sharpener

Not in fact the OP but @saveasteading, from whom despite several responses we have not heard since Sunday. Well aware what he asked, but he suggested the figure of £15k, and I agree with you what he is asking for is way beyond the capabilities of even a large domestic installation and certainly not achievable for £15k. As you wrote earlier: Is the right answer.

Reported in this link from Heat Pumps Today newsletter. Full report downloadable here. Well worth a read, IMHO contains many sound and practical recommendations for levelling the playing field (gas vs electricity and HPs vs boilers), simlifying PP and DNO approval, increasing/training the workforce, and international comparisons. @JamesPa and @Beelbeebub will be particularly interested I think as all readers of this forum.

As upthread you might get 10kW pk installed power for your £15k budget. Facing SW you would need something like 75 sq m plan area of roof for that allowing something for margins, chimneys etc.

Well what do you know! Every day a school day. 43C flow is quite high for UFH. Assuming you are running weather compensation turn the slope down by 0.1 per day until it gets too cold then back a bit. If not then switch it on. Well during the daytime a Willis heater will use peak rate electricity with a CoP of 1.0 which is less than ideal. If your tank has an immersion heater then it would be more economical to heat the DHW with it at night-time rate, freeing up some HP capacity if you need it. If not, can you fit one, might be cheaper and less disruptive than a Willis heater. So that is 42W per m^2 which is not very generous according to this cheat sheet and might not be enough in a cold snap, air changes per hour are crucial so stop up the draughts you mention in the OP!

Were it facing due S that ought to buy you something north of 10kW peak. Have you got the roof area? How will you get that much past the DNO? Even with a big battery in addition I don't think it would begin to keep an ASHP going. I have got 7kW of PV and at this time of year it has been generating about 11 kWh per day. This is enough to fully charge my 10kWh of domestic storage but that only provides 400W averaged round the clock. So the EV has to charge from the mains and the HP will I think have to do the same.

Yes but when does the HW go off? Until that time it will inhibit the operation of the UFH (unless the HW demand is satisfied first, by the tank being up to temperature). You say can you see the three-port valve at the point the circuits diverge and can you do anything that moves the valve actuator? Also in the pix above are the displayed values the setpoints or the actual temperatures?

I think we are at cross purposes here @Beelbeebub. I was merely trying to say (i) we have two existing appliances which run without any electricity at all so it would be wise to keep them as an insurance against power outages and (ii) we would need to expand our battery setup by a lot (like double it in size for ~£3 or 4k which I do not plan to do) to provide a worthwhile backup for the new HP. (I have already upped it from 7 to 10.5kWh in the light of experience the first summer but we would have to re-locate it to add a fourth module on top). Yes the existing battery will run it at full o/p for maybe 3 hours but that presupposes it is full to begin with. By nightfall that will not be the case unless it has been a really good day for PV. I have yet to do the modelling to see whether Octopus Cosy or some other tariff will give the lowest cost, and investigate whether it makes sense to re-charge the battery at daytime rate to run the HP during the peak 1600-1900. Controlling the system to optimise all this may not be easy without some additional hardware as for that we would want the HP inside the inverter control loop but otherwise not.

Sounds like your system is stuck in DHW mode, this will take priority over any heating. If there are backup heaters these should be fairly obvious both physically and from the setup screens. Suggest you set DHW to come on only 0500 to 0700 (or whatever suits your off-peak tariff) and see if things improve. If you need more HW than that provides, divide it up or find the lockout setting which should stop HW production after e.g. 30 or 60 mins to allow UFH to have its turn. Lots of help available here but need to post details of system, make and size of HP, size of HW tank, sq m of house, # of occupants etc

Planning to keep our AGA and WBS for exactly this reason. Existing 10kWh of Pylontech will keep the oil boiler running for a bit but would last no time once 12kW Arotherm Plus is installed (hopefully spring 2024), so it will go on the grid side of the inverter metering.

IIRC though I can't provide a reference it is better to have a 2-port buffer aka volumiser in the return to the HP so the stored heat is directly available for defrost. I don't think two cycles an hour (though not ideal) is much to worry about if you are achieving the target indoor temperatures.

Might not be trapped air. On my UFH the flow regulators are very susceptible to blocking with crud. Opening the regulator and closing all the others on the manifold usually shifts it. The bubbles might just be incidental. Do you have any filters, or air release valves?

Nor a storage heater I imagine.

Quite cunning but the drawback to all schemes involving mixing valves is that the HP has to run at the higher of the two temps, so you get the lower of the two possible CoPs all the time. Is there any possibility of a bit of time division multiplexing so you can run each zone on its own at the optimum flow temp, for part of the time at least? Similarly, I am about to re-do my (current, gas-fired) HW programming so it heats up while the CH is off and hence doesn't compromise the weather comp and the attendant condensing mode operation.

Very likely it will be (at least using MCS methodology) because if near the boundary it's more likely to be screened from the neighbours' windows by the fence. This gives you an extra 5dB if partial or 10dB if complete screening to play with.

Think where we would be now if we had pressed on with the Sizewell B design and built a fleet of those as was the original intention.

See this article in Telegraph

Not really a horror story. Mostly it's because elecricity is approx 3x as expensive as gas, but the CoP of an HP is also in the region of 3x so the cost relative to a gas boiler is down to small differences in the two and may be more or less. Hence the emphasis on running the HP from off-peak electricity as far as practicable. The amount of energy needed is beyond the scope of small domestic battery systems. The situation in Norway is rather different, they have a history of cheap hydroelectric power (dating from before their exploitation of oil and gas fields) so saving 2/3 of consumption by upgrading from resistive heating to heat pumps is a no-brainer. There is also much more use of MVHR which helps.

