JohnMo

Believe you need to be G3 certified to sign off an unvented cylinder install. You can do most the work yourself, as long as you can suitably certified plumber to sign it off. So no idea why you would want building control involvement.

Put some polythene over the top, as concrete reacts with the aluminium

Update After getting lots of other jobs done, got back to the ASHP install. Ended up spending about £2500 all in. I didn't have a cylinder to purchase. Basic description of the setup. From heat pump to house is run in 28mm a mix of copper and Hep2O. The summer house is about 8m from the 28mm pipe run and is run in 15mm Hep2O pipe, the UFH has 2x loops 50m long each. This system has a 2 port valve that closes on a DHW cylinder call for heat and when thermostat in summerhouse is hot enough. The summer house is not setup to call for heat. Once the 28mm pipe gets into the house it is reduced to 22mm and via a 3 way diverter, goes to the UFH manifold where it is distributed around the house via 7 loops. The cylinder is fed via pre existing 22mm Hep2O piping originally installed for the gas boiler to UFH manifold these pipes are around 8m long. Calculation shows the pressure drop for cylinder heating are way to high. To fix this I added a pump in to the return pipe from the cylinder, the pump is powered on, at the same time as the 3 way valve is powered to move to 3 way valve to DHW heating. It seems to work and gets the flow back to 1m3/HR. Had the Maxa heat pump running today. Very quiet in operation, have set to run on WC, and it is basically running on min temperature of 25 deg. Also tried it on cylinder heating, the heat output slowly ramps up until it get to 60 deg flow temp, after this it shuts down. Have set up to run without any pumps or mixer valves on the two UFH manifolds, one in the house and the other in the summer house. Bit of fine tuning to do tomorrow. And loads of pipe to insulate. Photo showing the return DHW pump set up, pump temporarily propped up in a surface mount switch box. Wiring to pump and 3 way valve needs to be clipped in place tomorrow. UFH wiring centre is no longer used as the house is run on a single zone. The thermostat controls the heat pump directly.

The original design by architect and structural engineer had the framing of the windows and supporting the roof in wood, the posts were huge and ugly. Challenged the design, and it came back in 200mm box section, so calculated what was needed and challenged again and ended up with this

That's a quick rabbit hole to close - no PV generation in winter is pants. About 10 to 20% of summer performance. Spend on insulation

Mounted inside next to consumer unit, so no meter box. During the build it was mounted in an external meter box, until wind and water tight, I then cut the box off the meter.

I started using Dulux trade paints a few years ago. Not cheap but good covering power. For anyone interested B&Q, and Screwfix and other outlets are way cheaper than Dulux trade centres.

Interesting that is how you do Durisol, 6 levels at a time, fill 5.5 blocks, repeat.

Did it myself, with the wife as additional labour.

That is not perfectly correct. It does allow a hybrid system to be used and installed. But the heat pump should be designed to match the design temp. The design temp our house is -3, but we had a few weeks this year, where for long periods it dropped to -9 or below. So for this circumstance hybrid is ok. There is also a whole section talking about hybrid controls. You can't get the £5k grant with a hybrid system but MSC allows a hybrid, within the design criteria. Here is the wording from MCS heat pump guide. Heat pumps should be selected as closely as possible to the design heat demands. MCS Standard MIS 3005, requires the unit to achieve 100% of the duty at an external temperature condition exceeded for 99.6% of the year, if reasonably practicable. It also stipulates that supplementary heat is not permitted from direct electric at external temperatures above the design external temperature (“bi‐valent point” or “balance point”), but other alternative auxiliary sources of heat are permitted where this is not reasonable practicable in which case the system becomes a ‘hybrid’ system. Although additional supplementary heat may be required when the external temperature drops below the bi‐valent/balance point, this will occur for very short periods of the year and therefore does not significantly affect overall seasonal efficiency even when direct electric heat is utilised. Therefore, heat pumps should be selected as closely as possible to the design demands.

Where did you find best? And what hysterisis are you using?

I think you may be correct, but I have it, so I will try to see what I can do with it.

Sorry not the best sketch, top sketch is hot water flow - if below 45 all water flows to combi. If above the the water goes via a mixer to the taps. The heating sketch, will now be cylinder heating, the UFH heating pipes are now deleted, and the combi will become an ASHP.

