Heat Used - Physics Question

nxdmsandkaskdjaqd

jack_pott wrote: »

It is interesting though, mine plots the temperature of the air and brickwork over the course of a day, and calculates the difference in energy consumption between running on a timer and leaving the heat on continuously. I was rather pleased to see the overall thermal conductivity of the building came out the same as I get calculating it from my energy bills: 300W/K for my three bed semi (~240m^3).

I would be interested in knowing your results in running the heating continuously verses the timer?

Your value "300W/K ". What is the the K? 300W per ??

zeupater

Hi

K is degrees Kelvin, effectively Centigrade rebased to absolute zero as opposed to the freezing point of water at STP.

Back to the last post ... the reason I questioned the Hrs/day is that heat-loss continues even when you're asleep so you really need to work your figures on a repeatable full cycle, not a partial one ... as it is you're working out the cost to increase the structure temperature to replace 24Hrs of heat-loss and then attempting to estimate 16Hrs of heat-loss based on a model ....

As for above post, jack_pott isn't recommending that you always run the GCH on continuous, just that this is done as a temporary measure to provide more accurate data on your heatloss .... if one of the variables (internal temperature) is forced to become a constant then your overall calculation becomes less complex.

HTH
Z

[Deleted User]

This is what I'm getting from my analysis:



The black line is the ambient temperature outside the house and green is the air temp in the room. Red is the interior partition walls, yellow the inner leaf of the exterior cavity wall, and blue is the outer leaf. Simulation is without cavity insulation, and heating switched off at 00:30, and on at 07:30.

Note that the air temperature cools much faster than the fabric of the building because it has little thermal inertia, and that its minimum temperature drops below that of the walls because of heat loss from the windows. Partition walls are warmer than external ones because they aren't cooled by the outside, and would reach the same temperature as the air if the heating remained on for long enough. The internal leaf of the cavity wall varies less in temperature because the outside temperature is constant, and the outer leaf varies less still.

The air warms faster than it cools because the temperature that the exponential is aiming toward is that which it would reach if the heating were to run continuously without the stat.

About two thirds of the heat loss from your body is via radiation not convection, so as the walls take until late afternoon to warm up you can see it's quite a long while before the room feels warm unless you faff with the TRV through the course of the day.

This is what it looks like with CWI, note how the inner leaf gets warmer, and the outer leaf colder:



The plot below is with diurnal cycle (in this case 9C max and 3C min), note the increased temperature variation of the outer leaf, and the secondary phase of warming in the air temp:

zeupater

jack_pott wrote: »

This is what I'm getting from my analysis: ......

Hi

That's a massive change in air and structural temperatures overnight ... we see a hall (house core) air temperature change of around 1C overnight (actual) with ambient temperatures well below the ~3C used. I take it that the property as modelled has low internal thermal mass (therefore the walls would be stud partition) as well as poor insulation, ie meeting 1960's/1970's building standards & practices ?

Z

Smiley_Dan

The "partition" walls - are they plasterboarded? If so, read up on "plasterboard tents".

Their temperature looks to be dropping way too much.