Hello,
I have build my own 'smart' thermostat. This was for my older on/off-type heater. Now I have a new heater which 'talks' OpenTherm. So, I want to alter my controller so that I uses OpenTherm. The hardware isn't the problem, info on the protocol is. Can anyone help me to get this info. 'OpenTherm' doesn't seem so 'open' as it should be...
Rob
OpenTherm
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MindBender
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You really don' want to control your boiler on the level your thermostat normally does that. The algorithms required for a room thermostat are frequently underestimated. Something you build yourself can work, but it will never be as energy efficient as a bought thermostat. And why would you?
What you want instead is to control your thermostat. You probably want to set the setpoint temperature and read out the current room temperature. Additionally you may want to enable and disable stand-by hot water, but these are all thermostat controlled.
Check out the Remeha GateWay I've discussed in this thread:
http://www.domoticaforum.eu/topic.asp?TOPIC_ID=113
What you want instead is to control your thermostat. You probably want to set the setpoint temperature and read out the current room temperature. Additionally you may want to enable and disable stand-by hot water, but these are all thermostat controlled.
Check out the Remeha GateWay I've discussed in this thread:
http://www.domoticaforum.eu/topic.asp?TOPIC_ID=113
OpenTherm
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by MindBender</i>
<br />You really don' want to control your boiler on the level your thermostat normally does that. The algorithms required for a room thermostat are frequently underestimated. Something you build yourself can work, but it will never be as energy efficient as a bought thermostat.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">I've investigated a bit on this and I don't agree from what I've seen so far.
Ofcourse, the 200+ Euro multi-stage modulating widescreen HDTV thermostats contain quite a bit of logic which might be hard to beat without a laboratory and 50 years of experience in the heating industry, but most of the thermostats the average joe has installed don't appear to do that much.
From what I've seen, the only "intelligence" in them is:
a) a simple hysteresis algorithm, usually only "turn on when 1 degree below setpoint, turn off when 1 degree above setpoint" and hard limits the number of on/off cycles for the burner per hour
b) an anticipation resistor, which (in a mechanical system) heats up the thermostat itself when the burner is operating, so that it'll turn off slightly before the setpoint is reached, to prevent overshoot (because your radiators will stay hot for a while after the burner is turned off)
Point a is easily simulated if you use a PC or intelligent controller. Point b is a bit harder but also quite doable with some trial-and-error, and this provision isn't even present in quite a few thermostats (not even in the $200+ RCS HA thermostats from what I get from the documentation). If you invest enough time you can probably make the system more efficient than a very expensive thermostat because you have more processing power and potentially a lot more data to work with (unlimited number of sensors, weather data, historic data, occupancy detection, etc).
Please correct me if I'm wrong (seriously - I'd be happy to know!), but as far as I can see it there's not much more involved.
My primary reason to go for a "controlling the thermostat" solution would be that it can operate independent from the HA controller if needed.
- Rick
<br />You really don' want to control your boiler on the level your thermostat normally does that. The algorithms required for a room thermostat are frequently underestimated. Something you build yourself can work, but it will never be as energy efficient as a bought thermostat.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">I've investigated a bit on this and I don't agree from what I've seen so far.
Ofcourse, the 200+ Euro multi-stage modulating widescreen HDTV thermostats contain quite a bit of logic which might be hard to beat without a laboratory and 50 years of experience in the heating industry, but most of the thermostats the average joe has installed don't appear to do that much.
From what I've seen, the only "intelligence" in them is:
a) a simple hysteresis algorithm, usually only "turn on when 1 degree below setpoint, turn off when 1 degree above setpoint" and hard limits the number of on/off cycles for the burner per hour
b) an anticipation resistor, which (in a mechanical system) heats up the thermostat itself when the burner is operating, so that it'll turn off slightly before the setpoint is reached, to prevent overshoot (because your radiators will stay hot for a while after the burner is turned off)
Point a is easily simulated if you use a PC or intelligent controller. Point b is a bit harder but also quite doable with some trial-and-error, and this provision isn't even present in quite a few thermostats (not even in the $200+ RCS HA thermostats from what I get from the documentation). If you invest enough time you can probably make the system more efficient than a very expensive thermostat because you have more processing power and potentially a lot more data to work with (unlimited number of sensors, weather data, historic data, occupancy detection, etc).
Please correct me if I'm wrong (seriously - I'd be happy to know!), but as far as I can see it there's not much more involved.
