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Ecodan tank temperature oddity

 
Air Source Heat Pumps (ASHPs)
Last Post by PumpItUp 4 years ago
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 PumpItUp
(@pumpitup)
Active Member Member
Joined: 4 years ago
Posts: 7
Topic starter 05/01/2023 12:10 am   [#724]

Hi there,

I’ve noticed the tank temperature in our new Ecodan system is showing strange readings after a shower.

I’ve set it to heat for an hour morning and evening, it is heating up to 48c at these times, as expected, then after a shower the reading drops right down to something like 12c, even though there is loads of hot water left.  Any ideas what’s going on with the temp readings here?  Wrong type of tank selected in the system settings perhaps?  

Cheers



   
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 AllyFish
(@allyfish)
Prominent Member Contributor
Joined: 4 years ago
Posts: 520
05/01/2023 9:11 am  

Same with the Grant pre-plumbed cylinder and digital thermostat. My 250L tank shows all manner of random temperatures after drawing hot water. I think this is due to the thermostat sensor pocket being in a position in the tank where cold water entering the tank at low level to replace hot water drawn off influences it. Mains pressure hot water tanks rely on temperature stratification, cold in at the bottom, hot out at the top. You don't want the cold and hot water to mix. I think it's just a feature of the control. My thermostat has shown 10degC before, yet the hot water drawn off is coming out at 45degC and has never run cold.



   
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 Bob77
(@bob77)
Trusted Member Member
Joined: 4 years ago
Posts: 36
05/01/2023 10:35 am  

My Daikin Altherma with integrated tank also often shows the water temperature to be below 20C even when there is still hot water coming out. It's not really a reliable guide - at first I was checking the tank temperature after the shower had been used to see if I needed to put it back on but that doesn't really work and I probably switched it on unnecessarily a few times.

Presumably it also means that the auto reheat will come on before it really needs to, if it is using a reading from low down the tank.



   
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 PumpItUp
(@pumpitup)
Active Member Member
Joined: 4 years ago
Posts: 7
Topic starter 05/01/2023 11:17 am  

Thanks folks, I’ll just not pay attention to that reading then.  Glad I have the water scheduled, sounds like it would cost a fortune if left on auto!



   
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 redbuzzard
(@redbuzzard)
Active Member Member
Joined: 4 years ago
Posts: 18
05/01/2023 1:26 pm  

Posted by: @pumpitup
↑

Thanks folks, I’ll just not pay attention to that reading then.  Glad I have the water scheduled, sounds like it would cost a fortune if left on auto!

I don't think you need worry in the short term about having water heating on auto if you want to experiment, although the cumulative cost is worth considering.

I have a Mitsubishi pre-plumbed 300L tank and both heating and DHW are 'always on'.  In the summer months with heating off, the heat pump meter  recorded 60kWh in July and 55kWh in August i.e. c. 2kWh per day.  

 


2021 built 2 storey detached house, 212 sq.m. / 2300 sq.ft. heated area. EPC 87B. Mitsubishi Ecodan 11.2Kw ASHP, weather compensated flow temp, UFH, MVHR.


   
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 PumpItUp
(@pumpitup)
Active Member Member
Joined: 4 years ago
Posts: 7
Topic starter 05/01/2023 9:38 pm  

Another reason for the scheduling is the tank is next to 2 bedrooms so it was doing our head in the water heating up through the night!

Not 100% sure on the tank size but it’s a small 3 bed semi and using 3kwh per day on our schedule, that’s 48c and enough for everyone to shower (including lengthy girl showers!) and wash dishes etc, seems reasonable enough.

Overall we are using around 10kwh per day in sub zero temps, cop is around 3 just now 

 



   
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