Solar HVAC for Green House

[FrankG]

The link below is to the 2nd part of the Green house project.

http://www.theworkshop.ca/energy/grnhouse/2/gh2.htm

FrankG

www.theworkshop.ca

[FrankG]

Admin(s),

please move to section "Heating" I posted in error, my humblest...

[richhagen]

I have a few old thermostats lying about from apartments and such, I think the mercury switches on the bimetal coils on the common honywell type I have are rated at about .4 amps at 24 volts or so.  It seems like a smart use of old equipment to regulate your temperatures and ventilate the greenhouse when it gets warm.  

If the mercury switch on a thermostat was capable of switching a fan directly, and if the fan wouldn't burn out when the voltage was low, or if a relay or other circuit was in place to prevent damage if not, then, if the panel can power the fan, you wouldn't really need a battery.  You will likely only need to ventilate if the sun is shining I would think. Rich

[FrankG]

Hey Rich,

I think you have a point, but given that the solar panel I'm starting with won't run the fan(s) the battery I'm hoping will be a sort of buffer.

I started out with mercury thermostats but found that thier good for "heating" applications, where I need fans turned on below a specific temp, but the issue of engaging the fans to cool didn't have an obvious solution (shy of mounting upside-down...)

The digital themostat, uses relays (barely audible when they are activated) and can handle 1Amp @ up to 30V AC/DC. It even has a "Compressor" delay feature that inserts a 5 minute delay between successive cooling cycles.

[richhagen]

The mercury ones I have generally have three contacts, a common, and one for each side of the bulb to activate the AC if it is too warm, or the heat if it is too cool depending on which way the temperature effects the bi-metal strip and causes it to tilt the bulb.  Rich

[ghurd]

Could run the fan from a mosfet, the 'heat only' mercury thermostat controling the mosfet.

Cheap and simple. Thermostat, mosfet, and a resistor.

G-

[GaryGary]

Hi,

This is a ways off the nice solar chimney concept you are developing, but I just ran across the paper below on solar a heating project for commercial greenhouses that was done back in the last oil shortage period.  The collector (which solar heats water) is 10,000 sqft and produces half a megawatt of water heating power at midday!

The collector is ultra cheap (about $2 per sqft).  It uses the same sort of double wall, inflatable technology that a lot of greenhouses use today for thir ceilings and walls.

I figure this collector generates heat energy at about 1/125th the price of the same amount of electric energy from a PV panel.

I think the same collector design (scaled down a bit) might make a great pool heater.

It here: http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#GreenhouseHeat

Just search down a page a little ways for "Mears".

Anyway, just thought it was interesting.

Gary

[umairhp]

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