Where to position your themostats?

[newhome]

I have every room on a different stat / zone, the advantage being that I can have the heating off in the 2 thirds of the house I never use, and for the rooms I do use I prefer to have warm downstairs (20), and cooler upstairs (16). Even then I can choose to let the temperature drop down overnight or when I am out of the house as I know how long it takes to bring the rooms back up to desired temperature and can set accordingly. Having individual stats is important to me as being on an electric system in a large non passive house the heating costs would no doubt be significant (and wasteful) if I was heating every room. 

 

I do have MVHR but don’t find that it works efficiently enough to balance the heat across every room. It probably helps to some degree but the non heated rooms are certainly a lot colder than the ones where the heating is switched on. 

 

 

 

 

 

[Jeremy Harris]

53 minutes ago, joe90 said:

I take my hat off to @TerryE and the like who can do this stuff, I have trouble programming the tv remote ?. The older I get the more I become a Luddite.

 

For me, I was well into experimenting with my own microcontroller-based control system when a birthday passed and I suddenly started thinking about long term maintainability.  It was great fun designing, programming and tweaking the control system, and I'm certain I could have got a controlled-temperature slab system to work very well in the end.

 

However, my wife keeps asking me how to look after things like the water system and the MVHR, as well as everyday stuff like turning the heating/cooling system on and off, changing the temperature, etc, and I realised that if something happened to me there would be a system controlling the house that no one would have a hope in hell of being able to understand or repair. 

 

That's what really made me shift away to a control system that any heating engineer can understand, after a few minutes of reading the instructions and wiring diagrams I've drawn up.  All the parts are now off-the-shelf standard items, and there are spares for pretty much everything as well.

 

Age is a bit of a bugger, too.  I recently went back and looked at a (well-commented) bit of code I wrote a couple of years ago, and struggled to get my head around what I'd done.  I got there in the end, but it took more effort to understand than it would have done ten years ago.

[TerryE]

@newhome,

4 minutes ago, JSHarris said:

That's what really made me shift away to a control system that any heating engineer can understand

 

My situation is somewhat different I've got a couple of sons and a son-in-law who understand programming and the last also does this stuff just to the chagrin of my daughter -- "I've just ended up marrying a copy of my dad!" (And she's done a bit of programming in her time but has made a point of selective amnesia here ?)  But coming back to Jeremy's point, I think that there is a flaw in this argument: a passive house like yours or mine is a completely different beast than a conventional one.  The time constants and rates of heat loss are just in a different league.  Unless the control system is well-matched to the system it is controlling, the net result won't be stable control.   

[ProDave]

18 minutes ago, JSHarris said:

 

For me, I was well into experimenting with my own microcontroller-based control system when a birthday passed and I suddenly started thinking about long term maintainability.  It was great fun designing, programming and tweaking the control system, and I'm certain I could have got a controlled-temperature slab system to work very well in the end.

 

However, my wife keeps asking me how to look after things like the water system and the MVHR, as well as everyday stuff like turning the heating/cooling system on and off, changing the temperature, etc, and I realised that if something happened to me there would be a system controlling the house that no one would have a hope in hell of being able to understand or repair. 

 

That's what really made me shift away to a control system that any heating engineer can understand, after a few minutes of reading the instructions and wiring diagrams I've drawn up.  All the parts are now off-the-shelf standard items, and there are spares for pretty much everything as well.

 

Age is a bit of a bugger, too.  I recently went back and looked at a (well-commented) bit of code I wrote a couple of years ago, and struggled to get my head around what I'd done.  I got there in the end, but it took more effort to understand than it would have done ten years ago.

That is largely why I wanted to mostly ignore the programmer that came with the ashp (and regard it as a curiosity / a means to adjust parameters) and wanted the heating system controlled by an ordinary central heating controller.

 

I must get around to writing the manual and in particular the wiring diagrams so in the future a third party might stand a chance of understanding it.

[joe90]

Yup, my missus asked me how to “work it” and I had to say “I need to work it out for myself first!”. Regarding a passive house needing “special systems” I think I understand that Jeremy has done that with simple controls. I am not worried about temps varying a bit, I know that response times will be long with what we have but like @JSHarris I am sure we will get there (with a lot of help from this forum ?).

