cooling a greenhouse

Large exhaust fan
Retractable/removable side curtains
Design roof vents in your plans (if you have not already built the greenhouse)

If these do not apply to you, we need more info about your greenhouse.

creger.robert said:

they have roll up side curtains-they are painting top white-they want to have showers-weddings in greenhouse

What are the owners expectations of the space when it is changed over to a wedding venue? are they planning to use it seasonally as a greenhouse, and then seasonally as a venue? Greenhouses can provide some shelter from rain, but are generally built in such a way that climate control for human comfort is nearly out of the question. If noise is not a problem I would just use some big fans, people are not going to rent a repurposed greenhouse for a wedding expecting A/C, it is basically like being outside

a thermostatic greenhouse window operator is how Larry controls his gravity radiant walls. No power required
Maybe he will post a pic

I can see that you are going to use this for "other than a green house" venue with a green house look. Then the regular rules of heat loss and heat gain will apply. I had an awning manufacturer as a customer who asked me about doing outdoor temporary structures at a country club. His problem was how to get those structures cool enough on some of the very hot afternoon receptions. And if heating them would work in the spring and autumn.

I came up with using a couple of package units on mobile carts that could be stored and moved around to the location of the structure using golf carts. The structure would have inflatable duct sewn into the walls and ceilings to distribute the cooled air across the interior of the enclosure. There were flex duct connectors attached to the side of the structure and you could place package unit several feet away from the structure behind a solid insulated wall to reduce the noise Temporary electrical hookup was placed at the proposed equipment location. The idea was to apply the side curtains and pre-cool or pre-heat the enclosure before people arrived, Then continue to use the package units as needed as the climate changed throughout the hours of the event.

Depending on the temperature and the wind conditions the side curtains could be raised as the evening approached, or lowered and the heat deployed, making the system usable well into the late fall and early spring. I have drawn up the plans for him and did preliminary load calculations for him based on the size of the room they had in mind, one of the larger rooms like yours (about 50 x 100) would take 5, five ton package units to even come close to the load with 150 guests inside during a 2 hour event. Of course if there was a little overcast or less people, then you could deploy less HVAC equipment.

After calculating the cost of the electrician, the structure, and the package units, the country club never purchased the system. The temporary structures were assembled without any added HVAC and only used seasonally, mainly for outdoor cover in the case of rain.

What about a poly sock duct running down center and using a mobile 15-20 ton or so a/c unit. Even can rent them. Then store when not needed.