"Neil Jones" wrote in message
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"Neil Jones" wrote in message
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"IMM" wrote in message
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"Neil Jones" wrote in message
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"IMM" wrote in message
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"Neil Jones" wrote in message
[snip]
Total losses for house = 12.3kW
Downstairs losses are 51.9% of total losses from house.
Losses through:-
Ground floor 4%
Downstairs solid wall 19%
Downstairs cavity wall 1%
Downstairs windows 6%
Ceiling to upstairs 3%
Roof 6%
Upstairs solid wall 18%
Upstairs cavity wall 2%
Upstairs windows 6%
Increase the loft insulation to 350-400mm and do the calcs
again.
OK.
Thermal conductivity of mineral wool = 0.038
1/0.5 + (0.3/0.038) = 2 + 7.9 = 9.9.
U val = 1/9.9 ~ 0.10
Losses through ceiling reduced to 70 * 0.10 * 21 = 147W
Saving 588W, 5% of the total loss previously. How much does it
cost
to
buy 70 m2 loft insulation, at a depth of 300mm?
What was the answer to this?
I'll answer my own question. About £300, as far as I can tell.
For the same price I can get enough boards of 25mm Kingspan to dryline
the solid walls downstairs, which would reduce the U-value to 0.6.
So the heat loss here would become
Walls = (27*2.1 - 5.9 - 3) * 0.6 * 24 = 688 W
+( 8*2.1 - 2.2 - 3) * 0.6 * 24 = 167 W
Walls Total = 855 W
Previous Walls Total = 2462 W
Saving = 1607 W
So I can either spend £300 to save 588 W, (£1.96/W) or I can spend the
same and save 1607 W. (£5.35/W)
If I go for 50mm Kingspan, the price goes up to £400, but the saving
goes to 1870 W. (£2.63/W for the extra £100, which still gives a better
return than more loft insulation).
Alternatively, I could spend another £300 on 25mm Kingspan for the
upstairs and get another 1573 W saving, at £5.24/W.
[If Andy is right, and I'm only saving 392 W with the extra loft
insulation, it's £1.31/W.]
Extra loft insulation comes well down the priority list for my house,
because the cost/Watt saved is easily beaten elsewhere.
You are looking at the house as a whole again. Duh! The extra insulation
benefits greatly the upper rooms.
The loft insulation is the depth over and above the 100mm. You have to
take into account the fixing of the downstairs wall Kingspan. Loft
insulation is cheap and easy, so do it. Also do downstairs too with
Kingspan, but the installation cost is greater.
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