Will we ever see “split” refrigerators?
Trevor_Lambert
| Posted in General Questions on
I don’t mean a fridge split with a freezer, but the fridge equivalent of a mini split heat pump. Or how about an indoor fridge unit that operates like an additional head on a multi-split heat pump? I’m imagining this in a cooling dominated climate, where the heat of a conventional fridge is almost always undesirable.
I did a google search and didn’t see anything that looked like this, but I’m surprised it hasn’t at least been tried. I guess the math does not work out between the potential energy savings and the capital cost and hassle, but that usually doesn’t stop some people from trying things.
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Interesting idea, especially in cooling-dominated climates where the ability of the refrigerant loop to be able to transport heat to outside the house is a plus. Normally, a refrigerator essentially IS a heat pump, since it moves heat from inside the fridge to the air in the house — very much like a heat pump water heater but in reverse.
The only issues I can see with this is that the fridge would need to be compatible with the mini split system, which probably would mean it would all have to be from the same
Manufacturer. The other issue is weather or not the refrigerant used in the minisplit system would be able to get down to the temperatures needed for a freezer. Different refrigerants have different minimum useable temperatures which limits how cold of an air temperature can be made when using them.
Bill
Yes, I wondered about the freezer part too. That's only an issue if you're trying for the second option, combining with a space cooling system. For a dedicated fridge system, you'd just use whatever refrigerant is standard for a fridge.
I'm thinking you could address the problem with a "booster" heat pump for the freezer portion.
Unless you need cryogenic temperatures, R410A, propane, R22, ammonia, all work just fine as refrigerants at the temperatures used in home refrigerators and freezers, no booster heat pump needed. Almost all home-fridges sold in North America currently use R410A.
While it's certainly POSSIBLE to do a home refrigerator as a zone off a multi-split, the additional installation expense for no real gain in efficiency doesn't make a lot of sense.
For high temperature (70C + ) output hydronic air source heat pumps it's common to use R410A for the main heat pump, with an R134A refrigerant booster compressor to take it from 30-50C up to 70C+ efficiently. Both Mitsubishi & LG do it that way on their commercial VRF systems when high temp water is needed, other vendors probably do too.
Commercial cold storage/freezer facilities and even restaurants with large walk-in coolers & freezers use split system heat pumps all the time, but I suspect the market for a split system home fridge would be vanishingly small, taking something that's pre-packaged and simple to install ( just plug it in) into something far more complicated, and not necessarily more efficient.
In Japan there were a few combination refrigerator/water heater products out there a couple decades ago but I'm not sure they were ever very popular. The amount of hot water delivered was pretty tiny (as was the average Japanese home refrigerator compared to those in the US.)
Trevor,
Maybe not exactly what you are talking about, but over a decade ago Fine Home Building did a feature on site-built refrigerators with remote compressor in an adjacent service room. So variations on the theme have been around for a while.
A natural match would be to have a desuperheater style coil to reject heat from the refrigerator into your DHW system.
But having linked fridge, freezer, DHW, and active drainwater heat recovery seems to make sense. Maybe add an outside coil for heat exchange (source/sink) when conditions are favorable or inside loads unbalanced.
It could be made economical but just using small gauge 1/4-3/8" tubing to connect them hydronically rather than running lineset's around the house.
Maybe there just isn't enough energy in play to make the complication worthwhile.
Just as a general note, I think most refrigerators actually derive the cooling air for the main fridge from the freezer section. The old style "freezer on top" units I have dealt with, simply let cold air fall from the freezer section via a small air passage located in the back center. My current "freezer on the bottom" style fridge has a blower assembly that forces the cold freezer air up a small tower at the back of the unit which has several holes in it to distribute cold air in the main box.
The main reason no one has created a heat pump refrigerator for homes may lie in the simplicity of a small sealed system which leaves the factory intact with warranty. Replacing a dead compressor in a modern fridge is often not sensible due to the labor and recharge issues. Having a specialist come to install a mini-split based fridge would likely be more expensive and negate any possible efficiency savings to be had with today's very efficient refrigerators. Think what it takes to redo central air.
If one really was looking to squeeze the BTUs, maybe introducing the infeed air from an HRV could polish the air temp a little as it passed over the fridge coils. Or maybe have the make up air for a range hood come in behind the fridge. I do suspect that total savings would be very little for all the effort though.
There are specialty refrigerators using a thermal effect derived from certain materials response to magnet fields. The magnetocaloric effect is a more difficult to design process than the Peltier effect for everyday usage for a host of reasons, but GE and others are working on it. Removing all green house gas destroying coolants used in refrigeration is the goal, however the technology does not seem there yet. Maybe surprises await.
In the scheme of things modern refrigerators do not use a lot of energy 460 kWh per year. In most places they have a heating season during which that energy is not wasted as it reduces the load on the heating system.
Would you pay $2000 dollars to have your refrigerator installed? All the labor and materials costs would be similar or above the cost of an air conditioner install.
Walta
Exactly.
Technically it's not a challenging problem, but it makes no financial sense to do it that way.
I have pondered this and aside from mansion sized walk ins it makes no sense.
First because half the time the remaining heat is useful [heating season]
Second refrigerators have become increasingly efficient, so you no longer notice the warm air coming off of them, it just isn't a thing
Water heaters might make sense as the heat pumps tend to be noisy and somewhat undersized.
Mini split water heaters (e.g. Sanden) stand to save more energy than fridges, yet even they struggle against the disproportionately high cost of a split system. As soon as you need an HVAC tech to come to your house, install a unit outside, snake pipes through the house, make connections, troubleshoot, warranty their work, etc., it's just clearly not financially viable except in the case of space heating/cooling.
I thought about it too and realized that if you already have a heat pump running in your kitchen, this would be useless. Think about it. The fridge heat pump takes its heat and dump it the kitchen. From there, the main house heat pump takes the heat and dump it outside. Why would you need another independant heat pump just for the fridge if you already have one working for the entire house?
Two energy conversions (fridge->air refrigeration + air->refrigerant split system) is less efficient than if the fridge was directly connected to the refrigerant loop of the split system.
As others have mentioned, it’s not a big technical problem, but it’s not really economically viable.
Bill
Here is a 2011 patent application on your idea by the cooling industry: US20120192586A1
Alas, the patent was abandoned.
https://patents.google.com/patent/US20120192586A1/