Control systems for temperature and relative humidity control

Abstract

A control system is provided that provides thermodynamically decoupled control of relative humidity and temperature in a heating, ventilation, air conditioning, and refrigeration (HVAC-R) system that includes a heat exchanger, wherein the thermodynamically decoupled control includes monitoring the temperature and relative humidity of the air or the temperature, pressure, or flow of the refrigerant, wherein the control system controls the temperature difference between the air side and the tube side of the heat exchanger by varying the air velocity through the heat exchanger and / or varying the coolant conditions including temperature, pressure, and / or heat transfer capacity to affect the extent of droplet ejection and / or reevaporation, wherein the thermodynamically decoupled control includes, at least in part, condensation of bouncing droplets on at least one surface of the HVAC-R system, and wherein the droplets are small enough to reevaporate and transfer latent heat to cool the air while increasing humidity.

Description

[0001] This application is a divisional application of the invention patent application with the application date of January 11, 2018, application number 201880006362.8 (international application number PCT / US2018 / 013228), and invention name “Temperature and relative humidity controller”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 445,434, filed January 12, 2017, which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a control system for controlling and maintaining temperature and relative humidity in a thermodynamically decoupled manner, for example, in conjunction with an HVAC system. Background Art

[0005] Current controllers for heating, ventilation, and air conditioning (HVAC) systems are thermostatically controlled and operate based on thermodynamic equilibrium. These thermostats control temperature through the laws of physics when coupled to relative humidity. These thermostats allow the user to set a desired zone temperature, and if the temperature drops far below this set point, the room will be heated. Alternatively, if the temperature rises far above this set point, the room will be cooled. Air cooling is primarily controlled by removing moisture through the condensation process that occurs within the HVAC unit. In certain interior environments and climates, the thermodynamic coupling of humidity with this thermostatic temperature control is problematic. For example, when cooling dry air in a desert environment, moisture is also removed, further drying the air and creating an uncomfortable living environment. Often, in these situations, separate hardware (humidifiers) are added to address this issue. Certain specialized applications, such as server and electronics assembly areas, can greatly benefit from the ability to control relative humidity, as electrostatic discharge is much more common in the dry environments that occur when indoor air is cooled.

[0006] An additional method for temperature control can be implemented using evaporative coolers. In these systems, moisture is added to low-humidity air. The air is cooled adiabatically along a line of constant enthalpy. The resulting air has increased humidity and a lowered dry-bulb temperature.

[0007] In addition to thermostatic (master) controllers, modern heating, ventilation, air conditioning, and refrigeration (HVAC-R) systems may also include sensors to identify inefficient operating conditions, such as frost formation. Furthermore, usage, weather, spatial, and temporal data can be used to manage the operating conditions of the HVAC-R system, including the duty cycle and operation of the defrost cycle. Some modern HVAC-R systems also vary the heat load on the exchanger through variable refrigerant flow.

[0008] HVAC-R systems coated with hydrophobic materials cause water to bead up on the surface. As air is pushed across the cooling surface by the fan, the droplets are also pulled across the surface and into a collection pan. Inevitably, some of these droplets will be entrained in the air stream and re-evaporate, resulting in a decrease in the temperature of the air stream and an increase in humidity. For typical uncoated systems, hydrophilic coating systems, and hydrophobic coating systems, this droplet re-evaporation is negligible.

[0009] Refrigeration systems require regular defrosting of the evaporator coils, resulting in increased energy consumption, increased equipment downtime, higher equipment costs, and higher temperatures for the product being cooled. For forced-air cooling and freezing systems, this often requires stopping the system mid-cooling cycle to defrost the cooling coils. This reduces throughput and results in lower quality of the cooled / frozen product.

[0010] There is a need for improved methods and systems for controlling temperature and humidity and for cooling materials. Summary of the Invention

[0011] Control systems and methods of using the control systems are provided, for example, to independently control temperature and relative humidity in a room or environment (e.g., to provide thermodynamically decoupled control of temperature and relative humidity), and / or, for example, as components of an HVAC or HVAC-R system, to reduce or prevent frost formation or remove previously formed frost in devices such as heat exchangers.

[0012] In one aspect, a control system is provided that provides thermodynamically decoupled control of relative humidity and temperature in a system, such as a heating, ventilation, air conditioning, and refrigeration (HVAC-R) system, such as an HVAC-R system that includes a heat exchanger. In one embodiment, the HVAC-R system includes a heat exchanger, and the independent (thermodynamically decoupled) control includes varying the velocity of air passing through the heat exchanger. In some embodiments, the independent (thermodynamically decoupled) control includes, at least in part, condensation of bouncing droplets on at least one surface of the HVAC-R system, such as at least one surface of a heat exchanger that air traverses. In some embodiments, the condensation of bouncing droplets occurs on a nanostructured composition or layer. In one embodiment, the condensation of bouncing droplets occurs on a nanostructured composition or layer on a structure, such as a fin-like structure, such as a fin-like structure that includes or consists of aluminum or an aluminum alloy.

