Ours has no cooling capacity at the moment other than a fan at one end.  The plan is to upgrade over this winter to a high capacity exhaust fan on one end and an evaporative cooler at the other to allow us to moderate the temperature in the greenhouse during the summer months.

We use a garage-style electric heater in the winter.  The heater is a 14, 500 BTU 220v heater that hangs from a bracket over the entry door to the greenhouse.  We typically set a small fan at the far end of the greenhouse and point it upward to create more air circulation.

We also heat the water in our aquaponics system.   We use an inline titanium spa heater, 110/220v flow through heater to keep the water at a constant 70 degrees F during the colder months.  The net effect of the warm water in the tanks and growbeds and the small electric heater are amazing.  Our greenhouse rarely gets below 50 degrees F even during the longest cold spells we have experienced.  Because the water stays warm in the aquaponics grow beds, the plants there never get their roots cold and the warm water circulating through the grow beds mitigates the temperature around the plants creating a micro-climate above the grow bed.

Do you use any shade cloths in the summer? Also off this topic but approximately how many gallons do you have in your aquaponic system?