OpenTherm protocol PDF document

Post by **Bwired** » Wed Jan 07, 2009 11:11 pm

Good Idea, Nefit isn't telling anything. And the Nefit opentherm protocol is also different, they adjusted some things!
I have a Nefit HVAC

Post by **Snelvuur** » Thu Jan 08, 2009 12:36 am

nefit: http://www.picbasic.nl/thermostaat_nefit.htm alternatief?

// Erik (binkey.nl)

Post by **LittleBit** » Sat Jan 10, 2009 7:27 pm

Hi Pieter,
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Good Idea, Nefit isn't telling anything.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">OpenTherm is an association with dutch roots, initiated by FME in Zoetermeer.
For the detailed info, it is probably not useful to contact NeFit,
because they purchase OT-technology from www.hccp.nl
See also http://www.hccp.nl/products.htm

With best domotica regards,

Post by **Arjen_g** » Wed Jan 21, 2009 9:00 pm

To all OpenTherm Protocol fans,

Have a look at the following site that a Ziggo-customer has recently put there:
http://members.ziggo.nl/opentherm.protocol/

Good luck,
Arjen_g

Post by **phil_in_china** » Mon Feb 02, 2009 2:41 pm

The spec is very old and only a part of what would be needed. Being an OpenTherm designer (as well as a past member of the OpenTherm Technical committee) I fail to see that trying to home brew an OpenTherm control system is a wise or even fruitful thing to do. Having spent quite a few years (over 25) designing HVAC controls, any home brew would be a poor imitation of what is available from any of the OpenTherm manufacturers. Just having access to the data will not provide a good and/or efficient temperature control system. The idea that someone armed with a data sheet can do better than a team of skilled engineers spending months refining a control strategy in a dedicated climate controlled test room is not plausible.
For example how would you cope with a low load situation, which is a problem that frequently occurs when controlling a modulating boiler?

But to those who think they know better, as the OP said "good luck with it", you will most certainly need it. I plan to get an OpenTherm boiler myself soon and you know what, even with all the latest data and all the skills necessary to do an OpenTherm "home brew" I will still buy one.

Phil

Post by **Bwired** » Mon Feb 02, 2009 3:24 pm

Hi Phil,
I Understand, But what we want is to put a Set Temp on the line as if it was done with the existing thermostat. So integrate that piece with our home automation system. And the ability to read all the settings like outside/inside temp. All the other fancy stuff can be handled by the existing technology!

Post by **Snelvuur** » Mon Feb 02, 2009 4:12 pm

indeed, we dont want to re-invent the wheel, we only want to be able to control it.

// Erik (binkey.nl)

Post by **Lempens** » Mon Feb 02, 2009 4:27 pm

We want to see all the data that the display on our Ketel shows. So we don't need to go upstairs, to see it.

Post by **phil_in_china** » Mon Feb 02, 2009 4:27 pm

It's not easy to do those things even if you have a lot of experience.
1) The set room temperature is a value that the thermostat is using internally to adjust the boiler output, therefore just sending a "set room temp" command to the boiler is utterly useless. The boiler has no idea what to do with it, using your spec v2.2 ID16 "room setpoint" is only a value sent to the boiler in case it has a display, then the boiler can display what the room setpoint is. No more than that.
2) It's the thermostat that controls the boiler using many IDs, not just one or two and ID16 is just an information ID (see the spec), not a control ID. So to modify the room setpoint cannot be achieved by intercepting the OpenTherm comms line and inserting a new value. The only way it to tell the thermostat to do it. How you do that depends upon which thermostat you are using.
As for reading the room temp, buy a stat that display's it.
For the OAT, test's I had done showed that an outside sensor was totally not needed with an OpenTherm system, it made not a jot of difference.

