Abstract:
A refrigerant system for cooling a comfort zone is selectively operable in a cooling-only mode and a reheat mode. The system operates in the cooling mode to meet sensible and latent cooling demands of a room or area in a building when the room temperature is appreciably above a target temperature. The reheat mode is for addressing the latent cooling or dehumidifying demand when the room temperature is near or below the target temperature. In some embodiments, a generally inactive condenser stores excess refrigerant during the reheat mode, thereby avoiding the need for a separate liquid refrigerant receiver. To maintain a desired level of subcooling in the reheat coil, refrigerant can be transferred accordingly between the inactive condenser and the reheat coil. In some embodiments, the system&#39;s evaporator and reheat coil can be connected in a series or parallel flow relationship.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention generally pertains to refrigerant systems and more specifically to a refrigerant circuit that offers a reheat mode of operation. 
     2. Description of Related Art 
     Conventional refrigeration systems comprising a compressor, a condenser, an expansion valve and an evaporator can be used to meet the sensible and latent cooling demands of a room or area in a building when the room temperature is appreciably above a target temperature. In some circumstances, however, high humidity can leave a room feeling uncomfortable even though the room temperature might be at or even below the target temperature. Although further cooling of the room can reduce the humidity, the additional cooling can make the air in the room feel cold and dank. 
     To avoid this problem, many refrigerant systems include a reheat mode where a heater downstream of the evaporator raises the temperature of the supply air after the evaporator cools the air to reduce the humidity. Such systems can effectively address the latent cooling or dehumidifying demand without subcooling the room. Although the reheat mode can be provided by electric heat or combustion, the system can be less expensive to operate if the reheat is provided by the refrigerant circuit itself. In some cases, for instance, the compressor discharges relatively hot refrigerant gas into an additional heat exchanger that reheats the air that was previously cooled by the evaporator. 
     Using an additional heat exchanger in such a manner, however, can create a problem regarding the system&#39;s refrigerant charge. Air conditioning systems typically require less refrigerant during a reheat mode than during a cooling-only mode. Unless the system has some means for adjusting its refrigerant charge, the system might have an excessive amount of refrigerant during the reheat mode or an insufficient supply during the cooling mode. Thus, the system&#39;s efficiency might suffer in the cooling and/or reheat mode. 
     Previous systems addressing reheat and charge control include those shown in U.S. Pat. No. 6,122,923 to Sullivan; U.S. Pat. No. 6,170,271 to Sullivan; U.S. Pat. No. 6,381,970 to Eber et al.; and, U.S. Pat. No. 6,612,119 to Eber et al.; all of which are commonly assigned to the assignee of the present invention and all of which are hereby incorporated by reference. Although some systems include a liquid receiver for storing excess refrigerant during the reheat mode, such systems can be expensive due to the cost of the added receiver and associated control valves. Consequently, a need exists for a simpler, more cost effective refrigerant reheat system. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a simpler, more cost effective refrigerant system with a reheat mode. 
     Another object of some embodiments is to adjust a refrigerant system&#39;s effective charge without using a liquid receiver dedicated for that purpose. 
     Another object of some embodiments is to monitor and control the amount of subcooling occurring in a reheat coil. 
     Another object of some embodiments is to adjust a refrigerant system&#39;s effective charge by using the auxiliary side connector of an expansion valve, wherein the auxiliary side connector is downstream of the valve&#39;s flow restriction and upstream of the valve&#39;s multi-line flow distributor. 
     Another object of some embodiments is to control the amount of subcooling in a reheat coil by adjusting a system&#39;s effective refrigerant charge. 
     Another object of some embodiments is to determine the level of subcooling in a reheat coil by sensing the temperature of the refrigerant leaving the coil and sensing the temperature of the refrigerant at a strategic intermediate point within the coil. 
     Another object of some embodiments is to switch the operation of a refrigerant system between a cooling-only mode and a reheat mode by selectively deactivating a main condenser or a reheat coil. 
     Another object of some embodiments is to store liquid refrigerant in an inactive condenser during a reheat mode. 
