Optimization of greenhouse substrate heating

This study contains an energetic efficiency assessment of two greenhouse substratum heating systems: buried pipes and vegetation heating. A special procedure was applied to find optimum values of the following endogenous (decision) variables: the depth and span of heating elements in the soil substratum, as well as the temperature of the medium fed into the system (for the buried pipe system) and the fed-in water temperature and span between heating elements (for the vegetation heating system). The heat losses were studied, temperature differences in the soil space observed, and the required heating efficiency of pipes defined. The basic analysis shows that for similar substrate temperature conditions, the vegetation heating system requires 3 K higher water temperature than does the buried pipe system, and heat loss is higher for the vegetation system. The uneven temperature distribution in the substratum and heat losses were defined for the optimum values of decision variables in both systems. (C) 2000 Silsoe Research Institute.