JohnMo

Well done, plus good thinking out the box.

Not sure if these comments have been made before. Accessibility toilet - missing TV room is tiny Utility just looks wrong and is plain daft in scale, really long and thin. Entrance hall looks a waste of good space. As @Thorfun says, get the professionals in and do a proper job. Worth every penny if you choose well.

Every EPC I have had done (possibly 10) I walked around with the surveyor and told him the answers, he needed. Our new house came back with loads of incorrect inputs, so clarified and provided evidence as required. These things are treated by many as a one way street, but most are just a desk top exercise, so the person completing often needs assistance, to get the correct output.

Mine is cold to touch and its only a C rating, piping losses will exceed any cylinder losses.

Heat pump sizing is simple enough. you need a heat pump that can deliver your required heat in about 22 hours, this leaves 2 hours for DHW heating. Other other thing to look at is output at your flow temp temperature and lowest outside temperature. This where you need to start looking at different datasheets. Some manufacturers quote the best output figure others the minimum, so headline 7kW doesn't mean the same thing, when comparing products. So you looking for around 8kW output at say -3 to -5 A 10kW Grant heat pump at -7, has a rated output of 8.1kW. So is fine, the next size down is 6kW and is too small. A 7kW Vaillant for example is fine until flow temp required at -5 goes above 45, at 50 it will struggle and outside temperatures below -5 would struggle also.

As an experiment I installed 2 Salus auto balancing actuators, one for each loop, on the garden room manifold. Reset the WC curve with a start flow temp of 34 (normally 29.6 deg). And it started to heat the floor, so left to run overnight, the summer house settles at 14.7 degs with an outside temp of 5 degs. A result - No need to have electric heater on all the time. The Salus actuators go fully open for a long time (hours), then start to set the flow rate. The other mod I made, was to remove all outside control from the ASHP, the only influence is the WC curve. So it starts and stop as it wants. Moved the house thermostat to control the two mixer valve set points (via a volt free switch on the controller), instead of when the heat pump runs. Mixer valve control set point T, is set to a flow temp of 27 and T2 set to 38 (so it goes to a fully open position). Used the thermostat timer to have a target of 19.5 for 07.30 to midnight and 20.5 during E7 time period. So running regime is, no call for heat - UFH pump stays running and mixer valve modulates to keep flow at 27 degs, call for heat - mixer goes fully opens take all the heat the ASHP is delivering into the floor. Outside temp has been a steady 5 degs, from last year's monitoring, I found the calculation of house heat loss to be very accurate. So for the last 24 hrs the CoP including DHW has been around 4.5. Maybe a little fine tuning of the WC curve as temperature drops, but quite happy at the moment. Pipes now insulated

Think it's supposed to say "it uses 10-14kWh of energy."

Two things to consider when buying an MVHR unit, based on sizing. Normally the bigger the better, they make less noise for a given flow rate than a small unit only just big enough. The other is allowing for turndown, once you have it commissioned and build signed off, as you may want to reduce flows especially if a few people live in the house. So all things considered a unit that has your duty point in the middle of the units capacity range, us about right. Your lounge also needs a good flow rate as it normally has plenty of people in it.

That misses the point I never really realised, if said zone is behind a mixer it doesn't count. Yes they can, mine has volt free contacts that allow two settable flow temperatures for heating and two for cooling. You can only do one temperature at a time. So could us a diverter valve with microswitch to control it and simple time switch. Not sure about that, mine inhibits defrost when doing DHW. You just compensate with slightly higher flow rate to compensate. So mean flow temp is ok.

Maybe, maybe not, if you add a mixer to the UFH your engaged water volume could very low as the mixer valve isn't always open. Volume and flow rate are important, all heat pumps come with a minimum flow rate requirement, having 8 open loops of pipe behind a mixer valve is meaningless as the mixer comprises both volume available to the HP and flow rate the heat pump can deliver. To have no buffer or volumiser the system needs to be fully open.

MVHR units themselves leak, we had a similar issue, we blocked the inside room terminals, but I could feel the air leaking into the room where the MVHR units are located during air test. Our final air test was no better than our pretest and all leaks during that test were fixed. If you are not passivhaus certified, the air test is just a piece of paper to keep building control happy.

Smaller the volume the shorter the cycle times. 8 degs here at the moment, I have 2x 50m loops and 50L volumiser/buffer, and almost nothing going in the house floor (mixer valve almost closed), cycle time is around 10 to 15 mins on-off. Last night with house floor engaged (an additional 6-700m of pipe) had a 5 hours run without stopping.