     Another object of some embodiments is to use a plurality of simple check valves to minimize the use of solenoid valves and other externally actuated control valves in switching a refrigerant system between a cooling-only mode and a reheat mode. 
     Another object of some embodiments is to use a combination evaporator and reheat coil that share a common set of heat exchanger fins rather than using two individual heat exchangers for cooling and reheat functions. 
     Another object of some embodiments is to reverse a refrigerant&#39;s direction of flow through a reheat portion of a heat exchanger while leaving the refrigerant&#39;s direction of flow through an evaporator the unchanged. 
     Another object of some embodiments is to deactivate a condenser during a reheat mode of operation. 
     Another object of some embodiments is to use a reheat coil in both a reheat mode and a cooling-only mode, wherein the reheat coil provides heat in the reheat mode and provides cooling in the cooling-only mode. 
     One or more of these and/or other objects of the invention are provided by a refrigerant system that is selectively operable in cooling mode and a reheat mode, wherein a main condenser is deactivated in the reheat mode and in some cases excess liquid refrigerant is stored therein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a refrigerant system selectively operating in a cooling mode. 
         FIG. 2  is a schematic view of the refrigerant system of  FIG. 1  but shown operating in a reheat mode. 
         FIG. 3  is a schematic view of another refrigerant system selectively operating in a normal cooling mode. 
         FIG. 4  is a schematic view of the refrigerant system of  FIG. 3  but shown operating in a reheat mode. 
         FIG. 5  is a schematic view of another refrigerant system selectively operating in a normal cooling mode. 
         FIG. 6  is a schematic view of the refrigerant system of  FIG. 5  but shown operating in a reheat mode. 
         FIG. 7  is an algorithm that illustrates various method steps recited in the claims. 
         FIG. 8  is another algorithm that illustrates various method steps recited in the claims. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A refrigerant system  10  includes a directional valve  12  that can configure system  10  in a cooling mode as shown in  FIG. 1  or a reheat mode as shown in  FIG. 2 . System  10  generally operates in the cooling mode to meet sensible and latent cooling demands of a room or area in a building when the room temperature is appreciably above a target temperature. The reheat mode is typically used to address the latent cooling or dehumidifying demand when the room temperature is near or below the target temperature. 
     For the embodiment of  FIGS. 1 and 2 , system  10  comprises a compressor  14 , a condenser  16 , an evaporator  18 , a reheat coil  20 , an expansion device  22  (e.g., thermal expansion valve, electronic expansion valve, orifice, capillary, etc.), and various valves that may include one or more of the following: a check valve  24 , a check valve  26 , a solenoid valve  28  and a solenoid valve  30 . 
     In the cooling mode, directional valve  12  directs relatively high-pressure, high-temperature refrigerant discharged from compressor  14  to condenser  16 , and reheat coil  20  is generally inactive. An outdoor fan  32  can be energized to force outside air  34  across condenser  16  so that air  34  cools and condenses the refrigerant in condenser  16 . From condenser  16 , the refrigerant flows sequentially through check valve  24  and expansion device  22 . Upon passing through expansion device  22 , the refrigerant cools by expansion before entering evaporator  18 . The refrigerant flowing through evaporator  18  can cool a stream of air  36  that an indoor fan  38  forces across evaporator  18  and the currently inactive reheat coil  20 . After passing through evaporator  18 , the refrigerant returns to compressor  14  to perpetuate the cooling cycle. 
     In the cooling mode, check valve  26  inhibits liquid refrigerant from bypassing expansion device  22  thereby preventing the flooding of the inactive reheat coil  20 . Solenoid valve  28  is closed to inhibit refrigerant from bypassing check valve  24  and expansion device  22 . Solenoid valve  30  is normally kept open continuously. When open, solenoid valve  30  can convey refrigerant from reheat coil  20  to a point  40  between expansion valve  22  and evaporator  18 . 
