What is a good chiller efficiency in kW per TR, and how do I measure it?

Lower is better. As a rough guide, a modern water-cooled centrifugal or screw chiller uses about 0.55 to 0.65 kW per TR of cooling at full load, and an air-cooled one about 1.0 to 1.2. Measure it by dividing the chiller's input kW by the cooling delivered in TR.

The formulas

The ranges in the short answer are typical figures for the compressor alone. Pumps and cooling towers add to plant kW per TR, so state which you measured.

• Cooling delivered (TR) = chilled water flow (m3 per hour) x 1,000 kg per m3 x 1 kcal per kg per degree C x temperature difference (degree C) / 3,024. One TR is 3,024 kcal per hour, or 3.517 kW of cooling.
• kW per TR = chiller input power (kW) / cooling delivered (TR).
• COP = 3.517 / kW per TR.

How to measure it in the field

1. Run the chiller at a steady load for at least 30 minutes.
2. Measure chilled water flow with a clamp-on ultrasonic meter on a straight pipe run.
3. Measure supply and return temperatures with calibrated sensors reading to 0.1 degree C; with a 5 degree difference, a 0.2 degree error shifts the result by 4%.
4. Log chiller input kW with a power analyser over the same interval.
5. Repeat at a few load levels, since efficiency changes with load and condenser water temperature.

Full load is not the whole picture

Most chillers spend most hours at part load. AHRI 550/590 rates part-load performance as IPLV, weighting efficiency at 100%, 75%, 50% and 25% load by 1%, 42%, 45% and 12%. Compare vendors on IPLV as well as full-load kW per TR. For buildings covered by ECBC, check the minimum COP and IPLV in its tables for your chiller type and size.

Common reasons for a poor reading

• Fouled condenser or evaporator tubes.
• Chilled water set point lower than the process needs.
• High condenser water temperature from a weak cooling tower.
• Low refrigerant charge after a leak.
• Several chillers running at low load instead of fewer at higher load.

Worked example: test and saving

• Flow 180 m3 per hour; return 12 degrees C, supply 7 degrees C, so a 5 degree difference
• Cooling: 180 x 1,000 x 5 / 3,024 = 297.6 TR
• Input power 190 kW: 190 / 297.6 = 0.638 kW per TR, COP 3.517 / 0.638 = 5.51
• After tube cleaning, 0.580 kW per TR at the same load: saving 0.058 x 297.6 = 17.26 kW
• Over 4,000 hours: 17.26 x 4,000 = 69,040 kWh
• Emissions saved: 69,040 x 0.710 kg CO2 per kWh = 49,018 kg, about 49 t CO2

Running hours and the post-cleaning figure are illustrative.

What Senseible does here

Senseible reads electricity bills (period, tariff category, sanctioned load, units) and applies 0.710 kg CO2 per kWh, so a chiller saving shows up in your Scope 2 figure month by month. It does not measure chiller efficiency itself; meter and sub-meter feeds are not self-serve and are set up with the Senseible team for each customer.

• Low GWP refrigerant for a new chiller
• Measuring savings from efficiency projects
• Cold storage energy per tonne
• Energy audit for MSMEs in India

Sources: BEE, Energy Auditor Guide Book 3, chapter on HVAC and refrigeration (kW per TR test); Energy Conservation Building Code 2017, chiller tables, AHRI Standard 550/590, part-load rating (IPLV), referenced in ECBC, CEA CO2 Baseline Database

Last reviewed 2026-10-16.