Commissioning is very straight forward, the main thing is getting the air out the system before you start. Then set a low flow temp and press start. Initial run should have all thermostats set high, see you are getting warm water everywhere. Once running they look after themselves with out much or any input. After 24hrs take a note on we here room temps settle to and start to balance the system. And see what DHW does make sure the 3 way valve opens, you will need the G3 person to sign off the cylinder commissioning. As for temperature outside almost any temp is ok, but with the freeze valve you are best to get the system filled and running above zero. (Still not convinced by freeze valves)

Basically check you have immersion heaters kicking in. Set a low flow rate and leave it to run. If you are heating a floor, it will take as much heat as you throw at it. Wind any room thermostats out the way see where is settles. Something like 28 deg flow. Then check to see if you are getting lots of start stopping, certainly for the first 24 hrs while it heat soaks you be getting very steady running.

Low cost, but do you then need a thermostat in every room to control the system and individual heat output. Having a couple of long loops in an internal hallway, ends up being very warm. You can only change output so much with flow control alone.

At the design stage you can size the emitter by changing how much pipe is in a room and its spacing, so some room could have 300mm, 200mm, 150mm spacing others 100mm if required, same way as you do radiator sizing based on room heat loss. So then the output could be varied house wide by increasing flow temperature only up or down. Programs like LoopCad have this capability when you design the UFH array. It tell you how much over or under the room is being heated compared to design requirements. Companies providing design a service never show this on the drawing, because they just pick 150mm centres and fill every space they can with pipe. They are selling product not a design. That's why you see floor plans with with 100s of meters of loops in hallways, when in must cases, next to nothing is required.

My lessons learned about buffers People want zones, they think (or have been told) its the good thing to do or have a mixed system with different flow or temperature requirements. The more things you add the more important the buffer becomes. Operated my system without a buffer, but fully open on WC. But one part of the system really needed a different temperature and different running regime. So added a buffer for two different things. UFH in house required a mixer so I could operate at lower flow temperature, chose an ESBE mixer, this stays fully open until set point is reached, then closes to almost fully closed, killing forward flow from HP. The other reason is a small zone of 2x 50m loops can operate on its own if required.

Why is a mid point valve even installed on a heat pump, goes against every install manual I've read (loads of them). If connected to an unvented cylinder a mid point valve requires a 2 port valve to positively isolated the cylinder. It should be a diverter and fail to the heating side being open, DHW cylinder being closed unless powered. The other way as @ProDave says is 2x 2-port. But they need to be timed so both are not allowed to open at the same time, which isn't idiot proof.

Think the best way to install a heat pump or boiler is as simply as possible. No zones, no buffer, limited interaction with thermostats, design for sub 35 degs for most the year, set to WC and leave it manage itself. In real life zones are required for many, if more than two zones and/or coupled with a mixer valve, you need a buffer, as the mixer valve or a zone can close. If you need a buffer, install either in flow, return or across flow and return, as a glorified min flow loop with capacity to help mitigate short cycling. When a 4 port buffer is used, it is really important to design well, have good internal design to promote stratification and flow either side of the buffer be balanced to prevent mixing. 35 deg flow temp, should achieve a CoP of 3 at zero and about 5.25 at 12 degs. Most the winter is nearer 7 than 0, so if flowing at 35 that should give a CoP 4.5, if you can flow at 30 a CoP over 5. But we all make things more complex than they need to be, mostly at the negative impact to CoP.

Mine has a sump heater, and antifreeze, plus below 5 degs it circulates on and off anyway so no mention anything special.

@JamesPa did a spreadsheet a while ago, for setting up a WC curve and comparing the CoP. On a low W/m2 the difference in CoP is very small between set flow temp and WC. The CoP hit from 30 to 37 at 2 Deg is around 0.5. I have been doing the same internal debate on this. We are on E7, DHW uses about an hour of that, so I have 6 hours of charging time, at the moment am using a WC curve, but it not right for batch charging, so have been thinking set temp from HP, and two set points on mixer (electronic), high temperature during E7 and a maintain temp with a flow of around 28 after. Not sure how it work though, would it be better just switching off.

My problem was I let my floor get too cold, so the heat pump took 12+hrs to get up to temperature. Has your system always performed like this? New install or old? What is your system layout like?

Think the following happens - found this the other day with my ASHP. Both ASHP and GSHP manage dT first based on return temp, as return temp increases the flow temp increases towards set point. Our flow from the UFH completely overwhelms all other flows which are very small. So as the floor heats up the flow temperature increases. So just running the radiators has a different feedback to the heat pump compared to UFH on its own or as a mixed system. A mixing valve on the UFH resolve?

No they don't require them, most installs can be driven from the ASHP circulation pump, all depends on how you design the system. Another assumption, all depends on what is currently installed. Maybe an upgrade to T22 may be needed, you don't know without running the calcs. All depends on the install design, installer not always the same person, that does the design.

Back to the question and my first response https://www.ofgem.gov.uk/environmental-and-social-schemes/boiler-upgrade-scheme-bus/property-owners "We do not check EPC reports for eligible self-builds." So no need for an EPC if you qualify as a self build. Fig 2 on page 28 of the attached clearly say no EPC needed at any stage, in the guidance notes by ofgem. So fill your boots and get it installed ASAP. BUS PO guidance V2.3.pdf