Session: 12-04-01: Heat and Mass Transfer in the Natural and Built Environments

Paper Number: 165106

An Investigation of the Indoor Climate of a Commercial Rooftop Greenhouse 

The purpose of this paper is to evaluate the indoor climate of a commercial rooftop greenhouse. The greenhouse is built on the rooftop of a building in the city center of Johannesburg, and are used to address issues of food security in the city. There is a growing concern for safe and sustainable food sources which leads to the need for new agriculture methods. Many regions worldwide have a shortage of arable land; the land is scarce in urban and industrial areas, and space is a commodity. Under such conditions, alternative cropping systems can be introduced. Hydroponics is a horticultural method of cultivating plants using a mineral nutrient solution in a soilless medium. Soilless (Hydroponic) culture which was initially developed for studying plant material nutrition is thought to be one of the main elements of sustainable cropping systems under greenhouse conditions.  A greenhouse provides a suitable environment for the intensive production of various crops. The commercial rooftop greenhouse is an agricultural structure that is able to extend the production season by providing controlled indoor microclimatic conditions appropriate to the cultivation of various types of crops. This study was conducted both experimentally and numerically using Computational Fluid Dynamics (CFD). The experimental tests were conducted over a two-day summer period with the greenhouse doors in open and closed positions. The experimental results include the graphical analysis of the data obtained during experimental testing outside and inside the greenhouse. The temperatures for the experimental tests were consistently higher than the forecasted weather temperature for the day. The commercial rooftop greenhouse was then numerically analyzed, using the experimental values as boundary conditions. The overall temperature and velocity distribution were investigated at different greenhouse sections. The temperature and velocity distributions at the crop level were of particular interest. The numerical results were compared with the experimental results. The experimental results were higher than the numerical results. The numerical and experimental results’ temperature and airflow velocity profiles displayed a similar trend. Furthermore, it was found that the openable doors are insufficient when left open to remove all the warm airflow velocities generated inside the greenhouse. When the doors are closed, it adds to the thermal discomfort altogether. A solution was proposed wherein an additional openable door at the back of the greenhouse and rolling back certain ‘compartments’ on either side of the greenhouse were considered. The results showed that the greenhouse’s indoor climate is significantly impacted by the insertion of openable doors and side vents.

Presenting Author: Sunita Kruger University of Johannesburg

Presenting Author Biography: Dr. Sunita Kruger is a senior lecturer at the University of Johannesburg in the Postgraduate School of Engineering Management

Authors:

Abdul Razik Khatri University of Johannesurg
Sunita Kruger University of Johannesburg
Leon Pretorius University of Johannesburg