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Daikin Altherma 3 11 kW Heat Pump – More Efficient But Not Necessarily Cheaper To Run?

 
Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 2 hours ago
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 Optimistic Optimiser
(@optimistic-optimiser)
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Topic starter 07/03/2026 7:07 pm  

I have a Daikin Altherma 3 11kw heat pump which was installed by Octopus about 15 months ago.  Octopus set it up to follow the weather curve but also referencing the Madoka thermostat.  Over time I have refined the weather curve to try to improve the efficiency (COP c. 3.3 based on the cumulative information from the Madoka MMI) with some success.  Last year the heating and hot water consumption was about 4000 kwh.  I am trying to convince myself that I should change from the current setup to pure weather compensation, but the thing that is stopping me is I understand (please tell me if this is wrong) that the 11kw Daikin consumes a minimum of about 900w when the compressor is working and I understand that the aim is to keep the compressor working (heating low and slow). If you were the middle of winter I can understand that this might be fine, but 900w multiplied by 24 hours is 21.6kwh per day as a minimum.  My consumption for a day earlier this week when the weather was between about 6 degrees and 8 degrees  for the whole day was 16kwh.  These numbers suggest to me that pure weather compensation used all through the year would be more expensive but quite possibly give me a higher COP/SCOP. 

What is it that I am missing?

 


This topic was modified 3 hours ago by Mars

   
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JamesPa
 JamesPa
(@jamespa)
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07/03/2026 9:31 pm  

Posted by: @optimistic-optimiser
↑

What is it that I am missing?

The fact that when the demand (ie house loss) is less than the minimum that the heat pump can turn down to' the heat pump will cycle on and off so that on average the demand and output are matched

Like this (from my heat pump) between about 11am and 1800 on the first day and after 11am on the second day.

 

 

image

This post was modified 2 hours ago 2 times by JamesPa
This post was modified 39 minutes ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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