How do I calculate heating requirement?

iwb

Sorry if this is answered elsewhere. I didn't find it in a search.
I am building a dormer of 250 sq m and would like to decide for once and for all what type of heating I will use.
If I know the u value and area of walls, windows, doors, floors, ceiling and am going to seal the house and use HRV, is there a formula for working it out?
I am going with the emmedue system with concrete on both sides. Anyone out there built one of these yet? I wanted to use the 300mm wall with a .11 u value but they want more money now that originally quoted and I am thinking of going with 250mm and a .15 u value to save the extra money.
If there was a formula I could plug in values for, it would be great as I can decide this and also if my windows are silly given the walls used.
My wife wants sash windows and the u value is 1.8. At 15% of the surface area of outside walls, I would imagine it is a significant loss.
Thanks.

Mellor

yeah there is a formula to give basic results.
You need to calculated the losses through fabric for middle of winter. Then calculate infiltration losses (normally hard but seeing as you have HRV it should be easier)

the sum of these losses is the total losses for the house, and will size the heating element.
This is normally how a radiator or similar is sizes for a room also. The more accurate you are the more accurate the result will be.

iwb

Thanks for the quick reply. Any links to a formula? What do you mean loss through fabrics in winter?

Mellor

BY fabric in winter I mean U-Values.
The losses through U-values are proportional to temp difference, so this will be highest in winter. So taking the mean low winter temp and the u-value will return the fabric losses.

iwb

Good to know. So, is there a formula I can download somewhere? Maybe a spreadsheet or something?

Mellor

There should be, but its simple enough, maybe can work it out. Something like below, but double check as it right of the top of the auld head

(elemental U-value*elemental area*delta-temp) + (total volume*air changes*air density*heat capacity*delta temp)

davidoco

http://www.quinn-radiators.co.uk/downloads_heatloss.php

This app is great for working out complicated design heat requirements. You can put in your own uvalues.

iwb

Thanks to you both. That program looks like exactly what I wanted. I am feeding in the values now and hope to get a good understanding of what I require from it.