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A north-south orientation is recomended so that any shadow from the greenhouse frame moves across the floor during the day. In an east-west orientation the shadow tends to stay in one area of the crop.
The main considerations are light transmission and, for roof vented models, wind direction.
Greenhouse Roof Design
Greenhouse roof designs range from the domed or tunnel roof profiles to the opening sawtooth or gullwing venting roofs.
The domed designs allow the greatest amount sunlight to be transmitted on an annual basis and are more cost effective to build.
The sawtooth or gullwing designs provide effective natural ventilation and hot air release which are the single most important features in a greenhouse design. The growth and health of a crop is directly dependent on plants accessing an environment that promotes transpiration, fresh air and adequate levels of carbon dioxide, and inhibits the development of disease.
This is achieved when the greenhouse air is continually replaced and there is positive air movement through the crop.
The height of a greenhouse is important for the quality of the greenhouse environment.
Increased height provides increased air volume and promotes a more stable environment, lower maximum temperatures and less variability in both temperature and relative humidity.
Side wall heights of between 2m and 5m are recommended with a roof heights starting at 3.5m and increasing to 8m.
Adequate side wall height is also required to accomodate climate control equipment such as internal screens and fogging systems.
Increased height advantages include:
- More stable environment due to increased air mass
- Lower maximum temperatures
- Less fluctuations in relative humidity
- Crop is further away from hot air at the top of the greenhouse
Greenhouse covers (extruded greenhouse film or Solarweave reinforced greenhouse film) need to meet some fundamental performance criteria in order to be successful and viable.
- Provide solar radiation and light transmision levels that optimise crop growth
- Provide protection from the elements and be robust and durable
- Reduce heat loss during winter
- Be UV stabilised and have a satisfactory serviceable life
Internal Retractable Screens
The incorporation of a retractable screen that acts as both a shading and an energy saving screen is the most valuable addition to any greenhouse.
A retractable shade screen changes the microclimate of the crop by reducing the solar energy absorbed by the crop. At times of high solar radiation and temperature this energy reduction is important. Crop temperatures are lower and the plants are not stressed due to excessive transpiration and high temperature.
The retractable screens are also an efficient winter energy (heat) saving device. The air below the screens can be up to 4deg.C warmer.
- Most plants need shade – but if you move the shade plants develop up to 15% faster
- Diffused shade equals more photosynthesis, more photosynthesis equals more growth by a further 5-10%
- Plant temperature can be up to 11deg.C cooler in summer
- In winter plants can be up to 4deg.C warmer
- Plants will be dryer with less disease
- Winter heating costs can be reduced up to 47%
- Plant quality improves
- Reduced water, fertiliser and running costs
- Increased light during early morning, evening and cloudy periods.
- Workers comfort is improved
Climate Controller Computers
The digital climate contoller (computer) has multiple functions that can monitor and activate systems within the greenhouse to allow the growing conditions to be optimised.
Climate controllers can monitor:
- Light intensity
- Air and leaf temperature
- Relative humidity
- Wind speed and direction
Climate controllers can operate:
- Greenhouse roof and wall vents
- Retractable screens
- Circulation and exhaust fans
- Fogging, misting and irrigation systems