A Resistance–Capacitance Model for Real Time Calculation of Cooling Load in HVAC R Systems

Abstract

Simulating the realtime thermal behavior of rooms subject to air conditioning (AC) and refrigeration is a key to cooling load calculations. A wellestablished resistance–capacitance (RC) model is employed that utilizes a representative network of electric resistors and capacitors to simulate the thermal behavior of such systems. A freezer room of a restaurant is studied during its operation, and temperature measurements are used for model validation. Parametric study is performed on different properties of the system. It is shown that a reduction of 20% in the walls thermal resistivity can increase the energy consumption rate by 15%. The effect of set points on the number of compressor starts/stops is also studied, and it is shown that narrow set points can result in a steady temperature pattern in exchange for a high number of compressor starts/stops per hour. The proposed technique provides an effective tool for facilitating the thermal modeling of air conditioned and refrigerated rooms. Using this approach, engineering calculations of cooling load can be performed with outstanding simplicity and accuracy.