[newhome]

1 hour ago, joe90 said:

I know that response times will be long 

 

Response times are long if you have UFH regardless of whether it’s a passive house or not. Goes with the territory. The speed at which the temperature drops will vary but even then in a non passive house mine only drops 1.5 - 2 degrees in 24 hours at current temperatures. It then takes an hour or maybe just over to recover those 2 degrees when the heating comes on in the evening. It’s not yet dropping down low enough overnight to require it to come on in the morning. The main thing with UFH I have found is understanding how your own behaves and to work with that to suit your lifestyle. There is no one size fits all. 

 

[joe90]

5 minutes ago, newhome said:

There is no one size fits all. 

 

 

Yup, even house location makes a big difference, it’s down to trial and error till we achieve what suits best.

Edited November 13, 2018 by joe90

[lizzie]

3 hours ago, joe90 said:

I take my hat off to @TerryE and the like who can do this stuff, I have trouble programming the tv remote ?. The older I get the more I become a Luddite.

+1

[MikeSharp01]

18 hours ago, TerryE said:

For those not familiar with what this is all about and have some mathematical toleration, try the Youtube Computerphile videos by Mike Pound on this general topic.  Amazing stuff.  However,  I see this is more of a classical control systems issue rather than a deep learning one.  Deep learning requires huge amounts of training data across a catholic set of scenarios, and this just the case for the thermal control of a passive class house. 

I tend to agree that it might well be just a classical control theory problem if it were not for the fact that this deep learning stuff is disrupting classical theories across the piece.  Although a vast training set it required in supervised networks for improved accuracy one might envisage a situation where an unsupervised network might learn from a number of houses which while being very different do have similar reactions to similar stimuli. Good to chew it over though.

[Gone West]

When we designed our house we wanted a low energy usage, low maintenance house, and Wendy insisted on a KISS approach to operating it. So we have one simple control for water temperature and air temperature. Water is set at 45C and air at 23C and Wendy is happy that if I'm not around she is able to keep everything going. I'm hoping that we will be able to gradually reduce the air temperature as we get used to living in a PH. We had the thermostat set to 24C in the bungalow because of the cold spots that existed in there but as there are none in the house we should be able to get it down to 21C eventually without Wendy feeling uncomfortable.

[TerryE]

Since we use SunAmps to provide DHW, we don't have any control on the HW setpoint other than the master TRV in the DHW manifold.  As I commented above, we also keep or temp at around 23°C.  At the moment, I set  a configuration parameter in the the Database to change this, but I also have a browser dashboard that we can use to monitor the system and change it -- not that I want anyone to do so trivially, because it takes a few days for the house to settle down even if you want to change this by a degree.

 

So functionally we do pretty much the same thing.  My implementation is in software, but the advantage of having kids in the IT business is that this isn't an issue for us.

Edited November 14, 2018 by TerryE

[TerryE]

One corollary to this is whether you can use the slab temperature as an alternative to an inside room / fabric temperature to control an UFH system, and the following plot demonstrates this issue:

 

This is a plot of our hourly slab temperature and it seems to be all over the place for two reasons:

• We heat the slab twice a day (and if the weather is milder then the day period if 0 hrs long).  The excess heat is slowly dumped into the house environment creating the sawtooth.  Yet the 1-σ room temperature against target is between ¼ and ½°C.
• The heat needed to maintain the overall fabric temperature is practically a straight-line relationship to the delta from the average external air temperature: as it gets colder you need more heat  and the slab has to provide it.  In our case each extra °C of the slab surface temperature averaged across the day outputs about 10 kWh per day.   If our external temperature drops by about 11°C then I need an extra 20kWh heat daily, so my slab has to be 2°C hotter (or I can keep the averaged slab temperature fixed and let the house get 2°C cooler -- which I wish to avoid).

There are a number of approaches to adapt your average slab temperature.  One is to use an internal fabric / room stat to feed an on-off demand to your UFH system and indirectly implement the needed mark-space ratio that way as a side-effect.  Another is what I do, which is to use a few dozen lines of JavaScript to do some simple heat calcs and set the heating parameter on this basis.  Both work. Both have advantages and disadvantages, but my main message for this post is: don't attempt to control the air temperature using the slab temperature alone; this doesn't work, IMO. 

