Greenhouses need to be designed to not merely capture solar energy but also adequately ventilate excess heat if temps get too hot.
You should always be sure you have adequate vents in the roof of your greenhouse as heat rises and you want that heat to flee.
Greenhouse roof vents work really well as they are located where heat gathers naturally at the peak of the roof.
If vents in the roof are not possible, be sure to at least have a screen to two you can open.
Ideally you want to have cross ventilation so two windows on two sides of the greenhouse work greatest.
Greenhouse Auto Vent However you should not leave the vents or windows open at nighttime as you’ll lose any heat gain and cool your greenhouse an excessive amount of.
Which means you close the vents or windows during the night and what occurs the next morning: you forget! Right now your greenhouse overheats and if you’re unlucky, you lose some plants.
Or you forget to close the vents at nighttime as well as your plant life suffer if the night is 
too cool.