     In a currently preferred embodiment, point  40  is an auxiliary side port of expansion device  22 , wherein expansion device  22  in this case comprises a Sporlan expansion valve p/n OZE-25-ZGA (expansion valve  22   a ), a Sporlan multi-line distributor p/n 1117-13-1/4″-C17 (multiline distributor  22   b ), and a Sporlan auxiliary side port connector p/n ASC-11-7 (point  40 ). Sporlan is based in Washington, Mo. and is a division of Parker Hannifin Corporation. Point  40  is downstream of Sporlan expansion valve p/n OZE-25-ZGA (expansion valve  22   a ) and upstream of Sporlan multi-line distributor p/n 1117-13-1/4″-C17 (multiline distributor  22   b ). Since multiline distributor  22   b  is downstream of expansion valve  22   a  and point  40  is not upstream of expansion valve  22   a , it naturally follows that flow from point  40  to multiline distributor  22   b  does so via bypassing expansion valve  22   a . Although the Sporlan assembly is currently preferred, other examples of expansion device  22  are well within the scope of the invention. 
     In the reheat mode, as shown in  FIG. 2 , condenser  16  is generally inactive, and directional valve  12  directs relatively high-pressure, high-temperature refrigerant from compressor  14  to reheat coil  20 , thereby heating coil  20 . From reheat coil  20 , the refrigerant flows sequentially through check valve  26  and expansion device  22 . Upon passing through expansion device  22 , the refrigerant cools by expansion before entering evaporator  18 , thereby cooling evaporator  18 . To remove latent heat from air stream  36 , air stream  36  is cooled by evaporator  18  and heated by reheat coil  20 . After passing through evaporator  18 , the refrigerant returns to compressor  14  to perpetuate the reheat cycle. 
     During the reheat mode, check valve  24  inhibits liquid refrigerant from backflowing into inactive condenser  16 . Directional valve  12  and solenoid valves  28  and  30  are controlled to maintain a desired level of subcooling in reheat coil  20 . To do this, a system controller  42  determines and monitors the level of subcooling in reheat coil  20  and compares the level to an established subcooling target. The subcooling target can be a predetermined range of acceptable values, wherein the range lies between certain upper and lower limits. 
     In some embodiments, controller  42  (e.g., computer, programmable logic controller, or suitable electrical circuit) determines the level of subcooling in reheat coil  20  based on the difference between a first refrigerant temperature and a second refrigerant temperature, wherein a first sensor  44  monitors the first temperature at a first point that is between an inlet  46  and an outlet  48  of reheat coil  20 , and a second sensor  50  monitors the second temperature at a second point that is downstream of the first point. The location of the first point can be about twice as far from inlet  46  than from outlet  48  so that the first temperature reflects the refrigerant&#39;s saturated temperature within reheat coil  20 . The second point is preferably near outlet  48  so that the difference between the first and second temperatures, as determined by controller  42 , reflects the level of subcooling in reheat coil  20 . 
     If the level of subcooling is substantially at the subcooling target (e.g., within the predetermined acceptable range), controller  42  leaves solenoid valves  28  and  30  closed. Valve  28  being closed generally traps a substantially fixed amount of liquid refrigerant within condenser  16 , and valve  30  being closed prevents subcooled liquid refrigerant within reheat coil  20  from bypassing expansion device  22  and rushing into evaporator  18 . 
     If the level of subcooling is below the subcooling target, controller  42  opens solenoid valve  28  while leaving solenoid valve  30  closed. This allows solenoid valve  28  to convey liquid refrigerant from condenser  16  to evaporator  18  and ultimately to reheat coil  20  as compressor  14  forces gaseous refrigerant from evaporator  18  to reheat coil  20 . Once the subcooling level increases to the subcooling target, controller  42  closes valve  28  while valve  30  is already closed. 
     If the level of subcooling is above the subcooling target, controller  42  temporarily shifts directional valve  12  to its position of  FIG. 1  and opens solenoid valve  30 . Valve  30  being open conveys liquid refrigerant from reheat coil  20  to the inlet of evaporator  18 , and directional valve  12  allows compressor  14  to force refrigerant from evaporator  18  to condenser  16 , thus effectively transferring refrigerant from reheat coil  20  to condenser  16 . After the subcooling level decreases to the subcooling target, controller  42  shifts directional valve  12  to its position of  FIG. 2  and closes valve  30  while valve  28  is already closed. 
