The Heating Load of Greenhouses

(1) Convective heat transfer coefficients at the inside cover surface of a greenhouse as influenced by heating pipe positions

Abstract

The convective heat transfer coefficient at the greenhouse inside surface has been one of the unknown variables for heating designs and its relevant problems are discussed in the present paper in relation to the form of heating pipe placement.
Several forms of pipe placement were examined using a small greenhouse model and each produced a considerably different pattern of the inside air temperature distribution. Largely due to these different temperature patterns, the heat transfer coefficient which determines the convective heat flux from a growing area to the inside cover surface varied with each form of pipe placement. Both low pipe placement and piled side pipe placement revealed a uniform temperature profile in the growing area, but the coefficient was smaller in the low pipes. This was due to the fact that the temperature near the cover surface was higher in the piled side pipes. Full overhead pipe placement resulted in pronounced thermal stratification, air temperature above the pipes being much higher than that in the growing area. This caused exceptionally large values of the coefficient. Both the thermal stratification and the large coefficient were reduced to a certain degree when the combination of overhead and low, side pipes was applied.