US20100281893A1

US20100281893A1 - Desiccant dehumidifier utilizing hot water for reactivation, and related method

Info

Publication number: US20100281893A1
Application number: US12/777,633
Authority: US
Inventors: Kenneth Wheeler
Original assignee: Stulz Air Tech Systems Inc
Current assignee: Stulz Air Tech Systems Inc
Priority date: 2009-05-11
Filing date: 2010-05-11
Publication date: 2010-11-11

Abstract

An air conditioning system includes a refrigeration cooling coil in fluid communication with process air, a refrigeration circuit containing refrigerant, a heat exchanger in fluid communication with the refrigerant and water, the heat exchanger adapted to transfer heat from the refrigerant to the water, a hot water coil in fluid communication with the water, a desiccant rotor having a process portion in fluid communication with the process air and a reactivation portion, and a reactivation blower adapted to move reactivation air over the hot water coil and through the reactivation portion of the desiccant rotor. A method of conditioning air is also described.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 61/177,115, filed May 11, 2009, the entire content of which is expressly incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to air conditioning systems and related methods. More specifically, the present invention relates to desiccant dehumidification systems using waste heat to reactivate a desiccant rotor, and related methods.

BACKGROUND

Desiccant dehumidification systems can be used to dehumidify a user-defined space or process application below levels typically obtained with a refrigeration-based dehumidification system. The main components typically include a cabinet, motorized fans (e.g., one each for process air and reactivation air), a reactivation heater system (e.g., electric, steam, hot water or gas-fired), a desiccant rotor, and a motorized drive system for the rotor.
An example of a desiccant rotor 10 is shown in FIG. 1. The rotor 10 may include a series of channel openings (e.g., flutes) 12, shown in FIG. 1A, which may allow air to flow through from one side 10 a of the rotor and exit on the opposite side 10 b, and vice versa. The desiccant rotor 10 may have a center hub 14 and axle (not shown) upon which the rotor 10 rotates.
Referring to FIG. 2, moisture can be removed from the air through an adsorption process using a dry desiccant material that is located in or on the surface of the desiccant rotor 10. Air to be dehumidified (process air) can pass through the desiccant rotor 10, whereby moisture is adsorbed by the desiccant. The conditioned air exits the desiccant rotor 10 at a lower humidity and a slightly higher dry bulb temperature than its inlet condition. Simultaneously, a second air stream (reactivation air) can be heated by a reactivation heater 20 and passed through a separate segment of the desiccant rotor 10. The heated air can remove the previously adsorbed moisture from the rotor 10 and exhaust it to an area other than that being conditioned. When operating, the desiccant rotor 10 moves through the process and reactivation sections of the dehumidifier, such that any given time, a portion of the rotor 10 is in communication with the process air, and another portion of the rotor 10 is in communication with the reactivation air. The process and reactivation airstreams are typically counterflow to each other to maximize the efficiency of the adsorption process and to help prevent the rotor 10 from fouling. The process and reactivation airstreams are typically separated by seals 22 and/or internal fluting in the rotor 10.
The reactivation heater 20 is typically designed to raise the temperature of the air entering the reactivation segment of the desiccant rotor 10. The energy from the heated reactivation air is used to desorb the moisture from the rotor 10.

SUMMARY

According to an exemplary embodiment, an air conditioning system comprises: a refrigeration cooling coil in fluid communication with process air; a refrigeration circuit containing refrigerant; a heat exchanger in fluid communication with the refrigerant and water, the heat exchanger adapted to transfer heat from the refrigerant to the water; a hot water coil in fluid communication with the water; a desiccant rotor having a process portion in fluid communication with the process air, and a reactivation portion; and a reactivation blower adapted to move reactivation air over the hot water coil and through the reactivation portion of the desiccant rotor.
According to another exemplary embodiment, a method of conditioning air comprises: circulating refrigerant through a cooling coil; moving process air over the cooling coil; moving the process air through a process portion of a desiccant wheel; exchanging waste heat from the refrigerant to a flow of water; heating a hot water coil with the flow of water; and moving reactivation air over the hot water coil and through a reactivation portion of the desiccant wheel.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other features and advantages of the invention will be apparent from the following drawings wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

FIG. 1 is a perspective view of a desiccant rotor according to the prior art;

