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  1. #1
    Join Date
    Mar 2003
    Location
    NY
    Posts
    2,163

    ec-67 SNVT_HVAC_Overid

    I need to code an nvo of snvt_hvac_overid. Does anyone know the math to do this. What I want to do is send an output of HVO_Maximum to vav boxes. based on an HEAT_MAX application mode from the ahu. I think I can do this with a type translator but it seems it might be easier in the EC-67.

    Any suggestion would be appreciated.

  2. #2
    Join Date
    Aug 2006
    Location
    New England
    Posts
    520
    I think you're SOL. You can't configure a freeprog nvo as SNVT_hvac_overid - it's not one of the available selections. You can do SNVT_hvac_emerg, but that will open the dampers, not set them at max flow.

  3. #3
    Join Date
    Mar 2003
    Location
    NY
    Posts
    2,163
    ctrlguy, that was my first thought because this SNVT was not an option in the 'Network Var Outputs' ->type selection but then I added a function block in LonMaker and an nvo. There I changed the snvt to hvac_overid and it show up that way now in the Network Var Outputs list. If I use 0,0,0 in the EC-67 I get HVO_Off, 0, 0 monitored at the fb output. I tried 7,0,0 but that didn't work. If I use 17, 0, 0 the result looks like HVO_Maximum, 10.54, 0 but the input at the VAV conrtoller still reads HVO_Off,0,0. I suspect that you are correct but was hoping for a solution. It looks so close.

    I have used this before to send a 'full' switch snvt. Looking at the format now I wonderif I might be able to make it work.

    *NETWORK VARIABLE OUTPUT WITH A SNVT_SWITCH*****
    The percentage and status is sent with the same variable in the SNVT_switch format
    SNVT_switch, resolution = 0,5%, lengh = 2 bytes
    1. 1st byte = 0-100% value
    Value is multiplied by 2 to match the resolution and by 256 to go in the 1st byte
    2. 2nd byte = On/Off value
    COMPRESSOR_ENA = ALM_PCT * 2 * 256 + ALM_STATE

  4. #4
    Join Date
    Aug 2006
    Location
    New England
    Posts
    520
    Interesting. Lonwatcher would not let me change the type to hvac_overid (nor did the plug-in). You might try creating an NVL in your iLON, default it to HVO_maximum and bind it to a freeprog nvi and see what the value is in the plug-in.

  5. #5
    Join Date
    Mar 2003
    Location
    NY
    Posts
    2,163
    I tried that now and it does not work. Everything looks ok but the value recieved by the ec-67 is all wrong.

  6. #6
    Join Date
    Feb 2005
    Posts
    1,255
    I believe you are trying to manipulate a 5 byte SNVT, and ec-67 can only handle 2 byte nvs, so as far as I know you are sol.

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