wall heat transfer coefficient measurement

[Lc_shi]

Hi dear sir
Heating and cooling load depend heavily on the building envelop's K value. Now energy efficient building is 1/3 of the traditional building's K value. I want to know if there's equipment to measure the building's wall K value. Who knows it,pls share with . thx in advance!


regards
LC

[Abby Normal]

Measure outdoor wall surface temperature and indoor wall surface temperature and indoor air temperature.

You will have to translate the following into metric

A still air heat flow resistance value is about 0.68 Btu/(hr* ft^2*deg F)

so the heat flow per square foot (unit area) is temperature difference divided by thermal resistance

Get heat flux by comparing indoor wall surface temperature to the indoor air temperature

Example Wall temperature is 70F, air is 72F

Flux = (72-70)/0.68= 2.94 Btu/(hr*ft^2)

Now compare exterior wall surface temperature to interior wall surface temperature with same heat flux

Example Outdoor Wall 40F and interior wall still 70F, heat flow is the same as it is in series

Flux = delta T/ R

R= delta T/ flux

R = (70- 40)/2.94
R= 10.2 Btu/(hr*ft^2*F)

If you have a framed wall, the surface temperature may fluctuate. Colder by studs, warmer by the insulation. Have to average the temperature then, weighted by area

[lraja]

Hi

I believe you refer to thermal conductivity (K) when you say heat transfer coefficient (HTC). These two are different entities such that the K is a material specific property and HTC depends on a number of other fluid parameters.

If you are looking for K measurements, you can find small hand held devices now, try for instance Decagon device web site. e-mail me if you want the web address



hope this heps

raja

[Lc_shi]

thanks for your good comment.

Raja,pls tell me the web site address.

rgds
LC

[lraja]

Hi LC

Could you send me your e-mail address, You could do it through this forum itself. Then I will e-mail you the web adresses, I haven't got suficient posts on RE to gain access on posting web site addesses

cheers


raja