Water control valves ...

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  • chris_j_hunter
    Automated Home Legend
    • Dec 2007
    • 1713

    Water control valves ...

    the RAV001 looks interesting :



    as a control device ... but I'm not altogether sure I understand how it works (!) - ie: how it's commanded to do what it does - eg: when the datasheet says :

    with a pulse-pause clock signal, which effects a periodic open/close position, a quasi-continuous control system can be achieved with a cycle duration of 4 minutes ... permissible cycle duration: either <4min or >12min ...

    is it just saying the control is just on / off (but that's still fine - given the heating system is slow to respond anyway) ? And why <4min or >12min ??

    the reason for my question, is that I'm looking at options for controlling our heating system (thermal store, UFH, direct HW with trickle feed) & I was hoping the control might allow setting the valve to any desired position between its extremes - not just at one extreme or the other - plus I was wondering if it might be used to control the setting of a thermostatic valve ?

    PS: looks like the power consumption, at about 3W, when operating, could be a bit on the high side ... 3W x 24hr x 365days x 10p/unit x 50% duty = about £1.50 per annum per valve ...
    Last edited by chris_j_hunter; 28 January 2009, 10:35 PM. Reason: PS
    Our self-build - going further with HA...
  • Karam
    Automated Home Legend
    • Mar 2005
    • 863

    #2
    That's an interesting observation. Must admit I'd not noticed this snippet before (its an item that we re-sell, rather than being our own product). I shall investigate.

    However from practical experience I'm not so convinced of the statement since we have found operational times to be as long as 3 minutes. I'm not sure of the variance of this parameter and I also don't know about the linearity of the stroke vs. average power applied. I had always assumed that it was likely not to be so linear (being based on phase change) so the idea that stroke extent could be linearly controlled never entered my head. But also I guess it was more natural to imagine longer cycle periods using only the on/off states if PWM were to be used, since heating dynamics are in general relatively slow.

    There are other actuators from the same suppliers as well as others which use motorised mechanics and provide an analogue input to set the actual stroke position. But these are quite a bit more expensive. So you have to consider whether your heating dynamics are fast enough to warrant this requirement.

    Some motorised actuators may have an advantage in terms of energy consumption in that the motor may be switched off at stroke extremities. I'm not so sure that 50% duty is really what would be used across a year, but anyhow if you operate the actuator in true logic mode then the 3W will just be a contribution to the heat input for that zone. Ok, its using more expensive electrical energy but this could be 'greener' depending on source . Besides which, 3W relative to the circa 1 or more kW that you are controlling to greater effect is maybe not too great a worry - i.e to put the £1.50 in context I think you need to work out what the cost of the energy being controlled is.

    Having said all this I'm a perfectionist too and would prefer it if the actuator consumption were closer to zero

    Comment

    • Gumby
      Moderator
      • May 2004
      • 437

      #3
      Don't forget that if you are going to go mad with optimising this, you need to work out which way the duty cycle goes since the valves can be changed between power-to close and power-to-open

      I chose power to open after wrestling with the idea that it should be power to close as a fail safe. As far as I can tell, from the power efficiency point of view I got it the right way round, and in a fail situation the valves are fairly easy to unscrew.
      ----------------------
      www.gumbrell.com

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