Where Qr is the thermal load coming from the resistors and Qw is the power dissipated through the chamber walls. Qr is calculated as the product between the resistor absorbed current,
Ir, and the grid voltage, V, while Qw depends on the mean heat transfer coefficient of the chamber walls, the thermostatic chamber exchange surface, S, and the gap between the outdoor and indoor temperatures, Text _ Tchamb. During the experimental campaign setup, the thermostatic chamber features are experimentally validated. Particularly, the factor kS is field assessed at a nominal chamber temperature of 50_C. In stationary conditions, the heat dispersions through the walls, Qw, equal the thermal load, Qr, inside the chamber so that k$*S is from Equations (2)e(3).
The preliminary analysis shows k*S = 8:2 W/_C. Finally, the COP is calculated as the ratio between Qf and the electric power absorbed by the compressor and the auxiliaries coming from the product between the measured current, Is, and the grid voltage, V. The derived errors induced by the measurement system to the previously mentioned factors are ±3.4% for the COP and ±1.6% for the Qf.