Generally, fans are used to pull in cooler outside air from ground level at the north wall and dispelled via an exhaust fan set as high as possible on a wall at the opposite end, but I can't tell you how you would mount intake vents and an exhaust fan on a Rion. Other Rion owners here will hopefully come along and fill that gap.

However, just floor fans can make a difference, especially when the GH floor has been paved with unglazed bricks or patio blocks. Then, soaking the floor with cold water, coupled with a floor fan aimed up will result in cooler air at plant level

But the easiest and surely first line of defense aganst the heat of direct sunlight and one you could take advantage of now, while sellers are begging for customers, is a shade cloth. I discovered the benefits of the Aluminet shade cloth here from another poster; that if hung with the stretchy part running from the GH peak down the sides; the automatic roof vents will open easily under the Aluminet; it's that lightweight and stretchy- at least in one direction of the weave.

Lining the GH interior with clear bubblewrap also helps. It allows light penetration, yet serves as insulation against both heat and cold. I leave mine up all year and the plants have done even better in the bright but evenly diffused light produced with the bubble than they did before I installed it.

I have a Rube Goldberg gh about the same size you describe. I can share a couple things about fans and cooling that you may find helpful.

First, fans are notoriously inaccurately rated with respect to CFM. For years I used a single 20" Lasko box fan for exhaust, with acceptable results. The rating for this fan is 3226 CFM on high, but I question that number. I have roughly an interior volume of 890 cubic feet, which means I should have been exchanging air every 20 seconds. No way. Some of this discrepancy may be accounted for by the fact that air under vacuum has a "weight" to it (inelasticity as a result of molecular attraction?), which means an exhaust fan doesn't perform the same under load. More on this below.

This spring the fan died, so I replaced with the 20" Lasko 3300 Wind Machine. Tremendous improvement. They rate this fan at 4,750 CFM, and I'm guessing I can turn the air over about every 90 seconds or so...just guessing.

But here's the interesting part. Since I also added an air chiller (of my own design) at the intake side, I installed another 20" Lasko box fan heading the chiller to force air through it. The addition of this second fan on the intake doubles the air flow through the gh, which doesn't make sense, since the CFM is essentially identical to the exhaust. The reason, I believe, has to do with the "weight" of air within a closed space, and the additional horsepower pushing the air from the other side has a positive effect.

I'm going to expand the air chiller for next year. The effect from it is substantial at humidity levels below 50%, but since our summer conditions rarely dip under that number, I'm hopeful that the increased capacity will achieve the results I'm looking for.

My gh is for orchids too, BTW. On my "cool wall" where I hang my angraecoids, temps are typically ~5-8F less than incoming air at higher humidity levels, and approaches ~20F less the closer to 20% humidity it gets outside.

I find that exterior shade cloth doesn't meet my needs very well. First, securing it for high winds can be difficult. (Most folks install shade cloth incorrectly -- it should be held away from the gh by at least a couple of inches.) Second, with seasonal changes in the angle of the sun, getting optimal light for plants is an ever-changing project. What I do is hang shade curtains inside to get the light correct for different species, and depend upon the chiller to get the temps as low as possible. Growing orchids is a bit more dependent upon light, and given the poor light conditions in most backyards, you don't want to sacrifice any if you don't have to.

I concur with birdwidow that pulling air up from the floor level will produce the best results. This means that you'll probably never use the roof vents. Also, opening it up that much (via roof vents) will drop your humidity too low. By operating under a slight vacuum you can preserve some humidity, which your orchids will appreciate.

-Bruce

Hi Alex,

Here's my 2 cents:

I have a similar size greenhouse (12 x 16) and grow similar items (orchids, succulents, palms, cycads). We don't get quite as hot here and it gets more humid. (good for plants, bad for humans).

When I put my greenhouse in I thought it was all about setting up an environment to keep growing through the winter. I quickly found out that its easier to control temps in the cold than it is the heat.

Bottom line is that exhausting air/ventilation and shade cloth will get you, at best, to the same temps as the outside air. Without both of these in place you will be amazed at how fast your orchids will get fried. You greenhouse will become an oven. Keeping the humidity high will also help your plants survive the hotter weather.

To get to the lower temps you want, you're going to need to use a misting system (my solution) or an evaporative cooler, etc. Lots of options there, but nothing simple.

paul

Paul's observations about regulating temps inside the gh in cold versus warm temps made me think of something else to add.

It's probably more difficult to retrofit a prefab gh, so maybe this has limited value for you. Since mine is wooden frame, I can make changes as needed. One bugaboo with my gh previously was sealing up the exhaust vents on cold winter nights so they were tight, then loosening them during the day when temps soared. My vents are a simple affair -- strips of gh fabric stapled to wood slats. I used to use duct tape to close them up, but that was a pain, didn't work well when cold, and tore the lamination off the fabric...requiring repair with Goop.

