Abstract:
An air conditioning system is disclosed which takes advantage of low ambient temperature conditions so as to activate a refrigerant flow that bypasses the compressor. The activation of the refrigerant flow is achieved by the intelligent control of a pump positioned between the outlet of the condenser and the inlet of an expansion device upstream of the evaporator. The refrigerant flow produced by the pump does not require any particular positioning of the condenser and evaporator components with respect to each other. The evaporator preferably absorbs heat from water circulating in a secondary loop which is used to remove heat from a building by one or more fan coil units.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to the refrigerant heat exchange loop in systems which remove heat from one or more parts of a building that are to be cooled. In particular, this invention relates to the effective use of the refrigerant heat exchange loop in association with a water heat exchange loop in systems which employ water as a heat exchange medium to remove heat from various parts of a building.  
           [0002]    It is desirable that a system for cooling one or more parts of a building be as efficient as possible. This includes minimizing the consumption of energy by the various components of the system when performing their respective functions. Various approaches have been taken to achieve this goal. These include the use of energy efficient components that minimize the consumption of electricity while performing their particular functions within the system. Examples of such components include energy efficient motors which drive compressors and/or fans within the system. Still other approaches include maximizing the efficiencies of the heat transfer mechanisms such as the evaporator and condenser elements of these systems.  
           [0003]    Another approach to increasing system efficiency is to eliminate when possible the operation of the compressor. An example of such an approach is disclosed in U.S. Pat. No. 6,370,889. The compressor within the disclosed system in this patent is bypassed under certain conditions so as to provide a natural cooling circuit for cooling a room. The system is premised on taking advantage of gravitational flow of the more dense refrigerant as it moves to the evaporator from the condenser. Such a system however requires that the condenser be mounted above the evaporator. This system will not work in situations where the condenser unit and the evaporator unit cannot be so positioned relative to each other.  
         SUMMARY OF THE INVENTION  
         [0004]    It is an object of the invention to provide a system which will eliminate, when possible, the need to use a compressor within a refrigerant loop without relying on the positioning of the condenser relative to the evaporator.  
           [0005]    It is another object of the invention to provide a system employing water in heat exchange relationship with refrigerant in a refrigerant loop that will eliminate the need to use a compressor under favorable outside temperature conditions.  
           [0006]    The present invention includes a system which takes advantage of low ambient temperature conditions so as to activate a refrigerant flow from condenser to evaporator while bypassing the compressor. The activation of the refrigerant flow is achieved by the intelligent control of a pump positioned between the outlet of the condenser and the inlet of an expansion device upstream of the evaporator. The intelligent control activates a bypass of the compressor while also activating the pump. The refrigerant flow produced by the pump does not require any particular positioning of the condenser and evaporator components with respect to each other. In a preferred embodiment, the evaporator absorbs heat from water circulating in a secondary loop which is used to remove heat from a building by one or more fan coil units. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    For a fuller understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein:  
         [0008]    [0008]FIG. 1 is a schematic view of a system for delivering chilled water to a series of heat exchangers having zone controllers associated therewith;  
         [0009]    [0009]FIG. 2 is a schematic diagram of the chiller within the system of FIG. 1;  
         [0010]    [0010]FIG. 3 is a flow chart of a method used by a controller for the chiller of FIG. 2 to bypass the compressor by activating a refrigerant pump within the refrigerant loop of the chiller. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    Referring to FIG. 1, a chiller  10  delivers chilled water to fan coil heat exchangers  12 ,  14  and  16 . Water from the chiller  10  flows through the fan coil heat exchanger  12  in the event that a zone controller  18  authorizes such a flow by the positioning of a control valve  20 . The zone controller  18  may also divert any water flow around the fan coil heat exchanger  14  by a further positioning of the control valve  20 . It is to be appreciated that the fan coil heat exchangers  16  and  18  operate in a similar fashion in response to the positioning of control valves  22  and  24  under the control of zone controller  26  and  28 . Each fan coil heat exchanger conditions air flowing through the fan coil heat exchanger. The resulting conditioned air is provided to spaces to be cooled. Each space is often referred to as a “zone of cooling”. It is finally to be noted that the water circulating through or around each fan coil heat exchanger is ultimately pumped back into the chiller  10  by a water pump  30  when the chiller  10  has been activated.  
         [0012]    Referring now to FIG. 2, the chiller  10  is seen to include a condenser  32  having a fan  34  associated therewith. The heat of condensation of the hot refrigerant vapor refrigerant passing through the condenser  32  is removed by the flow of air produced by the fan  34 . This produces high pressure sub cooled liquid refrigerant at the outlet end of the condenser  32 . This high pressure sub cooled liquid refrigerant flows into a thermal expansion device  36  and is discharged at a lower pressure. The thermal expansion device is preferably an electronically controlled expansion valve, but may under certain circumstances also be a fixed orifice valve or a thermal expansion valve. The refrigerant thereafter enters an evaporator  38 . The liquid refrigerant in the evaporator will extract heat from water circulating in one or more pipes immersed in the liquid refrigerant within the evaporator. The circulating water in the one or more pipes in the evaporator is the water that has been returned from the fan coil heat exchangers  12 ,  14 , and  16  via the pump  30 . The resulting chilled water leaves the evaporator  38  and is returned to the fan coil heat exchangers via an outlet line  40 . On the other hand, low pressure refrigerant vapor from the evaporator is normally directed to the suction inlet of a compressor  42 . The compressor  42  compresses the refrigerant vapor that is thereafter discharged to the condenser  32 .  