My primary reason to go for a "controlling the thermostat" solution would be that it can operate independent from the HA controller if needed.
- Rick
OpenTherm
Rick,
100% ACK from here.
@Mindbender: somehow i get the idea you have knowledge (or seen things) about algorithms used in thermostats "we" don't know about.
Why not share this knowledge? Just like Rick i would like to know more about these sophisticated algorithms that seem to be used in our thermostats.
Please, teach me or at least give me some solid arguments why to "not to try this at home" [;)]
I'm pushing the up-down buttons on my thermostat too much, especially in the winter; so this should be automated somehow...
Regards,
Robert.
100% ACK from here.
@Mindbender: somehow i get the idea you have knowledge (or seen things) about algorithms used in thermostats "we" don't know about.
Why not share this knowledge? Just like Rick i would like to know more about these sophisticated algorithms that seem to be used in our thermostats.
Please, teach me or at least give me some solid arguments why to "not to try this at home" [;)]
I'm pushing the up-down buttons on my thermostat too much, especially in the winter; so this should be automated somehow...
Regards,
Robert.
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MindBender
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No, don't worry; I don't think I have any more knowledge on the topic than the rest of you guys.
But just like you guys, I was tempted to build my own thermostat so I can hook it up to my domotica system. But the more information I gathered, the more complex the problem became. At the end it became a project on it's own, so I decided not to it myself and look for an alternative instead. As I said before, I went for the Remeha Celcia 20 OpenTherm thermostat and the optional GateWay. Gee, I just realize that I wanted to reverse-engineer the serial protoctol is uses but it's installed for almost a year now and I still didn't put myself to it. May be this winter, when the topic gets a little more attention.
Anyway, for those who still like to persue this project I can tell what I've learned. First of all it's quite difficult to measure room temperature. Honeywell does this pretty well by measuring both the surrounding air temperature and the wall temperature. I don't know how these two parameters lead to the room temperature, but I know that the wall temperature is used to estimate how quick the room will heat up. Heating up the room is quite difficult anyway because you need to determine in thermal capacity (ie. how much energy you can put in it) and while determining this thermal capacity you need to take the delay of transfering this heat into account. So this delay must be measured first. This can be done by a couple of iterations cylces of heating up and cooling down. During these cycles, the thermal insulation (ie. how much heat leaks away from the house) can be determined too. If you have an outside temperature meter, you can store different parameters for different outside temperatures. I'd suggest to store all three parameters as time instead of apropriate scientific units: The time it takes to heat up the room a degree, the time it takes to cool down the room and the delay between switching on the burner and the radiators to heat up.
Then there's to topic on efficiency. Modern proportional boilers can vary (modulate) the throttle of the burner. And the highest efficiency is achieved at the lowest temperature. So you only want to heat up the water just enought to maintain the set temperature. Ideally the burner should be on permanently at the lowest burn rate possible to maintain the set temperature. This also minimizes extra inefficiency of switching the burner on and off.
All these tasks are done by modern OpenTherm thermostats. Of course it's not rocket science and you could do it yourself, but you'll never know if your system will be at the best possible efficiency simply because you have no point of reference and no means of testing. Manufacturers however do have 50 years of experience, they can do measurements and they do test their software intensely because they lower fuel consumption they can advertise, the more they will sell, the more profit they will make.
Yet one argument wipes away all of mine: Making one yourself is more fun
But just like you guys, I was tempted to build my own thermostat so I can hook it up to my domotica system. But the more information I gathered, the more complex the problem became. At the end it became a project on it's own, so I decided not to it myself and look for an alternative instead. As I said before, I went for the Remeha Celcia 20 OpenTherm thermostat and the optional GateWay. Gee, I just realize that I wanted to reverse-engineer the serial protoctol is uses but it's installed for almost a year now and I still didn't put myself to it. May be this winter, when the topic gets a little more attention.
Anyway, for those who still like to persue this project I can tell what I've learned. First of all it's quite difficult to measure room temperature. Honeywell does this pretty well by measuring both the surrounding air temperature and the wall temperature. I don't know how these two parameters lead to the room temperature, but I know that the wall temperature is used to estimate how quick the room will heat up. Heating up the room is quite difficult anyway because you need to determine in thermal capacity (ie. how much energy you can put in it) and while determining this thermal capacity you need to take the delay of transfering this heat into account. So this delay must be measured first. This can be done by a couple of iterations cylces of heating up and cooling down. During these cycles, the thermal insulation (ie. how much heat leaks away from the house) can be determined too. If you have an outside temperature meter, you can store different parameters for different outside temperatures. I'd suggest to store all three parameters as time instead of apropriate scientific units: The time it takes to heat up the room a degree, the time it takes to cool down the room and the delay between switching on the burner and the radiators to heat up.
