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An Overview of my House Heating and Controls 4 years on

TerryE

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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:

  1. 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.
     
  2. 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.
     
  3. 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.

 

 image.thumb.png.edd654631141f8e2a6eee153594c5988.png image.png

 

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.

 

image.thumb.png.6cdcb1d60175d8d7610023c12cf8fc54.png

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Bramco
20 hours ago, TerryE said:

I am quite surprised that you managed to fit 1200m of UFH heating in your slab. We only have  280m or so.  IIRC we have ~ 230m² living space (but that's over 3 floors) and only the slab is heated by UFH

 

Hi Terry, ours is only 1000m and we have 260m2 of space but only half of the build is 2 storey, so a lot of ground floor and not much 1st floor.

 

20 hours ago, TerryE said:

we were literally living next door to the new build and being retired we were able to provide lots of tea, coffee, and bacon butties to the onsite crews as well as being able to keep a very close eye on build process and quality without being overtly intrusive.  We were also very lucky with the crews who were extremely hard working and committed to doing a quality job.  Even so we did pick up a couple of major design cock-ups early enough that we could liaise with MBC and get fixes put in before the consequential ripple forward.

 

We're in the same village but not on top of the build, so we were only there once or twice a day.  Agree though the guys are very hard working.

 

20 hours ago, TerryE said:

IMO, you really need a project manager who is independent of the construction crew on-site daily during this work to do quality control, trouble shoot and handle supplier liaison.  In our case I was competent enough and also had the free time to do this role.  So many self-builders seem to think that you can leave it to the subs and trades and assume that magic will happen.

 

I think we had assumed that MBC would have the required QC in place for the erection. For example the cowboy 1st crew from the subcontractors managed to get the sole plates out. The knock on effect of this has been massive as you can imagine.  I would have expected MBC having laid the slab, to also want to set out the sole plates to make sure everything was in the right place. As it transpired, the MBC QC chappie turned up late in the 1st week, didn't do any serious checks, just walked round and did a bit of nitpicking and then didn't come back for another 10 days.  The impact of the sole plate issue wasn't noticed until my son and I started to do some checking because of other issues. Long story short, I would insist on MBC setting out the sole plates - it's a THE interface between the slab as poured and the panels to be delivered from the factory. 

 

20 hours ago, TerryE said:

But my CH control system uses a directly connected DS18B20 embedded inside an internal stud wall as the reference internal temperature. 

 

Yes, I've used these on our Heat Bank with an ESP8266 board reporting through to and open energy monitor system.  Very easy to set up and we'll use the again in the new house.

 

20 hours ago, TerryE said:

One other thing my CH control does is to circulate the water in the slab for  8 mins every hour throughout the year.  This has two benefits: (1) this redistributes heat from hotspots (e.g. from direct sunlight through windows) to the whole slab (Thanks to @Jeremy Harris  for this suggestion); and (2) the averaged UFH return flow temp is an extremely accurate measure of the overall slab temperature.

 

We're also planning to do this, although I was thinking of doing it only on sunny days to redistribute the solar gain.  Doing it on a timer is much simpler - so thanks for the tip.

 

20 hours ago, TerryE said:

I only use one thermostat for feedback into the CH control system because (i) this was easy to directly wire up; (ii) when you go around the house with a FIR temperature probe, every surface is the same temperature within a degree or so, so a single probe is quite adequate. 

 

Again, when you think things through, this is obvious - although the plumber from our main contractor insists we'll need zones for every part of the house - don't want to fall out with the guy and the cost of a few extra thermostats isn't great, so we may install them but ignore them....

 

Thanks again for documenting your experience it has been very helpful.

 

Simon

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TerryE

@Bramco, Clearly too late for you now, but other members who tend to use this blog as a reference, this daily QR during these intensive periods is absolutely essential IMO.  I discussed a good example in our case in this post,  Coping with a thermal flaw in the design. I picked it up before the actual pour and agreed the workaround with MBC within a couple of days including getting it signed off by their SE before the pour was done.  We also helped the crew by taking off XY offsets of rising pipes etc from the nearest slab corners directly from the AutoCAD files, and Also checked the levels and diagonals of the EPC framing before the pour to make sure the mold was true and ditto the poured slab before the frame was shipped.

