I thought I’d post some notes on the ASHP we’re having put into a new build.

First, the house. It’s quite big, around 200m2, and we’re trying to make it fairly well insulated and airtight. It’s slightly earth-sheltered, since it’s partially dug into a hill, which means both the upper and lower floors are “ground floors”, which is weird.

The lower floor is made from brick and block with 90mm Kingspan cavity insulation. Upstairs is timber frame with 150mm warmcell insulation, with 60mm of Diffutherm wood fibre board on the outside. On top is a flat green (actually rubble) roof. U values are 0.2 for lower ground floor walls, 0.18 for upper ground floor, 0.2 for the roof, 0.21 for the floor, 1.24 for the windows. (I don’t have airtightness figures to hand.) So not too bad, and the hope is that the heating system won’t have to work too hard as a result.

We were going to have a combination of efficient gas boiler and solar panels. This would have been comprehensible (you know where you are with a gas boiler!) and moderately green (with the bonus of having pretty solar panels on your roof!). The downsides were that gas prices are a hostage to fortune (I suspect the current dip in prices is the prelude to frighteningly vast increases over the next few decades) and solar wouldn’t do both heating and hot water for the scale of panels that we could afford. But it was a compromise we were happy to live with.

Until, that is, the builder suggested we take a look at air source heat pump. Now, our builders are a great firm but they would be the first to admit that they are not experts in green technology. However, they had seen one in action as a result of working on a visitors’ centre where the architect had specified an ASHP. They were impressed by what they saw and suggested we take a look at it.

What we liked was that it did both heating and hot water, was fairly efficient, and that you could get a load of different services done by one supplier – air source heat pump, heat store / boiler, and underfloor heating. The other route would have meant different suppliers for the boiler, the solar panels, much of the plumbing and the underfloor heating – it’s good to have one point of contact. Plus in the end it was a couple of grand cheaper. If we’d have moved a bit quicker we could have got them to do the MVHR as well, but we went with our original supplier due to time constraints.

But before we took the plunge we wanted to check a few things. Firstly, as a non-expert, I wanted to know that ASHP would actually generate hot water (knowing that some solar installs occasionally go a bit tepid). Second we wanted to know how big and ugly the units were. And thirdly and most importantly, we wanted to know how much noise the fan makes. So we went off to a few sites to see what they were like in practice. The first port of call was a new children’s centre (soon to be nursery school). Large spaces were being heated very nicely indeed and the fans, being on the roof, were inaudible, though there was a fair amount of ambient noise. The second site was a shower block in an aluminium smelting plant. Again, a small unit was generating plenty of hot water and heat, and the heat could be turned up pretty rapidly via a thermostat – within 11 minutes. The unit seemed very quiet, although it was next to some much noisier ventilation fans. Third visit was a community centre where an array of PV solar panels were driving the pump; again, no issues with performance, and the fan itself was a pretty gentle whirr, but the mountings were squeaking, apparently due to cost-cutting on the installation – they hadn’t used the right grommets.

Overall, we were satisfied and went ahead with the order, on the proviso that it doesn’t squeak(!). It’ll be in a light well and under a bridge anyway, which should help. I’ll let you know how it gets on…

Thanks for sharing your experience agu. Yes, water coming off it could be an issue - we have a drain for it.

The amount of condensation produced by an ASHP can be as much as 25 litres a day.

Unguided

Absolutely, the condense from an ASHP is only water, there is no acidity, PH is neutral. So yes, ideally suited to direct into rain water harvesting.

Pressure, before you plump for a particluar ASHP make sure you compare all models on a like for like basis. You need the A-7W35, A-7W50, A0W35, A0W50, A10W35, A10W50 data (kW capacity and COP) as a minimum I suggest.

[A0W35 = Air input at 0 degrees C, water output at 35 degrees C, etc)

oh dear - i probably shouldn't have mentioned the manufacturers on this website - very, very, sorry,

fluffy

have been pricing up a ashp in france to fit in a barn conversion (large) cost 14000euro for units oniy but we can claim half back from french goverment, this system is german and at -15 will give 55c at rads, we do not require it to be used for the hot water c/h only, the system we inspected was twice as big as the one we need it ran 9 apartments h/w and c/h and the noise level of the unit was about the same as a hairdryer, all units are 3 phase (no probs most houses in france have this) running cost for the large unit last winter between 5 and 7 euros.

This might affect your budgeting ... The money you get back from the French government is in the form of a tax credit. If you don't pay French tax then you don't get your money back.

On the other hand, I believe one benefits from a preferential TVA / VAT rate of 5% if you have it supplied and installed by a firm that has all the proper accreditations - otherwise it's TVA @ 19.6% as per normal.

Hi there again,

I've just found out that although GSHP's are allowed under the new permitted development planning laws, ASHP are not due to noise and affect on neighbours, therefore a planning application is needed, also I only ended up with one of the ASHP quotes (not 2) as the hot cylinder company for one of them has gone bust. so.. back to the drawing board..my architect and I have been looking at GSHP's again as planning is very difficult on the site. It is so dificult,

Thank you,

Fluffy

It was covered in the last amendment to the GPDOs that came out this year which allowed solar but excluded ASHPs and wind turbines pending further consultations on noise levels so these continue to need planning approval until the next set of changes come into force. Individual planning departments sometimes make their own local exceptions to this, such as needing planning approval but not charging a fee for it. The implementation dates for the GPDO changes are also different in England and Wales.

HansardGood progress has been made on the associated test standards that will apply to wind turbines and air source heat pumps, as part of the Microgeneration Certification Scheme. The scheme and standards have been developed in consultation with stakeholders and industry. In due course, the GPDO will incorporate standards to ensure that habitable rooms of any neighbouring residential property are not exposed to an outside noise level exceeding 45 decibels. The noise limit will apply to free-standing wind turbines and those mounted on detached dwellings. Similar provisions will apply to air source heat pumps. The decibel level will be reviewed after two years in the light of conditions prevailing at the time.

http://www.publications.parliament.uk/pa/cm200708/cmhansrd/cm080313/wmstext/80313m0001.htm