COP Explained: The Ratio Every Efficiency Claim Rests On
Every efficiency claim on an aircon reduces to one division: cooling out over electricity in, performed once while the machine holds full output. The answer then gets quoted as if it described a whole year.
By Team Snowflake | Updated 16 Sept 2026
What the ratio actually divides
COP is a division sum with a formal name. NEA defines the full-load version as cooling capacity divided by effective power input at full load. Cooling produced sits on top, electricity bought underneath, and the answer is what gets printed and argued over.
The phrase effective power input carries weight there. It means the electricity the whole machine draws, not the share the compressor takes: fans at both ends and the control board are inside the denominator. A ratio worked out against compressor draw alone would flatter the model.
Both halves are measured in kilowatts, so the units cancel and a bare number is left. The figure describes a relationship and states neither quantity. Which figure belongs on top, and which underneath, is settled by the guide separating cooling kW from power kW.
A value above one surprises people, and it should not. An aircon moves heat the room already held rather than manufacturing anything, and transport costs far less energy than creation. Every registered household machine locally sits well above one.
One trap follows from the ratio being a ratio: it says nothing about size. A machine four times the size of a bedroom unit can post the same figure, because both are measured against their own output. Efficiency and capacity are separate; a strong ratio on an undersized machine buys nothing.
Any two of the three numbers give you the third
Three quantities are locked together by one sum, so a missing one can be recovered. Capacity divided by the ratio returns the draw; draw multiplied by the ratio returns the capacity. A sheet listing any two has already told you the third.
Use that as a consistency check before trusting a page of figures: work the arithmetic and see whether the printed answer comes back. Where it does not, the values were not lifted from the same row; the culprit is a rated capacity paired with a minimum draw.
The check costs nothing and catches a class of error. Specification tables carry several columns of capacity and draw, and a figure copied into a quotation loses the heading that made it meaningful. Ask which operating row each number came from before treating the set as one machine.
One condition, and what the reading leaves out
The last clause is where the limits live. At full load cooling capacity means the compressor was held at maximum output for the whole measurement. Everything the figure claims belongs to that state and no other.
The air on both sides was held still as well. A test fixes the indoor and outdoor conditions, then holds them there while readings are taken. NEA names an international method for each machine type, and a different one covers a multi-split than a single split. Two figures from different methods are two measurements wearing the same label.
So the omissions are large and predictable. The reading knows nothing about the hours a machine spends throttled down, nothing about outdoor air hotter than the test condition, and nothing about the flat the system ends up in. What a rated figure gives up between chamber and room has its own guide.
The measurement is not dishonest for any of that. Holding the condition still is the only way two machines can be ranked, and a shared condition makes a published figure worth reading. The error sits downstream, in reading a controlled comparison as a year.
| Part of the definition | What it pins down | What it therefore excludes |
|---|---|---|
| Total cooling capacity | Heat removed while the test conditions hold | Output at any other indoor or outdoor condition |
| Effective power input | Electricity drawn by the whole machine | Nothing, and that is the point of the wording |
| At full load | The compressor pinned at maximum output | Every hour the machine spends throttled down |
| Under a named test method | Conditions that two models both had to face | Comparability with a figure from another method |
- Part of the definition
- Total cooling capacity
- What it pins down
- Heat removed while the test conditions hold
- What it therefore excludes
- Output at any other indoor or outdoor condition
- Part of the definition
- Effective power input
- What it pins down
- Electricity drawn by the whole machine
- What it therefore excludes
- Nothing, and that is the point of the wording
- Part of the definition
- At full load
- What it pins down
- The compressor pinned at maximum output
- What it therefore excludes
- Every hour the machine spends throttled down
- Part of the definition
- Under a named test method
- What it pins down
- Conditions that two models both had to face
- What it therefore excludes
- Comparability with a figure from another method
A ratio is comparable only inside its own method
Efficiency figures travel badly between documents, and the label rarely says which method produced them. A brochure, a regional review and the local registration can each carry a different value. All three can differ, and none need be wrong.
Treat a number with no metric named beside it as unusable rather than roughly right. The instinct is to assume the larger figure belongs to the better machine. That holds only when both came from the same method, and fails quietly otherwise, because nothing on the page announces the mismatch.
Why one reading was not left to stand alone
A single full-output reading describes a fixed-speed machine reasonably and a modulating one poorly. A compressor that changes speed spends most of its life away from the test condition, so the local criteria stopped resting on that reading alone.
For a machine that modulates, NEA blends two readings into a weighted COP, with more weight on the half-output reading than the full-output one. The reasoning behind the weighting and the seasonal metric belong to the guide on part-load efficiency.
The two scales are not interchangeable, and NEA has published the conversion that proves it. In a November 2024 presentation on the labelling regime, the agency gave CSPF as 1.1917 multiplied by COP, plus 0.3111. It then set each current split-type minimum beside its seasonal equivalent, and every equivalent lands over a full point above the figure converted from.
Read those pairs as a warning about arithmetic, not a lookup table. The same machine scores higher on the seasonal scale than the single-point one, by construction. A sheet quoting a seasonal figure beside a local requirement written in COP has placed two scales side by side, flattering the model.
A straight line fitted across a population estimates where a whole market sits, which is what a regulator needs when setting a level. It cannot translate one particular machine, because two units posting the same single-point figure can behave differently at part load. Running it on a showroom model produces a number nobody tested.