Edited November 22, 2018 by TerryE

[joe90]

9 hours ago, TerryE said:

don't attempt to control the air temperature using the slab temperature alone; this doesn't work, IMO. 

 

Is this not what @JSHarris does with his?, using a room stat?

[Ed Davies]

1 hour ago, joe90 said:

Is this not what @JSHarris does with his?, using a room stat?

 

As you say, he uses a room (hall) stat so he's not controlling the slab temperature alone.

 

@TerryE could you say how your system currently works? AFAIKS in this thread you've said a couple of times various ways it doesn't work but not actually spelled out how it does other than saying it measures the slab temperature and uses that to adjust the amount of heating overnight (and in the afternoon). Is it that it looks at the drop in slab temperature or what?

[TerryE]

3 hours ago, Ed Davies said:

@TerryE could you say how your system currently works? AFAIKS in this thread you've said a couple of times various ways it doesn't work but not actually spelled out how it does other than saying it measures the slab temperature and uses that to adjust the amount of heating overnight (and in the afternoon)

 

Ed, to be honest, I haven't really decided what my end control algo will be.  What I did decide to do was to try a temporary simple control regime to see how it performs, and to gather enough data to refine it, before doing so.  My system is implemented in software rather than bespoke hardware, so a change involves tweaking a few lines of JavaScript in my NodeRED setup and hitting Deploy, rather than having to buy and to install wiring and bits of kit.

• I use a two on/off time scheduling system and during the on times, the Willis puts 2.88 kW into the slab. The main one ends at 7am and so is entirely in the E7 cheap rate window; the other starts at 5pm. 
• I run the UFH pump for 10 mins before each hour and average the return temperatures on the hour.  The 10 min value was a matter of trial and error: when I take the temps every 30 secs, I can see that it takes about 7 mins or so for the three return thermometers to stabilise to a steady flow return temperature, so after 10 mins I am confident that their average is the actual average slab temp to the resolution of the thermometers.   (The other upside of this regular circulation is that as @JSHarris has found doing a regular recirculation redistributes the local heat from any hot spots from sunlight by windows.)
• From my 3D modelling of the heat flows (and which really tracks the actual slab characteristics well) I know that  the temperature is hottest immediately around the UFH pipes and falls away as the heat flows radially into the slab during the heating periods, but that the heat has spread pretty uniformly throughout the slab by 6 hrs or so after the heating has turned off.  (There is a residual uniform gradient towards the slab surface, so the surface is about ½°C cooler than at the level of the UFH pipework.)   But by 1pm, the measured temperature is a good estimate of the actual slab temperature.
• So I do a linear fit of the hourly temperatures from 1pm to 5pm and take the 3pm point as my surrogate datum (yes, I know that I could have taken the average, but I wanted to track the rate of heat loss as well).
• I use an incremental approach to determine how much heat that I need to put into the slab.  Based on the heat needed, I can calculate the temperate offset that I need the slab to be at.  This gives me a target temperature for the slab, and by comparing to this 3pm actual. I then adjust the total heat for the day up or down depending on this error.

By now my crappy explanation has lost most readers.  Sorry for this.   But for those still tracking this explanation, I've included the bit of NodeRED code that implements this as a footnote. 

 

This isn't a perfect solution, just a "let's hope that it is good enough" one until I get a good handle on what I need to do to implement a more robust approach.  I also collect the hall temperature using a DS18B20 thermometer which in the studwork against the back of the hall plasterboard (and this entirely invisible), and I use a Met Office feed to collect the daily forecast data.  I also plan to add another temperature probe in between the stone skin and TF.  I might use these in the future, but the reality is that my first stab at this works pretty well -- so well that there isn't enough pressure to try to improve it.  Over the last month the total heating time has wandered from 2hrs a night to 11hrs as the external temperature varies, but does this purely by comparing the actual slab temp with what I calculate it should be.

 

The hall temperature varies by about +¼ to -¾°C from our target set point, but the low drops are more to do with our comings and goings letting in cold air into the hall than the temperature in the rest of the house.  Jan and I have never lived in such a comfortable environment before and we are still getting used to this, let alone planning to improve it further.   

