# Heat Transfer between two temperatures

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1. Feb 17, 2016

### ShimaParty

Hi,

I'm trying to calculate energy loss between two areas. One area is -25C and another is +15. The contact area(door) is 20m^2. Is convective heat transfer formula the right way to calculate it, or what should I use? I want to find out the how many kW I need to keep cold area at -25 when the door is open.

Thank you

2. Feb 17, 2016

### Nidum

Sounds like a lost cause from your description so far .

If this is a cold room type problem the solution may lie more in redesigning the door system than in calculations and installation of high power cooling equipment .

Anyway not enough information to give proper answers . Please describe the problem in more detail .

3. Feb 17, 2016

### ShimaParty

I agree that the solution lies in door system, but the payback on that door system depends on how much do I lose by not doing it.
I appreciate there might be no way how to easily calculate it.

My problem is: I've got a site that is cooled down to -25C. I was told that opening the door(10.2m^2) to the yard(+15C) costs me 500KWh , but I've got no way of verifying that statement. Is there a way how to verify that or not?

Thank you

4. Feb 17, 2016

### Nidum

It may be possible to come up with an answer experimentally .

You will have a power usage meter supplied by the power company .

Keep the door permanently closed for at least 24 hours - maybe during a holiday period . Measure the power used during this period .

Measure the power used on a normal working day with doors opening and closing for the same period .

See how much difference there is in power usage .

Ideally repeat the experiment a few times .

The above will give reasonable answers if the cold room uses most of the power coming into your site .

You can do a very accurate assesment if you privately install a power usage meter specifically for the cold room .

5. Feb 17, 2016

### Nidum

What fraction of the time is the door open for during normal working ?