Hysterisis setting during prolonged cold spells

Hey ​@AliSmi,

I’ll tag a few of our heat pump users to see if they can offer some advice! 

​@juliamc, ​@nealmurphy & ​@Peter E do you have any suggestions or insight you can help with?

Not sure I can help - I don’t set hysteresis on the Daikin except for hot water reheat. It could be an installer setting, but not one I know about.

Thank you both for taking a look anyway! ​@Peter E ​@juliamc 

​@AliSmi I came across this thread on another Forum which might help - https://forum.buildhub.org.uk/topic/37184-best-thermostat-hysteresis-for-ashp/ from what I understand from it having a smaller hysterisis would cause your system to run more often to maintain temperatures. 

Thanks all for coming back to me and ​@Chris_OVO for the link, I’ll continue to investigate.

FYI ​@Peter E the house temp is fine so there aren’t any issues per se, its just when it’s this cold (and w/ a hysteresis setting of 0.2 degree, if the temp is set to 20, and 19.8 the heating will start heating again, however in these temps the house temp will often drop another 0.1 (before the heating has had any impact on the house temp) so it needs to heat 0.3 degree rather than 0.2 which takes longer

On the other hand the heat pump is off longer so the total heating is the same. Having the hysteresis too large could result in the temperature alternating between too hot and too cold but doesn't affect the amount of energy used, in fact, a larger hysteresis can result in a slightly lower losses due to fewer start up cycles per day. Each start up cycle consumes energy without producing any heat so you want to minimise those. I hope that explanation helps.

Peter