Calculate chiller kW per ton from input power and cooling tons, convert cooling kW to refrigeration tons, or convert kW/ton to COP and EER.
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What Is kW per Ton?
kW per ton (kW/ton) is the standard efficiency metric for commercial and industrial cooling systems. It measures how many kilowatts of electrical power a chiller or refrigeration system consumes to produce one ton of cooling (one refrigeration ton = 12,000 BTU/h = approximately 3.517 kW of thermal power removed). A lower kW/ton value means the system removes more heat per unit of electricity consumed, making it more efficient.
kW per Ton Formula
Where P is the electrical power input in kilowatts and Q is the cooling capacity in refrigeration tons. For example, a chiller drawing 164.9 kW while producing 253.1 tons of cooling operates at 164.9 / 253.1 ≈ 0.65 kW/ton.
Typical kW/Ton by Chiller Type
The ranges below are illustrative, not verified AHRI ratings or acceptance limits. Compare manufacturer-certified performance at matching load and rating conditions.
| Chiller Type | Typical kW/ton Range | Equivalent COP Range | Typical Capacity (tons) |
|---|---|---|---|
| Centrifugal (water-cooled) | 0.45 – 0.65 | 5.4 – 7.8 | 200 – 10,000+ |
| Screw / Helical-Rotary (water-cooled) | 0.60 – 0.80 | 4.4 – 5.9 | 70 – 450 |
| Scroll (water-cooled) | 0.60 – 0.72 | 4.9 – 5.9 | 20 – 200 |
| Reciprocating (water-cooled) | 0.70 – 1.00 | 3.5 – 5.0 | 10 – 200 |
| Air-cooled (all compressor types) | 0.80 – 1.30 | 2.7 – 4.4 | 5 – 500 |
Part-load performance may improve or worsen depending on compressor controls, variable-speed operation, auxiliaries, load and ambient conditions. Use the applicable manufacturer performance curves rather than assuming a fixed degradation.
Converting Between kW/ton, COP, and EER
The three primary efficiency metrics are interconvertible using the constant 3.517 (the kW equivalent of one refrigeration ton) and 12 (the thousands of BTU/h per ton, divided by 1,000 W/kW).
| From | To | Formula |
|---|---|---|
| kW/ton | COP | COP = 3.517 / kW/ton |
| COP | kW/ton | kW/ton = 3.517 / COP |
| kW/ton | EER | EER = 12 / kW/ton |
| EER | kW/ton | kW/ton = 12 / EER |
| COP | EER | EER = COP x 3.412 |
| EER | COP | COP = EER / 3.412 |
COP is cooling output divided by electrical input in matching power units. EER is cooling Btu/h per input watt. Under the applicable AHRI rating conditions, A, B, C and D correspond to 100%, 75%, 50% and 25% capacity. For COP/EER, IPLV = 0.01A + 0.42B + 0.45C + 0.12D; for kW/ton, IPLV = 1 / (0.01/A + 0.42/B + 0.45/C + 0.12/D). A single operating-point conversion does not establish an IPLV/NPLV rating. See AHRI 551/591, Appendix D.
Quick Reference: kW/ton to COP to EER
| kW/ton | COP | EER (BTU/Wh) |
|---|---|---|
| 0.40 | 8.79 | 30.00 |
| 0.50 | 7.03 | 24.00 |
| 0.60 | 5.86 | 20.00 |
| 0.70 | 5.02 | 17.14 |
| 0.80 | 4.40 | 15.00 |
| 0.90 | 3.91 | 13.33 |
| 1.00 | 3.52 | 12.00 |
| 1.10 | 3.20 | 10.91 |
| 1.20 | 2.93 | 10.00 |
| 1.30 | 2.71 | 9.23 |
Why 3.517 kW Equals One Ton of Refrigeration
The refrigeration ton originated from the 19th-century ice harvesting industry. One ton of refrigeration is the rate of heat absorption needed to melt one short ton (2,000 lb) of ice at 32 °F in 24 hours. The latent heat of fusion for water is 144 BTU/lb, so: 2,000 lb x 144 BTU/lb = 288,000 BTU per 24 hours = 12,000 BTU/h. Converting to metric: 12,000 BTU/h / 3,412.14 BTU/kWh = 3.517 kW. This is the fixed thermal constant that links all chiller efficiency metrics together.
Factors That Degrade kW/Ton in Practice
Published ratings use specified test conditions. Actual efficiency changes with condenser temperature, fouling, refrigerant charge, controls, load and system boundaries. Measure these conditions and compare with manufacturer guidance; generic numerical penalties are not reliable for every system.
Assess maintenance or replacement using measured trends, manufacturer guidance, load and ambient conditions, and a documented economic analysis; no single kW/ton threshold determines the decision.
Estimating Annual Energy Cost from kW/Ton
kW/ton can be translated directly into operating cost. Multiply kW/ton by the cooling load in tons by the number of operating hours by the electricity rate in $/kWh. For a 500-ton chiller at 0.60 kW/ton running 2,000 equivalent full-load hours per year at $0.12/kWh: 0.60 x 500 x 2,000 x 0.12 = $72,000/year. Upgrading that same chiller from 0.80 kW/ton to 0.55 kW/ton saves $30,000/year, illustrating why even small kW/ton improvements translate to significant cost reductions in large facilities.
Frequently Asked Questions
What is a good kW per ton for a chiller?
A useful benchmark depends on equipment type, load, ambient conditions and the measurement boundary. Compare documented manufacturer ratings and measured trends under the same conditions.
What is the difference between kW/ton and COP?
Both measure the same thing from different directions. kW/ton measures input per unit of output (lower is better). COP measures output per unit of input (higher is better). They are inversely related through the constant 3.517: COP = 3.517 / kW/ton. A chiller at 0.60 kW/ton has a COP of 5.86.
Why does kW/ton change at partial loads?
Compressors are designed for a specific operating point. At partial loads, components like inlet guide vanes or slide valves throttle capacity, introducing aerodynamic or mechanical losses. Centrifugal chillers in particular lose efficiency at low loads due to surge control requirements and fixed parasitic losses (oil pumps, controls) that become a larger fraction of reduced output. The IPLV metric accounts for this by weighting efficiency at 25%, 50%, 75%, and 100% load.
Does condenser type affect kW/ton?
Significantly. Water-cooled condensers reject heat to a lower-temperature sink (typically 85 °F cooling tower water) compared to air-cooled condensers (95 °F+ ambient air). Lower condensing temperatures reduce compressor lift, which directly reduces compressor work. This is why water-cooled chillers achieve 0.45-0.65 kW/ton while air-cooled units of similar capacity operate at 0.80-1.30 kW/ton.
