HVAC and Wet heating system

Discussion in 'General Discussion' started by gcummings, Feb 16, 2012.

  1. gcummings

    gcummings

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    Please help.

    I have a centralised HVAC system with dampers and a wet underfloor heating system.

    This is how I need the system to work:

    Senario,

    I come home from work in the winter and it is cold, so I want to press a button on the stat which starts boost heating (via HVAC system), when the desired temperarure is met, say 21 degrees, on via the HVAC set point, the HVAC system turns off, the second set point on the underfloor heating system will then monitor the temperature via its own set point which would be different, say 23, to the HVAC system to prevent them fighting each other.
    There would be a deadband on the HVAC system of say 5 degrees before the Heating turne to cooling! So the HVAC would only switch to coling mode at 26 degrees.
    Please advise if this can be done uisng the Cbus thermostats.
     
    gcummings, Feb 16, 2012
    #1
  2. gcummings

    ashleigh Moderator

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    I think you can do this.

    You would need 2 thermostats, one controlling each system.

    You would NOT tied them together (because then they would share a common set point, which you don't want).

    The wet underfloor system has a very slow response time (hours), because it takes a while to heat concrete. This means you MAY need to tune the PID settings of the thermostat for that system, if you do, there are instructions (somewhere) on how to do this but beware the tuning takes a long time. [This applies to all systems that need tuning, not just this one. The system response time of hours means that to check a setting change may take about a day, so tuning might mean fiddling about for a week.]

    You would set each system up with appropriate deadbands, and if really keen you can link the on/off control of them both via a group so that a single turn-on would work.

    The setback function means that when the building is not occupied they allow a wider deadband, saving energy. The guard function will prevent damage by turning heating on, even when the system is off, at some extrreme that you define.

    Summary: Pretty sure you can do this. You will need to set up the thermostats carefully, and you will need to spend a bit of time in Toolkit to get the settings exactly right. Use a pre-canned configuration and then modify it.
     
    ashleigh, Feb 17, 2012
    #2
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