Post and beam Posted August 3, 2023 Posted August 3, 2023 I have today received a 32 page SAP calc report from my TF builders. Having scanned through it once i am overwhelmed by the amount of detail. It appears to repeat the same blocks of tabulated data. Is there a document that explains what to look for. On a summary sheet that has some but not all of the same figures i see a Design airtightness figure of .3m2/hm2 @ 50Pa And a primary energy target of 37.82 Kwh/m2. Which does not sound very good. Also see a primary heating efficiency of 219%. Does this translate to a scop of 2.2 or am i hopelessly off the mark? Thanks in advance as always keith
JohnMo Posted August 3, 2023 Posted August 3, 2023 There are generally, I think, 3 sections. Your house built to min building regs, your house as designed, your house improved. All looks similar but aren't. First make sure you are reading the correct section. Also there are a whole load of assumptions made if they were not given anything different, so shite in shite out if you are not careful. Design airtight doesn't look realistic for one, you are assuming 0.3 or better, not that realistic. Heating efficiency is a basic look up table, that will assume a number of things. Unless your drawings say different. The take away, it is as designed, a further report is generated at the end of the build - as built, that's the important one. This one is just a tick in the box, say it is or isn't compliment with building regs.
Post and beam Posted August 3, 2023 Author Posted August 3, 2023 7 minutes ago, JohnMo said: Design airtight doesn't look realistic for one, you are assuming 0.3 or better, not that realistic. How so?
JohnMo Posted August 3, 2023 Posted August 3, 2023 14 minutes ago, Post and beam said: How so? It is achievable, but very rare. You are stating you are so good you will achieve half the leakage of a passivhaus. Good luck, and well done, if you can.
Post and beam Posted August 3, 2023 Author Posted August 3, 2023 30 minutes ago, JohnMo said: stating you are so good you will achieve half the leakage of a passivhaus Yes, that is what i thought it meant. Its a figure that comes from the TF and was a surprise to me to be honest. Initially their target design value was 1.5-3
JohnMo Posted August 3, 2023 Posted August 3, 2023 If there building it and stating it hold them to it.
HughF Posted August 3, 2023 Posted August 3, 2023 Attach it here and I'll highlight the areas you need to look at. They are quite simple to understand once you've seen one or two
Post and beam Posted August 3, 2023 Author Posted August 3, 2023 7 hours ago, HughF said: Attach it here and I'll highlight the areas you need to look at Done. I took my address out of it. You know, in case i dont apply for planning for my ASHP install. And thank you Full SAP Calculation Printout Combined_2023-08(1).pdf
HughF Posted August 3, 2023 Posted August 3, 2023 (edited) Not the first SAP I've seen where they calculate the heat loss at un-realistic outside temperatures. I'd be happier if they used -2 or something instead of 4.3 degrees for January. Anyway, you need around 2.4kW to heat this place when it's 4.3 degrees outside and you want 18 degrees inside. Edited August 3, 2023 by HughF
Post and beam Posted August 4, 2023 Author Posted August 4, 2023 Thanks Hugh That section 8 is repeated, on page 3 it shows 26.5 W/m2 (99) Then... page 7 = 33 page 11 = 34.5 page 15 = 36.9 Etc I am missing, and or, misunderstanding something in this.
torre Posted August 4, 2023 Posted August 4, 2023 Quote i see a Design airtightness figure of .3m2/hm2 @ 50Pa ... Initially their target design value was 1.5-3 As @JohnMo can you hold them to achieving this figure? What's changed in the design to improve airtightness so that it exceeds passivhaus standard? If this figure is over optimistic just to pass the SAP as-designed stage then once built, if you only achieve 1.5 your actual ventilation heat losses will be 5 times as much, hurting your SAP rating and your pocket! Useful guide to good airtightness practice here Heating efficiency of 219% will be taken from the Product Characteristic Database - just look up your heat pump model (anecdotally, the fairly standard Mitsubishi Ecodan we intend to fit has a figure of 267% so there are more efficient units out there) The full SAP procedure guide is a bit overwhelming but covers the calculations in excruciating detail. I'm no expert but managed to dig out specific details that impacted our report. All the similar-but-different sections take much of the same base information and then apply it separately to figure out different parts of the assessment - carbon emissions, energy costs etc. For example, a gas boiler is worse than ASHP for emissions but still good for running costs. The section you're probably most interested in is 'Calculation of Energy Rating' (starts page 15 of yours) as that determines the A/B/C rating that is the only thing most buyers will care about. Your space heating cost will rise a lot if you miss that airtightness figure. Are you installing any renewables? Solar or WWHRS? If so I'd expect those to show up as a negative figure, reducing energy costs, under 'Energy saving/generation technologies' on page 18
Kelvin Posted August 4, 2023 Posted August 4, 2023 I got the same 32 page style report and mostly ignored it. I took some of the dimensions from it and plugged it into the Jeremy Harris heat loss calculator on here which gets you close enough. The as designed tends to err on the side of caution ad they expect to better it as built. In my case it was the cautious as designed ACH target of 3 they quoted me as they know they’ll beat it. I very much doubt they are claiming to achieve 0.3? They are setting themselves up to fail that. Are you reading it correctly?
torre Posted August 4, 2023 Posted August 4, 2023 Quote Are you reading it correctly? Measured/design AP50 = 0.3000 (17) in the report, but a simple explanation would be it's a mistype and should be 3 (the pessimistic end of their original range). Definitely something to query with the builder.