My cylinder is a 160L thermal store, already fitted with a PHE, on the heating side in addition to the really small coil designed for 80 degree flow. It is currently only heated as buffer from UFH flow to temper water going to a combi boiler in winter via the DHW coil. And heated in summer with PV. My intension is to heat to 50 (or the max temp I can get) using ASHP between 10 and 11 using excess solar (more efficient than immersion) then let excess solar drive the immersion to whatever temp I can get. I am leaving the almost new combi in place for now, but it will not be hooked to the UFH.

My heat pump install (6kW) is not next to house so the pipe run up to the manifold for the UFH about 10m (28mm copper and Hep2O), to get to the cylinder is another 8m each way. The piping I want to use from 3 way valve to the cylinder is already pre installed and it 22mm Hep2O, so the pressure drop is way to high. My solution is to add a pump to the return leg from the cylinder. The 3-way valve and additional pump will be supplied from the same supply via the heat pump. When DHW calls for heat, the 3 way valve is powered so will the pump. Heat pump demands its own pump runs at 100% speed at all times during DHW heating, so I should be able to fine tune the running speed of the additional pump without it all chasing it's tale.

You do intelligent installs, you do close spacing for given reasons, the UFH warehouses that do paperwork design are really doing sales based design, they just want to sell products, so all designs come out with a house full of pipe, every room has a thermostat and it needs a buffer.

Really they should outlaw S and Y plan, and make hot water priory or X plan mandatory for all new gas installs. They should also make low temp emmiters run on weather compensation and 3m2 cylinder coils mandatory, so all gas installs are HP ready, but make gas boilers condense in all conditions, to give efficiency over 100%.

I will be try cooling via 300mm centres this summer, flow temp at 18 for a start, to see how it goes and should have condensation issues. Last summer drained some water out of the floor mid summer and it was sitting at 25 degs. So 18 deg should give a cooling effect - I hope.

Basically the supplier are being bone idle, they assume everyone has crap insulation. As little thought goes into the design as possible. Although I know @Nickfromwales likes to use close centres, but I prefer to use wider spacing, easy to install, run on WC, it slow and stable, you will still have plenty of water in floor assuming single zone not to need a buffer for a suitable sized heat pump, on a single zone or may be ok for two zones equally sized. Most heat sources will not go below 25 degs in heating mode, I still only need 25 deg flow close to zero degrees. Different flow temps for gas or heat pump is strange as they are assuming you will have different delta T across the UFH depending on heat source which isn't correct. You certainly won't d.get a delta T of 20 at flow temp below about 60 from a gas boiler. I used euro cones and euro cones to 15mm adapters. Think that's the one I down loaded loopcad.

Someone did that near us, company rep went to site, just before first pour and told them to take the whole lot down, as blocks had not been consistently stacked sometimes the thick insulation was inside and then outside, inside corners had been butchered to use as outside corners etc...

I took a year to get my gas boiler running as efficiently as it could, oversize boiler installation in low energy requirements and low flow temp house. Basically got it to around 110% efficiency doing heating. From about 50 to 60% due to short cycling. The heat pump is basically installed now, just a couple pipes at the UFH manifold to sort and fill and bleed, other work keeps getting in the way.

I used Durisol, half the the house is clad in stone slips, these are attached directly with flexible outdoor tile cement, the other half is wood clad, used breather membrane, wooden battens directly screwed into the woodcrete. All pretty simple.

Really all depends on how you compare. ICF, can be put in just about any weather, block work has limitations. You can easily do it yourself, or are you paying for a squad to do it for you? You need to do a couple of concrete pours, do you have access for the concrete lorry and the concrete pump lorry and boom, depending ICF system, you may need to factor in support props for the pour. Block work you need access for a cement mixer, and somewhere to drop of blocks. Really depends on a number of factors. I did ICF and there is a post I did a while ago that details all our costs, it wasn't that expensive. But I did all the work myself with a paid guy to assist me. The walls were completed in Dec 2020 and me 4 weeks to complete, 70m perimeter by an average of just over 3m tall.

I used 10mm

Just to counter the above what about the hour or two heating the cylinder when the ASHP could be running flat out even in the summer.