Another important feature of the invention is the use of injected compressors. Especially useful in heat pump systems according to the present invention is the type of injected compressor disclosed and claimed in the copending U.S. patent application of William H. Wilkinson, the present inventor, and James H. Saunders, Ser. No. 07/161,189, filed Feb. 26, 1988, for Crossed Piston Compressor with Vernier Offset Port Means, now U.S. Pat. No. 4,936,111, issued June 26, 1990. This copending patent relates to systems and apparatus for compressing gaseous fluids, especially refrigerant gas vapors operating in refrigeration cycles, combining reciprocating pistons in a rotating cylinder member that is mounted for rotation in a stationary frame and is driven by an external source of rotative power. The cylinder block rotates in an encircling port ring member which contains inlet, interstage, and outlet port sets. The number of port sets is greater or less than the number of cylinders, to provide a vernier effect in the timing of connections between the port sets and the cylinders.
The above mentioned copending patent is assigned to the assignee of the present invention. It is hereby incorporated herein by reference, and made a part hereof the same as if fully set forth herein, for purposes of indicating the background of the invention and illustrating the state of the art.
The term injected compression is used herein to mean the injection of high pressure vapor into the compression space of a compressor after the inlet suction of vapor from an evaporator is at least substantially complete. U.S. Pat. No. 4,332,144, Shaw, discusses the advantages of utilizing a scavenge vapor as a means of increasing the coefficient of performance of a refrigeration device and/or to increase the refrigeration (heat pumping) capacity of a given compressor displacement.
The copending patent cited above provides improved injection capability and also offers the option of providing two stages of compression in which the discharge of one stage of compression is fed to the second stage of compression with either or both of the stages capable of injected operation. So typical compressors according to the copending patent can be designed to have as many as four vapor inlets; the lowest pressure inlet being the output from the evaporator, the next higher pressure being the injection to the first stage of compression, the third pressure level being the interstage pressure, and the fourth being the injection to the second stage of compression.
Various advantages of such compressors are explained in the copending patent relative to refrigeration in general, but the patent does not specifically describe the advantages that an injected compressor of that type can have with NARB's as working fluids. The present invention includes additional novel system arrangements based on the general characteristics of that type of compressor. It also employs a novel type of control arrangement that provides a significant improvement over current heat pumps that extract heat from the ambient air for heating a dwelling. Improvement is shown with this system using a single refrigerant; and further improvement is shown for the slightly more complex system using a NARB as the working fluid.
The novel control arrangement for the single-stage heat pump compressor has direct application as the lower stage of a two-stage compressor system for low temperature freezer applications. One version of the system uses a single refrigerant as the working fluid; while a slightly more complex version uses NARB as the working fluid and is useful for reaching lower temperatures than the single-refrigerant system.