Firstly, thank you all for the replies so far.
When I have visited the USA I have stayed in hotels with a device fitted under the window (therefore an outside wall). Most trips have been in summer when such devices act as an air conditioner but in winter they act as heaters. Are they a form of heat pump? The idea of having such a dual purpose machine has some attractions.
heat pumps, fridges and air con all use the same principle so a ?monoblock air-to-air system can do both heating and cooling.
Yes they work both ways, this diagram is the cop versus temperature for an air sourced heat pump:
Installation has to be considered. Those fitted under the window in hotels are possibly only heating/cooling one room. For dual use central heating would possibly have to be whole house air ducting.
They are, although they are not always designed to run in reverse (pumping heat not cold into the room). For example they need defrost cycles when the outdoor unit ices up. It doesn't take massive changes to make them reversible, but it needs to be designed in. Additionally the efficiency of a device designed primarily for cooling may not be as good in heating mode.
We would call them 'air to air heat pumps'. They have pluses and minuses against traditional wet central heating.
Theo
Beware that domestic ASHPs don't use R134a - they're mostly R290 or R32 (and a few R700), with older ones being R410a. Every model of ASHP has different COP performance. So your diagram is not very representative, although the COP derating factor looks plausible.
You can get multi-split systems, one outdoor box with multiple room units. Just refrigerant pipework connecting them (+electrics and condensate drain).
US folks also have a/c units which fit in a window opening - they're leaky and not very efficient, a bit like our portable a/c units.
Theo
I just wondered then, if a fridge would actually warm up the inside if you put it into a really deep freeze like you might used to freeze co2. Brian
So can one of these splits run a unit with a coil in DHW tank to a low temperature,say 40C? Which can be then boosted by an immersion?
The one we had fitted into a sash window and was a boon during the 40C nights in Boston Massachusetts.
No, they have no water interface to them. They're purely refrigerant lines with fan-air heat exchangers at both ends. I've not seen DHW tanks with refrigerant coils.
In the US they have separate heat pump water heaters, with either a single tank+fan unit (installed somewhere like a garage in the South) or a water tank with an external box (a bit like our ASHPs). They then use splits or a ducted air system for space heating/cooling, so you can heat water and cool the house at the same time.
A lot of the world installs A/C without thinking about efficiency or insulation, which explains why they spend so much on electricity.
Theo
Oh well that is what I wondered, a refrigerant coil in a DHW tank with an immersion.
The thing is an air2water heat pump is three times as expensive as a small air2air which would suit a house down to ~10C outside.
Ideally I would like air2water with underfloor and preheated DHW, making use of off peak electricity in deepest winter but capital cost puts it out for our old house.
Yes seen them by Daiken and Valiant here.
In my case A/C is only used a few days a year and that coincides with high solar PV production.
you can have reversible (as opposed to heat-only) ASHP, they are still monobloc with only water connection going indoors, installer doesn't need F-gas qualification, all the refrigerant stays outdoors and is pre-filled.
The system as a whole would need solenoid valves and relays to control which mode it's in and where the water flow goes to; in heating mode one set of valves open to your HW cylinder and/or UFH, and be switchable to cooling mode with another valve chilled water flows to wall mounted fan/coil aircon unit.
Most water ASHP will actually do cooling too, but for historical grant-related reasons some of them hide it by deleting sections of the UK manual or hide it behind a setting. If you get the global manual it's all documented there.
Much like a regular heating system in fact. I'm thinking of adding another zone for a fan coil, which would turn my system from S Plan to S Plan Plus.
Fan coils are a bit of a rare breed in the UK, although this is changing:
Yes, I see that with some it's just a case of a pin header that needs a resistor on a plug, presumably others would actually have the reversing valve omitted for cost reasons?
Other than not expecting a chilled flow from a combi!
Yes, one that I found last time I looked now says "This product is not yet available"
Most ASHP are a global product so are designed for markets where both heating and cooling are used. There isn't much point in hobbling them for a few bucks worth of components.
This one is 'designed for the UK' and maybe doesn't do cooling:
Just need to burn that magic anti-hydrogen :)
These look good, if a bit pricey:
Theo
How small is small? A small room a2a might be 9000BTU/hr or 2.7kW. Most houses are going to need 2-4x that.
Depends on your sizing, but something like this is not far off boiler pricing (especially oil boiler):
Ah, thanks I hadn't seen those. The Daikin one is quite hidden on their site. Here is the Vaillant one:
Theo
In a tradition water based CH heating with underfloor or radiators would reversing the system and circulating cold water actually produce a comfortable environment in summer? Radiators drop the the cooled air to the floor and with underfloor piping you would get cold feet. You then need to get this cold air to fully circulate in the rooms by using fans.
I doubt it. You’d also get condensation dripping off the radiators. You really need zone controlled fanned units (with condensate drains) to spread the “coolth” properly I reckon.
Tim
I know of people who find the noise of a fan in a laptop or PC annoying especially if they are the one not using the equipment so a fanned solution may not be ideal for all.
I wonder how much those fanned radiators concentrate the dust to the wall above/beneath the installation leaving black marks on the walls.
Rads don't work for cooling unless you mount them upside down. The cold water goes from inlet to outlet without troubling the warmer water in the rest of the rad, meaning only the bottom few inches are cold. When heating you pump in hotter water at the bottom which rises, establishing a convection cell. You'd only get that for cooling if the cold water went in at the top forcing mixing with the warmer water inside.
UFH can work for cooling - the cold stone floor effect. You need to make sure it's not cold enough to get condensation (or run a dehumidifier as well). UFH plus ceiling fans might work nicely.
Theo
Any kind of air conditioning requires a fan. I suppose apart from just dumping a block of ice in the middle of the room. Or maybe mounting cooling radiators on the ceiling.
No idea, but ask any user of an air conditioner in the rest of the world and they'll tell you.
Theo
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