JohnMo

UFH running is down to how much insulation you have below the UFH pipes and how you operate. So 150mm is good so not down to that. Heating 10s of tonnes of concrete takes quite a bit of energy, so there are two fundamentally different ways to operate the heating regime. Throw a load of heat at it over 4 to 8 hour period, just like a storage heater, then let is trickle out. This is pretty much what you are doing. So it uses a bunch of kWh in a short period. Doing this wrong you can get thermostat overshoot, which is waste full and will use more energy. The other way is a gentle flow of heat into the floor, so heat in, matches heat out, the heating period is pretty much 24/7, this entails using a lower flow temp. If coupled with weather compensation this operation can be automated. Otherwise, it can be done with a little bit of fiddling manually with the UFH mixer. As a comparison our flow temps at -5 are about 30 degs - yours 45 degrees, ours is running 24/7. Either way will use a similar amount of kWh other a couple of days. If you can reduce boiler flow temp, there are small gains to be had, as you will be condensing more.

If you install the system around a flow temp of 30 at -7, so a well insulated UFH, there is no reason it should cost more to heat your house. A Media 6kW monobloc at -7 and 30 degree flow temp will give a CoP of 3.4. Gas boiler at low flow temps so a like for install should give a system efficiency of about 97% (that is what is currently running at). So a heating day uses 100kWh (nice round number) going in to the floor. Gas 100 / 0.98 =102 kWh Cost = 9.78p kWh = £9.97, plus standing charge of 27p = £10.24 Electric 100 /3.4 = 29.4 kWh Cost = 33.068p kWh = £9.72 So gas is slightly more expensive but pretty close But at 7 degrees instead of -7 the CoP goes up to 5 at the same flow temp, so costs reduce for electric by 32%, then gas wins by a good margin. A poor install costs you more (45 degree flow the CoP drops to 2.4, so cost 30% more to run). A good one can cost you less.

The floor is unlikely to be much warmer than the room, so will feel cool to touch. If it was hot, your heat loss from the house would be higher. Ours is also cold to touch, but house is warm. We have a very similar house floor area, 192m2, but single storey, the ground floor area is 192m2, all vaulted ceilings and an outside surface area of 624m2, so twice as much area to leak heat. If on the coldest day your thermostat is clicking off, you could be flowing at too higher temp, that means there are gains to be had by reducing flow temp, which will increase CoP and use less kWh. Also review your domestic hot water flow temp and set point. Another thing to check especially if your flow temps are high or if you are close to capacity when in heating mode, do any immersions kick in, controlled by the heat pump? Your heat pump could be asking for them to work as well as the heat pump.

Is there an issue with the heating? Other than the flow meters reading high? Have you tried turning your pump down?

It does sound big, they are only there to reduce short cycling, when min output from heat source and min load required and small system water volume would lead to a short run times. They also act as hydraulic sepereration between various pumps. So your heat of pump should turn down to about 5kW. So have run some run-times calcs, that show the following. With a minimum CH heat demand load of 1kW. System volume 300 plus 100, 400L in the ch system, run time 28.mins, off time 111 mins. Reducing the total system to 145 incl a buffer, would give a run time of 10.1 mins and off time 40.4 mins. Which isn't short cycling for an ASHP. Increasing you min heating load to 2kW gives a 13.5 min run time. So for run times and eliminating short cycling a system volume of 145 L is fine, you may already have close to this without a buffer.

My take on flow rates is. All bedrooms have people in them and bedrooms have the doors shut at night, go will building regs flow rates. Anything else, passivhaus rates or above.

Assume when you say manifold you are talking UFH manifold. The temp on the manifold will never be the same temp as the buffer. Why, because there is a mixer on manifold, the mixer will alway mix a percentage of the return water with the incoming water, the gauge on the manifold represents a mixed flow temp. There is an issue with most mixers, in that they like to have set temp, 10 degrees lower than the supply temp into it. Because they operate with a fixed minimum mixing all the time. So if buffer is set to 55 it is unlikely you will get more than 45 on the manifold. Have to say having to heat a large buffer to 55 with a heat pump, doesn't sound the most efficient way to heat a house. If you are having to run UFH at those high temps sounds like you would have been better with radiators.

No don't think so, enough other jobs to think about. MVHR is all sorted setup and running nice and quietly.

It surprises how much over thinking that goes into a ventilation system, which designed to run at a constant rate, except when on boost. Set to building regs or passivhaus flow rates, or somewhere in-between. Push the boost button as you go for a shower, job done. Manage the filters as deemed by the manufacturer.

