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We wanted to take the heat from the sun that accumulates in a greenhouse during the day, store it to be released during the night. We needed to move the hot air across rocks. Computer fans, taken from desktop computers typically operate at 12 volt, .5 amp and are durable induction fans. Moving warm air across beds of cobbles warmed the cobbles and cool the air. Moving cool air across beds of warm cobbles will cool the cobbles and warm the air. This principle is used to store and release passive solar heat efficiently and at low cost.

Materials

  • Desk top computer fan (12 volt, .5 amp)
  • Power supply 120 volt input, 12 volt, ,5 amp output
  • 4" PVC section 4"
  • 4" PVC connector

Step 1: Matching the Fan and Power Supply

Match the fan with the power supply. These should be roughly the same wattage but do not need to be an exact match.

Step 2: Trim the Fan

Trim the edges of the fan with a bandsaw. Then sand the edges of the fan so that it fits inside the 4" PVC pipe.

Step 3: Sealing Around the Fan

Wrap 1/8" weather stripping around the fan so that it creates a tight seal inside the 4" PVC pipe. Pass the fan electrical cords through a small hole drilled into the PVC pipe. Strip 1/2" of coating from the cord and connect to inverter to ensure the fan works.

Step 4: Hooking Up the Heat Exchanger

The fan arrangement is placed in the 4" PVC pipe so that air can be pushed through the perforated pipes. The hot air in the greenhouse is pushed across beds of rocks that are under the soil in the greenhouse beds. The fan moves hot air during the day time, warming rocks and in the night, cool air is warmed as it is pushed across the warmed rocks.

<p>Very interesting, I had not thought about using rocks for thermal storage. Nice idea about recycling old fans to route the air through your system.</p><p>One small correction: you suggest using an inverter to power the fan(s). An inverter takes direct current (DC - usually 12V, or something that can be easily stored by batteries) and converts that into alternating current (AC - usually 110-120V, or what normally comes out of your wall outlet.) Your description shows using a 120V to 12V device, that is almost always 120V AC input and 12V DC output; this is called a power supply, rather than an inverter. Other than that, this looks pretty good.</p>

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