Calculation of the amount of energy released by heating pipes in a greenhouse and its allocation between convection and radiation

The energy output from a heating system in a greenhouse is mostly known only within broad limits and for long periods of time. The values for heat transfer coefficients calculated for a single pipe in laboratory conditions cannot easily be applied to conditions in the greenhouse where heating pipes are usually grouped within the canopy. The method described allows the heat transfer coefficient of a given pipe system to be estimated using simple temperature data, measured when the system is cooling. The parameters of the theoretical cooling function, i.e. the total heat transfer coefficient and the apparent thermal conductivity of the pipe system, can thus be derived by bestfitting. The small difference between the latter parameter and the thermal conductivity of water is discussed. It is further shown that, when the effect of radiation is eliminated from the total heat transfer coefficient, the Nusselt number can be calculated for the system. The resulting relation is then applied to estimate the system's energy output and temperature when cooling. .'-•" H H » A G ^ S I G N : W-V2.0-O3 EX. NO* MLVÏ «Ja^SoS» • « « % i m J » / 3 '::[ S EX. *