TerryE

@Jenki IMO, implicit to all this is that I have a passive class house in terms of U-values, air tightness, MVHR, etc. In this, inter-room or inter-zone heat transfer is an order of magnitude higher that interior to exterior transfer. I have what is called a warm slab -- that is the entire reinforced floor slab is within the insulated perimeter so my total thermal mass internal to the external insulation barrier (I did the sums once and reported these on a post somewhere) IIRC is equivalent to that of ~100 tonnes of concrete. If the heating fails, then the house as a whole cools at around 1°C per day. In my previous house we heated by room, with only a few rooms kept at a comfortable temperature. In our current house every room and touchable surface is essentially at the same temperature within a degree or so; zones make no sense in this new context. Our UFH, loops were laid into the slab by being tied to the rebar before pour. The layout avoided walls etc, but MBC advised that we keep the loops all the same length (and close to the 100m roll length). We could have just about fitted in 4 × 100 loops, but this was tight. As I only needed to pump a few kW into the entire floor, we spaced the runs out a little and dropped heating the utility room, so that we could make do with 3 loops (which when laid actually varied from 93 – 100m, IIRC). I trimmed the manifold valves by setting them to max and slightly closing them as need so that the temperature drop across all three zones when heating was the same. The Willis actually draws 2.88 kW, so an entire 7 hour heating budget works out at just over 20 kWh. 2 × Willis seemed like overkill at the time, as a single unit should have been enough to keep within cheap rate for maybe 95% of the year with our planned 20°C target, given our expected other waste heat. However as I said previously, we upped the heating set point for comfort ending up with an average some 2.8°C higher. BTW, pretty much all electricity used within the house ultimately cascades down a waste heat within the environment. In practice our new lighting, computers, and our other base electric load ended up being quite a bit more energy efficient in the new house, so this waste heat element was less than anticipated from previous use. The electric rad on the landing typically adds 8 kWh over night for a full 7 hour window. We have maybe 30 days a year where we need to top up over this 28kWh threshold, and end up using peak rate electricity. So yes, using a bigger resistive heater such as a 5kW inline or just 2 × Willis (as others have done) could have kept heating in the cheap rate window, but it just wasn't worth the hassle to make this change, as our current arrangement only adds maybe £10 - 15 to our annual electricity bill.

Just a dissenting perspective for anyone considering a Loxone route. You are looking at something like £10K +/- a factor of 2 for this route, and building, configuring and maintaining this type of system will either require a lot of expertise on your part or having to pay pretty high unit-rate Loxone certified engineer time to do this. Yes, this type of system might be sensible if you want a 100% automated house, but IMO if you are a more typical builder then an approach of only automating stuff where there is a good reason to do so means that you can sensibly look at options which will cost £100s rather than £1000s. If you have basic IT literacy and any basic programming skills then such more budget route is to use low cost server modules (such as PRi4s) and open-source components such are Home Assistant (HA) and Node RED. I spent 35 years in the IT industry from engineer through to CTO and there is nothing "cheap and cheerful" about these H/W and S/W components. The build quality and documentation are absolutely 1st rate. I use one RPi4 to run control my CH + DHW, another for HA doing general home automation, and a third as a gateway / general Docker host. I have around 50 Zigbee devices controlled by HA, plus a few Sonoff and Shelley devices running Tasmota and controlled through MQTT. The CH system has ~20 directly connected sensors and controls 4 directly connected power relays. This give me precise control of CH, DHW, various lights and external systems, etc. all for around £500.

