I want to be able to control my Elga heatpump with the OTGW, but without the Honeywell Touch Modulation thermostat. Reason is that I have several rooms with their own Vision on/off thermostat. Long story short: I capture the on/off signals on a Netduino microcontroller and would like to instruct the Elga to start heating when one of the thermostats switches to "on".
The OTGW site (http://otgw.tclcode.com/standalone.html#onoff) tells me that this should be pretty easy. Just disconnect the thermostat from the terminals and short the terminal. The Elga should then start heating.
It turns out that the Elga needs three inputs: the command to start heating, the room temperature and the room setpoint temperature. The first is simple, just short the terminals. My question is about the latter two:
How do I override the room setpoint and room temperature when I have no thermostat connected?
BTW: the way it works now is by means of the tele-input of the thermostat. But I want to get rid of the thermostat; I have an OTGW....
Elga heatpump vs OpenTherm, does this setup make sense?
Moderator: hvxl
Re: Elga heatpump vs OpenTherm, does this setup make sense?
Are you sure the heatpump needs these values? That seems in violation of the opentherm specs, which specify: "The control Setpoint [...] represents directly a temperature Setpoint for the supply from the boiler. The slave does not need to know how the master has calculated the control Setpoint, e.g. whether it used room control or OTC, it only needs to control to the value." So normally it should suffice to send a control setpoint to the boiler.
As a result of this statement, I have not felt the need to add the possibility to the OTGW to send the setpoint or room temperature. If you want that, you will have to modify the code. Note that also some thermostats don't provide this information.
As a result of this statement, I have not felt the need to add the possibility to the OTGW to send the setpoint or room temperature. If you want that, you will have to modify the code. Note that also some thermostats don't provide this information.
Schelte
Re: Elga heatpump vs OpenTherm, does this setup make sense?
Am I sure?
I Am sure that the Elga controller needs these values to compute a setpoint to send to the external unit. That setpoint is communicated through the Carrier brand protocol.
The other thing that I am sure of is that the heatpump does not start when I short the thermostat terminals. Perhaps Techneco violates the OpenTherm specs, I don't know.
I would -of course- be very, very cool if the GW could act as a gateway and a OpenTherm master, I would then be in total control of the heatpump (and I could sell the Honeywell Touch...). One other advantage is that would be impossible to manually change the behaviour of the heatpump, because there's no thermostat with a direct link to it; there's only the on/off thermostats. The only device communicating with the Elga would be my Netduino/OTGW combo.
A code change....it's been a while since I did assembler, that was with a Z80A from Zilog...I Guess that this feature is not on top of your to-do list, right?
One other thing... When I issue a setpoint command (TT= or TC=), it takes a while (> 90secs) before the setpoint turns up on the thermostat. Hence, it takes even longer before the heatpump starts. Can I shorten this period somehow? Or is it a thermostat quirk?
I Am sure that the Elga controller needs these values to compute a setpoint to send to the external unit. That setpoint is communicated through the Carrier brand protocol.
The other thing that I am sure of is that the heatpump does not start when I short the thermostat terminals. Perhaps Techneco violates the OpenTherm specs, I don't know.
I would -of course- be very, very cool if the GW could act as a gateway and a OpenTherm master, I would then be in total control of the heatpump (and I could sell the Honeywell Touch...). One other advantage is that would be impossible to manually change the behaviour of the heatpump, because there's no thermostat with a direct link to it; there's only the on/off thermostats. The only device communicating with the Elga would be my Netduino/OTGW combo.
A code change....it's been a while since I did assembler, that was with a Z80A from Zilog...I Guess that this feature is not on top of your to-do list, right?
One other thing... When I issue a setpoint command (TT= or TC=), it takes a while (> 90secs) before the setpoint turns up on the thermostat. Hence, it takes even longer before the heatpump starts. Can I shorten this period somehow? Or is it a thermostat quirk?
Re: Elga heatpump vs OpenTherm, does this setup make sense?
An alternative option is to load the interface firmware in the gateway and completely put the netduino in control of which opentherm messages to send to the heatpump.
In an opentherm installation the thermostat is the master. It controls which messages are exchanged. The gateway can only wait for the thermostat to request a setpoint. It has no way to force it. A Honeywell touch normally does this once every minute. I would therefor expect a setpoint change to be picked up on average after 30 seconds. But perhaps it wants to see the value twice before it really accepts it.
In an opentherm installation the thermostat is the master. It controls which messages are exchanged. The gateway can only wait for the thermostat to request a setpoint. It has no way to force it. A Honeywell touch normally does this once every minute. I would therefor expect a setpoint change to be picked up on average after 30 seconds. But perhaps it wants to see the value twice before it really accepts it.
Schelte
Re: Elga heatpump vs OpenTherm, does this setup make sense?
Interface firmware? Could you point me in the right direction please?
Thanks for your help, btw.
Thanks for your help, btw.
Re: Elga heatpump vs OpenTherm, does this setup make sense?
The interface firmware is available from the download page. There's a description available here.
Schelte
Re: Elga heatpump vs OpenTherm, does this setup make sense?
Nice.
Let's see whether I understand this...
- I load the interface firmware
- every second I put a Hex messages on the serial line with the "master" bit unset to trick the heatpump into thinking there's a thermostat connected.
- I cannot make use of TT and TC commands, but in stead I need to create Hex codes for those.
- I need to build my own routines to interpret the heatpump's response codes.
Then I would not need a thermostat anymore, right?
Let's see whether I understand this...
- I load the interface firmware
- every second I put a Hex messages on the serial line with the "master" bit unset to trick the heatpump into thinking there's a thermostat connected.
- I cannot make use of TT and TC commands, but in stead I need to create Hex codes for those.
- I need to build my own routines to interpret the heatpump's response codes.
Then I would not need a thermostat anymore, right?
Re: Elga heatpump vs OpenTherm, does this setup make sense?
Looks like you understood it. By the way, the responses from the OTGW with the interface firmware are no different than with the gateway firmware. You would have had to write the code to interpret those anyway.
Schelte
Re: Elga heatpump vs OpenTherm, does this setup make sense?
Plan A was to be able to control the power of the Elga. It worked:
I bought a "good ole" Honeywell Chronotherm Modulation. By fiddling with the setpoints in relation to the room temperature, the Elga reacts with different power levels:
If you set the setpoint 0.4 lower than the room temperature, the Elga starts. From that point on you can decrease the setpoint further to 0,49 degrees below the room temperature. That's the minimum power level. Max power is reached when you set the setpoint a little higher dan room temperature.
Plan B is to get rid of the thermostat altogether and use the Interface firmware.
I bought a "good ole" Honeywell Chronotherm Modulation. By fiddling with the setpoints in relation to the room temperature, the Elga reacts with different power levels:
If you set the setpoint 0.4 lower than the room temperature, the Elga starts. From that point on you can decrease the setpoint further to 0,49 degrees below the room temperature. That's the minimum power level. Max power is reached when you set the setpoint a little higher dan room temperature.
Plan B is to get rid of the thermostat altogether and use the Interface firmware.