Simon R

Absolutely fundamental to your planning. Only once you have the Watts per degree figure for the building will you be able to look at options. Living in a well insulated and airtight structure is very different from a conventional build. Getting the place air tight/well insulated will reduce inputs and pay huge dividends. Also in winter solar gain from east and south facing windows can easily keep a well insulated house warm, but you do need to makes sure you can shade them to prevent overheating in summer. Using split air-conditioning units rather than radiators is a simple alternative and much better in energy and cost terms. Low cost Midea units have a SCOP of 4.9.

That's the way I expected it to work, but on our Blauberg it appeared to be kicking in when the outside temperature is above target, so I disabled it. I'll have to check if it's still operating that way with the current software.

We ended up with more solar gain than our model forecast and installed two A2A units. My experience is that you need far less than expected. Our open plan living area is approximately 120m2 and has significant east facing glazing. The house is south facing, but the windows are shaded and don't get direct sun May-October. The east facing glazing caused the house to get uncomfortably warm. A 3.5kW A2A unit running from 7am to 7pm keeps the living area at a very comfortable 22c with no difficulty, indeed it's way below capacity, consuming just around 3kWh yesterday which was a very warm day indeed (all of which is from solar). We also have a second 2kWh unit for the master bedroom which has not been required for cooling but is lovely for a blast of warmth on a winter morning. Just as an aside, once you have an A2A unit disable your MVHR summer bypass feature as the cool air from the house will cool the incoming air.

I'm for option 1 and spend the difference on battery storage. Our place is ICF and we use a small combi gas boiler for hot water, no HW storage. We don't have UFH either, and rely on a 3.5kW A2A unit in the open plan living area to provide heating and cooling as required. Using an A2A split unit was a lot simpler and cheaper than going for an ASHP and UFH. Even at this time of year we are getting enough power to run the house with very minimal import, 0.39Kw yesterday and 7.7kW export. Our battery is 9.5kWh. I've got and EV but only charge it from the Octopus Intelligent tariff overnight, trying to charge it from the solar during the day was more complex than initially envisaged. Hopefully I'll get it sorted soon so I'm no longer exporting.

If GSI doesn't work try https://www.sennocke.co.uk/ they were easy to deal with.

We fitted internal electric blinds on our roof lights, they do a pretty good job of stopping unwanted thermal gain. We also ended up with an A2A split unit run of PV to keep everything comfortable.

Our house is upside down and like yours is 18C downstairs and 21C upstairs all running happily with and MVHR. The upstairs living area is largely open plan with vaulted ceilings. Setting it up this way was a simple matter of setting the flow rates during installation. I've not had to touch it since I did the setup. Another benefit of having an MVHR beside pollen and spore filtering is the recovery of energy. Here is a shot of our MVHR when the outside temperature is 3.8C the air entering the house is at !6.5C heated from the outgoing air which is at 19.8 as it enters the MVHR and just 6.3C when it leaves the house. This is something you just don't get with natural ventilation where the incoming air is essentially at the outside temperature making for appreciably cold drafts. In summer when the A2A is keeping the living area at 21C the outgoing air cools the incoming air, again minimizing energy loss.

Well, my daughters place in Germany is pretty airtight with no MVHR. The conventional approach is throw all the windows open for 15 minute morning and evening. That way you don't get too much thermal input from the outside air. It work pretty well but the CO2 levels do tend to spike especially when there are visitors. Besides a draught free house a big benefit of using an MVHR for me is it's wonderful for people who suffer hay fever and for my wife who's asthma can get triggered by mould spores in autumn. I've disabled the summer bypass on our unit to always recover energy as we have A2A cooling in summer. In summer we find running the unit from early evening through early morning and in winter running from morning to late afternoon keeps the CO2 levels good and minimises energy loss.

I too hate fixing into plasterboard. These are the things I've found "GripIt" . The downside is they have a large hole to cover 15-25mm dependent on the strength required.

I got it from Totton Timber in Southampton, I'm inside their delivery territory. I had a choice of two local merchants and went with Totton as they had the best saw equipment, an automated computer controlled table. For a heck of a lot of cuts they charged me £30 on top of the material. Using bits of your Larch cladding may be tricky from a point of view of stability, birch ply is very good both in stiffness and dimensional stability.

Thanks, it was worth the effort and saw dust. Regarding insulation, our build is ICF so the inside is fully insulated. The JUB ICF system provides a really well insulated window opening.

Birch ply worked well on our windows, but you will need a track saw to make a decent job of it. My wife spotted a post on build hub which we copied using birch play.

Our build is near passive and about 180m2. When we did the sums we needed about 2.5kWh to maintain a 20c difference. Looking at costs we decided to have a small gas combi and run towel rails in our two bath rooms. It was a lot cheaper and less complex than going the uhf route. In practice we quickly found keeping cool was much more of a problem than keeping warm. The energy modelling had got the solar gain from our east facing windows badly wrong. Fortunately the problem was easily fixed by installing a 3.5kW a2a unit in our open plan living area. Run from PV in summer and cheap overnight electricity in winter it's proved a very economical solution. If the sun shines we need no heating.

It certainly enough to show the kettle boiling. The spike at 14:00 was the kettle and toaster running together and pushing demand over 3.6kW ...and should not have involved grid power....should have waited for the kettle to boil.

