Tue, 27 Oct 2026 00:40:36 +0000 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212895#Comment_212895 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212895#Comment_212895 Mon, 10 Nov 2014 11:12:14 +0000 GarethC
Slightly disappointing SPF results overall, and GSHP only 17% better than ASHP despite twice the capital cost.

SPFs Number Mean 75th percentile
ASHP 289 2.34 2.72
GSHP 124 2.74 3.18

None of my favourite AAHPs in here (unfortunately).]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212915#Comment_212915 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212915#Comment_212915 Mon, 10 Nov 2014 16:41:06 +0000 gustyturbine https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212916#Comment_212916 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212916#Comment_212916 Mon, 10 Nov 2014 17:09:48 +0000 GarethC
And I find the modest difference between GSHP and ASHP SPFs very, very surprising. Even the 75th percentile, which has got to have a lot of well installed systems in it (for GSHP, read deep enough bore holes or long enough slinkys), still only has a 17% performance difference.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212920#Comment_212920 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212920#Comment_212920 Mon, 10 Nov 2014 18:17:28 +0000 SteamyTea https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212921#Comment_212921 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212921#Comment_212921 Mon, 10 Nov 2014 18:31:58 +0000 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212934#Comment_212934 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212934#Comment_212934 Mon, 10 Nov 2014 19:49:19 +0000 SteamyTea Posted By: tonyis it right to take the 75% percentile?Still not read it. But if it referring to the top CoP performing 25%, then no.
A normal mean would be the useful gauge as you are taking your chances on it being supplied the right size and fitted correctly. If there is a mode, and it is over 50% of the test, then it is meaningful, though there is some scope if one model was accounting for the mode. You would know how that model performs.

Trouble is we probably know more about these than the people that fitted them. Or more to the point, know more about the pitfalls.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212946#Comment_212946 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212946#Comment_212946 Tue, 11 Nov 2014 07:03:50 +0000 Chris P Bacon
http://sparenergi.dk/forbruger/varme/varmepumpe]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212948#Comment_212948 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212948#Comment_212948 Tue, 11 Nov 2014 09:09:08 +0000 ringi
Air source can give a very good SPF on the days you don’t need us much heat….]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212960#Comment_212960 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212960#Comment_212960 Tue, 11 Nov 2014 11:53:17 +0000 Ed Davies
SPF is, by definition, over the whole year. The 'S' stands for “seasonal” as in heating season. https://www.ofgem.gov.uk/key-term-explained/seasonal-performance-factor-spf]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212963#Comment_212963 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212963#Comment_212963 Tue, 11 Nov 2014 12:14:36 +0000 ringi
I would also question if it was a cold or warm winter.

(I get the same issue when choosing who to buy gas from, should I pay a higher standing charge, so I get a lower per KW rate that will benefit me if the winter is colder than last year?)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212966#Comment_212966 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=212966#Comment_212966 Tue, 11 Nov 2014 12:59:13 +0000 Ed Davies
“…lower per KW rate…” - again, kWh is probably what you're thinking of; it's far more common to quote costs as amounts of money per amount of energy rather than rates of money for a given amount of power.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213019#Comment_213019 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213019#Comment_213019 Wed, 12 Nov 2014 10:12:28 +0000 GarethC
SPFs Mean
ASHP 2.45 (vs. 2.34 above)
GSHP 2.82 (vs. 2.74)

Their figures suggest high performing GSHPs achieve about 3.0-3.2, so again consistent with 75th percentile stuff above. High performing ASHPs manage 2.8-3.0, again consistent.

Overall, that's a wealth of data to suggest:

- ASHPs and GSHPs, even high performing ones, provide somewhat lower SPFs than (certainly I) would have expected, particularly the GSHPs (depressing given how much they cost).
- the difference between GSHPs and ASHPs performance seems surprisingly low.

BUT, on the positive side, DECC's quite large sample results (page 8) suggest that:

- for ASHPs, it is perfectly possible to achieve SPFs of 3.0-3.5, presumeably if you have a very well installed, high spec unit. 34 units achieved this or better.
- for GSHPs, it is perfectly possible to achieve SPFs of 3.0-4.0. 35 units achieved this, again if similarly high spec/well installed.

Interestingly, not a single GSHP exceeded 4, while three ASHPs did (but I'm inclined to treat those as outliers).

My key takeaway is that on the basis of these data, GSHPs are absolutely not worth the significant (£5k+?) price premium over ASHPs, as the performance premium is marginal to zero. Better installing an ASHP, and spending your extra cash on more insulation.

Thanks for the Danish info Chris. I'll dig into it. As suggested by the Swedish stuff, and based on common sense, I still believe that AAHPs will routinely manage SPFs of 4.0+ for a fraction of the cost of the water based ones. DECC's data give me more confidence of that (if 35 air to water units can achieve 3.0+, with their extra complexities and losses, then simpler AAHPs should do significantly better).]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213053#Comment_213053 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213053#Comment_213053 Wed, 12 Nov 2014 15:10:50 +0000 ringi
Have a building with poor insulation so it needs lot of heat when it is “warm” outside, e.g. heat inside to 22c when it is 15c outside. And then light a log burner in winter so the ASHP is not used much at all when it is cold outside.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213063#Comment_213063 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213063#Comment_213063 Wed, 12 Nov 2014 17:38:52 +0000 skyewright Posted By: GarethCMy key takeaway is that on the basis of these data, GSHPs are absolutely not worth the significant (£5k+?) price premium over ASHPs, as the performance premium is marginal to zero. Better installing an ASHP, and spending your extra cash on more insulation.
Have they been around long enough for unit lifetimes to be assessed? Aside from the loop (& even that's underground), most bits of a GSHP set up can live in a benign environment. At least part of the ASHP set up must inevitably be in a reasonably exposed position. Maybe that's a factor to consider, especially if you live near the sea?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213073#Comment_213073 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213073#Comment_213073 Wed, 12 Nov 2014 19:01:51 +0000 Paul in Montreal
Paul in Montreal.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213075#Comment_213075 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213075#Comment_213075 Wed, 12 Nov 2014 19:12:01 +0000 ringi
Also I expect that the building with ground source may have been more demanding on their locations or heat need.

My current view is that if you have a digger on side, the space, and the garden is being destroyed by building work anyway that it is worth putting the loop in for a ground source pump, otherwise take the easy option if possible and use an air sourced pump.

Of cause given mains gas, it is hard to justify using anything else and in a few years time when CHP becomes affordable, it will make the case for mains gas so much more.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213127#Comment_213127 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213127#Comment_213127 Thu, 13 Nov 2014 10:57:51 +0000 mike7 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213131#Comment_213131 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12769&Focus=213131#Comment_213131 Thu, 13 Nov 2014 11:34:40 +0000 ringi
However in a new build, with much better insulation, so little heat would be needed when it is 10C outside.]]>