 

    onTime1     = msg.onTime;   // This is the total ontime for the previous day

    for (j = 0; j<2; j++) {
        heatReq = onTime1 * WILLIS_OP;
        tGoal   = (TARGET_T + heatReq/KWH_PER_DELC_SLAB).toFixed(2);
        error   = (tGoal - t15).toFixed(2);
    
        let sign = error >= 0 ? 1 : -1;
        if (Math.abs(error) > 0.25) {
            onTime1 += 0.5;
        }
        node.warn (`${j}: ${msg.onTime} to ${onTime1} for error ${error}`);
    }
    
    onTime2 = (onTime1 < 6) ? onTime1 : (onTime1 < 7) ? 6 : 7;
    onTime1 -= onTime2;
    let on1 = 0, off1 = 0, on2 = 0, off2 = 0;
    
    if (onTime1 > 0) {
        on1 = today + 17*HOUR; off1 = on1 + onTime1*HOUR;
        node.send({topic   : 'house/heating/time1',
                   payload : JSON.stringify({on: on1, off: off1})
                   },  null, null);
    }
    
    if (onTime2 > 0) {
        off2 = today + (24+7)*HOUR; on2 = off2 - onTime2*HOUR;
        node.send({topic   : 'house/heating/time2',
                   payload : JSON.stringify({on: on2, off: off2})
                   },  null, null);
    }

 

Edited November 23, 2018 by TerryE

[Ed Davies]

Thanks @TerryE, getting there but I'm finding the code a bit puzzling. I take it t15 is the nominal 3pm temperature derived from today's measurements? So what's TARGET_T, the set target temperature which is only adjusted very occasionally? But the temperature of what? Some sort of nominal temperature of the slab after a day's heat delivery to the room?

 

Should

onTime1 += 0.5;

be

onTime1 += sign * 0.5;

 

[Jeremy Harris]

Without wishing to derail the thread, I can add an interesting data point.  On Wednesday we had a removal van here, shifting the rest of our furniture over from our old house, plus both our cars were filled with stuff that we had to carry indoors.  It was damned cold here on Wednesday, around 2 deg C and snowing in the morning, dropping through the day and evening to well below zero.

 

During all the unloading, the front door was wide open for a couple of hours, and this leads directly into the entrance hall where the room stat is located, even though that is ~5m from the front door, so not in the direct influence of it being open.  However, the temperature in the hall did drop to around 18 deg C, and the room stat is set to come on at 20.5 deg C, so the ASHP was on, heating the UFH for a lot of the time on Wednesday.

 

I expected that we would get a big temperature overshoot in the evening, as we'd effectively over-charged the slab with heat.  However, because the slab temperature is limited to about 23 to 24 deg C max, this didn't happen, much to my relief.  We got a small overshoot, up to about 21.8 deg C, early in the evening, but that settled back to the normal 21.5 deg C or so later, and things were very comfortable, with the bedroom temperature at around 20 deg C.

 

All told I was impressed with the way this simple control system behaved.  I think the key is controlling the maximum flow temperature into the slab, as well as using room temperature sensing with a low hysteresis (+/-0.1 deg C).  Limiting the UFH flow temperature sets a limit on the amount of heat the slab can be charged with, which in turn seems to limit the overshoot from the mismatch in response time between the fairly rapid air temperature sensing and the fairly slow response of the slab.

 

The most important point is that Wednesday was the first night that SWMBO had spent here, and she was very impressed with the comfort level, so much so she keeps going on about it.  I have a feeling she wasn't convinced by any of my arguments about the virtues of a passive house, but is now very much a convert, especially when it comes to MVHR and the very much better air quality than we had in our old house.

[Pete]

34 minutes ago, JSHarris said:

Without wishing to derail the thread, I can add an interesting data point.  On Wednesday we had a removal van here, shifting the rest of our furniture over from our old house, plus both our cars were filled with stuff that we had to carry indoors.  It was damned cold here on Wednesday, around 2 deg C and snowing in the morning, dropping through the day and evening to well below zero.

 

During all the unloading, the front door was wide open for a couple of hours, and this leads directly into the entrance hall where the room stat is located, even though that is ~5m from the front door, so not in the direct influence of it being open.  However, the temperature in the hall did drop to around 18 deg C, and the room stat is set to come on at 20.5 deg C, so the ASHP was on, heating the UFH for a lot of the time on Wednesday.

