Abstract:
A water-cooled air conditioning system using a regenerative condenser water circuit to reheat the supply air during a dehumidification mode. The air conditioning system may be any type of water-cooled system, including a water source heat pump or water-cooled air conditioner. The reheat circuit circulates water leaving the condenser through the reheat heat exchanger and then returns the water to the condenser inlet. Thus, the reheat circuit ensures that water leaving the condenser is warm enough to provide sufficient reheating for the supply air, regardless of the water source temperature. In addition, a modulation assembly controls the amount of water flowing through the reheat circuit, and thereby its temperature, so that the temperature of the reheated supply air can be maintained within a narrow range.

Description:
[0001]     This application claims the benefit of the filing date of provisional application Ser. No. 60/522,124, entitled “Condenser Water Regenerative Reheat for Water-Cooled Air Conditioners and Water-Source Heat Pumps,” filed Aug. 18, 2005, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to air conditioning systems and, more particularly but without limitation, to water-cooled air conditioning and water source heat pump systems equipped with supply air reheat to provide dehumidification without sensible cooling.  
       BACKGROUND OF THE INVENTION  
       [0003]     Modern heating and cooling systems are increasingly required to control indoor humidity levels in addition to the sensible air temperature. One reason for this is the desire to provide ever higher levels of occupant comfort. Improving indoor air quality through dehumidification is important for health reasons as well, because high humidity is associated with mold and mildew and other unpleasant and hazardous conditions.  
         [0004]     In the cooling mode, air conditioners typically provide dehumidification only as a byproduct of the cooling process, with 20-30% of the total cooling capacity usually being apportioned to latent cooling (dehumidification) and the balance to sensible cooling (the measurable reduction in air temperature across the cooling coil). In most applications, this proportionate level of dehumidification is adequate during those periods when the cooling system is operating on a nearly continuous basis. However, during periods of low space cooling demand, the cooling system will not operate long enough to remove the amount of moisture required to control indoor humidity. There are also applications where dehumidification is required during periods when sensible cooling is not needed at all. Thus, there are situations where an air conditioning system must provide dehumidification independent of sensible cooling.  
         [0005]     One means of providing a dehumidification mode in a cooling system is referred to as a “reheat” process. In a reheat process, the supply air is reheated to a comfortable level after being cooled for adequate dehumidification. There are several known techniques to perform the reheating process, such as electric resistance heaters, desuperheating or condensing heat exchangers connected to the cooling refrigerant system, and heat exchangers connected to a boiler. The heat source in the preferred methods is some form of waste heat generated in the system as a result of the cooling process. This greatly improves the energy efficiency of the dehumidification process, as no new energy is consumed for reheat. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a schematic of a first embodiment of the present invention comprising a water-cooled air conditioning system with a regenerative condenser water reheat circuit in which the flow through the reheat circuit is controlled by means of a diverting valve located in the return conduit of the condenser where the reheat circuit connects.  
         [0007]      FIG. 2  is a schematic of a second embodiment of the present invention comprising a water-cooled air conditioning system with a regenerative condenser water reheat circuit in which the flow through the reheat circuit is controlled by means of a mixing valve located in the supply conduit of the condenser where the reheat circuit connects.  
         [0008]      FIG. 3  is a schematic of a third embodiment of the present invention comprising a water-cooled air conditioning system with a regenerative condenser water reheat circuit in which the flow through the reheat circuit is controlled by means of a variable speed water pump. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0009]     Referring now to the drawings in general and to  FIG. 1  in particular, there is shown therein and designated generally by the reference number  10  an air conditioning system constructed in accordance with the present invention. The air conditioning system  10  shown and described herein is a water source heat pump system illustrated in the cooling mode. However, the present invention is not so limited and can be implemented equally well in systems that provides cooling only. Accordingly, as used herein, “air conditioning system” refers to a system that conditions or adjusts the temperature and humidity of the air in a structure or space, and includes but is not limited to cooling-only systems as well as systems that heat and cool the air.  
         [0010]     The air conditioning system  10  of the present invention comprises a water-cooled air conditioning system designed to condition the air in an enclosed space (not shown in the drawings), such as a building or other structure. As used herein, “water-cooled air conditioning system” denotes a system that uses a water source  12  as a heat sink or heat source, and includes water-cooled air conditioners and water-source heat pumps, such as the system illustrated in the drawings.  
