JohnMo

https://re.jrc.ec.europa.eu/pvg_tools/en/ Use the tool, to get a good estimate of output by month

Little confused. In Jan your output from PV for the month will be around 150kWh, some days the output will be zero, but if we average to 31 days of equal generation, 4.8kWh per day. Even getting a CoP of 4, that less than 2 hours of running the heat pump. So full use from PV without any other loads. In summer you are generating circa 400kWh per month, 13kWh per day, a couple of hours doing hot water, would 5.6kWh, other background uses, washing machine, dishwasher etc plus immersion to bump up cylinder temp to max, all the PV is used.

You don't mention size of ASHP nor PV array size. We have 3.1kW of PV and gas boiler (so should be easier for you to self use). Since middle of June I have exported 43kWh (5 to 600kWh generated), this was only exported because my immersion was miss reading and only charging the cylinder to 55 degC. This has since been fixed and now exporting nothing.

Does that make sense? A storage combi should give you an endless supply of hot water, at better flow rates than a normal combi. Our Atag combi was doing two high flow showers at a time this weekend without complaint from the boiler or the users.

Have you got a huge gap in your insulation between roof and wall?

Gas -June to today, average 2kWh, mostly 2 of us, but had a long weekend with 6 in the house. Combi boiler with preheat cylinder upstream, heated by solar. Electric average 8.4kWh for same period. Have 3.1kW solar with diverter

Oil price haven't got to levels they were at during the five years, 2010 to 2015. Think the issue is not the oil price, but processing capacity; as we out sourced most things (diesel and petrol) to other countries like Russia to make a CO2 emissions look good.

We are the same, one heating season no issues. We are on a 100mm concrete screed. We had elevated humidity in the floor, so had to apply a liquid (epoxy) DPM prior to glueing the floor down.

I used Rye Oil Cedar Cladding oil. £200 for 75l. Easy to apply, goes along way, one heavy coat applied 6 months ago, looks the same today.

Thought I understood what you were doing, now just confused.

But who does that - no-one. Small trees are no use for anything, same as the branches they chop off which are just left in the forest. These parts are not harvested unless you do it yourself and air dry for a couple of years before you burn it. True, or not without trying hard. Again true A tree used to construct something - not burnt, will capture carbon will keep it captured until it rots away.

A young tree absorbs very little CO2, it's not until the they are in the middle growing phase that they absorb lots of CO2. The issue is we cut a tree down at 20 to 40 years old and it's in the absorb lots of CO2 phase. And replace it with a tree that sequester very little CO2 in comparison for 10 to 15 years. Planting a tree is good, chopping them down is not. You can kid yourself on, its sustainable but, really it's not.

Its only carbon neutral if the tree fell over, died or the part used to burn fell off the tree and would otherwise decompose where it fell. A tree chopped down for firewood, isn't carbon neutral. As the tree would continue to absorb CO2 all the time it lived. When the tree is burnt it releases all the trapped CO2, but also releases lots of particulates and other pollutants.

Easy enough. VCL/airtight layer below insulation, tape to wall junction. Then install 50mm counter battons, then your plasterboard. Use low profile down-lights circa 15-20mm deep., They come with a small module that is about 50mm high that installs in the void, wiring can be run in the void also.

Sorry I missed that

To be picky, title says "Door to garage - need to be make it air tight"

Not sure it would be that eco. Trees cut down with a chainsaw - hydro carbon powered. tree pulled out of wood with tractor - hydro carbon powered, transported with lorry to processing plant - cut and dried - hydro carbon powered etc etc - possibly clad with wood from the other side of the world. Put together with a gas powered nail gun. Not much eco about it - same as most buildings in reality Made in China, with coal powered electricity and then shipped across the world, not very eco either really. If it used 1W that nearly 9kWh per year that does not need to be consumed.

Garage and airtight - what the point? Your brick won't be that airtight either That door is not meant to be airtight and would not be easy to get it so.

forgot to mention, if you are heating TS via a coil any a system boiler would be needed. If direct heating a heat only boiler.

You just need a boiler that can connected to a vented system. As most of the housing stock in the uk is fitted with a vented system (header tank in loft) it shouldn't be that hard to find one. I assume your thermal store is open vented - either loose lid on top of cylinder or header tank Here are 99 of them - you are looking for a heat only boiler not a system boiler, system boiler need to connect to a pressurised system. The boiler doesn't know if its connected to an open vented DHW cylinder or radiator or a thermal store. https://www.screwfix.com/c/heating-plumbing/boilers/cat6660001#category=cat6660001&boilertype=heat_only

No way you will get a one liner. SAP/EPC are the same, they are a legal requirement for new and being sold houses. Full of flaws, but all reports have the same flaws, so are comparative. PHPP, is a passivhaus design tool and takes a more robust approach to heat loss and gain. DIY heat loss calculation, usually misses the difficult areas of solar gain, which can be difficult to model as there are many variables. Main things you need to know are the highest heat loss, coldest day and least solar gain, then you can size your heating system. For this you need whole house heat loss and room by room heat loss. Then you need to know the heat loss on say a 10-12 degree day to get a heating curve, from this you can look at modulation rates of the heat source and define requirements for buffers etc.

So are you just heating the thermal store, the UFH flow coming off the thermal store? Or are you heating the thermal store and the UFH flow is separate?

To make it work you need somewhere to dump heat that is useful. A thermal store would normally be scorned on here. But install a large one, 500 to 1000 lts. Use a plate heat exchanger for domestic hot water take off, size the heat exchanger to work with 50 degC water. Heat TS to 50 degC. Take central heating direct from thermal store. That should give the ASHP plenty to work against and no short cycling. Make sure you site the TS where lost heat is useful.

You are making life complicated for yourself. Keep it simple. Not sure I would do a SA with a heat pump, just use an UVC. Take heating and cooling flow from heat pump via a buffer cylinder. Feed to mixer valve /pump at manifold (low temp). Run downstairs as a single zone. Run DHW cylinder at 46-48 degC UFH flow should be circa 26-30. Don't limit yourself to one pump manufacturers heat pump. Valiant heat pumps use propane, so limits your placement of the outdoor unit. Also I believe Vaillant unit is only reversible with a £300 (should be £1) resister in a plug.

People usually avoid PIR in blockwork walls because it's difficult to get gap free insulation. Every gap is a heat leak, mineral wool cavity batts would be more forgiving and possibly better performing in real life. Or as mentioned EPS beads.