[0013] In some embodiments, the control system reduces or eliminates frost and / or prevents frost formation. In some embodiments, independent (thermodynamically decoupled) control comprises varying the air velocity through the heat exchanger such that the air velocity is greater than a critical air velocity for frost formation, thereby preventing frost formation. In some embodiments, during at least a portion of the time the control system is in operation, the air velocity through the heat exchanger is increased to a value greater than the critical air velocity for frost formation, thereby removing frost formed prior to operation of the control system. For example, in some embodiments, for air having a relative humidity of 0% to about 100%, about 40% to about 80%, such as about 60%, and a temperature of about 0°C to about 60°C, about 5°C to about 40°C, about 10°C to about 30°C, or about 15°C to about 25°C, the critical air velocity is about 1 to about 20 m / s, such as about 3 m / s. In some embodiments, the heat exchanger comprises a coating composition on at least one surface of the heat exchanger over which air passes, and wherein the onset of frost formation is reduced relative to an uncoated system, thereby preventing frost formation. In some embodiments, independent (thermodynamically decoupled) control is provided for condensation of bouncing droplets on at least one surface of the HVAC-R system, such as at least one surface of a heat exchanger over which air passes. In some embodiments, condensation of bouncing droplets occurs on a nanostructured composition or layer.

[0014] In another aspect, a controller is provided that decouples (e.g., independently controls) the control of relative humidity and temperature. In some embodiments, the controller improves efficiency and / or reduces energy usage by reducing run time compared to a system in which relative humidity and temperature are not independently controlled (thermodynamically decoupled). In some embodiments, the controller establishes desired comfort settings for occupants of an environment exposed to a process fluid such as temperature and humidity controlled air. In some embodiments, the control of relative humidity and temperature comprises condensation of bouncing droplets on a surface, such as a heat exchanger, such as a surface having a coating such as a nanostructured coating composition or layer. In some embodiments, the controller controls a first temperature set point and a second humidity set point, such as in an HVAC-R system.

[0015] In another aspect, a coating composition is provided. When deposited on an air-side surface of a heat exchanger, the composition causes a change in tube-side temperature, pressure, and / or heat transfer capacity in the heat exchanger. In some embodiments, the coating is nanostructured. In some embodiments, the coating promotes improved condensate rejection compared to a surface not comprising the coating composition. For example, the improved condensate rejection may include bouncing droplet condensation or droplet ejection.

[0016] In another aspect, a heat exchanger is provided comprising a coating composition as described herein on at least one air-side surface.

[0017] In another aspect, a controller for a heat exchanger comprising an air side and a tube side is provided, wherein the controller varies the tube side temperature, pressure, and / or heat transfer capacity, for example, in an HVAC or HVAC-R system. In one embodiment, the controller adjusts the cooling capacity of the HVAC or HVAC-R system.

[0018] In some embodiments, the controller regulates a variable frequency compressor, such as an inverter. In some embodiments, controlling the tube-side conditions in the heat exchanger comprises varying the air-side heat transfer rate. In some embodiments, at least one air-side surface of the heat exchanger comprises a coating or surface modification, and the air-side heat transfer rate is increased due to increased condensate rejection compared to a heat exchanger not comprising the air-side coating or surface modification. For example, the increased condensate rejection may comprise bouncing droplet condensation or droplet ejection. In some embodiments, bouncing droplet condensation or droplet ejection on at least one air-side surface of the heat exchanger may be facilitated by a coating or surface modification of the air-side heat transfer surface. For example, the coating or surface modification may comprise a nanostructured composition. In some embodiments, the heat exchanger surface comprising a coating or surface modification, such as a nanostructured coating composition or layer, comprises or consists of aluminum or an aluminum alloy.

[0019] In another aspect, a controller is provided that controls air velocity and coolant temperature, pressure, and / or capacity to achieve desired decoupled (eg, independently controlled) air temperature and air humidity output conditions in an HVAC-R system.

[0020] In another aspect, methods and systems are provided for achieving frost-free blast cooling and or frost-reduced blast freezing by modifying the evaporator coil using a droplet spray surface and thermally controlling the coil temperature as part of the refrigeration system. The droplet spray coating is capable of inhibiting frost formation below the freezing point of water. This provides, completely or substantially, a frost-free blast cooler and a blast freezer with less defrost when operated in a prescribed manner. The droplet spray surface modification reduces the rate of frost formation or completely prevents frost formation ( Figure 7 ).

