There seems to be a lot of mystery and misinformation about air-air systems. These are basically reversible air-conditioners, and I have personal experience of some very successful installs. However, they don’t suit everyone, and in the depths of winter, they might struggle as they defrost and the COP drops. I occasionally hear wildly optimistic winter COP claims. So, I will be monitoring this unit and try to estimate the COP (heat output / power input)
Watch this space https://emoncms.org/thehub
The values above are examples, and will vary considerably as the outside air temperature changes.
How can we estimate the COP?
It is very easy to measure heat delivered to water by measuring the flowrate and the temperature rise, however, it is very difficult to measure heat delivered to air. The alternative is to look at the refrigeration circuit and estimate it from there. Sadi Carnot was a very clever chap and worked out the theoretical efficiency of a heat pump back in 1824. The formula he worked out only used the refrigerant temperatures.. One of it evaporating in the ‘cold side’, the other of it condensing in the hot side.
We must use absolute temperatures (starting at 0 from absolute zero)
We know from experiment that the actual real-life COP for this type and size of compressor is likely to be between 45 and 50%. From this, we can plot an estimated COP on our graphs. At outside temperatures below about 7°C, 45°F, defrosts can occur. We will need to estimate the duration and cooling during this process to allow for it.
Watch this space.