External Control Logic for Humidity-Controlled Boost and Summer Bypass

[MJNewton]

Having picked up a Titon HRV1.25Q Plus Eco for a price that was too good to pass on I now find myself with slightly less controllability than the Xpelair Natural Air 180 unit previously planned for. Specifically, the Titon's humidity-controlled boost function is based on an absolute threshold rather than rate-of-rise, and its summer bypass has fixed thresholds that cannot be adjusted at all.

 

All along I have been planning on employing a Pi Zero to monitor system temperatures and control boost and setback flows, and so I have decided now to bring humidity-controlled boost and summer bypass within its scope also. The former can piggyback the existing boost input but with the bypass being internally controlled I have had to pinpoint on the control PCB where to tap into to influence (actually take over) this function.

 

What I would like the panel's input on is the control logic for these features in case there's something I haven't considered (or just got plain wrong!).

 

Humidity-Controlled Boost

 

I am attracted to rate-of-rise control on the assumption that it'll ride out seasonal variations better whilst also being more sensitive and reactive to genuine need. To achieve this control I think I need to consider:

 

Inputs: Extract (i.e. from rooms) humidity
Outputs: Boost
Settings: Rate-of-rise threshold ($rateofrise), time period ($timeperiod), when to turn off again ($deactivatethreshold)

 

Control Logic: 1) If the humidity rise over $timeperiod exceeds $rateofrise activate the boost. 2) Continue with boost until the humidity falls to $deactivatethreshold.

 

This sounds reasonable I think? What should $deactivatethreshold be though? The pre-rise humidity value, or at least something near it in case the background humidity has risen slightly in the meantime?

 

My starting figures are likely to be something like 5% for $rateofrise and 5 minutes for $timeperiod. Incidentally, I was planning on taking measurement every five minutes so that'll be the minimum boost time period.

 

Summer Bypass

 

From what I have read it seems that summer bypass works better in theory than in practice but I like the idea of it and given the Titon has the capability I may as well make use it. As per the previous process I think I need to consider:

 

Inputs: Extract (i.e. from rooms) temperature, Intake (i.e. from outside) temperature, time of day(?)
Outputs: Summer bypass, boost(?)
Settings: Room temperature threshold ($roomtempthreshold), Outside temperature minimum ($outsidetempmin), quiet time ($quiettime), when to disable bypass again ($deactivatethreshold)

 

Control Logic: 1) If the temperature of the air being extracted from the rooms exceeds $roomtempthreshold and the outside temperature is at least $outsidetempmin then activate the summer bypass (unless the outside temperature exceeds the room temperature).  2) Additionally (and optionally?), with the bypass active also activate boost unless we are within $quiettime (e.g. at night). 3) Continue with the bypass active (and, optionally, boost) until the room temperature falls below the $deactivatethreshold.

 

Typical figures might be 22C for $roomtempthreshold, 15C for $outsidetempmin, 2300-0700 for $quiettime and 18C for $deactivatethreshold.

 

Thanks for reading this far. Should I be considering a different approaches? Is there anything I should/could consider?

Edited May 16, 2018 by MJNewton

[Jeremy Harris]

I like the idea of using rate of change of humidity as the boost control parameter, rather than just a set RH level to trigger boost.  I fitted a humidistat to ours, with the remote sensor in the extract plenum, and it's not great, as the threshold has to be changed in the spring and autumn to account for the general shift upwards of RH in winter and down in summer.  I'd be inclined to just use something simple, like a boost timer that's triggered by the RH increasing by 2 or 3% in a short time period, say 2 to 3 minutes.  I have our humidistat set to keep boost on for 20 minutes once triggered and that seems to be about  long enough.  I suspect you'll need to do some monitoring for a time to get some data on how RH changes with time in order to set the rate of change figures. 

 

As far as I can tell, our summer bypass (which is continuously variable) just works on the basis of intake air temperature versus the room temperature set point (the Genvex can heat and cool so has a programmable thermostat built in to the room controller).  I'm not convinced it really makes that much difference, as by the time the thing is at 100% bypass the cooling system almost always comes on, and when I experimented with turning air cooling off, to see what effect bypass alone would have, it didn't seem to do much, if anything. 

