US 20060225445 A1
A refrigerant system is provided with tandem compressors. As is known, tandem compressors operate in parallel to provide a refrigerant system designer with the ability to achieve a stepped capacity control of the refrigerant system. At least one of the tandem compressors is provided with a variable speed drive. Further, at least one of the tandem compressors may be provided with the economizer and/or unloader functions. System configurations with multiple compression stages and multiple injection ports are disclosed. In this manner, the stepless capacity control can be achieved.
1. A refrigerant system comprising:
at least two tandem compressors operating in parallel, with at least one compressor having a variable speed drive for varying a speed of said at least one compressor;
a condenser downstream of said compressor and an evaporator downstream of said condenser; and
a control for selectively varying said speed of said at least one compressor.
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11. A method of controlling a refrigerant system comprising the steps of:
(1) providing at least two tandem compressors operating in parallel, with at least one compressor having a variable speed drive for varying a speed of said at least one compressor, providing a condenser downstream of said compressor and an evaporator downstream of said condenser, and a control for selectively varying said speed of said at least one compressor to achieve varying levels of capacity control; and
(2) determining a desired capacity, and operating one or the other, or both of said at least two compressors, and varying a speed of said at least one compressor to achieve said determined desired capacity.
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This invention relates to a variable speed motor for driving a compressor that is incorporated into a refrigerant system with tandem compressors.
Refrigerant systems are utilized in many air conditioning and heat pump applications for cooling and/or heating the air entering an environment. The cooling or heating load on the environment may vary with ambient conditions, and as the temperature and/or humidity levels demanded by an occupant of the building change.
In some refrigerant systems, a single compressor is utilized to compress the refrigerant and move the refrigerant through the cycle connecting indoor and outdoor heat exchangers in a closed loop. However, under many circumstances, it would be desirable to have the ability to vary the capacity, or amount of cooling or heating provided by the refrigerant system. Thus, known refrigerant systems may be provided with tandem compressors. Tandem compressors are essentially at least two compressors operating in parallel, where the compressors are interconnected with each other via common suction and/or discharge manifolds. For instance, a control for the two-compressor system may actuate both of the compressors or either one of the two compressors. The two compressors may have different sizes to provide distinct stages of capacity during part-load operation. Rather than having a single level of capacity, a refrigerant system provided with tandem compressors would have several discrete levels of capacity.
In the prior art, controls can be programmed to optionally actuate the tandem compressors. However, the capacity control provided by the tandem compressors is increased or decreased in large discrete steps. It would be desirable to provide the ability to improve system control capability to continuously vary capacity between these discrete steps to precisely match external load demands at a wide spectrum of environmental conditions.
Variable speed drives are known for driving compressors at a variable speed in a refrigerant system. By driving the compressor at a higher or lower speed, the amount of refrigerant that is compressed per unit of time changes, and thus the system capacity can be adjusted.
Variable speed drives have not been utilized in refrigerant systems incorporating tandem compressors, where a selected number of the tandem compressors is driven by a variable speed drive, for the purpose of varying the system capacity to control temperature and humidity levels within the conditioned space.
In the disclosed embodiment of this invention, a variable speed drive is provided into at least one compressor in a refrigerant system having tandem compressors. By selectively controlling this one compressor, capacity adjustment between the discrete steps provided by tandem compressor operation can be achieved.
A control identifies a desired cooling capacity, and then achieves this desired capacity by first actuating the tandem compressors to accurately approximate the necessary capacity in the most efficient and reliable manner. Then, the speed of the at least one compressor provided with variable speed is changed incrementally. The capacity is then monitored. When a desired level is finally achieved, the at least one compressor is operated at that new speed. If the capacity still needs to be adjusted, then the speed is again adjusted incrementally, and the resulting condition is again monitored.
In disclosed embodiments, one of the tandem compressors may be provided with the variable speed drive while the other is not. In other embodiments, plural compressors are provided with a variable speed drives.
Embodiments are disclosed which incorporate economizer cycles and unloader cycles into the schematic along with the variable speed drive.
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.
A refrigerant system 20 is illustrated in
As is known, the two compressors 22 and 26 may preferably be provided with distinct capacities such that varying total levels of capacity can be achieved by operating one or the other, or both of the compressors 22 and 26. In this case, it is at the system designer's discretion to select whether a larger or smaller compressor is provided with a variable speed drive. The decision will depend on many factors including (but not limited to) application requirements, cost, system operation efficiency, etc. An expansion device 34 is positioned downstream of the condenser 32, and an evaporator 36 is located downstream of the expansion device 34. A common suction line 38 leads to distinct suction lines 39 for returning refrigerant to the compressors 22 and 26.
As also shown, an economizer circuit can be incorporated into the
As shown, the tapped refrigerant is returned through a line 46 to an intermediate compression point 48 in at least one of the compressors, here illustrated as compressor 22. While refrigerant in the tap line 42 is shown flowing through the economizer heat exchanger 40 in the same direction as refrigerant in the main liquid line 45, it should be understood that in a preferred embodiment, the two flows would actually be in counter-flow arrangement.
A bypass line 50 is also incorporated, and allows a portion of refrigerant from the intermediate compression point 48 in the compressor 22 to be returned to the suction line 39. When it is desired to have unloaded operation, a valve 52 is opened while the expansion device 44 is preferably (but not necessarily) closed. In this way, refrigerant that has been partially compressed by the compressor 22 will be returned to the suction line 39, thus providing the unloading function.
It has to be understood that the economized compressor 22 may have more than one injection port 48 and more than one associated economizer heat exchanger 40. Also, as known, the economizer heat exchanger arrangement can be substituted by a flash tank. Further, multi-stage compression system may be employed instead of a single economized compressor. In such multi-stage compressor system, one or several of the stages may be provided with a variable speed drive.
As shown, electric motors 200 are associated with fans for blowing the air over the condenser 32 and evaporator 36. One or other of these electric motors 200 may be provided with a variable speed drive 202. A worker of ordinary skill in the art would recognize when the variable speed control of the fan, or other components such as a secondary loop pump, motors associated with the refrigerant system might be desirable.
A control for either refrigerant system 20 and 60 is able to identify a desired cooling capacity, and operate the tandem compressors and/or the economizer and unloader functions as necessary. Thus, as shown in
It has to be noted that variable speed tandem compressors can be utilized in conjunction with other system components such as fans or pumps also operated at variable speeds.
Although preferred embodiments of this invention has 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.