     To carry out the operations just described with respect to the cooling and reheat modes, controller  42  can provide one or more various output signals  52  in response to one or more various input signals  54 . Examples of inputs  54  might include, but are not limited to, an input  54   a  from temperature sensor  44  and an input  54   b  from temperature sensor  50 . Examples of outputs  52  might include, but are not limited to, an output  52   a  to control fan  32 , an output  52   b  to control fan  38 , an output  52   c  to control compressor  14 , an output  52   d  to control directional valve  12 , an output  52   e  to control solenoid valve  28 , and an output  52   f  to control solenoid valve  30 . In cases where expansion device  22  is an electronic expansion valve, controller  42  controls device  22  via an output signal  52   g  in response to a leaving refrigerant evaporator temperature input  54   c  from a temperature sensor  56 . In cases where expansion device  22  is a thermal expansion valve, signal  54   c  might control expansion device  22  directly. If expansion device  22  has a fixed flow restriction as opposed to having an adjustable one, signal  52   g  might be eliminated. 
     In an alternate embodiment, shown in  FIGS. 3 and 4 , a refrigerant system  58  comprises compressor  14 , condenser  16 , evaporator  18 , reheat coil  20 , expansion device  22 , a directional valve  60 , and three check valves  62 ,  64  and  66 . For illustration, expansion device  22  is shown as a thermal expansion valve being controlled by a conventional temperature bulb  56 ′ on the suction line leading to compressor  14 ; however, other types of expansion devices (e.g., electronic expansion valve, fixed orifice, capillary, etc.) are well within the scope of the invention. Evaporator  18  and reheat coil  20  are connected in parallel flow relationship with respect to the flow of refrigerant and are disposed in series flow relationship with respect to air stream  36 . Although evaporator  18  and reheat coil  20  are schematically illustrated as two separate heat exchangers, they can actually be a single unit with multiple rows of refrigerant conduit sharing common heat transfer fins. Directional valve  60  determines whether system  58  is operating in a cooling mode, as shown in  FIG. 3 , or operating in a reheat mode, as shown in  FIG. 4 . 
     In the cooling mode, directional valve  60  directs refrigerant from compressor  14  to condenser  16  where air  34  cools and condenses the refrigerant therein. From condenser  16 , the refrigerant flows sequentially through check valve  62  (first check valve) and expansion device  22 . Upon passing through expansion device  22 , the refrigerant cools by expansion. After passing through expansion device  22 , a first portion of the cooled refrigerant enters evaporator  18  while a second portion passes through check valve  64  (second check valve) to enter reheat coil  20  now functioning as a supplemental evaporator. Check valve  66  (third check valve) prevents liquid refrigerant leaving condenser  16  from bypassing expansion device  22 . The refrigerant in evaporator  18  and reheat coil  20  cool air stream  36 . After passing through their respective heat exchangers, both portions of the refrigerant return to the suction side of compressor  14  to perpetuate the cooling cycle. 
     In the reheat mode, shown in  FIG. 4 , condenser  16  is generally inactive, and directional valve  60  directs refrigerant from compressor  14  to reheat coil  20 , thereby heating coil  20 . From reheat coil  20 , the refrigerant flows sequentially through check valve  66  and expansion device  22 . Check valve  62  prevents liquid refrigerant from backflowing into condenser  16 , and check valve  64  prevents liquid refrigerant leaving reheat coil  20  from bypassing expansion device  22  and flowing directly into evaporator  18 . Upon passing through expansion device  22 , the refrigerant cools by expansion before entering evaporator  18 , thereby cooling evaporator  18 . To remove latent heat from air stream  36 , air stream  36  is cooled by evaporator  18  and heated by reheat coil  20 . After passing through evaporator  18 , the refrigerant returns to compressor  14  to perpetuate the reheat cycle. 
     In the cooling mode, the refrigerant flows in a forward direction through reheat coil  20 , but in the reheat mode, the refrigerant flows in a reverse direction through reheat coil  20 . The refrigerant passing through evaporator  18 , however, flows in the same predetermined direction regardless of whether system  58  is operating in the cooling or reheat mode. 
