I live in Hamilton, New Zealand. The winter is cold and wet. In my record, the highest temperature is about 15ish the lowest can go down to minus 4, which the frost occurs.
Although I choose most plants as cool grower specices, some ideas are from people in local orchid society to overcome the winter coldness. (Because I do not have the power supply to my glasshouse.)
Bubble plastic wrap for packaging is used inside of glasshouse from under the roof to about 1 feet above the ground. The idea is to keep the heat through the night.
Also combined with...
Collecting the lawn clipping to make a compose heap and store the heap inside the greenhouse. The heap will creat heat through the decomposition; or,
Filling up the black stained water in clear soft drink bottle to absorb heat during the day and release heat after sunset.
Other similar idea is to have stones or gravels laying above the black weed matt. The stones release heat during the night.
Of course, the vent is shut in the evening. But it can be half open for air circulation during the day time.