Ballpark figure for ASHP?

[Crofter]

I'm finally starting to think about upgrading our laughably bad 1970s house, in order to reduce our bills and improve general comfort levels.

We have (shock, horror) electric storage heaters and an electric immersion vented cylinder for DHW. It's horrible and it costs a fortune, especially as SSE have now put our tariff up to the point where even the cheap rate is something like 15p a unit.

 

ASHP seems to be the most promising way to go for a system that will give a big (three fold?) reduction in running costs compared to direct electric, without all the worries and costs associated with ground works. I'm open to other ideas but my understanding is that for low initial cost, reasonable running costs, and general simplicity, ASHP has a lot going for it.

 

Being a cheapskate I am quite happy to tackle the vast bulk of the install myself. We have a big underfloor space so running pipes will be no trouble at all. I also understand why you need to have oversized radiators, or preferably UFH, for any kind of heat pump to work well. I don't know much about getting DHW from one- is it worth doing, since it presumably still needs a boost from an immersion element to reach a usable temperature.

The other unknown is whether there are aspects of the install that would be best left to a pro- e.g. anything involving refrigerant lines?

 

So, for a 90m2, three bedroom, bungalow, should I be budgeting something like £2-£3k for this? Or am I way off the mark?

[ProDave]

UFH is best IF you can get enough under floor insulation. That may be a big or messy job to retro fit.

 

Domestic hot water is no problem.  I heat the DHW to 48 degrees with the ASHP. I have a 300 litre unvented cylinder.  48 degrees was chosen by experiment as the hottest I could hold my hands under for any length without it hurting. No point having it hotter than that and no need for an immersion boose (other than using up excess solar PV)

 

The hot water cylinder was almost £1K so that doesn't leave much in your budget. you should get an ASHP for £2K if you shop hard, but then there is all the insulation, UFH or high capacity radiators.

 

I assume you are on Total Heating or something similar. Sounds like you need to ditch that in favour of a single rate tariff or even simple E7 or E10

 

What is your current heating input requirement? simply look at a years worth of off peak, how many KWH is that. That will give you a good idea of the heat input the house needs so you can work out what size ASHP you are likely to need.

[Crofter]

Thanks. That's good news about DHW.

I think certain rooms in the house will be OK with radiators, as there is sufficient wall space for them. The kitchen is a bit more of a concern, harder to find free space there.

Does it complicate things to mix and match UFH and rads?

 

A new tariff is definitely on the 'to do' list...

[Nickfromwales]

10 hours ago, Crofter said:

The kitchen is a bit more of a concern, harder to find free space there.

Plinth heater  Wet and electric are available, but the wet version should work ok even at the lower flow temps.

Example only

 

10 hours ago, Crofter said:

Does it complicate things to mix and match UFH and rads?

Yes, as they will heat up at different times to each other. Tha can result in an UFH circuit running a lot on its own resulting in short-cycling. Would ideally need a decent ( 100L + ) buffer tank to feed everything from in order to hydraulically separate the two mediums.

[Hobbiniho]

I had a ashp system retrofitted into my 80m2 3 bed house it cost 10k because i used an mcs approved installer, it is a 7kw panasonic minoblock with a 255l Dhw cylinder with a combination of normal radiators and panasonic air rads i also got a 10k interest free loan from home energy scotland aswell as getting RHI payments which will basically cover the cost of the system if i done my system Diy i probably could have done it for 5-6k but would not get the loan or the RHI payments

[patp]

We have been looking into ASHP. Should the domestic hot water temperature not be raised to 60 deg at least once per fortnight? This is what we have been told as it is to prevent legionnaires disease.

[SteamyTea]

4 hours ago, patp said:

We have been looking into ASHP. Should the domestic hot water temperature not be raised to 60 deg at least once per fortnight? This is what we have been told as it is to prevent legionnaires disease.

Not really as the water in the thermal store is not the water that you bath in, that just comes from the mains via the coil in the cylinder.

And, as far as I know, there has not been a proven case of Legionnaires Disease in the domestic environment.

 

[ProDave]

5 minutes ago, SteamyTea said:

Not really as the water in the thermal store is not the water that you bath in, that just comes from the mains via the coil in the cylinder.

And, as far as I know, there has not been a proven case of Legionnaires Disease in the domestic environment.

 

But you do not want to be using a thermal store with an ASHP, you really want an unvented cylinder.  In which case the water in the tank is your bath water.

 

However we have discussed before that in a sealed tank, as long as the water entering is free from bacteria then there is no risk,. and the consensus was treated mains water was safe.

[SteamyTea]

1 minute ago, ProDave said:

But you do not want to be using a thermal store with an ASHP, you really want an unvented cylinder

I never remember which way around they are.

Is a TS a normal cylinder, and a UVC the one with the coil heat(s) exchanger in it only?

They seem to be used interchangeably too much for my liking.

[Ed Davies]

12 hours ago, SteamyTea said:

Is a TS a normal cylinder, and a UVC the one with the coil heat(s) exchanger in it only?

 

Nope, a thermal store just stores therms; the actual water to be heated is not stored in it (apart from the small quantity in the coil which is completely changed every time a significant draw off is made so not much chance for bugs to breed [¹]). An unvented (or vented) cylinder also stores therms but also the water itself.

 

[¹] Edit to add: maybe not even the volume in the coil if the heat take off is done via a separate heat exchanger.

Edited November 17, 2019 by Ed Davies

[patp]

Friends moved into a house with ASHP fitted. They called out an engineer for some problems they were having and it was he who recommended running the immersion heater on a fortnightly basis.

[joe90]

Like @ProDave says above, some still recommend anti legionella heating cycle but I also do not because of lack of bacteria in a sealed system and no residential cases can be found.

[SteamyTea]

3 hours ago, patp said:

They called out an engineer for some problems they were having and it was he who recommended running the immersion heater on a fortnightly basis.

Probably covering his arse, I would do the same if I was not paying the bill.

[joth]

To be fair it'd be totally unnecessary risk for any professional to ignore or  actively recommend against  following the current HSE guidance

 

http://www.hse.gov.uk/legionnaires/hot-and-cold.htm

 

Edited November 19, 2019 by joth

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