Refrigerator modification - heat pump

Hello - sorry for the unorthodox request, but in short I was wondering if I could modify a regular kitchen refrigerator or maybe a small chest freezer to heat up inside instead of cooling down.

In theory, if I:
- remove and collect the refrigerant
- cut open the fluid lines and insert a 4-way "reversing valve"
- carefully solder the valve
- create vacuum and re-fill with refrigerant
- make the necessary electrical connections, those would not be a problem

I should be able to switch between "cool down" and "heat up" modes. I assume the thermostat will be replaced and the compressor controlled by something suitable.

Is this crazy or could it work in practice? What comes to mind is that:
- the "internal" tubing of the evaporator might not be designed to work on the high-pressure side
- the capillary tube might not work "reversed"

??? Any opinion???

 

The reason I want to do this is to build a levitation/fermentation chamber. This, is, something I can control (with a computer) to vary the internal temperature of the chamber between 4C (39F) and 40C (104F) according to a profile, to allow the ideal conditions for several stages of fermentation/levitation/maturation process, all of this independently of the outside weather conditions.

For example, I might want to keep my dough at 25C for 24 hours: during the night the T outside might go down to 13C, and during the day it might go up to 34C: this system will have to "warm up" during the night to keep the dough at 25C and cool down during the day.

It is easy to control the compressor motor with a relay, and start the "cool down" mode when needed. Some people use electric heat generators to warm up, but I was really curious to see if, by using a 4-way reversing valve, I could obtain the "heat up" cycle without having to install a heater inside the refrigerator.

 

I'm not 100% sure but I don't think that would work. Basically you want to turn the fridge into a heat pump that you can change at will. One problem I can see is that heat pumps use dual direction or two expansion valves for controlling the flow of the refrigerant thru the coils. You will not be able to control that.

In my opinion you would be better off leaving the cooling system as it is and add a fan forced electric heating element. That should be just as easy to control.

To carry the idea one step further.... you could almost add a control system to the defrost element and use that as a heat source.

 

Interesting, I did not think about the defrosting element.

About the expansion valve: as far as I know, refrigerators do not use expansion valves but a capillary tube... and that is not directional, as far as I know...

PS no I cannot use a fan because moving air is generally detrimental to fermentation processes.

 

Correct.... capillary tube.

The cap tube keeps the evaporator from becoming flooded with refrigerant. You'd need some way to keep that happening at the compressor side.

 

Well my understanding is that the cap tube lowers the pressure to allow the refrigerant to change phase. In your chart, if the fluid goes in a way or the other, the cap tube is "always there" to restrict the flow...