     In another embodiment, shown in  FIGS. 5 and 6 , a refrigerant system  68  comprises compressor  14 , condenser  16 , evaporator  18 , reheat coil  20 , expansion device  22 , directional valve  60 , a solenoid valve  70 , and three check valves  62 ,  64  and  66 . Evaporator  18  and reheat coil  20  are connected in series flow relationship with respect to the flow of refrigerant and air stream  36 . Directional valve  60  determines whether system  68  is operating in a cooling mode, as shown in  FIG. 5 , or operating in a reheat mode, as shown in  FIG. 6 . 
     In the cooling mode, directional valve  60  directs refrigerant from compressor  14  to condenser  16  where air  34  cools and condenses the refrigerant therein. From condenser  16 , the refrigerant flows sequentially through check valve  62  and expansion device  22 . Upon passing through expansion device  22 , the refrigerant cools by expansion. After passing through expansion device  22 , the cooled refrigerant passes through evaporator  18 . From evaporator  18 , check valve  64  conveys the refrigerant through reheat coil  20  (functioning as a supplemental evaporator). Solenoid valve  70  is closed to prevent refrigerant leaving evaporator  18  from bypassing reheat coil  20 , and check valve  66  prevents liquid refrigerant leaving condenser  16  from bypassing expansion device  22 . The refrigerant in evaporator  18  and reheat coil  20  cool air stream  36 . After passing sequentially through evaporator  18  and reheat coil  20 , the refrigerant returns to the suction side of compressor  14  to perpetuate the cooling cycle. 
     In the reheat mode, shown in  FIG. 6 , condenser  16  is generally inactive, solenoid valve  70  is open, and directional valve  60  directs refrigerant from compressor  14  to reheat coil  20 , thereby heating coil  20 . From reheat coil  20 , the refrigerant flows sequentially through check valve  66  and expansion device  22 . Check valve  62  prevents liquid refrigerant from backflowing into condenser  16 , and check valve  64  prevents liquid refrigerant leaving reheat coil  20  from bypassing expansion device  22  and evaporator  18 . Upon passing through expansion device  22 , the refrigerant cools by expansion before entering evaporator  18 , thereby cooling evaporator  18 . To remove latent heat from air stream  36 , air stream  36  is cooled by evaporator  18  and heated by reheat coil  20 . After passing through evaporator  18 , open solenoid valve  70  conveys the refrigerant back to compressor  14  to perpetuate the reheat cycle. 
     In the cooling mode, the refrigerant flows in a forward direction through reheat coil  20 , but in the reheat mode, the refrigerant flows in a reverse direction through reheat coil  20 . The refrigerant passing through evaporator  18 , however, flows in the same predetermined direction regardless of whether system  68  is operating in the cooling or reheat mode. 
       FIGS. 7 and 8  show algorithms according to which refrigerant systems  10 ,  58  and/or  68  can operate. Block  72  represents selecting the refrigerant system&#39;s operating mode using valve  12  or  60 . Block  74  represents the refrigerant system operating in the reheat mode. Block  76  represents the refrigerant system operating in the cooling mode. 
     Block  78  represents placing the reheat coil in heat exchange relationship with the stream of air. 
     Block  80  represents sensing a second temperature of the refrigerant at a second point that is downstream of the first point with respect to the refrigerant flowing through the reheat coil; determining a difference between the first temperature and the second temperature; and during the reheat mode, monitoring a level of subcooling occurring in the reheat coil, wherein the level of subcooling is a function of the difference. 
     Block  82  represents during the reheat mode, monitoring a level of subcooling occurring in the reheat coil, wherein the level of subcooling is a function of the difference between the first temperature and the second temperature. 
     Block  84  represents establishing a subcooling target. 
     Block  86  represents comparing the level of subcooling to the subcooling target, thereby determining whether the level of subcooling during the reheat mode is above the subcooling target, below the subcooling target, or at the subcooling target. 
