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

Canonical: https://senseible.earth/answers/chiller-efficiency-kw-per-tr

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.

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Sources: [BEE, Energy Auditor Guide Book 3, chapter on HVAC and refrigeration (kW per TR test); Energy Conservation Building Code 2017, chiller tables](https://beeindia.gov.in), [AHRI Standard 550/590, part-load rating (IPLV), referenced in ECBC](https://beeindia.gov.in), [CEA CO2 Baseline Database](https://cea.nic.in/cdm-co2-baseline-database/?lang=en)

Last reviewed 2026-10-16.