Patent Abstract:
A tandem compressor refrigerant system where an economizer circuit and reheat coil are incorporated to provide additional flexibility and control over overall system capacity and sensible heat ratio as well as to increase system efficiency. In this system, tandem compressors deliver compressed refrigerant to a common discharge manifold, and then to a common condenser. From the common condenser, the refrigerant passes to a plurality of evaporators, with each of the evaporators being associated with a separate environment to be conditioned. Each of the evaporators is associated with one or several of the plurality of compressors. By utilizing the common condenser, yet a plurality of evaporators, the ability to independently condition a number of sub-environments is achieved without the requirement of the same plurality of complete separate refrigerant circuits for each compressor. In particular, the economizer circuit provides additional capacity to any of the evaporators that have a relatively high load while the reheat coil provides improved dehumidification. Various design schematics and system configurations are disclosed.

Full Description:
BACKGROUND OF THE INVENTION 
   This application relates to a refrigerant system utilizing tandem compressors sharing a common condenser, but having separate evaporators, and wherein an economizer circuit and a reheat coil are incorporated. 
   Refrigerant systems are utilized in applications to change the temperature and humidity or otherwise condition the environment. In a standard refrigerant system, a compressor delivers a compressed refrigerant to an outdoor heat exchanger, known as a condenser. From the condenser, the refrigerant passes through an expansion device, and then to an indoor heat exchanger, known as an evaporator. In the evaporator, moisture may be removed from the air, and the temperature of air blown over the evaporator coil is lowered. From the evaporator, the refrigerant returns to the compressor. Of course, basic refrigerant systems are utilized in combination with many configuration variations and optional features. However, the above provides a brief understanding of the fundamental concept. 
   In more advanced refrigerant systems, a capacity of the air conditioning system can be controlled by the employment of so-called tandem compressors. The tandem compressors are normally connected together via common suction and common discharge manifolds. From a single common evaporator, the refrigerant returns through the common suction manifold to each of the tandem compressors. From the individual compressors the refrigerant is delivered into the common discharge manifold and then into a single common condenser. The tandem compressors are also separately controlled and can be started and shut off independently of each other such that one or both compressors may be running at a time. By controlling which compressors are operating, control over the capacity of the entire system is achieved. Often, the two compressors are selected to have different capacities, such that even greater flexibility in capacity control is provided. Also, tandem compressors may have shutoff valves to isolate some of the compressors from the active refrigerant circuit, when they are shutdown. Moreover, if these compressors operate at different suction pressures, then pressure equalization and oil equalization lines are frequently employed. 
   One advantage of the tandem compressor is that more capacity control is provided, without the requirement of having each of the compressors operating on a dedicated circuit. This reduces the system cost. 
   However, certain applications require cooling at various temperature levels. For example, in supermarkets, low temperature (refrigeration) cooling can be provided to a refrigeration case by one of the evaporators connected to one compressor and intermediate temperature (perishable) cooling can be supplied by another evaporator connected to another compressor. In another example, a computer room and a conventional room would also require cooling loads provided at different temperature levels, which can be achieved by the proposed multi-temp system as desired. However the cooling at different levels will not work with an application of a standard tandem compressor configuration, as it would require the application of a dedicated circuit for each cooling level. Each circuit in turn must be equipped with a dedicated compressor, dedicated evaporator, dedicated condenser, dedicated expansion device and dedicated evaporator and condenser fans. This arrangement having a dedicated circuitry for each temperature level would be extremely expensive. 
   In addition, a technique known as an economizer circuit has been utilized in refrigerant systems. The economizer circuit increases the capacity and efficiency of a refrigerant system. To this point, a system having a common condenser communicating with several evaporators has not been utilized in combination with any economizer circuit. Notably, applicants have a co-pending application, filed on even date herewith, entitled “Refrigerant Cycle With Tandem Compressors for Multi-Level Cooling, and assigned Ser. No. 10/975,887. 
   In some cases, while the system is operating in a cooling mode, the temperature level at which the air is delivered to provide comfort environment in a conditioned space may need to be higher than the temperature that would provide the ideal humidity level. Generally, the lower the temperature of the evaporator coil is the more moisture can be removed from the air stream. These opposite trends have presented challenges to refrigerant system designers. One way to address such challenges is to utilize various schematics incorporating reheat coils. In many cases, a reheat coil placed in the way of an indoor air stream behind the evaporator is employed for the purposes of reheating the air supplied to the conditioned space after it has been cooled in the evaporator, where the moisture has been removed as well. 
   While reheat coils have been incorporated into air conditioning systems, they have not been utilized in an air conditioning system having an ability to operate at multiple temperature levels by employing tandem compressors, with at least one of the tandem compressors operating in conjunction with the economizer circuit. 