     Blocks  88 - 96  represent when the level of subcooling is above the subcooling target during the reheat mode, shifting refrigerant out of the reheat coil and into the condenser by doing the following: (block  90 ) conveying refrigerant from the reheat coil into the evaporator via a route that bypasses the expansion valve; (block  92 ) momentarily inhibiting refrigerant from flowing into the reheat coil; (block  94 ) conveying refrigerant from the evaporator into the compressor; and (block  96 ) momentarily discharging the refrigerant from the compressor into the condenser. 
     Blocks  98 - 106  represent when the level of subcooling is below the subcooling target during the reheat mode, shifting liquid refrigerant out of the condenser and into reheat coil by doing the following: (block  100 ) momentarily conveying refrigerant from the condenser to the evaporator via a route that bypasses the expansion valve; (block  102 ) discharging refrigerant from the compressor to the reheat coil; (block  104 ) via the expansion valve, conveying refrigerant from the reheat coil to the evaporator; and (block  106 ) inhibiting the refrigerant from flowing from the compressor into the condenser. 
     Block  108  represents when the level of subcooling is at the subcooling target during the reheat mode, maintaining a substantially fixed amount of refrigerant in the condenser. 
     Block  110  represents during the cooling mode, transferring heat from the refrigerant in the condenser. 
     Block  112  represents during the cooling mode, transferring heat to the refrigerant in the evaporator. 
     Block  114  represents during the cooling mode, momentarily transferring refrigerant in a liquid state from the reheat coil through the evaporator to the condenser and subsequently rendering the reheat coil substantially inactive. Blocks  116 - 120  represent performing block  114  by doing the following: (block  116 ) momentarily conveying refrigerant from the reheat coil to the evaporator via a route that bypasses the expansion valve; (block  118 ) inhibiting the compressor from discharging refrigerant into the reheat coil; and (block  120 ) discharging refrigerant from the compressor to the condenser. 
     Referring to  FIG. 8 , block  122  represents placing the reheat coil in heat exchange relationship with the stream of air with the reheat coil being downstream of the evaporator with respect to the stream of air. 
     Block  124  represents during the reheat mode, monitoring a level of subcooling occurring in the reheat coil. 
     Block  126  represents performing block  124  by sensing a first temperature of the refrigerant at a first point that is between a refrigerant inlet and a refrigerant outlet of the reheat coil; sensing a second temperature of the refrigerant at a second point that is downstream of the first point with respect to the refrigerant flowing through the reheat coil; and determining a difference between the first temperature and the second temperature, wherein the level of subcooling is a function of the difference. 
     Block  128  represents establishing a subcooling target. 
     Block  130  represents comparing the level of subcooling to the subcooling target, thereby determining whether the level of subcooling during the reheat mode is above the subcooling target, below the subcooling target, or at the subcooling target. 
     Block  132  represents when the level of subcooling is above the subcooling target during the reheat mode, shifting refrigerant out of the reheat coil and into the condenser. 
     Block  142  represents when the level of subcooling is below the subcooling target during the reheat mode, shifting liquid refrigerant out of the condenser and into the reheat coil by momentarily conveying refrigerant from the condenser to the evaporator via a route that bypasses the expansion valve. 
     Block  150  represents when the level of subcooling is at the subcooling target during the reheat mode, trapping a substantially fixed amount of refrigerant in the condenser. 
     Blocks  134 - 140  represent simultaneously doing the following: (block  134 ) conveying refrigerant from the reheat coil into the evaporator via a route that bypasses the expansion valve; (block  136 ) momentarily inhibiting refrigerant from flowing into the reheat coil; (block  138 ) conveying refrigerant from the evaporator into the compressor; and (block  140 ) momentarily discharging refrigerant from the compressor into the condenser. 
     Blocks  144 - 148  represent performing block  142  by doing the following: (block  144 ) discharging refrigerant from the compressor to the reheat coil; (block  146 ) via the expansion valve, conveying refrigerant from the reheat coil to the evaporator; and (block  148 ) inhibiting the refrigerant from flowing from the compressor into the condenser. 
     Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. The scope of the invention, therefore, is to be determined by reference to the following claims.