@Dan F I've just added a new post. Enjoy

We moved into our new build mid-December 2017 in time to host an extended family Christmas. We are now over 4 years into living in our new home. We have lots of accumulated experience and made a few small tweaks. However, we are delighted about how the house has turned out, and we love living here. There were no material cock-ups, or regrets on design decisions, so we have probably fared a lot better than most new purchasers or self-builders. Maybe a general experiences post should be on the to do list, but what I want to focus on here, and a couple of follow-ups, is a general topic that others on the forum have asked about over the years: that is how our central heating system works in practice, and how I control it. The system as currently implemented is still largely the same as when I first commissioned it, that is a now 5 year-old RPi-based custom control system directly controlling the CH and DHW subsystems. This is a pretty minimal headless system running Node-RED, MySQL and MQTT client for control. The three material changes that I've made since moving in are: I have followed my son and son-in-law in using Home Assistant (HA) for general Home Automation. My server (an RPi4 in an Argon One case) uses an attached Zigbee gateway, and I have a lot of Zigbee devices around the house: switches, relays, light sensors, etc. and I do the typical home automation stuff with these. There are loads of YouTube videos and web articles covering how to implement HA, so please refer to these if you want to learn more. My HA installation includes an MQTT service for use as a connection hub for these IoT devices. I also have another RPi4 acting as an Internet-connected portal / Wireguard gateway/ file-server for caching video snippets from my PoE security cameras. Note that none of my IoT devices directly access the internet, and the only in-bound access into my LAN is via Wireguard tunnelled VPN, and my HTTPS-only blog. All other ports are blocked at the router. Before moving in, we assumed a target internal temperature of 20°C. In practice, we have found this too cold for our (fairly inactive OAP) preference and so we have settled on a minimum control threshold of 22.3°C. As you will see below, because we largely heat during the E7 off-peak window the actual room temperatures have a ~1°C cycle over the day, so the average temperature is about 22.8°C. This hike of 2.8°C increases the number of net heating days since my design heating calcs and the increased delta against external temperatures in turn increases our forecast heating requirement by roughly 18% over our initial 2017 heating estimate. Because our UFH is only in the ground-floor slab, we found that our upper floors were typically 1-2°C cooler than the ground floor in the winter months. We also need more than the 7 off-peak hours of heating in the coldest months, so I have added an electric oil-filled radiator on our 1st-floor landing; HA controls this through a Zigbee smart plug that also reports back on actual energy drawn during the on-time. HA uses MQTT to pass the actual daily energy draw back to the CH control system. This radiator provides enough upper-floor top-up heat, and does so using cheap rate electricity. Note that all servers are directly connected to my Ethernet switch, and the CH/DHW system has all of its critical sensors and output controls directly attached. It can continue to control the CH and DHW subsystems even if the HA system or Internet is offline. There is also no direct user interface to the system, with all logging data is exported to MQTT, and key CH/CHW set-points and configuration are imported likewise. This integration with MQTT, enables user interfacing to be done through the HA Lovelace interface. If there is sufficient interest I can do follow-up posts on some more of the "Boffins Corner" type details on these implementations, or if this turns out to be more of a discussion then it might be better to move this stuff to its own BC topic. However, for the rest of this post I want to focus on the algorithmic and control aspects of the heating system. In terms of inputs and outputs to the control system, these are: There are ~20 DS18B20 1-Wire attached digital thermometers used to instrument pretty much all aspects of the CH / DHW systems. Few are actively used in the control algorithms but were rather added for initial commission, design verification and health checking. Some are also used to monitor and to trip alarms; for example, there is a temperature sensor on the out and return feed for each UFH pipe loop. These were used to do the initial zone balancing. However, the average of the return feeds is used as a good estimate of the aggregate slab temperature. One of the temperature sensors is also embedded in the central hall stud wall to act as a measure of average internal house temperature. There are two flow sensors on the cold feed to my 2 SunAmp DHW storage units to monitor DHW use and to help automate during-day DHW boost. There are 4 240V/20A SSRs used to switch the power to my (2-off) SunAmps, my (1-off) Willis heater, and my (1-off) circulation pump. These and the rest of my 240V household system were wired up and Part P certified by my electrician. These SSRs are switched by a 5V 50mA digital input, and so can be driven from an RPi or similar. (I used a I²C attached MCP23008A multi-port driver to do this, as this can drive 5V 50mA digital inputs, but its input I²C side is compatible with RPi GPIO specs.) There are many ways to "skin this cat", but whichever you choose for your control implementation your system will need to control some 240V/12A devices and take some input temperature sensors. My preference was to directly attach all such critical sensors and outputs. My heating algorithm calculates a daily heating budget in kWh (each midnight) as a simple linear function of the delta between average local forecast temperature for the next 24 hrs and the average hall temperature for the previous 24 hrs. This budget is then adjusted by the following to give an overall daily target which is converted in minutes of Willis on time. heat input from the heater mentioned above. a simple linear function of the delta average hall temperature and the target set-point (currently 22.3°C). This is a feedback term to compensate for systematic over or under heating. I initially calculated the 4 coefficients of the two functions using my design heating calcs and an estimate of the thermal capacity of the interior house fabric within the warm space. After collecting the first year's actual day, I then did a regression fit based on logged actual data to replace the design estimates by empirical values. This was about a 10% adjustment, but to be quite honest the initial values gave quite stable control because of the feedback compensation. The control system runs in one of three modes: No heating is required. Up to 420 mins of heating is required. The start time is set so that heating ends at 7 AM, and the slab is continuously heated during this window. More than 420 mins of heating is required. 420 mins of heating is carried out in the off-peak window. On each hour from 8 AM to 10 PM, if the hall temperature is below the set-point (22.3°C), then an N-minute heating boost is applied, where N is calculated by dividing the surplus heating into the 1-hour heating slots remaining. Here are two history outputs from HA showing some of the logged results. The LH graph is the slab temperature over the last 7 days. The general saw-tooth is identical from my 3-D heat flow modelling discussed in my earlier topic, Modelling the "Chunk" Heating of a Passive Slab. The 7 hr off-peak heating raises overall slab temperature by ~4-5 °C; well within UFH design tolerances, and no need for any HW buffer tank: the slab is the buffer. The RH graph is the hall temperature. Note the days where on-hour boosts were needed. (Also note that the CH system only updates the MQTT temperature data half-hourly, hence the stepped curves.) So the approach is fairly simple, and the system works robustly. ? And here is a screenshot of my HA summary interface, which gives Jan the ability to control everything she needs from her mobile phone or tablet.

