What is Ton of refrigeration (TR)?
A ton of refrigeration (TR) is a unit of cooling rate equal to 12,000 Btu per hour, about 3.517 kilowatts of heat removed. It describes cooling, not the electricity used to produce it.
Where TR is used
Chiller, cold store and air conditioning capacity is quoted in TR across North America, India and the Gulf, while European suppliers usually quote kilowatts of cooling. Plant engineers, auditors and vendors use it when sizing equipment and comparing plants.
Conversions and calculations
NIST's Guide for the Use of the SI lists one ton of refrigeration as 12,000 Btu per hour, or 3,516.853 watts. Delivered cooling on a water loop is calculated from flow and temperature difference: tons equal flow in US gallons per minute times the temperature difference in degrees Fahrenheit, divided by 24. Glycol and brine need a correction for their lower specific heat. Efficiency is then expressed as kW per TR, the electrical input divided by delivered tons.
How Aqueduct calculates delivered tons
With a flow meter and supply and return temperature sensors on the chilled water or glycol loop, Aqueduct computes delivered TR minute by minute and divides plant electrical load by it. Nameplate capacity becomes something to check: a plant rated far above its peak delivered tons is oversized, and one that never reaches rating at full power has a capacity problem.