Patent Grant
7975495
The subject invention generally pertains to refrigerant systems and more specifically to a control scheme for adjusting and coordinating the variable capacities of certain system components.
To meet the varying cooling and/or dehumidifying load of a comfort zone, some HVAC refrigerant systems might include a system component of adjustable capacity. Examples of adjustable capacity components include compressors, indoor evaporator fans and outdoor condenser fans.
U.S. Pat. No. 5,303,561 discloses adjusting the indoor fan speed to meet the latent cooling needs of a comfort zone. U.S. Pat. No. 4,590,772 suggests varying the draft volume to a condenser based on the refrigerant pressure therein. U.S. Pat. No. 5,062,276 discloses a refrigerant system where the fan speed is varied linearly with compressor speed, and their speed relationship is altered in response to the need for dehumidification. U.S. Pat. Nos. 5,305,822; 5,345,776; 5,426,951 and 6,826,921 disclose varying the speed of an outdoor fan. And U.S. Pat. No. 6,223,543 discloses varying the speed of an indoor fan.
Although adjusting the capacity of a single component might be relatively straightforward, it can be challenging to control a refrigerant system that includes more than one component of adjustable capacity because varying the capacity of one component can affect the performance of another.
Consequently, there is a need for a refrigerant system that provides a method of adjusting and coordinating the variable capacities of multiple, interrelated components of the system.
It is an object of the invention to provide a refrigerant system that can adjust in a coordinated manner the variable capacities of a compressor system, an evaporator fan system and a condenser fan system.
Another object of some embodiments is to provide a control scheme that minimizes the power consumption of a refrigerant system that includes multiple variable capacity components.
Another object of some embodiments is to minimize the capacity of a refrigerant system in a prioritized order with the compressor system being first, the evaporator fan system being second, and the condenser fan system being third.
Another object of some embodiments is to minimize the capacity of a compressor system by periodically attempting to reduce the compressor capacity in a trial-and-error method.
Another object of some embodiments is to minimize the power consumption of a refrigerant system while maintaining a comfort zone within a target comfort range and maintaining at least a minimum saturated suction temperature of refrigerant leaving the system's condenser.
One or more of these and/or other objects of the invention are provided by a refrigerant system that periodically attempts to reduce the compressor capacity when the comfort zone is within a target comfort range. If the attempt succeeds, the evaporator fan capacity is then minimized. The condenser fan capacity can also be minimized provided the refrigerant system can maintain at least a minimum saturated suction temperature of the refrigerant flowing from the condenser to the compressor.
It is well known to those of ordinary skill in the art that there are countless ways of varying the operating capacities of individual compressor and fan systems. Some ways include, but are not limited to, variable speed drive for a fan or compressor, variable position slide valve for a screw compressor, variable inlet guide vanes for a centrifugal compressor, multiple compressors or fans that are individually energized in stages, etc. For sake of example, the present invention will be described as compressor system 14 comprising four equivalent compressors that are selectively energized to provide variable compressor capacity, evaporator fan system 18 comprising a single blower driven at varying speed to provide variable evaporator fan capacity, and condenser fan system 22 comprising four equivalent fans that are individually energized to provide variable condenser fan capacity.
Compressor system 14, condenser fan system 22, evaporator fan system 18, and other operating components of system 10 are controlled by output signals 26, 28, 30, 32, 34 and 36 from a controller 38 in response to feedback signals 40, 42 and 44 from various sensors. For the illustrated embodiment, for example, signal 40 is an indoor air temperature signal from a temperature sensor 46 that senses the dry bulb temperature of the indoor air of comfort zone 12, signal 42 is a humidity signal from a humidity sensor 48 that senses a humidity characteristic of zone 12 (e.g., relative humidity, or specific humidity), and signal 44 is a suction refrigerant signal from a suction refrigerant sensor 50 that senses a temp/press value of the refrigerant flowing to compressor system 14. The term “temp/press value” as used throughout this patent means a temperature or pressure value, thus a temp/press value of a refrigerant means the temperature or pressure of the refrigerant. Examples of a “temp/press value” include, but are not limited to, the saturation temperature and/or pressure of the refrigerant leaving evaporator 16 or entering compressor system 14.