 

I expected that we would get a big temperature overshoot in the evening, as we'd effectively over-charged the slab with heat.  However, because the slab temperature is limited to about 23 to 24 deg C max, this didn't happen, much to my relief.  We got a small overshoot, up to about 21.8 deg C, early in the evening, but that settled back to the normal 21.5 deg C or so later, and things were very comfortable, with the bedroom temperature at around 20 deg C.

 

All told I was impressed with the way this simple control system behaved.  I think the key is controlling the maximum flow temperature into the slab, as well as using room temperature sensing with a low hysteresis (+/-0.1 deg C).  Limiting the UFH flow temperature sets a limit on the amount of heat the slab can be charged with, which in turn seems to limit the overshoot from the mismatch in response time between the fairly rapid air temperature sensing and the fairly slow response of the slab.

 

The most important point is that Wednesday was the first night that SWMBO had spent here, and she was very impressed with the comfort level, so much so she keeps going on about it.  I have a feeling she wasn't convinced by any of my arguments about the virtues of a passive house, but is now very much a convert, especially when it comes to MVHR and the very much better air quality than we had in our old house.

Don't make it to comfy she will want to stop!!

[TerryE]

38 minutes ago, JSHarris said:

On Wednesday we had a removal van here, shifting the rest of our furniture over from our old house, plus both our cars were filled with stuff that we had to carry indoors.

 

Jeremy, perhaps that's the most important point: you are now in, and theory gets replaced by practice.  congrats  

Edited November 23, 2018 by TerryE

[TerryE]

1 hour ago, Ed Davies said:

So what's TARGET_T, the set target temperature which is only adjusted very occasionally? But the temperature of what? Some sort of nominal temperature of the slab after a day's heat delivery to the room?

 

It's the nominal room temp that we want to maintain.   If we can a target of 23°C, say, and this requires 30kW input then the slab surface on average needs to be (30/10)  above this or at an average of 26°C.

 

Thanks for the sign cock-up.  Just check my git history and did a crap edit about 5 days ago.  The temp has been steadily falling since then and the error in catch-up so has always been slightly +ve since -- hence my not picking this up.

[Stones]

 As many of you know we opted for a pre-plumbed ASHP and cylinder package that came with a master controller.  As I've reported in my blog, it works really, really well, the only input from me being the target house temperature.  The control system works on a weather compensation basis but 'actively learns' what the house requires in terms of heat input.   Internal temperature is very, very stable, (house generally sits 0.5C over set temperature) and only spikes if we have prolonged periods of solar gain.

 

This is the second house we have lived in where there is an even temperature 24/7.  Wouldn't revert back.

[joe90]

2 hours ago, Pete said:

The most important point is that Wednesday was the first night that SWMBO had spent here, and she was very impressed with the comfort level, so much so she keeps going on about it.  I have a feeling she wasn't convinced by any of my arguments about the virtues of a passive house, but is now very much a convert, especially when it comes to MVHR and the very much better air quality than we had in our old house.

 

I wish my other half felt the same, because she can’t rack up the stat and feel radiant heat from a source she thinks it’s cold in here (despite friends visiting for a long weekend and saying how warm the house felt). Also despite the MVHR (and my waxing lyrical about @JSHarris doing an analysis on it and opening windows) she still insists on opening a window and complaining it’s cold. I’m going out to the garage (man shed) ?

[ProDave]

11 hours ago, joe90 said:

 

I wish my other half felt the same, because she can’t rack up the stat and feel radiant heat from a source she thinks it’s cold in here (despite friends visiting for a long weekend and saying how warm the house felt). Also despite the MVHR (and my waxing lyrical about @JSHarris doing an analysis on it and opening windows) she still insists on opening a window and complaining it’s cold. I’m going out to the garage (man shed) ?

That is one reason for the WBS. Once in a while you can crank that up and indulge in a room temperature I would not choose to pay to achieve (wood is free)

[joe90]

1 hour ago, ProDave said:

That is one reason for the WBS. Once in a while you can crank that up and indulge in a room temperature I would not choose to pay to achieve (wood is free)

 

Exactly, we do have a WBS and plenty of wood ?.

[jack]

13 hours ago, joe90 said:

 she still insists on opening a window 

 

Why? Is it a perception that air isn't fresh unless it's cold?