         [0011]     Typically, the water source  12  will be one of three basic types: (1) liquid circulating in a temperature-controlled piping loop with temperature control being mechanical, such as cooling towers and boilers or similar devices; (2) ground water pumped from a well, lake, river or stream; or, (3) liquid circulating through a sub-surface heat exchange piping loop, which may be placed in horizontal trenches or vertical bores, or submerged within a body of surface water.  
         [0012]     With continued reference to  FIG. 1 , the system  10  includes a condenser  14  that comprises a refrigerant to water heat exchanger, that is, it is adapted to conduct heat from a refrigerant to water. The condenser  14  has a water inlet  16  and a water outlet  18 . Also included is an evaporator  20  comprising a refrigerant to air heat exchanger, that is, it is adapted to transfer heat from air to a refrigerant. The evaporator  20  and condenser  14  are connected within a refrigerant circuit  22  with a compressor  24  and an expansion device  26 . The refrigerant circuit  22  also comprises conduits  28  adapted to circulate refrigerant between the various components of the refrigerant circuit. As used herein, “refrigerant” denotes a suitable phase-changing heat exchange fluid for use in a vapor-compression air conditioning or heat pump system. The refrigerant circuit  22  may include a reversing valve  30  where the system comprises a heat pump.  
         [0013]     The system  10  also comprises a condenser water circuit  32 . The condenser water circuit  32  includes a supply conduit  34  adapted to circulate water from the water source  12  to the water inlet  16  of the condenser  14  and a return conduit  36  adapted to circulate water from the water outlet  18  of the condenser back to the water source.  
         [0014]     Still further, the system  10  includes an air circuit  38  for circulating air in the space (not shown) through the system  10 . More specifically, the air circuit  38  is adapted to receive return air from the space at an air inlet  40 , to circulate the air through the evaporator  20 , and to direct the conditioned supply air leaving the system  10  through an air outlet  42  back into the space. The air circuit  38  usually will include one or more blowers  44  for moving the air.  
         [0015]     Referring still to  FIG. 1 , the system  10  comprises a reheat heat exchanger  52  in the form of a water to air heat exchanger for transferring heat from water to the supply air. The heat exchanger  52  is positioned in the air circuit  38  downstream of the evaporator  20 . The heat exchanger  52  has a water inlet  54  and a water outlet  56 .  
         [0016]     To provide a heat source to the reheat heat exchanger  52 , the system  10  is equipped with a regenerative condenser water reheat circuit  60  comprising conduits  62  and a water pump  64 . The reheat circuit  60  is adapted to circulate water from the return conduit  36  of the condenser water circuit  32  to the water inlet  54  of the reheat heat exchanger  52 , and from the water outlet  56  of the reheat heat exchanger to the supply conduit  34  of the condenser water circuit.  
         [0017]     In the embodiment of  FIG. 1 , the pump  64  is located in the supply conduit  34  of the condenser water circuit  32  between the water inlet  16  of the condenser  14  and the junction of the reheat circuit  60  with the supply conduit. Alternately, the pump  64  may be positioned in the return conduit  36  between the water outlet  18  of the condenser  14  and the flow control device, which is described below. In either of these positions, the pump  64  is in a portion of the condenser water circuit  32  which is between the condenser  14  and the junction of the reheat circuit  60  with the condenser water circuit  32 . In either of these locations the pump  64  can support condenser water circulation in other modes, such as cooling or heating (if a heat pump). Where the pump  64  serves the single purpose of circulating water through the reheat circuit  60 , it can be located anywhere within the reheat circuit.  
         [0018]     As explained previously, the reheat function preferably is activated only in the dehumidification mode when the space requires little or no sensible cooling, but the humidity is still higher than desired. During dehumidification mode, the reheat circuit brings the cooled, dehumidified air leaving the evaporator back up to within a comfortable target temperature range. Thus, as shown in  FIG. 1 , to control the operation of the reheat circuit  60 , the system  10  also includes a reheat control assembly  70 . Preferably, the control assembly  70  includes a temperature sensor  72  for detecting the temperature of the supply air leaving the air circuit  38  and entering the space through the air outlet  42 . The control assembly  70  also includes a controller  74  to receive the temperature data from the sensor  72  along the data line  76  and, in response to such data, to communicate by means of a data line  78  with a flow control device.  
         [0019]     The flow control device of the control assembly  70  can be a switch that simply activates the reheat circuit  60  in response to a target temperature. However, in most instances, a simple on/off control permits undesirably wide fluctuations in the supply air temperature. Thus, in the preferred practice of this invention, the flow control device has the capacity to vary the amount of flow that is directed through the reheat circuit  60 . In this first preferred embodiment of  FIG. 1 , the flow control device is a diverter valve  80 . In the system illustrated, the diverter valve  80  is located at the junction of the reheat circuit  60  and the return conduit  36  from the condenser  14 .  
