# Talk

## heat transfer rate -someone with a good head for physics needed please

(4 Posts)
Tue 29-Sep-09 11:54:56

DS had a homework about a 'Hockerton House' They are houses built into the side of a hill with thick concrete walls and floor which retain heat and a layer of insulation on the outside between the wall and the earth.There was a list of temperatures ,summer and winter of the floor , wall , air inside the house and earth below and behind the house.
So how would you tell whether the wall or floor had the fighest heat transfer rate ? Would ahigher temperature difference indicate a higher or a lower heat transfer rate ?
He has handed it in now but I can't get my head round it .Pleae could someone help ?

Tue 29-Sep-09 12:26:20

A higher temperature difference, between say the wall and the earth behind it, would mean it was better insulated and so had a lower heat transfer rate.

If there is a low temperature difference, that's probably because the heat is going out through the wall, so would be a high heat transfer rate.

Does that sound logical?

RachaelandAgatha Fri 02-Oct-09 14:44:58

Hmmm, assuming your DS is key stage 3 and not doing A Level physics AMumInScotland is right but the question he was set is potentially confusing.

Newton's Law of cooling says that the rate of heat transfer depends on the temperature difference between the two objects involved, the bigger the difference the faster the heat is transferred from the hot object to the cold one. This is true if the two things transferring heat from one to the other are touching each other and free to pass heat energy to each other so they must not be separated by some insulation.

If the Hockerton House is maintaining a constant temperature difference between its snug, insulated inside and the colder air temperature and ground outside then the bit of the house which has the greatest difference in temperature to the outside is the best insulated and therefor has the slowest transfer of heat. Which is the opposite of what would happen if there was no insulation. Presumably the point of the homework was to show how effective insulation can be.

I hope the teacher explained that the house had on average a warmer temperature compared to the outside and these were the measurements written on the diagram.

I'm a physics teacher (degree and PhD).

vinblanc Fri 02-Oct-09 18:39:02

ISTR that heat transfer = UAdeltaT, where U is the heat transfer coefficient of the materials, A is the area, and deltaT is the temperature difference.

Agree with what others have said.

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