5.3.1 — Capacity
Capacity refers to the rate at which a refrigeration system can remove heat from a conditioned space or process. It is the fundamental measure of what a refrigeration system delivers and is used in equipment selection, system design, and performance verification.
Ton of Refrigeration (TR)
The most common capacity unit in North American HVAC/R. One ton of refrigeration equals 12,000 BTU/hr (3.517 kW). The unit is derived historically from the rate of heat absorption required to melt one ton (2,000 lb / 907 kg) of ice over 24 hours. Residential equipment is typically rated in tons (1–5 TR); commercial and industrial equipment in tons or kilowatts.
Kilowatt (kW) of Refrigeration
The SI unit for refrigeration capacity. 1 TR = 3.517 kW. Used in equipment specifications, engineering calculations, and energy compliance reporting. Increasingly common in Canadian specifications alongside or replacing the ton rating. To convert: capacity in kW × 0.2843 = TR; capacity in TR × 3.517 = kW.
Factors That Affect Delivered Capacity
A compressor’s rated capacity applies only at the rated conditions (suction pressure, discharge pressure, suction superheat, and ambient temperature specified by the manufacturer). In the field, actual delivered capacity changes with compression ratio, refrigerant type, and evaporating and condensing temperatures. Always consult the manufacturer’s capacity tables for actual operating conditions.