21 - Refrigeration load estimation

Abstract

Refrigeration loads are from two sources: To cool something down, or to keep something cool. Conducted heat is that going in through cold store surfaces, tank sides, pipe insulation. It is normally assumed constant and the outside temperature an average summer temperature, probably 25–27°C for the UK, unless some other figure is known. Coldroom surfaces are measured on the outside dimensions and it is usual to calculate on the heat flow through the insulation only, ignoring other construction materials, since their thermal resistance is small. Warm air will enter from outside mainly during the opening of doors for the passage of goods. This must be estimated on the basis of the possible use of the doors, and such figures are based on observed practice. The main sources of internal heat are fan motors and circulating pumps. Where the motor itself is within the cooled space, the gross energy input to the motor is liberated as heat that must be removed. Where the motor is outside, only the shaft power is taken. A practical approach would be to install plant having a maximum product-cooling capacity of 146 kW (to which must be added the other load components of heat leakage, internal heat, and service). After an estimate of the total cooling load has been formed, this must be converted into a refrigeration plant capacity.