Phil

Post by **Bwired** » Mon Feb 02, 2009 6:18 pm

Yes I know it's difficult to do and the Opentherm protocol is difficult too!
It's about time companies like Nefit etc develop something that can work with Homeautomation.
A Company like Remeha is opening up a bit and delivering a controller these day, but as of my understanding still not that great!
I guess it will take a couple of years!

Post by **phil_in_china** » Mon Feb 02, 2009 7:03 pm

The protocol is difficult I agree, but that's why it's tailored for the manufacturers of thermostats & boilers to implement. Controlling the temperature in a home or room is not as easy as most people think. We have come a long way from the days of switch it on when we are below the demand temperature and switch it off when we reach the demand temperature. All modern electronic thermostats contain complex PI algorithms that provide excellent room control. With OpenTherm heating control designers have been given a tool that makes vast improvements in maintaining room temperatures while also reducing significantly the energy used. But as I tried to say in my first post here I really dont think its a protocol for the non-professional. The "control" is still within the thermostat, what the OpenTherm protocol allows thermostat designers to do is modulate (reduce/increase) the power output of the boiler. In a conventional boiler the thermostat designer has only two possibilities either switch the boiler on or switch it off, thats it. To help explain it a bit more imagine the task of controlling the speed of a car. If we could only either push the accelerator to the floor or lift our foot off it completely our control of the speed would be poor. But now what if we could press the pedal gently to increase the power a bit more and simply lift the pedal a little instead of having to lift completely? That's what OpenTherm has given thermostat designers !!
Hope if nothing else at least you have a better understanding of OpenTherm.

Phil

Post by **phil_in_china** » Mon Feb 02, 2009 9:30 pm

I just had a look at the post:
nefit: http://www.picbasic.nl/thermostaat_nefit.htm alternatief?

// Erik (binkey.nl)

and it looks quirky but it should work !!
I think it would be simpler to use with the Danfoss ORT10 if you need an LCD version or if not the Danfoss ORT01. This gets over the need to mess with the OpenTherm communications completely. All that's needed is the PIC and the X9C103. Power both devices from an external source and only connect only the three pot terminals from the X9C103 in place of the existing pot, the resistors are not needed. If you try and power the PIC and X9C103 from the Opentherm supply you may run the risk of overloading the current. The X9C103 can take 3mA and depending on what's being used the PIC can take 2mA which will therefore exceed the OpenTherm spec.
But at least this solution it will allow you to remotely alter the room setpoint.

Phil

Phil

Post by **RDNZL** » Mon Feb 02, 2009 10:25 pm

Didn't know that the thermostat did all the calculations, a bit the world upside down.

I would be a happy camper if I could only combine this solution http://www.picbasic.nl/thermostaat_nefit.htm together with my moduline 400 thermostat so I can have them parallel/daisy chained whatever, or make the pic controlled one active when i'm away and the moduline 400 when i'm back home with a relays or something like that. What is your idea about this Phil is it doable?

About the current which can be drawn, my Nefit 400 moduline thermostat ( non opentherm / alike ) has backlight on it's rather big lcd display, so I guess the max current spec is a bit higher for that nefit protocol too, I know the engineer talked about problems controlling the backlight on earlier models... somethign to do with firmware in the uba, if i remember correctly.

Regards,
Ron.

Post by **phil_in_china** » Tue Feb 03, 2009 10:31 am

Not sure I understand what you are trying to achieve, I presumed that you wanted to remotely alter the room/house temperature?

By modifying a dial type thermostat as detailed in http://www.picbasic.nl/thermostaat_nefit.htm by replacing the existing thermostat pot with a programmable pot is in theory possible. Then you can transmit (by a variety of means ie. wire / RF) a new pot position remotely. The resistance value of the pot that you remove from the thermostat has to match the new programmable pot, but most are 10K ie 103. For a Home Automation remote control of the heating setting you don't need anything else.

Phil

Post by **Lempens** » Tue Feb 03, 2009 11:57 am

But we want to know more. Like whats the tempature of the water. Whats the speed of the fan. Waterpressior etc.