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How to Calculate Chiller COP

COP, kW/TR, EER, IPLV — five ways to express chiller efficiency. Calculate any of them from the others, benchmark against ECBC 2017 and ASHRAE 90.1, and understand why the catalogue number rarely matches the measured one.

Inputs

For absorption chillers, electrical input is the parasitic pump/fan load only — the thermal input (steam, hot water) is a separate COP/COP_thermal metric.

Result

COP
5.86
kW per TR
0.600
EER
20.00
IPLV (estimated)
6.74
ECBC 2017 minimum (6.1 COP / 0.577 kW/TR)
Below ECBC minimum — upgrade candidate
COP = cooling kW ÷ electrical kW  |  kW/TR = 3.517 ÷ COP

How this works

Chiller efficiency is the ratio of useful cooling delivered to electrical energy consumed. Five different metrics express the same ratio in different units — pick whichever your spec or standard uses.

COP = Cooling output (kW thermal) ÷ Electrical input (kW)

Unit conversions:
  1 TR = 3.517 kW thermal = 12,000 BTU/hr
  kW/TR = 3.517 ÷ COP
  EER = COP × 3.412 BTU/(W·hr)
  IPLV = weighted avg at 100%/75%/50%/25% load (AHRI 550/590)

Example: a 500 TR centrifugal chiller consuming 315 kW compressor power has COP = (500 × 3.517) / 315 = 5.58, or equivalently 0.63 kW/TR.

Measuring it correctly

A COP number is only as accurate as your instrumentation. Follow this sequence.

  1. 1

    Install a BTU meter on the chilled-water loop — flow sensor + matched temperature probes on supply and return. EN 1434 Class 2 or better.

  2. 2

    Install a Class 0.5S 3-phase energy meter on the compressor feed. For total plant COP, also sub-meter pumps and cooling-tower fans.

  3. 3

    Measure simultaneously — both readings must share a timestamp. Transient loads and start/stop events distort any ratio computed from non-synchronous data.

  4. 4

    Hold a stable load for at least 60 minutes before reading. COP is meaningless during start-up or load-change transients.

  5. 5

    For IPLV, repeat at four part-load points (100/75/50/25%) at their corresponding condenser-water temperatures per AHRI 550/590.

ECBC 2017 & ASHRAE 90.1 benchmarks

Minimum full-load efficiency for chillers ≥150 TR. Green-rated buildings target 10–15% better.

Chiller typeMin COPMax kW/TRTypical measured
Centrifugal — water cooled6.10.5775.0–6.5
Screw — water cooled5.60.6284.8–6.0
Scroll — air cooled3.11.1352.8–3.4
Screw — air cooled3.21.0993.0–3.6
Absorption (single-effect)0.65.860.5–0.7 (thermal COP)
Absorption (double-effect)1.22.931.0–1.3 (thermal COP)

From a snapshot to a live COP dashboard

Every chiller-plant commissioning report has a COP number on page one. Then the meter gets forgotten, condenser tubes foul, CHW setpoint drifts, and by year three the plant is running 15% worse — but nobody is measuring.

Titan Plus BTU combines a Class 0.5S electrical meter and a BTU meter in a single DIN-rail device — guaranteeing synchronous measurement on the same timebase. Paired with the Energy Intelligence Platform, it gives you a live COP trend, automatic alerts when efficiency drops more than 5% below the baseline, and the audit trail for LEED/IGBC re-certification.

This matters for district cooling operators in particular — where every 0.1 COP point across a 10,000 TR plant is ₹40+ lakh per year in electricity. No other Indian manufacturer ships an integrated electrical-plus-thermal meter in one SKU. We built it because we saw operators wrestling with timebase-mismatched readings from three different vendors.

See Titan Plus BTU →

Frequently asked questions

Six questions on COP, IPLV, and measurement best-practice.

For a large centrifugal water-cooled chiller (>150 TR), ECBC 2017 minimum is COP 6.1 (0.577 kW/TR). Green-rated buildings target ≥ 6.5 at full load. For screw water-cooled chillers, minimum is 5.6. Air-cooled scroll/screw chillers sit much lower — 3.1–3.2 COP is the ECBC floor. What matters more than the nameplate number is the actual measured COP at your real operating conditions, which is almost always 10–25% worse than the catalogue number.
At part load, compressors run less efficiently (off-design point), pumps and fans often run at fixed speed delivering excess flow, and auxiliary loads become a larger fraction of total electrical input. Centrifugal chillers actually improve efficiency moderately down to 40–60% load, then drop sharply below that. Screw and scroll machines degrade more linearly. IPLV weights performance at 100/75/50/25% load (0.01/0.42/0.45/0.12) to give a realistic annual-average efficiency.
COP (or kW/TR) is the efficiency at one specific operating condition — typically rated full-load per AHRI 550/590. IPLV (Integrated Part-Load Value) weights four points (100/75/50/25% load at corresponding condenser temperatures) using AHRI weights that approximate a typical US commercial cooling season. IPLV is more useful for whole-year energy estimation; instantaneous COP is what you measure on site.
For a meaningful COP trend, you want total combined uncertainty under ±5%. That means a BTU meter at EN 1434 Class 2 or better (≤ ±4% worst-case), matched Pt500/Pt1000 temperature probes (not Pt100 — the resolution is inadequate at low ΔT), and a Class 0.5S electrical meter on the compressor feed. Critically, you need synchronous measurement — both readings timestamped to the same second — otherwise transients distort the ratio.
Yes. Measuring at the evaporator gives you chiller COP (the compressor's direct efficiency). Measuring at the secondary loop gives you plant COP — which includes pump, cooling tower fan, and piping losses. Plant COP is typically 10–20% lower than chiller COP and is the more useful number for actual building energy performance. Most operators measure both, and the delta tells you how much energy is lost in the distribution.
Not accurately. Some BMS systems estimate COP from flow (modelled, not measured), supply/return temperature, and electrical power — but the flow estimate is typically ±15%, which makes the COP estimate useless for optimisation. For real COP trending you need a permanent BTU meter on the CHW loop. Titan Plus BTU combines the BTU meter and the electrical meter in one unit, so synchronous measurement is guaranteed and the COP calculation happens on-device.

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