Renewable Heating Hub Heat Pump Forums

Search with Wattson
Forums
Renewable Heating
Air Source Heat Pum...
Long term efficienc...
 
Notifications
Clear all

Joining the Renewable Heating Hub forums is completely free and only takes a minute. By registering you’ll be able to ask questions, join discussions, follow topics you’re interested in, bookmark useful threads and receive notifications when someone replies. Non-registered members also do not have access to our AI features. When choosing your username, please note that it cannot be changed later, so we recommend avoiding brand or product names. Before registering, please take a moment to read the Forum Rules & Terms of Use so we can keep the community helpful, respectful and informative for everyone. Thanks for joining!

Long term efficiency degradation

 
Air Source Heat Pumps (ASHPs)
Last Post by Scalextrix 1 year ago
3 Posts
2 Users
0 Reactions
1,370 Views
RSS
 Scalextrix
(@scalextrix)
Estimable Member Member
Joined: 2 years ago
Posts: 127
Topic starter 10/08/2025 8:30 am   [#2415]

I'm pleased to say we just signed a contract to install an ASHP on our home.

As part of this decision we have been thinking about the spark gap and running costs.

Of course, we don't know the efficiency of our 18 year old gas boiler to understand its contribution.  We can look at it's specifications and see as new it was rated at 88.9% efficiency.  Interestingly we don't know under what conditions that is, and it might vary widely depending on what percentage of duty cycle it's condensing function is used.  But even then, with scaling build up in the heat exchanger, and general wear and tear, it's bound to be less effective than it was out of the factory.

So let's say it's now 80% efficient for arguments sake.  Our new heat pump should be 360% efficient, giving a 4.5 multiplier, and should be cheaper to run, yay!

But how long is that 360% efficient heat pump going to stay at 360%?  What levels of performance degradation are reasonable?  My solar panels came with a guarantee of less than 0.7% performance degradation for 20 years, 10 years in I can't see any difference in output.

The boiler has been maintained well over its life, it even had a new heat exchanger in it's warranty period, so we have to assume good regular maintenance of the ASHP too.

Anyone have long term performance numbers?  Would they be comparable to newer designs?



   
Quote
JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 5555
10/08/2025 8:47 am  

It's a good question to which I have never seen any answers.  The princial mechanisms I can think of are wear and tear on the compressor and bunging up of the heat exchanger.    Both should be very slow if the system is well designed and maintained.  Bunging up of the heat exchanger should be reversible, wear and tear on the compressor not so.  

The main determinant of efficiency (actually COP, coefficient of performance, or SCOP, seasonal COP) is anyway system design and how you operate it.  This can make the difference between a SCOP of 2 and a SCOP of 4 or more.  Best focus on that initially.  The next main influence (albeit on cost not scop) is electricity tariff.


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.


   
ReplyQuote
 Scalextrix
(@scalextrix)
Estimable Member Member
Joined: 2 years ago
Posts: 127
Topic starter 10/08/2025 9:10 am  

@jamespa yes as I thought thanks.

 

We have a reasonable design I think, certainly not the best but pretty good considering diminishing returns.

Done a lot of work to the house so it's got decent insulation and draught exclusion considering it's vintage.



   
ReplyQuote
Forum Jump:
  Previous Topic
Next Topic  
Share:

SPONSORS

Join Us!

Installer Finder

Degrees of Separation

Latest Posts

SPONSORS

Click to access the login or register cheese
Protected By
Shield Security PRO