Good work, Nancy (getting it all set up, and documenting it so nicely for others.) I know they stock the solar fans at our local HF too. This is one item I didn't spend hours researching since our greenhouse is only about 4' from one corner of the house, so the electric line was no problem. Of course, we still have to buy the electric exhaust fan, and figure out how to get it installed. More fun.

Seems like this would be a help for a greenhouse not located close to electricity. I hope the addition of vents on the opposite side will get it working well for you.

Hope the technical difficulties on your website get resolved. I've noticed the free site I'm using for my HFGH 10x12 blog is dropping some of my photos...no idea why...I just keep reinserting them, arrgh. As you said, it's hard to complain about a free site!
Sheri

Sheri,

Looks like we're responding to each other's posts simultaneously!

Yeah, we've got electricity near the GH and I suppose we could've gone with an electric fan. But given that the fan is going to be running nearly all-day, every day (during sunny days), I think (hope?) we're getting the biggest "Bang for our Buck" by going with the solar option (besides, hubbie's one of those Techie Engineer Types and he likes to be on "The Cutting Edge!" So Solar is right up his alley!).

Would that there was a viable, inexpensive heating option for winter! (but at least the heater won't have to run so long...)

-Nancy

Ah, that makes sense. I'm afraid we're the people who get dragged kicking and screaming into new technology. No brave techie engineers here! :-)

imqtpi,
Thanks for your posts on the solar fan. Having just now replaced a panel on two small solar fans of my own, I wanted to give you a little feedback on what to expect as far as effectiveness. You mention 251 cfm for a 6X8 GH. The fan will provide roughly 0.75 air exchanges per minute. The charts say that 1.0 exchanges will result in a GH 8 deg. hotter than outside. O.5 exchanges = 15 deg. hotter. So, you could expect the GH to get about 12 deg. hotter than outside with the fan.

Cuestaroble,

Are you saying that the fan results in temperatures that are hotter in the greenhouse? Isn't the point of a fan to reduce the temp?

Thanks.

DG

DG,
Thanks for your question. I should have added one more point in my posting. A closed greenhouse can get 30+ deg. warmer than the outside on a sunny day. With one air exchange per minute, whether from passive ventilation and/or exhaust fans, the inside heat gain will be "only" 8 deg. higher than outside. Misting, shade cloth, etc can further reduce the inside temps. CR

Well... Ambient temps have been hitting triple-digits here this week (FINALLY! We've got minimal humidity [Plus a swimming pool] so *I* love it!).

I've eliminated the self-opener on the roof vent and put 60% shade-cloth on the entire roof; entire south-side; and 3/4 of the front (East, blasting-morning-sunshine) side of the GH.

I've also drilled a series of (so far, 6) 3" round vent-holes (covers are appx $2-3 @ from Home Depot) along the bottom back-side of the GH. I drilled the wooden base with a hole-saw and I'm keeping the "plugs" so I can remove the vents and replace 'em with the plugs in wintertime.

I was hoping to generate some cross-ventilation: Cool bottom backside air sucking in, and blowing out the hot front-side top.

Nice theory but...

After doing all of that, the GH *still* seems to want to stay 20* above ambient (today it was 122* in there! Ouch!!!).

So I definitely agree with CR's assessment that 251 CFM is insufficient!

To be honest, when I had no "lower, passive vents" and was relying solely on the roof vents, fan, and open door (and Bugs Galore!) - I got the same result (+20*).

Adding a second solar fan is not an option. The panels only put out about 1.5 amps (max), and the fan seems to draw 1.2 amps. I don't have room for more panels (and I'm hesitant to cut holes in any panels, anyway).

I'm still 'tweaking around' with it at this point. And this *probably* isn't the best time of year for this kind of "experimentation."

I really don't plan to use the GH in summer ayway, but I still want to get a sense for "When I do this, That happens..." I'm sure any knowledge gleaned will come in handy for when I *do* have plants in it.

My big challenge will be the "Tween" Seasons. Late Fall and Spring. Too cold at night to leave the plants out, but still sunny + warm (hot?) during the day (I'd hate to roast 'em! But I'm also too lazy to be dragging plants in-and-out every day!!!).

It's definitely still a Work-In-Progress! And I'll keep you guys apprised of my progress (or lack thereof! ;-)

Oh, Good News: My Freeservers Site is fixed, so the GH/Solar Fan Page has been moved back to where it belongs (new link below, and I'm still updating it)

Thanks - AGAIN - for all the feedback!

