Wired magazine: The Hunt for the Most Efficient Heat Pump in the World

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The Hunt for the Most Efficient Heat Pump in the World | WIRED


Trystan, Good Evening.

This article made me wonder about what is the best conceivable performance for a heat pump.

Starting the Carnot formula, and adding a temperature difference at the cold and hot ends for the heat exchanger, the COPS still look much higher than anyone in practice achieves.

Do you know which other factors are responsible for this imperfect performance. I can think of inefficient compressors, and heat losses, but I can’t think of much else. Do you know what it is that limits real heat pump performance to just a fraction of the ideal COP.

No hurry. Best wishes


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If CoP is based on total measured outdoor unit power consumed (as it should be) then the evaporator fan (for ASHPs) or brine circulation pump (for GSHPs) will also be included. (This can be up to 100W, so not insignificant.)
If the comp is variable speed there are also inverter losses (may only be 5% but my inverter needs a cooling circuit and that energy has to go somewhere).
But the main loss I see on my ASHP is low comp polytropic efficiency, which I’ve put down to motor losses, friction losses (shaft/seals etc), and wasted energy on lube oil circulation.
I also see quite a bit of desuperheating between the comp exit and the condenser (20degC or so) which I assume is down to poorly insulated piping in the outdoor unit (I haven’t looked).
Then there is defrosting (on ASHPs) - a negative CoP, even if only for a few minutes each cycle.
Even the electronics (EEV/SOV actuators and board P/S) may consume a few W, but it all adds up.


The really interesting aspect of this article, and the link to the article on SCOP Envy Heat Pump COP Envy is pointless is that it’s more important to consider total cost per square meter.

My other observation is that there is no way to know how well calibrated any of the systems reporting into https://heatpumpmonitor.org are.

Hello @Guff666

Most of the systems on HeatpumpMonitor.org have MID heat and electric meters. E.g using the metering package here Level 3 Heat Pump Monitoring Bundle (emonHP) - Shop | OpenEnergyMonitor. See tick for MID on the right hand side of the table.

Have you seen the fabric page https://heatpumpmonitor.org/#mode=heatpumpfabric and the costs page: https://heatpumpmonitor.org/#mode=costs&tariff=agile these try to provide different ways of looking at the data.

There are issues with every measure, cost/m2 will favour those that have invested in fabric performance upgrades or high performance new build or/and large floor areas. Certainly no use having COP envy but I also think it’s worth celebrating that some folk have managed to get SCOP’s of 4.5-5 from well designed, installed and optimised installations even if those houses are more leaky than others.

Plotting systems with at least 290 days of data, comparing electricity consumption per m2 vs SCOP, it’s interesting how wide the spread of values is here. E.g you can have a SCOP of 3 or a 4.6 from a system that consumes ~20 kWh/m2 electric.