 

Another unnamed MBC customer who was a member here expected magic to happen.  Their groundworks sub didn't do the compaction layering correctly and so the entire slab slumped by about 3 cm in one corner during pour.   This was a cockup that could have been largely mitigated with an extra few days work to reshutter and add a self levelling layer whilst the slab was still green.  Because no one checked, so this cock-up wasn't discovered until the framing crew arrived with all the cassettes on a couple big lorries only to find the slab base was out of design spec.

 

This issue of your trades not understanding the characteristics of designing and fixing services in a passive house is a real PITA, IMO.  I gave up with plumbers and did it all myself, with some absolutely invaluable remote advice and help from @Nickfromwales.  Ditto all of internal woodworking and MVHR install.

 

 

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Bramco
7 hours ago, TerryE said:

Clearly too late for you now, but other members who tend to use this blog as a reference, this daily QR during these intensive periods is absolutely essential IMO.  I discussed a good example in our case in this post,  Coping with a thermal flaw in the design. I picked it up before the actual pour and agreed the workaround with MBC within a couple of days including getting it signed off by their SE before the pour was done.  We also helped the crew by taking off XY offsets of rising pipes etc from the nearest slab corners directly from the AutoCAD files, and Also checked the levels and diagonals of the EPC framing before the pour to make sure the mold was true and ditto the poured slab before the frame was shipped.

 

I've also been over things carefully and helped whenever I can but........    I have a contract with a company to do a highly specced job.   I don't expect to have to provide the QC on the job myself - surely they should have all those procedures in place.   So I shouldn't have to be doing these things.  As for analysing what's gone wrong and identifying the root cause and fix - well that's not my responsibility - but it ended up being that - mainly 'cos the QC person was a ........     Apologies but he really was.   We were in a site meeting with my son and the QC person was just staring out of the window. When asked what he was looking at, he said 'Oh, that sign on the fence, I'd not noticed that before.'  

 

But now I've hijacked an excellent post on experiences with alternative heating strategies, so let's just agree that if you are going into this kind of thing, you need to already be an expert, or have done one before to have the experience to say 'Whoaaaa stop right there.....'

 

I will try to remember to come back to this post with our experiences in a year or so's time.  Hopefully not cold......

 

Simon

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7dayworker
On 30/01/2022 at 12:52, TerryE said:

@Bramco Simon, I am quite surprised that you managed to fit 1200m of UFH heating in your slab. We only have  280m or so.  IIRC we have ~ 230m² living space (but that's over 3 floors) and only the slab is heated by UFH.  We were lucky to have a large plot that we could get planning permission to split off a plot for a new dwelling, so we were literally living next door to the new build and being retired we were able to provide lots of tea, coffee, and bacon butties to the onsite crews as well as being able to keep a very close eye on build process and quality without being overtly intrusive.  We were also very lucky with the crews who were extremely hard working and committed to doing a quality job.  Even so we did pick up a couple of major design cock-ups early enough that we could liaise with MBC and get fixes put in before the consequential ripple forward.

 

The MBC build process compacts their onsite work into three intense 7-10 periods.  IMO, you really need a project manager who is independent of the construction crew on-site daily during this work to do quality control, trouble shoot and handle supplier liaison.  In our case I was competent enough and also had the free time to do this role.  So many self-builders seem to think that you can leave it to the subs and trades and assume that magic will happen.

 

IMO you don't need in-slab sensors as you can measure out and return water temperature directly.  I have a quite few Zigbee Aqara temperature / humidity dotted around the house for my home automation system.  But my CH control system uses a directly connected DS18B20 embedded inside an internal stud wall as the reference internal temperature.  I also bought 20 of these. They were cheap as chips and I ran some calibrations on them to ensure consistency and discarded 3 that were out of my spec.  I also determined a temperature offset for each individual thermometer so that the reported temperature for all were within a ¼°C tramline across the operating range. (I posted about this calibration exercise).    

 

One other thing my CH control does is to circulate the water in the slab for  8 mins every hour throughout the year.  This has two benefits: (1) this redistributes heat from hotspots (e.g. from direct sunlight through windows) to the whole slab (Thanks to @Jeremy Harris  for this suggestion); and (2) the averaged UFH return flow temp is an extremely accurate measure of the overall slab temperature.

 

I only use one thermostat for feedback into the CH control system because (i) this was easy to directly wire up; (ii) when you go around the house with a FIR temperature probe, every surface is the same temperature within a degree or so, so a single probe is quite adequate. 

