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When we first decided to self-build in 2014, Jan and I visited quite a few passive house builds and talked to various experts; we soon decided that a low energy approach was broadly the way to go for our build. One of these experts, a passive-house evangelist called Seamus O'Loughlin, emphasised that a conventional heating approach (where boiler demand is based on some central thermostat set point) doesn't work well in a passive house, because the time constants of a high-thermal capacity low energy house are a couple of orders of magnitude longer than those anticipated by conventional CH control systems. At the time this seemed a controversial assertion, but because I have done some mathematical modelling professionally, I was able to and decided to do some time-dependent heat-flow modelling and control strategy simulation of how our designed house would behave and this very much supported this assertion. I have already covered a lot of detail of my CH approach in previous posts and discussions, but it’s probably worth summarising some key headlines to set the context for my changes to our heating strategy: We were cash-flow limited during the build phase, so had to make various cost-benefit trade-offs on our build, like most members here. I based these on a general net 10-15 year payback, and it was clear that we wouldn’t be able to achieve a true zero-input passive house largely because of design compromises owing to planning restrictions and our plot size and orientation. However, we would be able to build a low-energy house that would need generally low levels of supplemental heating for maybe 6 months a year, with overall heat losses an order of magnitude less than a conventional build, and the thermal capacity of the heated fabric be many factors more. We decided to go all electric in the house with wet UFH embedded in the ground floor slab only. Cost benefit trade-offs didn’t even support installing an ASHP, though I did future proof the installation to simply the later addition of one if the cost numbers changed. I decided to adopt a simple but unconventional strategy for heating the house: calculate the total heating requirement for the coming day daily at midnight; this is based on actual averages for energy use, average house temperature and forecast average external temperature for the coming 24 hrs. This allows me to dump as much of this heat into the house fabric as practical at the cheapest electricity rate, and for us this is in the 7 hour overnight off-peak window on our E7 tariff. We used to get some spill-over into peak rate top-up in the coldest months, but a year ago I added an oil-filled electric radiator on my 1st floor landing, and one in my son’s 2nd floor bedsit controlled by my Home Automation System, with these scheduled to come on in the overnight E7 window to dump extra heat in the upper floors. This simple addition reduced the thermal layering from ground to second floor, and almost eliminated the need for daytime slab top-up. In practice we have roughly a 1°C daily ripple on overall winter house temperature. Because using a daily forecast computation does have some intrinsic prediction error, this can add typically less than 0.2°C day-to-day ripple on top, but any longer term drift can be corrected by the daily feedback. I have RPi3B running NodeRED attached to some digital thermometers and 4 GPIO controlled solid-state relays (SSRs) to control the time of the UFH pump and Willis heater, plus the 2 × SunAmps for DHW. This was very cheap to implement, and basically has no monthly or annual maintenance. With the current Electricity price hikes, we have decided: To trim our house temperature set-point back from 22.3°C down to 21°C To hard limit automatic heating of the slab to the cheaper 7-hour off-peak window. (We can still do peak by request in one hour chunks if we want to.) To use electric oil-filled radiators overnight to do any additional top-up. I can automate this through my Home Assistant (HA) that runs on a separate RPi4 and do this using MQTT via WiFi connected powered/metered sockets. This strategy currently limits heat into the house to: ~21 kWh through the slab and ~7 kWh through the two radiators. 28 kWh is enough to maintain overall house temperatures so long as the external temperature is at ~7 °C or higher, and it clearly isn’t the case at the time of posting. The house needs about 2½ kWh/K, so with the average daily external temperature at zero today this is 17½ kWh too little to maintain house temperatures. The long term Dec / Jan average where we live is about 4°C, so to maintain temperatures in this case we would need an extra 7½ kWh/day. (This last year, we had 26 days where the average external temperature was 4°C or below and only 2 where temperature was below zero or below.) So what happens when we underheat our house? Simple: it slowly cools down, and very slowly. For example, in the last 5 days of cold-spell, capping the heating has dropped the average house temperature from 22.3 down to 21.3°C, and given an average of -1°C for today, it will be down to our new target of 21°C by tomorrow . At this point I will need to add more heat or to accept that the house temperature will fall further. I will definitely need to add another 7kWh or so extra radiative capacity for overnight topup. We will play it by ear over the next week or so. I can either accept that I will be paying £0.38/kWh for extra peak period top-up during these really cold spells, or let the average temperature fall a little further if we find it comfortable enough (wear a thicker jumper, etc.) This approach works well for us because our house is so insulated and it has a huge amount of thermal capacity within the heated envelope. If we accept a small heating ripple then it really doesn’t matter that much when we heat within the day and so we can time-shift our demand to make use of the best tariff rates: currently over 85% of our electricity use is at the off-peak cheap-rate price. This latest exercise of clamping the heat output to 28 kWh when the maintain level is closer to 40 kWh underlines that the heat budget for and given day can be off by 30% or so and the net temperature drift is still on 0.1 °C or so; the time constants of the system are of the order of a week rather than days or hours. By way of a contrast my daughter lives in a pretty large but conventional 1990s house. When her heating goes off in the evening, the living room temperature drops maybe 4-5°C within an hour.

