# Air Cooling Dynamics problem

1. Sep 28, 2008

### cxo

The problem is as follows, my friend and I want to make a fridge that uses cold air from outside, instead of an electrical compressor. We plan to simply use a fan, and pipe to bring cold air from outside into the fridge.

So if our variables are:

- Pipe length / Diameter
- Fan speed / CFM
- Wind temperature outside
- Temperature inside the fridge
- Desired temperature to reach inside the fridge
- Heat capacity of fridge contents
- Volume of fridge / Volume of contents

How do we calculate, how long the fan needs to run, at what CFM to bring the temperature in the fridge from its current temperature down to the desired temperature in a particular amount of time?

Assuming the outside temperature is always below the desired temperature.

Thanks.

2. Sep 28, 2008

### Staff: Mentor

Welcome to PF. I'm not sure why you would care to measure how long the fan has to run. Why does it matter? You use a thermostat to control the temp and the fan goes on and off as necessary.

3. Sep 28, 2008

### cxo

Yes, the end result would eventually be something like that. Moreover we'd like to have finer grained control over the cooling process, than just ON|OFF of the fan, ie adjust the RPM etc..

We would like to model the system on a computer before implementing it. Basically to determine the amount of energy needed to maintain the fridge temperature. It's meant to be an energy efficient solution, and I'd like to prove it using a computer model.

4. Sep 28, 2008

### Pumblechook

""Assuming the outside temperature is always below the desired temperature.""

It wont be. If you do live in a very cold place it is going to be too cold a lot of the time. Bit of a.. daft idea..sorry to say.

5. Sep 28, 2008

### cxo

How does this help the thread?

And actually the city I live in, the temperature outside is below -20degC over 5months in a year.

6. Sep 28, 2008

### Pumblechook

Just move the fridge to a cold part of the house then.. Outbuilding. Zero electricity use for a good part of the year.