Then there's to topic on efficiency. Modern proportional boilers can vary (modulate) the throttle of the burner. And the highest efficiency is achieved at the lowest temperature. So you only want to heat up the water just enought to maintain the set temperature. Ideally the burner should be on permanently at the lowest burn rate possible to maintain the set temperature. This also minimizes extra inefficiency of switching the burner on and off.
All these tasks are done by modern OpenTherm thermostats. Of course it's not rocket science and you could do it yourself, but you'll never know if your system will be at the best possible efficiency simply because you have no point of reference and no means of testing. Manufacturers however do have 50 years of experience, they can do measurements and they do test their software intensely because they lower fuel consumption they can advertise, the more they will sell, the more profit they will make.
Yet one argument wipes away all of mine: Making one yourself is more fun
OpenTherm
I live in a small 3 room (rental) well-insulated appartment (so probably not comparable to a bigger house) with a new AGPO heater and honeywell opentherm thermostat...
the AGPO heater has both opentherm and flame on-off connections, which can be used in parallel.
the heater does all the modulation stuff automatically, if you use the flame on-off connection.
I left the opentherm thermostat in place (but set at 17C) and connected the on-off via X10 to girder...
I get room temperature via a 1-wire DS1820 temperature sensor placed near the honeywell thermostat
I monitored the room temperature trend for a few weeks with the honeywell thermostat and after that with the X10 controlled temperature and I didn't notice any difference. (of course, this is not very scientific [:D])
I use the simplest algorithm possible : I check the room temperature every minute and switch on/off when under/over setpoint.
I don't even use hysteresis control !
I didn't see any more over/undershoot in the temperature trend than with the modulating honeywell opentherm thermostat, so I didn't bother implementing it..
the AGPO heater takes care of modulation etc....
It's probably more complicated if you have a bigger house or an older heater, but I'm happy with this simple solution. (also my electronics/halogen lights generate a considerable amount of heat)
the opentherm thermostat is set permanently at 17C so it will prevent any pipes from freezing (not an issue in a flat anyway)
I used an optimus mini to change the temperature setpoint (and other stuff, like alarm clock etc.)
http://www.artlebedev.com/everything/optimus-mini/
the AGPO heater has both opentherm and flame on-off connections, which can be used in parallel.
the heater does all the modulation stuff automatically, if you use the flame on-off connection.
I left the opentherm thermostat in place (but set at 17C) and connected the on-off via X10 to girder...
I get room temperature via a 1-wire DS1820 temperature sensor placed near the honeywell thermostat
I monitored the room temperature trend for a few weeks with the honeywell thermostat and after that with the X10 controlled temperature and I didn't notice any difference. (of course, this is not very scientific [:D])
I use the simplest algorithm possible : I check the room temperature every minute and switch on/off when under/over setpoint.
I don't even use hysteresis control !
I didn't see any more over/undershoot in the temperature trend than with the modulating honeywell opentherm thermostat, so I didn't bother implementing it..
the AGPO heater takes care of modulation etc....
It's probably more complicated if you have a bigger house or an older heater, but I'm happy with this simple solution. (also my electronics/halogen lights generate a considerable amount of heat)
the opentherm thermostat is set permanently at 17C so it will prevent any pipes from freezing (not an issue in a flat anyway)
I used an optimus mini to change the temperature setpoint (and other stuff, like alarm clock etc.)
http://www.artlebedev.com/everything/optimus-mini/
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Snelvuur
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Just a simple question, might be dumb of me. But why would you want to control more? If you set your temperature to say 21 degrees on the heater, you can use the on/off point of the honeywell in case you come in earlier or whatever reason. I presume you dont change the heating constantly and keep it at 21 then? Since i dont have a central heating at the moment i'am just speculating though. So correct me if this doens't work in real live.
// Erik (binkey.nl)
// Erik (binkey.nl)
OpenTherm
snelvuur, I'm not 100% sure what you mean ?