How are others coping on site with the cold temperatures? I thought I would share what I'm doing, which could probably be a fair bit better. We don't yet have central heating in the build. I've set up a cheap "Diesel Heater" from eBay that I'm using Kerosene in. There aren't many of the "All In One 5kW" type left on eBay like the one we have: Last night was properly cold, below -7C in Cambridge which is below most year's minimum (bottom third 1995-2021). We recorded -6.8C in the garage (no doors) and the kerosene heater upstairs in the house stopped at around 3am unfortunately (-6C in garage), so the temperature dropped there more quickly. We're putting about 2.3kW of heat in (heater set to 3Hz to make 5L last ~24 hours) from the Kerosene heater plus the log burner downstairs, but that stopped at around 10:30pm. I'm surprised the log burner can't raise the temperature downstairs more than ~7.5C but there are quite a number of drafts / weak points downstairs (e.g. Polythene over a 2.2m x 2.1m door opening which has some gaps). I'm quite pleased that we can keep the temperature in the house above 8C upstairs (bar it stopping) and above 5C downstairs in such an extreme outside temperature. I was hoping for 10C or above, but these are extreme temperatures (for here). Only upstairs is MF framed and plasterboarded so far. So far the loft only has 1 layer of 100mm / 150mm Loft Roll (44) with some areas not yet done. The walls have been blown with their cavity insulation (beads). All windows are in but not all doors. I have a dehumidifier running to take some of the water away that the heater will be producing. Garage: Upstairs: Downstairs: Cambridge Weather Station minimum temperatures calculated in Excel: ThermoPro TP357 Bluetooth Hygrometer Mini Room Thermometer: https://www.amazon.co.uk/gp/product/B093PT1NL1/

So you will be looking at essentially a petrol generator with an LPG conversion. You will need a proper generator changeover switch, not difficult.

If they are from the same range I am not sure I'd let the sound level difference influence the decision. A 10kW pump running at 7kW is likely to be no more loud than a 7kW pump of a similar design running at max, and its quite likely to be quieter. The amount of air they have to shift (at equal power) is the same so that starting point would be that they would be about the same volume. However larger capacity pumps often have larger air heat exchangers, which for a given volume flow of air will reduce the sound volume. If the manufacturers publish sound vs power curves you could check, but otherwise I would probably ignore this particular factor, unless of course it trips a regulatory issue.

Heat will escape; insulation just slows down the rate. Looks like you need more ventilation in the loft space to get rid of the condensation. Perhaps check the eaves are not blocked with insulation.

