Thermal shading screens offer benefits to managers of glasshouses that can’t be ignored. Simply put – they enable you to control the environment in which your plants grow.
This is done by regulating the amount of heat that is generated inside by the light (energy) that passes through the glass.
Thermal shading screens come in a variety of materials. There is no such thing as a correct type to use; rather it all depends on what your needs are.
The thermal screen material that you use depends on whether it will be inside or outside. Some screens block light entirely, enabling you to simulate night-time, while others are almost entirely translucent – diffusing the light evenly across the plants.
Some shading screens do more than just determine the amount of light that passes through them when they are closed. They also have small gaps in the weave that permits air to pass through and moisture, including small drops of rain, to descend.
Thermal shading screens are an important part of the microcosm that you create inside of your glasshouse. Typically, this is done by using very clever software; but some people prefer to do it manually. It has to be said that the degree of precision using this latter method is open to question. No doubt there will be those who believe that they are more sensitive to atmospheric changes than any computer-aided equipment.
A fine balance between too much heat and not enough has to be found. Sometimes this is through trial and error. This approach can be very costly because by the time you discover your error, the entire crop could be damaged.
Too much heat will dry out the plants and if left unattended could kill them. However, warmer air holds more moisture, and so when the temperature is just right, no dew will form on them either. This alone significantly reduces the chances that fungus will grow.
Thermal screen material lasts for about ten years. After that, it and the cable responsible for opening and closing it, needs to be replaced. The constant back and forth movement eventually causes jagged edges to form on the cable, and this tears the fabric.
Nevertheless, it is still a relatively inexpensive option. That’s because they have a direct effect on the size of the heating system you need to build, and the amount of fuel to need to buy to heat your glasshouse.
Let’s take a look at an example.
The technology behind thermal shading screens has come a long way. Twenty years ago, heat loss could be reduced by only around 40%. Today it’s more like 60% and some believe that it is higher than that. For the sake of simplicity, we’ll use this figure.
The time required to recover the cost of installing these screens is estimated to be about two years. Some report less time; others a bit more.
Suppose that you normally spend about £10,000 to heat your glasshouse each year and that the cost of the screen installation was £8,000. If you saved 60% on your heating expenses, then your net heating cost would be £4,000 per year.
In two years, you would have saved enough on this overhead alone to pay for the screens.
After that, however, your operating costs would decrease at the rate of £6,000 per year. Since screens generally last for 10 years you would save, in this example, nearly £50K in ten years.
This savings doesn’t even consider the fact that the size of your heating systems would be less with screens than without them.
Fuel costs are at historic lows. They won’t stay there forever.