[0021] The refrigeration system can operate in several possible modes: (a) cooling; (b) freezing; or continuous mode (a) + (b). In cooling mode (a), the refrigeration system will operate at a temperature sufficient to quickly cool the product and remain above that temperature within the initial onset of frost formation on the evaporator coil. Due to the droplet jet surface modification, the coil can maintain a temperature below 0°C, about 0°C to about -25°C, about -5°C to about -10°C, or any of about -5°C, about -10°C, about -15°C, about -20°C, or 25°C without frost forming on the coil. In some embodiments, at the temperature and Figure 7 Operation of the system occurs within the air velocity range depicted in FIG. Operation within this range allows for rapid cooling of the product without frost formation on the coils and commensurate defrost-related problems.

[0022] When operating in freezing mode (b), the refrigeration system lowers the coil temperature to rapidly freeze the product until the desired set point is achieved. By first operating in cooling mode (a), as outlined above, and then transitioning to freezing mode (b), the air is dehumidified and the water vapor pressure is reduced. When operating in these sequential cooling and freezing modes (a) + (b), frost formation is minimized by the prior dehumidification in the cooling mode, and condensate is drained away rather than forming frost. The result of operating in these sequential modes is an increase in the throughput of cooled product for a given refrigeration system. For example, throughput can be increased by at least about 10% or at least about 20%.

[0023] Both technologies reduce frost buildup, which improves coil and system performance and increases the throughput of product cooled by the refrigeration system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1Depicting a controller in an HVAC-R system in a hot and dry environment compared to a conventional cooling path.

[0025] Figure 2 Depicts the controller and general cooling paths in an HVAC-R system under hot and humid outdoor conditions.

[0026] Figure 3 Depicts the interaction of controllers as described herein within an HVAC-R system.

[0027] Figure 4 A 9 mm wide field image is shown. The nanostructured surface is located at the bottom of the image. Droplets of varying sizes can be seen. The white area at the top is the background, uncoated substrate, which readily shows frost. The operating speed for this image is above the critical speed for frost formation.

[0028] Figure 5 An operating scheme for air velocity that can be used as part of a control algorithm to avoid or minimize frost formation is shown.

[0029] Figure 6 Samples are shown under conditions that induce frost formation (t=0 to 12 minutes) and thawing (12 to 13.5 minutes).The velocity profiles for these test configurations are shown in the top portion of the figure.

[0030] Figure 7 The frost on a droplet spray coated coil and an uncoated coil is shown for saturated air as a function of inlet air velocity and temperature. In this figure, the inlet air is saturated, but similar graphs can be generated depending on the inlet relative humidity. DETAILED DESCRIPTION

[0031] A control system and controller are provided for independently regulating temperature and relative humidity, for example in an HVAC or HVAC-R system.Temperature and relative humidity are thermodynamically decoupled in the system described herein.

[0032] Known super-hydrophobic materials allow droplets to be ejected or "bounced" from surfaces with very small sizes, which can increase the amount of entrained droplets by many orders of magnitude compared to unmodified hydrophilic or hydrophobic surfaces. The entrained liquid from these surfaces later comes from large turbulence or discharge action. The resulting droplets are large and have a limited re-evaporation rate. By contrast, on some super-hydrophobic surfaces, a very large number (e.g., millions) of droplets are entrained and taken downstream per second. In addition, these droplets are small enough to evaporate quickly and will transfer latent heat to cool the air while increasing humidity. This type of material is described herein with respect to heat exchange and subsequent control of temperature and relative humidity (RH).

[0033] The number of droplets that bounce or eject from the surface to become entrained depends on the air velocity in the heat exchanger. By controlling the face velocity across the exchanger, the amount of reevaporation can be controlled, allowing for a range of independent temperature and RH options, rather than the coupled temperature and RH control provided by current thermostatic systems. Furthermore, the degree to which the condensation driving force is controlled by the temperature difference between the refrigerant (tube side) and the air (fin side) in the heat exchanger will affect the degree of droplet ejection and reevaporation. This can be achieved in a variety of ways, including but not limited to refrigerant velocity, by controlling the refrigerant temperature (refrigerant pressure) of the compressor, and / or air flow as described above.

[0034] In certain embodiments, the coating composition promotes the change of the face velocity described herein and the potential degradation phenomenon, and the coating composition causes the change of the tube side balance in the heat exchanger. In certain embodiments, the coating composition comprises nanostructured materials. In certain embodiments, the nanostructured materials promote the spraying of droplets from the surface. The significant increase of the air side heat transfer coefficient can greatly increase the capacity of the heat exchanger, and therefore, will also need the capacity of the tube side to increase. This can be achieved by variable capacity compressors such as inverter compressors.

[0035] This new coupling of air velocity, air cooling capacity, and consequent tube side capacity requires novel control systems to maximize the functionality of the coated HVAC-R system and maximize its operating efficiency. Figure 3 A schematic diagram of an example control system is shown in FIG.