         [0013]    Referring again to the compressor  42 , a check valve  44  is positioned between the inlet and the outlet of the compressor. Another check valve  46  is positioned between the outlet of the condenser  32  and the inlet of the expansion valve  36 . A refrigerant pump  48  is furthermore positioned between the outlet of the condenser  32  and the inlet to the expansion device  36 . The refrigerant pump may be either of the fixed speed or variable speed type and should be appropriately sized for the refrigerant flow requirements of the particular chiller.  
         [0014]    The refrigerant pump  48  and the expansion device  36 , when an electronically controlled expansion valve, are controlled by a controller  50 . The controller also receives various sensed temperatures. In this regard, the controller receives the temperature of the chilled water leaving the evaporator  38  from a water temperature sensor  52  installed in the outlet line  40 . The controller also receives the temperature of the outdoor ambient temperature from a sensor  54 . As will be explained in detail hereinafter, the controller  50  is operative to activate the refrigerant pump  48  whenever the temperature of the chilled water leaving the evaporator is greater than the outside air temperature. The resulting flow of refrigerant is through the check valve  44  thus bypassing the compressor  42 . The check valve  46  also assures that the refrigerant is recirculated through the refrigerant pump  48 .  
         [0015]    Referring now to FIG. 3, a process utilized by a programmable processor within the controller  50  is illustrated. The process begins with a step  60  that inquires as to whether the chiller  10  has been activated. It is to be appreciated that the chiller will have been activated when the controller  50  receives demands for chilled water from one or more of the zone controllers. When the chiller is activated, the pump  30  will begin circulating water through the evaporator  38 .  
         [0016]    The processor within the controller  50  will proceed to step  62  as long as the chiller remains activated. The processor will either directly read the leaving water temperature sensor  52  in step  62  or it will note a previous reading of this temperature sensor and set the same equal to the variable “LWT”. The processor will next proceed to step  64  and do the same reading, or noting of a previous reading, of the outdoor ambient temperature as sensed by outdoor temperature sensor  58 .  
         [0017]    The processor within the controller  50  will now proceed to a step  66  and inquire as to whether leaving water temperature, LWT, is greater than the leaving water setpoint “LWSP” as previously defined for the chiller  10 . When this occurs, the processor proceeds to step  68  and inquires as to whether leaving water temperature, LWT, is greater than the outdoor air temperature, OAT. If LWT is not greater than OAT, then the processor will proceed to step  70  and inquire as to whether the refrigerant pump  48  is active. If the refrigerant pump is active, then the processor will proceed to step  72  and deactivate the refrigerant pump. When the refrigerant pump  48  is not active, the processor will proceed from either step  70  or step  72  to step  74  and activate the compressor  42 . Activation of the compressor  42  will initiate the normal compression of refrigerant as has been previously explained. The processor within the controller will in a step  76  also initiate the control of the expansion device  36  when it is an electronically controlled expansion valve. The control defines the appropriate refrigerant flow to the evaporator  38 .  
         [0018]    Referring again to step  68 , in the event that LWT is greater than OAT, then the processor will proceed to step  78  and inquire as to whether the compressor  42  is active. In the event that the compressor is active, the processor will proceed to step  80  and deactivate the compressor. When the compressor is not active, the processor will proceed out of either step  78  or step  80  to a step  82  and activate the refrigerant pump  48 . As has been previously noted, this will cause refrigerant to flow through the check valve  44  instead of the compressor  42 . The refrigerant will hence circulate directly into the condenser where the heat of condensation of the refrigerant will be extracted by the low outdoor ambient temperature. The check valve  46  assures that the refrigerant from the outlet of the condenser will be pumped by the refrigerant pump  48  to the inlet of the expansion valve  36 . The refrigerant expands through the expansion device  36  under the control of the processor in step  76  when the same is an electronically controlled expansion valve before entering the evaporator  38 .  
         [0019]    Referring again to step  72 , the processor will exit this step and proceed to a step  84  where a suitable delay will occur before again proceeding to step  60  to determine whether the chiller is still activated. It is to be noted that the processor within the controller  50  will also proceed out of step  76  to implement the delay of step  84  before proceeding to step  60 . It is thus to be appreciated that the controller will be operative to either have initiated compression of the refrigerant if LWT is less than LWSTP and LWT is equal to or greater than OAT. On the other hand, the controller will not initiate the compressor if LWT is less than OAT. In this latter case, the pump  48  in combination with the check valves  44  and  46  will initiate an alternative refrigerant flow to remove the heat from the circulating water.  
         [0020]    It is to be appreciated that a preferred embodiment of the invention has been disclosed. Alterations or modifications may occur to one of ordinary skill in the art. For instance, the control algorithm executed by the controller  50  could require that LWT is greater than OAT by some predefined amount that would assure enough temperature difference at the condenser to remove the heat of condensation.  
         [0021]    It will be appreciated by those skilled in the art that further changes could be made to the above-described invention without departing from the scope of the invention. Accordingly, the foregoing description is by way of example only and the invention is to be limited only by the following claims and equivalents thereto.