Control of a transcritical vapor compression system

A method of controlling a transcritical vapor compression system, the method comprising:

• providing a compressor for compressing a refrigerant;
• providing a first heat exchanger for cooling the refrigerant;
• providing an expansion device for decreasing the pressure of the refrigerant;
• providing a second heat exchanger for absorbing heat into the refrigerant;
• calculating a first energy difference across the second heat exchanger;
• calculating a second energy difference across the compressor;
• calculating an energy ratio by dividing the first energy difference by the second energy difference;
• comparing the energy ratio to a previously calculated energy ratio;
• and
• adjusting operating parameters of the system based on the comparison of the energy ratio with respect to the previously calculated energy ratio.

A transcritical vapor compression system, comprising:

• a compressor for compressing a refrigerant;
• a first heat exchanger for cooling the refrigerant;
• an expansion device for decreasing the pressure of the refrigerant;
• a second heat exchanger for absorbing heat into the refrigerant;
• a first blower for directing a first fluid over the first heat exchanger;
• a second blower for directing a second fluid over the second heat exchanger;
• a first temperature sensor and a first pressure sensor positioned proximate an inlet to the compressor for measuring temperature and pressure, respectively;
• a second temperature sensor and a second pressure sensor positioned proximate an outlet of the compressor for measuring temperature and pressure, respectively;
• a third temperature sensor positioned proximate an inlet to the second heat exchanger for measuring temperature;
• a fourth temperature sensor positioned proximate an outlet of the second heat exchanger for measuring temperature;
• a third pressure sensor positioned proximate one of the inlet and the outlet to the second heat exchanger for measuring pressure;
• and
• a controller programmed to calculate the internal energy of the refrigerant proximate the inlet to the compressor, the outlet of the compressor, the inlet of the second heat exchanger and the outlet of the second heat exchanger based on the measurements of temperature and pressure, to calculate a first energy difference by subtracting the internal energy of refrigerant proximate the inlet to the second heat exchanger from the internal energy of refrigerant proximate the outlet of the second heat exchanger, to calculate a second energy difference by subtracting the internal energy of refrigerant proximate the inlet to the compressor from the internal energy of the refrigerant proximate the outlet of the compressor, to calculate an energy ratio by dividing the first energy difference by the second energy difference, to compare the energy ratio to a previously calculated energy ratio, and to adjust at least one of speed of the first blower, speed of the second blower, speed of the compressor and opening of the expansion device based on the comparison of the energy ratio with respect to the previously calculated energy ratio.