The direction is toward more sampling points, not fewer. Three-phase commercial equipment is graded on an integrated figure blending four COP readings at quarter, half, three-quarter and full output, with most weight on the three-quarter reading. EER and SEER appear on imported sheets as the same idea on a different unit basis.
The local floor is written in this ratio
This is not a spec-sheet curiosity: the efficiency minimum for household aircon is stated in the same quantity. NEA writes it as a full-load figure where the compressor runs at one speed, and a weighted one where it modulates, with a standby power ceiling beside it. The MEPS floor guide carries current values and tick-band coverage.
That places the ratio upstream of everything else printed about a machine. A model that misses the number cannot lawfully be supplied here: no label is printed, no showroom displays it. Every efficiency figure a buyer sees belongs to a machine that cleared this measure.
It is also the one term in the transaction that cannot be renegotiated. Capacity can be revised, the outdoor position argued about, the pipe route improved, the price moved. The ratio was fixed in a factory and tested before the machine reached the country, and the system carries it for life.
Push back on any efficiency claim that arrives without a metric attached. Ask which measure it is, and at what load it was taken. A seller quoting a large overseas figure against a local threshold is not lying and still not answering, because the two numbers were never on the same scale.
Why a regulator writes a floor as a ratio
A ratio has one property that makes it usable as law: it is free of scale. A bedroom unit and a system serving four rooms both produce a figure between roughly three and six, each measured against its own output. One threshold therefore governs a whole class of machine.
Write the minimum in kilowatts instead and it falls apart. A ceiling on electrical draw would ban large systems and wave through small inefficient ones; a floor on cooling output would say nothing about consumption. Neither means anything on its own, which is why neither belongs in a running-cost claim.
The same property lets the figure travel where nothing else on a sheet can. Capacity cannot be compared across a bedroom unit and a whole-flat system, and draw cannot either. The ratio holds two machines against one yardstick, which is why tick bands could be built on it.
One boundary survives all of that. The figure travels across brands, capacities and formats but not across metrics. A number is only usable beside another produced by the same method, and scale-free does nothing to rescue a comparison between measures.
What to do with the figure you are handed
The ratio ranks machines and refuses to forecast bills. Between two identical models, the higher figure buys its cooling with less electricity, and that ordering holds. What neither figure knows is how many hours the machine runs, what setpoint it holds, or what the room throws at it.
The useful question at the counter is narrow. Establish that every figure on the shortlist is the same measure taken the same way, then read the gap. A gap inside one tick band is real but small, and moves a bill less than sizing, condenser position and install standard.
The table below sorts the forms an efficiency claim arrives in: the middle column is what the number is a ratio of, the right-hand what to settle first.
Where a figure cannot be produced at all, that is information too. A registered model has a tested value behind its band, and a retailer who cannot reach it has described the shortlist rather than narrowed it.
- Ask for the tested figure and the metric name together. A number without its metric cannot be compared with anything.
- Ask at what load the figure was taken. Full output and a blended value answer different questions about the same machine.
- Keep one measure across the whole shortlist. Mixing a single-point value with a seasonal one ranks the scales, not the machines.
- Read a ratio as a ranking tool rather than a cost forecast. Runtime and conditions decide a running cost, and no published figure has seen either.
- Treat a strong ratio on the wrong capacity as no advantage. Efficiency is measured against a machine's own output, so it says nothing about fit.
| How the claim reaches you | What the number is a ratio of | What to settle before ranking on it |
|---|---|---|
| A single figure on a brochure | Cooling at full output over what that output cost | Whether the rival model's figure was taken the same way |
| A weighted figure on a registered model | Two readings blended, leaning on the lower output | That every model quoted uses the identical blend |
| A seasonal figure from an overseas sheet | A spread of conditions averaged on a foreign profile | That nobody is reading it against a local threshold |
| It meets the national standard | Nothing specific to this model at all | How far above the minimum the tested figure sits |
| This one will cut your bill | Nothing measured anywhere | The hours, setpoint and room behind the promise |
- How the claim reaches you
- A single figure on a brochure
- What the number is a ratio of
- Cooling at full output over what that output cost
- What to settle before ranking on it
- Whether the rival model's figure was taken the same way
- How the claim reaches you
- A weighted figure on a registered model
- What the number is a ratio of
- Two readings blended, leaning on the lower output
- What to settle before ranking on it
- That every model quoted uses the identical blend
- How the claim reaches you
- A seasonal figure from an overseas sheet
- What the number is a ratio of
- A spread of conditions averaged on a foreign profile
- What to settle before ranking on it
- That nobody is reading it against a local threshold
- How the claim reaches you
- It meets the national standard
- What the number is a ratio of
- Nothing specific to this model at all
- What to settle before ranking on it
- How far above the minimum the tested figure sits
- How the claim reaches you
- This one will cut your bill
- What the number is a ratio of
- Nothing measured anywhere
- What to settle before ranking on it
- The hours, setpoint and room behind the promise
Common questions
What does COP mean on an aircon specification?
Is a higher COP always better?
Why does the energy label show ticks instead of COP?
Does COP tell me what my bill will be?
Which details must accompany a quoted COP figure?
Sources
- Minimum Energy Performance Standards
National Environment Agency · Checked
Singapore COP definitions and minimum energy performance standards.
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