SE—Structures and Environment: Analysis of Thermally Driven Ventilation in Tunnel Greenhouses using Small Scale Models

✍ Scribed by J.I. Montero; A. Antón; R. Kamaruddin; B.J. Bailey

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 421 KB
• Volume: 79
• Category: Article
• ISSN: 0021-8634
• DOI: 10.1006/jaer.2000.0680

✦ Synopsis

A laboratory method for studying natural ventilation by thermal e!ects was applied to a single-span tunnel greenhouse with di!erent opening arrangements. One-tenth scale models of the tunnel greenhouse were made of Perspex and immersed in a water tank. The buoyancy #ux due to solar heating of the #oor in real greenhouses was simulated in the laboratory by adding a salty solution through the #oor of the inverted scale model. Tests were video recorded and images digitized so that the temperature distribution in a cross-section could be obtained. Dimensional analysis and the scaling laws established relationships between variables in the model and at full scale.

First, the method was veri"ed by comparing laboratory results on temperature rise and air exchange rate with measurements from a 3 m wide tunnel greenhouse. The e!ect of insect-proof screens on the air exchange rate was also investigated in the laboratory and compared to full-scale results. After veri"cation, tests were conducted on a scale model of 6 m wide tunnel greenhouses. Four vent arrangements were considered: 16 and 33% of sidewall openings, 8% sidewall opening plus 10% roof opening and 16% sidewall opening plus 10% roof openings. For each con"guration, expressions of the temperature rise as a function of the sensible heat given to the greenhouse air are presented. Also, the air exchange rate of all con"gurations studied with three types of net over the openings is given. The results show the importance of combining roof and sidewall ventilation, especially when netting of reduced permeability covers the openings.