   SUMMARY OF THE INVENTION 
   For the simplest system that has only two compressors, in this invention, as opposed to the conventional tandem compressor system, there is no common suction manifold connecting the tandem compressors together. Each of the tandem compressors is connected to its own evaporator; while, both compressors are still connected to a common discharge manifold and a single common condenser. Consequently, for such tandem compressor system configurations, additional temperature levels of cooling, associated with each evaporator, become available. An amount of refrigerant flowing through each evaporator can be regulated by flow control devices placed at the compressor suction ports, as well as by controlling related expansion devices or utilizing other control means, such as evaporator airflow. In addition, in this application, an economizer circuit is incorporated into the refrigerant system. The economizer circuit maybe utilized with one or several of the evaporators. In particular, the economizer circuit may increase the capacity of each evaporator, and thus it would preferably be utilized (to obtain the most benefits) with the evaporator associated with the environment that must be controlled at the lowest temperature. 
   In addition, a single or multiple reheat coils are associated with one or several evaporators. The reheat coils may be positioned in a parallel or serial flow relationship with an economizer heat exchanger and condenser and can be located either upstream or downstream of each heat exchanger. 
   In embodiments, only one or several of the evaporators may be associated with the economizer circuit. In the economizer circuit, a portion of the refrigerant is then returned to an intermediate compression position in at least one of the compressors and can be tapped from the main circuit either upstream or downstream of the economizer heat exchanger, as known. Also, the teachings of this invention can be equally applied to compressors connected in series or economized compressors having multiple injection ports. 
   These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an earlier system. 
       FIG. 2  is a first schematic. 
       FIG. 3A  is a second schematic. 
       FIG. 3B  shows another option. 
       FIG. 4  is a third schematic. 
       FIG. 5  is a fourth schematic. 
       FIG. 6  illustrates another option. 
       FIG. 7  illustrates yet another option. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , earlier tandem compressor system  10  is shown to include two separate compressors  11 , a common evaporator  17 , condenser  15 , expansion device  14 , condenser air-moving device  16 , evaporator air-moving device  18  and associated piping. An economizer circuit has an economizer heat exchanger  15  receiving a main refrigerant flow and a tapped refrigerant flow in line  7 . As known, the tapped refrigerant flow passes through an expansion device  9  to be expanded to lower pressure and temperature. Downstream of the economizer heat exchanger  15 , the tapped flow is returned through a line  8  to an intermediate point in at least one of the compressors  11 . Such a system was disclosed in a prior U.S. patent application Ser. No. 10/769,161, filed 30 Jan. 2004, entitled “Refrigerant Cycle With Tandem Economized and Conventional Compressors” and assigned to the assignee of the present invention. As known, the tap line  7  may also be located downstream of the economizer heat exchanger  15 . 
   A refrigerant system  20  is illustrated in  FIG. 2  having a pair of compressors  22  and  23  that are operating generally as tandem compressors. Optional discharge valves  26  are positioned downstream of these compressors on discharge lines associated with each of the compressors  22  and  23 . These valves can be controlled to prevent backflow of refrigerant to either of the compressors  22  or  23  should only one of the compressors be operational. That is, if for instance the compressor  22  is operational with the compressor  23  stopped, then the discharge valve  26  associated with compressor  23  will be closed to prevent flow of refrigerant from the compressor  22  back to the compressor  23 . The two compressors communicate with a discharge manifold  29  leading to a common condenser  28 . From the condenser  28 , the refrigerant continues downstream and is split into two flows, each heading through an expansion device  30 . From the expansion device  30 , one of the flows passes through a first evaporator  32  for conditioning a sub-environment B. The refrigerant passing through the evaporator  32  passes then through a suction modulation valve  34 , and is returned to the compressor  22 . The second refrigerant flow passes through an evaporator  36  that is conditioning a sub-environment A. The refrigerant also passes through an optional suction modulation valve  34  downstream of the evaporator  36  and is returned to the compressor  23 . An air-moving device F drives air over the evaporator  32  and another air-moving device F drives air over the evaporator  36  and into their respective sub-environments. Usually, sub-environments A and B are preferably maintained at different temperature levels. 
   A control  40  for the refrigerant system  20  is operably connected to control the compressors  22  and  23 , the expansion devices  30 , the discharge valves  26 , and suction modulation valves  34 . By properly controlling each of these components in combination, the conditions at each evaporator  32  and  36  can be controlled as necessary for the sub-environments A and B. The exact controls necessary are as known in the art, and will not be explained here. However, the use of the tandem compressors  22  and  23  utilizing the common condenser  28  and separate evaporators  32  and  36 , preferably operating at different temperature levels, reduces the number of components necessary for providing the independent control for the sub-environments A and B, and thus is an improvement over the prior art. 
