can I reverse the cycle on a refrigerator to warm the inside?

So I have just built (mostly) a workshop shed, and it's about time to move in work benches, tables, small appliances, etc. 
I want to be able to move some temperature sensitive stuff out, too, and I don't want them to get too cold. I'm probably over thinking this and there's a simpler solution, but a refrigerator is already a well sealed, temperature controlled, shelf. If I could get a second hand or scratch and dent, could the condenser be put on the inside to make a "warm box" for winter?  

sort by: active | newest | oldest
-max-1 month ago

While I agree that the most practical way to do this would be to install a heating element of some sort (whether it be a heat lamp or an oven heating element) and a temperature controller, it would be kind of cool to do it by simply reversing the direction the freezer works!

.

Generating heat using electricity is essentially 100% efficient. Nearly all of the electrical power put into the system is converted into heat and a very small amount of visible light (which BTW will also turn into heat once it strikes a surface that absorbs light.)

.

However by reversing the direction of the heat pump to pump heat into the fridge, you can actually improve the efficiency, since a large portion of the heat entering the fridge really just being taken from the surroundings, You can achieve efficiencies on the order of 300%, minimizing the actual electricity required to heat the inside. The disadvantages are that heat pumps (in general) are not able to move heat energy at a very high rate when compared to more traditional methods of producing heat, and are most efficient when the temperature differential is small. So you might find that you are not able to heat the inside of the fridge fast enough or very efficiently, especially if there is not a lot of heat available outside (like on a very cold day.)

.

However, although this method is complicated, there is some commercial success with using heat pumps to produce heat for heating residential homes. Many manufacturers are now making AC's which can be reversed to pump heat into a household. But of course they to, suffer from the same problems as described above and are only practical in mild climates with only only moderate heating/cooling needs.

harlyquin (author) 1 month ago

Nice idea. I wanted an e-z bake oven when I was a kid. Thanks everyone, I was sure I was overthinking it. I've been using cfls and LEDs for enough years that I forgot all about the e-z bake oven!

kelseymh1 month ago

A 60W incandescent bulb makes a surprisingly efficient heater. Get a decently sized open cabinet (like a cheap IKEA armoire) and line it (walls, top and bottom, and doors) with a layer of hard insulation foam (R-tech or something equivalent). Put the lightbulb inside, with an external switch so you can turn it on and off (or even better, hook it up with a temperature probe inside the box to control the switch).

Let's do some math to see what you can get. Assume the cabinet is 1.5 x 1 x .5 m, for a volume of 0.75 m^3, and filled with ordinary air. Air has a specific heat capacity (at STP) of 1297 J/m^3/K, so your cabinet (empty) has a heat capacity of 973 J/K, or just under 1 kJ/K. That means if you put 1 kilojoule of energy into your cabinet, the temperature inside will go up by a bit over 1 degree C (== 1 K). A 60W bulb produces 60 joules of energy per second (that what a "watt" is :-), 1 kJ in 17 seconds, or 216 kJ per hour (!).

So if you close up your perfectly insulated cabinet and turn on the light, in one minute the temperature inside will have gone up about 4 degrees. Left overnight (8 hours), it would theoretically be over 1700 degrees hotter than when you forgot to turn off the bulb!

That assumes perfect insulation of course, and no cooling losses to the outside. You can plug in your favorite value for the insulation efficiency (70%? 50%?) and rescale the temperature rise accordingly.

A temperature probe and controller (a combination we like to call a thermostat :-) for the light switch will allow you to maintain whatever temperature inside you like. With realistic insulation, you should end up with a duty cycle somewhere around 1:10 (half a minute warming every five minutes or so).

In fact, standard (at one time) incandescent light bulbs were the basis for the "easy bake oven" (A popular toy for girls during the 1960s and into the 1970s), in which one could cook a cake or brownies...

As I recall, they had a silvered liner (thin aluminum or steel) with ~1/2 of insulation around the "oven"

I used to an incandescent light bulb in a cardboard box for spray painted items to bake off the volatiles between coats.

Unfortunately, incandescent bulbs are getting harder and harder to find. Maybe instead, those little spotlights used in lava lamps, or "appliance" bulbs, which are afaik still incandescents...

Yup! This energy output, mostly in the form of heat, is why incandescent bulbs are slowly (s----l----o----w----l---y) being phased out. Using a blackbody spectrum to generate visible light is horribly inefficient. Much better to use atomic (CFL) or engineered quantum (LED) energy transitions to produce narrow-band radiation in the visible range.

It is called a heat pump. But as kelseymh said a light bulb is easier.

rickharris1 month ago

After some thought, although this isn't at all practical and you would be far better off getting an old fridge and stripping out the cooling cct and insert a 60 watt light bulb as DU says.

You could remove the cooling coils from the inside of the fridge and put the heat dissipation coil from the back inside.

This means your trying to cool the world and dissipate the heat inside the fridge.

As I say not practical. Go for the bulb.

wheather

Does not work like that.
Evaporator and condenser are matched to the expanding refrigerant.
So even if you could revers the workings on the compressor side it would fail quickly.
If you need to keep things warm in a fridge or freezer than use a lightbulb or heat lamp together with a sensitive temperature controller.
A fan helps to keep the inside at even temps in all areas.