Hi all,
Thanks for clicking on this topic.
I have a 12KW Arotherm plus, 5 person household. Adults shower in the am, children shower/bath in the pm. We like to have hot water available when we need it for washing up etc.
I’m on a standard energy tariff.
I thought i had my DWH for best COP/energy consumption. I had it on Eco mode, target of 45degC with an offset of 3K; i had a hysteresis of 5K.
I then switched Eco off so that when the children run bath and showers simultaneously, the HP can keep up. I had the hysteresis of 5K so that we had hot water most of the time.
I was watching/reading something that made me think that perhaps I am better off increasing the target (to 50degC) and lowering the hysteresis point (15K). Idea being that HP will come on less often as there is more energy in the tank, and also the call for heat is lower; thus ultimately saving energy as the HP will have a more efficient run and less likely come on in the early hours when it is colder outside.
I appreciate it is a trade off with heating 45-50 being worse than 40-45.
I am grateful for peoples thoughts.
Thanks
Jed
Emoncms - app view
Hi Jed,
Not in anyway saying I’ve got it right, but my optimisation at present is to have 1 DHW cycle per day at 2pm. Evening baths are sorted and morning showers are OK.
Octopus Cosy tariff takes the sting out of lunchtime heating and topping up the battery.
Cheers, David.
Hi Jed,
how large is your DHW storage cylinder?
The charging offset setting in the controller is ignored by the heatpump, so this has no bearing on anything.
Regarding the hysteresis, 5K is quite low and you’d definitely get better efficiency at something like 15K. You could try whether you get sufficient hot water when heating the tank just once a day (in the afternoon to do it when it’s warmest), maybe to a higher temperature like the 50°C you proposed.
This is all really dependent on your specific storage cylinder, actual usage pattern and comfort expectations, so I suggest to experiment.
Thanks Andre, sorry I meant to say - it is a “250” litre unistor. Jed
With 250l for 5 people it might be tough to get through a day with a single charge. For me it was quite some experimentation to get to an optimized DHW schedule. However, without sacrificing a lot of comfort comfort I think you can go to a 10 K hysteresis, which will already be more efficient than 5K. Do you know where your tank temperature sensor is located (top/middle/?)
We’ve got a similar system and household environment; 7kW Arotherm Plus, 250l Vaillant Unistor cylinder, 4-person household, a couple of showers/baths per day. I’ve settled on the following DHW settings to balance comfort/cost/efficiency:
- DHW reheat once per day, 14:00-16:00
- Eco mode
- 50degC store temp
- 10K hysteresis
Works well for us with no intervention almost all of the time. We just had relatives staying for a week, an extra family of 4. Had to manually boost the DHW via the app a couple of times in the morning, no drama.
I’m not quite clear about use of the term hysteresis here. Are you saying that if your tank is above 40c your daily DHW cycle is cancelled and doesn’t happen?
If so, that could give evening baths quite a low comfort score in my household where having water very close to the target store temp is “preferred”.
FYI, We have a 300L tank and family of 4 we top to 50° each day during the afternoon. 2 showers in the evening and 2 showers the morning + the dishwashing. There’s enough for 2 extra shower if needed, not more.
First, the temperature measurement probably does not happen at the very top of the tank, so the top temperature is probably higher than the temperature measured by the heat pump. For me it’s around 3-5K. Second - do you bathe at 40+°C?
Comfort is highly relative. My warm water currently sits at 35°C, but we typically shower in the evening so it’s fine for my reheating to only start in the afternoon when it’s warm outside.
I force a DHW cycle every day even if the hysteresis is not reached because I know from experience that otherwise I might have insufficient water ehen it’s needed.