Johnson Controls MetaSys

Jeff LockyearJeff Lockyear Junior MemberPosts: 147
Does anyone have any experience with Johnson Controls' MetaSys N2 System protocol? I have the protocol document from Johnson, but I'm under a time constraint and it looks a little beyond what I've been working on until now. Any tips or advice would be gladly appreciated!

Jeff Lockyear

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  • ericmedleyericmedley Senior Member - 3709 Posts Posts: 4,159
    Does anyone have any experience with Johnson Controls' MetaSys N2 System protocol? I have the protocol document from Johnson, but I'm under a time constraint and it looks a little beyond what I've been working on until now. Any tips or advice would be gladly appreciated!

    Jeff Lockyear

    Can you post the protocol? What are you needing to know specifically?
  • Jeff LockyearJeff Lockyear Junior Member Posts: 147
    Truthfully, I'm not sure what I need. The HVAC system uses BACNet, and the N2 protocol is supposed to be the interface (similar in idea to ModBus, I guess). Anyway, I forwarded the protocol to our AMX tech support guy in Canada to see what he says. The protocol document is 100 pages long. I was just wondering if anyone else had any experience with it.

    Jeff
  • ericmedleyericmedley Senior Member - 3709 Posts Posts: 4,159
    Truthfully, I'm not sure what I need. The HVAC system uses BACNet, and the N2 protocol is supposed to be the interface (similar in idea to ModBus, I guess). Anyway, I forwarded the protocol to our AMX tech support guy in Canada to see what he says. The protocol document is 100 pages long. I was just wondering if anyone else had any experience with it.

    Jeff

    I think there's some other threads on this board concerning BACNet. It is a very bloated protocol. I almost had to do a system at one point at a bank. I was happy when they decided to do something else. However, I never got around to actually creating any programming for it.

    There didn't seem to be a simple way to get what I needed from the controller system or the local zones. Plus there was a lot of IP protocol that the BACNet controller needed to see from my system. I wasn't even sure I could provide what they wanted.

    Also, there seemed to be a lot of overhead that the I needed to track that had nothing at all to do with the actually getting things I needed but had to do with parsing messages from all the devices on the net.

    I'm kinda speaking out of my ear, I'll admit because I never really got far enough to speak intelligently about.

    Here's a tutorial from the BACNet site that might help.

    http://www.bacnet.org/Tutorial/index.html

    Good luck with that!
  • John PaulJohn Paul Junior Member Posts: 143
    Bacnet over serial

    I am able to control the Johnson Controls N2 over bacnet using a bacnet over serial interface box. The box used here is the intesis box, i have uploaded the data sheet for it.

    The field controllers used over here in Villa for AHU controls is UNT and the Thermostat is AP-TMZ series. The Controllers used for FCU's are TEC series

    Now the HVAC can be controlled via AMX but the Johnson controls thermostats are locked and cant set any values manually. Both intesis box and Johnson controls are set to a priority value of 16 but some how the AMX value keeps getting fixed
  • Jeff LockyearJeff Lockyear Junior Member Posts: 147
    We have 5 JC systems we're integrating with at the moment (all in one compound). So much depends on the HVAC contractor I don't even know where to start.

    We have an NI-700 sitting on the JC 485 network as a device (with an address etc) for each system. The integration is working pretty well, but it isn't super reliable. We keep coming up against these inexplicable JC controller lockups. The HVAC guys don't really know the code (think Landmark) so they're not much help at byte-by-byte troubleshooting.

    Although I have the five systems under my belt, they're all effectively identical. We plugged into the 485 bus and based everything on the addresses supplied by the HVAC programmers.

    The bus is really traffic intensive, so I definitely recommend a dedicated processor.
  • John PaulJohn Paul Junior Member Posts: 143
    I have attached the response i received from Johnson Controls regarding the lock ups. So you are able to communicate with the Johnson Controls N2 via a 485 . My integration is less traffic and i can receive only the responses i need but the local thermostats are locked so i am trying to rectify it .



    "
    Based on the information below, I am guessing that you have N2
    communication from the NAE to the UNT and TEC devices. At the N2 device
    level, there are only two priorities (instead of the 16 used by BACnet).
    These two N2 priorities are local control and override. When there is an
    N2 integration, any BACnet command to the N2 integration is handled as an
    override at the N2 device causing it to use the BACnet setting rather than
    the local setting.

    As stated before:
    "....you need to release all commands for the settings (setpoint) including
    priority 16 in order for the local closed-loop control to fully work. It
    may also be necessary for the NAE to be set to Ignore Relinquish Default
    and/or set Local Control...."

    What this means is that any command in the N2 Integration BACnet priority
    table will be treated as an override at the N2 device. Even a command at
    BACnet priority 16 will be handled as an override at the N2 device.

    The settings Ignore Relinquish Default and Local Control at the N2
    Integration are intended to help with this. Ignore Relinquish Default is
    used to disconnect the BACnet Relinquish Default from the N2 device so
    BACnet doesn't try to override the N2 device based on a Relinquish Default
    setting. This is required for local control to operate. The Local Control
    setting is used to lock out NAE user interface use of BACnet priority 16
    (adjust priority level) while allowing operator override (BACnet priority
    8). This is useful because it is difficult to release a BACnet priority 16
    operator command at the NAE user interface.

    My local "N2 expert" is not available today, so I am not able to get much
    more detailed.

    Please take a look at the Metasys N2 Integration objects in question using
    the NAE user interface. If there is any value in the BACnet priority table
    or Ignore Relinquish Default is not set, then the corresponding N2 device
    will be commanded to override.

    The way N2 Integration is intended to be used is that BACnet priority 8
    (BACnet operator override command priority) should be used to control from
    the NAE by overriding the N2 devices. Releasing BACnet priority 8 (AND ALL
    OTHER BACnet PRIORITIES) allows local control to resume (if Ignore
    Relinquish Default is set). Using BACnet priority 8 also allows the NAE
    user interface to find all the N2 devices in override since this priority
    is used by the override summary."
  • John PaulJohn Paul Junior Member Posts: 143
    So what you are saying is that without a interface box, we are able to connect to the Johnson Controls to the AMX NI controller and control it.

    Can you give me more details about the HVAC in your site. The details of the field controllers for AHU and FCU and the thermostats ?

    The field controllers used over here in Villa for AHU controls is UNT and the Thermostat is AP-TMZ series. The Controllers used for FCU's are TEC series
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