We built our first house in Brimpton, nr Reading, sold it and are now working with Fleming on our project in the Scottish Borders. We're at building warrant stage (Building regs in England and Wales). I can honestly say that Flemings' service, advise and communication to date has been excellent. Working with them we got planning approval in 11 weeks from submission and all it cost us was our application fee to the Council. We looked at MBC but unfortunately they did not have an inhouse design team, and as we knew exactly what we wanted it made sense to engage with a company that had an inhouse design team. We also spoke to a number of other TS and SIP providers but unfortunately got the impression that they were only interested in selling their portfolio of designs and not in anything of a bespoke nature. Fleming have also proactively offered to amend their quotation downwards to us on the basis that some building material costs have come down in price! You don't hear of that happening often!

It's so subjective. I used to build PC's with passive cooling chassis just to eliminate the last vestiges of noise that disturbed me when trying to think. Yet now we're in an energy crisis (of multiple makings) I seem to be fairly oblivious of the noise the indoor units make. Although they're very quiet and have multiple options for fan control) It's actually a sound I now find soothing as I'm being warmed for minimal cost. Air movement is probably the biggest difference that has to be reconciled but the units that have thermal occupancy sensors do a good job of keeping the airflow away from you. Placement is worth thinking about very carefully. The most comfortable area seems to be at the furthest point from the wall unit. Pretty obvious except it also seems the warmest (not quite so obvious).

Right to the boundary if you want. On my daughters semi the roofers had a join in the tiles on the boundary so we set the rails in line with the join and the edge of the panels 75mm in from the rail ends. At the edges I think the recommendation is 300-400mm but if youre not in an exposed location, I'd be happy to go down to 200mm if it allows you to have an extra column of panels or to use larger panels.

This will be down to a lack of physical contact between the diffuser and the upper floor. I see this christ knows how many times. Did you witness this being installed, and do you know if the deck boards are sitting snugly against the UFH system? If there's even a couple of mm gap the results ( unless it was a passive style dwelling ) would be dramatically reduced.

I expect he's too busy trying to get it all ready to move in by xmas.

This document https://mcscertified.com/wp-content/uploads/2021/10/MIS-3002_Solar-PV-Systems-V4.0.pdf This section. 5.5.2

This is the carrot. A small scale experimental scheme to pay a small number of people to not use electricity. The stick will come later when all those with smart meters will get charged more in peak times with no choice in the matter. Just my humble speculation. That is after all the agenda for a "smart grid"

It's easy spending other people's money (AKA being a government). But this one could be reasonably cost-neutral depending on the work for either approach being contracted out (time being money).

thanks. each pump has an NRV on it. there's no chance of water never being in there! even during the drought last summer there was still a trickle of water coming in. I'm tempted to put a monitor on the 1st pump to record when it runs and for how long to keep some form of stats and so I can see if it is running or when it last ran etc. but that's a very nice to have and can wait.

afternoon all. I've finally got my dual pump system up and running. the new pumps are really good and clear the water very quickly. one is 200mm higher than the other so if that one ever kicks in we know there's an issue and I will eventually get alerted if that happens. thanks to @pocster for that suggestion. I've also got a separate float that will go to an external alarm that also has a trigger that will feed the HA system as a last line of notification if both pumps have failed. that will go in at some point soon but I need the electrician to come over and wire all this up properly as it's just on 13A plugs for now. still got the Shelley flood sensor on the floor of the courtyard so if the sump does overflow that will alert me. feeling a LOT better about the risk of flooding occurring again now. Basement is free of water now as well. we've got a hired dehumidifier running and a 2kW convection heater going to try and get some heat down there. it's 'kind of' working but I'm now speaking to companies to bring forward our ASHP/UVC install so we can get the UFH going in the basement to help dry it out. thanks also to @Nickfromwales for his advice and effort in assisting. I'm just waiting to hear back from the second company with their quote and timelines before I make a decision between the 2 companies. Sadly, though, this has had an impact on the schedule for our house build. all the stuff we were storing in the basement is now in the house above ground so we can't really do any work as there are boxes and things all over the place drying out. hopefully we can get the basement fully dry again soon so we can put that stuff back down there and get on with working on the build. no one ever said self-building was easy!

