Modeling Heat Transfer in Substrates Heated by Electric Cable Depending on Heating Cable Spacing
2007
Fernández, M.D. | Rodríguez, M.R. | Díaz, F.
Substrate heating in greenhouses shows important benefits for crop development. Yet, the high energy costs of these systems demand the application of energy-saving strategies, which requires an appropriate dimensioning of the system that allows for prediction of substrate temperature distribution and energy performance. In this study, we analyze the effect of heating cable spacing on these two factors. To perform the analysis, we simulated the operation of an electric cable heating system during one day. The heating cable was buried in a sand substrate at 225 mm depth and at spacings of 100, 150, 200, 250, 300, and 350 mm. The simulation was carried out by using a model developed with a general-purpose finite element code that enabled the study of the thermal behavior of different geometries in a two-dimensional space and in a transient state. The results of the model revealed a rather homogeneous substrate temperature distribution for heating cable spacings of up to 250 mm. In addition, the percentage of the heat flow supplied that reached the root zone was similar for all the configurations studied, with values of 66% to 67%, which suggests that the use of the heat supplied was very similar in all configurations. Moreover, energy consumption decreased with the increase in spacing between cables. However, the temperatures required under the boundary conditions applied in the analysis were not achieved for spacings larger than 300 mm.
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