 

If you can control bypass so that you can set it to do as many in hotter areas, like around the Med, do, and go to 100% bypass at night, so you can get the MVHR to do a traditional "night purge" then that might be useful.  I find a cooler night time temperature more comfortable, and using the cooler night air to take the previous day's heat out of the internal structure may well help to keep the house cooler during the day.  That's the traditional practice in places where there is a big day/night temperature swing, leave the windows open with just ventilated shutters closed at night, then close the windows during the day to reduce the amount of hot air that can get in.  Combined with a house that has a high decrement delay structure it's a technique that seems to work well.

[ProDave]

I am taking a different view that I want all ours under simple manual control.

 

Firstly the boost.  There will be a simple button next to the bathrooms and one in the kitchen that you press before showering or cooking to trigger boost mode for a set time period.  This has the advantage of the boost starting immediately, not a bit later in the showering process when the humidity has risen.

 

The summer bypass I found was an odd one. We have one of the Kingspan Lossnay units.  Lets just say the instructions are just about useless.  It has 2 inputs labeled "heat" and "cool" which make no sense at all as it has no inbuilt heating or cooling function. Reading the pidgeon English description seemed to talk about summer bypass being activated by temperature sensors, but without knowing what and how it was trying to control it, I did not like the idea of some unknown algorithm controlling it.  I then found by experiment that an unlabelled and undocumented input directly and immediately actuates the summer bypass flap valve.  So I have a simple switch to operate that when I feel it might be needed.

 

This is not to say don't try your automated control, just to say that I will at least to start with stick with something very simple.

[joe90]

37 minutes ago, ProDave said:

I am taking a different view that I want all ours under simple manual control.

 

Firstly the boost.  There will be a simple button next to the bathrooms and one in the kitchen that you press before showering or cooking to trigger boost mode for a set time period.  This has the advantage of the boost starting immediately, not a bit later in the showering process when the humidity has risen.

 

The summer bypass I found was an odd one. We have one of the Kingspan Lossnay units.  Lets just say the instructions are just about useless.  It has 2 inputs labeled "heat" and "cool" which make no sense at all as it has no inbuilt heating or cooling function. Reading the pidgeon English description seemed to talk about summer bypass being activated by temperature sensors, but without knowing what and how it was trying to control it, I did not like the idea of some unknown algorithm controlling it.  I then found by experiment that an unlabelled and undocumented input directly and immediately actuates the summer bypass flap valve.  So I have a simple switch to operate that when I feel it might be needed.

 

This is not to say don't try your automated control, just to say that I will at least to start with stick with something very simple.

 

I think I have the same unit as you Dave, shame I did not think to wire manual switches as that’s a great idea in my mind, I might be able to retro some  in the bathrooms ( pull switches) but not in the kitchen ?. Could you let me know where you found that manual input for summer bypass as it’s something I would like to do ( later when I get that far).

[Jeremy Harris]

There are some remote control switches that use a battery-powered wall switch and a receiver that could drive a mains relay, to give dry contacts and isolation, so could be used with an MVHR, which would save any tricky wiring runs.  The Smartwares range (which used to be branded Homeeasy) isn't too costly.  You can programme one receiver (like this one: https://www.uk-automation.co.uk/smartwares-built-in-power-switch-1000w-sh5-rbs-10a/ ) to operate from several wall switches like this: https://www.uk-automation.co.uk/smartwares-wireless-single-gang-wall-switch-sh5-tsw-a/

 

All you'd need to add would be a suitable 230 VAC relay in an enclosure to operate the boost function on the MVHR.

[PeterW]

The Quinetic switches can do this (crossed with @JSHarris) and I'm using them for lighting https://www.tlc-direct.co.uk/Main_Index/Wiring_Accessories_Menu_Index/Quinetic/index.html

 

 

[SteamyTea]

I am still thinking about this.

My first thoughts are that there is a big difference in comfort levels at different RH levels when the temperature changes.

I don't think that it is simply a case of trying to keep the RH fixed regardless of the temperature.

The second thought I had was how will it cope when conditions are out of range i.e. high internal temperature and very high external RH (like yesterday).  would the boost just be permanently on.

