HOW CALCULATE GREENHOUSE HEAT LOSSES ACCORDING TO THE PLANT COMFORT AND THE TYPE OF GREENHOUSE HEAT EXCHANGER

Y. Cormary
Fueloil is the main source of energy used in heating greenhouses, but there are substantial savings from other energy sources such as geothermal energy, industrial water wastes, or the heat pump. However, the maximum water temperatures available from such sources are limited, and traditional pipe systems must be replaced by transmitters with larger surfaces such as plastic radiant ducts laid on the ground or the water air heater which possesses a large heat exchange coefficient due to blowing. The various sytems have very different annual rates of consumption for the same thermostat setting and a particular proportion of radiative or convective heating. We observe from experiences that for the same air temperature:
  • the air heater consumes one quarter less energy than pipes,
  • the duct consumes one quarter more.

The thermal gradients differ mostadly according to the heating system used (graph 1a). However, these variations occur mainly in the first and the last fifty centimeters of greenhouse height, the remaining two meters being quite homogeneous, and for vertically growing plants (tomatoes, cucumbers), the effect of the thermal gradient is not probably the main thermal phenomenon;

  • with the same water we observe little difference in air but generally the duct system produce more agricultural yields than classical pipes. The pipe system produce more than air heater system. For these reasons the air temperature is not a good index of plant comfort.

Therefore the differences in consumption measured between the various heating systems must therefore be explained, together with the differences in agricultural yield observed, in particular with tomatoes.

Cormary, Y. (1981). HOW CALCULATE GREENHOUSE HEAT LOSSES ACCORDING TO THE PLANT COMFORT AND THE TYPE OF GREENHOUSE HEAT EXCHANGER. Acta Hortic. 115, 637-648
DOI: 10.17660/ActaHortic.1981.115.71
https://doi.org/10.17660/ActaHortic.1981.115.71

Acta Horticulturae