So, this year I made a double insulated shutter. It's basically a wooden frame with two layers of gh fabric, hinged above the exhaust vents. It's easy to prop open in the morning on a hinged 2x2, and I can seal it tight using wire wrapped around nails on each side that are secured against the gh studs. (I do things on the cheap!)

It takes me 30 seconds, and I no longer have to be concerned about wind getting through cracks in the vents on cold nights. Before I would just prop open the gh door during the day and hope that errant air currants would keep things cool (Not!), when it was too difficult to open the vents and turn the exhaust fan on. Now that's no longer an issue.

-Bruce

In the summer your temps will get HOT in that GH. My greenhouse is 18x25x9 ft ceiling and I use a fogger to cool it. It works great. The wind speed along with the fog will cool my GH down to between 70 and 80 depending on the temp outside and the humidity. It normally runs about 80 degrees most summer days. You can check out AquaFog for a great cooling system. I think they make a smaller version that might work for your length.

Rob

Hi all,

I really appreciate all of the great responses! Thank you.

I was really concerned about making sure that I consistently have good air flow over the plants to prevent disease, and improve growth. It sounds like I need to think about things differently and approach this from the angle of getting the temperature under control first since the ventilation of the greenhouse is a part of this. I wish this whole thing would plan itself so that I could just focus on growing, but I guess that this is a good learning experience!

Now I just have to sort through your responses and digest some of this information...and then come up with a good approach to solving this temperature problem. I'll be back! I didn't expect so much help so quickly. Thank you all again.

Alex

Hi again,

I was able to give your responses more time, and here's what I've come up with so far that I am thinking of pursuing.

The fact that the greenhouse is prefab does create some problems, but in what concerns time and money it's not such a bad trade off. First, I doubt that the greenhouse will require too much modification at this point. In building it some of the pieces are really difficult/annoying to assemble, but overall it's not a bad unit. But what I like about it the most is that it is expandable, and it's already looking like I will need an extra 4-8 ft to accommodate my aloes and cycads in the cooler months. I really would have preferred something about 3-4 times the size, but time and space are constraining factors here! Besides that, I will be able to leave most of the large plants outside for most of the year, which leave space for my primary concern: orchids and propagation of shrubs and perennials.

Birdwidow, I really like the bubble wrap idea. The extra layer of insulation could reduce the heating costs in the winter. Luckily, I am in a pretty good zone heating wise, and it does not get too cold here, so heating costs would not be incredibly high in the first place, but every little bit helps. I think that the diffuse light is really going to help with plant growth too. Is it better to use unglazed brick or pavers instead of gravel? I had previously though of putting down a gravel floor, but now I am reconsidering the pavers since you brought them up.

Bruce, the first thing I noticed is that it sounds like I should maybe not install the automatic vent openers on the roof of the greenhouse since this may cause too high of a decline in humidity, but maybe this will work all right if I use a fogger. I also like the idea of "doing things on the cheap"! I was trying to do this (really only so that I could save the money for plants), but I have now decided that I can't take this approach only because I decided that I would have to get a greenhouse to keep all of my plants alive at the last minute. I really liked the idea of making my own evap wall, and then I realized that it would be somewhat difficult to mount it and get everything else done at the same time, so I have decided to accept that I will likely need to use something like a fogger like Rob recommended. Since humidity here is typically low in the summer, early fall, and late spring I think that this should be very effective at keeping the structure cool. I guess this line of reasoning contradicts what I wrote previously since I should have time to plan something out between now and April!

Sunlight is definitely not an issue where I decided to locate the greenhouse. There are no structures/large trees within about 20-30 ft of it, at least. I was very lucky in being able to find a location that had so much sunlight throughout the year. Of course, that creates a whole set of other problems, but at least there is enough of it to keep the orchids happy! Maybe, some of my non blooming Laelias will finally bloom this coming year!

I think that for the time being I will use a box fan to circulate the air on the inside of the greenhouse, and a small heater to keep the temperature from getting too low. I have to figure out how much electricity I will need and how many outlets I will need to have in order to keep the greenhouse up and running too. It's not really looking like I will need that much though.

I'll be back! Thank you again.

Alex

It's all about what you're planning on growing. If you were only planning on aloes, cycads, shrubs/perennials, etc., then the open roof vents and perhaps a fogger would be fine. Orchids changes things a bit.

I know there are orchid hobbyists that use foggers, but most report mixed results. I believe those that have the best results from foggers also have enough interior volume to deal with the droplets. I know that I would have trouble with excessive/persistent dampness in my gh with a fogger (considering the fact that it's pretty well-packed), and I suspect you will have the same issue. Your low humidity will help reduce the problem of droplets, but it will mean you'll have to eliminate plants from underneath the unit and perhaps about six to eight feet downstream. That'll undoubtedly affect your plans for bench arrangements and/or hanging stuff. You already are suspecting that 8x16 isn't going to give you enough room, and I can tell you that it will be easy to make things cramped in that size!

