Some Results of Actual Observations of Net Radiation and Soil Heat Transfer in Unheated Greenhouses

Abstract

The net radiation and soil heat transfer have been measured day and night in multi-span greenhouses.(1) The heat storage ratio: The ratio of the soil heat transfer to the net radiation in the daytime became larger under the shade and the high value of larger than 0.5 was obtained in the case with high soil moisture.(2) The radiant heat ratio: The ratio of the net radiation to the soil heat transfer in the night-time was about 0.8, therefore the ratio of heat convection was estimated so small as about 0.2.(3) The good proportional relation was found between the soil heat transfer and the soil temperature difference from the floor surface to the depth of 1cm. The thermal conductivity of 0.4-0.5kcal/m·hr·°C was obtained for the wet volcanic ash floor.(4) The convection heat transfer coefficient of floor surface in the night-time was calculated from the temperature difference between soil surface and room air, and the convective heat flux which was obtained from the difference between net radiation and soil heat transfer.The typical value of 1.7kcal/m2·hr·°C was obtained for the double-roofed multi-span greenhouse.(5) The design values of soil heat transfer should be modified a little larger than the present values, in reference to the temperature difference between inside and outside as shown in the figure.