There is a voltmeter and an ammeter for determining the power input to the electric motor driving the compressor. Note that this crude diaphragm-type compressor has only a 55% efficiency, and the heat loss from the compressor to the surrounding air is estimated to be 18 W under typical operating conditions.



OPERATION:

Turn on the water supplies (arbitrary amounts) to the evaporator and condenser, then switch on the compressor and allow the cycle to stabilize. DO NOT RUN THE UNIT WITH ZERO WATER FLOW. Carefully observe the following processes in the cycle:

• Process 1 - 2: The compressor creates a low pressure in the evaporator and a high pressure in the condenser.
• Process 2 - 3: In the condenser, the refrigerant condenses at high (in relative terms) pressure and temperature while rejecting energy to the water flowing through the coil. Thus the water is heated, producing the heat pump effect. Heat transfer between the condenser and the surrounding air can be estimated as 0.8(T_air, - T_cond) in Watts.
• Process 3 - 4: The high pressure liquid leaves the condenser through a float controlled expansion valve. The pressure drop in the valve causes some of the liquid to flash into vapour, resulting in a two-phase flow which can be observed through the sight-glass located along the return line to the evaporator.
• Process 4 - 1: In the evaporator, the refrigerant boils at low pressure and temperature while removing energy from the water flowing through the coil. Thus, the water is chilled, producing the refrigeration effect. Heat transfer between the evaporator and the surrounding air can be estimated as
  0.8 (T_air, - T_evap) in Watts.