What a COP figure does not tell you
A single coefficient of performance is measured at one ambient, one flow temperature and one load. Here is what to ask for instead.
COP is the number on the front of the brochure, and it is the number every comparison spreadsheet has a column for. It is also a single point on a surface, and quoting it without its conditions is a little like quoting a car's top speed without mentioning the gradient.
A coefficient of performance is heat out divided by electricity in, measured at a specific ambient air temperature, a specific water flow temperature and a specific load. Move any one of those and the figure moves with it. The headline number on a datasheet is, almost universally, the most flattering combination available: a warm ambient, a modest flow temperature and full load.
The three variables that matter
Ambient. Air-source performance tracks the outdoor temperature, and the rated condition is often 20 °C or higher. If your plant runs hardest on a January morning in Delhi, the rated COP describes an operating point your system will rarely occupy when it matters.
Flow temperature. The lift between source and delivery is what the compressor is paid to do. A unit rated at 45 °C flow and one rated at 60 °C flow are not comparable numbers even if both say "COP 4.2", and a hotel with a legionella regime needs the 60 °C figure.
Load. A heat pump running at 30 % of capacity is not running at 30 % of the power for the same efficiency. Inverter units hold up reasonably well down to part load and then fall off; fixed-speed units cycle, and cycling is where efficiency goes to die. An oversized system spends its whole life here.
Ask for the map, not the point
What is actually useful is the performance table across the operating envelope — output and input power at several ambients and several flow temperatures — plus an honest part-load curve. Every serious manufacturer has this data; it is simply less marketable than one large number.
From that table you can build a seasonal figure weighted by your own bin hours and your own flow temperature, which is the only efficiency number that predicts a bill. It will be lower than the brochure COP. That is not a defect in the equipment — it is the difference between a measurement and a forecast.
If a supplier will not give you the table, that refusal is itself the answer.
Send us the occupancy pattern, the laundry schedule and the plant-room envelope. We’ll model the peak and come back with a plant and storage selection.
Ask for a load model