   As shown in  FIG. 2 , an economizer circuit  100  is incorporated into the refrigerant system  20 . An economizer heat exchanger  102  receives a refrigerant from an economizer tap  104  and a main refrigerant flow line  106 . Notably, the refrigerant heading to the evaporator  32  does not pass through the economizer heat exchanger  102 , while the refrigerant heading to the evaporator  36  does. In this embodiment, the evaporator  36  and its sub-environment A is preferably the environment that must be maintained at a lower temperature. The use of the economizer circuit will provide additional cooling capacity for the evaporator  36 , as known. The refrigerant passing through the tap  104  passes through an expansion device  108  to be expanded to lower pressure and temperature. This refrigerant thus subcools the refrigerant in the main flow line  106  in the economizer heat exchanger  102 . The tapped refrigerant, having been expanded and passed through the economizer heat exchanger  102 , returns through a return line  110  to an intermediate compression point in at least one of the compressors, shown here as compressor  23 . Notably, while the flow in the lines  104  and  106  are shown in the same direction through the economizer heat exchanger  102 , for all of the embodiments in this invention, it is preferred that these two flows are arranged in a counter-flow relationship, however, they are shown in the same direction for illustration simplicity. 
   The use of the economizer circuit  100  provides additional cooling capacity to the refrigerant system  20 . 
   For this embodiment, and for all other disclosed embodiments, there is an option where the control can also selectively open the economizer expansion device to either allow flow through the economizer heat exchanger, or to block flow through the economizer heat exchanger. When the economizer expansion device is shut off, refrigerant would still pass through the economizer heat exchanger through the main flow line, however, the economizer function would not be operational. Rather than having a single economizer expansion device that also operates as a shut-off valve, two distinct flow control devices could be utilized. Also, as mentioned above, the tap refrigerant line  104  may be located downstream of the economizer heat exchanger  102 , providing similar benefits. 
   In addition, a reheat circuit is incorporated into the system  20 . In particular, the reheat circuit includes a flow control device  116  for selectively tapping a refrigerant through a reheat coil  118  associated with the sub-environment A. When the control  40  determines that a reheat function is desired, the valve  116  will be opened and refrigerant will pass through the reheat coil  118 , through a check valve  120 , and be returned at point  122  to the main refrigerant circuit, upstream of one of the expansion devices  30 . At least a portion of air driven by the air-moving device F over the evaporator  36  will also now pass over the reheat coil  118 . As is known, this air can be cooled in the evaporator  36 , and in particular cooled to a lower temperature by employment of the economizer circuit  100 , such that greater dehumidification can be achieved. If the temperature of the air having passed over the evaporator  36  is lower than would be desired in the sub-environment A, then the reheat coil  118  is utilized to heat the air to a desired temperature level after the moisture has been removed in the evaporator  36 . 
   Obviously, the economizer heat exchanger  102  and reheat coil  118  can be associated with different evaporators  32  and  36  if desired. Furthermore, although a warm liquid approach (with the reheat coil  118  located downstream of the condenser  28  and arranged in a parallel relationship with the economizer heat exchanger  102 ) is shown in  FIG. 1 , any reheat concept (e.g. hot gas, warm liquid, two-phase mixture) as well as reheat circuit configuration and relative position can be employed, providing similar system advantages in flexibility and control of satisfying a wide spectrum of potential applications and various external sensible and latent load demands. Thus, in systems employing such reheat concepts, the position of the reheat coil in the refrigerant circuit in relation to the condenser  28  and economizer heat exchanger  102  may be sequential or parallel as well as upstream or downstream. 
   As shown in  FIG. 2 , a bypass line  315  may bypass refrigerant around the condenser  28  when a flow control device such as valve  316  is opened. This bypass may be selectively utilized by the control  40  when dehumidification is desired with a lower sensible cooling load. Such bypasses are known in the art, and a worker of ordinary skill in this art would recognize how to incorporate this feature into the schematic  20 , and when to utilize the feature. 
     FIG. 3A  shows another embodiment  50  that is quite similar to the embodiment  20  of  FIG. 2 . However, the refrigerant flowing to both of the evaporators  32  and  36  passes through the economizer heat exchanger  102 . As shown, the main flow of refrigerant  106  leads to a downstream manifold  116 , which then breaks into branches leading to both evaporators  32  and  36 . The benefits of additional capacity are thus provided to both of the evaporators. As shown, the refrigerant being returned to the compressor  22  would still return through the line  110 . An optional line  114  may also return refrigerant to the other compressor  23 , if this compressor is equipped with intermediate injection port as well. 
