HughF Posted November 10, 2022 Share Posted November 10, 2022 (edited) I’ve been casually helping my friend/builder with some unwanted advice on his new build barn conversion project. He’s forwarded me his SAP for comment and I’ve been giving it a read over. It seems pretty comprehensive, I assume it’s been done off the plans, but what can we do with it now that we’ve got it? Is it appropriate to use it for sizing the heat generator (an ASHP driving ufh) for example? Or would that be a catastrophic mistake? I’d probably also run the plans through either heatpunk or the freedom toolkit to get a feel for the heat loss but I haven’t done so yet. Edited November 10, 2022 by HughF Link to comment Share on other sites More sharing options...
crispy_wafer Posted November 10, 2022 Share Posted November 10, 2022 Depends how accurate or diligent the SAP assessor has been I suppose, mine was done from the BRegs Drawings I had, & didnt ask me anything about any improvements I was making Increased insulation levels in the floor, roof etc, MVHR, window types, Airtightness levels etc So could be accurate or way off kilter. I would get hold of one of the heat loss calculators (I think Jeremy's one is highly though of ????), spend a bit of time and plug in some numbers, that ought to then give you a base figure to work from. Link to comment Share on other sites More sharing options...
nod Posted November 10, 2022 Share Posted November 10, 2022 Sap reports are quite generic Lots of pasting and copying While we are including an ASHP this time round our sap still mentions a gas boiler No gas where we are building While they look comprehensive Probably two thirds are included in each one that they write Link to comment Share on other sites More sharing options...
ProDave Posted November 10, 2022 Share Posted November 10, 2022 I think the SAP report is as good as the assessor and what you instruct him to do. Ours was pretty detailed and used the actual calculated U values for the floor wall and roof make up, and reasonable assumptions about windows and a random choice of ASHP and MVHR units. and a pretty poor assumption of air tightness. At completion time I got them to update it to include actual as fitted window UW values, correct a mistake that got the roof U value too poor, include the actual ASHP, MVHR and stove used, and include the actual air tightness test result. This improved the score somewhat. Link to comment Share on other sites More sharing options...
saveasteading Posted November 10, 2022 Share Posted November 10, 2022 13 minutes ago, ProDave said: the SAP report is as good as the assessor Indeed. I have seen buildings which should have a poor rating, get a good one. Ignorance, lazyness, lack of effort worthy of a tiny fee, or writing the rating the client wanted? Probably all the above occur. The algorithm is flawed in the first place anyway, but of use in comparisons if completed professionally ( i mean honestly and thoroughly) I don't think designing a heat system to suit a SAP is the best idea. The Jeremy table is probably better. Link to comment Share on other sites More sharing options...
JohnMo Posted November 10, 2022 Share Posted November 10, 2022 Daft question, is the pre build one or as built post build. I made lots of changes to the as-built one to make sure thermal bridging wasn't generic etc. likes other have done. In the end it seems to a fairly close, on a monthly average basis. Although I don't recall seeing what the actual heat loss was on the coldest design day. Just monthly averages, which may not be that useful for heat pump sizing. Jeremy's tool may be better. Link to comment Share on other sites More sharing options...
MDC Posted November 10, 2022 Share Posted November 10, 2022 What is Jeremy's tool? Link to comment Share on other sites More sharing options...
Onoff Posted November 10, 2022 Share Posted November 10, 2022 4 minutes ago, MDC said: What is Jeremy's tool? A clever spreadsheet. Avoid @pocster's tool. 1 2 Link to comment Share on other sites More sharing options...
MDC Posted November 10, 2022 Share Posted November 10, 2022 3 minutes ago, Onoff said: A clever spreadsheet. Avoid @pocster's tool. Understood! Link to comment Share on other sites More sharing options...
Onoff Posted November 10, 2022 Share Posted November 10, 2022 30 minutes ago, MDC said: Understood! 1 Link to comment Share on other sites More sharing options...
HughF Posted November 10, 2022 Author Share Posted November 10, 2022 1 hour ago, JohnMo said: Daft question, is the pre build one or as built post build. I made lots of changes to the as-built one to make sure thermal bridging wasn't generic etc. likes other have done. In the end it seems to a fairly close, on a monthly average basis. Although I don't recall seeing what the actual heat loss was on the coldest design day. Just monthly averages, which may not be that useful for heat pump sizing. Jeremy's tool may be better. Pre-built, I assume off the plans (I haven't asked him this yet). No changes to the plans are being made during construction. It's block/block, 200 cavity with 150mm PU fill (double 75, taped), 150mm in the floor, 100-120mm concrete on top of the PU with 16mm pipes at 150 centers. UPVC windows/doors, metal roof (I don't remember the details of the roof build up). SAP attached for reference. Dwelling 3 SAP Calculation EPC Data-redacted.pdf Link to comment Share on other sites More sharing options...
