something like this....shutter motor

Seems rather obvious now that you post it! LOL! Thanks. I'm wondering if there might be a less expensive option.

These motors are cheapest if you can buy them at an auction attached to a bent shutter. I just purchased two for a dollar. Look for the ones that have an arm that lifts a draw rod. If you don't need them to open as much then adjust the draw rod as needed.

That's quite a deal! At what kind of auction did you find them?

I have 4 functioning louvers and never purchased any new. Consignment auctions are good places to look and occasionally a farm dispersal. I recall one that I wanted at one auction and kids were jumping on it and I was sure it would be bent but it works fine. It sold for $3.

I used these on my roof vents. They work great and don't require power:

https://www.amazon.com/Univent-Automatic-Vent-Opener-Standard/dp/B0036EJ9HW

Good luck!

Barrie, I'll look around but I suspect there aren't many such auction in Las Vegas. Hopefully I'm wrong though.

P-Town, I'll look for a couple of those - that's a much more affordable option.

I don't imagine you'll want to hear my advice. But that's an awfully big greenhouse and Vegas is terribly hot for such an inefficient setup. What you need is exhaust fans and a wet wall on the opposite end. The exhaust fans vent the hottest air and replace it with the coolest air possible, that coming off the wet wall. In my greenhouse with that type of setup I can keep it cooler inside than out as long as dew point isn't too high. In summer below 65F dew point works well.

Having a swamp cooler blowing in cool air is vastly less efficient. The cool air coming in mixes with the hot air inside and a mix of the two goes out every crack and opening throughout the greenhouse. Not much is going to go out the louvers on the far end unless your greenhouse is unusually tight. That's what's happening now. Opening the louvers will help a little but not as much as you are hoping for. As a result the greenhouse will be hotter than it might be esp on the far end.

I think you'd be better off with roll up sides and top vents. But if you want to stick with the swamp cooler you'd be better off with big top vents on the far end. That would let the hottest air out the top to be replaced with cool air off the swamp cooler. That cool air would tend to stay down near the plants where you want it. A large open area on top on the end opposite the cooler would be vastly better than louvers down lower. That setup would be a hybrid of natural ventilation and evaporative cooling.

Think hottest air out and coolest air in. Hot air rises so let it go that way. Don't try to force it out a low vent.

Hi Fruitnut, I do appreciate your advice. Thank you! I had a smaller version of this greenhouse with a swamp cooler and it worked very well - well, at least for Vegas - I had corn 10 feet high the season before I took it down to start the new version. I set the thermostat on the swamper at 95.

How is a wet wall different from a swamper? I'd be interested in learning how one would be more efficient. How large would the wet wall need to be for a greenhouse this size.

I think I may have given an incorrect impression of my set-up. I have no concern about air escaping through any cracks because the point is for a complete exchange of air approximately every minute. My swamper is rated at 6,500 CFM and given an average ceiling height of 12' I need about 5,300 CFM. At the current CFM I'm getting a complete exchange of air less than every minute. Both vents/shutters are at the opposite end of the greenhouse from the swamper so the flow of air will be one directional (for the most part - there are some cracks around the sliding door at the swamper end of the greenhouse but not enough to worry about. I've been able to consistently get at about a 20 degree temperature drop as long as the outside humidity doesn't get too high which it seldom does here. That's been enough to keep the GH at an inside temp of 95 degrees or less. My experience has been that plants have thrived during the hottest part of the summer with the inside set to 95.

The key with swampers is ensuring sufficient venting space. The rule of thumb is to have 2 sq. ft of vent space for each 1,000 CFM which means I need about 11 sq. ft. With my shutters, at about 15 sq. ft. each, I have about 30 sq. ft which is much more exhaust venting space than I need.

I would have liked to have roll up sides but with an Airedale Terrier that cannot be taught to not dig in the garden that was simply not an option. I'm hopeful (and fairly confident) that the placement of my shutters will be sufficient to combat the summer heat but if not I may have to look into other options such as the roof vents. That would probably take some serious remodeling in which case I'll be drawing upon the knowledge of my friends here!

I'm going to have to research the wet walls you speak of. If that's a better way I may be interested in making changes down the road.

If yours is working well enough that's what counts. Vegas does have very dry air, a big plus.

If you decide you need a change it won't be cheap. A 15ft pad is about $1700. Plus you'd need a 36 inch exhaust fan.

http://www.greenhousemegastore.com/product/complete-pvc-evap-pad-system/greenhouse-cooling

https://edis.ifas.ufl.edu/ae069

Ouch! That's not cheap. We'll see how the swamper works in the newer larger version and perhaps I'll have to change over. Hopefully not. Thanks.

Looks like these can be built for much less: https://www.youtube.com/watch?v=dnLgL3KdXxg

This looks like a great option if the swamper doesn't work.

or you could make roll up sides and fence the dog out with plastic poultry fence fastened to the ground posts.

Yeah, I thought about that, also an option if the current set-up doesn't work.

I like the video link above about the homemade wet wall. His wall isn't fully wet but that can be an issue with any setup including a swamp cooler. It's also important to change the water out to avoid salt buildup.

It's refreshing to have a poster who communicates. So many post and disappear. I learned something so thank you for that.

Good growing in your greenhouse..!!