[usrnm]

> if not a heat pump

Most heat pump installations in Europe are air-to-water systems fitted to use the existing piping in old homes and is used only for heating. Such installations can, in theory, be used for cooling, but very inefficiently.

[aaronbrethorst]

Seems like a good thing for them to reconsider between now and next summer!

[KaiserPro]

> Most heat pump installations in Europe are air-to-water systems

I'm not sure thats true.

Most aircon in "warm" europe is standard split aircon

The "heatpump" shit that the UK is sorta looking at is as you describe. However its half the price to install "aircon" over heatpumps (because grants, amongst other things)

Like most recently refurbished offices will use normal aircon (certainly all the one I have worked in)

[dom96]

The annoying thing is that UK at least has a bigger grant for air-to-water systems.

I've been doing some research into this, because I would ideally like to get this system so I can make use of the existing radiators in my old house, but I do also want to have the option of cooling my home. It does seem like Fan Coil Units (FCUs) are an option for this. Anyone have experience with these? Are they really inefficient compared to standard air-to-air units?

[thyristan]

The problem is, if you feed cold water into your normal heating pipes, all the piping and radiators will get wet from condensation. So you would have to have a regulator that measures air moisture and temperature in all your rooms and only feeds water with a temperature above the dew point. This is possible, but inefficient and (especially on hot+wet days) doesn't cool very well.

The possible real fixes are either to section off your water circuits in summer, and only run the properly cold water through FCUs, wall or ceiling loops.

Or to get a multisplit heat pump, use a normal refrigerant-air indoor unit to cool and a refrigerant-water indoor unit to heat the water loops.

[dom96]

Yeah, I wasn't planning to run the cold loops through the existing radiator piping. I just want the ability to cool at least 1 room by reusing the air-to-water system, even if that means the FPU requires its own piping from the outside.

In that scenario, are FPUs a good option? Are there other drawbacks?

[spockz]

Most Francoils I know don’t have a way to get rid of any condensation that happens in the unit like internal air conditioning units do. So even if you run the piping outside of the house you have condensation in the unit and the floors, not to mention the walls.

Even then, there is a fair limit in cooling and efficiency you can get from them because of the lack of phase changes occurring.

If you have a balanced mechanical ventilation (both inlet and outlet) that would be one of the best options to condition the whole house without putting air conditioning units everywhere. Having said that, we turn on the air conditioning in the attic during hot days which removes the biggest heat and moisture from the house. Next up is installing more sun blinds to prevent the heat from entering in the first place.

[thyristan]

Yes, they are a good option, provided you get one that has a condensate drain. Always use a piped drain, never just a tray that you have to empty, make the hose wide enough and clean it every few months, because algae will clog it if you don't, and then you'll have your own privat lake. But that's basically the same as for any air conditioning.

Insulate all piping properly, the outdoor part will freeze in winter, and the indoor part will drip in summer if you don't. The best products for this are foamed rubber based. Make the insulation seamless with the right glue or tape, every opening will drip.

Add manual or automatic valves to shut off the heating loops in summer, so you don't accidentally get cold water in there. Your cold water loop might also need an extra circulation pump, depending on how you run your piping, but that's hard to say without a lot more detail.

FCUs are available in the same form factors as indoor units for refrigerant-based systems, including a thermostat remote control, e.g. https://www.sinclair-solutions.com/files/user-manual-en/fan-... . But get one from the manufacturer of your outdoor unit, so the communication lines work, e.g. so the indoor unit can instruct the outdoor unit to start/stop/regulate.

[quickthrowman]

Fan coil units work just fine, you’ll need to install a condensate drain but other than that it works like a mini-split evaporator/fan air handler.

You just have the added equipment and maintenance for the water/glycol loop vs an air to air system that only pipes refrigerant around. Fan coil units or VAV boxes are the usual terminal units for commercial HVAC systems that have a chilled and hot water loop, VAVs are used in a system with ducted AHUs and FCUs are used for apartments (stacked FCUs with vertical supply/return risers) or spaces not served by ducted air handlers for whatever reason.