Determining Greenhouse Design

A greenhouse is more than just a protective bubble for pampered plants, it serves to coax the best out of your hydroponic system and creates a pleasant, relaxing and productive space.

Why a greenhouse?

Having a tropical oasis to take refuge in during a hot, dry summer might seem ideal, but a good deal of planning and research needs to be carried out first to make sure the right design for the local climate has been selected. A greenhouse can be a beautifully lit, fantastically green, comfortable and airy space, or it can turn into every plant’s worst nightmare—baking hot in summer, frozen solid in winter and dripping with condensation all year round. The difference is all in the design.

Hot Climate Greenhouses

In dry desert environments, temperatures can be extremely high—hot enough to frazzle  most plants inside a greenhouse structure unless cactus is the only crop being grown.  Temperatures of well over 38°C year round combined with low humidity are typical in  this sort of climate. The main environmental threats are high winds carrying dust or  sand, which can blast both crops and greenhouses. A proven type of greenhouse structure for this type of extreme climate is actually just  a simple tent with poles set deeply into the ground, constructed with high-tensile steel  wires to form a basic framework over which a single layer of fine insect mesh is  stretched and secured around the edges.

This forms a shaded and insect-proof structure that allows adequate air exchange to  prevent heat buildup. Inside, the humidity can be increased by fogging or misting,  which also acts to reduce temperatures—often to levels well below those of the outdoor  environment. Low humidity levels allow for the effective use of evaporative cooling,  which is the main feature of cropping in this kind of dry, arid climate. Air movement is essential inside this type of structure to maintain good levels of  transpiration within the crop, as this is another method of natural plant cooling.  More advanced high-tech, computer controlled and air-conditioned structures are also  in use in climates like this.

Types of plastic coverings

Acrylic is resistant to weathering and breakage and is very transparent. Its ultra-violet radiation absorption rate is higher than glass.  Double-layer acrylic transmits about 83 percent of light and reduces  heat loss 20-40 percent over single-layer. This material does not yellow.  Its disadvantages are that it is flammable, very expensive, and easily scratched.

Poly carbonate resists impact better and is more flexible, thinner, and less expensive  than acrylic. Double-layer poly carbonate transmits about 75-80 percent of light and  reduces heat loss 40 percent over single-layer. This material scratches easily, has  a high expansion/contraction rate, and starts turning yellow and losing transparency  within a year (although new varieties with UV inhibitors don’t yellow as quickly).

Fiberglass reinforced polyester (FRP) panels are durable, attractive, and moderately  priced. Compared to glass, FRP panels are more resistant to impact, transmit slightly  less light, and weathering over time reduces light transmission. This plastic is easy to  cut and comes in corrugated or flat panels. It provides superior weather ability only  when coated with Tedlar. Fiberglass has a high expansion/contraction rate.

Polyvinyl chloride film has very high emissivity for long-wave radiation, which creates  slightly higher air temperatures in the greenhouse at night. UV inhibitors can increase  the life of the film. It is more expensive than polyethylene film and tends to accumulate  dirt, which must be washed off in winter for better light transmission.

N/B: Height; We talk about a gutter height, low greenhouses are generally 2m, highest greenhouses now are moving closer to 8M.Height can give longer crop cycles(pepper),height also improves climate.The higher the greenhouse the cooler it will be