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Sizing of heat pumps

 
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Air Source Heat Pumps (ASHPs)
Last Post by benson 9 months ago
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 bobbt9866
(@bobbt9866)
Estimable Member Member
Joined: 5 years ago
Posts: 46
25/03/2021 4:06 pm  

@optimum-energy-solutions

I am not suggesting that they will get a proper sizing and cost from a budget rule of thumb. However we are trying to get more knowledge out there so that the novice owner has some idea of what he/she will require.

You started off going on about, correctly, the benefit of having a a proper heat loss calculation on a property. I agree with that.

What I have suggested, in the past, is that a 'rule of thumb' is helpful in getting an idea of their requirements. Its not rocket science and its not final, but many engineers do use that 'rule' as a guide for initial sizing.

You disagree, and that is your prerogative. Lets leave it there!



   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4351
Topic starter 25/03/2021 4:26 pm  

I agree @bobbt9866. The objective of these forums to is help novices make better informed decisions, and any rule of thumb metric or guidance gives novices a starting point from which to have a conversation with an installer. It's up to the installers to then do a proper heat loss analysis and to recommend the right system.

We're a prime example of this. We had no guidance or clue what size heap pump we needed. We had proposals ranging from a 9kW, 12kW, 18kW and 2x16kW systems. That's all over the radar. So any ballpark estimate to get the conversation going is critical.

 


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 bobbt9866
(@bobbt9866)
Estimable Member Member
Joined: 5 years ago
Posts: 46
25/03/2021 4:37 pm  

@editor

I have many great contacts in the heating sector and when these guys mention loads calculated I automatically mentally check against 100w/m2 and invariably the figures match.

As the writer stated, there are many cases where load calcs are made and many where guestimates are done, i am dealing with one that you know about. We need a savvy public, where possible to improve the domestic market, at the bottom end.

I want people to show more interest when buying a house, in regard to their heating systems. They can only do that with knowledge.

I have got Sam her support from the manufacturer this afternoon, by the way!



   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4351
Topic starter 25/03/2021 4:57 pm  

@bobbt9866, as the UK pushes towards heat pumps, consumers and homeowner knowledge needs to increase. Heat pumps are a bit of dark science and people need to get educated to make better decisions – that's primarily the reason behind this site and these forums.

I bet Sam will be relieved, because I think she was getting despondent again as there wasn't much happening. Great news you've been able reignite things for them again.


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 Des@Exeter
(@desexeter)
Active Member Member
Joined: 5 years ago
Posts: 5
19/04/2021 1:42 pm  

Second installer coming to survey shortly. Very old house but much better building fabric than you'd expect. Previous EPC C with more improvement since. Huge thermal mass, facing south etc. Naturally warm house. 169sq m. First quote 17kw and say goodbye to downstairs WC with massive tank! Estimate suspiciously close to 'bog standard' 1kw per 10sq m.

The standard heat loss calculators are bad at our type of house. It's a niche case and understandably retrofit maths is focused on older houses of brick etc rather than 2 foot thick cob (rammed earth) 😀 

Anyway my own research suggests something nearer 12kw coupled to compact Mixergy cylinder or Sunamp heat battery. External must be v quiet and small as possible because it needs planning permission (listed house/conservation area). Internal needs to be compact as we prefer not to cross our legs...



   
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 batalto
(@batalto)
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Joined: 5 years ago
Posts: 1092
19/04/2021 1:47 pm  

I would suggest you try speaking to the installers. I got a tool sent to me developed by Freedom Heat Pumps which works through all the steps you might need to take. I've converted it into a google sheet you can download and use at your leisure. Its not my tool, so might have issues. However Freedom are a pretty big company, so anything they developed is probably pretty legit for your use case.

 

https://docs.google.com/spreadsheets/d/1HAGXEC7WOhjsmXFf8Noh9CUvafc8E-DvoKn96zehmYc/edit?usp=sharing


12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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 bobbt9866
(@bobbt9866)
Estimable Member Member
Joined: 5 years ago
Posts: 46
19/04/2021 1:57 pm  

@batalto

That sheet/programme was probably created by Graham Hendra who certainly knows his stuff.

Always worth finding blogs done by Graham for their information.



   
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 batalto
(@batalto)
Noble Member Member
Joined: 5 years ago
Posts: 1092
19/04/2021 2:01 pm  

@bobbt9866 That might be. I've not interacted with Freedom at all, I just got sent it when I was getting quoted by one of the companies as an FYI. Seems pretty good and I had to go through the room by room and correct a number of assumptions the survey made about wall insulation. For instance they assumed our upstairs as double glazed, when it is triple. However that isn't an option, so they I had to manually find the U value and edit it myself. Overall though the figures tally with the quoted ASHP and give me a good idea of running costs I can work with


12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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 Des@Exeter
(@desexeter)
Active Member Member
Joined: 5 years ago
Posts: 5
19/04/2021 2:08 pm  

@batalto Thanks. V helpful. I'll give it a spin 👍 



   
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 Des@Exeter
(@desexeter)
Active Member Member
Joined: 5 years ago
Posts: 5
19/04/2021 2:09 pm  

@bobbt9866 Thanks for the tip! I'll look out for Graham Hendra's name. Cheers



   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4351
Topic starter 20/04/2021 8:45 pm  
Posted by: @bobbt9866

@batalto

That sheet/programme was probably created by Graham Hendra who certainly knows his stuff.

Always worth finding blogs done by Graham for their information.

We've been in touch with Graham (about three weeks ago) and he's given us permission to repost his articles on Renewable Heating Hub. We've posted the first one last week, more to follow in weeks to come. He's written on some very interesting subjects.


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 bobbt9866
(@bobbt9866)
Estimable Member Member
Joined: 5 years ago
Posts: 46
21/04/2021 11:43 am  

@editor

Yes, Graham is very experineced and write with the client/contractor in mind.

He also create manuals for the products he sells.



   
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