Heat loss calculation: averaging u-values

[oranjeboom]

Right, so I've started playing with Jeremy's heat loss spreadsheet and have started going over my figures to see if I have screwed up somewhere big time, as my heat loss seems a bit high.

 

So, I have a number of different walls of differing u-values (column D) with respective % of total wall area (E). I have then mutliplied each u-value with that % (F)

 and then totalled the figures in F to get a final u-value.

 

 

 

Is that an accurate method of dealing with differing u-values?

 

TIA!

 

[SteamyTea]

Yes, it should be decimal fraction wall area, not percentage though.

It does not take into account shape of wall and if it faces the wind/sun.

But they are minor details at this stage.

[Guest Alphonsox]

Yep - Look at Jeremy's spread sheet cell34. It's effectively doing the same thing.

((area1 * U1) + (area2 * U2) + (area3 * U3))/ (area1+area2+area3)

[oranjeboom]

29 minutes ago, SteamyTea said:

Yes, it should be decimal fraction wall area, not percentage though.

It does not take into account shape of wall and if it faces the wind/sun.

But they are minor details at this stage.

Thanks. 

 

Yes, i have  lots of S facing glazed walls which will help a bit in the winter but potentially overheat the place in summer (although the sun is already nice and high now to reduce that by quite a bit).

 

27 minutes ago, Alphonsox said:

Yep - Look at Jeremy's spread sheet cell34. It's effectively doing the same thing.

((area1 * U1) + (area2 * U2) + (area3 * U3))/ (area1+area2+area3)

Cell34? 

 

I can see that B27 incorporates window and door areas values, but I don't see anywhere in there that you can list all of your different walls with respective u-values:

 

 

 

So you have to work out your average wall area first and enter that in B7: 

Edited May 4, 2018 by oranjeboom
pics!!!

[Guest Alphonsox]

15 minutes ago, oranjeboom said:

Cell34? 

 

I can see that B27 incorporates window and door areas values, but I don't see anywhere in there that you can list all of your different walls with respective u-values:

 

 

 

So you have to work out your average wall area first and enter that in B7: 

 

Sorry I was replying in a rush and using an old version of the spread sheet...In the latest version Cell B31 shows the technique of averaging U-Values

B31=((B19*B27)+(B20*B30))/B23 where B23 =SUM(B19:B20)

 

You are correct, you will need to average your wall U-value then enter it into B7

 

EDIT > Feel free to PM me your spreadsheet if you want a second pair of eyes to give it a once over.