FIG. 1A is an enlarged view of a portion of FIG. 1;

FIG. 2 is a process diagram depicting process air and reactivation air flowing through a desiccant rotor according to the prior art;

FIG. 3 is a schematic diagram depicting a first exemplary embodiment of an air conditioning system according to the present invention;

FIG. 4 is a schematic diagram depicting a second exemplary embodiment of an air conditioning system according to the present invention;

FIG. 5 is a schematic diagram depicting a third exemplary embodiment of an air conditioning system according to the present invention; and

FIG. 6 is a schematic diagram depicting a fourth exemplary embodiment of an air conditioning system according to the present invention

DETAILED DESCRIPTION

Exemplary embodiments of the invention are discussed in detail below. In describing embodiments, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. A person skilled in the relevant art will recognize that other equivalent parts can be employed and other methods developed without departing from the spirit and scope of the invention.
The present invention relates to a method, system, and apparatus that utilizes waste heat, instead of, or in addition to, a reactivation heater, to reactivate a desiccant rotor in desiccant dehumidification systems. An example of a dehumidification system in which the present invention can be used is the line of DESICAiR® desiccant dehumidification systems sold by Stulz Air Technology Systems, Inc., located at 1572 Tilco Drive, Frederick, Md. 21704, the assignee of the present application. Use of waste heat to reactivate the desiccant rotor, in addition to, or as a substitute to, using a reactivation heater, can increase the energy efficiency and the effectiveness of the unit to control process air humidity. The resulting benefits can include a significant reduction in unit energy consumption as well as an enhanced ability to control the condition of a process air supply, resulting in increased control over the temperature and humidity conditions within a space or process.
When using, for example, a hot water fluid coil as the reactivation heater, as will be described below, heat that is otherwise wasted may be drawn from available energy sources for reactivating the desiccant rotor. This can result in a more energy efficient desiccant dehumidification system, and in more design versatility, thereby expanding the system's air conditioning capability and/or enhancing the ability to more precisely control room conditions.
A desiccant dehumidification system can be operable to separate or remove moisture from air. The unit may include any kind of an air dehumidification system where a desiccant rotor (e.g., a desiccant wheel), or other desiccant device having an operable open area to receive and dispatch an air flow, is deployed within a cabinet in which air is moved through the desiccant. The unit may also include a refrigerant-based air cooling coil with an operable open area to pass moving air through it to condense and remove water from the air. The unit may also include a heating water/glycol fluid coil with an operable open area to pass moving air through it to transfer heat to the air for the purpose of reactivating the desiccant contained within the desiccant rotor.
According to an exemplary embodiment, the system can include a pre-cooling coil (e.g., of the direct expansion type), a desiccant rotor, a refrigerant compressor, a refrigerant condenser (e.g., cooled by water and/or glycol), a fluid coil, a fluid pump, a supply fan, a reactivation fan, and/or other components integrated together as a self-contained air conditioning system.
Typical applications for the systems and method of the present invention can include, but are not limited to, healthcare facilities, surgical suites, schools, restaurants, theaters, convenience stores, hotels, office buildings, and/or anywhere approximately 100% makeup air is required to be delivered at or below space neutral conditions. Additional applications can include the water remediation market, tank coating, and storage facilities. Systems and methods of the present invention can also be used in recirculation or mixed air HVAC scenarios to provide a moderate level of humidity control with minimal energy consumption.
Referring to FIG. 3, an exemplary embodiment of the present invention is shown. As shown, process air enters the system at point A, for example, through an air inlet. This may be make-up air from ambient, and may have, for example, a temperature of about 95° F. and a humidity ratio of about 118 gpp. The process air can pass through a cooling coil 30, such as a multiple-circuit cooling coil, which may lower the dry bulb temperature of the air exiting the cooling coil 30 at point B to, for example, about 55° and the humidity ratio to, for example, about 64 gpp. The aforementioned temperature and humidity ratio values are exemplary and non-limiting.
If the process air prior to the cooling coil 30 (e.g., at point A) has a higher dew point than the temperature of the cooling coil 30, water will condense on the cooling coil 30. This lowers the moisture content of the process air and brings it to a nearly saturated condition. The cool, nearly saturated air exiting the cooling coil 30 (e.g., at point B) can then pass through a “process” portion 32 a of the desiccant rotor 32. The desiccant in the rotor 32 can remove water vapor from the air. The temperature of the air increases as moisture is removed by the desiccant rotor. Thus, the process air exiting the process portion 32 a (e.g., at point C) may have, for example, a temperature of about 72° F. and a humidity ratio of about 44 gpp.
Process air can be provided to the space or process being served through an outlet or other opening, for example, by a fan or blower 34. The process at this point D may be close to space-neutral temperatures, yet at lower humidity than achieved by the cooling coil 30 alone. For example, process air at point D may have a temperature of about 75° F. and a humidity ratio of about 44 gpp.
