Sat, 05 Sep 2026 16:22:57 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61529#Comment_61529 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61529#Comment_61529 Fri, 04 Sep 2009 16:48:29 +0100 RobinB
The initial calcs were done based on Windows u 1.1, walls u 0.13, roof 0.2, floor 0.17. 4 square metres flat plate solar collectors. First variant increased roof U value from 0.2 to 0.14, the second added 1 KW PV, the third left off the solar hot water panels.

I was surprised to see no change at all in energy requirement for space heating in any of the variant (12052.18kWh/year). Assuming it was an error I called SAP-man and he said that was correct and that it's not a design tool and some default value - based on he know-not-what was used.

Does this make sense? I couldn't believe at first that there was no difference! Am I at the eco-point where the changes I can make will add very little benefit for quite a big outlay? And that perhaps the added materials would not recoup the cost of their manufacure (in carbon or money terms) in their lifetime.

For example would it make much difference if the wall were just 0.19? ( I could save the hassle/expense of insulated plasterboard).

Is there another way to go about this that isn't too expensive?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61537#Comment_61537 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61537#Comment_61537 Fri, 04 Sep 2009 18:06:10 +0100 Cassie
My SAP calculations got worse when we added MVHR and if I dont insulate the house on the outside - insulate it from the thermal mass of the surrounding earth, then the Heatloss assumed by SAP will fail me as well.

If the airtightness is as good as we think it will be then it will overcome this, but by this time the house is built and buried so the MVHR and external insulation remain.

Of course if it ends up a high B or an A I will be gloating !]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61540#Comment_61540 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61540#Comment_61540 Fri, 04 Sep 2009 19:59:48 +0100 delboy
For those of us sad enough to know where to look, you can see it in the SAP worksheet (see http://projects.bre.co.uk/sap2005/pdf/SAP2005_9-82.pdf).

Go to PDF page 124 (p 123 of the document), and look at to box 35. This is a sum of all heat loss through the envelope fabric (walls, doors, windows, roof & floor) - derived from the sum of boxes 26-31.

You then add box 35 to box 36 to get box 37 - this is the Heat Loss Coefficient which is the amount of heat which leaves your building in Watts per degree difference outside (W/K).

You multiply box 37 (the HLC) by the amount of degree days (and also multiply by 0.024 - god knows where that number came from), and this gives you box 81, which is the total annual space heating requirement.

Therefore if you alter the u-value in box 29 (for example), this will change the number in box 35 which will change the number in box 37 which will change box 81. If you see what I mean.

Is it possible that there is no change in heating demand when you are altering other things such as the renewables?

As an aside, I'd say that 12,052kwh was a pretty hefty heat demand. Are you building a massive house?

PS Your SAP assessor is right that SAP is not a design tool.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61561#Comment_61561 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61561#Comment_61561 Fri, 04 Sep 2009 22:01:03 +0100 sipman
I would place more emphasis on workmanship i.e how well the insulation is utilised, rather than chasing notional "U" values. Good airtightness and a moderate level of insulation (well utilised) will result in a home that requires minimal heating]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61603#Comment_61603 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61603#Comment_61603 Sat, 05 Sep 2009 19:42:44 +0100 RobinB https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61647#Comment_61647 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=61647#Comment_61647 Mon, 07 Sep 2009 09:47:56 +0100 sipman
This small development may be worth a visit, not far from where you are building

underfloor heating to the GF only, from an airsource heat pump

http://www.claysllp.co.uk/SIPS-Housing-Project-Stones-Methodist-Church---Phase-1-development/11444

http://www.claysllp.co.uk/Second-Phase---Stones-Methodist-Church,-Ripponden-development/11748]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=67852#Comment_67852 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=67852#Comment_67852 Wed, 02 Dec 2009 20:50:29 +0000 kotpat
Hot water requirement

it takes 1.16 watts to heat 1 litre of water

say you have 4 people in a house CIBSE says 45 litre per person that is

45 x 4 = 180 litre hot water cylinder

main cold water is normally at 4 deg C/ and hot water is 60 deg C -hence 56 deg rise

180 litre x 56 deg c rise x 1.16 watts = 9.744 kw/ hr
hence it will atke 9.7kw to heat 180 litre in one house

so please clarify were the 2.5 litre comes from

a shower at 7litre/ min for 7 mins = 49 litre x 4 people = 200 litre

200 litre x 56 deg c rise x 1.16 watts = 12.99kw/hr


9.7 kw required / 2.5 kw as stated by your notes = 3.38 hours to reheat to reheat a 180 litre tank

12.99 kw required / 2.5 kw as stated by your notes = 5.19 hours to reheat a 200 litre tank

hence 6 kw for heat loss and 9.7/ 12.99 for dhw 15.7kw/ 18.7kw = 23 kw boiler

cheers]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=67860#Comment_67860 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4504&Focus=67860#Comment_67860 Wed, 02 Dec 2009 21:46:34 +0000 sydthebeat
1. do not use default values.. they are terrible. if using HRV refer to SAP appndix Q and choose a good efficiency and lo fan power
2. changing thermal mass should be reflected in the 'thermal mass' catagory... sounds simple but its a common error to simply choose 'medium' all the time.
3. SAP (and DEAP) is only meant as to produce comparative ratings, using a lot of conventions and assumptions. It is not really any good for making accurate reflections on end user quantities.]]>