 

Also, would the rate of change curves be fixed or dynamic? In the UK it really is possible to have 4 seasons in one day.

 

I am sure it is all solvable, just a case of working out what is really wanted.

[MJNewton]

Thanks everyone you the input.

 

2 hours ago, JSHarris said:

I'd be inclined to just use something simple, like a boost timer that's triggered by the RH increasing by 2 or 3% in a short time period, say 2 to 3 minutes.  I have our humidistat set to keep boost on for 20 minutes once triggered and that seems to be about  long enough.

 

Perhaps a timed boost would be more reliable as I don't want to be trapped in a boost just because some turn-off threshold hasn't quite been reached. As you said, some monitoring of our system and how it and the house reacts should give more of an idea of what is required.

 

Quote

If you can control bypass so that you can set it to do as many in hotter areas, like around the Med, do, and go to 100% bypass at night, so you can get the MVHR to do a traditional "night purge" then that might be useful.

 

Yes, I like the idea of that. I've noticed what little effect opening windows has on very calm nights when it's hot inside and yet the outside air temperature is cool. Hopefully the MVHR will be able to at least get some air moving.

 

1 hour ago, ProDave said:

Lets just say the instructions are just about useless.

 

I've found that with quite a few units, and yet others are full of really useful information. I can't be the only one whose buying decisions are heavily influenced by the presence (or lack) of such detail.

 

To be fair to Titon whilst their installation manual simply said the summer bypass was 'automatically controlled' (and nothing more than that!) I got in touch with them and received a very helpful reply from their technical department explaining the control strategy and openly inviting any other questions about such details.

 

Quote

This is not to say don't try your automated control, just to say that I will at least to start with stick with something very simple.

 

Understandable. What I might actually do is run cables with some of the ducting runs so that I can add on, perhaps in parallel, some manual controls should I conclude that they will serve us better. Truth be told though, I'll quite happily (and consistently) manually trigger the boost function prior to showering but I'm not so sure I can depend on my wife doing the same (and perhaps daughter too when she's old enough - she's only 1 though so still plenty of time for training!).

Edited May 17, 2018 by MJNewton

[Jeremy Harris]

2 minutes ago, SteamyTea said:

I am still thinking about this.

My first thoughts are that there is a big difference in comfort levels at different RH levels when the temperature changes.

I don't think that it is simply a case of trying to keep the RH fixed regardless of the temperature.

The second thought I had was how will it cope when conditions are out of range i.e. high internal temperature and very high external RH (like yesterday).  would the boost just be permanently on.

 

Also, would the rate of change curves be fixed or dynamic? In the UK it really is possible to have 4 seasons in one day.

 

I am sure it is all solvable, just a case of working out what is really wanted.

 

 

It's really just a way of turning boost on when the shower or bath is running, or when cooking, rather than as a way to control comfort.  TBH, it doesn't make a massive difference if you don't boost the MVHR when having a shower, as the room dries out pretty quickly anyway.

[joe90]

3 minutes ago, SteamyTea said:

I am still thinking about this.

My first thoughts are that there is a big difference in comfort levels at different RH levels when the temperature changes.

I don't think that it is simply a case of trying to keep the RH fixed regardless of the temperature.

The second thought I had was how will it cope when conditions are out of range i.e. high internal temperature and very high external RH (like yesterday).  would the boost just be permanently on.

 

Also, would the rate of change curves be fixed or dynamic? In the UK it really is possible to have 4 seasons in one day.

 

I am sure it is all solvable, just a case of working out what is really wanted.

That’s why I like Daves solution, manual control. If you have a shower or bath and no excess steam is produced don’t put it on, if your doing lots of cooking, put it on. We have only had a few showers and baths in our new build and the MVHR is not yet up and running and we have not needed it ( so far)

[Jeremy Harris]

20 minutes ago, MJNewton said:

Understandable. What I might actually do is run cables with some of the ducting runs so that I can add on, perhaps in parallel, some manual controls should I conclude that they will serve us better. Truth be told though, I'll quite happily (and consistently) manually trigger the boost function prior to showering but I'm not so sure I can depend on my wife doing the same (and perhaps daughter too when she's old enough - she's only 1 though so still plenty of time for training!).