Note, that the heater on-off connection, doesn't mean : switch the thermostat on-off, it means, switch flame on-off...
you're right that I never change the temperature setpoint, so the only objective for me, is to automatically switch off the heater when I go to bed and switch it on in the morning, or not if I'm not home... (all done through motion detectors, not timers)
The current opentherm thermostat doesn't have an external control signal nor does it have any timer functionality...
so the only option was to use the flame on-off signal of the heater instead, but this meant that I would have to take over the opentherm thermostat's job and actually control the temperature...
Marcel
Note, that the heater on-off connection, doesn't mean : switch the thermostat on-off, it means, switch flame on-off...
you're right that I never change the temperature setpoint, so the only objective for me, is to automatically switch off the heater when I go to bed and switch it on in the morning, or not if I'm not home... (all done through motion detectors, not timers)
The current opentherm thermostat doesn't have an external control signal nor does it have any timer functionality...
so the only option was to use the flame on-off signal of the heater instead, but this meant that I would have to take over the opentherm thermostat's job and actually control the temperature...
Marcel
OpenTherm
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by snelvuur</i>
<br />Just a simple question, might be dumb of me. But why would you want to control more?
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
1) you have girlfriend who frequently cranks up the heating to retirement-home temperatures (and leaves it there)
2) I'd like different setpoints for "sleeping", "away", and possibly even for morning, daytime and the evening.
3) you *might* want to switch between different sensors depending on occupancy of a room, to get that room up to the desired temperature (ofcourse zoning would be much more efficient in that case)
<br />Just a simple question, might be dumb of me. But why would you want to control more?
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
1) you have girlfriend who frequently cranks up the heating to retirement-home temperatures (and leaves it there)
2) I'd like different setpoints for "sleeping", "away", and possibly even for morning, daytime and the evening.
3) you *might* want to switch between different sensors depending on occupancy of a room, to get that room up to the desired temperature (ofcourse zoning would be much more efficient in that case)
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Snelvuur
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ah, marcel.. now i know why you created it. But if you look at http://www.waakzaamwonen.nl/catalog/pro ... ouchscreen for instance, then this device should do everything for you. It does have an input so it will go to a preset value via an x10 on/off device.
// Erik (binkey.nl)
// Erik (binkey.nl)
OpenTherm
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">then this device should do everything for you<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
you're right, but, where's the fun in that ? [:D]
also, you would have to connect two wires on your wall going from the thermostat to the x10 device (I don't have spare wires in the wall)...
now I have everything in the heater cabinet and I got an excuse to use the optimus display device [8D]
I also have the chronoterm device still connected as a backup, with your solution I'd have to remove it (not really a problem)...
Marcel
you're right, but, where's the fun in that ? [:D]
also, you would have to connect two wires on your wall going from the thermostat to the x10 device (I don't have spare wires in the wall)...
now I have everything in the heater cabinet and I got an excuse to use the optimus display device [8D]
I also have the chronoterm device still connected as a backup, with your solution I'd have to remove it (not really a problem)...
Marcel
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MindBender
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Marcel, you seem to turn the burner on and off behind the thermostats back. That kind of defeats the purpose of having a thermostat at all. You're not using all it's nifty internal algo's. Even worse: You're might be messing up the internal algo's by turning on the burner while the thermostat isn't expecting that. It may not get this info through OpenTherm. This method far from energy efficient, expecially if you have a boiler with a proportional burner.
But why so difficult? Many modern OpenTherm thermostats (including the Celcia 20) have an external input which can override the setpoint with a preset setpoint. You could set the setpoint to 17 degrees and program the preset setpoint to 20 degrees. This way you can switch on the heating by closing the external input and turn it off by opening it again. And you'd still be using all the nifty algo's that make the system so efficient.
Alternatively you can reverse it by programming the preset to 17 degrees, to enable the user to change the setpoint and to override the user.
But why so difficult? Many modern OpenTherm thermostats (including the Celcia 20) have an external input which can override the setpoint with a preset setpoint. You could set the setpoint to 17 degrees and program the preset setpoint to 20 degrees. This way you can switch on the heating by closing the external input and turn it off by opening it again. And you'd still be using all the nifty algo's that make the system so efficient.
Alternatively you can reverse it by programming the preset to 17 degrees, to enable the user to change the setpoint and to override the user.
