Setting up GH airflow
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  #1  
Old 08-13-2017, 08:02 PM
tropterrarium tropterrarium is offline
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Setting up GH airflow
Default Setting up GH airflow

This is related to my other post on GH manufacturers. As this is a bit more general, I started a new thread.

Trying to figure out the logic of air movement in a larger (500 sqft) GH. Can you confirm or correct or comment? Location is Santa Barbara, CA.

Horizontal air flow fans. Not sure whether fix mounted ones producing a race track air flow are better, or whether oscillating ones will be better. Or both? That is pretty simple to retrofit. Those run 24/7.

Exhaust fans are turning on once temp reaches say 78F. Cubic feet/minute (CFM) is indicated as area x 8 to 12, depending on source. Middle is 10, so 5000 CFM. Exhaust fans are mounted rather high under the gable as hot air rises.

Intake louvres are on opposite side of GH. Elevation? Very low to ground the outside air is often hotter than a few feet up. Should they also be mounted quite high? But that may encourage stratification. So split the difference and put them in the middle?

Swamp cooler with side-discharge is on same side as intake louvres. Turns on when temp reaches >82F (+/- 1 hysteresis). Given weight, they are on the ground.

A) Do the extractor fans continue running? It will add to electrical cost and power consumption (16.8 A for swamp coolers, 7.6A for extractor fans).
Alternatively, the extractor fans are shutting off, because the swamp cooler has its own fan. Can the louvers of the exhaust fans passively get rid of hot air, or is there a need for separate louvres?

B) Are the intake louvres going to lower the effect of the swamp cooler? Or are they actively closed? Or is the approach to have the CFM of the swamp cooler to be greater than the CFM of the extractor fans? Will build a bit of pressure, but that will all balance out steady-state. In that case, I don't think there is a need for exhaust louvres for the swamp cooler.

Thanks for bearing with me!
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  #2  
Old 08-14-2017, 08:55 AM
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Two fans in diagonally opposite corners from each other, facing down the sides, will give you good, circulating air. Fixed is fine, and one less thing to break. Placed up near the roofline, there will be a gentle, tumbling action all along the benches.

I would have the swamp cooler come on before the exhaust fans. If it works well enough, the fans won't come on, except as a backup, and yes, free air intake and exhaust will increase the temperature and decrease the humidity.
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Old 08-14-2017, 05:06 PM
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On cold nights I have found air circulation top to bottom makes a big difference in maintaining more even temperatures.
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Old 08-15-2017, 11:11 AM
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Giving it a shade more thought, I'd have to say that - having the space to do it - I'd have used ceiling fans blowing downward in my greenhouse. Great, "tumbling" air flow, and no stratification. Plus, it helps dry out crowns faster.
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Old 08-16-2017, 01:41 AM
tropterrarium tropterrarium is offline
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I might opt for a mixed approach with upper circular and ten some lower oscillating fans, possibly at a downward angle. This is reasonably easy to alter quickly.
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Old 08-16-2017, 11:28 AM
dounoharm dounoharm is offline
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In my old greenhouse, I had intake louvers that were on a thermostat, that I set to open 5 degrees before the exhaust fan came on, to make sure there was good airflow. that was a 12 x24 in north Carolina.

in my present lean-to, I thought I would try using passive intake shutters, and gosh golly, they work fine! my gh is roughly 8 x16, with 2 sides next to the house and garage. getting the equipment right was a bit more complicated.

the slope of the roof is not as steep as I would have liked, but it is working excellent to date.the sidewall is 6 feet, and the house side is tucked under the eaves and is about 8.5 feet.

I toyed with the idea of a roof exhaust fan, but ended up with a 2' side wall exhaust fan. it is set at the top of the sides. that was the hard part, placing that....the intake shutters are about halfway up the front, near the door....and just above the position of the evap cooler....the exhaust pulls thru the passive louvers as well as the evap cooler...which has been set on hi cool and runs almost continuously, as we have had 100 degree days all summer.

those items are the hardest to figure out....especially with only 2 sides to work with! I figured in my head for ages!

my exhaust fan is set to pull air out on a thermostat set at 90 degrees....

the door on the 'front' of the greenhouse is centered, with the evap cooler and intake shutters on the 'house' wall. this allows me to place my jaybird 700 on the benchtop on the opposing side of the door. the jaybird is also set to run at 50% humidity.

above the jaybird, there is a 12" fan at the top at the ceiling, sort of angled a bit, that runs continuously down the benches, and also hits the hanging plants. another 12" fan also running continuously is on the house wall, towards the end....but not blowing into the exhaust! so far, so good....I have a little fan I use when I am in there working at the table.

so, I have an airflow that runs from one end out the back side. I bought a pretty large exhaust fan BECAUSE IT WAS ON SALE....and what girl can refuse that? lol....also a nat gas heater 30,000 btu ON SALE....(they have a great 'steals and deals') section at farmtek) I got a great buy on all the equip about 9months before I built....

under the benches, I have a couple types of plants that are easy and pest free, for humidity purposes....the floor is gravel 4-6" deep, for humidity also....

my cattleyas mostly hang from the rafters, and love it...I have a few on the benches, to view them better...and the benches hold slippers and some phals....and some misc orchids. all working well in their micro climes.....

at the back near the exhaust, I have an enormous (climbing the rafters) night blooming cereus and a few cymb....my benches are cedar topped on treated legs, and 2' x 4' which we constructed.

I wish it could have been larger, but its what we get here, and I am lucky that it has worked as well as it is working....

oh, the heater is nat gas, with a blower and thermostat, and cost less than $125 WHAT A DEAL!
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