Just to clarify….why not underfloor heating on all floors.?

are you using radiators as well on top floors?

are you able to zone areas to avoid heating some areas or a floor?

is your hot water from a tank ?

sorry but this is all new to me ….thanks for texting info..

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SteamyTea
8 hours ago, 7dayworker said:

why not underfloor heating on all floors

Many people have found with a well designed, well insulated and airtight house, that there is no need to add heating upstairs (a bathroom may have some).

Internal convection, solar gain and the MVHR is often enough to keep the temperature acceptable.

My house is a small terrace, 1987 vintage, but reasonably well insulated and airtight, and I have never bothered heating the upstairs, except for a handful of days when the weather has been extremely cold (for down here).  A ten quid fan heater takes car of that.

Your local climate in Poole is going to be similar to mine.  Neither of us get very cold.

 

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TerryE
9 hours ago, 7dayworker said:

Just to clarify….why not underfloor heating on all floors.?

are you using radiators as well on top floors?

are you able to zone areas to avoid heating some areas or a floor?

is your hot water from a tank ?

sorry but this is all new to me ….thanks for texting info..

@7dayworker, you miss an important benefit of living in a passive-class house: all of the insulation is on the outer barrier, and the thermal mass on the inside.  So there is minimal room-to-room or time of day variation: essentially everything is always at the same temperature within a degree or so.  This allow you to remove entirely a lot of CH subsystems and control complexity.

 

As Nick says UFH on upper floors isn't needed, and adding it adds a lot of cost and complexity for no benefit.

No wall rads, though I do use a  free standing (<£100) oil-filled rad which I control with a Zigbee plug for maybe the 3 coldest months each year.  (It's back in the storeroom now.)   In the winter months it puts maybe 6 kWh into the 1st floor hall, and this is enough to keep the 1st floor bedrooms toasty.

 

DHW is by electrically heated SunAmps (search the forum for more info).  They are super insulated so you really only put E7 kWh into these to heat the water you actually use.  Surprising cheap to run.

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SteamyTea
3 minutes ago, TerryE said:

thermal mass

Ahhhhh, run for the hills.

 

{\displaystyle e={\sqrt {\left(\lambda \rho c_{p}\right)}}}

Edited by SteamyTea
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TerryE
3 minutes ago, SteamyTea said:

Ahhhhh, run for the hills.

 

It's OK;  Sadly Jeremy isn't around to tell me off for this sloppy terminology. 🤣

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joe90
51 minutes ago, TerryE said:

 

It's OK;  Sadly Jeremy isn't around to tell me off for this sloppy terminology. 🤣

Mores the pity 🤷‍♂️

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7dayworker
On 22/03/2022 at 07:48, TerryE said:

@7dayworker, you miss an important benefit of living in a passive-class house: all of the insulation is on the outer barrier, and the thermal mass on the inside.  So there is minimal room-to-room or time of day variation: essentially everything is always at the same temperature within a degree or so.  This allow you to remove entirely a lot of CH subsystems and control complexity.

 

As Nick says UFH on upper floors isn't needed, and adding it adds a lot of cost and complexity for no benefit.

No wall rads, though I do use a  free standing (<£100) oil-filled rad which I control with a Zigbee plug for maybe the 3 coldest months each year.  (It's back in the storeroom now.)   In the winter months it puts maybe 6 kWh into the 1st floor hall, and this is enough to keep the 1st floor bedrooms toasty.

 

DHW is by electrically heated SunAmps (search the forum for more info).  They are super insulated so you really only put E7 kWh into these to heat the water you actually use.  Surprising cheap to run.

Thanks  . That is useful and thanks to Nick . My builder has built his house and will do ours similarly . The architect reckons a spend of £1,000,000 .  The builder regrets that the third floor is too hot and that’s where they sleep . He also says the 2 lantern lights by the bifold doors create heat and huge discomfort in the summer .  He regrets not using triple glazing . Something we can’t allow to happen with our build . The only solution I found is attic insulation and gazing blinds and positioning glass away from south facing areas 

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TerryE

@7dayworker, If you do have an decent energy efficient design then one thing that you can consider is using room-style bi-block ASHPs. @Jeremy Harris did a blog entry on his fitting one on his upper floor -- not in his bedroom but in a landing area. The 9,000 BTU / 3 kW units are pretty cheap and will pump / dump enough heat to equalise inter-floor heat layering.

 

As to lantern lights, the LED versions are typically under 10W.

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