Thermostat controlling via PC Interface - HVAC Mode & Flags issue

Discussion in 'General Discussion' started by greefon, Sep 8, 2011.

  1. greefon

    greefon

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    Hi everyone!

    I?ve got question regarding the thermostat control via PC serial interface.
    AMX used as an external interface, but actually it doesn?t matter what RS232 is to used ? controller or PC. To program thermostat I used direct commands to and from it.

    And the question itself ? there is such a data that comes out from thermostat called ?HVAC Mode and Flags? such was up to determine the current HVAC Mode: Off/Heat/Cool/Heat & Cool/ Vent&Fan and so on (chap. 25.6.3 in Air Conditioning protocol). This data is being transmitted in commands like ?Set Zone HVAC Mode ? $2F? (chap. 25.8.10) and ?Set Plant HVAC Level - $36? (chap. 25.8.11).

    Note for ?Set Plant HVAC Level - $36?: in this command ?HVAC Mode and Flags? data doesn?t show the real mode condition when thermostat works in Heat & Cool (auto changeover) mode ? it shows only separate modes like Heat only, Cool only, etc.

    Note for ?Set Zone HVAC Mode - $2F? command informs the real mode state (also supports sending hybrid Heat & Cool mode state) BUT, it is sent to PC Interface only when thermostat is manipulated with another devices such as Wiser.

    So if one changes the mode on thermostat itself to Heat & Cool (auto changeover) it doesn?t replies to PCI with the current mode state ? only with ?Set Plant HVAC Level - $36? which doesn?t show the Heat & Cool (auto changeover) condition.

    In my installation is used several types of interfaces such as: AMX panels, Wiser interface and Thermostat itself for HVAC applications. So if user changes the mode to Heat & Cool on thermostat ? AMX panel wouldn?t receive a reply with proper mode changing.

    It?s my first C-Bus application so I need an advice of more experienced programmers please!
     
    greefon, Sep 8, 2011
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  2. greefon

    ashleigh Moderator

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    Hi

    In the HVAC protocol document, you will see that the first 5 pages (or something like that) describe the internal operation of the thermostat.

    The Thermostat internall has a PLANT CONTROLLER. This is a piece of software which controls the actual A/C equipment. (In English, big pieces of machinery are called "Plant" - which is very strange because plants are normally thing things that grow in the ground!).

    Anyhow, the Plant Controller responds to the Plant Control commands, and is used to do things like turn the heating on, or off, or turn the cooling on or off.

    So, the thermostat should be though of as having 2 parts - the part that does the settings & measurement, and the part that controls the equipment.

    The part that does the settings and measurement works out a Demand Level, which it then applies to the Plant Controller (this is the Set Plant Level commands). The Plant controller does not know anything about hybrid modes like Heat/Cool. It just knows that it can heat. Or Cool. Depending on the Plant Level demand that it gets.

    So, if you want to set the HVAC mode, you send a command (using PCI). If this command is accepted by PCI and transmitted to network, the result is that thermostat gets this command and accepts it. There is no feedback, but nature of C-Bus is that if you could send OK then it was received OK - so like sending lighting commands, you should not need feedback!

    Hope this helps.
     
    ashleigh, Sep 8, 2011
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  3. greefon

    greefon

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    That's the point - I know how to "set the HVAC mode" using any type of present interfaces & know how to make it with internal logic in AMX.

    But HVAC application much more complicated rather than controlling IR/Media/TVs where it less matter wheather TV is on or off or which type of input is used because you are infront of it. In HVAC I need full info on each zone before i send any changing commands, and again after sending I need FB on what changes were made.

    As for my problem - it's rather strange that FB of Heat&Cool (auto changeover) mode is sent only after changes were made by Wiser and not sent at all if the mode was set in Thermostat. I need all thermostats, Wiser and AMX panels to be synced with each other on the HVAC info: current mode, temp, set level and so on. Every needed FB work like a charm except this strange limitation on Heat&Cool (auto changeover) mode.

    Maybe there somekind of debug mode or command that applies to thermostat making it send back $2F data?
    Or maybe I should try use c-bus logic to solve it somehow?
     
    Last edited by a moderator: Sep 8, 2011
    greefon, Sep 8, 2011
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  4. greefon

    greefon

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    Yippee!
    I got it!
    I used Diagnostic Utility - and it showed such FB:
    05 03 AC 00 79 01 2F 01 01 63 09 16 00 00 1F <CR>
    Source Unit 03, HVAC, HVAC: Zone Group 01 On; HVAC: Set Zone Mode, Zone Group 01, Zones 0, Mode: Heat & Cool, Flags: Aux, Guard, Type: Hydronic / Heat pump Cooling, Level 22,00?C, Aux: Automatic
    Two messages in one with the same chksum! $2F info is presented within $79 command.
    Thanks everyone & diag tool!
     
    greefon, Sep 8, 2011
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  5. greefon

    ashleigh Moderator

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    Yes, this is called a concatenated command. You can get 2 (or more) commands in a single C-Bus message. (Check lighting application.... you will sometimes see 5 or 6 commands in a single message.)
     
    ashleigh, Sep 8, 2011
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