Using arduino to heat a few cubic feet by a few degrees?

Hello,

I’m trying to create a space that is exactly 30-31 degrees fahrenheit. My idea is to use a chest freezer and put an insulated box inside. The chest freezer will be set to its warmest setting but that’s still too cold. Therefore, I want to have an arduino heat the inside of the box by those extra few degrees. I’ve found several great arduino thermometers, but how can I can control a heating element and tiny fan to circulate the air inside the box?

It can’t take much to heat 2 or so cubic feet by a few degrees, right? Any ideas in how I should tackle this would be greatly appreciated.

-Grant

It kind of depends on how much heat you need and what level of control you need.
which will probably depend on the thermal mass of whats inside your box

You can get these heat pads which are PCB's that require 12V at around 20A
http://www.ebay.com/itm/New-RepRap-3D-Printer-PCB-Heatbed-MK2B-Heat-Bed-Hot-Plate-Update-of-MK2A-12-24V-/281146845595

They are used by 3D printers, and turned on and off by power FET's (RAMPs board)

If you don't need that much heat, you may just want to consider some 12V filament lamps. e.g car indicators or stop lamps and module those

But I think the heat pad PCB would be more reliable as its designed to heat things up !

You will need to do an experiment to determine how many watts is required of the heating element to maintain the inside temperature of the box. The actual heat flow (in watts) is determined by the difference between the inside and outside temperatures of the box, and the total area and thermal conductivity or "R value" of the wall, floor and ceiling material of the box. See Heat Transfer

Rather than work out the R value, area, etc., put a light bulb of some known wattage (W) inside the box and let it sit for an hour or more, until the inside temperature stabilizes. Measure the inside and outside temperature. Then, W = (a constant to be determined) times the temperature difference. Of course, you need to circulate the air inside the box so that the walls, floor and ceiling are all at the same temperature.

starts with a small fan. like on your video card or cpu. let that run for abut an hour and see what effect it has. then start with a Christmas tree/night light bulb. the best one is the one that over heats the box in a long time period.

Incandescent ones will offer more heat.

the location of the temperature sensor is the key.
too high in the box and it will see the heat rising from the heater. too low and it may not see the heat.
the fan will keep the air more uniform. and the fan motor will yeild some small amount of heat.

You might be able to use an inexpensive aquarium heater that uses a thermostat. Small light bulbs can be used as heater elements. You might need a small fan in the box to prevent temperature stratification.

If this is a typical freezer with a mechanical thermostat there is more than likely an additional adjustment that can be made to change the range of temperature control.

Example: