"Lean" Design

[Stones]

On ‎05‎/‎09‎/‎2018 at 14:52, TerryE said:

 

To me what this all underlines is that the slab itself is the biggest heat capacitor in the system, so there is little point in adding complexity of external smoothing using TMVs and buffer tanks.  So long as you are pumping enough heat per day into your slab then a passive class house with warm slab + UFH + cellulosic filler will stay comfortable.  In my experience your divide the year into three broad zones:

• No active heat management is required (roughly 6 months / year) because the intrinsic heat excess is enough to keep the house at a comfortable equilibrium and MVHR exchange / bypass gives adequate trim.
• One per day heat adjustment is sufficient (roughly 3-4 months / year). This is my overnight top-up / cool-down.  Again so long as this adjustment gives enough bulk heat-balance, the MVHR exchange / bypass gives adequate trim.
• One per day heat adjustment is insufficient (roughly 2-3 months / year).  Here for the mid winter months a single heating period starts to give a daily heat ripple that is noticeable, so you need multiple heating periods per day.  For the UK climate range IMO you will never need more than 3, but at 4 the ripple will be less than 0.1°C.

At the moment I use the day-to-day average temperature as a control feedback to compute the total amount of daily heat (and in future cooling) needed to apply.  Because I use a fixed input heater this maps directly to heating time.  If you are on E7 it does make sense to have an asymmetric cycle with a bulk heat overnight, but the tops can be spread through the day.  It sounds like you are going to adopt similar ASHP heating  scheme to the one that I plan to and @jack has done, which is to set the ASHP output temperature at a low setpoint (in my case around 27-28 °C).  You then need to control the mark/space ratio to maintain the overall daily thermal balance.   And the CoP at this set point is excellent.  (Though if you have kids and use lots of HW and want to use your ASHP to preheat this then this would greatly complicate this approach.)

 

There are a number of strategies here, eg. use a fixed cycle (say 6 hours) and then control the on time or use a fixed on-time and control the off-time to give a variable cycle, but IMO these are all based on macro thermal balance.  This will work well for my house, but if you have "acres of S facing glass" then day-to-day highly variable solar gain will become an issue that you need to factor in.

 

Jeremy and I started out at very different design conclusions from a very similar problem analysis and our solutions are conditioned by historic investment decisions.  Even so we have significantly converged in our approaches.  Jeremy uses a single internal datum, I daily average a couple of DS18B20s measuring room temperature.

 

To be honest, if mid-winter heating was my only concern then I'd stick with the largely E7 Willis approach.  Yes, the running cost is maybe  £300 p.a. more than using an ASHP,  but I have no complex mechanical systems to maintain and to replace every 10 years or so, so there is no cost benefit case here.  The real issue that makes me plan to introduce an ASHP is the summer cooling one: for about a month a year, I need to dump heat from the house actively to keep a comfortable internal environment, and I can't do this by an additive heat solution.

 

One last comment.  I've mention the impact of solar gain which can throw a "big spanner in the works".  You can get very sunny days in December and if you have a large south-facing area of glass, this can be a big pulse of kWh into the house.  The other one that causes us fun is visitors.  When our kids+family or others come to visit,  then just the heat and activities around hosting these guests adds environmental control challenges.  For example, 6 people sitting in a room will cause it to start to warm up noticeably!

 

Terry, having determined your daily heating time (derived from day to day average temps) do you have to manually adjust the timer controlling your Willis heater to limit / increase the on time or have you reached a point, knowing how the house reacts to a given input of heating time, where the control is automated?

 

As you know, we went down the ASHP route with an off the shelf control system.  It operates in exactly the way you describe in terms of the split between no heating, shoulder and heating seasons.  The biggest difference is that we are not tied to an E7 or E10 tariff and therefore the ASHP will input heat as and when required to even out the ripples.  This is helpful for us as we have fair bit of SW facing glass which can cause spikes (albeit welcome ones) in internal temp. Our ASHP is set up on an auto adaptive, weather compensating setting, and flow temps do vary depending on heating demand, albeit it doesn't seem to go over 30C, and is usually a lot lower.  

[TerryE]

1 hour ago, Stones said:

The biggest difference is that we are not tied to an E7 or E10 tariff and therefore the ASHP will input heat as and when required to even out the ripples.  This is helpful for us as we have fair bit of SW facing glass which can cause spikes (albeit welcome ones) in internal temp. Our ASHP is set up on an auto adaptive, weather compensating setting, and flow temps do vary depending on heating demand, albeit it doesn't seem to go over 30C, and is usually a lot lower.

 

Jason, I feel that both you and @pdf27 have similar concerns, and ones that I can only partially answer.  This is almost as a consequence of policy / strategy on my part, and of "walking on the shoulders of giants".  I saw that Jeremy's thoughts evolved in the course of his experience of controlling his own house system and he's rejigged his system 3 times and may do so again when he and his wife are in continuous occupation.  So I decided to adopt a lazy and evidence-based approach, that is rather than develop and implement a complex fully featured system only to have to rework it later.  Jan and I decide to do this in a number of phases so that each was "good enough for now", and then only implement subsequent phases once we had the experience, data and understanding to do so.  IMO, there isn't a good rule book that we can use for this class of house design.

 

Phase zero was to do appropriate design validation and modelling to ensure that the house as system had suitable macro characteristics for use to control and keep it within a comfortable living range.  This convinced me that a simple Willis-heated UFH system would be capable of maintaining the house over the winter period, but that there was a question over whether we could cool the house enough over peak summer.  Ditto using the 2×SunAmp for DHW.

 

Phase 1 was using the Willis heater, circulation pump and 2×SunAmps controlled by a NodeRED instance on an RPi with a simple ON1/OFF1 ON2/OFF2 scheduler and a dozen DS18B20s collecting sensor data every 2 minutes (for 10 months now).  I adjusted the ON and OFF times manually based on average outside temperature as required which was maybe a couple of times a week.  We can't have PV so optimising this around a cheap E7 tariff just seemed economic sense.   This experience and the data showed us that our house worked and performed within an acceptable tolerance of our design predictions.  

 

The summer heat wave has underlined that we do need an ASHP -- something that wouldn't really have been cost justified based on our data purely for the winter heating problem.   However this is still desirable rather than essential.  Unfortunately, I want to place it against the side of a new summer house style shed that we will be building maybe next summer as part of landscaping our rear garden.  I don't want to have to move it, so we can't install it until after these rear ground works are completed.  If we have to delay it another year then this isn't really a big concern for us.   Also unlike a conventional central heating boiler, the ASHP isn't a critical system (as we can heat the house happily albeit more expensively with the Willis) so I can take a more cost aggressive view on its purchase and maintenance.

 

So Phase 2 is to add autonomous control, and I will do this in the next month or so.  This is a software only exercise adding a some extra nodeRED / Javascript modules; the interface is tablet / phone friendly browser-based, so just like my chromecast, Jan or I can configure the system through one of the various Android devices that we carry or have to hand.  From our experience last winter, I am confident that a two period heating regime  will give us a good level of control; that is where the OFF1 and OFF2 times are fixed and the ON1 and ON2 are set based on a daily adaptive calculation of T1 and T2 from three input: the daily average internal temp, the maximum internal ripple, and the average external temperature.  We will always have a T1 and T2 to calculate, but sometimes their value will be 0.

 

Incidentally some have expressed concerns about the "what if I drop down dead" scenario doing this sort of approach, but I have a son and son-in-law who both work in IT and are already dabbling with this technology themselves.  I am sure that they can take over maintenance if needed.  

 

Phase 3 will be the addition of the ASHP and its integration into the heating system.  My current thinking is that I will treat this very much the same as the Willis in terms of house control.  I will set it to a specific fairly low output by setting the output temperature from the ASHP so that it gives say ~2kW and have a fixed number (say 3×) ON/OFF scheduling cycle, with the T1,T2,T3 set to produce a good thermal balance and acceptable ripple.   The reason that I can do this is that the ASHP circuit is coupled to the slab UFH circuit through a plate heat exchanger (PHE).  On the UFH side I know what the circuit flow rates are (as I calibrate these from the ΔT from the 3kW Willis element); I can measure / integrate the corresponding ΔT in and out of the PHE to compute the actual heat input from the ASHP into the slab; that is I am treating the ASHP as a black box heat source / sink.  These total heat figures will plug into essentially the same control algo as for phase 2.   At a tuning level, I can experiment with numbers of heating cycles /  ASHP settings, on a day-to-days to find a good set to use, but I won't attempt to use these actively in house control. 

 

As I said previously we minor solar gains in winter in our house, so unlike Jason I don't have to adjust for this in my control system. 

Edited September 9, 2018 by TerryE

[joe90]

Like Terry above I do think you have to see how your house behaves before making firm decisions, saying that, installing UFH is a must for heating or cooling. We don’t have PV, electric only, and a cheap Ebay ASHP (not working yet) we moved in about 4 months ago and have not needed any heating and DHW is using Imersions. I confess I do not understand a lot of the complicated control systems that some talk about, I am also a bit of a Luddite, KISS works for me (and is easy to repair) I like the idea of setting a thermostat to a set comfortable temp then letting the system self regulate. 

[ProDave]

5 minutes ago, joe90 said:

Like Terry above I do think you have to see how your house behaves before making firm decisions, saying that, installing UFH is a must for heating or cooling. We don’t have PV, electric only, and a cheap Ebay ASHP (not working yet) we moved in about 4 months ago and have not needed any heating and DHW is using Imersions. I confess I do not understand a lot of the complicated control systems that some talk about, I am also a bit of a Luddite, KISS works for me (and is easy to repair) I like the idea of setting a thermostat to a set comfortable temp then letting the system self regulate. 

I too am keeping it simple

 

Standard UFH manifolds, standard room thermostats. Room stats set at 20 degrees, so what if there is 1 degree hysterises, that's well within the comfort zone limits.

 

I am starting out without a buffer tank and will see how the ASHP deals with driving the UFH directly, I will only add a buffer tank if I find something does not work with this simple approach.

 

The bit that irked me is i wanted to use a standard central heating control timer to set the heating and hot water on and off times, a 3 channel one so I can have the upstairs heating on at different times to downstairs if I want to.  But the ASHP designers had other ideas and just wanted you to use their fiendishly complicated controller, so it was a challenge finding a way to integrate the two, most notably now to turn hot water on or off externally to the heat pump.

 

Now I have cracked that, the heat pump's controller is just for setting parameters if I want to tweak something, not for day to day use.

[Stones]

18 hours ago, TerryE said:

 

Jason, I feel that both you and @pdf27 have similar concerns, and ones that I can only partially answer.  This is almost as a consequence of policy / strategy on my part, and of "walking on the shoulders of giants".  I saw that Jeremy's thoughts evolved in the course of his experience of controlling his own house system and he's rejigged his system 3 times and may do so again when he and his wife are in continuous occupation.  So I decided to adopt a lazy and evidence-based approach, that is rather than develop and implement a complex fully featured system only to have to rework it later.  Jan and I decide to do this in a number of phases so that each was "good enough for now", and then only implement subsequent phases once we had the experience, data and understanding to do so.  IMO, there isn't a good rule book that we can use for this class of house design.

 

Phase zero was to do appropriate design validation and modelling to ensure that the house as system had suitable macro characteristics for use to control and keep it within a comfortable living range.  This convinced me that a simple Willis-heated UFH system would be capable of maintaining the house over the winter period, but that there was a question over whether we could cool the house enough over peak summer.  Ditto using the 2×SunAmp for DHW.

 

Phase 1 was using the Willis heater, circulation pump and 2×SunAmps controlled by a NodeRED instance on an RPi with a simple ON1/OFF1 ON2/OFF2 scheduler and a dozen DS18B20s collecting sensor data every 2 minutes (for 10 months now).  I adjusted the ON and OFF times manually based on average outside temperature as required which was maybe a couple of times a week.  We can't have PV so optimising this around a cheap E7 tariff just seemed economic sense.   This experience and the data showed us that our house worked and performed within an acceptable tolerance of our design predictions.  

 

The summer heat wave has underlined that we do need an ASHP -- something that wouldn't really have been cost justified based on our data purely for the winter heating problem.   However this is still desirable rather than essential.  Unfortunately, I want to place it against the side of a new summer house style shed that we will be building maybe next summer as part of landscaping our rear garden.  I don't want to have to move it, so we can't install it until after these rear ground works are completed.  If we have to delay it another year then this isn't really a big concern for us.   Also unlike a conventional central heating boiler, the ASHP isn't a critical system (as we can heat the house happily albeit more expensively with the Willis) so I can take a more cost aggressive view on its purchase and maintenance.

 

So Phase 2 is to add autonomous control, and I will do this in the next month or so.  This is a software only exercise adding a some extra nodeRED / Javascript modules; the interface is tablet / phone friendly browser-based, so just like my chromecast, Jan or I can configure the system through one of the various Android devices that we carry or have to hand.  From our experience last winter, I am confident that a two period heating regime  will give us a good level of control; that is where the OFF1 and OFF2 times are fixed and the ON1 and ON2 are set based on a daily adaptive calculation of T1 and T2 from three input: the daily average internal temp, the maximum internal ripple, and the average external temperature.  We will always have a T1 and T2 to calculate, but sometimes their value will be 0.

 

Incidentally some have expressed concerns about the "what if I drop down dead" scenario doing this sort of approach, but I have a son and son-in-law who both work in IT and are already dabbling with this technology themselves.  I am sure that they can take over maintenance if needed.  

 

Phase 3 will be the addition of the ASHP and its integration into the heating system.  My current thinking is that I will treat this very much the same as the Willis in terms of house control.  I will set it to a specific fairly low output by setting the output temperature from the ASHP so that it gives say ~2kW and have a fixed number (say 3×) ON/OFF scheduling cycle, with the T1,T2,T3 set to produce a good thermal balance and acceptable ripple.   The reason that I can do this is that the ASHP circuit is coupled to the slab UFH circuit through a plate heat exchanger (PHE).  On the UFH side I know what the circuit flow rates are (as I calibrate these from the ΔT from the 3kW Willis element); I can measure / integrate the corresponding ΔT in and out of the PHE to compute the actual heat input from the ASHP into the slab; that is I am treating the ASHP as a black box heat source / sink.  These total heat figures will plug into essentially the same control algo as for phase 2.   At a tuning level, I can experiment with numbers of heating cycles /  ASHP settings, on a day-to-days to find a good set to use, but I won't attempt to use these actively in house control. 

 

As I said previously we minor solar gains in winter in our house, so unlike Jason I don't have to adjust for this in my control system. 

 

Terry, very interesting.  When we were discussing heating options a couple of years ago, it was the control mechanism, i.e. how you would determine how long to pump heat into the slab for that had me concerned, and that was really based on my experience with storage heaters which needed frequent adjustment to prevent either under or overshoot in relation to the ambient temperature forecasts (and even then still resulted in cold or overly warm rooms). 

 

Now that you have your data set, you can create what I assume is a fairly simple set of control parameters.  Perhaps a difficult question to answer, but could a novice, someone with little or no programming experience, replicate your (intended) autonomous control system?  Can you say how much time you have spent developing your control system?  Is there an off the shelf alternative that would work for your system (providing autonomous control)?

 

As you know I went for an off the shelf system firstly for ease, secondly my good lady wouldn't have put up with anything that required input beyond pressing a button, and thirdly because we needed a responsive element to deal with solar gain spikes, but also Atlantic gale battering.  There is of course a price to be paid for this, in that the controller isn't cheap, and we are tied into the manufacturer if anything goes wrong / bang.

 

 

 

 

[AliMcLeod]

10 minutes ago, Stones said:

Is there an off the shelf alternative that would work for your system (providing autonomous control)?

 

Isn't this what Nest (and their like) are trying to achieve? Not sure they're quite yet there though.