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newgen_gw

Heating/venting my GH, your thoughts please.

newgen
9 years ago

Pertinent facts:

HFGH 10 x 12
Tropical fruit trees (cherimoya, guanabana, wax apple, sugar apple, sapodilla, rollinia,...)

Only used for cold months, roughly Nov, Dec, Jan, Feb where average low temp is 40s and average high is 60s. The rest of the year I'll cover it with some cloth to protect the polycarbonate panels from UV deterioration, the GH will probably be used as a storage shed during that time.

I've read through many HFGH threads to get info, and I'm planning on the following:

1 exhaust fan at the back wall, thermostat, on at 90F
2 motorized shutters at the front wall, thermostat, also on at 90F
2 1500-watt ceramic oscillating electric heaters, thermostat, keeping inside temp at 60-65
2 small oscillating fans on the floor, on at all times at low power, (even when the motorized shutters are closed), to provide circulation.

Previously, I was thinking of getting the Bayliss autovent openers, but with the exhaust fan/motorized shutters, I don't think I'll need them, am I right?

I'd appreciate your opinions, does it sound like a good plan?
Thank you!!

Comments (6)

  • oakhill (zone 9A, Calif.)
    9 years ago

    Newgen,

    Since I live in your same vicinity, and have a similar sized, non-hfgh, 10 x 14, perhaps a description of my setup will be useful. I do not grow tropicals, only vegetables, so make some adjustments as necessary.

    The top vents are on bayliss autovent openers, set at 70. I added two bottom side vents, also on bayliss at 70. I have an exhaust fan set to 90. Since the bayliss vents will be open by the time the exhaust fan comes on, there is no need for an additional intake vent, electrical or otherwise. My one 1500 watt electric heater will keep the greenhouse above 40 even on the coldest nights, which is enough for most vegetables. A small camping tent propane heater is used if the occasional power interruption occurs, or it is especially cold. Since most of the time, either the vents will be open or the heater with fan will be on, I do not need any circulation fans, other than a few small solar powered computer fans. One electric circulation fan should be more than enough for your crops. To keep the greenhouse at 60-65 F. , you probably will need two 1500 watt heaters, at least on very cold nights. However, you will need either a 220 v line or two separate 110 v lines from the source if they are both running. Run the calculations on how much operating two heaters will cost per hour.....

    A non-electric, inward opening intake vent should work almost as well as a powered one, and is less expensive to buy and no cost to operate. When the exhaust fan comes on, the negative pressure opens the intake vent.

    Hope this is of some use to your planning. CR

  • newgen
    Original Author
    9 years ago

    Do you use the GH year round? I'm speculating that in the cold months, if the Bayliss vents open at 70, then the GH interior may never get to 90 to trigger the exhaust fan. I could be wrong here, as I'm just guessing, having never had a GH before. In the summer, I totally agree with you.

    Thanks,

  • oakhill (zone 9A, Calif.)
    9 years ago

    Yes, I use the greenhouse all year. And also yes, in the nov. to feb. months, the exhaust fan rarely comes on. In fact, I seal if off from the outside and unplug it during the coldest months.

    Also, for the winter, I turn back the bayless vents to about 80 F, which allows my 500 gallons of heat sink water containers to absorb more heat during the day. They provide a little extra heat until about midnight, then the heater starts.

  • newgen
    Original Author
    9 years ago

    Thank you for your input. Since I will only use the greenhouse in the cold months, it looks like I may be able to skip the exhaust fan and inlet motorized shutters. I can have all 4 of the roof windows open at 80ðF and a circulating fan running. That should provide enough fresh air, right?. In your situation, I assume you get fresh air by natural wind (and the computer fans), since you don't use a circulating fan

  • oakhill (zone 9A, Calif.)
    9 years ago

    The key to a passive ventilation system is to have both top vents and bottom side vents. For summer cooling, the top vents should be 20% of the floor area; the bottom vents 10% of the floor area. For your 10 x 12, that would be 24 sq. ft roof vent and 12 sq. ft. floor vent. With that, it should provide for the needed one air exchange per minute. However, for only venting in the winter, you could probably have considerably smaller vents, but I have no data on that.

  • chadinlg Zone 9b Los Gatos CA
    9 years ago

    Keeping the min temp above 60 F sounds expensive even in Zone 9.
    I have an exhaust Fan (on at 85-90) in my 8x10GHS but it almost never runs from Nov - Feb. I do have 3 large Windows on auto-vent openers and doors at both ends which are open in warm weather.
    I keep plumeria etc. over winter without extra heating, but for more tender small plants I have a Cold Frame inside the GHS with a soil heating cable buried in sand. It is set for 50 F and keeps things like Coleus happy through winter with little expense. If I had your situation I would plunge the pots in a sand bed with a soil heating cable rather than depend on heating the air only. You might be able to get away with only heating air to 50F at night.