sharpener

I built a little circuit which is triggered by turning on any of the bathroom lights, it pulls in a relay which increases the MVHR fan speed for 8 mins. (SWMBO did not want 15 mins which is AFAIR the time stipulated in the Building Regs for WC extractor fans.) Only occasion I have designed an OR-gate using 240V AC logic levels.

This has puzzled me too, I guess the explanation that the refrigeration cycle requires it on efficiency grounds it the closest we will get. The other constraints are the available head from the pump and a velocity limit of ~ 1 m/s to avoid flow noise in the pipework. For instance here is a result I got yesterday when considering a Grant 10kW - which has a min flow rate of 10 l/s and a max pump head of 6m i.e 600 mbar - to see what happens when only one TRV is open. From this ready-reckoner the pump can push 10 l/s through 44 m of 15mm copper pipe (which is about the distance to my furthest rad) with a velocity of 1.2 m/s. But with 15mm plastic pipe a head of 600mbar will only cope with a 15m run and the velocity is 1.6 m/s which is too high. The cross-section area is only reduced to 3/4 but the resistance is 3x as much because it is proportional to a higher power of the velocity. So this HP should happily supply my furthest rad on its own, there is about 10m of plastic but OTOH at least some of the intervening pipework is 22mm. In any case I am planning to maintain the minimum flow rate by way of an automatic bypass to the return to the buffer tank.

Yes I was interested in them for the thermal store capability. As they are less than 50 miles away I will take advantage of their face-to-face consultation option since what I want to do is quite complicated.

Chelmer Heating seem to design and supply integrated systems for self build and renovation projects. I wonder if anyone has used them in the past and can give me any pointers as to their capability?

I have been wondering about this. ATM I am charging to ~50% at night rate and the sun does the rest most days and there is enough left over for the HW. I don't think when I install the HP I will put it downstream of the battery system, as in a power cut it would exhaust the battery very rapidly leaving nothing for lights or cooking. If I tee it in before the battery CT then the battery will have priority but the HP will still have the benefit of any residual PV before it is exported. Like @SteamyTea I have a timer so the immersion heater can come on to top up the HW temp after the HP has done most of the heavy lifting with the benefit of the CoP. Currently I do the reverse, the immersion stat is set higher than the tank stat so the oil heating only comes on at the end of the day if the PV was insufficient.

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.