OpenTherm
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">You're not using all it's nifty internal algo's<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
All the nifty algo's are inside the AGPO heater (modulation, 'anti-pendel beveiliging' etc.)...
and I'm not using ANY thermostat anymore. (the honeywell is just there for 'decoration'... It doesn't actually do anything anymore )
And the on/off connection i'm using is also meant for mechanical thermostats. (i.e. a bimetal switch, which was my thermostat for 10 years before my landlord replaced it with the opentherm device)...
If you look at above trend graph, you can see that I control within 0.5C without any fancy algorithms.. 0.5C is the accuracy of the temperature sensor inside the honeywell, so I'm pleased with the result)
(note that my gas bill is a fraction of my electricity bill anyway, but that's another story )
Marcel
All the nifty algo's are inside the AGPO heater (modulation, 'anti-pendel beveiliging' etc.)...
and I'm not using ANY thermostat anymore. (the honeywell is just there for 'decoration'... It doesn't actually do anything anymore )
And the on/off connection i'm using is also meant for mechanical thermostats. (i.e. a bimetal switch, which was my thermostat for 10 years before my landlord replaced it with the opentherm device)...
If you look at above trend graph, you can see that I control within 0.5C without any fancy algorithms.. 0.5C is the accuracy of the temperature sensor inside the honeywell, so I'm pleased with the result)
(note that my gas bill is a fraction of my electricity bill anyway, but that's another story )
Marcel
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MindBender
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<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by mhwlng</i>
<br />All the nifty algo's are inside the AGPO heater (modulation, 'anti-pendel beveiliging' etc.)...<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
That's most definitely not true.
First of all the anti oscillation protection isn't a nifty feature at all, it's a <i>protection</i>, hence the the name 'anti oscillation <b>protection</b>'. It prevents the gas valve to break down from premature wear.
Secondly, you boiler will vary the burner level, but the regulation algorithm will be severly crippled. The only inputs the regulator can use is the return water temperature and the digital switch you're using as a thermostat. The boiler will still vary its burner level, but only if the temperature of the returning water becomes higher than anticipated. But your system can't anticipate very well because it doesn't have a clue on how much heat is demanded: There's has no thermometer in the room. Therefore it will not be able to determine the required supply water temperature to achieve status quo, the level that exactly compensates for the rate of heat leaking from your house. And since efficiency of modern boilers peaks at the lowest supply water temperature you will not be able to benefit from that efficiency with your system.
Finaly there's no anticipation measure with a matching feed-forwared correction in place. This may not be nessecary in case of a small appartment.
<br />All the nifty algo's are inside the AGPO heater (modulation, 'anti-pendel beveiliging' etc.)...<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
That's most definitely not true.
First of all the anti oscillation protection isn't a nifty feature at all, it's a <i>protection</i>, hence the the name 'anti oscillation <b>protection</b>'. It prevents the gas valve to break down from premature wear.
Secondly, you boiler will vary the burner level, but the regulation algorithm will be severly crippled. The only inputs the regulator can use is the return water temperature and the digital switch you're using as a thermostat. The boiler will still vary its burner level, but only if the temperature of the returning water becomes higher than anticipated. But your system can't anticipate very well because it doesn't have a clue on how much heat is demanded: There's has no thermometer in the room. Therefore it will not be able to determine the required supply water temperature to achieve status quo, the level that exactly compensates for the rate of heat leaking from your house. And since efficiency of modern boilers peaks at the lowest supply water temperature you will not be able to benefit from that efficiency with your system.
Finaly there's no anticipation measure with a matching feed-forwared correction in place. This may not be nessecary in case of a small appartment.
OpenTherm
Ok, but not everything I do for hobby, has to be efficient or easy. I like the challenge of doing things like this. Besides, I have a manual thermostat now, installed with the new heater, rental house.. ,and I forget most of the times to turn down the thermostat at night, how efficient is that.
Plus I programmed my own thermostat exactly with the functionallity I find usefull, all with dimming backlight and so on, so I would like to have that again.
But having the protocol saves a lot of time, otherwise I have to hook up a oscilloscoop and find all the manchester codes transmitted and that I don't have them all I guess.
So, if anyone has this protocol, please help me.
Plus I programmed my own thermostat exactly with the functionallity I find usefull, all with dimming backlight and so on, so I would like to have that again.
But having the protocol saves a lot of time, otherwise I have to hook up a oscilloscoop and find all the manchester codes transmitted and that I don't have them all I guess.
So, if anyone has this protocol, please help me.