Kelvin Posted August 4, 2023 Posted August 4, 2023 I’d say so. Why quote better than passive. Is it a passive design?
Post and beam Posted August 4, 2023 Author Posted August 4, 2023 1 hour ago, Kelvin said: Are you reading it correctly? Well this is extracted from the document i posted. On page 1 Measured/design AP50 = .3 page 5 Measured/design AP50 = 5 page 9 Measured/design AP50 = .3 page 12 Measured/design AP50 = 5 page 15 Measured/design AP50 = .3 page 19 Measured/design AP50 = .3 page 24 Measured/design AP50 = .3 page 28 Measured/design AP50 = .3 I dont yet have any idea what variables change that require the repeat of the tables 8 times. Yes i have asked them to explain it. The house is not a Passivehaus design. They have always said they expect to beat the 1.5 - 3. But the get out is, final result is down to costomer and chosen main contractor. TF company do the frame and weathertight but do not consider themselves as main contractor.
ProDave Posted August 4, 2023 Posted August 4, 2023 13 minutes ago, Post and beam said: Well this is extracted from the document i posted. On page 1 Measured/design AP50 = .3 page 5 Measured/design AP50 = 5 page 9 Measured/design AP50 = .3 page 12 Measured/design AP50 = 5 page 15 Measured/design AP50 = .3 page 19 Measured/design AP50 = .3 page 24 Measured/design AP50 = .3 page 28 Measured/design AP50 = .3 I dont yet have any idea what variables change that require the repeat of the tables 8 times. Yes i have asked them to explain it. I wonder if there is a typo there that has been copied and pasted? It would be very unusual to assume an air tightness of 0.3 unless it was being built by a passive house company with a track record of building very air tight houses. A much more common assumption for a design SAP would be an air tightness of 3 That is three not zero point three. In Scotland at least, 3 is a critical value, get better than 3 in an air test and you must install mvhr, so if you are not planning mvhr a value between 3 and 5 would be a reasonable target.
Post and beam Posted August 4, 2023 Author Posted August 4, 2023 2 minutes ago, ProDave said: get better than 3 in an air test and you must install mvhr From day one they have been saying that MVHR is mandatory for the figures they quote and are expecting.
Post and beam Posted August 4, 2023 Author Posted August 4, 2023 (edited) 2 hours ago, torre said: anecdotally, the fairly standard Mitsubishi Ecodan we intend to fit has a figure of 267% I cannot see a specific % anywhere on the graphs i have been looking at on this site. Is it an interpretation of a Scop of 2.67? Edit due to blindness: Scratch that. i am an idiot Edited August 4, 2023 by Post and beam
ADLIan Posted August 4, 2023 Posted August 4, 2023 Re the air pressure test. 0.3 has been assumed for the as designed dwelling. Agree this may be a typo so get it checked. 5 is used in the target calculations as this is used in the ‘model’ house that is the comparison dwelling.
Post and beam Posted August 4, 2023 Author Posted August 4, 2023 Thanks ADLlan, so if they confirm this is not a typo i am in a good place.
Kelvin Posted August 4, 2023 Posted August 4, 2023 (edited) 10 minutes ago, Post and beam said: Thanks ADLlan, so if they confirm this is not a typo i am in a good place. It’s unlikely as they are saying the result depends upon a few things not least of all your main contractor. Does the timber frame cost include the airtight membrane and tapes being supplied and fitted, just supplied, or neither? In my case the timber kit company supplied the membrane and tape but didn’t fit it as it needs to be done a bit later on in the schedule plus I wanted to do it myself. I also didn’t use the stuff they supplied. Edited August 4, 2023 by Kelvin
Post and beam Posted August 4, 2023 Author Posted August 4, 2023 14 minutes ago, Kelvin said: Does the timber frame cost include the airtight membrane and tapes Membrane yes and the Sips panels are pretty good on Airtighness by default. Tapes are down to me and i am happy to do this bit. I have been talking to their frame erector. He does all of them for this particular Tf company and has done literally hundreds if not more. 46 this year alone. His view is that we can easily smash the 1.5 figure.
Post and beam Posted August 5, 2023 Author Posted August 5, 2023 Update to the apparently repeating listed 8 options within my 32 page report. Ap50 space heating Kw Kw/m2 Emissions for regulation compliance .3 5301 26.5 Target emissions 5 6617 33 Fabric energy efficiency .3 6908 34.5 Target Fabric energy efficiency 5 7372 36.8 Energy rating .3 4731 23.6 ECP costs, emissions & primary energy .3 4532 22.6 Energy rating for improved dwelling .3 4730 23.6 EPC costs, emissions & primary energy for improved dwelling .3 4532 22.6 So the 'Target' figures are, for some reason, the outliers. I still dont really understand this yet
Post and beam Posted August 8, 2023 Author Posted August 8, 2023 On 03/08/2023 at 22:21, HughF said: Anyway, you need around 2.4kW to heat this place when it's 4.3 degrees outside and you want 18 degrees inside. Forgive my ignorance but if i want 21 degrees inside and work on an outside temp of -2 can you extrapolate what the requirement is. Isn't 21 and -2 the usual range?
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