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We having a bit of an issue that I'm looking for some help/thoughts on. We built a house last year and have GSHP and Solar thermal. We specified having a stove (we supplied stove and told company what stove we were going to buy right at the start) with back boiler connected into the system. I've attached a diagram that is a rough plan showing how things are connected.
Basically the stove heats water in a buffer tank and when that's up to temp excess heat from the stove goes to the 2 heat dump rads. The buffer tank transfers heat from the vented system that the stove is on to the unvented system that VPAS cylinder is on. When the VPAS cylinder needs heat it pulls water from the buffer tank if it's up to temp.
The issues is that the VPAS is only being used for domestic hot water. Space heating the in the form of UFH uses JUST the GSHP. The heating company that has done this work for us has said the following: "you cannot ever connect an unvented stove into this type of system" and if we did connect the UFH to the stove "this would not comply with the unvented regs and building regs and thus no accredited MCS installer can sign this off"
I'm really not sure about this. Our installers have said that this is what NIBE (heat pump suppliers say) but I can't see how this is the case as basically the buffer tank is just a big heat exchanger that effectively moves the heat from the vented to invented system safely.
Don't expect a large corporation such as NIBE to offer bespoke apps, won't happen. And no, you can't connect an uncontrolled appliance directly to an unvented cylinder under G3. The comments about connecting a stove to UFH are not of course accurate - though may not be possible in the system you have installed!
In principle, however, what you want to do can be done. Just not directly. The question is whether there is enough benefit now that the system has been designed to 'waste' heat aka heat dump rather than store it with suitably-sized TS. Cannibalising a newish system may not be high on your wish list.
If you can give buffer size, VPAS detail (what does that stand for? WHat kind of cylinder is it other than the obvious?) and stove boiler output you will be more likely to get some analytical comment.
Buffer is 120L, VPAS is a NIBE tank in tank cylinder (http://www.nibe.co.uk/Home-Owner/NIBE-Heat-Pumps/Water-heaters/Water-Heaters/VPAS/) with a 300 litre tank for domestic hot water with a 450 litre jacket to heat it and also for heating although as we're going straight from the heat pump to the UFH we don't use the jacket water for that purpose. Boiler output from the stove is about 9kw.
This has come about because the heating company said they couldn't attach the stove to the UFH (despite this being part of the tender) so I found the attached docking diagram on the NIBE Swedish website that shows (in Swedish) how to attach wood burner to our heat pump so you can use heat from it for DHW and space heating. Apparently this can't be done this way because it would contravene UK building regs. What I don't understand is we have a system that safely transfers heat to the buffer tank which is on the un-vented system so surely that will satisfy the UK regs?
Sorry for delay, took a butchers at the KoKKSPISS (drunken rooster drew it?) and it is classic 'do not fiddle' stuff. Ideally what you want, with a decent 9KW from the stove boiler(assuming the space heating area is enough to dissipate the resulting radiant heat) is to heat a decent-sized thermal store rather than a buffer, the store acting as the heat leak too, THEN send heat to your unvented cylinder via motorised valve.
This isn;t going to happen with the installation you have, sadly. They seem afraid of mixing temperatures - ie heat pump and woodburner. What made you decide on this system?
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