I so wanted to mention something rude and totally inappropriate.

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.

As others have said, and even your assessor has said - see part in bold above in the quoted email.

Celotex. Cut to fit inbetween the timbers. No too thick, so at least some of the timber vertical face is visible. That way, the timers can half a decent chance of staying dry, and not rotting away. Celotex needs to be a good fit. Gapotape is your friend. If expensive.

Your quote or at least the data sheet says external expansion - the excelsior is an odd internal one that I’ve not seen before.

Nobody else having a go so I will stick my oar in. I would put your periscope in but make up the opening part that takes the airbrick larger than needed. If you do some sums you can work out the difference between a full brick and halfbond. So your opening letter box will be a brick and a half long, then when you put the slips on you can get the position right and cut a blank plug of eps and glue it in and put your slips over the top.

HI @Paene Finitur Make shuttering that fits inside the the box sticking out as much as the wall. 4 pieces of OSB or ply or whatever. fill the inside with wate ever to hold it tight - bricks, bits of wood - then plaster around the outside of the shuttering. I coat my shuttering with bits of plastic so it comes out easily. Y0u could pop each piece of wood in a plastic bag. Don't leave to long before removing the shuttering in case you have to do a bit of adjustment..

CVC in oxford.

That is a McDonald isn't it?

They're heat pumps but only heat the air directly rather than water, sometimes called A2A on here. They're fast response, cheap, offer excellent heating and cooling performance if you pick the right model. Where space heating is the bulk of the energy requirement they make a lot of sense. They're in almost every commercially building. The cardboard cathedral in Christchurch NZ I quite liked. Made from cardboard tubes and double walled polycarbonate post the earthquake. I second the call for a proper "passivhaus"professional. Otherwise you may struggle to keep overheating etc under wraps. With Sustainability in mind I had 2 thoughts. 1. A safe secure and dry bike storage area. 2. An area for breast feeding, nappy changing and kids + parents.

Pile in folks, lots of folk on BH will be happy to help. To get the best out of this then it all starts in the ground and you work your way up from there. If you can post more info then will be happy to chip in with what I know as I'm sure others will.

Agreed, you don't want to be charged business rates for a row of EV chargers.

Check your charitable status, easy to get caught out.

It sound like you want to build a to Passive House Standards, check that your architect has experience in building to PH Standard. Far too many architects are more concerned on how it looks than energy and comfort IMHO. When not in use this would make a great community EV charging station and would generate you some welcome funds.

This changes the usage ratio somewhat, but also the income potential. Because of that the heating system may be better being on constantly and take advantage of UFH in a large concrete slab. As buildings get larger, they tend to have a smaller exposed surface area to volume ratio, so in effect, use less energy per square meter of floor area. Having said that, overall usage is the important bit. Having a thermal load of 20 W/m2 may sound impressive, but if you are heating a 500m2 building, it is not as good as 30W/m2 for 300m2. You seem to have focused on the inside space, but do you want it to look like a Methodist Chapel, or a generic village hall, or worse, fit in with the local vernacular? Most Methodist Chapels down here have a very grand frontage, then 'tin shed' built behind then. If you want to take advantage of PV, and I think you should, most of the front should become PV modules, that will make a really big statement. Just make sure the Cross does not cast a shadow. So avoid porches, trees and street lamps/telegraph poles that could cast shadows as well. 3 Chapels in a town in I avoid. OK, that last one has become a community hub.

Yes interesting project. It would make a change for such a building to be something other than a very cold impossible to heat stone building. Net zero is easy. Any house with enough roof space could fit enough PV to generate in a year more than the building uses. It would NOT mean zero bills or off grid because most generation would be in the summer so you would be exporting and most usage would be in winter and you would be importing.

