ISHS Acta Horticulturae 534: International Conference and British-Israeli Workshop on Greenhouse Techniques towards the 3rd Millennium
CONSTRAINTS AND LIMITATIONS IN GREENHOUSE COOLING: CHALLENGES FOR THE NEXT DECADE |
| Author: | D.H. Willits |
| Keywords: | Cooling, temperature, greenhouse, models |
| Abstract:
This paper examines the limitations and constraints facing greenhouse cooling designers as described by models of varying complexity. Design trade-offs are discussed as they affect inside air and leaf temperatures. Predictions from one of the models (Willits et al., 1991) is compared to data from a two-year study in which the effects of two levels of air flow (0.041 m-3 m-2 s-1 and 0.087 m-3 m-2 s-1), evaporative pad cooling, mixing fans, conventional shading (50% black knitted cloth) and canopy density (LAI from 0.05 to 3.13) on leaf and air temperatures in a tomato crop were examined. The most effective treatments for reducing leaf temperatures were increased air flow, increased canopy density, evaporative cooling and shading. Mixing fans were the least effective. The most effective treatments for reducing air temperatures were increased canopy density, increased air flow and evaporative cooling. Shading decreased air temperature very little and mixing fans not at all. A strong interaction was found between air flow and evaporative cooling. Increased air flow was more effective in reducing leaf temperature when evaporative cooling was used than when it was not. The model predicted leaf temperatures well, but over-predicted air temperatures at the higher flow rate. Based on the information presented, challenges will be issued to reconsider the traditional recommendations for greenhouse cooling. | |
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