FIELD OF THE INVENTION

The invention relates to control systems for thermodynamically decoupled control and maintenance of temperature and relative humidity, for example, in conjunction with an HVAC system.

BACKGROUND

Current controllers for heating, ventilation, and air conditioning (HVAC) systems are controlled thermostatically and operate based on thermodynamic equilibrium. These thermostats control the temperature as it is coupled to the relative humidity by physical laws. These thermostats allow the user to set a desired area temperature, and if the temperature drops too far below this setpoint, the room will be heated. Alternatively, if the temperature rises too far above this setpoint, the room will be cooled. Cooling of the air is largely controlled by the removal of humidity through a condensation process which occurs within the HVAC units. In certain interior environments and climates, the thermodynamic coupling of humidity to this thermostatic temperature control is problematic. For example, when cooling dry air in a desert environment, moisture will also be removed, further drying the air and resulting in an uncomfortable living environment. Often in this case, separate pieces of hardware (humidifiers) will be added to solve this problem. Some specialty applications, such as server rooms and electronic assembly areas could greatly benefit from the ability to control the relative humidity as electrostatic discharge is much more common in dry environments that occur when indoor air is cooled.

Additional methods for temperature control can be carried out with 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 an increased humidity and reduced dry bulb temperature.

In addition to the thermostatic (primary) controllers, modern heating, ventilation, air conditioning, and refrigeration (HVAC-R) systems may include sensors for determining inefficient operating conditions such as frost formation. Furthermore, usage, weather, spatial and temporal data may be used to manage the operating conditions of HVAC-R systems including operating duty cycles and operation of defrost cycles. Some modern HVAC-R systems also vary the heat duty of exchangers through variable refrigerant flow.

HVAC-R systems coated with hydrophobic materials cause the water to bead on the surface. As the air is pushed across the cooling surface by the fan, the droplets are also dragged across the surface and into a collection pan. Inevitably, some of these droplets will become entrained into the air stream and revaporize, resulting in a decrease in temperature of the air stream and an increase in humidity. For typical uncoated systems, hydrophilic coated systems, and hydrophobic coated systems, this droplet revaporization is negligible.

Refrigeration systems need to periodically defrost the evaporator coil, which results in increased energy consumption, equipment downtime, increased equipment cost, and increases in the temperature of the products to be cooled. For blast chilling and freezing systems, this often requires to the system to stop in the middle of the chilling cycle to defrost the cooling coil. This reduces throughput and results in a reduction in quality for the chilled/frozen product.

Improved methods and systems for controlling temperature and humidity, and for chilling materials, are needed.

BRIEF SUMMARY OF THE INVENTION

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

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, e.g., an HVAC-R system that comprises a heat exchanger. In one embodiment, the HVAC-R system includes a heat exchanger, and the independent (thermodynamically decoupled) control includes varying the air velocity through the heat exchanger. In some embodiments, the independent (thermodynamically decoupled) control at least partially includes jumping droplet condensation on at least one surface of the HVAC-R system, for example, on at least one surface of a heat exchanger through which the air travels. In some embodiments, the jumping droplet condensation occurs on a nanostructured composition or layer. In one embodiment, the jumping droplet condensation occurs on a nanostructured composition or layer on a structure such as a fin structure, for example, a fin structure that comprises or consists of aluminum or an aluminum alloy.

In some embodiments, the control system reduces or eliminates frost and/or prevents frost formation. In some embodiments, the independent (thermodynamically decoupled) control includes varying the air velocity through the heat exchanger such that the air velocity is greater than the critical air velocity for frost formation, thereby preventing the formation of frost. In some embodiments, during at least a portion of the time that 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 that formed previously to operation of the control system. For example, in some embodiments, critical air velocity is about 1 to about 20 m/s, e.g., about 3 m/s, for air with relative humidity of 0% to about 100%, about 40% to about 80%, e.g., about 60%, and 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. In some embodiments, the heat exchanger includes a coating composition on at least one surface of the heat exchanger through which air travels, and the onset of frost formation is reduced relative to an uncoated system, thereby preventing formation of frost. In some embodiments, the independent (thermodynamically decoupled) control at least partially includes jumping droplet condensation on at least one surface of the HVAC-R system, for example, on at least one surface of a heat exchanger through which the air travels. In some embodiments, the jumping droplet condensation occurs on a nanostructured composition or layer.

