To make your greenhouse more of a year round functioning entity, there are two main areas in which you have to make the structure more efficient-Heating and Ventilation.
1. Heating is your biggest expense for the winter so retaining heat is a priority.
The easiest way to retain heat in your greenhouse is to install a double poly cover with air in between. A small squirrel cage blower attached to the inside layer of plastic aids in maintaining air between layers.
The more dead air space between these layers you can create, the closer you will be to achieving a 30% reduction in heat loss. Holes will result in air movement and therefore less efficiency. 3″-5″ consistent space is ideal. It is a given that you would have less then that around the edges and over the ridge.
Double plastic will have a considerably longer life span. It is important to realize that as plastic gets older, the light transmission will be reduced which will reduce production.
Infrared plastic (IR poly) does further reduce heat loss and increase light diffusion so it can also be a consideration when looking for ways to reduce heating costs.
2. Ventilation is also one of your biggest considerations for the warmer times of the year. Ventilation can be done through forced or mechanical methods or passive through vents or roll up sides.
Vents are extremely effective since they can be placed higher up where the heat needs to be expelled. Mechanical ventilation is more costly both up front and to operate but it is easier to control since it is attached to a thermostat. For mechanical ventilation to be effective, it needs to be sized and located properly.
Roll up sides are less costly and simpler to install but are restricted by the fact that you have to be there to open and to close.
Climate control is especially challenging in the spring and the fall since most days you will have the need for both ventilating and heating.
One area that you need to be especially aware of is stagnant air. Without proper air movement, circulation and exchanging, stagnant air can cause many different types of diseases. It is important to understand what your plants require