Skip to main content
Rank 1
AliSmi
Rank 1
Jan 9, 2025 1:12 PM UTC
Solved

Hysterisis setting during prolonged cold spells

What do people find is the most effective hysteresis setting (for heating) for their ASHPs during a prolonged cold spell like we’re having currently (UK)? 

I have a Grant ASHP (radiators) and it’s currently 0.2 but I’m thinking I could remove it completely whilst so cold.

 

Interested to hear what others do.

Thanks in advance.

A

    Peter E
    Peter EBest Answer
    Super User
    Jan 10, 2025 2:15 PM UTC

    I'm not an expert on ASHP and the hysteresis setting but my best guess is that it prevents excessive cycling of the unit which would otherwise significantly reduce the efficiency of the unit with start up periods.

     

    I need to ask why you need to change the hysteresis. Is it because that the house is getting alternately too cold and too hot at times? If that's the case then maybe reducing the hysteresis will stop that without the ASHP cycling too much when the house is presenting a much bigger load on the unit.

     

    It's only a guess. I'll see if there is anything I can find out on that

     

    Peter

     

    Reducing my yearly fossil fuel usage with an EV (-900 litres petrol saving about £950/year), A2AHP (-8,700 kWh gas, cost neutral) and Timed Immersion heater (-1,500 kWh gas, £20/year more expensive but reducing as the gas price goes up)
    View in thread

    6 replies

    Chris_OVO
    Community Manager
    Chris_OVO
    Community Manager
    Jan 10, 2025 12:12 PM UTC

    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?

    Renewable energy jokes never get old.
    Peter E
    Super User
    Peter ESuper UserBest Answer
    Super User
    Jan 10, 2025 2:15 PM UTC

    I'm not an expert on ASHP and the hysteresis setting but my best guess is that it prevents excessive cycling of the unit which would otherwise significantly reduce the efficiency of the unit with start up periods.

     

    I need to ask why you need to change the hysteresis. Is it because that the house is getting alternately too cold and too hot at times? If that's the case then maybe reducing the hysteresis will stop that without the ASHP cycling too much when the house is presenting a much bigger load on the unit.

     

    It's only a guess. I'll see if there is anything I can find out on that

     

    Peter

     

    Reducing my yearly fossil fuel usage with an EV (-900 litres petrol saving about £950/year), A2AHP (-8,700 kWh gas, cost neutral) and Timed Immersion heater (-1,500 kWh gas, £20/year more expensive but reducing as the gas price goes up)
      juliamc
      Rank 20
      juliamc
      Rank 20
      Jan 10, 2025 2:17 PM UTC

      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.

        Chris_OVO
        Community Manager
        Chris_OVO
        Community Manager
        Jan 10, 2025 3:10 PM UTC

        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. 

        Renewable energy jokes never get old.
          Rank 1
          AliSmiAuthor
          Rank 1
          Jan 10, 2025 4:40 PM UTC

          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

            Peter E
            Super User
            Peter ESuper User
            Super User
            Jan 10, 2025 6:30 PM UTC

            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

             

            Reducing my yearly fossil fuel usage with an EV (-900 litres petrol saving about £950/year), A2AHP (-8,700 kWh gas, cost neutral) and Timed Immersion heater (-1,500 kWh gas, £20/year more expensive but reducing as the gas price goes up)
              Terms & ConditionsAccessibility statement

              OVO Energy Ltd, Floor 5, Crescent, Temple Back, Redcliffe, BS1 6EZ, (Company no. 06890795) registered in England and Wales.

              OVO (S) Gas Limited is registered in England and Wales (Company No. 02716495) at Floor 5, Crescent, Temple Back, Redcliffe, BS1 6EZ.

              OVO (S) Gas Limited is part of OVO Group Ltd