Design criteria of greenhouse for cooling and healthy purpose | Planning and design of greenhouse | site selection and orientation | what is dead load | what is live load | what is wind load | what is snow load | covering and cladding material | covering material life span | Planning and construction of greenhouse

PLANNING AND DESIGN OF GREENHOUSE

Planning and design of greenhouse

■ Greenhouse planning and design is intended to provide and maintain a growing environment that will result in optimum production at the highest pitch.

■ The plant requires a portion of visible light from solar radiation for photosynthesis, so the structure must be transparent.

■ Also, for the cooling effect, ventilation should be required during the summer, while insulation is required during the cold night. Therefore, a greenhouse acts as a barrier between the plant's production area and the external or general environment.

SITE SELECTION AND ORIENTATION IN GREENHOUSE PLANNING AND DESIGN

■ A greenhouse is designed to withstand local wind snow and crop load for a specific growing activity.

■ The construction site must be flat, ventilated and receive good solar radiation and a drainage system can always be provided.

■ In the region where snow is expected, the tree should be at a distance of 30.5 to maintain the drift of the greenhouse and to prevent the shadows on the cultivated tree located on the east, south or west side being at a distance 2.5 times its height.

GREENHOUSE PLANNING AND DESIGN GUIDE

■ Guaranteed east-west orientation Better lighting in winter.

■ In multi-span greenhouses, the gutter must be oriented from north to south.

■ In a naturally ventilated polyhouse, the fan must open to the leeward side.

STRUCTURAL DESIGN

■ The greenhouse structure is designed with careful consideration of the loads on the individual components.

■ Loads are commonly classified as dead load, live load, snow load, wind load and, in some places, earthquake.

DEAD WEIGHT

■ Dead loads are gravitational loads of constant magnitude throughout the life of the building. They include ceiling glazing and stationary equipment, suspended heater with fan, and overheated pipes for water or heat are considered a dead load, as they are permanently attached to the structure.

LOAD LIVE

■ Real-time load is more difficult to calculate as it can change. Example: - short term crops, such as hanging baskets, are normally considered a live load. A common moving load is a maintenance crew who repairs the roof windows.

WIND LOAD

■ The wind load can come from any direction, but is generally believed to be acting horizontally against the wall.

■ The base wind speed for the designer is 160 km per hour.

■ The base wind speed is adjusted for factors such as site exposure, the height and shape of the roof slope of the building.

■ The wind lift value must not exceed the dead load of the structure, otherwise the structure may lift off the ground.

SNOW LOAD

■ It is very considerable from 0 Pascal to more than 4.79 kg Pascal depending on the position. The snow load design is generally adapted to take into account the exposure of the building, the slope of the roof, the heat loss through the roof and the type of occupation.

■ Since the heat loss through glazing in a heated greenhouse is high, it is generally assumed that most of the snow will melt or slide through the project. ◇ The most important function of the greenhouse structure and discovery is the production of the crop against hostile climatic conditions such as high and low temperatures, snow, hail, rain and wind, diseases and pests.

■ It is important to develop the greenhouse with maximum intensity of natural light inside.

■ Its structural part which can cast shade to the east in the greenhouse should be minimized.

■ Different structural designs of greenhouses are available depending on the type of frame.

■ A straight side wall and an arched roof are perhaps the most common form for a greenhouse, but the gable roof is also widely used.

■ The vaulted ceiling and the circle greenhouse are often constructed of galvanized iron pipes.

■ If tall crops are to be grown in a greenhouse or when using benches, it is better to use a straight side wall structure rather than a house with a roof, this ensures the best operational use of the greenhouse.

■ A hook greenhouse is suitable for crops such as lettuce or nursery material.

◇ Important points

☆ The greenhouse structure must be designed to withstand wind speeds of up to 30km per hour.

☆ A general rule of thumb is to allow for daily watering of around 20 liters per square meter if growing in soil beds.

COVERING AND CLADDING MATERIALS

■ The following factors should be considered when selecting a greenhouse roofing material that has light transmission, impact resistance, weather resistance and thermal stability over a wide temperature range.

■ In temperate regions where high temperatures are required on the coating material with high light transmission and for IR absorption, it should be selected. Furthermore, the loss of heat by conduction should be minimal.

USEFUL LIFE OF COVERING MATERIALS

1. Glass and acrylic sheet 20 years

2. polycarbonate and fiberglass from 5 to 12 years

3. polyethylene and plastic for two to six months

4. Polyethylene set for UV rays from 2 to 3 years.

■ The ideal selective greenhouse planning should have the following properties: -

1. It must transmit the visible light portion of the solar radiation used by the plant for photosynthesis.

2. The small amount of radiation present must be absorbed and convert some of the fluorescence into visible light useful for plants.

3. It must reflect and absorb the radiations which are not useful for sowing and which cause the interior of the greenhouse to overheat.

4. It should have a minimal cost and a useful life of 10-20 years.

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