Greenhouses are designed to capture solar energy. However in climates with a lot of sun and in summer when the outside temperatures are warm, all that solar energy can overheat a greenhouse. The easiest and most reliable way to avoid this is to install automatic vent openers.
One way many gardeners expect to save money is to do everything themselves. That is an applaudable goal and something I strive for as well. However not everything should be done by the gardener, especially if it could injure someone or cause property damage. Time to call in the experts!