How Does Greenhouse Glazing Work?

Greenhouse glazing as it is known is the material that covers your greenhouse; it is the very thing that most people think of when they think of a greenhouse; glass paneling or plastic sheeting.  But perhaps before buying your glazing material you have wondered how it worked, or what the science was behind how both the glazing and your greenhouse work.

A greenhouse aids in plant growth by using the same principles that heat our own earth. The first step is light transmission itself; the passing of the sun’s rays through the glazing material and into the greenhouse. The sun’s rays are short wave as they pass through the glazing material. As these waves pass through the greenhouse they are absorbed and turned into heat by the contents your greenhouse. Everything from the soil, to the plants, to the benches absorbs these waves. The greenhouse materials then in turn emit heat in the form of long length IR that cannot escape back through the glazing material. This is what is commonly referred to as the “greenhouse effect”. (In relation to the discussion of climate change, the ozone layer acts to allow in the short wave sunlight, while not allowing the long wave “heat” to escape.)

Inside the greenhouse, heat is generated and kept through a process known as “convection”.  By this, we just mean that warm air, because it is lighter than cold air, will rise to the top of the greenhouse and then sink to the bottom of the greenhouse as it cools. Because the greenhouse, when sealed, does not allow the air to escape the convection continues in a constant loop as the air rises and falls– which allows the greenhouse air to absorb more and more heat as the cycle continues.

Different types of greenhouse glazing have different efficiency levels, as with anything the more you pay the better type of material you can get. In general you should be looking for two important items; the amount of light that the material allows through and the R-value of the material for holding in heat. Although not as important, you should also look to see if the material offers light “diffusion” as this will mean your plants will receive a less “harsh” sunlight and you can avoid “burning” your plants. Any material you purchase should have this information available. If you cannot immediately find it, the company you are purchasing your glazing material from should be able to help you without much concern.

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Suggested Greenhouse Glazing References and Materials

We’ve written may posts about different types of glazing materials and their pros and cons – please take some time to read through our other articles as well to see what greenhouse glazing works best for you!

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