sharpener

Grant (Chofu) seem to have versatile units where you can interface external controls to many useful functions with a simple contact closure, plus weather comp. Cool Energy much the same. Are there drawbacks with either of these brands?

If you give them the capability they will play with it.

Well if British Gas have already exercised their powers of entry to have their agents fit prepayment meters - against OFGEM rules and the wishes of the householder - you can imagine how much more likely they are to remotely disconnect customers at will if they can do so without leaving their heated offices. One of the reasons I do not want a smart meter. And given that MCS standards are already part of the BUS and Permitted Development rules I can forsee that the remote control of the HP will be incorporated into the MCS rules and disabling it will be made impossible - just as the capability to use HPs for air conditioniing in summer is disabled on MCS listed HPs already.

Yes. EV charging points now have to have remote control built in to them for these reasons. The industry thinking about HPs is I imagine going in the same direction, particularly as they require much the same paperwork as EVCPs. I am not convinced that these are the reasons Octopus told the OP they cannot use his spare way. It will be interesting to see what explanation they give the OP when he asks. I suspect it is more to do with avoiding surprises during the installation process. E.g. is the CU correctly specified for the additional load, do they need to swap the breaker for a Type C (as mentioned above) and then can they source a replacement breaker for that particular manufacturer and board? I have just put a new breaker in a 10 y/o Volex board, couldn't get an exact match so had to modify the busbar slightly, Octopus probably wouldn't want to do that as it voids the warranty. Alternative was to buy a s/h breaker but they wouldn't want to do that either.

Not a tariff I would want to have. My intended use case includes a burst of heating to bring the living room temp up from setback, so full power for a bit at precisely that time of day. If the financial incentive is sufficient I suppose I could add a thermal store to bridge the demand with water heated earlier in the day, it would take maybe 6kW x 30 mins which is a feasible amount.

The Cool Energy 10kW only needs a 20A MCB so I very much doubt a Daikin 8kW needs more. Technically 2.5 mm^2 cable is sufficient for the current but for a 20m run I have a feeling you would need 4 mm^2 because of voltage drop. Would it be longer or shorter taken direct from the meter? If they do take a new supply from the meter position they will have to fit Henley blocks and a new mini-CU with main switch as well. They may deliberately be trying to avoid the HP using the batteries. However as Nick implies, if there is a current transformer that can be moved to a point nearer the meter than the HP connection this will put the HP inside the control loop if that is what you want. But you may find that 19kWh does not go very far when it comes to daily HP usage. (OTOH it is twice as much as I have for a 4-bed barn conversion.) Over what range of SoC do you routinely exercise it at the moment? This will give you an idea of the spare capacity available for the HP.

I can believe that, the ability to create swept bends at will is a definite plus. As posted elsethread the new ch in our house was plumbed in plastic but using swaged elbows at every bend so they have got neither the penny nor the bun!

Advice towards the end of that thread looks more sensible e.g. this <The higher flow rates requirements comes from the smaller dT across the radiators that is sought - gas/oil systems typically specify 20°K across the rads, whereas heat pump wants 5. All else being equal, the flow rate is quadrupled. In round numbers, 1m3 per hour for each 6kW of output. Typically we want the water velocity less than 1m per second in the pipes, so more about 6kW then best to have 28mm flow from the heat pump and branch to 2x 22mm circuits to the radiators (e.g. upstairs/downstairs might be convenient).> I will probably bring 28mm from the HP into the house up to the point the various utilisation circuits split off, after that I am expecting 22mm to be adequate. There is a useful flow rate calculator here. I am a bit surprised @PeterWsuggests 22mm Hep20 as this shows its cross-section is only 2/3 that of the equivalent copper but I might use it for the 28mm run as above, I hope it will be sufficiently flexible to avoid a lot of small joggles done with elbows.

I have noticed that some brands of ASHP require special coatings/treatment of the heat exchanger fins in coastal areas but equally other brands say their HXs do not need it, sorry can't remember the specifics. As well as Blygold there is a blue coating IIRC. Have by co-incidence asked CoolEnergy about this today and will post their reply.

Yes I know, bad idea, I was not advocating @DanDee's suggestion just trying to point out the practical difficulties of implementing it! Mostly I don't think either DIYers or professionals would want to plumb up an arrangement like that. If you have the flexibility your controller provides, the pipework is conventional and it is a lot easier. The eternal trade-off between the optimal CoP and the costs of a retrofit. (In my case the rads are not required simultaneously with the UFH as posted here.) Have forgotten what you have, is it a third party controller?

And not acid like boiler condensate so no need for limestone chippings in the soakaway. Probably better doing this than putting it into a foul drain, you might get smells and I can't think of a good trap that doesn't dry up in summer or have the pressure drop of a bladder trap.

Indeed possible. Would need complicated pipework, you would need to connect the DHW & rads in parallel and then the UFH zones in series, with shunt valves and/or bypass valves to control and balance the flows. And in the end the UFH flow might still be hotter than ideal.

A workaround would be to wire it so the rads and DHW both call for heat at the DHW temp e.g. they have their own motorised valves and you connect the microswitches in parallel to the HP. From the efficiency point of view this is not perfect but you do not suffer from the inefficiency of mixing the flow down from a higher temp when you need only the UFH, which might be for much of the daytime.

As @IanR suggests, being an engineer also involves wanting to have system designs that combine known technolgies in novel ways, are elegant, and do not waste resources. Which is why I am slowly working out how to optimise a heat pump installation for a sprawling barn conversion. So I would rather have to fire up the woodburning stove and the 3kW fan heater on 2 days a year than over-engineer it for an OAT of -15C.