[0036] In some embodiments, the conditions of the incoming air and the fin temperature cause condensation to form on the exchanger. This frosting limits heat transfer from the evaporator, reducing the amount of useful cooling from the device and additionally increasing the pressure drop across the evaporator coil, which can adversely affect energy efficiency.

[0037] In certain embodiments, utilizing nanostructured coatings applied as described herein, it has surprisingly been shown that at certain speeds at which frost readily forms on materials without the nanostructured coating (i.e., speeds obtainable in typical HVAC systems), no frost formation is observed. Figure 4 An example of this phenomenon is shown in . Condensation was observed to continue in the unfrozen area.

[0038] In certain embodiments, HVAC-R system designs are provided in which the design air velocity is greater than the critical air velocity for a particular nanostructured surface, where the onset of frost formation is severely delayed or even completely prevented. In certain embodiments, it is desirable that the velocity across the surface be minimized to limit pressure drop and potential noise generation.

[0039] Surprisingly, it has also been observed that changing the air velocity alone is sufficient to defrost a sample coated with a nanostructured coating. In this scenario, the sample was subjected to conditions that would otherwise cause frost formation. The air velocity was increased, and the frost formed under the previous conditions was removed into liquid water and removed from the sample.

[0040] In some embodiments, an HVAC-R control system design is provided in which the main operating air speed can lead to conditions where frost formation can occur in a prescribed or otherwise controlled manner, and the main air speed is increased to remove any potential frost and prevent additional frost formation and its proportionately harmful consequences. The periods of increased speed can be relatively frequent to prevent frost formation and prevent heat transfer fouling due to frost, or can be relatively infrequent to remove frost that has already formed.

[0041] Air velocity can be adjusted by fan speed, spacing or proximity, bypass ventilation, baffles or dampers (the latter being the case with the inlet cooler of the turbine where the turbine is located downstream and is the prime mover of the process fluid (air) and the speed can be varied by affecting the position of the damper on the front end).

[0042] definition

[0043] "a," ​​"an," and "the" include plural referents unless the context clearly dictates otherwise.

[0044] A "nanostructured" coating refers to a coating composition having features smaller than 100 nanometers in at least one dimension.

[0045] "Non-condensable gas" or "NCG" refers to a gas that does not change phase under the expected condensation conditions of vapor. For example, oxygen and nitrogen are NCGs when dehumidified.

[0046] "Condensing conditions" are those conditions where the surface is cooled below the dew point of the vapor.

[0047] "Supersaturation" refers to the condition where the vapor pressure of a vapor is higher than the equilibrium vapor pressure at a given temperature and pressure. A supersaturation of 1 refers to 100% relative humidity, and any further increase promotes condensation.

[0048] "Jet" with respect to a liquid droplet means leaving a surface at a velocity having a non-zero normal component.

[0049] "Surface tension" refers to the tension at the surface of a liquid caused by cohesive forces in the bulk of the liquid, which pull the volume inward and tend to minimize the surface area of ​​a given volume.

[0050] "Droplet adhesion" refers to the forces responsible for causing a droplet to pull outward and spread on a surface, thereby preventing the droplet from forming a sphere. Conversely, "cohesion" is those forces, such as surface tension, that cause a droplet to pull itself inward and form a sphere.

[0051] A "refrigerant" is a substance or mixture used as the working fluid in a refrigeration cycle. This fluid often undergoes phase changes, but need not be active. Commercial refrigerants include, but are not limited to, R-22, R-134a, R-401, and other formulations. A non-limiting list of refrigerants can be found at https: / / en.wikipedia.org / wiki / List_of_refrigerants.

[0052] A "working fluid" is a liquid or gas that absorbs or emits energy. For example, the working fluid in an air conditioning system is a coolant such as a chlorofluorocarbon, glycol, ammonia, propane, or water used to cool a process fluid.

[0053] A "process fluid" is a liquid or gas that is processed by interaction with a working fluid. For example, in an air conditioning system, the process fluid is the air being cooled.

[0054] "Sensible heat" refers to the change in temperature of a gas or object without a change of phase.

[0055] "Sensible heat ratio" refers to the ratio of sensible heat cooling capacity to total cooling capacity.

[0056] "Control system" and "controller" are used interchangeably herein to refer to control logic, machine code, design, concept, configuration and / or supporting hardware.

[0057] "Relative humidity" refers to the amount of water vapor present in the air, expressed as a percentage of the amount required to reach saturation at the same temperature.

[0058] The "air side" with respect to a heat exchanger refers to the surface adjacent to and area associated with a process fluid, such as air to be cooled.

[0059] The "air side heat transfer rate" refers to the amount of heat transferred from the process fluid to the main evaporator unit.