MDC Posted November 10, 2022 Share Posted November 10, 2022 57 minutes ago, Onoff said: Thank you very much for this. Link to comment Share on other sites More sharing options...
Onoff Posted November 10, 2022 Share Posted November 10, 2022 2 minutes ago, MDC said: Thank you very much for this. Nor sure if it was his final revision... @Ferdinand, @SteamyTea etc might know. Link to comment Share on other sites More sharing options...
Pocster Posted November 10, 2022 Share Posted November 10, 2022 Just now, Onoff said: Nor sure if it was his final revision... @Ferdinand, @SteamyTea etc might know. Blah blah blah Link to comment Share on other sites More sharing options...
Onoff Posted November 10, 2022 Share Posted November 10, 2022 7 minutes ago, pocster said: Blah blah blah Well you certainly won't! 😂 Link to comment Share on other sites More sharing options...
SteamyTea Posted November 10, 2022 Share Posted November 10, 2022 1 hour ago, Onoff said: Nor sure if it was his final revision Not sure either, though I think the last two versions were just tidying up, nothing fundamentally different. 1 Link to comment Share on other sites More sharing options...
HughF Posted November 11, 2022 Author Share Posted November 11, 2022 So I’ve had a bit of time in front of this SAP and I’ve come to the following conclusions: They’ve only done the heat loss down to 4 degrees or so, at an indoor temperature of 21. This gives around 3.3kW of heat input required. They haven’t taken into consideration the air changes from the proposed wood burner flue (I will suggest to my builder that they fit a DEAS stove, if they still want a stove at all. They’ve assumed 170% efficiency (COP of 1.7 if you will) for the ASHP when doing both the DHW and the Heating. Not particularly accurate and assumption. That’s about it I think? Should be good with a 5kW ASHP on this job. Link to comment Share on other sites More sharing options...
nod Posted November 11, 2022 Share Posted November 11, 2022 50 minutes ago, HughF said: So I’ve had a bit of time in front of this SAP and I’ve come to the following conclusions: They’ve only done the heat loss down to 4 degrees or so, at an indoor temperature of 21. This gives around 3.3kW of heat input required. They haven’t taken into consideration the air changes from the proposed wood burner flue (I will suggest to my builder that they fit a DEAS stove, if they still want a stove at all. They’ve assumed 170% efficiency (COP of 1.7 if you will) for the ASHP when doing both the DHW and the Heating. Not particularly accurate and assumption. That’s about it I think? Should be good with a 5kW ASHP on this job. Yes they are quite general man’s your final Sap report is totally reliant on you or the builder having done what you say that you have done Link to comment Share on other sites More sharing options...
HughF Posted November 11, 2022 Author Share Posted November 11, 2022 21 minutes ago, nod said: Yes they are quite general man’s your final Sap report is totally reliant on you or the builder having done what you say that you have done These guys are following the plans very well. Link to comment Share on other sites More sharing options...
nod Posted November 11, 2022 Share Posted November 11, 2022 4 hours ago, HughF said: These guys are following the plans very well. But say you put 70 mil insulation in instead of the 120 that is on your plans Your final sap would be accessed on 120 unless you told them otherwise Like air testing In reality They mean very little Link to comment Share on other sites More sharing options...
ProDave Posted November 11, 2022 Share Posted November 11, 2022 3 minutes ago, nod said: But say you put 70 mil insulation in instead of the 120 that is on your plans Your final sap would be accessed on 120 unless you told them otherwise Like air testing In reality They mean very little Few self builders would cheat themselves would they? It is the mass house builders that are often suspected of only building a few properly, the sample that needs inspecting by BC, and cutting corners on the rest where they hope nobody will notice. Link to comment Share on other sites More sharing options...
nod Posted November 11, 2022 Share Posted November 11, 2022 Yes of course Dave No one one here would knowingly cut corners But most of the mass produced homes I work on are scoring around 2 on an air test We know that is nonsense It’s years since I saw an air test being carried out on site Most are done from a desktop Sap relies on people like us following the detail Yesterday our LA BC came to inspect the work I’d done on the roof He remarked that it was good to see all the gable restaurants built in and said most just plug and screw them in afterwards He we really should make them take the gables down But they don’t The whole system needs changing Link to comment Share on other sites More sharing options...
HughF Posted November 11, 2022 Author Share Posted November 11, 2022 3 hours ago, nod said: But say you put 70 mil insulation in instead of the 120 that is on your plans Your final sap would be accessed on 120 unless you told them otherwise Like air testing In reality They mean very little I don’t think they’ll cut corners on what are their own houses. Link to comment Share on other sites More sharing options...
Pocster Posted November 12, 2022 Share Posted November 12, 2022 @Onoff got his batteries installed I see …. 1 Link to comment Share on other sites More sharing options...
nod Posted November 12, 2022 Share Posted November 12, 2022 31 minutes ago, pocster said: @Onoff got his batteries installed I see …. Brilliant 😂 Link to comment Share on other sites More sharing options...
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