Still basically the same technology to this day. (I used to work for S & H who supplled all your u/w weapons handling gear so have been on quite a few boats whilst alongside including SSNs.) Yes, a lamentable tale. But our Magnox and the later AGR stations all used CO2 as the heat transfer medium, at a pressure that achieved a density about half that of water. (S & H also made the refuelling machines which load the 4 tonne fuel strings into the reactors whilst they are still under pressure.) For Sizewell 'B' we abandoned all this know-how and the UK had to license the pressurised water reactor design from Westinghouse in the US. That is basically the same technology as the submarine reactors, these were originally licensed from the US as well, though AFAIK the design and manufacture are now independent. Hot off the press: nuclear power is now officially classified as "envionmentally sustainable". About 20 years too late.

Small Modular Reactor (as defined here and proposed here - mentioned in the budget so will be in tomorrow's papers)

It's a wonder that piping flammable gas into homes is as safe as it is. Now that open gas fires are less common the flame visibility is not important except that hysdrogen requires new flame failure detection methods in boilers. More important is that CO poisoning is not possible. The recent and seemingly more frequent incidents of property demolition by gas explosion probably don't have much to do with the exact constiution of the gas. Perhaps more likely due to tampering with the supply e.g. bypassing the meter. True. As you say, the equation changes once the renewables displace more than just the load-following CCGT generation. Large-scale nuclear not much help here, SMRs might be a bit better as they were developed for nuclear submarine propulsion. But then again they have in the past been plagued by thermai stress/cycling issues so am not holding my breath. And the RR SMR concept is not really "small" anyway.

Thanks both, will have to factor that in. Flow rates seem to be almost exactly 1/2 with 10mm and 2/3 with the rest. Hope I might save as much on bends as lose on straights though. Had refit of ch in another house ~8 yrs ago, plumbers used all plastic (except for rad tails for appearance), must have cost them (?me) a fortune in fittings and labour as they still had a copper-pipe mentality and put in heaps of elbows instead of just bending the plastic.

I notice all the gleaming new copper pipe in these two pix, albeit with push-fit fittings. What do ppl think about using PolyPlumb, I have used it a lot for my rainwater harvesting system and found it so much easier to work with.

So up to date then. The difference might explain the better CoP figures mentioned by @DanDee in this thread.

Sorry @JohnMo but it is the same R410a one, the current Grants use R32 though it is not clear what exactly the OP has bought, perhaps he will tell us? <It is normal to have a buffer on the central heating side of the 3 way valve.> Not what the Grant manual shows, [6] is the volumiser in the pic below. If you are going to have one at all then I would think it would still help to have it in circuit for the DHW (as they do). But you could argue that when the CH cuts in you have the extra volume of water at a higher temperature than you want/need/is good for the efficiency. N.b. the pic shows an S-plan setup, this allows both circuits to be in use at once, best not to allow this as the temps you want are very different esp without a blending valve. As others have said this allows for a drop-in boiler replacement in a system with just rads, but the downside is you get far from optimal efficiency with any attached UFH. @JamesPa <wrote Conclusion was that a 5 C temp diff and a 3sq m coil was ok with my planned hp which modulates down to 4kW> So almost certainly OK with the OP's 6kW unit then.

Useful stuff @JohnMo but what is the volume of the DHW circuit and how do you stop it short cycling on DHW only? I imagine this is why the Grant manual requires a volumiser under all circumstances. Though AFAICS the Chofu manual does not. (Also it may not be current as I have just noticed it says R410a refrigerant.)

How small is a "small" unit? Stick with the min pipe size to match the HP tappings as per the Grant instructions here, which is 3/4 in or 22mm for the smallest. There are also the Chofu instructions here which do show UFH but unlike the diagram on p14 you could omit the blending valve. As @DanDeeimplies this is only required for a boiler flow at ~60C, then you do not need a secondary pump or LLH either. As you will see from the curves on p13 even the 6kW unit has a pump easily able to push 16 l/s against a sizeable pd, actually it can develop a higher pressure than the 10kW. Grant do stipulate using a volumiser, you will still need this to prevent short cycling on DHW only. On p13 they say install it on the flow if it has an auxiliary heater, however on p18 they show it on the return which has lower losses, there are extensive discussions about this on this forum. Good luck, let us know how you get on!

That's one of the constraints I'm working with. The previous owners who did the barn conversion built the cyl into a loft void above the airing cupboard in a way that makes it extremely difficult and costly to replace. However from p99 of the installation instructions kindly posted above it looks possible to command the Grant/Chofu HPs to produce DHW by an external contact closure with the thermistor input disabled (p. 97) Can you see any reason why the existing thermostat (or the switch on the S-plan valve) could not do this? This control interface is for me one of the attractions of this particular HP, it is supposedly marketed as a replacement in S-plan boiler systems though I clearly want to optimise its performance as a HP. The other bright spot is that the wiring for this valve is already in place down to the utility room. Although the 4 cores + E could be re-purposed I am not sure whether the tank has a suitable pocket for a thermistor. No I don't know why they didn't just bring the 2 stat wires down and put the valve downstairs where you could get at it but there are a lot of things I would have done differently. Luckily I am ATM still able to get parts for the Kidd boiler even though they have gone out of business, but the former service manager who now holds the stocks is nearing retirement so it is very much on borrowed time.

Yes but I see no harm in first giving the HP a chance to do what it can 0300 to 0500. Depending on the siting of the coil vs immersion vs sensor the convection might mix the tank better giving you more stored heat overall.