Patent ID: 7891201

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 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 a liquid level sensing device disposed in operative association with said flash tank receiver for sensing the level of liquid refrigerant within said flash tank receiver, at least one sensor operatively associated with said refrigerant circuit for sensing an operating characteristic of the refrigerant circulating through said 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 operating characteristic sensed by said at least one sensor to determine a desired liquid refrigerant level within said flash tank receiver to provide a circulating refrigerant charge consistent with a desired operating characteristic of the refrigerant and to selectively adjust said secondary expansion device to increase or decrease the flow of refrigerant passing therethrough in response to a signal from said liquid level sensing device indicative of the sensed level of liquid refrigerant within said flash tank receiver to control the level of liquid refrigerant to said determined desired liquid refrigerant level, said operating characteristic of the refrigerant circulating through the refrigerant compression device being at least one of (a) the vapor refrigerant passing through a refrigerant line from said flash tank receiver to an intermediate pressure stage of said compression device, and (b) the refrigerant discharged from the compression device.