-Nancy

Here is a link that might be useful: 2007 Greenhouse Solar Fan

Nancy, I'm sorry that the solar fan hasn't given you the results you'd hoped for, but I really appreciate your honest appraisal! That's the kind of open sharing of experience that keeps me wandering through these posts. It's really helpful (especially to newbies like me.)

Maybe the fan will still play a helpful role when the temps are not in the triple digits? I understand your "tweaking" process...I know this is the only way I'll learn what works for me in my situation, and that's why I'm pushing hard every day to get ours further along. I need to get the learning curve started as you have.

On a much smaller scale, we installed our doors yesterday. Tweaked, swore and pummeled until they worked more smoothly. Then I shopped for a rubber gasket to close the gap between the doors, and a door latch. Both purchases proved WRONG. Back to the drawing board today. Good thing we're stubborn, eh?
Sheri

Hi again, Guys!

Can anyone point me to a realistic 'calculator' that will tell me the optimal (square inches) size of passive intake vents per CFM?

And CR, you'd mentioned a 'table' that said "if all CF were discharged, per minute, the GH would be 8* above ambient." Where can I find that table?

As much as I hate math (and I really, really do!!!), I want to run through some 'calculations' of "If I do this, then this is the expected result..." scenarios (and compare 'reality' to the hypothesis!).

I'm still running *well* above 20* over ambient, and I'm not sure what I'm doing wrong!!!

I've calculated that the GH is 292 cubic feet (interior space) and the fan is 251 CFM, so that should equate to 85% efficiency. But/And... I've got 6 x 3" diameter holes in the bottom back-side (which may, or may not be enough!) and 60% shade-cloth covering all sun-exposed sides (except for 12" [max] along the bottom, front [east-facing] side).

It's not "deadly" at this point b/c I don't have any plants in there, but I'd like to get a better "handle" on what I should be doing to regulate temps during sunny days (so I'll know what to do when I *do* have plants in there!!!).

I'd SURE appreciate any feedback!!!!!!!

Thanx a million!!!

-Nancy

Nancy,
I can answer a few of your questions, but need to let you know that most of the "tables" and other research data are based on large commercial sized greenhouses. The information can be used as an approximate starting point for hobby structures.
There is no calculator for intake vent size in a passive (naturally) vented GH that I am aware of. Based on the comparison of many different GH's, the roof vent area should be 20% of the GH floor area. The bottom intake vents should be 10%. This will give you around 1 air exchange per minute, depending on the amount of wind and the temperatures. If also using exhaust fans, these can be added to the calculation.
The "table" for the temperature vs. CFM was made from data in several research papers. The only internet site that has something close to the chart is attached here as a link. Basically, the complete list of numbers are:

air exchange/min - GH temp. rise above outside
--------------------------------------------
2.0 - 4
1.0 - 8
0.5 - 15
0.25 - 25

Hope this helps. CR

Here is a link that might be useful: greenhouse ventilation

Thanks CR! That's very helpful!!!

I'm still experimenting. I think I need to drill a few more holes along the base (gotta do more mathematical calculations now - Argh!), and I'll probably add another fan to the mix (although now I'm wondering 'where' the air's gonna go if I leave the GH vents/door closed).

Hubbie's not too hip on me using any electricity to cool the GH during the summer months, but he'll just hafta deal with my "Experiments" for the time being!!!

My 'Theory Du Jour' is: What if I add a bubbly kinda smallish (appx 24" diameter) fountain in front of a fan on the floor? Would the combination of cooler-bottom-air flowing over a bubbly water source increase humidity and decrease the heat?

That's a rhetorical question! I'm gonna test it and see what happens!!! (And I'll post my results!)

A full-blown Misting System isn't an option - too expensive - and we don't want to leave any spigots open all-day

Alternatively, I have a 'walk-thru-it-and-it-closes-itself' screen door on order - so I'll probably tweak around with that idea, as well. Just to see what happens...

Temps have dropped to the mid-80's here, but the GH is still hovering over 100*. Again, still pretty 'extreme' for keeping plants alive. But then again, I don't need to move the plants in 'cuz they LOVE the 80* temps! (although nighttime temps are starting to dip into the upper 50's - still not 'threatening.' But soon... That might become a concern!)

I figure I've got at least a month ahead of me for 'experimentation' - but after that, I'd better get my sh** together 'cuz it'll be "Do Or Die" for the plants!!! (And 'Die' really isn't an option!!!)

Stay tuned, I'll keep ya'all posted on my results. And I'm definitely open to any suggestions/feedback, in the meantime!!!

Thanks - AGAIN (for, like, the hundredth time!) - for all the insight and advice!!!

-Nancy