For the illustrated embodiment, output signal 26 controls the compressor capacity; signal 28 controls the evaporator fan capacity; signal 30 controls the condenser fan capacity; and signals 32, 34 and 36 control the operation of valves 52, 54 and 56 respectively.
For normal cooling and dehumidifying operation with reheat coil 24 inactive, valve 52 is open, and valves 54 and 56 are closed. Refrigerant discharged from compressor system 14 flows in series through condenser 20 to condense therein, through a check valve 58, through an expansion valve 60 to cool the refrigerant by expansion, through evaporator 16 to remove heat from supply air 62, and back to the suction side of compressor system 14. Evaporator fan system 18 forces supply air 62 across evaporator 16, across reheat coil 24, whereby the conditioned supply air 62 helps improve or maintain the comfort in zone 12.
To achieve dehumidification with little or no cooling of comfort zone 12, i.e., reheat operation, valve 52 can be closed and valve 54 opened, or the two valves 52 and 54 can be modulated to direct all or some of the refrigerant discharged from compressor system 14 to reheat coil 24. Valve 54 being open conveys generally hot, pressurized refrigerant from compressor system 14 to reheat coil 24. The refrigerant condenses in reheat coil 24, thereby heating the supply air 62 previously cooled and dehumidified by evaporator 16. Thus, supply air 62 delivered to zone 12 is dehumidified but warmer than if reheat coil 24 were deactivated.
When reheat coil 24 is deactivated and perhaps flooded or partially flooded with liquid refrigerant, valve 56 can be opened to convey the accumulated liquid refrigerant in reheat coil 24 to evaporator 16 for use in the remaining active portions of refrigerant system 10.
To keep the indoor air of comfort zone 12 within a desired temperature/humidity comfort range, system 10 can be controlled in any conventional way well known to those of ordinary skill in the art. A novel aspect of the invention, however, is how controller 38 minimizes the overall electrical power consumption of system 10 while comfort zone 12 is within a predetermined target comfort range 64, shown in
Comfort range 64 can be defined in various ways and may change from one season to another. For sake of example, comfort range 64 of
To minimize the power consumption of system 10 while keeping zone 12 within the predetermined target comfort range 64, controller 38 can function according to a novel algorithm 80, which is stored in a memory 83 of controller 38 and illustrated in
If, however, zone 12 is within comfort range 64 and the refrigerant flowing to compressor system 14 is above a predetermined minimum temp/press value, then controller 38 periodically attempts to decrease the compressor capacity as indicated by control block 86.
After decreasing the compressor capacity (e.g., by deactivating one of the four compressors), controller 38 per block 88 tries to keep zone 12 within the target comfort range 64 by adjusting the evaporator fan capacity (e.g., increasing the evaporator fan capacity). In block 90, controller 38 also adjusts the condenser fan capacity. Controller 38, for example, might increase the condenser fan capacity to maintain zone 12 within comfort range 64, or controller 38 might decrease the condenser fan capacity to ensure at least a minimum saturated suction temperature of the refrigerant leaving evaporator 16.
Block 92 determines whether controller 38 was successful in the attempt to decrease compressor capacity while maintaining zone 12 within comfort range 64 with the refrigerant flowing to compressor system 14 above the minimum saturated suction temperature. If the attempt was successful, block 94 directs controller 38 to minimize the evaporator fan capacity without exceeding target comfort range 64. Next, to further reduce power consumption, block 96 directs controller 38 to minimize the condenser fan capacity without exceeding target comfort range 64 and without causing the saturated suction temperature to drop below the predetermined minimum temp/press value. Following a certain time delay after block 96, control returns to block 82.
However, if in block 92 it is determined that the attempt to decrease the compressor capacity failed (e.g., the indoor air of zone 12 exceeded the target comfort range), then control shifts from block 92 to block 98, and controller 38 returns the compressor capacity to where it was just prior to block 86.
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:
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| Number | Date | Country | |
|---|---|---|---|
| 20100107668 A1 | May 2010 | US |
