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Need to replace my oil boiler soon and am wondering about fitting an ASHP in its place. We also have a wood burner and an AGA so it won't be a standard MCS installation or qualifiy for grants. Plan to install it myself +/- a small amount of FGAS work if not a monobloc.

Have extensive zone controls already, using Honeywell Evo wireless TRVs, so specifically don't want an all singing all dancing whole house system like Vaillant which I can't interface to. Living room has large rads for quick warmup plus old u/f heating which could take on a new lease of life. In addition we have a stainless h/w tank which I see no need to replace.

Calcs lead me to think in terms of one capable of 6 - 8 kW at 60 - 65 C together with a large thermal store ?3-500 litres to timeshift and make best use of off-peak by night and PV by day in accordance with solar forecast.

Pro's and con's I can already see:
Monobloc - bigger outside unit, can install by myself but would need antifreeze in entire system
Two part - smaller ?quieter? outside unit, need fgas fitter to complete the install, would take up more space in boiler room

What brand would you buy for this application and what else do I need to think about?

All thoughts and contributions gratefully received!

Monobloc for me every time. Far lower likelyhood of the magic gasses leaking out. And you can then use Propane as the refrigerant without worry as it's outside - Propane was used 100 years ago, and is back in fashion again - good high temp capability, and GBW potential of 3.
Personally I'd go for tapwater & inhibitor, and an anti freeze valve at the lowest point outside, instead of glycol - avoiding a heat exchanger.

No antifreeze in my hot water or heating circuit for my outside monobloc, just plenty of lagging.

nowty wrote: ↑Wed Feb 22, 2023 4:15 pm No antifreeze in my hot water or heating circuit for my outside monobloc, just plenty of "lagging".

And the ability to keep powering the house when the leccy goes down.

My plan now that we have battery storage and a generator is to run the heat pump to push a few degrees round the loop if we have a 4 day sub zero power cut again. The COP should be pretty good. We got to 1 degree in one room last time without the ability to run any electrics. I was very close to draining the whole heating loop.

By "anti freeze valve at the lowest point outside" are you talking about a drain valve? Wouldnt want to rely on that, house might be unoccupied in winter but still want to be able to switch on heating remotely.

But revenons a nos moutons. What brand would you buy for this application?

Do you already have a heat store cylinder or is that also going to be new also ? If space is a constraint what about a sunamp phase change heat battery ? that could be linked the the ASHP and any other heat source you have to give you the same output with less space taken up.

Moxi

Thanks, yes I have been looking at Sunamp. In principle ideal, constant temp (if expensive). Two years ago they were offering versions for ch storage but stopped. Was told they will reintroduce 2023 but ATM only for dhw, various versions for different HPs. See also this thread

If not I will have plenty of space where the oil boiler currently is, big floor-standing Archie Kidd job.

What do people think of Grant HPs? They seem to have all the features I want, controlled by voltage-free relay contacts so easy to interface.

Or Samsung for somewhat higher flow temperature?

If you don't care about efficiency chuck whatever you like in.

If you do then design out that thermal store and you'll be needing to use the manfu controls - UK 3rd party options are ****.

Swwils wrote: ↑Thu Feb 23, 2023 10:01 am If you don't care about efficiency chuck whatever you like in.

If you do then design out that thermal store and you'll be needing to use the manfu controls - UK 3rd party options are ****.

Heating system demand is almost entirely 0700 - 0900 and 1800 - 2300, neither period has PV or cheap elec. so I think the thermal store will improve efficiency measured on a cost/delivered kWh basis.

Some manu controls are OK (see Grant remarks above), some are impossible to integrate with what I have got already (Vaillant).

Can you enlarge on yr comments a bit?

sharpener wrote: ↑Thu Feb 23, 2023 9:40 am
What do people think of Grant HPs? They seem to have all the features I want, controlled by voltage-free relay contacts so easy to interface.

I've been looking at a Grant. It seems that you don't actually need the expensive controller you can build your own controls inluding cheap-rate electric, DHW, and the rest.