According to an exemplary embodiment, the refrigerant can be condensed by a closed loop water/glycol heat exchange system 36. In the exemplary embodiment of FIG. 3, heat can be transferred from the refrigerant to a liquid, such as a water/glycol solution, in first and second condensers 38, 40. Water flow through each condenser 38, 40 can be controlled by valves 42, 44, respectively, to maintain adequate refrigerant head pressure. Water flow can vary by controlling the speed of water pump 46 to match the load. Refrigerant can be pumped through condenser coils 38, 40, for example, using fixed-speed or variable- speed refrigerant compressors 39, 41, respectively.
Water used for refrigerant condensing leaves the condensers 38, 40 at an elevated temperature, for example, about 130° F., and is pumped to first and second hot water coils 48, 50. The system can provide the ability to control hot water flow to each of the two hot water coils 48, 50. For example, a control valve 52 can ensure proper water flow to each of the two hot water coils 48, 50 to maintain required reactivation energy and/or to provide adequate refrigerant system head pressure.
Reactivation air can enter the system under the force of reactivation fan or blower 51 at inlet point E having, for example, at a temperature of about 95° F. and a humidity ratio of about 118 gpp. This reactivation air can then pass through the first hot water/glycol coil 48, and have it's temperature raised to a sufficient level at point F (e.g., about 120° F.) to provide reactivation of the “reactivation” portion 32 b of desiccant rotor 32. The reactivation air can remove water from the reactivation portion 32 b of the desiccant rotor 32, and can exhaust through an outlet to ambient at point G. According to an exemplary embodiment, the reactivation portion 32 b can comprise about 25% to 50% of the surface area of the desiccant rotor 32, however, other configurations are contemplated.
Ambient air can enter the system at inlet point H and can pass through the second hot water coil 50. Any excess heat (e.g., not needed for reactivation) can be rejected through the second hot water coil via a blower or fan 54 to ambient at outlet point J. Cooled water from both hot water coils 48, 58 can return to the refrigerant condensers 38, 40, for example, at a temperature of about 115° F. By utilizing otherwise wasted heat to regenerate the desiccant rotor 32, the efficiency of the air conditioning system may be significantly increased.
The water/glycol reactivation system and method presented by exemplary embodiments may provide flexibility for use in a variety of configurations, and may provide advantages such as greater dehumidification capability, more accurate reactivation controllability, and/or process air heating and utilization of other waste energy from outside sources.
According to exemplary embodiments, waste heat from all refrigeration circuits 38/39, 40/41 may be utilized. Traditional system designs may use multiple, independent refrigerant compressors and circuits. In these systems reactivation energy is typically taken from an air cooled condenser of just one refrigerant circuit and one compressor of a multi-circuit system. This may limit the available reactivation energy at higher ambient temperatures, and/or may result in minimal reactivation energy availability at lower ambient temperatures.
Dehumidification capacity may be affected by reactivation energy. When reactivation energy is increased, the moisture contained by the desiccant rotor 32 may be decreased, thus improving the dehumidifying capacity of the rotor. The water/glycol reactivation method can permit most or all condenser heat to be available for reactivation, whether from a single, variable speed compressor system, or from multiple circuit systems. More heat is available for reactivation, therefore greater dehumidification may be available than is provided by a single circuit of a multi-circuit system.
Exemplary embodiments can improve control of reactivation heat. The water/glycol desiccant rotor reactivation method can provide the ability to accurately vary the amount of reactivation energy. Since fluid volume to the reactivation heater coil 48 can be easily varied using the control valve 52 and/or by varying the flow rate of the fluid pump 46, better control may be achievable throughout a wide range of ambient conditions as compared to a prior art, air-cooled condenser used to provide reactivation heat. The use of second hot water coil 40 can ensure adequate refrigerant system head pressure is maintained despite varying reactivation load.
According to exemplary embodiments, refrigeration system operation may be optimized. A water/glycol condenser can improve the ability to control refrigerant head pressure throughout varying ambient conditions as compared to an air cooled condenser. The water/glycol fluid loop can infinitely vary flow volume to more accurately match the actual refrigerant load. Stable refrigerant head pressure may lead to more stable refrigerant system operation.
Another exemplary embodiment of the present invention is shown in FIG. 4. This embodiment is the same as shown in FIG. 3, except for the following differences. The exemplary embodiment of FIG. 4 may use a single, variable-speed compressor 39 to operate the system throughout all operating conditions, rather than using multiple, independent compressors. The compressor 39 can pump refrigerant through a single condenser coil 38, as shown, or alternatively, through multiple condenser coils. The variable speed compressor can allow variable capacity and better system control than staging multiple compressors which have defined capacities at each stage. As a result, this can provide greater controllability of process supply air conditions. This method can also allow for fewer components and/or more simplified piping, which may reduce costs.
