Patent ID: 8459052

Claim:
A refrigerant vapor compression system comprising: a refrigerant circuit including a refrigerant compression device, a refrigerant cooling heat exchanger for passing refrigerant received from said compression device at a high pressure in heat exchange relationship with a cooling medium, a refrigerant heating heat exchanger for passing refrigerant at a low pressure refrigerant in heat exchange relationship with a heating medium, and a main expansion device disposed in the refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said refrigerant heating heat exchanger; a flash tank receiver disposed in the refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said main expansion device; a secondary expansion device disposed in the refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream with of said flash tank receiver; said secondary expansion device operative to expand the high pressure refrigerant flowing therethrough to a liquid/vapor refrigerant mix at a lower pressure intermediate the high pressure and the low pressure and to control the flow of refrigerant into said flash tank receiver; and a refrigerant charge control apparatus including at least one sensor operatively associated with said refrigerant compression device for sensing an operating characteristic of the refrigerant circulating through the refrigerant compression device, and a controller operatively associated with said secondary expansion device and said at least one sensor, said controller operative in response to at least the system operating characteristic sensed by said at least one sensor to selectively adjust said secondary expansion device to increase or decrease the flow of refrigerant passing therethrough to maintain a circulating refrigerant charge consistent with a desired operating characteristic of the refrigerant, said sensed operating characteristic being at least one of (a) the vapor refrigerant passing through a refrigerant line from the flash tank receiver to an intermediate pressure stage of the compression device, and (b) the refrigerant discharged from the compression device.