What an interesting project. I'm guessing it's circa 300m2 internally so not drastically different from a large house. I second the notion of rapid response heating. If UFH you'll be best to do it in as thin a screed as possible with closely spaced pipes. However I think a multi split air to air unit would be more than sufficient. A good brand should be near silent as well as keeping the building cool in hot weather. Aim for excellent airtightness and install an on demand MVHR unit and the building will never get too cold. For the kitchen an undersink water heater on a timer would be economical. Given the intermittent occupation and very low water demand almost all solar power will go unused if off grid. I would completely isolate the ideas of power generation and usage because unlike an office or house there'll be tiny overlap. If aiming for the lowest environmental impact using materials with low embodied energy is important. If you build just from things that used to be plants you won't go far wrong.

This sounds like an interesting project. Net Zero is an odd concept, pretty meaningless as well because it just relies on accounting i.e. self generation, at any time = usage, at any time. It is the 'at any time' that is the problem. I could make my small house net zero by just closing it up and moving out. So, in my opinion, the first thing you need to do is work out the weekly occupancy of the place i.e. how often is it open and needs to be usable. From that an energy profile can be established. It will not be 100% accurate, but even if it is within 20%, it is something to work to. When the building is in use, the power requirements will be quite high, when it is not in use, they should be close to zero. Most of the time the building will be empty I suspect (the large Methodist Chapel near me is very underused and has an all or nothing heating system). So while adding additional insulation (better than commercial building regs) may help if constantly heating, it may not be the best usage of the cash you have to spend. A fast acting heating system may be best, this is usually forced air i.e. change the cold air to warmed air, rapidly. The problem with this is that it tends to be noisy, and a Chapel should be quiet (my Quaker background wants it silent and no echo/reverb). It should be possible to have a system designed that is suitable, and the heat source can be whatever you like, as long as it is outside the building. PV is always worth fitting, especially in an underused building, the excess generation benefits everyone, not just the congregation. Now you ideally want excess generation all year round, but this is problematic in the winter. A 30° roof angle is less than idea, you really want the modules hanging off the SSW walls as they are then at a better 'winter' angle. Forget the NNE side, modules will be just expensive cladding. Ideally you will need some sort of energy storage to run the lighting, kitchen, ventilation, and the organ (get an electronic one and make some fake pipes). Some heating could be done by storing in a large concrete slab, but that means you are heating 24/7, which may not be optimal (depends on your initial energy profile). You could also store excess PV generation is a large water cylinder, then, when the building is going to be occupied, release that energy though a forced air heating system. Any stored hot water can be heating by any method i.e. gas, oil, solid fuel, PV, GSHP/ASHP, or a combination of any of them. It really depends on that energy profile. Other things to look into are any electrical equipment needs to have zero power draw when no being used. So don't go over board on the technology, a small kitchen can have a basic induction hob and an oven (usually larger than needed, commercial ovens are pretty basic inside), empty any fridge and switch it off when not needed (food will generally come in cold so will help cool the fridge anyway). Think about lighting very carefully. Single Phase or 3 Phase is really down to the expected maximum load, design it for Single Phase i.e. 100A maximum (23 kW). Then if close to that, get 3 Phase. Be careful how any PV is wired into it though, the Community Centre in Redruth has the PV wired into the two lightly used phases, while the more heavily used one has nothing (was a pre FiTs system, so totally useless). You will probably struggle to find an Architect that will understand the problems of spasmodically used, low energy, novel buildings that need to be off grid (even if connected to the grid). Use an off grid mentality when designing it. So to push the point one more time, work out what it needs energy wise, and when it needs it, then work on ways to reduce it, then look at ways to generate and store it. Not the other way around. You could end up with a very architecturally interesting building that need not cost any more to build than a basic building.

Don’t worry about it . A year or 2 or 3 … late ; no worries 😎

Unlikely to be effective for extended periods. Maybe when i was younger............