Dan, TL;DR it continues to work extremely well albeit with a few tweaks. I have been meaning to do an update for some time. Let me put together an update post. I'll do it later today, and ping you back to let you know when I've posted it. ?

In my (previous) farmhouse which was a ~18C stone-built construction in a village, we used to get a repeat invasion most winters as the little buggers decided to opt for life indoors. IMO, the only good indoor mouse is a dead one; the worst kind is at least one of each sex as this will turn into an infestation in weeks. So we used a mix of poison boxes, and snap traps baited with chocolate which seemed to get any incomers before they could breed. Still, it could a lot worse!

Yup Nick, however we've got a largish detached 4 double bedroom + ward storage / drying room which we keep at ~ 22½ °C all day, all year -- this may seem profligate, but we're getting old now and I just like being able to walk around in bare feet and shorts when I want without feeling cold; my wife and son ditto. As we discussed on the forum previously, if you don't have fundamental design flaws in your build (unsealed air-gaps, missing insulation, cold bridges, etc.) then the macro heat-loss is pretty straightforward: just the sum-product of area × U-value × ΔT for external surfaces + the air heating of cold replacement air -- which is basically what JSHs spreadsheet represents. The overall heat-loss is driven by the cost trade-offs on the coefficients in this calculation that you can control. As you and others have shown, it is quite possible to significantly reduce heat losses by retrofit, but in my experience this is a lot easier to achieve in a new self build where the owner has far more control over the design itself and can monitor build quality. In our case the extras incurred for going to passive standard were pretty much offset by savings elsewhere (e.g. no CH system other than the in-slab UFH loops -- my entire heating system cost about £2½K and is pretty much maintenance-free). Even though 90+% of our electric heating is done at off-peak rate E7 tariff, with the expected tariff increases when our fixed price contract finishes, the ~4-5 MWh that I could save by installing an ASHP might just about cover its investment cost so long as I do the install myself. As Joe said on another post, IMO dot&dab boarding out counts as a major design flaw, as this is rarely done as the videos on YouTube demonstrate, and too many internal thermal images of such external walls show that these voids often act as a large plate heat-exchangers dumping heat into void behind the plasterboard where the external draft air circulating here carries it out as convective losses. If you must use a conventional blockwork + insulation + external brick skin, then going for wet plaster on block if a far safer option, as well as making sure that all interfaces are properly taped during 1st fix.

TBH, this is because of crap quality control during typical builds. Our actuals are closer to 0.5, because we designed in airtightness into our build and made sure we chose subs who knew how to build to this standard. You posted elsewhere that you are still in the planning phase so what targets you design your house to and how you implement this is still very much under your control.

