Fenton H

Thanks for this, I actually found this solution a few days ago, just what I'm looking for and having researched the market Vaillant seem one of the best for providing whole systems that are readily available in the UK.

I agree ProDave, mad price. At least there's possibly less installation work, no additional compressor outside and the controls are included/integrated (no additional remote to lose or eat up those AAA batteries ?). I've also come across various half decent looking 'refurbed' wall hung models (radiator type heat/cool similar to the panasonic aquarea) on sites such as ebay for 250 quid. I haven't looked at them in detail as not something I'd use for our new-build but might be worth considering as a low cost option?

Well I found a nice wall mounted model (panasonic), there's some really good sizing data for them in the specs, such as here: https://www.seconrenewables.com/panasonic-aquarea-air-radiator-4237-p.asp You're right that they are a bit expensive (£600 for the small model- £700 for the bigger one on https://www.easyheatpumps.com/cart/) - but they're designed for heating and cooling bedrooms, and look pretty easy to install. As my only other option is UFH, which wont cool very well, I can justify the cost but if its an additional unit on top of UFH I can see it's a bit prohibitive.

Have you thought of a backup electrical heater downstream of the ASHP? Many models (e.g. air-to-water split systems) include them as standard in the indoor hydro unit, typically 3, 6 or 9kW. Or you can buy as a separate item. The idea is you don't need to oversize the ASHP too much to allow for short bursts of extra heat to get up to temperature, or for the few coldest days at the bottom end of your design envelope.

Thanks I'll take a look at plate heat exchangers. I did come across a Panasonic model that uses a intermediate brine circuit which I assume is the same principle, but I havent looked at installing an additional exchanger . The house will be empty for extended periods in the middle of the winter and I'd rather avoid having to leave everything running, plus even if I did leave it on low heat then power trips would shut it down (I'd rather not need to worry about it).

I'm in the process of selecting an air-to-water ASHP for our upcoming house renovation. I prefer a split system to remove the risk with a monobloc of the external water supply/return freezing when the unit is shutdown (we often spend long stints away from home in the winter). Plus our planning permission requires it to be on the wall of the house so I want to minimise size and weight. However I really like one of the Vaillant arotherm models as they use propane as a refrigerant rather than the usual high GWP refrigerants - the only problem (for me) is that it's a monobloc. I was wondering what others' experience is with monoblocs. I can get around the size/weight issue but it's the freezing I'm wondering about. Is it a major task adding glycol to the entire heating circuit and does it affect how the system is maintained? I'd use non-toxic propylene glycol so no problems with leaks/draining etc. Or are there other solutions? I'm not too keen on the freeze protection valves as I prefer passive solutions (i.e avoiding the problem) rather than secondary protection.

Thanks for all the info. I'll definitely update with prices if I manage to find any decent units. I'm also hoping that even if FCUs are a bit expensive it will compare favourably with the cost of installing UFH. And in any case there's no other way to cool using an air-to-water ASHP is there? I'd be interested if anyone can recommend other options for cooling using air-to-water (cooling via UFH isn't really an option in the bedrooms as they'll be carpeted). I'm not keen on air-to-air as it's outside of RHI payback, doesn't provide hot water, I don't want 2 separate ASHP systems etc.

Yes I noticed that too. When looking for an ASHP I've been wary of monoblocs due to the risk of the outside portion of water freezing when shutdown, plus having to use glycol in the entire heating system etc. Vaillant are one that have brought out a propane model, but its a monobloc, however I'm now thinking it's a lesser evil than using high GWP refrigerants.

Thanks, there's some really useful info here. The topic has moved on a bit but one thing with DIY installation is that most refrigerants are potent greenhouse gases. I'm not sure what quantity is in small units like these but say it's 0.5kg R410, losing it all is the equivalent in terms of global warming of driving an average car approximately 7000km. A fair compromise might be to install most of the kit and arrange an F-gas engineer to hook up parts required by the regulations.

Hi I found this group forum when looking for a reliable way to size fan coil units (FCUs). I'm about to start a major renovation of our house in the south east of England which will include an ASHP for heating and cooling. Does anyone know whether the FCU heating outputs quoted by suppliers are normally about right for an ASHP operating at 40-45C? The house will be close to passive standards so I'm not too concerned about being exact, but I don't want to seriously oversize the kit. Same for cooling, I'm not too concerned as it's only a secondary consideration and I'm assuming that if the FCUs are right for heating they should be fine for cooling. It looks like I might have to start getting into the detail and estimating the temperature drop across the FCUs to size them - can anyone with ASHP experience please advise a typical temperature difference between the ASHP water inlet and outlet when operating at efficient temperature, say 45C ASHP outlet temp?