It's five minutes give or take. The level of detail from the GE cloud server and Octopus billing is far more detailed than I had anticipated.

That's out grid consumption, actual is 19-21kWh, the balance coming from solar.

I should have mentioned that Octopus are offering a home package with inverter +PV + battery. I don't know the price, but from my dealings with them I expect it will be good.

It's a gen 1 hybrid and our daily average is in the 12kWh region, which includes our EV charging. Our MVHR and other odds and ends result in around 400w background usage. With a 4kW PV array we are exporting even at this time of year, so if the suns shining the washing machine and dish washer get used during the day. Our battery was full by 10am today, so a lot of your peak usage 11.5kWh will come directly from PV. Dark blue is battery charging, green is load, yellow solar and red grid.

Hi, I'm running a GivEnergy system 3.6kW inverter + PV with their 9.5kWh battery storage with Octopus intelligent tariff. Our house is heated/cooled with small 3.5kW Midea a2a unit. Our practical experience is that we use very little peak rate electricity. In winter we run the a2a unit to heat overnight 23:00 to 05:30 and then as we need it depending on solar gain, it's unusual to draw from the grid during the day. In summer we use the a2a to keep the house down to 22c and it's always running on solar, so again no peak rate. I also have an EV which I'm setting up to charge automatically when the battery store reaches 90% (and PVs are inputting) and stop when the battery is depleted to 40%. By doing this I should be able to reduce my export to a minimum.

Hi, first damp should not be a problem, we have the opposite problem and now have lots of house plants to keep teh humidity at comfortable levels. We did our build with ICF and put a fair bit of planning into reducing heat loss, to the extent that we had no need for a heat pump. By not having a heat pump and underfloor heating it save a lot on costs. If you use an insulated raft the floor is at room temperature anyway. MVHR is essential, we have vaulted ceilings and it took a bit of head scratching to work our our best ducting options. Yes Yes We did our build on a very tight budget and you can build an very comfortable home with very low running costs for not a lot of money, especially if you can do some of the work yourself. We did a blog of the build which you may find useful as it sounds as though your build may be similar to ours.

We have this setup with a Midea 3.5 kW unit which delivers about 3.5 to 1 and a 9.5kwH battery store. The battery gets charged up over night on the Octopus Intelligent tariff (21:30-5:30) to either 50% if we are expecting sun or 100% for dull days. In our case we run the unit at 22C with a 30% fan rate and it consumes in the region of 500W . Using this setup we use virtually no full rate electricity. In summer we run the unit to cool when required but it's always running of PV rather than grid. The split unit was added as an afterthought to help with rather more solar gain than our energy model suggested. It's been brilliant and I wished it had been planned in from the start.

I'll second that. We're grid tied and it has many benefits, for example we can set our battery to charge to a given percentage (enough for an average days consumption) using the cheap overnight 7.5 per kWh rate from Octopus. In winter this means we can get through days with little or no solar. It takes a bit of trial and error with setup parameters but you can get very close to never taking any electricity at the full rate. Stay within the 3.6 kW for G98 unless you have a real need to bigger. It's surprising how few times you need more power if you simply avoid using the oven and kettle at the same time.....

Me too. Ours is all done now, hep push fit and plastic pipes used to keep the number of joints down. I don't have underfloor heating but do have pumped rain water. I air pressure tested each section of piping as I went, pressurising it and checking the gauge the next morning. Also where practical I tried to keep joints in accessible locations, we have lots of "routabout" hatches. By testing as I went along it was fare less stressful when the water got switched on. I had a couple of leaks where I managed to put a plasterboard screw through central heating pipes, but dry other than that. Pressure testing threw up a few bad joints, all where I had failed to fully insert the pipe into the fitting. I pretty quickly got into the habit of using a sharpie to mark the pipe so I could easily see if it had fully located. One area that cased a few headaches were shower trays. Our ground floor is a concrete raft and despite best efforts to accurately position soil pipes it took a bit of fiddling to get the trays right. I even ended up building a partition wall in slightly different location so the shower drain matched. The toilets were not so bad as we have wall mounted pans which means there is some flexibility in the couplings. I'm on the south coast, just west of Portsmouth so probably not to far from you. Let me know if you want some help.

I'm a bit late to this thread, but noticed no mention of solar gain. The effects of solar gain in a very well insulated structure comes as a bit of a surprise and has caught out several build hub members. Our ICF build came out with a figure of 68W per degree difference. In practice we think this is more like 80w but still incredibly low by normal standards, too low to make an ASHP financially sensible. So we have a small gas combi boiler which got us through the winter very comfortably. On sunny days we seldom had any heating requirement. Spring however was rather different and our east facing glazing started to cook us. We now have two split aircon units, one 3.5kW and one 2.5kW which we run very happily from a 4kW PV system. The two units from Midea cost £1800 installed and now we have very comfortable house, one runs the open plan living area and the smaller one our bedroom. We havn't been through a winter with them installed yet to experiment using them for heating. Looking at your idea to 'zone' areas you may find that a number of small aircon units may be a flexible and cost effective option.

I've sprayed a little, but as an easy but slightly more costly option there are outfits like WoodByPost that sell edged sheeting that mean you can make your own stuff. Here's our utility room, all our own sizes and a fraction of the cost of bespoke.