[0060] "Tube side" with respect to a heat exchanger refers to the surface adjacent to the working fluid, such as the refrigerant.

[0061] "Condensate rejection" refers to the amount of condensate that condenses from the air stream and is removed from the primary heat transfer surface per unit time.

[0062] "Bouncing droplet condensation" or "droplet spray" refers to condensate formed on a primary heat transfer surface where the droplets leave the surface at a velocity out of the plane of the primary heat transfer surface (as opposed to rolling along the surface, finding an edge, and separating). Typically, but not necessarily, the droplets are subject to external forces (drag, vibration, coalescence, gravity, etc.).

[0063] "Throughput" refers to the amount of product or commodity that can be cooled or frozen per unit time (eg, pounds per day).

[0064] Controller

[0065] exist Figure 3 A diagram indicating a non-limiting example of how a controller as described herein may be interfaced within an HVAC-R system is shown in FIG. In this case, the controller operates as a negative feedback controller, where the input temperature and humidity set points are subtracted from the sensor readings of the air output. This differential error in the set points is reduced by the controller adjusting the air speed to increase or decrease the effect of the droplet spray and thereby increase or decrease the potential for degradation. For example, in some embodiments, the controller may operate at an air speed of approximately 300 feet per minute (fpm) for part of the time, such as most of the time, and increase the speed to approximately 600 to approximately 800 or approximately 1000 fpm to remove frost, then return to approximately 300 fpm. The air speed can be adjusted by varying the fan speed. Additionally, the compressor capacity can be controlled by varying the frequency of the variable frequency drive. The benefits of this control system with a droplet spray coating on the coils are decoupled output air temperature and humidity, and more efficient operation.

[0066] The systems described herein (e.g., nanostructured coated heat exchangers) can be used within existing controller systems, such as variable refrigerant flow systems, to control tube-side HVAC conditions. In some embodiments, variable refrigerant control can be achieved through variable refrigerant compressor speed or variable pressure drop across an expansion valve.

[0067] The refrigeration system herein can be controlled to operate in a frost-free zone to prevent the need for defrosting. This can be achieved by generating, for example, Figure 7 The inlet humidity, temperature and velocity graphs shown in define this operating range. The refrigerant pressure temperature and mass flow of the system can be monitored. The inlet humidity, temperature and velocity of the system can be monitored. Combinations of parameters in the system can be monitored. The air velocity and refrigerant mass flow can be controlled by valves and / or programmable fan motors or other means known to those skilled in the art. As an example, an algorithm can be developed and employed to control the speed of the fan, where the result is to avoid or regulate frost. In Figure 5 and 6 Examples of operating schemes and control algorithms for controlling frost are provided in .

[0068] Droplet jet coating

[0069] In some embodiments of the temperature and relative humidity control systems described herein, a droplet jet coating material is provided that ejects condensed liquid droplets from a surface of a substrate, such as a heat exchanger, in an HVAC system. In some embodiments, the droplet jet coating material comprises nanostructures deposited on a substrate and, optionally, a hydrophobic material deposited on the nanostructured material. The nanostructured material comprises geometric structures that provide a driving force for ejecting droplets from a surface. The geometric structures may include, but are not limited to, nanostructures that cause the droplets to assume a deformed shape upon condensation.

[0070] The droplet jetting coating material may comprise a surface that is textured so that condensed droplets are ejected when surface tension exceeds droplet adhesion forces, thereby generating a net force vector having a component out of the plane of the substrate.

[0071] The coating materials disclosed herein can spray a condensing fluid from a surface in the presence of one or more non-condensing gases (NCGs). For example, the coating material can spray a fluid in the presence of air, a gaseous component of air, or an inert gas. In some embodiments, the NCG is selected from air, nitrogen, oxygen, carbon dioxide, hydrogen, helium, argon, or a combination thereof. In some embodiments, the NCG is selected from air, oxygen, nitrogen, carbon dioxide, argon, or a combination thereof. In one embodiment, the NCG is air.

[0072] The coating materials disclosed herein can eject condensed fluid from a surface at a supersaturation greater than about 1.0, about 1.1, about 1.2, or about 1.25, or at a supersaturation of about 1.0 to about 1.1, about 1.1 to about 1.25, about 1.1 to about 3.0, or about 1.1 to 5.0.

[0073] The condensed fluid droplets that can be sprayed by the coating disclosed herein include, but are not limited to, water, ethanol, and refrigerants. In some embodiments, the condensed fluid is selected from water, ethanol, hydrofluorocarbons (HFCs), and hydrofluoroolefins (HFOs), or combinations thereof. In some embodiments, the condensed fluid is selected from water, ethanol, difluoromethane (HFC-32), difluoroethane (HFc-152a), pentafluoroethane (HFC-125), 2,3,3,3-tetrafluoropropylene (HCO-1234yf), 1,3,3,3-tetrafluoropropylene (HFO1234ze), or combinations thereof. In one embodiment, the condensed fluid is water. In some embodiments, the condensed fluid is an industrial process or working fluid.

