Heat pump hot water cylinders

QrizB

Does anyone here have, or have seriously considered installing, a heat pump hot water cylinder? Something like the Tesy Aqua Thermica (other brands are available)?

At first glance it looks an interesting idea. A regular hot water cylinder, complete with coil for CH or solar HW, but with a small (2kW thermal) air-source heat pump on top of it.The idea is that it can draw air from outside (or from your living space, if preferred) and use it to heat the water, returning cold air outside (or to your living space, if preferred). There's a 1.5kW immersion heater for anti-Legionella and "boost" heating purposes.

If you would othewise heat water electrically it seems a quick win, potentially reducing your water heating electricity demand by 2/3rds. For those of us with mains gas it's less simple but you could imagine using it as a conventional cylinder in the winter months, then switching to ASHP from late Spring to early Autumn. With a 9p-or-less TOU electricity tariff it could be cheaper than mains gas, even in the depths of winter.

During the summer you'd potentially benefit from free cold air, too. And it would pair well with solar PV (there is mention of a solar diverter option).

Any thoughts?

Hexane

Very interesting. Based on the current location of our existing hot water cylinder, the cold air output would be directly into our home office, which is (as I type) exactly where it's needed.

Martyn1981

I've seen these, and vids explaining their benefits, for the US, where water heaters often sit (loose) in a garage or basement, but I don't think I'd seen one that (logically) can extract air from outside the property ..... in which case, could be brilliant for the UK.

BTW the US vids explain that they cost quite a lot more to buy, but the cost of running them (all water heaters in the vids run on leccy) gives a fast payback, perhaps 2 or 3yrs.

shinytop

Looks like a good idea.  I really like the idea of cooling as a 'waste product'.  Setting aside the green credentials, the economics may be a problem if it's up against gas at current prices. It would pay back compared to direct electricity but in these cases a full ASHP system might be a better bet.  Maybe good for flats? 

QrizB

Thanks for the feedback. My water tank (and boiler) are both 15 years old and will no doubt need replacing before too long. My current tank is in an airing cupboard directly off my landing, and immediately above it is my loft; I could imagine drawing hot air from the loft and venting cool air into my house in summer, or back into a loft and out of the eaves via a duct in winter.

Of course my boiler could last another 15 years, by which time we'll all no doubt have flying cars and/or be living on the moon

Reed_Richards

QrizB said:

 I could imagine drawing hot air from the loft and venting cool air into my house in summer, or back into a loft and out of the eaves via a duct in winter.

Generally I am all in favour of heat pumps but just trying to think of potential downsides.  Would it really be cool air or just air that is a bit cooler than the air in your loft?  Lofts can get pretty hot in summer, even when partially shaded by solar panels  The other issue is fan noise, would having the fan for the heat pump inside the building create an unpleasant level of noise?