 , the HVAC system 40 may be Figure 3 Fresh air mode as shown or Figure 4 Operate in the recirculated air mode shown. First refer to Figure 3 In the fresh air mode, the supply airflow 68 is fresh air drawn from outside the vehicle 10 through the fresh air duct 76. The blower 70 pushes the supply airflow 68 through the evaporator 54. Downstream of the evaporator 54, the first airflow portion 68a can be directed to bypass the condenser heater 52, while the second airflow portion 68b can be directed to pass through the condenser heater 52. The ratio of the first airflow portion 68a to the second airflow portion 68b depends on the airflow temperature selected to be output by the HVAC system 40 and is controlled by the operation of the mixing valve 90. The first airflow portion 68a and the second airflow portion 68b are mixed at the mixing chamber 78 and output to the passenger compartment 20 ( Figure 2 as shown in ).

[0035] Reference now Figure 4 , when operating in the recirculation air mode, the supply airflow 68 is a recirculation airflow from the vehicle passenger compartment 20 through the recirculation air duct 82. The blower 70 pushes the supply airflow 68 through the evaporator 54. Downstream of the evaporator 54, the first airflow portion 68a can be directed to bypass the condenser heater 52, while the second airflow portion 68b can be directed to pass through the condenser heater 52. The ratio of the first airflow portion 68a to the second airflow portion 68b depends on the airflow temperature selected to be output by the HVAC system 40 and is controlled by the operation of the mixing valve 90. The first airflow portion 68a and the second airflow portion 68b are mixed at the mixing chamber 78 and output to the passenger compartment 20 ( Figure 2 The supply air flow 68 is then recirculated through the recirculation air duct 82 .

[0036] When it is necessary to heat the passenger compartment 20, it is generally more efficient to operate the HVAC system 40 in the recirculated air mode, particularly when the ambient temperature is relatively low, such as below 40 degrees Fahrenheit. This is because the recirculated air is warmer than the ambient air and therefore requires less heating of the supply air 68. However, using the recirculated air mode generally increases the relative humidity in the passenger compartment 20, thereby increasing the occurrence of window fogging.

[0037] To reduce the relative humidity of the passenger compartment 20 while still operating in the recirculated air mode, the HVAC system controller 84 ( Figure 4 Operation as shown) Figure 5 The humidity control method shown. To start the humidity control method, the HVAC system controller 84 checks at step 100 for initial conditions that are met for participation in the method. The initial conditions include the following. The ambient air outside the passenger compartment 20 must be cold enough to be heated via the HVAC system 40. The temperature may be, for example, less than 40 degrees Fahrenheit. In addition, the HVAC system 40 must be set to operate in a recirculated air mode. Furthermore, the temperature of the supply air flow 68 must be high enough so that the supply air flow 68 is cooled to a value above the freezing point when flowing through the evaporator 54. Finally, the dew point of the supply air flow 68 must be above the freezing point so that water condensate does not freeze on the evaporator 54.

[0038] When these four conditions are met, the humidity sensor 86 (eg Figure 2 The humidity is monitored by a humidity sensor 86 (shown), which is disposed in the passenger compartment 20 and detects the temperature and relative humidity of the passenger compartment. The dew point of the air in the passenger compartment 20 can be calculated based on the detected temperature and relative humidity. If an increase in humidity is detected, a humidity control operation is initiated at step 102. More specifically, when humidity control is initiated, the evaporator expansion valve 64 is opened, thereby passing the refrigerant flow through the evaporator 54. Thus, the operation of the evaporator condenses excess moisture from the supply airflow 68. The excess moisture is collected at the evaporator 54 and discharged through, for example, the drain pipe 88 ( Figure 4 ) is exhausted from the HVAC system 40. The operation of the refrigerant circuit is controlled by the operation of the evaporator expansion valve 64 to maintain the evaporator superheat greater than zero and to maintain the low-side refrigerant pressure so that the saturation temperature is below the dew point of the supply airflow 68. In addition, the chiller 56 is controlled via the operation of the chiller expansion valve 62 so that the chiller provides increased superheat to compensate for the lower evaporator superheat and to maintain the low-side refrigerant pressure so that the saturation temperature is below the dew point of the supply airflow 68. In addition, the compressor 48 is operated to maintain sufficient passenger cabin 20 heating performance to meet the temperature target of the condenser heater 52.