[0074] Fluid droplet jet coating materials as described herein can jet condensed fluid droplets from a surface having an average diameter of less than about 2 millimeters, less than about 1 millimeter, or less than about 500 microns.

[0075] In some embodiments, the nanostructured coating comprises a nanostructured metal, ceramic, glass, or polymer.

[0076] In some embodiments, the nanostructured coating comprises a ceramic that is a metal oxide. The metal oxide can be, for example, a transition metal oxide, tin (IV) oxide, magnesium oxide, or aluminum oxide. In some embodiments, the transition metal oxide is selected from zinc oxide, iron (II, III) oxide (Fe3O4), iron (III) oxide (Fe2O3), manganese (IV) oxide (MnO2), manganese (II, III) oxide (Mn3O4), manganese (III) oxide (Mn2O3), nickel (II) oxide (NiO), nickel (III) oxide (Ni2O3), zirconium (IV) oxide (ZrO2), titanium (IV) oxide (TiO2), chromium (III) oxide (Cr2O3), copper (II) oxide (CuO), cobalt (II) oxide (CoO), cobalt (III) oxide (Co2O3), and cobalt (II, III) oxide (Co3O4).

[0077] In some embodiments, the nanostructured coating comprises glass. In some instances, the glass comprises silicon dioxide or a silicate.

[0078] In some embodiments, the nanostructured coating comprises a polymer. In some instances, the polymer is a fluoropolymer, polyethylene, or polypropylene. In some embodiments, the polymer is a fluoropolymer selected from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), and fluorinated ethylene propylene (FEP), or a combination thereof. In some embodiments, the polymer is a block copolymer, such as, but not limited to, each block of the copolymer is less than about 500 monomer units or less than about 200 monomer units. For example, the block copolymer can be a hydrophobic polymer comprising two or more monomer units. In some embodiments, the block copolymer can include one or more monomers, such as, but not limited to, propylene, ethylene, tetrafluoroethylene, trifluoroethylene, vinyl fluoride, hexafluoropropylene, 1,1-difluoroethylene, 1,2-difluoroethylene, and isobutylene.

[0079] In some embodiments, the hydrophobic coating may include one or more hydrophobic functional groups selected from alkyl, vinyl, phenyl, and fluoroalkyl groups. For example, the hydrophobic functional group may include, but is not limited to, alkylsilane, vinylsilane, phenylsilane, or fluoroalkylsilane. In certain non-limiting embodiments, the hydrophobic functionality is hexamethyldisilazane, sodium methylsilicate, potassium methylsilicate, polydimethylsiloxane, perfluorooctyltriethoxysilane, perfluorooctyltriethoxysilane, perfluorooctyltrimethoxysilane, perfluorodecyltrimethoxysilane, octadecyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, or phenyltriethoxysilane. In some embodiments, the hydrophobic coating refers to a coating that imparts a contact angle greater than or equal to 90 degrees when added to a smooth substrate.

[0080] Method for producing droplet jet coating

[0081] Methods for producing a coating, such as by ejecting droplets of condensed liquid from a substrate under condensation conditions, are provided. In certain non-limiting embodiments, the method comprises: (a) depositing a nanostructured coating on a substrate; and optionally (b) depositing a hydrophobic functional layer, i.e., a hydrophobic material comprising one or more hydrophobic functional groups, on the surface of the nanostructured material.

[0082] The nanostructured layer can be deposited on the substrate by any suitable means, including but not limited to sol-gel processing, chemical bath deposition, dip coating, spray coating, physical vapor deposition, or chemical vapor deposition. In one embodiment, the nanostructured coating is a metal oxide deposited by, for example, sol-gel processing, chemical bath deposition, or dip coating. The hydrophobic functional layer can be deposited onto the nanostructured layer by any suitable means, including but not limited to vapor deposition or dip coating.

[0083] Non-limiting examples of nanostructures and hydrophobic coating materials are described above.The substrate may comprise a metal, metal alloy, glass, or ceramic material.

[0084] In some embodiments, the substrate is pretreated prior to depositing a coating composition, such as a nanostructured coating as described herein, to remove debris or matter on the surface and / or smooth the surface (i.e., to access the substrate to promote adhesion and prevent defects), with one or more treatments selected from cleaning, degreasing, rinsing, etching, desmearing, oxidizing, removing previous treatments, roughening, planarizing, steam cleaning, thermal oxidation, and smoothing.

[0085] The following examples are intended to illustrate but not to limit the present invention.

