where QCDt1 is the total heat-energy pumped out during the total test period Dt1 and
PDt2 the energy input to the cooling unit during the same test-period (where Dt2 is
the sum of the periods when the cooling unit is switched on). In a steady state,
QC is equal to the sum of the heat leak into the refrigerator, Ql, and the heat supplied
by a heater placed inside the refrigerator, QH. The heat leakage rate, Ql, is also referred
to as the unladen heat-pumping capacity of a refrigerator because it is the
thermal load when the refrigerator is empty. Since the refrigerators investigated employ
different temperature-controlling methods, the technique outlined has to be
modified slightly to meet individual requirements.