Why not combine Fridge and Air Conditioner?

I have an RV that needs both a refrigerator and an air conditioner. Maybe I’m missing something, but don’t these two devices work pretty much exactly the same way. They both use the same process of cooling through freon. Provided you have a vent to get rid of the hot air (waste), why not have the same machine provide for both refrigerating the food and the room??

Through some lazy google searching I gather this invention does not exist. Any insights as to why not?

For one thing, the two devices are designed to operate efficiently at different scales. The large motor and compressor in the air conditioner would be inefficent for the much lighter cooling requirements of the refrigerator.

The compressoron an AC unit cycles onand off according to the load and ttemperature of the space.

On a vapor compression fridge the compressor cycles on and off according to the temp in the box.

The evaporator on a fridge will be around 0 degrees and on a AC unit around 40 degrees. Two different pressures. A duel system will be more complex and require more controls and costing mor than two seperate units. Also most fridge units in RV are not vapor compression but absorption and run on propane or electric heat.

Why not just set your AC to keep your whole RV at fridge temperatures? :slight_smile:

I think the correct answer would be related to drewtwo99’s remark.

Specifically, it is a two-part answer: (1) The refrigerator is set to a much lower temperature than the A/C. (2) The A/C cools a much larger space than the refrigerator.

A machine that tries to do both jobs would not only be confused about how cold to get, but also about when to cycle on an off. I suppose it might be done with two separate thermostats and properly organized ductwork, but why bother? It would be easier to just get two separate machines.

A compromise which tries to accomplish two different things, might actually accomplish both goals. But usually, neither will be done excellently.

And besides, where would you put it? Most RV and 5th wheelers I’ve seen have the A/C on the roof. Kind of inconvenient for getting a soda, ya know?

I converted a freezer into a keg cooler at 36 degrees, I pump the cold air form the keg cooler into my fermenter which is about 2/3 the size of the freezer and I am thining it is not too efficient. The fermenter ranges from about 45 degrees to 62 degrees depending on the beer my son is making.

In my caravan I have a gas powered fridge. This uses a small gas flame to ‘power’ the evaporator. Would it not be possible to use the waste heat from the air con unit to do the same thing?

My brother worked at a place where they had to keep the machines cool with big coolers on the roof. In the winter they recycled the waste heat to warm the factory.

This. It’s not too far different from trying to power a Smart car and a semi from the same engine.

That said, I think we will see a “central power unit” for housing in the future, a single module that handles all the site powered amenities. Heat, cool, fridge, stove, water heating all in one efficient unit. The living unit would have to be built (or rebuilt) around both the system and its function. Some modern European installations are close.

Big industrial installations use exterior devices - chillers - to do everything, sort of like having “cooling” wired in with power, gas, compressed air, vacuum, etc. It has to be large-scale, though.

But just trying to get one appliance to do two different jobs is kinda Professor Knucklehead.

The short answer is that suzy homemaker doesn’t want to hire a consulting engineer when she decides she “needs” a new 'fridge.

You can do stuff like this when you engineer it as a system, and have engineers to figure out an appropriate replacement when an obsolete component fails. Supermarkets often have banks of compressors and condensers that handle multiple refrigerator and freezer cases for example.

This is a story I heard from the HVAC guy who kept our industrial chiller running:

The Supermarket decides to add another refrigerator case to the meat department, and the HVAC guy sets it up and it still works. Then they decide to add another frozen dairy case, and stuff starts failing. Then the third HVAC guy that can’t make it work finally calls in an engineer to figure out what is now needed.

The climate control in my car can be vented into my centre console and glove-box to chill-it, sort of the same thing but I wouldn’t keep a pound of bacon in there.

I’m going to go ahead and back up what Snnipe 70E said. Yes, your air conditioner and your freezer/refrigerator both run on similar principles, but they have different jobs to do. And to do those different jobs they have different refrigerants and different circuits. A freezer/refrigerator is designed to rely on the fact that the cooled zone is relatively well sealed. Which means that after the zone is cooled down, the humidity inside it should be fairly low. If you tried to use the refrigeration circuit from a freezer as an air conditioner, the evaporator would become a block of ice in short order.

I mean, a couple jobs ago I worked at a test lab and we had temperature chambers with cascade refrigeration systems which could get the interior of the chamber down to -73C. But the doors of the chambers had to be triple sealed because any ingress of moisture would have iced up the evaporators almost immediately.

The key difference I think, besides the difference in cooling capacities, is that the fridge ***must ***be on 24/7 (at least when the RV is active) else the food will spoil even in only moderately warm weather. That’s why they’re powered by propane. The A/C unit only needs to be on when you’re actually camped (in the case of trailers) or maybe, if you have a motor home full of people, when driving and the dash A/C isn’t enough. And in both cases only if it’s hot enough out. But in either case you have to power the roof A/C with 110V AC house current (via a plug-in or a generator).

Something a lot of RV owners don’t realize is that even when you’re plugged in and you switch your fridge from propane to AC, the AC current doesn’t power a compressor motor like a home fridge, it powers an electric heater (replacing its propane gas one). Works efficiently enough and greatly simplifies the fridge’s design. BTW, this is why RVs need to be reasonably level when camped, the fridge’s convection heating/cooling circuit won’t work well if it’s not.

Thanks for all the responses. This makes sense.

With the greatest of respect to everyone, I think you are all thinking of combining tow different functions. I believe the answer is not down that route but in totally discarding one function.

If you run an fanned aluminum air duct through the top of the fridge you will not need the A/C. To obtain more cooling just coil it.

But would it chill a zombie?

Something I recently found out, since our fridge has been acting up: refrigerators (well, ours, anyway) work sort of the way editorg suggests. The compressor cools only the freezer compartment. To cool the refrigerator, it just opens vents to let the cold freezer air enter the refrigerator side to cool it. There’s probably a small fan to move the air along.

That’s the way I’ve seen all modern refridgerator/freezers combos work, but that’s based on a limited sampling.

A combined cooling unit to run AC and a refrigerator might work out ok in the summertime, but around these parts we don’t run the AC in the winter time. In warm weather climates where the AC is on most of the time it might be efficient, but hardly seems to be worth the small savings of not having a separate refrigerator compressor. Then you’ll also need a flexible refrigerant line to the refrigerator so it can be moved, and you’ll need trained techs to install or remove a refrigerator.

And when it goes wrong you lose all of those functions at once?

That is not a good idea. A bit of redundancy works wonders when reliability counts.

Most of the cooling machines work on the same mechanism. But most of the Rv owners holds a small size refrigerator and a mini air conditioner. Working of refrigerator and ac is the same but you can’t keep the food fresh with your air conditioner cold air. Even you can’t freeze Ice cream in air conditioner.:wink: