Forums

Forums
Renewable Heating
Air Source Heat Pum...
Setback savings - f...
 
Notifications
Clear all

Setback savings - fact or fiction?

 
Page 11 / 11
Air Source Heat Pumps (ASHPs)
Last Post by cathodeRay 2 hours ago
121 Posts
12 Users
18 Reactions
7,331 Views
RSS
cathodeRay
 cathodeRay
(@cathoderay)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 2496
Topic starter 22/12/2025 8:21 pm  

Will come back to the above points, but for now, I've just taken a step back, to look again at the core of the contradiction we are trying to resolve here. As I see it, it is this:

(1) my 'observed vs expected' method strongly suggests running an overnight setback saves energy. My analysis of the 'two populations' hypothesis further suggests this is the case.

vs

(2) the conservation of energy principle says any savings must be modest (or strictly speaking non-existent, if overall a steady state is maintained), and furthermore any modest savings, if present, may be cancelled out by detrimental COP changes.

Some observations:

Since all the 'empirical' studies are observational studies, not controlled trials in lab conditions, there is a significant risk of bias. 

My 'observed vs expected' method is totally dependent on the expected (predicted) values being correct. 

The conservation of energy principle is beyond doubt, but are we applying it right in practice? Could there, for example, be another not obvious source of energy during the reheat period that we haven't accounted for? Or have we somehow over-estimated the actual loss during the setback?

Given the same (mean) OAT, if the mean IAT overall during a period of setback running is lower than that achieved during a period of no setback running, then there should be a saving. This has always be my supposed explanation of how the saving happens, but ever changing conditions and an  overall shortage of data have to date made comparing like with like a rather sketchy business, there simply aren't enough aggregate data points over a wide range of conditions. If I try to match setback days to non setback days with similar OATs, things get very sparse (note the small number of data points overall, which means wide confidence intervals, and nothing below 4°C OAT):

 

2025 matched pairs

 

Nonetheless, this is what my 'matched pairs two population' analysis is all about. If I can find a way to incorporate the mean IAT data (not the delta t, that will obscure what I want to look at, which is the actual mean IAT, to see whether it is less on setback days), then that may (or may not) throw some light on the question.             

 


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


   
ReplyQuote
Page 11 / 11
Forum Jump:
  Previous Topic
Next Topic  

Currently viewing this topic 4 guests.



Share:

Join Us!

Worth Watching

Latest Posts

Click to access the login or register cheese
x Powerful Protection for WordPress, from Shield Security
This Site Is Protected By
ShieldPRO →