 

One idea I had was to turn a boost timer on using a PIR switch.  That way the MVHR would boost whenever someone went into the bathroom.  Not ideal if you get up in the middle of the night to use the bathroom, but a time switch to disable boost at night would solve that problem.

[MJNewton]

Lots of options... thank you.

 

What I might do is keep an open mind and try a few different strategies. I do enjoy the engineering aspects of designing and experimenting with things like this and so the journey should be as worthwhile as the end result.

Edited May 17, 2018 by MJNewton

[joe90]

24 minutes ago, MJNewton said:

Lots of options... thank you.

 

What I might do is keep an open mind and try a few different strategies. I do enjoy the engineering aspects of designing and experimenting with things like this and so the journey should be as worthwhile as the end result.

 

Perhaps think about wiring that that you may or may not use ( not like me!) wiring is so difficult or impossible to put in afterwards!

[MJNewton]

Unfortunately for me this *is* afterwards! ? (in terms of it being a retrofit anyway). That said, the process of pulling through the ducting means it's a good opportunity to pull some cables through with them so, yes, it is definitely something to think about in advance.

 

 

[ProDave]

2 hours ago, joe90 said:

 

I think I have the same unit as you Dave, shame I did not think to wire manual switches as that’s a great idea in my mind, I might be able to retro some  in the bathrooms ( pull switches) but not in the kitchen ?. Could you let me know where you found that manual input for summer bypass as it’s something I would like to do ( later when I get that far).

I am planning to use Horstman Immersion heater timer switches. You press a button up to 3 times and it gives you a different timed ON period from half an hour up to 2 hours.  There will be one on the landing in effect between the two bathrooms, and one in the kitchen.  These will both turn on a relay to give the volt free contact that the mvhr unit needs.

 

Inside the Kingspan / Mitsubishi :Lossnay mvhr unit there is a 5 way terminal block for the fan speed selection.  That requires you to connect 1 fan speed input to "common" So the boost relay will be a changeover relay.  De energised it will connect common to fan speed 1.  When energised it will connect to a higher fan speed, I have yet to make any measurements to determine which speed will be needed for boost mode.

 

Re the summer bypass.  Next to the fan speed terminal block is another 3 terminal block, One labelled Heat, one labelled Cool and the third one not labelled or mentioned in the manual.  As I have already said the function of the heat and cool inputs is poorly described.  However if you connect the unlabelled input to the common terminal on the fan speed terminal block, it instantly actuates the bypass flap.

 

There seems to be a common theme here that a lot of these units do not fully describe how they function and it appears common to find undocumented features if you experiment.

[Jeremy Harris]

1 minute ago, ProDave said:

There seems to be a common theme here that a lot of these units do not fully describe how they function and it appears common to find undocumented features if you experiment.

 

Never a truer word said!

 

I spent tens of hours trying to reverse engineer our ASHP, and to a lesser extent finding out how to fit a humidistat to the MVHR, because of a lack of information.  I suspect that some of this is a form of protectionism, to try and restrict the level of publicly available knowledge so that installers can justify some of the very high prices that they seem to charge.

[MJNewton]

1 hour ago, ProDave said:

I am planning to use Horstman Immersion heater timer switches. You press a button up to 3 times and it gives you a different timed ON period from half an hour up to 2 hours.

 

Have you considered the Timeguard TGBT4? Looks quite 'modern' I think and well suited to an MVHR installation (I always think Horstmann's sometimes look a bit old school! ;-))

 

 

£20 from TLC.

 

Edited May 17, 2018 by MJNewton

[SteamyTea]

2 hours ago, MJNewton said:

I do enjoy the engineering aspects of designing and experimenting with things like this and so the journey should be as worthwhile as the end result.

I agree, and shall ponder it more as I drive up to Devon in a little while.

[ProDave]

35 minutes ago, MJNewton said:

 

Have you considered the Timeguard TGBT4? Looks quite 'modern' I think and well suited to an MVHR installation (I always think Horstmann's look a bit old school! ;-))

 

 

£20 from TLC.

 

Thanks, I like the look if that, and unlike the Horstman does not mention immersion heater. In fact just being described as "boost" could not be better.