ISHS Acta Horticulturae 148: III International Symposium on Energy in Protected Cultivation
HEAT AND MOISTURE TRANSFER IN HEATED GREENHOUSE SOILS AND FLOORS |
| Authors: | D.L. Elwell, W.L. Roller, T.H. Short |
| Abstract:
Extensive theoretical and experimental studies have been done in Ohio since 1972 on heating greenhouse soils and floors with warm water at temperatures from 25°C to 40°C. Comparing sand, peat-vermiculite, and silt-loam soil, sand had the greatest heat absorption rate of 75 W/m2 with 40°C water and 40 W/m2 with 25°C water. Heat lost to the ground was 30 to 40 percent of the heat absorption rate without insulation and 10 percent of the absorption rate with 25 mm of polyisocyanurate insulation. Warm pipes can dry the soil at the pipe surface and become insulated, but this was not a problem in irrigated soils with pipe temperatures less than or equal to 40°C. Lettuce growth was enhanced with a heated soil, especially during cold weather and low light periods. The concept in general has good application in greenhouses for using low temperature sources of heat such as power plant cooling water. A heated floor can provide from 25 percent to 100 percent of the winter greenhouse heating requirements, depending on the level of the night insulation. | |
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