Extractor fan and/or heat recovery

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  • chris_j_hunter
    Automated Home Legend
    • Dec 2007
    • 1713

    #16
    Interesting - how do you deal with the water the dehumidifier extracts, to stop it getting into the air again ? And drying washing ... good ventilation, even extraction, is often a very cost-effective way of reducing condensation, ideally with a heat-exchanger (extractor fans with them are available) to recover some of the heat or cool (as it were) ... ??
    Our self-build - going further with HA...

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    • Gumby
      Moderator
      • May 2004
      • 437

      #17
      The dehumidifier is a small portable one with a 10litre tank - about a week's worth, then I empty it

      If I had known then what I know now I would have investigated whole house ventilation systems - although I am not sure how beneficial they are in old houses with draughts and chimneys etc. So the PIV fan is a sort of half way house, but very easy to fit since it sits in the loft and has one duct onto the landing.

      The dehumidifier will release some heat as a side effect of condensing the water. I have not measured it's power consumption.

      As much as possible we line dry outside and the tumble vents outside. Biggest sources of condensation in our house is probably cooking (very difficult to vent the extractor), showering and breathing, not necessarily in that order.

      However ... this is starting to wander off-topic ...
      ----------------------
      www.gumbrell.com

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      • JonS
        Automated Home Guru
        • Dec 2007
        • 202

        #18
        I use dH/dt for controlling bathroom fan and hence humidity. It is the rate of change. So slowing changing humidity e.g. wiht the seasons (summer lower in our house) have low dH/dt; conversely showers which suddenly make the air moist have a high dH/dt.

        I've done quite a lot of trialling and found that dH/dT of 15 for switch on and 0 for switch off works well most of the time. It does cycle a little if in the bath for a long soak. I have tried a dH/dT and fixed threshold together for on-off and found this gace erratic behaviour as the thresholds competed. I've also had going above negative values for switch off (ie getting less damp but more slowly) but these tend to let the fan run for longer than necessary which got annoying.

        I think the position of the sensor will have an impact on the values you choosee and a little experimentation may be needed to satisfy your tolerance of either cycling or long running.
        HTH
        JonS

        Comment

        • jcmiguel
          Automated Home Jr Member
          • Apr 2008
          • 38

          #19
          dH/dt

          I will try dH/dt this weekend and will give feedback
          Thanks
          Originally posted by JonS View Post
          I use dH/dt for controlling bathroom fan and hence humidity. It is the rate of change. So slowing changing humidity e.g. wiht the seasons (summer lower in our house) have low dH/dt; conversely showers which suddenly make the air moist have a high dH/dt.

          I've done quite a lot of trialling and found that dH/dT of 15 for switch on and 0 for switch off works well most of the time. It does cycle a little if in the bath for a long soak. I have tried a dH/dT and fixed threshold together for on-off and found this gace erratic behaviour as the thresholds competed. I've also had going above negative values for switch off (ie getting less damp but more slowly) but these tend to let the fan run for longer than necessary which got annoying.

          I think the position of the sensor will have an impact on the values you choosee and a little experimentation may be needed to satisfy your tolerance of either cycling or long running.
          HTH

          Comment

          • TimH
            Automated Home Legend
            • Feb 2004
            • 509

            #20
            I've just finished my ensuite renovation and Chris thought some of the details might be relevant, so here goes
            [I don't run Idratek but it may still be relevant]

            Photos here: http://picasaweb.google.com/TimE.Hawes

            I have and Aqualisa Quartz digital shower with the processor box hidden in the loft. The pump and mixer valve is all in this black box. The silver round thing in the shower has two low voltage buttons “on/off” & “boost” and a dial (potentiometer) to adjust the temperature. The signals go back to the processor box and adjusted in there.

            The extractor fan (single speed with timed overrun) is wired through a DHW cylinder thermostat clamped to the hot pipe; the idea being the fan comes on automagically when the shower is running. This needs a bit more work as it takes a quite for the heat in the pipe to activate the fan, and even longer for the pipe to cool down (and then turn the fan off) afterwards. The timed overrun on the fan is set to minimum, so about a minute, but pipe cool-down is more like 25minutes… Maybe the contact between the pipe & stat isn’t great, maybe I need a different type of thermostat, but ideally I’d have the fan come on when the pump starts and overrun for 5mins when the pump stops. I’d rather avoid a flow switch, so a bit more head scratching I think.

            With three speeds you could drive the first (lowest) from the light switch (or a PIR), i.e. if the light is on, then someone is in, so gently ventilate.
            2nd speed activated by the temperature of the hot pipe to the bath increasing in temperature (i.e. a dT/dt condition, change in temp with time).
            For the 3rd speed use a humidity sensor; if the air becomes too humid then ventilate the bathroom at max rate.

            To turn the fan off, you could consider a rate of change condition for the bath waste pipe (pipe goes hot *and* feed pipe is/was recently hot). If you have a separate shower, again monitor the waste pipe temperature but look for a "cold" temperature; the waste pipe will heat up while the shower is in use, but then cool down again once showering has stopped.

            What I've found is that there seems to be too much thermal mass in the hot water feed pipe to turn the fan off - it just takes too long to cool down.

            Hope those thoughts are useful.

            Tim.
            My Flickr Photos

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