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    <div class="moz-cite-prefix">On 9/25/2013 2:21 PM, Ross Elliott
      wrote:<br>
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        <p class="MsoPlainText">Does anyone know of an off-the-shelf
          control system that would turn a ventilation fan on in a
          greenhouse and dump warm air into a high-mass heat storage
          room in winter / outside in summer? I want the fan to come on
          whenever the temperature in the soap-bubble greenhouse is
          warmer than the heat storage room, aka "the potting shed"
          (although since it's a Steve Kohrner flying concrete design
          it's more like a potting cathedral), so it’s not a fixed
          temperature sort of setup, it depends on the temperature
          difference between the two spaces.<o:p></o:p></p>
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    Most solar controllers are differential based.  You could probably
    use one like that.<br>
    <br>
    Thank You Kindly,<br>
    <br>
    Corwyn / Topher<br>
    <pre class="moz-signature" cols="72">-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
<a class="moz-txt-link-freetext" href="http://www.GreenFret.com/">http://www.GreenFret.com/</a>
<a class="moz-txt-link-abbreviated" href="mailto:topher@greenfret.com">topher@greenfret.com</a>
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