Some of the claims in that link are pretty doubtful though. Afinia aluminium radiators are more efficient than traditional radiator materials, such as steel and cast iron Incredibly effective thermal conductors and with low energy consumption, Afinia radiators can help lower energy bills The range can deliver exceptional room comfort, heating up and cooling down very quickly which allows Afinia radiators to respond quickly to any changes in the temperature demand set by the thermostat Except for heat lost from the back via an external wall (which will not vary a great deal) all radiators are 100% efficient in terms of the heat getting from the pipework into the room. The radiators themselves do not and cannot have any intrinsic "energy consumption", low or otherwise. (Even with fan-assisted radiators the motor power ends up in the room.) Claims about warm-up time are I think illusory, the thermal mass of the metalwork is small compared with the water content and very small compared with the room itself. All the usual misleading advertising guff IMO.

Why? The property owner may see a big bill for lots of short-term disruption and a very long payback time. If the property is rented the owner and occupiers interests are not very well aligned. The landlord will have to increase the rent to get a return on the capital investment, it is easier just to invest in more property. An issue peculiar to the UK is the large proportion of Victorian housing with solid brick walls. Insulating these either inside or outside is costly, disruptive and/or unsightly. Space to fit HPs to terraced housing under current planning rules is often non-existent. Tragedy of the commons. Benefits in terms of CO2 reduction do not accrue to individual households. Legislation gets watered down/delayed by powerful new build industry. Enforcement of building regs is poor leading to e.g. weather compensation being fitted but not actually commissioned to avoid callbacks. Peoples' expectations need managing too. HPs will in most cases not reduce heating bills significantly so why would they embark on retrofitting them? Hence unless part of a larger refurbishment it is a hobby activity for those with lots of interest, time and spare capital. Education about all this from basic science and arithmetic upwards, at all levels from householders to Cabinet is what needs the massive "improvement".

Can get quite cold there esp if up in the dales, the MCS design rules take account of predicted min temps and altitude. According to my go to cheat sheet yr house could need anything from 40 to 65 W/m^2, so a 5 to 8 kW unit. This means almost every manufacturer's single fan models so it will come within Permitted Development under the planning legislation. Also you need to verify your house power connection is adequate, but not likely to be a problem with this size of HP and age of property. Another consideration is choice of refrigerant, R290 will enable you to reach higher flow temps than R32 and if the rad sizes are marginal it might help, but the MCS (and hence BUS grant) rules don't really allow best advantage to be taken of this anyway. Try playing with this interactive toolkit.

I know lots of electricians and a couple of plumbers who have experience in heating. How difficult is it to install them? Not difficult but needs familiarity with heat pumps. To get the grant your installer must be MCS registered (like allseasonenergy). To provide extended warranty the installer must be approved by the HP manufacturer. Will heat pumps work with my designer radiators? Possibly. As part of the quote process an MCS firm has to do a full room-by-room heat loss and emitter survey, this will determine whether rads need upgrading. House is already well insulated but do I need more? Possibly. You will need to have an Energy Performance Certificate which does not have recommendations for more cavity wall or loft insulation. This normally means you need 270mm already in the loft. I’ve briefly spoke with this company https://allseasonsenergy.co.uk/ who seem to know their stuff and have some cracking reviews. Anyone know them? No. They look similar to many other MCS registered firms. Their web site is quite impressive but that's the easy bit. Talking to several bidders (ideally local) will give you more of a feel. Also the energy firms like Octopus and Good Energy are entering the market now for simple straightforward installs. Whereabouts in the country are you? Can you give us an idea of the age and construction of the house and its floor area in sq m?

You seem to want to run with the hare and hunt with the hounds on this one @Beelbeebub!!! I am sceptical too but I think this direction of travel is more or less inevitable. I fashioned my own internet controls in 2009 and my son has been using his Tado for many years now and moved house with it. I think you have to consider the fallback options available. If it optimises the HP settings in the light of its experience and after that makes only small adjustments, a temporary outage is not a big deal. And if all else fails £200 written off is not a big sum compared with the possible improvements in energy saving or comfort.

Seems things are moving in the right direction. Went this morning to a seminar by Paul Williams of Homely https://www.homelyenergy.com/. Uses wireless temp sensor plus UV sensor and online weather data to optimise HP settings, with a 14 day initial learning period. Claim it currently interworks over ModBus with Samsung, Midea/Riello, LG, Ebac, Airwell, Clivet. User interface is a simple phone app with intentionally limited settings. Integration with Vaillant & Mitsi in development but needs them to produce proprietary interface boards. Integration with EV and PV also in the works. In comparison with normal weather compensation they claim 3% improvement in CoP and 6% energy saving. Cost ~£200 plus £25/yr optional subscription for smart service to accomodate variable electricity tariffs.

Depending on how it is wired/timed this pump will be mixing the contents of the tank so will spoil any stratification. As @Gary68 says, your tank should be more than sufficient for two showers and a great deal else.

I am planning on a 12kW Vaillant Arotherm Plus. The quoted nominal flow rate is 2065 l/hr and the minimum is 995. The former is 34 l/min which according to this flow calculator is 1.0 m/s in a 28 mm Cu pipe which is about the max to avoid noise and erosion (opinions differ a bit). Vaillant do not make any specific recommendation about pipe sizes. 1 kW is 860 litre-degrees per hour (3600/specific heat of water). So to check the heat transfer capacity for 2065 l/hr at 5 deg delta T you divide 5 x 2065 by 860 which comes out at 12.005 kW. So yes it is possible, an 11kW unit with 28mm primaries will require a flow rate of only 11/12 as much for 5 deg i.e. 0.917 m/s which is fine and gives you a margin for using glycol.