Where about in the world are you, that makes a difference to what you choose.

Not familiar with that area at all, but you should be able to get hourly temperature, solar radiation and hours of sunlight data easily enough and you can work from that to compare between them.
I suspect that ASHP would be the most reliable/consistent but the most expensive.

Hi Chris,
Many thanks for your help.

Yes, it is a new build, 142mm sips panel with 90mm insulation on inside, two small wood burners but other than towel rails hopefully no further space heating necessary, just trying to get the most efficient and cost effective way for DHW. Was planning on 4kw PV and solar thermal for DHW with immersion top up when necessary.

Steamy, I'll have a look at the data, the site is southish facing so we should pick up all available light. I was wondering if a small ASHP will provide enough of the DHW to make it worthwhile.

Thanks again.

Hi David,
Two adults and two Pre-teen kids, four showers a day max, though sometimes taken under duress, depends how muddy!!

We would plan only to heat to 45-50 and then do a legionella boost cycle as necessary. Who are the BIg names in air conditioning? We had a quote for ASHP, however, that was for space heating as well, which we don't need; an 11kw unit which came in around £10k installed with ufh.

Bob

You should be looking at around £5k supply only on the 5 kW Mitsubishi Ecodan with a 180 litre Kingspan tank. That should adequately cover your needs.

I'm on the very south coast of Sweden so at a very similar latitude to yourself and a similar family size. As we are in a village it was a personal decision not to have any wood burners to pollute the neighbours with!

It's always difficult to estimate DHW demand but ours is presently somewhere under 3,000kWhrs/a but could well rise to 5,000kWhrs when the kids become teenagers.

You can do some calculations of what that will cost to heat by immersion with your current tariff, I'd guess that you will probably not get a payback on installing a heat pump for DHW alone particularly if if you can heat the tank overnight on E7.

It could well be that your best solution is to install a cheap direct electric water heater and install PV to offset some of it's consumption.

[Edit] Regarding the COP as mentioned by ST, I have based my calculations of a SPF (seasonal performance factor) of around 2.5 this takes into account the varying COP during the year depending on the ambient weather and heat demand. If you are using the heat pump only for DHW your SPF should be better than 3 as you are not losing out to a higher space heat demand in the winter when your COP is worst.

Just to hang some numbers on that:

If your DHW demand is 3,000kWhrs and your electricity is costing you 15p a unit this is going to cost you £450 a year.

With an ASHP with a SPF of 3 it will cost you £150 a year so a saving of £300 a year.

If the ASHP costs you £6,000 more to install than a simple immersion + tank then you are looking at a simple payback period of 20 years. (no inflation accounted for)

As I say if you numbers are similar to mine you won't have a reasonable payback on an ASHP which will probably only have a useful life of 15 years and will probably need servicing7repairs in that time also.

Chris,

Many thanks for that, a mine of information. We'll have a chat about it and go from there.

Thank you for all your help.

Cheers.

Bob

Hi an02ew,

Could you specify exactly what you have for me? Sorry, don't know the acronym AGS

Cheers

Ok, will do....thanks. I'd never heard of it but will have a gander.

Cheers

I went to a talk a couple of years ago about Sanyo ASHP using CO2 as refrigerant. Supposedly developed for the Japanese market where they use a lot of hot water. Might be worth seeing if there is any experience of these in the past two years.

I don't follow you which figures look suspect to you?

Posted By: MikelI went to a talk a couple of years ago about Sanyo ASHP using CO2 as refrigerant. Supposedly developed for the Japanese market where they use a lot of hot water. Might be worth seeing if there is any experience of these in the past two years.

Ecocute is the keyword to use if you want to search on this technology.

Indeed that figure seems out of place a typo I"d imagine. Time for an email to their technical dept. ST!

Brunei Bob

If you just want to heat DHW with an ASHP, why not use an Ecocent or similar ASHP cylinder at circa £2,000 + VAT? Duct it from outside or the loft and switch over to an immersion when it gets down to 0 deg C to reduce wear on the compressor.

Alternatively, go for a Hitachi Yutempo direct refrigerant split model with external condenser. SCOP of 3.1 approx. Cost circa £2,000 + VAT + installation (say £500).

Both these are optimised for DHW temperatures and will perform better than a larger monobloc ASHP unit with primary wet circuit.

Bob, a couple of thoughts on your house performance, rather than the ASHP discussion. If you've got 142mm plus 90mm (assuming PU) then you've got excellent Uvalues (guessing 0.1 or less) You really need to focus on the air tightness, otherwise you'll have wasted the effort on insulation (assuming MVHR).

You mention about running the log burners all winter - I suspect you'll have them on only a few hours each day. Get a reasonably sized log boiler stove, and a thermal store, light the log boiler stove at dinner time, and by bed time you'll have a full TS of hot water, and a warm house, until dinner time next day.

Solar thermal will get you DHW for most of the summer, but from now till May, it will only make occassional contributions. I believe it's worth doing on a new build, if you don't have solar PV. My advice to you would be log boiler stove, thermal store, elecric immersions, solar PV - and years of no equipment to service or maintain.

(I'm in Perthshire, passive style house, do this stuff for a living, so have a good unerstanding of your circumstances - geographical latitude makes a big difference).