Referring to FIG. 5, another exemplary embodiment is shown. This embodiment is the same as shown in FIG. 3, except for the following differences. The exemplary embodiment of FIG. 5 can include a secondary evaporator coil 60 to draw heat from ambient at air at point K. Although shown with independent refrigerant circuits 38/39 and 40/41, the exemplary embodiment of FIG. 5 can alternatively have a single compressor 39 and/or condenser coil 38, as in the embodiment of FIG. 4.
The refrigerant circuit(s) having the secondary evaporator coil 60 can provide additional condenser heat to supplement the water/glycol fluid loop without affecting the cooling function of the system. Ambient air at point K can pass through the secondary evaporator coil 60. Refrigerant in the secondary evaporator coil 60 absorbs heat from the ambient air. This ambient air can then be exhausted at a lower temperature at point L. The heat absorbed by the refrigerant in the secondary evaporator coil 60 can be rejected into the water/glycol fluid loop in the condenser. This additional heat can allow greater reactivation capability in lower ambient conditions, which in turn can provide greater dehumidification capability. During higher ambient when more cooling is required, the secondary refrigerant circuit 60 can be used for cooling of the process air. Valves in the refrigerant lines can control which evaporator coil is utilized. Other systems may require a supplemental heater to develop more reactivation energy. This method of using a refrigerant circuit to transfer heat from ambient air to reactivate the desiccant rotor can be more efficient to operate than a comparable electric heater.
The system of the present invention may be utilized as a heat pump for heating the process air during lower ambient temperatures when dehumidification is not required. Using a system of bypass valves, the flow of refrigerant from the compressor(s) 39, 41 may be reversed and the condenser/heat exchanger(s) 38, 44 may then act as the evaporator for the refrigerant. Ambient air may be passed through the water/glycol coil(s) 48, 50, 60, which absorb heat from the air and transfers it to the water/glycol solution. The flowing water/glycol carries the heat to the heat exchanger(s) 42, 44. The refrigerant flowing through the heat exchanger(s) 42, 44 transfers heat from the water/glycol solution to the coil 30 located in the incoming process air stream, heating the process air delivered to the space to be conditioned. This can provide energy efficient process air heating by supplementing or totally replacing other heat sources such as natural gas or electric heaters thus reducing their use of energy. Capturing heat energy from ambient air and transferring it to the process air can utilize energy which is otherwise unused, thus providing a more energy efficient air conditioning system.
Exhaust air from the conditioned space may also be used as a source of heat for reactivating the desiccant rotor. Stale room air can be exhausted as it's exchanged with fresh incoming process air. Because heat energy is still contained in the exhausted room air, it may be ducted into the reactivation air stream as a source of reactivation energy in conjunction with the water/glycol heat previously described, thus utilizing heat that would otherwise be wasted. This method can also provide greater controllability due to less fluctuation of reactivation air conditions.
The desiccant rotor may also be used in an air exchange system to provide energy savings during low ambient temperature conditions. Exhaust air may be ducted out of the room through the reactivation segment of a desiccant rotor. Latent heat and moisture can be removed from the exhaust air and retained in the desiccant rotor. The moisture laden portion of the desiccant rotor can be rotated into the incoming process (make-up) air stream. Latent heat and moisture will be released from the desiccant and reintroduced into the conditioned space by the incoming air. By allowing the desiccant rotor to transfer moisture from room exhaust air to incoming process air, the load on other process air heating and humidification equipment can be reduced.
The desiccant rotor may be reactivated using any other external sources of heat. Heat from available hot water sources and/or excess heat from equipment that requires cooling may be ducted into the reactivation air stream and/or transferred to the air stream by a water/glycol fluid coil. This heat may be used as the primary source of reactivation energy and/or may be used in conjunction with the water/glycol heat previously described. Utilizing external waste heat may increase the system efficiency and provide greater dehumidification capability.
Referring to FIG. 6, another exemplary embodiment is shown. This embodiment is the same as shown in FIG. 4, except for the following differences. Referring to FIG. 6, the second hot water coil 50 of FIG. 4 may be replaced with a fluid heat exchanger 70. Rather than rejecting heat from the second hot water coil 50 to ambient, the heat can be re-directed to another fluid through the fluid heat exchanger 70. This method may be desirable to provide a supplemental heat source for another fluid, domestic hot water for example. The control system of the exemplary dehumidification unit can vary fluid volume to the first hot water coil 48 for reactivation and fluid heat exchanger 70 using control valve 52. This method can provide energy savings by allowing otherwise wasted heat not required to maintain reactivation energy to be applied to another beneficial process.
The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above-described embodiments of the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described.

