Off grid passive refrigeration controller

[Tim C.]

My off grid cabin refrigeration project has changed. It was pointed out, 9 months of the year, the outdoor temp is 40 F or less. I want to take advantage of this. I am looking for a temp controller that will turn a fan on when the outdoor temp is less than the temp inside the cooler. Ideally such an item would operate on dc power.

 

[sunshine_eggo]

https://www.amazon.com/AITRIP-Thermostat-Temperature-Controller-Adjustable/dp/B08H7M55Q6

 

[12VoltInstalls]

You might also want to consider operable louvers as well. Typical cross-environmental cooling/heating employs a fan ducted to a point furthest from the source and a second louver not ducted to allow for exchange.

 

[Tim C.]

The challenge is a bit more complex than a simple thermostat. There needs to be a temp sensor outside the building and one inside the refrigerator. A ventilation fan would switch on if the outdoor temp is lower that the refrigerator. This would function similar to a thermal diode. Heat would only go in one direction. I was going to use a heat pipe. However the location of the refrigerator is not where I can install one. So I have to use pvc pipe to duct air

 

[12VoltInstalls]

There needs to be a temp sensor outside the building and one inside the refrigerator. A ventilation fan would switch on if the outdoor temp is lower that the refrigerator.

Basically a ‘proofer’ of sorts

All these devices are available on Amazon for fairly cheap money. Easy enough to pick what you need and install. It doesn’t require a central nervous system to operate unless you desire that

 

[Checkthisout]

Do you have excess solar power or are you trying to save juice?

Point being, your fridge is just heating the inside of your place at a time of the year it needs to be heated. If your solar can keep up just consider it some resistance heating.

Also, no you don't need to have two temp sensors. You just need to know your fridge set temp and set the fan to come on when the outside temp is below that.

 

[12VoltInstalls]

you don't need to have two temp sensors. You just need to know your fridge set temp and set the fan to come on when the outside temp is below that.

I see your point.

However, controlled temps would want two levels of test.
My mind got stuck on my experience: location-built walk in coolers.

Even in a home you’d want a) proofer; is outside air cooler by 2* than the call temp. And b) the call temp; only runs/draws when it is called for, probably set a degree or two above compressor thermostat.
If outside is too warm compressor takes over. If it’s cold out, then outside air is ducted and the fridge will never run.

To pay off in one winter the parts would probably have to cost very little to be worth it.

 

[Checkthisout]

I see your point.

However, controlled temps would want two levels of test.
My mind got stuck on my experience: location-built walk in coolers.

Even in a home you’d want a) proofer; is outside air cooler by 2* than the call temp. And b) the call temp; only runs/draws when it is called for, probably set a degree or two above compressor thermostat.
If outside is too warm compressor takes over. If it’s cold out, then outside air is ducted and the fridge will never run.

To pay off in one winter the parts would probably have to cost very little to be worth it.

I'm not sure of your setup. Is it a fridge/freezer or just a fridge? Or just a freezer?

You can just keep it outside or in an unheated area. This has the same net effect. It won't run when the temps outside fall below it's setpoint because thermodynamics of course.

Keeping this in mind, if the fridge is inside you can seal the condenser coil area and then vent that area to the outside.

 

[Tim C.]

Basically a ‘proofer’ of sorts

All these devices are available on Amazon for fairly cheap money. Easy enough to pick what you need and install. It doesn’t require a central nervous system to operate unless you desire that

Never heard of a proofer. I searched Amazon and only saw stuff to make bread dough.

 

[Checkthisout]

When temp is below say 35 degrees outside, a relay turns the fan on that blows outside air into the fridge. Another relay deactivates the the fridge. This temp sensor would need to to be set a few degrees below the fridge set temp.

If you have to keep stuff inside the fridge from freezing, another temp sensor that opens a relay would be placed inside the fridge. This relay would go between the fan outside and it's relay and shut the outside fan off when the temp in the fridge gets too.

The refrigerators compressor is still off at this point because the outside temperature sensor is keeping it deactivated and the temp sensor for the outside fan that you put inside the fridge is keeping the outside fan from running.

Easy peasy. 3 relays, some wiring, 2 temp sensors and a computer fan. All 12 volts : https://www.amazon.com/dp/B07VDRGK9F/ref=cm_sw_em_r_mt_dp_3J5P1C10AY1E3SH7EKK2?_encoding=UTF8&psc=1

 

[12VoltInstalls]

Never heard of a proofer. I searched Amazon and only saw stuff to make bread dough.

That was a loose reapplication of the word ‘proofer’ from a propane pilot light safety device. It’s not a thing with refrigerators beyond propane RV fridges I don’t think.
I just meant a high-low go-no go assembly to control out pumping 70F into fridge.

Didn’t mean to confuse anything. Letting bread dough or pizza dough rise is proofing, too. Totally different

 

[400bird]

Do you have excess solar power or are you trying to save juice?

Point being, your fridge is just heating the inside of your place at a time of the year it needs to be heated. If your solar can keep up just consider it some resistance heating.

I'll agree with this point.

Your refrigerator is moving heat from inside the fridge/freezer to inside the living space. That's probably a good thing in the winter as you're likely heating the living space.

The alternative of blowing cold outside are into your fridge/freezer is also introducing cold outside air into the living space.

 

[12VoltInstalls]

blowing cold outside are into your fridge/freezer is also introducing cold outside air into the living space.

I would use an insulated ductwork. Since an electric fridge makes more heat than cold that would transfer some heating ‘cost’ from the fridge to the central heating plant - whatever that may be.
I’m guessing a $40/year tops net “savings” in dollars but that’s a wildhat guess. It may not be worth it as you suggest.

 

[noenegdod]

My off grid cabin refrigeration project has changed. It was pointed out, 9 months of the year, the outdoor temp is 40 F or less. I want to take advantage of this. I am looking for a temp controller that will turn a fan on when the outdoor temp is less than the temp inside the cooler. Ideally such an item would operate on dc power.

This takes a different skill set that may not be available but how about just moving the condenser outside. In the summer, the heat is going outside where you want it to go anyway and in the cooler months you are getting a far better COP because the condenser is colder.

I will say after all that I think just leaving it alone is the most productive approach and agree with this:

your fridge is just heating the inside of your place at a time of the year it needs to be heated. If your solar can keep up just consider it some resistance heating.