3 way valve, or if you have 2x 2 ways, the one for the cylinder has stopped working?

Various trades I had on site, all confused by airtightness and insulation in general. But the best comment I had was when they saw how much insulation was going under the floor, told me straight I was stupid, and wasting my money, as heat only goes upwards, not down.

Depending on how efficient your heat exchanger is, in UK temperature they are not needed, maybe why it's not coming on. We had -9 the other day and the antifreeze function never even came on, as far as I could see.

If you use no buffer, make sure you water volume is acceptable for the heat pump manufacturer for warranty purposes, don't zone it to death, one or zones only. Some charts attached

The training needs to be more like that in Europe, you have to do a set number of years and qualifications, then work for a company for a further number of years. In the UK, can walk past a time served guy and then set up shop as a building firm.

Not willing to hold a breath for that to happen. Nothing special about Scottish building Regs. My heat loss is less than half the demanded rate for the same house built to Scottish building regs. And I am not even to Passivhaus house standards due to the shape coefficient less than efficient. So architects will all need more training, builders and all other trades, will need more training also, big builders will all push back. The unaware population will either switch off the MVHR or not change the filters, unaware what its for or why they have it. Then complain to the press that new house is full of black mould, government will U turn shortly after.

The 5 kW Vaillant does 6.7kW at -3 and a flow temp of 35 and 6.1kW at 45 degrees. Just make sure the install includes a buffer to keep the heat pump happy on a 10 degree day when heating loads are low. You also have a good margin available to do hot water on the coldest days. On full heat demand, will be nicely down its modulation curve, so happy and quiet. The alternative is 3.5kW unit, which is rated at 4.6 and 4.3kW, but that could end up running flat out just doing the heating, and being at full load may make more noise than you want.

Just turn the flow down, run at mid to high 20s, much better for CoP

I moved into a house years ago, who ever did the foundation measured wrong and it 1m longer than it should be. Brickie, just followed the foundation line. Everyone assume it was correct including building control. Great for me, a longer garage than expected.

Salus ones also fit a single wall socket Can be wired or wireless

DHW, Domestic hot water - Heating your cylinder.

So was your first photo showing the heat pump showing 47 degrees flow temp, on DHW heating, as it does not be match the heating curve?

I would agree with Dave when installed pre heat exchanger it's there for frost protection of the HE, not for heating the house. Post heat is for heating the house.

First observation is the flow temp is high at 47.8 from the heat pump. Do you know what your UFH flow temp is, or does your floor heat up quite quickly? If you could reduce that flow temp to about 35 you could gain an additional 1 on your CoP from low 2s to low/mid 3s. That could save 10kWh a day! My flow in the floor is 29 as a reference, it's -7 here, house sitting at 19 inside.

Also from the photo the flow rates look quite low. You may be better with a higher flow rate and slightly small DP across the loops, this would give more energy to the floor, you then reduce flow rate. Option to look at later. On the night set back, only drop it 2 degrees, then the boiler isn't having to work so hard to recover floor temp. But just alter one thing at a time, understand the outputs before changing something else.

Just looking at the dotted line on your graphs, which looks to be the thermostat set points. And the red part where it states heating is on. A couple of observations based on experience with my house. You have the heating on at various times and various temperature throughout the day. Looking at the red parts of the graphic your room temp is just about getting to temp and you switch it to a lower temp, then a few hours later a higher temp. So with floor inertia you boiler is playing catch up all the time. The other thing that may be happening you have multiple zone all programmed at differing times of the day. This is great, but in practice, you can have periods where you only have the lounge switched on, so the boiler is only being asked to do a couple couple of kWs of work, but the boiler may have a min output of 10kW. In practice this leads to the boiler short cycling. So boiler starts, a few minutes later trips on high return temps or minimum flow. Boiler is locked out for 10 mins, and this repeats until more zones are opened up. So why does this lead to poor heating performance and high consumption of gas. Short cycling, every time your boiler starts, the efficiency is low, it's heating a slug of cold water and lots of metal, once the boiler has been running for a 5 mins the efficiency climbs quickly. Continuous on off cycle means the boiler is in a low efficiency mode, the 10 min lock means no hot water is being pumped around. Timing efficiency, your floor is heating, you can see in the lounge at about 10am a big jump in temperature. So big it look like the flow temp is way too high. My recommendation as a trial, set all your thermostats to manual at say 19 degrees, and the boiler will have the whole UFH system to heat, see what happens. I suspect it will be fine and heat up quite quickly. If the temperature overshoots 19 then your flow temp is too high.