ASHP - to DIY or not to DIY

[Gerrybean]

Hi - after a major refurb I now have UFH on 2/3 of the ground floor (as much as I could screed in the new extension, plus a bit more) AND am being offered a second hand, 7-year old Mistubishi Ecodan W85. To me I thought it would be a no-brainer to fit the ASHP to the UFH and leave it quietly dribbling heat into the ground floor.

Then I got a quote for £4k PLUS controller (£750); PLUS electrics, PLUS elec and plumbing connections to the heat pump, PLUS the slab. Looking like £6k just to fit together the bits I already have.

How difficult actually is this? And should I try it myself? (And if I do, how difficult will it be to make my own controller - given that I've done just that perfectly well for the rest of the heating system?)

 

[Gasguru]

You want to check out the repair costs on this eco nonsense...with some of these units 3K bills are not uncommon.

 

[ianmcd]

I wouldnt have a brand new one,never mind a second hand one, the spares are eyewatering

 

[endecotp]

quietly dribbling heat into the ground floor.

Quietly?

As I write this, I am listening to the buzz of the ASHPs at the back of the hotel at the end of the road.

To be fair, they aren't as noisy as my upstairs neighbour's central heating pipes expanding and contracting...

 

[muggles]

It's not a boiler, you can't just lob it onto a pair of pipes and turn it on. They need to be fitted properly, and you'll need a buffer tank installing somewhere between the heat pump and the UFH

 

[dilalio]

And you need to have a glycol filled primary circuit, and all sorts of heat loss countermeasures.

 

[Gerrybean]

OK, all interesting, thanks. Point about repair and spares costs very well taken, thank you. Also I get heat loss calcs; and I get the need for glycol.

What I don't get is the need for a buffer tank. I can see it would be necessary for DWH, but this ASHP is just feeding UFH set in concrete, which is itself a buffer. Wouldn't a buffer tank big enough to store that sort of latent heat need to be humungous? What am I missing?

 

[muggles]

The buffer provides hydraulic separation between the heat pump and the UFH, so they can both flow at their respective optimum rates, which may well be different. Probably doesn't need to be very big, maybe 25-50 litres

 

[Gerrybean]

Ah, that makes sense. Thanks.