UKH

We're planning to dump our decrepit gas boiler very soon and switch to ASHP.  It's tricky to actually save all that much money when you're on mains gas, even taking RHI into account - gas is just ridiculously cheap - but the CO2 savings are considerable.

I'm looking at a few different ways of plumbing it all in - via a thermal store as a buffer or not, and incorporating a woodburner with a backboiler or not.  Rather than dumping a wall of text on here (my working document runs to seven pages) I wonder - is there anyone on here who'd be prepared to take a look at it for me?

I can comment on the high level strategy of it and it's potential payback etc which is my day job. Nothing practical though!

I'd also be interested to have a look as I'm doing some thinking about it on a personal basis also. I've just done some quick checks with some high efficiency propane heat pumps which are compatible with an existing leaky stone cottage and it looks operational cost natural at best (without RHI) which is poor when you look at the huge capital cost uplift.

DM me.

I design and install these systems as part of my job, so can advise on this. 

First note, is keep it simple, do not try and do the thermal store wood burner thing, I've seen it tried and it never work as well as a  simple efficient system. Systems with lots of inputs are complex and lack efficiency.

As s rule, get a Monobloc unit with an unvented cylinder. Connect this to UFH or Radiators designed to run at 40 degrees.

The Mitsubishi Ecodan with its own cylinder is by far the best and most refined unit we have dealt with. However like all heat pumps , it needs to be installed correctly or you won't get it to perform as it should.  All the horror stories you read are usually badly installed systems using poor quality products.

The first thing to work on should be the insulation in the house, concentrating on the details and edges everyone misses out. By reducing the heat loss, you reduce you bills going foward, and make any system work better.

When they are done right, heat pumps with low temperature heat emitters, are by far the most comfortable way to heat your house.

This is all good if you can reduce heat losses to something where a LTHW system running at 35 has the capability to meet your heating demand.

I think I will need +100 w/m2 and with big rooms, meeting this with radiators will be a challenge. Reducing this without a total refurbishment is going to be really tough.

Hence I've been looking at enablue units which can output at up to 90 with a CoP of 3.6 and plumb into existing distribution.

Here's my understanding:

For a HP to work with COP >> 1 you need the radiators to have as low a temperature as possible. That means them having to be really big, ideally as big as, and if possible actually being, your floor. If that is not big enough, because your house is not well insulated enough, you're stuffed.

If your house is well insulated enough, there will be carbon and in-use financial savings, but the latter will be so tiny as to make it seem like a bad deal. 

Nationally, that's the conundrum.

Hmmmmmmm….

Thanks, all - I have sent a couple of DMS.  We do have wet UFH so the big emitter side of things is sorted, and the insulation is good (and will be improved upon further).  

The biggie for me is trying to project carbon emissions and costs, and working out which combination will serve the best.  If I can simply break even cost wise and save CO2 then I'm quite happy with that.  

https://enerblue.it/en/natural-refrigerant/purple-hp 

Obviously there information could be bollocks but if taken seriously they deliver really hot water with high efficiency.

Thanks, to me the headline figures seem unfeasible in a real world Uk application. I can’t download the data sheet at the moment but intrigued to have a look next week

No they make you register. I got suggested them by a supplier who sells unfeasibly high efficiency combined heat exchanger plus DX coil air handling units.

He is either at the forefront of novel technology or pushing dubious efficiency data! I'm yet to decide.

If you're back up this way any time soon you can come and see ours.

For RHI you can't mix heat sources, so be careful with stove back boiler into the cylinder. I considered similar and couldn't - but it might have been that I was going to couple into the rads too - 7 years ago now, so can't fully remember. It's a good idea as a backup, we have solar thermal for summer HW.

Anyway, we put in a stove just in case and the heating is so good we have to turn off the lounge rads to justify the stove in winter! 1 cubic metre of firewood has not run out after 7 winters!

When you choose the heat pump, consider which have the necessary controllers to integrate with your electricity provider. You can link Nibe and Octopus Agile. https://www.homelyenergy.com/nibe

I'm kicking myself for not coming to have a look at your setup last weekend.  Possibly in the next couple of weeks I can get away again.

We're currently on Octopus Go (for the car).  I'm not sure if it'll make a significant difference switching to Agile; the guaranteed 5p for four hours is easy to plan around, and I have the problem that in the daytime the Agile price drops in sync with my PV output (so it's cheap just when I don't need it).

Where I think the real gains could be made would be a battery system combined with a big thermal store for the heat pump: charge the battery on cheap electricity overnight, use that to drive the ASHP in the warmest part of the afternoon, release that heat the following night.  Just need batteries to drop in price to make this financially viable...

Just out of interest, why is this?  It seems to me that the store is just, well, a store, and the inputs can each have their own coil at the correct height.

I ask because we have a gas boiler, solar panels and a back boiler all hooked to ours and it works great!