Heat pump system with multi-stage compression

A heat pump system comprising:

• a compressor section comprising first and second compressors, each having an inlet and an outlet;
• first and second heat exchangers selectively fluidically connected to the compressor section so as to enable flow of a refrigerant between the compressor section and the first heat exchanger, between the first and second heat exchangers, and between the compressor section and the second heat exchanger;
• valves for controlling the flow of the refrigerant through the first and second compressors and the first and second heat exchangers;
• means for controlling the valves so that the heat pump system is selectively operable in each of the following modes:
• the first and second compressors operating in series wherein the first compressor operates as a low stage compressor and the second compressor operates as a high stage compressor;
• the first compressor operating independently wherein the second compressor is bypassed by the refrigerant;
• and
• the second compressor operating independently wherein the first compressor is bypassed by the refrigerant;
• a lubricant equalization conduit fluidically coupled to the first and second compressors;
• and
• valve means for selectively fluidically connecting the first and second compressors through the lubricant equalization conduit and for selectively controlling flow of the lubricant through the lubricant equalization conduit so as to provide for equalization of levels of the lubricant in the first and second compressors;
• wherein the valve means operates to prevent flow of the lubricant through the lubricant equalization conduit if either of the first and second compressors are operating and operates to permit flow of the lubricant through the lubricant equalization conduit if both of the first and second compressors are not operating.

A heat pump system comprising:

• a compressor section comprising first and second compressors, each having an inlet and an outlet;
• first and second heat exchangers selectively fluidically connected to the compressor section so as to enable flow of a refrigerant between the compressor section and the first heat exchanger, between the first and second heat exchangers, and between the compressor section and the second heat exchanger;
• valves for controlling the flow of the refrigerant through the first and second compressors and the first and second heat exchangers;
• means for controlling the valves so that the heat pump system is selectively operable in each of the following modes:
• the first and second compressors operating in series wherein the first compressor operates as a low stage compressor and the second compressor operates as a high stage compressor;
• the first compressor operating independently wherein the second compressor is bypassed by the refrigerant;
• and
• the second compressor operating independently wherein the first compressor is bypassed by the refrigerant;
• means for separating a lubricant from the refrigerant flowing from the compressor section, the lubricant separating means having an inlet, a refrigerant outlet, and a lubricant outlet, the inlet of the lubricant separating means being fluidically connected to the outlets of the first and second compressors so as to receive the refrigerant flowing from at least one of the first and second compressors, the refrigerant outlet of the lubricant separating means being selectively fluidically connected to one of the first and second heat exchangers, the lubricant outlet of the lubricant separating means being fluidically connected to the inlets of the first and second compressors so as to return the lubricant separated from the refrigerant by the lubricant separating means to at least one of the first and second compressors;
• a lubricant equalization conduit fluidically coupled to the first and second compressors;
• and
• valve means for selectively fluidically connecting the first and second compressors through the lubricant equalization conduit and for selectively controlling flow of the lubricant through the lubricant equalization conduit so as to provide for equalization of levels of the lubricant in the first and second compressors;
• wherein the valve means operates to prevent flow of the lubricant through the lubricant equalization conduit if either of the first and second compressors are operating and operates to permit flow of the lubricant through the lubricant equalization conduit if both of the first and second compressors are not operating.