JohnMo

You are set to auto flow. So this will basically manage the flow through the system and I think how much energy is going into the floor. If your flow temp is high the flow rate doesn't need to as high to get the same energy transfer. Reduce the mixer flow temp, your flow rates should increase, but it may take a while to change. Worth a try. If you are connected direct to the boiler, can you control CH flow temp independent of cylinder flow temp,? If you can you could just reduce boiler temp to get more efficient operation from the boiler.

So your drawing is wrong. Have you tried to adjust a flow meter? Perhaps they are short runs under the floor and the loops are set to a flow rate of around 1? You state the floor is warm, so is there an issue? If the floors warm, turn your flow to min speed, (1 light) and job done.

Basic question first, is the two way valve opening? Is that a pressurised thermal store?

I would say you are generating nearly enough from PV and the diverter is flicking between about confused. Look at it tomorrow.

Not sure how you could unless the 3 zones had there own mixer and the opentherm controlled the mixer. Or each zone is run at a completely different time without overlaps. The opentherm bit just modulates the boiler output. I would try running as a single zone and balance down rates to manage temperature in areas

Here's a write up, if your plumber doesn't know what it is, he needs to get back to school. https://heatingacademynorthampton.co.uk/s_and_y_plans_should_be_banned/ Boiler efficiency is nothing really to do with where is runs within the available min and max allowable kW. The biggest effect on efficiency is return temperature. All new boilers in the UK have to be condensing. What this means, if your return temperature is below 53 degC, the steam within the exhaust flue is converted back to water, during this process the latent heat energy is captured and put back into the boiler. The lower the return temp the higher the efficiency. You get efficiency of around 110% with return in the high 20s low 30s. An oversized boiler or too many small zones can lead to the boiler short cycling, this will drop about 20 to 30% of efficiency as the boiler spends at lot of time doing in-effectively.

Gas, oil, heat pump, all provide heat, no one would install a heat pump rated at 30kW, so why would you need a 30kW system gas or oil boiler. Treat your heating system the same as you would if installing a heat pump, you will surprised how small your boiler could be. If you are getting a new cylinder get one with a heat pump coil, that way you can operate domestic hot water heating while the boiler is condensing at all times. You also need to go down X plan, not S or Y plan. X plan will allow the boiler run at two different temps, one for heating and the other for heating the cylinder.

Lounge is about 6m x 6m, with vaulted ceiling and at peak about 6m. Master bedroom 5 x 5m and average 3m tall. Wardrobe 2m x 2m and 2.5m tall, it as louvre door for unrestricted air flow.

Some background our houses and what I found Our master bedroom 12 l/s and wardrobe with 6l/s, (just checked the test report, figures in previous post were low) so a combined 20 l/s will get up to just over 1000ppm CO2, with the door closed over night, I wouldn't want a supply rate less than this in a double bedroom. Our living room has 2 terminals with a total of 20l/s combined. Had 6 in the room for about 6 hours by hour 4 the CO2 was at 1300ppm, so it was put on boost. With 2 or 3 people it stays in 5-600 region. Both rooms are big, but still need the air changes to keep CO2 low. Use most of your flow where you want good air quality, the rest of the house under ventilate, to get the correct average over the house. .

None of my extract were doubled up (90mm), longest runs about 12-14m. No issues Our master bed is approx 18m and 19m runs, we use two outlets and single run to each, which gave a combined flow total of 45m3/h. You definitely need 2 x90mm ducts at that length, to get 45m3/h over that distance, otherwise you would be turning up the fan speed too much to compensate. Just looking at your flow rates in your bedrooms and something doesn't look right. Master bed rate seems very low? Would expect to see around 45m3/h when combined with the wardrobe flow for a double room. Other bedrooms if a guest or single bedroom are fine. Your living area flow seems very low for a communal area, you have more flow in an under stairs cupboard for example.

+1 on that. The best change that happened on our build, original build had lots of wood and little of places to get pipes in and out of places. Posi joist/rafters are great. Also speed up the build as they are easy to move about due to the lower weights.

I just found it easier to use 90mm throughout, instead of 75mm. Most runs in our house would have been double runs in 75mm, but are a single run in 90mm. Less hassle running and ended up cheaper overall. The other thing to think about, and this why you are managing the pressure drop. You manage the pressure drop, because a low pressure drop allows the MVHR fans to run further down their performance curve, i.e. they run slower, so makes less noise and does less work (less kWh ultimately) for a given flow rate.

WC = weather compensation

I watch a guy in a ship yard, and he used a full roll on a 2" tapered fitting. Didn't seal and he then used another roll

That's almost the same as ours. That was the original plan, but managed to pick up a new ASHP that will do this and the house, for very little money.

Thanks for the suggestions, never thought about chicken wire. Fair bit of tree shading until mid afternoon, and about 5m by just under 4m footprint, double glazed windows. The MVHR unit looks a good choice.

A lot of the duct manufacturer will give clear guidance in the duct datasheets. Most ducting are pretty much the same, so would be worth going through some datasheets and taking a look. Zehnder for example usually have decent information.

Drill holes in the blocks, as I build up the levels, so it makes a continuous long deep hole. Roof build-up and how I insulate walls internally are are all open. Internal finish is going to be plasterboard, taped and painted. I am ok loosing some floor space, but not too much height, hense external roof insulation. External walls are staying as they are, so EWI isn't really an option.

Good idea for the roof. Not much electrics, just a light and a couple of sockets, and power for ventilation. May run wires inside the wall blocks to hide it away Heating likely to be UFH.

We just purchased a summer house, but will be insulating, and heating to make 365 day use. Will use single room MVHR or dMEV. Floor insulation will be circa 150mm PIR with floating wooden floor. Roof will be warm roof, EPDM, OSB, PIR, breathable membrane(?), Tongue and groove 18mm timber. Does this sound about right? Walls, are 70mm solid wood, wanting to add 50mm of insulation to inside and plasterboard. Can I just add this inside the timber walls, or do I need a membrane or any air spaces? Was wanting to screw through plasterboard and insulation into wall.

Screwfix do a liquid PTFE, quite easy to use and seem so far to water tight joints

Same as @Conor

If you divide 1/R you get the U value. U value is W/m2.k. You can then calculate how much heat transfer occurs. k is just the difference between the two temps, upstairs and down. So say 20-8=12. M2 is the ceiling area. 1/8= 0.125. Let's say 50m2 And 12 degrees W = U.m2.k = So about 75W or 1.8kWh per day will be lost to the cold space. Your insulation value better than most homes.

That's pretty much how our windows where done on our steel frame. The internal surfaces of the steel had 10mm aerogel and PIR basically because the steels go down to the foundations and it stops the ground temp being transferred to the room.

If you use PIR with aluminium layer, the membrane keeps the cement in the screed from a chemical reaction with the aluminium, which forms hydrogen and leaves bubbles in the screed.