         [0020]     In this embodiment, where the flow control is a diverter valve  80 , the amount of condenser water circulated through the reheat heat exchanger  52  can be varied or modulated. This enables the system to maintain a relatively constant selected or target temperature in the supply air. Thus, the control assembly  70  of this embodiment serves also as a flow modulation assembly. For example, if the target temperature selected is  72  degrees Fahrenheit, the control assembly  70  will cause more or less condenser water to flow through the reheat exchanger  52  to maintain the temperature of the supply air at about  72  degrees Fahrenheit.  
         [0021]     Having described a first preferred embodiment of the air conditioning system  10  of the present invention, its operation now will be explained. In the cooling mode, the evaporator  20  removes heat from the return air and the refrigerant circuit returns the heated refrigerant to the condenser  14  into which the heat is rejected. In the condenser  14 , the heat is transferred to the condenser water circulating through the condenser by means of the condenser water circuit  32 . In addition to the heat absorbed from the air being cooled, the heat rejected into the condenser also includes the heat generated by the electrical input of the compressor  24 .  
         [0022]     During the cooling mode, the control assembly  70  deactivates the reheat circuit  60 . That is, the diverting valve  80  is positioned to direct all flow from its inlet  80   a  to the outlet path  80   c  feeding the condenser water return conduit  36 , thus causing the water flow in the condenser water circuit  32  to completely bypass reheat circuit  60 . The condenser water flows from the water source  12  to the condenser  14  and then directly back to the water source.  
         [0023]     During times when the sensible space temperature is at or below the desired level so that sensible cooling is not required, but the space humidity level is higher than desired, the system  10  may be operated in a non-cooling dehumidification mode. During this mode, the refrigerant circuit  22  continues to operate in cooling mode.  
         [0024]     As the temperature of the supply air drops below a selected target temperature, the controller  74  activates the reheat circuit  60 . More specifically, depending on the temperature reading of the sensor  72 , the diverting valve  80  is modulated by the controller  74  to divide the outlet flow; a selected portion of the condenser water supply is caused to flow through the reheat circuit  60  and the remainder of the condenser water continues back to the water source  12 . The controller  74  continues to adjust the diverting valve  80 , as necessary, to maintain the supply air temperature at the desired set point or target temperature, such as 72 degrees Fahrenheit.  
         [0025]     Now it will be seen that the reheat circuit  60  forms a condenser water regeneration loop or circuit: water from the outlet  18  of the condenser  14  is circulated by the diverter valve  80  through the reheat heat exchanger  52  and then returned to the supply conduit  34  where it reenters the inlet  16  of the condenser through the pump  64 .  
         [0026]     The condenser water contains all of the heat removed from the air by the evaporator  20 , both sensible and latent, and also the heat generated by the electricity operating the compressor  24 . Consequently, there is more heat in the condenser water than is required to provide complete sensible reheating of the air. The diverter valve  80  operates to divide its incoming flow at  80   a  between the outlet  80   b  supplying reheat heat exchanger  52  and the outlet  80   c  returning the water to the water source  12 . The valve  80 , in response to the controller  74 , allocates to the reheat heat exchanger  52  only that portion of the condenser heat required for reheating and rejects the balance back to the water source  12 .  
         [0027]     The temperature of the water in the water source  12  can vary widely, typically ranging from 40 to 100 degrees Fahrenheit. When the temperature of incoming water from the water source  12  is near or below the target supply air temperature, the temperature of the water leaving the condenser  14  will be insufficient to provide adequate reheating of the supply air. With the condenser water regeneration feature of the present invention, the diverter valve  80  reduces the relative amount of input from the cold incoming water source in favor of input from the reheat circuit  60 . In this way, the reheat circuit water temperature can reach an equilibrium that is higher than that of the incoming water source temperature, as needed, to achieve the target supply air temperature. Thus, even when the water from the water source  12  is cold, condenser water regeneration ensures that the reheat heat exchanger  52  can reheat the cooled air sufficiently to maintain the target supply air temperature setting.  
         [0028]     It will be apparent that the complete system  10  can be implemented in its entirety at new installations. However, the present invention also can be employed by modifying existing water-cooled systems by retrofitting them with a combination of the reheat circuit  60 , the control assembly  70 , and the reheat heat exchanger  52 , together forming a reheat assembly designated generally herein by the reference numeral  86 .  
