Discussion ... ASHP(Air/Air) with Solar pv ....

BrianD wrote: »

I have found this a very informative and interesting thread and am about to obtain quotes for one of the Daseikai 8 heat pumps but before doing so can I ask if either Z or ASB would still purchase the same product or is there something newer which you would choose instead?

I have a 3.68K system of west facing panels installed in 2011 and based in Darlington

Hi

I'd certainly go for the same model again, here's a couple of reasons why ...

If you look back through the thread you'll gauge that the decision for our particular model resulted from comparison of loads of different models from most of the leading manufacturers and a realisation that the specifications and functionality of whatever models we looked at were generally being subconsciously measured against the Daiseikai range.

When looking into various alternatives I decided at an early stage that it would be better to effectively ignore the headline seasonal performance (SCOP) which manufacturers use in their specifications and concentrate more on the COP within the range of temperatures which would be likely during the daytime in the shoulder months (Spring/Autumn) when we would be using the heat-pump to utilise our own generation to provide the heat we wanted. The idea behind this was that as we intended to use the heat-pump when PV generation conditions allow, we would need to take into consideration that ... (i) the sun doesn't shine at night in the shoulder months ... and ... (ii) we had no intention to use the heat-pump as the main source of heating during the Winter ... so why would we need to consider a performance measure which took low overnight temperatures and temperatures outside the shoulder month period into account .... this effectively means that, although SCOP is a decent headline comparative measure, for what is being discussed on this thread, you need to delve a little deeper - which in itself can be pretty hard with some manufacturer published specifications, but others seem to be far more open to providing the detail you'd need ...

Amongst the myriad of other functional and performance information which would be relevant to the decision making process when attempting to match the capabilities of the heat-pump to those of domestic-scale PV generation is the range of operation of the heat-pump. A basic heat-pump effectively works on an on/off basis, controlled by a thermostat, therefore a small basic 3kW unit operating at a COP of around 4 will be drawing 750W, resulting in additional electricity imports when it's cloudy even with a 4kWp PV system (it's currently overcast but bright here & we're generating 489W). Moving away from the basic models we have inverter based units which generally have better comparative performance statistics, but importantly have the ability to vary their supply of heat proportionally to thermostatic set-point demand and the range of this variability becomes relevant to what we're looking to achieve ... some of the inverter heat-pumps with similar COP statistics when we were looking had a performance range which required a minimum of 400W of electricity up to their maximum, whilst others had the ability to ramp down to close to l00W .... anyone already familiar with the variability of PV generation will appreciate that being able to utilise the heat-pump to provide over 500Wt of shoulder month background heating whilst consuming close to 100W to 120W of electricity becomes very handy in dull/cloudy conditions ....

HTH
Z