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 increases efficiency and/or reduces energy usage through decreased runtime in comparison to a system in which relative humidity and temperature are not independently controlled (thermodynamically decoupled). In some embodiments, the controller establishes a desired comfort setting for occupants of an environment that is exposed to the resultant process fluid, for example, temperature and humidity controlled air. In some embodiments, the control of relative humidity and temperature includes jumping droplet condensation, for example, on a surface of a heat exchanger, e.g., a surface with a coating layer such as a nanostructured coating composition or layer. In some embodiments, the controller controls a first setpoint for temperature and a second setpoint for humidity, for example, in an HVAC-R system.

In another aspect, a coating composition is provided. When deposited on an air-side surface of a heat exchanger, the composition causes a change on the tube-side temperature, pressure, and/or capacity for heat transfer in the heat exchanger. In some embodiments, the coating is nanostructured. In some embodiments, the coating promotes an increased condensate rejection rate in comparison to a surface that does not include the coating composition. For example, the increased condensate rejection rate may include jumping droplet condensation or droplet ejection.

In another aspect, a heat exchanger is provided that includes a coating composition as described herein on at least one air-side surface.

In another aspect, a controller is provided for a heat exchanger that includes an air-side and a tube-side, wherein the controller varies the tube-side temperature, pressure, and/or capacity for heat transfer, for example, in an HVAC or HVAC-R system. In one embodiment, the controller modulates cooling capacity of an HVAC or HVAC-R system. In some embodiments, the controller modulates a variable frequency compressor, e.g., an inverter. In some embodiments, control of the tube-side conditions in the heat exchanger includes a change in the air-side heat transfer rate. In some embodiments, at least one air-side surface of the heat exchanger includes a coating or surface modification, and the air-side heat transfer rate is increased by an increased rate of condensate rejection in comparison to a heat exchanger that does not include the air-side coating or surface modification. For example, the increased rate of condensate rejection may include jumping droplet condensation or droplet ejection. In some embodiments, jumping droplet condensation or droplet ejection on at least one air-side surface of the heat exchanger may be promoted by a coating or surface modification on the air-side heat transfer surface. For example, the coating or surface modification may include a nanostructured composition. In an embodiment, the heat exchanger surface that includes a coating or surface modification, e.g., a nanostructured coating composition or layer, comprises or consists of aluminum or an aluminum alloy.

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

In another aspect, methods and systems are provided to achieve frost-free blast chilling and or reduced-frost blast freezing by using droplet ejection surface modified evaporator coils and thermal control of the coil temperature as part of the refrigeration system. Droplet ejection coatings are able to suppress frost formation below the freezing point of water. This provides completely or substantially frost free blast chillers and blast freezers with fewer defrosts when operated in a prescribed manner. Droplet ejection surface modifications reduce the rate of frost formation or prevent the formation of frost altogether (FIG. 7).

The refrigeration system can be operated under several possible modes, (a) cooling; (b) freezing; or consecutive modes (a)+(b). Under cooling mode (a), the refrigeration system will operate at a temperature sufficient to rapidly chill products and remain above the temperature for onset of frost formation on the evaporator coil. Due to the droplet ejection surface modification, the coil can maintain temperatures 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 about −25° C., without frost formation on the coil. In some embodiments, the operation of the system occurs within the temperature and air velocity range depicted inFIG. 7. Operation in this range allows for the rapid chilling of products without frost formation on the coil and the commensurate defrosting related problems.

When operating in freezing mode (b), the refrigeration system lowers the coil temperature to rapidly freeze the products until the desired set point is achieved. By initially operating in refrigeration mode (a) outlined above and transitioning into freezing mode (b), the air will be dehumidified and the vapor pressure of water will be reduced. When operating in these consecutive cooling and freezing modes (a)+(b), the frost formation is minimized via the previous dehumidification in the chilling mode, with condensate drainage instead of frost formation. The result of operation in these consecutive modes is an increased throughput of chilled product for a given refrigeration system. For example, throughput may be increased at least about 10% or at least about 20%.

These two techniques reduce frost formation which improves coil and system performance and improves the throughput of chilled products through a refrigeration system.

