Articles
A RATIONAL APPROACH TO GREENHOUSE DESIGN
Article number
281_11
Pages
111 – 118
Language
Abstract
Greenhouses are required to have high light transmission, adequate structural strength, low cost of construction and low operating costs, which, in northern latitudes, is predominantly the cost of heating.
The best design represents the compromise between these conflicting requirements which gives the highest financial return to the grower, and this can be established using optimisation techniques.
These have been applied to a multispan film plastic covered greenhouse.
The parameter varied in the optimisation process was the angle of inclination of a symmetric pitched roof.
The influence of this angle on the total natural light transmitted into the greenhouse over a season was calculated using a validated prediction model.
This was converted to tomato yield assuming yield is proportional to the light integral, and then to crop value.
The influence of roof angle on heat loss and the cost of heating was established using simulation models.
Finally the influence of roof angle on the material required to build a greenhouse to meet the wind loads required by the national greenhouse building code was determined.
The roof angle which gave the biggest margin between crop value and heating cost, i.e. the most profitable greenhouse to operate, was modified by the cost of materials to provide the roof angle for which the greenhouse gave the highest net income over its life.
The optimum roof angle is not an absolute value but is influenced by the prices of crop, fuel and construction materials.
The best design represents the compromise between these conflicting requirements which gives the highest financial return to the grower, and this can be established using optimisation techniques.
These have been applied to a multispan film plastic covered greenhouse.
The parameter varied in the optimisation process was the angle of inclination of a symmetric pitched roof.
The influence of this angle on the total natural light transmitted into the greenhouse over a season was calculated using a validated prediction model.
This was converted to tomato yield assuming yield is proportional to the light integral, and then to crop value.
The influence of roof angle on heat loss and the cost of heating was established using simulation models.
Finally the influence of roof angle on the material required to build a greenhouse to meet the wind loads required by the national greenhouse building code was determined.
The roof angle which gave the biggest margin between crop value and heating cost, i.e. the most profitable greenhouse to operate, was modified by the cost of materials to provide the roof angle for which the greenhouse gave the highest net income over its life.
The optimum roof angle is not an absolute value but is influenced by the prices of crop, fuel and construction materials.
Authors
B.J. Bailey, G.M. Richardson
Keywords
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