[0086] Examples

[0087] Example 1

[0088] In a hot and dry environment, such as 37°C and 20% relative humidity (RH), a controller as described herein operates in conventional cooling mode at a face velocity of, for example, 0 to about 3 m / s, such as about 1.5 m / s, and significantly cools the air to the desired comfort range. Alternatively, if the operator requires higher relative humidity and lower power consumption or the controller is programmed to minimize energy consumption, the face velocity is increased to about 1 to about 20 m / s, such as about 3.0 m / s, which will result in a greater droplet ejection rate, thereby increasing the reevaporation rate. This increases humidity and raises temperature. The controller enables the HVAC system to operate simultaneously as a conventional forced air coil and an evaporative cooler.

[0089] Figure 1 The cooling path on the psychrometric diagram is shown. When the operator requests higher humidity, the controller-enabled cooling path (1→2→4) is shown, as opposed to the conventional cooling path (1→2→3). The cooling unit operates conventionally, and the controller switches on at point 2 and increases the fan speed to raise the humidity, providing additional cooling capacity due to latent degradation and improving the unit's overall efficiency to achieve conditions in the comfort zone. This controlled latent degradation path allows for simultaneous evaporative cooling and forced heat dissipation, resulting in a greater than 50% reduction in energy use.

[0090] Example 2

[0091] The controller as described herein advantageously operates in hot and humid environments, such as outdoor conditions of 30°C and 80% RH. High humidity environments do not allow for any additional potential degradation. The controller thus allows the unit to be cooled using conventional operating routes to minimize energy usage at the desired set point. Figure 2 This cooling path is plotted in the middle.

[0092] In hot and humid environments, the controller will not increase the fan speed and will follow the normal cooling path. In this condition, due to the low sensible heat ratio, this is the most energy-efficient cooling route. The controller is programmed to recognize this situation in order to operate the unit as efficiently as possible.

[0093] Example 3

[0094] An aluminum plate of approximately 30 mm by 40 mm having the nanostructured coating applied as described herein was placed into a wind tunnel and mounted to a cold plate having an estimated temperature of -15°C. Uncoated aluminum positioned adjacent to the plate was covered with frost. The airflow conditions were ~20°C, 60% RH. The velocity across the plate was approximately 5 m / s. These conditions were maintained for over 1 hour. Frost was observed on the uncoated sections, while the nanostructured coating material showed only condensation. After steady state conditions were observed, the velocity was reduced to 2 m / s. After a few minutes, droplets and frost freezing were observed on both the nanostructured coating sample and the uncoated material. After a period of 12 minutes, the velocity was returned to 5 m / s and melting of ice and frost was noted on the frosted surface. After approximately 90 seconds, the previously observed steady state conditions were reestablished. Figure 6 The results are shown in .

[0095] Example 4

[0096] A fin-and-tube heat exchanger having surface-modified fins containing a surface material that promotes droplet ejection is placed in a controlled cooling environment where inlet air conditions, including humidity and temperature, are controlled.

[0097] This system uses a recirculating chiller filled with a glycol-water mixture on the tube side. This water-side circuit is measured for inlet temperature, outlet temperature, and coolant flow rate. These measurements allow the calculation of the heat transferred to the refrigerant.

[0098] The air flowing across the heat exchanger is also measured for inlet temperature, outlet temperature, inlet relative humidity, outlet relative humidity, and volume flow rate. These measurements are used to calculate the amount of energy removed from the air as it passes across the heat exchanger.

[0099] One coil was tested with a droplet spray coating. Another coil was tested in a similar manner without droplet spray. The coils were subjected to inlet air velocities ranging from 200 to 500 feet per minute. The inlet air was saturated with water (RH 100%), and the inlet air temperature was varied from 0°C to -6°C. During these tests, the coolant flow rate was set to ensure a minimum difference between the inlet air temperature and the coolant temperature. The coils were visually inspected for the onset of frost.

[0100] Surfaces with droplet spray coatings required lower inlet temperatures to observe frost formation than those without droplet spray coatings. The degree of frost initiation inhibition depended on air velocity, ranging from about -4°C at low velocities to about -6°C at high velocities. The velocity range corresponds to typical HVAC conditions, but the mechanism described should apply to a wider range of velocities. The uncoated coil showed frost initiation of about -1.5°C at low velocities to about -3°C at high velocities. These results are shown graphically as Figure 7 .

[0101] Example 5

[0102] Large blast chillers bring in large quantities of product to be cooled / frozen. Current systems are capable of freezing product at a rate of 10,000 pounds (lbs) of product per day. This limit can be set by the amount of time required to defrost the cooling coils. As an example, a cooling coil may operate for 11 hours and require a 1-hour defrost cycle. The operation of droplet spray coating and the embodiments of the operating conditions described herein provide for continuous operation without the need for defrost. This creates the ability to process approximately 11,000 lbs of product per day—a 10% increase in facility throughput.

