thermostat fan speed query

Discussion in 'C-Bus Wired Hardware' started by ICS-GS, Nov 10, 2009.

  1. ICS-GS

    ICS-GS

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    Just wondering does anyone know how the thermostat controls the 'fan speed 1', 'fan speed 2', 'fan speed 3'?

    Is it based on rate of change of temp, relative to the temp setpoint? If not what is it based upon?

    I am trying to interface to a brivis 529 interface for my gas ducted heating, and it has 'economy' and 'full' fan speed inputs. But as i have multiple zones it gets a little tricky. W1= zone 1 economy, W2= zone 2 economy, if both W1 & W2 are on simultaneously = both zones on & full rate. Also worth noting is that it does not utilize the 'W' (heat) signal...

    Same thing applies to the evap cooler, the pre-defined installation for the t/stat has 3 fan speed outputs...

    Also is there any reason why in the install manual the damper controls and external relay plant control are on two separate modules? or can you use the one 12ch module to achieve this?

    Also what is the damper modulation setting? and why is it advised not to use it?

    Cheers

    Grant
     
    Last edited by a moderator: Nov 10, 2009
    ICS-GS, Nov 10, 2009
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  2. ICS-GS

    ashleigh Moderator

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    They are just relay outputs. Contacts close for speed 1, and open so another set close for speed 2, and so on.

    The fan speed is what you set - manually.

    The fan operation is a different matter. See the help topic "fan operational modes selection". But basically - some systems run the fan all the time even if the plant is not doing anything. Example: Reverse cycle cooling, compressor not running. What should the fan do? If you dont run the fan the air does not circulate and you can get hot or cold spots in a house. If you do run the fan you can get complaints of it circulating air thats not cool. So you can tweak it.

    Without a vast amount of thought... my suggestion is that you use the fan speed inputs off a couple of relays and set the thermostat so it uses 2 fan speeds.

    The zones are independent of the fan speed. Just like many installations, you can turn zones (rooms or whatever) on and off as you like, and you can bump the fan speed up and down as you like. Don't try and be too clever about it.

    Same answer.

    Its just an example to show that it can be done this way if you want. You can use 1 x 12ch relay unit, or 3 x 4's, or a bunch of 1ch's, or whatever combo you want.

    Ahhhh. Damper modulation tries to open and close dampers to maintain the temperature in a zone. Provided you have a temperaure sensor in that zone. Damper modulation MIGHT operate the dampers A LOT. And if your dampers are not designed to be constantly opening and closing you can make them turn up their liddle toes and die.

    This is not to be confused with the variable fan coil settings which, in the right circumstances, allow a modulation of the control valve (for chilled water or similar, eg in hotels) to change the amount of flow thru a fan-coil heat exchanger. (You did ask...)
     
    ashleigh, Nov 10, 2009
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  3. ICS-GS

    ICS-GS

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    Reviewing the user guide there is no option to control the fan 'speed' just the mode as you suggest. I would have thought the 'auto' mode would control the fan speed...:confused:

    Cheers

    Grant
     
    ICS-GS, Nov 10, 2009
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  4. ICS-GS

    ashleigh Moderator

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    The auto mode and manual mode determine if the fan is to be turned off, or not, when the plant is turned off.

    This is no different to other thermostats and a/c controllers out there.

    Controlling fan speed automatically is possible in some cases, but exactly WHAT an auto mode means is usually left undefined by the makers - perhaps because they don't want to tell you how lousy the auto modes actually are :)
     
    ashleigh, Nov 10, 2009
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