With home HVAC, fridges, water heaters, and dryers all using now able to use of dependent on heat pumps I wonder how long it be before we see modular appliances that connect to coolant lines where the temperature differential is supplied by a central high efficiency heat pump.
Cars already have heat scavenging that can move heat from where it's being created through losses to places where it's valuable, like the cabin or battery pre-heating. Especially in cold climates it feels like homes should be next.
There's some commercial options for this, but it's not common. Usually, these devices just have their own compressors, because they all pale in comparison to the heat pump(s) used for climate control. For example, I have a HP water heater, and its heat pump is about 1/3 of a ton, whereas most homes need 3+ tons for climate control. Fridges are a fraction of that.
For HP clothes dryers, there's no efficiency to steal from somewhere else, because they use both the hot and cold coils - similar to (the same, really) dehumidifiers.
The tradeoff would also be running high-pressure refrigerant lines everywhere. That would require EPA certification (in the US, anyway) to connect/disconnect an appliance, and it would probably be less reliable. These sealed-system units are generally pretty reliable, because the refrigerant is installed at the factory under ideal conditions, and there's no connections that are made later that may be done poorly.
That is an interesting thought, but I assume that the working ranges of the different appliances are different so there would be some complexities and inefficiencies getting them all connected to a common circulation loop. If there was a thermal equivalent of a transformer used for alternating current, that would be amazing.
As far as I know all the common commercially available heat pump appliances all use the same refrigerants, so it doesn't seem like it would be that challenging.
In cars that have unified heat management the refrigerant cycle is handled as a separate element, with a manifold controlling individual coolant loops to each component. I'm picturing something similar for the home, with a coolant moving heat to and from each appliance using standardized communication to the manifold. There would probably need to be heat buffer tanks, but air to water heat pump systems for radiant heat already need this anyway.
A few years ago I was planning to build a velomobile that I would live out of for a year while circumnavigating Australia, and potentially indefinitely. (My plans changed.) I was disappointed at how hard refrigeration information was to come by (maybe I should have sought a traditional paper book), but I was kinda looking forward to figuring out if I could use one compressor to cool a small fridge, cool and perhaps heat the cabin, heat water, and heat a slow cooker (target 80°C). The bits I could work out suggested you might want a different refrigerant for the cooling and heating applications, or different back pressures; but I was rather hampered in my reckoning by my lack of domain knowledge—I was definitely going to have to talk to professionals! If so, and combined with the limited power collection available (<1m² usable solar panels on the vehicle, could lay out more while parked), butane was probably going to make more sense for cooking.
I even ran some naive numbers on the amount of water that would condense in expected conditions, concluding it could be handy but I’d probably still need to source more water.
It's worth noting that the very earliest electric refrigerators had a separate condensing unit outside; see this interesting 1920s Frigidaire training video for an example of what that was like: https://www.youtube.com/watch?v=W-t7DqOAMME
There were also centralised systems for apartments where one condensing unit supplied many evaporators in the refrigerator in each suite.
That would've been easily invalidated by prior art from nearly a century ago; as I mentioned in a sibling comment, this was a common arrangement in the early days of domestic refrigeration.
You can buy R600a on Amazon right now. One $60 can will charge the system ~5 times.