Evaluating heat loss

Mike T., Swampeast MO

Depending on their exposure different rooms will loose heat at different rates. Also, as the house cools (with steady outdoor conditions) the overall rate of heat loss decreases because the differential temperature has decreased. Sounds like some REALLY hairy math and LOTS of very accurate measurements.

Jay_17

a different method

I was thinking about methods of evaluating heat loss and an idea occurred to me, maybe it has been thought of already, but I had never heard of it.
This was inspired by a method used to measure drag on cars, the coast-down method. What you do is get the car going a certain speed and then put it into neutral, you then time how long it takes to drop say 10mph. From that and some math you can figure out the 'real' drag on the car.
The same could be done with a house, get the house heated up to 70, make sure it is steady state, then shut off the heat and let it cool off, do some math and you should be able to figure out the btu's lost (I think you'd need the house volume.
Hmmm, not sure it would work in reality, maybe it would need a 'fudge factor' to get it to work, but it may be as accurate as many systems.
Jay

jp_2

differential method you mean

dT/dt. change in temp / change in time.

will tell you how fast the house heats or cools. but not how much energy is involved.

Mike T., Swampeast MO

jp

If I have a modulating boiler driving a constantly circulating modulating flow system held under real-world "constant" indoor conditions how does the insulation affect "time"?

jp_2

zero!

mike, in the sense of this post, it would be zero!

we are looking for a change in inside temp compared to outside temp. if you keep putting heat in you get no temp drop.

calculation is not that complex. but what I wonder is how you calculated heat from radiation in the joist area with staple up? you talked about it in the other post a day or so ago. that sounds like a complex integral?

Mike T., Swampeast MO

Zero is what I thought. So, if this is a Vitodens boiler operating at low temperature with high boiler delta-t and it's fully modulating then my actual heat loss is right about 98% of input, right?

Much of that estimate regarding radiation and convection in joist suspended tube and staple-up came from a very good paper regarding radiation and convective models for commercial food processing. Found a well-documented model that was quite close to suspended tube. Again, it was an estimate only and mainly concerned with heat via radiation.

Ron Schroeder

Just like the coast down method needs the weight (mass) of the car, cool off time would need to know the thermal mass of the house. Calculating the thermal mass would be harder than doing a conventional heat loss calculation and wouldn't include infiltration either.

Ron