In article , Andy
Hall wrote:
Don't forget that the calculations for ground floors taking
account of perimeter use a table of fiddled U values, so a
spreadsheet would need some work unless there is a formula that
can be used instead.

Tony, do you know?

In the current release of SuperHeat we have hard coded in the
Appendix C tables and just interpolate. Previously we used the
formula from BRE Information Paper 3/90:

U (uninsulated) = 0.05 + 1.65PA - 0.6PA^2

where PA = exposed perimeter/area

For a 5m x 10m floor four edges exposed PA = 30/50 = 0.6

Uninsulated U-value = 0.824 (current AD App.C gives 0.78)

To get the U-value of an insulated floor (insulation under/over
whole of slab including perimeter) you take the reciprocal of
this value to get the thermal resistance, then add the resistance
of the insulation, then take the reciprocal again to get a new
U-value.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser
http://www.sda.co.uk/qsedbuk.htm