I would have cast that slightly differently. If you are truly losing 4 ACHP with no heat recovery, then this will be by far the largest source of heat loss. Think of your house as a system: it has to be in balance. There no point in having fantastic windows, etc., to keep the heat in whilst at the same time letting it escape through every crack in the house if there is the slightest wind. I have a passive-class house which is maybe 40% larger than yours, and our energy expenditure is just over 11 MWh p.a., (This is all electric, of which about 60% is resistive space heating – I can't make a case for installing an ASHP even though we've allowed for one in our initial design). Even with ~ 90% heat recovery, our MVHR circulation accounts for about a ⅓ of our heat losses. I would suggest as an option that you consider retaining the MVHR, but look at what mitigation you can do to get your ACHP under 1. You will find this will get you a more balanced system, and a more comfortable house as well as lower bills. BTW, in my case my FP contract with OVO will more than double in October which tilts the cost benefit case and so we may be installing an ASHP over summer. ?

NodeRED uses connect-the-block pre defined modules to implement control. Lots of YouTube videos on it. You can do complex stuff in JavaScript which is pretty straightforward if you've ever done any programming.

Having an in-slab UFH implementation helped us a lot and made everything pretty simple. We've got a 3 storey detached house with four largish bedrooms and one storage / drying room with the heating requirement peaking at around 30 kWh in the winter months (and little solar gain because of our house orientation and planning constraints). If we heat only in the E7 window, that's just under 4kW net heating, and the thermal mass of the interior is such that this gives us ~1°C ripple on room temperatures. If we don't heat the house (an accidental experiment) then it cools overall by around ~1°C per day. This all depends on the "devil in the detail" during construction: all insulation installed to spec; decent air tightness, MVHR; no oops thermal bridges. A constant heating strategy would peak at ~1½ kW so IMO a typical small 8 kW ASHP would be total overkill. I don't know what the true replacement life of an ASHP is, but it would need to be 10 years or so for us to justify its procurement and installation cost. Over 4 years in and I have made a few tweaks to our system: The CH + DHW is controlled by a dedicated RPi using Node-RED for sequencing etc. We have added a Home Automation System (HAS) running on another RPi and using Home Assistant with lots of ZigBee devices doing the usual home automation stuff. This system also controls an Oil-filled electric radiator we have on our 1st floor landing which we run 0-7 E7 hours in the winter; this uses a smart plug which also reports actual power used. This rad plus E7 Willis Heating keeps the whole house nice and toasty. The HAS and CH systems use MQTT to swap set-points and logged data, but it's all set up so that the CH system will still run happily if the HAS isn't available. This automation approach might seem complex, but the H/W and install costs were in the few £100s. It all works pretty much automatically with minimal maintenance. The biggest wobbles to our system are caused by visitors staying, such as one of our kids + family, as this adds an extra 4 bio-radiators that move from room to room and can cause local over-heating if we all sit in one room for too long. The simple answer here is passive-house heresy: open a window or two for a bit to dump the extra heat.?

There's a parameter in your /boot/config.txt which can be used to override the MAC addr: smsc95xx.macaddr=<whatever valid addr you want>.

IMO, the whole concept of zones gets very questionable as the spec of your house approaches passive class. It is a bit like trying to maintain storage zones inside a thermos flask. The internal heat flows are an order of magnitude greater than external losses. We run our 3 floor house as a single zone which is heated by the slab. My control system circulates water around the slab for 10 mins every hour when not heating. This redistributes slab heat from solar gain and enables taking an accurate average slab temperature. The only real exception to this is the floor to floor heat gradient in colder months, as the 1st and 2nd floors do tend to be a degree or two colder than the ground floor, but I trim for this with a couple small oil-filled electric heaters on the two floors and they turn on for a few hours overnight on timers and add a few kWh of space heating on each floor. The 1st floor one sits in the doorway of my office and this boosts the entire 1st and 2nd floors. My son occasionally uses his in his top floor area.

You really need to do the sums for a sketch design. Search for Jeremy Harris spreadsheet on this site. I have a 3 storey passive house with underfloor heating. Our heating days are quite high but the actual amount of heat is quite low (we heat the house with a Willis -- which is essentially a 3 kW immersion heater in a jacket.) At the moment it's on for maybe 3-4 hrs a night at E7. However, we have little solar gain because of the house orientation and planning restrictions limiting the area of windows facing SE (and non on our S/W gable). The same house with larger windows on a south facing principle axis wouldn't need any supplemental heating at the moment. You really can't generalise, but a properly constructed passive house should be within 10-20% of this rough-cut estimate. The caveat here is the "properly constructed" as the devil in the detail. If you've got building flaws which result is thermal bridges, missing insulation, significant air leaks, etc. then your actuals could be way off.

