Campesino is spot on.
Its possible to have a completely closed system if certain environment variables are controlled. Such as humidity, temperature, carbon dioxide with equipment such as air conditioning, carbon dioxide suppliments, dehumidifiers.
Exhuast is mainly for removal of heat and humidity. If those are maintained with other systems such as air conditioning and dehumidifiers, you can have a closed system with only an active intake for fresh co2. Summer heat can be addressed with these systems or as campesino suggest, venting in room is a viable option, so long as you are not pulling air back into the tent from the same room. You want to pull from a fresh, cool source. If venting in a room is not an option because of smell, you can invest in carbon filters that remove the odor of cannabis, which can be vented in or outdoors. In the winter time, heat is not a problem and lighting efficiency is thrown out the door as the heat becomes useful and so lights essentially become totally efficient.
You can extend on this with air cooled hoods, increasing the efficiency of heat removal and in the winter time, recirculating that heat to the bottom of the tent.
I spent a bit of time with greenhouse ventilation and looked at fluid dynamics to understand the movement of air, which is technically a fluid. Its helped me build many systems for people including myself, that are very efficient and effective grow system.
I wonder if i should write an article on airflow systems 😅