[0103] Although the foregoing invention has been described in detail by way of illustration and example for purposes of clarity of understanding, it will be apparent to those skilled in the art that certain changes and modifications may be implemented without departing from the spirit and scope of the invention. Therefore, the description should not be construed as limiting the scope of the invention, which is described in the appended claims.

[0104] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

[0105] A control system is provided that provides thermodynamically decoupled control of relative humidity and temperature in a heating, ventilation, air conditioning, and refrigeration (HVAC-R) system that includes a heat exchanger, wherein the thermodynamically decoupled control includes monitoring the temperature and relative humidity of the air or the temperature, pressure, or flow of the refrigerant, wherein the control system controls the temperature difference between the air side and the tube side of the heat exchanger by varying the air velocity through the heat exchanger and / or varying the coolant conditions including temperature, pressure, and / or heat transfer capacity to affect the extent of droplet ejection and / or reevaporation, wherein the thermodynamically decoupled control includes, at least in part, condensation of bouncing droplets on at least one surface of the HVAC-R system, and wherein the droplets are small enough to reevaporate and transfer latent heat to cool the air while increasing humidity.

[0106] In one embodiment, the thermodynamic decoupling control includes adjusting air velocity to increase or decrease the effects of droplet ejection and / or re-evaporation.

[0107] In one embodiment, the thermodynamic decoupling control includes regulating air velocity through the HVAC-R system by varying fan speed.

[0108] In one embodiment, the thermodynamic decoupling control includes adjusting the compressor capacity by varying the frequency of a variable frequency drive.

[0109] In one embodiment, the thermodynamic decoupling control includes adjusting a variable refrigerant compressor speed or a variable pressure drop across an expansion valve.

[0110] In one embodiment, the bouncing droplet condensation occurs on the air-traversed surface of the heat exchanger.

[0111] In one embodiment, the at least one surface comprises a nanostructured layer, the nanostructured layer being in contact with the air passing through the heat exchanger.

[0112] In one embodiment, the re-evaporation of the droplets and the transfer of the latent heat limit the formation and accumulation of frost and / or ice on the HVAC-R system.

[0113] In one embodiment, the HVAC-R system is controlled to operate within a frost-free operating range to prevent the need to defrost the system.

[0114] In one embodiment, the system is monitored for refrigerant pressure, refrigerant temperature, refrigerant mass flow, inlet air humidity, inlet air temperature, inlet air velocity, or a combination thereof, and wherein air velocity and refrigerant mass flow are controlled by valves and / or programmable fan motors.

Claims

1. A control system that provides thermodynamically decoupled control of relative humidity and temperature in a heating, ventilation, air conditioning, and refrigeration (HVAC-R) system that includes a heat exchanger. The thermodynamic decoupling control includes monitoring the temperature and relative humidity of the air or the temperature, pressure or flow of the refrigerant, wherein the control system controls the temperature difference between the air side and the tube side of the heat exchanger by varying the air velocity through the heat exchanger and / or varying coolant conditions including temperature, pressure and / or heat transfer capacity to affect the extent of droplet ejection and / or re-evaporation, wherein the thermodynamically decoupled control comprises, at least in part, condensation of bouncing liquid droplets on at least one surface of the HVAC-R system, and The droplets are small enough to re-evaporate and transfer latent heat, cooling the air while increasing humidity.

2. The control system of claim 1, wherein the thermodynamic decoupling control comprises adjusting air velocity to increase or decrease the effects of droplet ejection and / or re-evaporation.

3. The control system of claim 2, wherein the thermodynamic decoupling control includes regulating air velocity through the HVAC-R system by varying fan speed.

4. The control system of claim 1 , wherein the thermodynamic decoupling control includes adjusting compressor capacity by varying the frequency of a variable frequency drive.

5. The control system of claim 1, wherein the thermodynamic decoupling control comprises adjusting a variable refrigerant compressor speed or a variable pressure drop across an expansion valve.

6. The control system of claim 1, wherein the bouncing droplet condensation occurs on the air-traversed surface of the heat exchanger.

7. The control system of claim 6, wherein the at least one surface comprises a nanostructured layer that contacts the air passing through the heat exchanger.

8. The control system of any one of claims 1 to 7, wherein re-evaporation of the liquid droplets and transfer of the latent heat limits the formation and accumulation of frost and / or ice on the HVAC-R system.

9. The control system of claim 8, wherein the HVAC-R system is controlled to operate within a frost-free operating range to prevent the need to defrost the system.

10. The control system of claim 9, wherein the system monitors refrigerant pressure, refrigerant temperature, refrigerant mass flow, intake air humidity, intake air temperature, intake air velocity, or a combination thereof, and Air speed and refrigerant mass flow are controlled by valves and / or programmable fan motors.

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