@Bramco, I see that you've just done a like on my Heating the Slab – an overview post. After over 4 years the system works pretty much faultlessly. The 3 storey house is heated by what is essentially and immersion heater. The one tweak I have added is an oil filled rad in my office on the 1st floor which my home automation system turns on for a few hours overnight to add a bit of space heating for the upper floors (and more in cold snaps). Without this the temperature can drop below 20°C which is my comfort threshold. This actually works out cheaper as only need to supplement heating outside of E7 rates in the absolutely coldest weeks. Using resistive heating like this isn't really efficient in terms of run-rate as it costs us about £700 p.a. for space heating, but the upfront installation cost was pin-money, and zero maintenance because of no moving parts (I do have a spare Harvey heater for cold-swap if the current one fails.) Adding an ASHP might drop this energy cost by £500 p.a. or so, but at an upfront one-off cost of £5-10K for installation of a piece of kit that might just have a 10-year life. There is no economic case here. Our slab input temperature rarely gets above 35°C and if we were spreading our heating throughout the day then an ASHP with <5kW output in the range 30-35°C would be fine. Most installers wouldn't understand a house that operates in this domain. Our house pretty much exactly performs as the simple heat calc predicted -- we've got maybe + 20% on the slab losses due to a thermal bridging flaw discussed in the blog, but this is small-beer overall. And yes, air heating of leak churn is a big component. IMO using MVHR is pretty essential. This allow you to have an air-tight house but at the same time keeping it fresh and avoiding the damp + stuffiness that you would get without it.

Yes, you can pass SAP with electric only heating (at least the 2016 Rev), but you really need a passive-class house to make the numbers work.

It really depends on the internal moisture content within the walls. My last house was ~300 down to 150 year-old Cotswold-like stone around 600 mm in depth, with the internal face rendered then hard plastered. We had an injected DPC that worked really well: when we moved in the infill was like damp soil; within 10 years it had entirely dried out to a mix of grain husk and clay powder. Based on heat losses I reckoned the U-value was around 1.0 once dried out. Still a bloody cold house though to heat! You also be better off with MVHR than vents. That would also mitigate / remove any dampness.

Nick, you've got to admit it: you are just another cantankerous old man ? My kids would unanimously stick me in that category as well.

We have acoustic insulation between the rafters and in the internal stud walls. The floors still tend to drum.

@Russdl Thanks to our planners objecting to the impact on the street-scene, we had to drop rooftop PV from our plans, and so we are import only.

I've got an MBC TF with external stone skin. I don't have any issues with room-room noise except between floors, and this is because ecoJoists seem to be very effective at transmitting noise vertically. We have 12mm board. You can get a range of decent wall fixings which typically butterfly or balloon in the void, and some are rated up to 25 Kg per fixing, so we've never had any issues with fixings.

I am fairly lucky in that I planned to switch to the Agile Tariff, but had to wait until my meter got upgraded to SMETS2. In the meantime, the Agile rates went through the roof, so I aborted this plan. I am just entering the second year of an OVO fixed price tariff at 9.19p / kWh night rate (about 70% of my annual usage) and 15.81p / kWh day rate. Sometimes the dice roll for you. With my house system, I could easily implement supplier-friendly demand shaping, but I see no point without adequate price incentives.

As soon as you start instrumenting a house and wanting to do more them IMO, it is just easier to bite the bullet and install Home Assistant on an RPi 4. You get a Zigbee dongle for it and Zigbee thermometers cost a few £s each. No need for any wiring fabric.

Modern PIR + IR nightlight cameras are pretty low power these days. I've got a bunch of Reolink PoE cameras and IIRC the power draw is less than a quarter what the exterior CAT6 is rated for, and well with the specs of my PoE switch. In fact one of my cameras uses an existing 5m run of pre-laid CAT5E -- it's buried under the block paving drive and it was just easier to use it rather than lift and re-lay the paving (if it worked that is). I've had no problems with it.

True now, but not when I configured mine. My point is that 1Gb for a single link is ample, so don't get into sweat over 5E Vs 6 for internal wiring. If you are wiring everything as a star into a switch, then the issue is switch capacity which is nothing to do with the fabric bandwidth. My main point of that you don't need to be too worried about uplink bandwidth: if you are pumping that much data into the cloud then that's a serious concern in its own right. It is your data. Don't give it away lightly.