How can I verify calculated heat loss?

[tcdouglas]

Hi all,

I have calculated the expected heat loss (fabric not ventilation) of a room in a house using Q=Ʃ(UAΔT) for each building element (window, door, wall, ceiling etc) making the room. The units are Watts.

How can I measure the actual observed heat loss of the room? I am currently monitoring the internal room air temerature and the external air temerature. Shouldn't I be able to calculate the heat loss after switching the heating off and observing the rate of temerature decrease? Obviously I need the figure in Watts to compare against the calculated heat loss.

Thanks in advance...

 

[Simon Bridge]

Yep - Pretty much how you'd do any heat loss experiment.

 

[tcdouglas]

Thanks for the reply but I was hoping for an equation to plug my temperature readings into...

 

[Simon Bridge]

You don't have a model for heat loss?

The rate of heat loss depends on the current temperature, so it's actually an exponential.
You heat loss calculations assume a constant internal temperature - so they would correspond to the initial heat loss ... which involve curve-fitting.

You can relate a change in temperature to a change in energy right?
Ideally you want to determine this experimentally ... use a heating element of known power to heat air in a well insulated box and measure the temperature - plot Temp vs time. OR you can use one of the many theoretical models for air ... PV=(5/2)NkT (diatomic ideal gas) to get an approximate figure (you should apply such models to your theoretical heat-loss to turn it into a change in temperature).

Of course you could verify directly - since the calculation you did was for equilibrium at a particular operating temp, you can directly measure the energy pumped into the air from the heaters. This should match the heat loss.