[0039] After the humidity control operation runs for a preselected duration, the evaporator 54 is dried at step 104. This is accomplished by switching the operating mode of the HVAC system 40 to a partial recirculation mode so that at least a portion of the supply airflow 68 is fresh air entering via the fresh air duct 76. The mixture of relatively cool, relatively dry outside air and recirculated relatively humid air removes excess moisture from the evaporator 54 without freezing the water. In addition, the evaporator expansion valve 64 is closed, thereby stopping the flow of refrigerant through the evaporator 54. With the evaporator expansion valve 64 closed and the operating mode set to partial recirculation, moisture is blown out of the evaporator 54 and travels along the drain 88. This removes excess moisture from the evaporator 54 and flushes excess moisture therefrom. At step 106, the relative humidity is again monitored and the humidity control operation can be repeated if necessary. If the humidity is sufficiently reduced, normal operation of the HVAC system 40 can be resumed at step 108. In some embodiments, it is desirable to reduce and maintain the humidity at a sufficiently low level such that the dew point of the air in the passenger compartment 20 is at least 5 degrees Celsius below the detected temperature of the air in the passenger compartment 20 .

[0040] Utilization of humidity control operation allows efficient operation of the HVAC system 40 using a recirculated air mode while preventing high relative humidity in the passenger compartment 20 , which reduces the occurrence of window fogging.

[0041] The term "one" does not indicate a limitation of quantity, but rather indicates the presence of at least one of the referenced items. Unless the context clearly indicates otherwise, the term "or" means "and / or". References to "aspects" throughout the specification mean that a particular element (e.g., a feature, structure, step, or characteristic) described in conjunction with that aspect is included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it should be understood that the described elements may be combined in any suitable manner in the various aspects.

[0042] Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0043] Although the above disclosure has been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from its scope. In addition, many modifications may be made to adapt specific circumstances or materials to the teachings of the disclosure without departing from the basic scope of the disclosure. Therefore, it is intended that the disclosure is not limited to the specific embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A method of operating a heating, ventilation and air conditioning system of a vehicle, i.e. a method of operating an HVAC system of a vehicle, comprising: operating the HVAC system in a heating mode to heat a supply airflow and direct the heated supply airflow into a passenger compartment of the vehicle; as well as A refrigerant flow is selectively directed through an evaporator of the HVAC system to reduce the relative humidity of the supply air flow by condensing excess moisture from the supply air flow at the evaporator.

2. The method according to claim 1, wherein: The supply air flow is a recirculated air flow from the passenger compartment.

3. The method of claim 2, further comprising removing accumulated moisture from the evaporator by opening a fresh air duct to allow ambient air to enter as part of the supply air flow and stopping the flow of refrigerant through the evaporator. 4 . The method of claim 1 , further comprising controlling operation of the evaporator to maintain an evaporator superheat greater than zero.

5. The method according to claim 1, wherein: The ambient temperature outside the vehicle is less than 40 degrees Fahrenheit.

6. The method according to claim 1, wherein: The dew point of the supply gas flow is greater than zero degrees Celsius.

7. A heating, ventilation and air conditioning system, i.e., HVAC system, for a vehicle, comprising: A refrigerant circuit, the refrigerant circuit comprising: a compressor that causes a flow of refrigerant through the refrigerant circuit; Condenser heater; Evaporator; one or more supply air flow inlets configured to direct a supply air flow through one or more of the condenser heater and the evaporator; one or more outlet ducts configured to direct the supply airflow to a passenger compartment of the vehicle; and An HVAC system controller, the HVAC system controller being configured to: operating the HVAC system in a heating mode to heat the supply airflow by directing the supply airflow through the condenser heater and directing the heated supply airflow into the passenger compartment of the vehicle; and A refrigerant flow may be selectively directed through the evaporator to reduce the relative humidity of the supply gas stream by condensing excess moisture from the supply gas stream at the evaporator.

8. The HVAC system of claim 7, wherein: The supply air flow is a recirculated air flow from the passenger compartment.

9. The HVAC system of claim 8, wherein: The HVAC system controller is also configured to open a fresh air duct to allow ambient air to enter as part of the supply air flow, thereby removing accumulated moisture from the evaporator.

10. A vehicle comprising: a vehicle body defining a passenger compartment; as well as A heating, ventilation and air conditioning system, or HVAC system, is configured to condition the passenger compartment, the HVAC system comprising: A refrigerant circuit, the refrigerant circuit comprising: a compressor that causes a flow of refrigerant through the refrigerant circuit; Condenser heater; Evaporator; one or more supply air flow inlets configured to direct a supply air flow through one or more of the condenser heater and the evaporator; one or more outlet ducts configured to direct the supply airflow to the passenger compartment; and An HVAC system controller, the HVAC system controller being configured to: operating the HVAC system in a heating mode to heat the supply airflow by directing the supply airflow through the condenser heater and directing the heated supply airflow into the passenger compartment; and A refrigerant flow may be selectively directed through the evaporator to reduce the relative humidity of the supply gas stream by condensing excess moisture from the supply gas stream at the evaporator.

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