BTU vs TR vs kW: refrigeration capacity units explained

What each unit measures

• kW (kilowatt): the SI unit of power. As a cooling capacity it means heat removed at a rate of 1,000 joules per second.
• BTU/h: British thermal units per hour. One BTU is roughly the heat to warm one pound of water by 1 °F. Often written loosely as just BTU, but a capacity is always per hour.
• TR (ton of refrigeration): 12,000 BTU/h. It comes from the heat needed to melt one short ton (2,000 lb) of ice in 24 hours: 2,000 lb × 144 BTU/lb ÷ 24 h = 12,000 BTU/h.
• kcal/h: kilocalories per hour, still seen on older equipment and some cold storage documents.

The exact conversions

Using the factors published by NIST: 1 TR = 3,516.85 W ≈ 3.517 kW; 1 BTU/h = 0.293 07 W; so 1 kW = 3,412 BTU/h. For kcal/h, 1 kW ≈ 860 kcal/h and 1 TR ≈ 3,024 kcal/h.

Why horsepower is not a cooling capacity

HP describes the size of the compressor motor, which is an electrical and mechanical input. How much cooling that compressor delivers depends heavily on the temperatures it works between. The same compressor gives much less cooling in a freezer than in a chiller, and less on a 43 °C afternoon than in a 32 °C room. Two 1 HP units can differ widely in TR.

When a quote says '1 HP condensing unit', ask for the cooling capacity in kW or BTU/h at your evaporating temperature and at a condensing temperature that suits your ambient.

Capacity always comes with conditions

A capacity figure without its rating conditions cannot be compared with another. For a condensing unit the key conditions are the evaporating temperature (set by the product temperature you need) and the ambient or condensing temperature. Freezer duty means a lower evaporating temperature and therefore less capacity from the same hardware. Indian sites should be checked at a realistic summer ambient, not a mild test condition.

Manufacturers publish capacity tables or software that show output across a grid of evaporating and ambient temperatures. Read the row and column that match your job. If a supplier gives only one capacity figure, ask what conditions it was measured at before you convert it into TR or compare it with anything.

Linking cooling to electricity: COP and EER

COP (coefficient of performance) = cooling output in kW ÷ electrical input in kW. Both are kW, so COP has no unit. EER expresses the same idea in mixed units: BTU/h of cooling per watt of input, so EER = COP × 3.412.

Worked example with assumed figures: a condensing unit delivers 2.6 kW of cooling at your conditions while drawing 1.2 kW. COP = 2.6 ÷ 1.2 = 2.17; EER = 7.4 BTU/h per W. In TR, 2.6 ÷ 3.517 = 0.74 TR, or 2.6 × 3,412 = 8,871 BTU/h. If it runs 60% of the time, it uses 1.2 kW × 24 h × 0.6 = 17.3 kWh a day.

kW versus kWh: power versus energy

kW is a rate. kWh is an amount: one kilowatt for one hour. Cooling loads calculated per day are often written in kWh/day of heat; dividing by running hours gives the kW of refrigeration needed. Your electricity bill counts kWh of electrical input, which is the cooling energy divided by the COP. Mixing the two, or mixing cooling kW with electrical kW, is the most common error in comparing quotes.