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Control strategies to enhance the performance of greenhouse thermal screens


, : Control strategies to enhance the performance of greenhouse thermal screens. Journal of Agricultural Engineering Research 40(3): 187-198

A simulated comparison was made of five control strategies which could be used to operate greenhouse thermal screens. The energy required to produce an early tomato crop was calculated using a model of the heat loss from a greenhouse and hourly meteorological data. Reductions in yield, caused by reductions in light reaching the crop, were quantified using data from recent horticultural experiments. Using the early tomato regime temperatures, the most effective method of controlling both transparent and high performance aluminized thermal screens was to close the screen whenever the Value of the energy saved exceeded the value of the crop lost because of the reduction in light. Almost as good was operating the screen at a specified value of solar irradiance, but delaying and/or advancing, the opening and closing of the screen by a fixed time interval, was least satisfactory. The fourth method of control involved reducing the day heating setpoint temperature and increasing the night temperature, when the thermal screen was used, to achieve the same 24 h average temperature as occurred in an unscreened greenhouse. This gave greater monetary savings with no crop losses. The final control strategy was a combination of optimized control with reduced day and increased night temperatures. This was the most profitable giving net reductions in heating costs of 26 to 41% depending on the screen and the reduction in day temperature compared to 21 to 33% when the screens were used from sunset to sunrise.

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Accession: 001554917

DOI: 10.1016/0021-8634(88)90206-5

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