Sunroom thermostat

Discussion in 'Alternative Energy' started by Ed Norman, Dec 14, 2006.

  1. Ed Norman

    Ed Norman Well-Known Member

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    We built a simple sunroom on our house. It has 9' high 8mm double wall polycarbonate walls and an insulated ceiling. It isn't sealed up tight yet but when the sun comes out, it easily gets 30-50 degrees temp rise. The other day it was 21 outside and 86 in the sunroom. We open a window into the kitchen and let the heat come in.

    What I'd like to do is mount a squirrel cage fan up near the ceiling and have it blow into the window whenever the sunroom gets hotter than the house. We usually keep the house around 68. Would an air conditioner thermostat be what we need? I want the room to warm up then blow in the hot air until the room cools, but I don't want it cycling on and off every minute or two. I plan to have a simple flap seal the vent up when the fan is not running.
     
  2. rzrubek

    rzrubek Flying Z

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    I think you may need two thermostats. A AC thermostat in the sunroom to tell the blower that it is warm enough and a heater thermostat in the house to ask for heat. Or you could just use a AC one in the Sunroom, but it would send in heat if available whether you wanted it or not. I would start with just the one and see how it worked out. For your flap, you may be able to make use of a dryer vent. Good luck, Great Idea.
     

  3. SolarGary

    SolarGary Well-Known Member

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    Hi,
    One easy solution is to use a thermal snap switch. These switchs open or close at a set temperature. They will directly switch the power to your fan -- that is, they will switch a moderate size 120 VAC load directly without relays or the like.

    Home Depot sells a thermal snap switch that has an adjustable temperature, so you can adjust temperature at which the fan turns on. It is a replacement for the switch that comes on one of the attic ventilation fans that they sell. When I bought mine last year, it was $13. Basically what you want your fan to do is the same as what an attic vent fan does -- turns on when the air gets hot -- turns off when the air cools down. You might even consider using an attic vent fan if you have not already bought your fan.

    You will probably want a switch on your fan to turn it off and on. You can wire the thermal switch in series with that such that for the fan to be on, 1) you must have turned the on/off switch to on, and 2) the temperature must be above whatever you set on the dial of the Home Depot thermal switch.

    Gary
     
  4. Ed Norman

    Ed Norman Well-Known Member

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    Thanks guys. The fan will be powered in the heating months only, and we don't really care how hot it makes the house. If it gets the house up to 80, it will be that much longer until it cools and the heater has to come on.

    For the fan, I plan to use a squirrel cage that I pulled out of a dumpster. It works great and is quiet. Our window slides sideways, so I thought to cut a leftover piece of the polycarbonate and jam the slider window against it. Then have a hole near the top for the incoming air, and some piece of plastic hanging over it for a flap. A dryer vent is a very good idea, too.

    Do you set the temp where the thermal snap switch shuts off, or is it preset? How low a temp can you set it to come on? If it's made to work in attics, my last attic had real high temps. I'd want this one coming on around 75-80.
     
  5. SolarGary

    SolarGary Well-Known Member

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    Hi Ed,
    The snap switches vary. Some are for a fixed temperature, and you can buy one for the temperature you like. Grainger.com sells some of this type.
    The one that I got at Home Depot has a knob and dial that you set for whatever temp you like. As I recall the low end is around 80F, and it goes well above 100F on the high end. I think the adustable is a nice feature.

    Just as an aside, you can shut the fan off when the house goes above some set temperature by just wiring one of those line voltage thermostats that are commonly used to control electric baseboard heaters in series with the snap switch. This way, the sunspace has to be above the snap switch setting, and the house has to be below the line voltage thermostate setting -- all for $25 :)

    Gary
     
  6. ericjeeper

    ericjeeper Well-Known Member

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    it uses two sensors. You can set it to where when the sun room gets 8 degrees hotter than the house.. it will turn on that fan.. When the temp gets less than 8 degrees warmer the fan will shut off.
     
  7. Ed Norman

    Ed Norman Well-Known Member

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    Nope, what I'm after is to pump the house as full of hot air as I can while the sun is shining, then let it slowly cool off after sundown. That way, our furnace stays off longer.