Effect of heating control strategies on greenhouse energy efficiency: experimental results and modeling
2006
Perdigones, A. | Garcia, J.L. | Pastor, M. | Benavente, R.M. | Luna, L. | Chaya, C. | Plaza, S de la
This study evaluated the energy efficiency of greenhouse heating systems in a Mediterranean climate by comparing the overall heat transfer coefficients obtained with heating strategies involving either heated floors or air heaters. The overall heat transfer coefficient is composed of the various heat transfers through the greenhouse, including losses by conduction, convection, infiltration, and radiation; it was calculated per unit of floor area. Four factors were found to influence this coefficient: wind speed, heat input, outside temperature, and heat capacity of the greenhouse. Greater heat input resulted in an increase in the heat transfer coefficient: 1 W m(-2) degrees C(-1) for every 50 W m(-2) of heat input. This was explained by the heat released by the greenhouse structures and soil, which reinforced the effect of heating with low values of heat input. The thermal behavior of the greenhouse was studied by modeling. Dynamic models decreased the absolute error in the calculation of inside temperatures by more than 1 degrees C with respect to a static model. The best dynamic model was used in simulations of control strategies. Step control of two or three groups of air heaters improved the thermal efficiency of the greenhouse (4% to 10% energy saving), and led to fewer temperature variations, compared to the use of all the heating power as one only group. With heated floor systems, a recommended strategy in mild climates is to turn off the heating at dawn.
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