   Reheat coils are also incorporated into the refrigerant cycle  50 . Here, a first three-way valve  52  is positioned downstream of the economizer heat exchanger  102 , and directs refrigerant through a first reheat coil  54  associated with the evaporator  36  and sub-environment A when a reheat function desired. Refrigerant flowing through the reheat coil  54  then passes through a check valve  56 , and is returned at point  58  to the main circuit refrigerant line, upstream of the expansion device  30 . In this case, a warm liquid approach is utilized once again, but now with the reheat coil  54  located downstream of both condenser  28  and economizer heat exchanger  102 . A second three-way valve  60  selectively taps refrigerant off of a main refrigerant line, and passes it through a second reheat coil  62  associated with the sub-environment B. Refrigerant flowing through the reheat coil  62  then passes through a check valve  64  and is reconnected at point  66  to the main refrigerant line. Here, a hot gas design is employed with the reheat coil  62  positioned upstream of the condenser  28 . The control  40  will selectively operate each of the reheat coils dependent on the desired humidification and temperature needs of the sub-environments A and B. As shown in  FIG. 3B , both reheat coils  54  and  62  can be associated with a single evaporator ( 32  or  36 ) and consequently with a respective sub-environment (B or A), providing multiple reheat stages for this sub-environment. Although the reheat coils  54  and  62  are shown in series (one behind the other) relative to the air path, a parallel configuration is also feasible. 
     FIG. 4  shows a refrigerant cycle  80 , wherein, once again, there are reheat coils associated with each of the two sub-environments A and B. However, in this embodiment, a single three-way valve  82  is positioned downstream of the main flow line passing through the economizer heat exchanger  102 . Refrigerant having been tapped from the three-way valve  82  passes to a connection  94 , through two lines  86 , and selectively operable flow control devices  84 , can pass to the two reheat coils  88  and  90 . These two refrigerant flows recombine at a point  89 , pass through a check valve  92 , and are reconnected at the point  94  upstream of the expansion device  30 . Thus, in this relationship, the two reheat coils  88  and  90  are in generally parallel configuration such that the refrigerant conditions at the entrance to the reheat coils is generally the same. The control  40  will selectively operate both flow control devices  84  associated with the reheat coils  88  and  90  to be either open or closed to provide refrigerant flow to each of reheat coils associated with sub-environment B and A respectively when the reheat function is desired in each sub-environment. Obviously, the flow control devices can be of an adjustable type to control amount of refrigerant to each reheat coil through modulation or pulsation. As it would be recognized by a worker ordinarily skilled in the art, other parallel configurations of the reheat coils are also feasible. 
     FIG. 5  shows an embodiment  190  where the two reheat coils are in a serial flow relationship. A three-way valve  192  taps refrigerant through a first reheat coil  194  associated with the sub-environment B, and the refrigerant then passes downstream serially to a reheat coil  196  associated with the sub-environment A. The refrigerant then passes through a check valve  198 , and is reconnected at a point  200  to the main refrigerant flow. As can be appreciated, the refrigerant will have a higher temperature at the reheat coil  196  than it would at the reheat coil  194 , and thus the selection of which sub-environment A and B should first receive the refrigerant flow should be made based upon which sub-environment requires a higher amount of reheat. As it would be recognized by a worker ordinarily skilled in the art, other serial arrangements of the reheat coils are also feasible. 
     FIG. 6  shows yet another schematic  200 , wherein there are serially connected compressors  202  and  204  (instead of a single economized compressor). A discharge line  206  downstream of the second stage compressor  204  delivers refrigerant to a condenser  208 . A refrigerant line  210  downstream of the first stage compressor  202  accepts refrigerant from the economizer heat exchanger at an intermediate pressure level. Obviously, any economized compressor can be substituted by a serially connected compressor stages and more than two sequential compressor stages can be employed as well if desired. 
     FIG. 7  shows an embodiment  250 , having an economized compressor  252 , such as mentioned above, wherein there are plural intermediate taps  254  and  256 , each connected to a respective economizer heat exchanger operating at a different pressure and temperature level and thus providing different amount of subcooling. Such economizer heat exchangers can be arranged in a sequential or parallel configuration to each other. Of course, more than two taps are feasible. 
   In all of the disclosed embodiments, the economizer circuit and reheat coils assist in providing the distinct temperatures and humidity levels that are to be achieved by one or several of the evaporators. That is, by providing the economizer circuit and reheat coil, the present invention is better able to meet the temperature and dehumidification goals for a wide spectrum of potential applications as well as sensible and latent load demands. 
   Other multiples of compressors and compressor banks can be utilized. 
   Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Technology Classification (CPC): 5