         [0029]     Turning now to  FIG. 2 , there is shown therein a second embodiment of the present invention designated generally by the reference numeral  10 A. The system  10 A of  FIG. 2  is similar to the system  10  of  FIG. 1 , and like reference numerals indicate like elements. More specifically, the system  10 A comprises a condenser  14 , an evaporator  20 , a refrigeration circuit  22 , and water condenser circuit  32 . A similar air circuit  38  also is included.  
         [0030]     The reheat assembly  86 A differs from the reheat assembly  86  of  FIG. 1  in that instead of the diverting valve  80  in the first embodiment, the control assembly  70  comprises a mixing valve  90 . The mixing valve  90  is positioned in the supply conduit  34  of the condenser water circuit  32  at the junction of the reheat circuit  60  with the supply conduit. The control assembly  70  is similarly provided with a supply air temperature sensor  72  by which the controller  74  regulates the reheat circuit operation through the mixing valve  90 . The mixing valve  90  serves the same function of proportioning or modulating the condenser water flow between the reheat circuit  60  and the water source  12 . As in the reheat assembly  86  of  FIG. 1 , the pump  64  of the reheat assembly  86 A of  FIG. 2  can be repositioned to support condenser water flow in other modes, or to provide flow only for the reheat circuit  60 , as may be desired.  
         [0031]     A third embodiment of the present invention is illustrated in  FIG. 3 , to which attention now is directed. The system  10 B of  FIG. 3  is similar to the systems  10  of  FIG. 1  and  10 A of  FIG. 2 , and like reference numerals indicate like elements. More specifically, the system  10 B comprises a condenser  14 , an evaporator  20 , a refrigeration circuit  22 , and water condenser circuit  32 . A similar air circuit  38  also is included.  
         [0032]     The reheat assembly  86 B differs from the reheat assembly  86  of  FIG. 1  and the reheat assembly  86 A of  FIG. 2  in that instead of the diverting valve  80  or the mixing valve  90 , the control assembly  70  comprises a variable speed water pump control  92  connected to the pump  64 . The pump  64  and pump control  92  are positioned in the reheat circuit  60  between the outlet  56  of the reheat heat exchanger  52  and the junction of the reheat circuit with the supply conduit  34  to the condenser  14 . A check valve  94  is included in the reheat circuit  60  to prevent the water source supply water from flowing in a reverse direction through the reheat circuit  60  when the pump  64  is inactive.  
         [0033]     The control assembly  70  is similarly provided with supply air temperature data by the sensor  72 , and the controller  74  regulates the reheat circuit operation by regulating the pump flow through the pump control  92 . Thus, the pump flow control  92  modulates the speed of the pump  64 , thereby serving the same function of proportioning or modulating the condenser water flow between the reheat circuit  60  and the water source  12 . The pump  64  and the check valve  94  may be positioned elsewhere within the reheat circuit  60  between the reheat heat exchanger inlet  54  and the condenser water return conduit  36 . In the embodiment of  FIG. 3 , the water pump  64  provides flow only for the reheat circuit  60 .  
         [0034]     In accordance with the method of the present invention, a condenser water regeneration circuit is employed to reheat supply air in a water-cooled air conditioning system. In response to the temperature of the supply air leaving the air circuit, condenser water from the return conduit of the condenser water circuit is circulated in heat exchange relation with air in the air circuit downstream of the evaporator. Thereby, the temperature of the supply air is adjusted towards a selected target temperature and then directed into the space. The condenser water then is returned to the supply conduit of the condenser water circuit. Preferably, the method includes modulating the amount of the condenser water return flow that is circulated in heat exchange relation with the air to maintain the supply air near a selected target temperature or set point.  
         [0035]     Now it will be appreciated that the condenser water regeneration reheat circuit of the present invention provides several advantages. The reheat assembly provides an air conditioning system in which complete and precise air reheating is possible, regardless of the condenser water supply temperature. The modulating nature of the reheat assembly also compensates for variations in return air temperature. Thus, the supply air temperature delivered to the space can be maintained at any reasonable target temperature or set point during the dehumidification mode, greatly improving comfort in the space. Moreover, while this reheat system is ideal for dehumidification applications, it is suitable for use in other applications where precise temperature control of the supply air is desired.  
         [0036]     The reheat energy source of the present invention is waste heat generated by the cooling and dehumidifying process, which is highly preferred from an energy efficiency standpoint. Still further, this is accomplished in a simple design and without modifying or complicating the refrigerant circuit.  
         [0037]     Changes can be made in the combination and arrangement of the various parts and steps described herein without departing from the spirit and scope of the invention as defined by the following claims.