If you've got laelias (especially anceps and rupicolous-types...ones like rubescens and purpurata can take warmer), you definitely must keep the summer temps below 88F or so (the lower the better) while maintaining good humidity. Sounds like you have the low humidity enough of your season to support some sort of chilling arrangement. You like things on the cheap and don't have time to fuss with an evaporative cooler? Build a frame out of 1/2" PVC outside your gh and above your intake vents (see below). Get some 1/2" irrigation tubing, some elbows, tees, and caps, and a few 3/4gph fogging heads. There's a special hole-puncher, and pop the heads into the tubing such that they're spaced to make a dense curtain that incoming air is drawn through. This won't give great results when the wind's blowing, but if you think it through as you design it, it should give you respectable results. This keeps any potential wetness away from your orchids, and can be operated either with a simple timer on a garden hose, or a thermostat.

Rion didn't make it easy for you...but you're going to have to retrofit. You absolutely will not be able to maintain proper conditions without an exhaust fan! Opening the roof vents (those two little ones shown in the picture on their website really won't do much of anything) and running a box fan inside just isn't going to allow the proper elimination of solar-heated air, especially if your outside temps are already 100F. Plus, you'll have the low humidity problem I mentioned. If it were me, I'd put two smaller exhaust fans on either side of the door, which allows space on the back wall to do whatever you need in terms of chilling incoming air -- where you'll need to cut in your intake vent(s).

My air chiller is an exterior addition, and as long as your humidity is below 50%, you should get the results you're looking for with relative ease. If you go with a paver floor, under-bench misters will do a good job as well (if your intake vents are somewhere at floor level), although this will reduce the available floor space for plants.

Another potential problem is the one of light -- again for your laelias. If you use bubble-wrap for insulation, your laelias aren't going to get enough light in the winter...and you mentioned some stubborn ones. Light is probably the number one reason why orchids won't bloom when they've reached the correct size. You've got coated 4mm twinwall -- if you're not below USDA Zone 8a, a single 1500-watt heater is all you'll need. On high, that heater will get you +15F. (Make sure your door and vents fit tightly.) You'll have to experiment (and is also dependent upon the species), but it may be that you will need no shading at all for your laelias. I can't tell from the Rion picture how heavy that coating is. At any rate, no more than an additional 10 to 20% shading.

There's certainly a lot to consider to get an operational orchid gh, and it sounds as if you're spending a good amount of time thinking things through. Hope this helps.

-Bruce

I just noted in your original post that you have three roof and three side vents, which changes the dynamics a bit from what I originally thought. Without knowing exactly how they're configured, though, I'll stick with my recommendations above.

-Bruce

Hi Bruce,

I really think you're right about the light issue. For the most part what I've noticed is that I tend not to give enough light to the plants for fear of burning them, and so what I end up with are really interesting looking foliage plants. I actually like the way that orchids look out of bloom, but it would be nice if they could at least give me one flower. Come on! I have a L. lobata alba with 50 growths or so that I've had for 6 years and not one bloom!

You're right on with what I am trying to grow. For some reason garden web seems to have lost the list of orchids that I am growing, but it is mostly Laelias, Catts, Encyclias,Coelogyne and Masdevallias. The Masdies do well so long as I haven't let temps get above 85, and I haven't managed to off any Laelias in spite of my best efforts to kill them by neglect. The sides of the greenhouse are clear, which is why I was thinking that the bubble wrap could be a pretty good idea for me, but I see your point that the bubble wrap may hurt more than help where I am as added insulation is probably unnecessary for this zone, and it could cut down too much on light. (I think that this is zone 9a). I will probably opt for shadecloth instead for now since I have it on hand.

Thanks a lot for making me rethink this whole forced ventilation idea again! What you have written makes sense, but I was trying to convince myself that my optimistic idea of not requiring the extra ventilation was correct. I guess, I will just have to figure those back in to the greenhouse plan for now.

In reconsidering the different options to keep the greenhouse cool, it didn't really occur to me that the fogger would produce too many excess droplets or too much condensation on the inside. This seemed like a good idea because I could skip the whole plumbing part of the design process and keep the cooling in a nice, simple package. Before the fogger, I had thought of the nozzles/misters as a cheap cooling solution until I realized that the water here is pretty hard, and that the potential for clogged/failed heads in hot weather is high. This probably is still, all things considered, a good option though, at least until I am sure of what the exact needs of the greenhouse are for temperature control, and I happened to get a set of these for free from someone who had them lying around their house who thought that I could use them for the greenhouse.

I'll let you all know how the plan is coming along. Thank you again Bruce!

Alex