Claims

1. An air conditioning system, comprising:

a refrigeration cooling coil in fluid communication with process air;

a refrigeration circuit containing refrigerant;

a heat exchanger in fluid communication with the refrigerant and water, the heat exchanger adapted to transfer heat from the refrigerant to the water;

a hot water coil in fluid communication with the water;

a desiccant rotor having a process portion in fluid communication with the process air, and a reactivation portion; and

a reactivation blower adapted to move reactivation air over the hot water coil and through the reactivation portion of the desiccant rotor.

2. The air conditioning system of claim 1, further comprising:

a process air blower adapted to move the process air over the refrigeration cooling coil and through the process portion of the desiccant rotor.

3. The air conditioning system of claim 1, further comprising:

a refrigerant compressor in fluid communication with the refrigeration circuit.

4. The air conditioning system of claim 3, wherein the refrigerant compressor comprises a speed-controlled compressor.

5. The air conditioning system of claim 3, further comprising:

a second refrigerant compressor in fluid communication with a second refrigeration circuit; and

a second heat exchanger in fluid communication with the second refrigerant circuit and the water.

6. The air conditioning system of claim 5, wherein the first refrigerant compressor and the second refrigerant compressor are fixed-speed compressors.

7. The air conditioning system of claim 5, further comprising:

a second refrigerant cooling coil in fluid communication with ambient air, the second refrigerant system in fluid communication with a heat exchanger;

wherein the heat exchanger is in fluid communication with the water, and the refrigerant system absorbs heat from the ambient air to heat the water.

8. The air conditioning system of claim 1, further comprising a second hot water coil in fluid communication with ambient air and in fluid communication with the hot water.

9. The air conditioning system of claim 1, further comprising:

a secondary fluid heat exchanger in fluid communication with the hot water and in fluid communication with an external fluid to be heated;

wherein excess heat is rejected into the external fluid to be heated through the secondary fluid heat exchanger.

10. A method of conditioning air, comprising:

circulating refrigerant through a cooling coil;

moving process air over the cooling coil;

moving the process air through a process portion of a desiccant wheel;

exchanging waste heat from the refrigerant to a flow of water;

heating a hot water coil with the flow of water; and

moving reactivation air over the hot water coil and through a reactivation portion of the desiccant wheel.

11. The method of claim 10, further comprising:

moving the process air into a room or process space.

12. The method of claim 10, further comprising:

moving ambient air over an evaporator coil to extract heat from the ambient air to the refrigerant; and

transferring the heat from the refrigerant to the flow of water and to the hot water coil.

13. The method of claim 11, wherein the heat is transferred from the flow of water to the hot water coil through a heat exchanger.

14. The method of claim 10, further comprising:

directing the flow of water through a heat exchanger;

exchanging heat from the flow of water to a fluid; and

using the heated fluid in an external process.