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Heat pumps and on/off working - starting to quantify it

 
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Air Source Heat Pumps (ASHPs)
Last Post by Derek M 2 years ago
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 ChickenBig
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16/09/2023 9:54 am  

Posted by: @cathoderay
↑

I suppose one way to do it might be to have five column grid and a pencil, and mark off on a scale of 1 to 5 how comfortable one felt every hour.

Perhaps this is what the Octopus 'Cosy Pods' room sensors are all about; gather data on air (and IR) temperatures and humidity and ask for feedback (or in the absence of feedback interpret that as approval for the current operating conditions). Combine that with a bit of server-driven experimentation and you've got yourself a way of determining personalised human comfort levels. I feel there is a startup in there.

 


   
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cathodeRay
 cathodeRay
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16/09/2023 8:27 pm  

Posted by: @derek-m
↑

Do you go out among the 'sick' people?

I did, before I retired. But then so too did Jesus, before he got retired. Minister: 'CMG?' Civil Servant: 'Call Me God. And KCMG is Kindly Call Me God.' Minister: 'What about GCMG?' Civil Servant: 'God Calls Me God.'  


Midea 14kW (for now...) ASHP heating both building and DHW


   
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 newhouse87
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18/09/2023 7:16 pm  

does anybody have idea how much extra electricity is used from having house at 22 instead of 21. Women are cold creatures. 10%?



   
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 Fazel
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18/09/2023 7:31 pm  

Posted by: @newhouse87
↑

does anybody have idea how much extra electricity is used from having house at 22 instead of 21. Women are cold creatures. 10%?

2000 joules/m3 air/degree C

 



   
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 newhouse87
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18/09/2023 7:34 pm  

Posted by: @fazel
↑

Posted by: @newhouse87
↑

does anybody have idea how much extra electricity is used from having house at 22 instead of 21. Women are cold creatures. 10%?

2000 joules/m3 air/degree C

 

for a far less knowledgeable poster like me, in plain language as a %?

 



   
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 Derek M
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18/09/2023 8:22 pm  

Posted by: @newhouse87
↑

does anybody have idea how much extra electricity is used from having house at 22 instead of 21. Women are cold creatures. 10%?

It mainly depends upon the outside temperature and how hard your heat pump is working, but will probably be in the 5% to 6% range.

 



   
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JamesPa
 JamesPa
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Topic starter 18/09/2023 8:24 pm  

Posted by: @newhouse87
↑

does anybody have idea how much extra electricity is used from having house at 22 instead of 21. Women are cold creatures. 10%?

A deceptively simple and important question but not actually that easy to calculate (for the avoidance of doubt I don't think the previous answer was correct).  

To get a good answer you would need to compare degree days (see degreedays.net) when the house is at 21, with degreedays when the house is at 22, in both cases for your location.

To do this you need to know the 'base temperature' for the house (at 21), which is (in essence) the outside temperature at which the house is warm enough to switch off the heating.  This depends on comfort, other sources of heating in the house, including electrical equipment, cooking and of course people, and degree of insulation.  Its often said to be 15.5 for the UK, based on a house temperature of 20, but this is a broad brush average.

So for example with a house temp of 21 its likely that the base temperature is around 16.5.  Based on a location in the South East of England there were on average 2289 degree days on average each year for the past 3 years.  If the base temperature is increased to 17.5 (for a house temperature of 22) then the average number of degree days over the same period is 2591, a 13% increase.

Thats very probably in the right ballpark unless you live in an exceptionally well insulated or an exceptionally poorly insulated house, or in a location where the climate is very different from South East England.

 

 


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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 Derek M
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18/09/2023 9:11 pm  

Posted by: @newhouse87
↑

does anybody have idea how much extra electricity is used from having house at 22 instead of 21. Women are cold creatures. 10%?

Are you referring to instantaneous electrical energy increase or the increase over a year, since the two will probably be different.

 



   
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JamesPa
 JamesPa
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Topic starter 18/09/2023 9:22 pm  

Posted by: @derek-m
↑

Posted by: @newhouse87
↑

does anybody have idea how much extra electricity is used from having house at 22 instead of 21. Women are cold creatures. 10%?

Are you referring to instantaneous electrical energy increase or the increase over a year, since the two will probably be different.

 

 

Good question!

The total used over the year will be the sum (mathematically the integral) of the instantaneous, so on this interpretation they are same.

The _peak_ instantaneous (and thus the required system capacity) will be different though.  The peak will increase much less than the total as it's proportional to inside temp - outside temp at the design OAT.  Based again on South east of England, this is roughly 5% as opposed to roughly 13% 

 


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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 Fazel
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18/09/2023 9:24 pm  

10% could be a real ballpark

https://energy-stats.uk/vaillant-arotherm-weather-curve-information/



   
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 newhouse87
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19/09/2023 9:57 am  

@derek-m suppose instantaneous as in ever over a day period to keep house at 22 from 7am to 10pm, difference between 21 and 22 for the day kwh?



   
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 newhouse87
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19/09/2023 10:01 am  

@jamespa hmm, was thinking it was simple question with maybe not so simple answer. House newly built very well insulated. Monitoring the house at 21 and 22 on 2 different similar cold days would tell me as you said.



   
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