An Analytical Approach for Sustainable Greenhouse Heating in Lebanon: A Focus on Air Source Heat Pumps

Abstract

In Lebanon, where economic challenges and Mediterranean climate dominate, protected cultivation methods, such as greenhouses, are widely used for sustainable agriculture. Tomatoes, with an annual production of around 250,000 tons in Lebanon, are the focus of this study. Tomato leaves require a temperature range of (18-25ºC) for optimal growth. The present study explores the potential of air-source heat pumps as a sustainable heating method. It includes a comprehensive literature review and discusses alternative heating methods. A dynamic energy model was developed after using statistical models to plot the temperature and solar radiation profiles for the worst-case scenario for heating. This energy model sizes the heat pump to maintain 18 ºC in a standard 332 m2 Quonset greenhouse with thermal polyethylene covering. The model’s validity was demonstrated by comparing its temperature profiles with a study conducted in West Bengal, India. The results indicate the adequate size for the studied case is 16 kW. Sensitivity analysis showed the required power for different temperature settings (12-18ºC) and the effect of wind speed by analyzing the heat transfer coefficient of the cover, which doubled the power when the heat transfer coefficient increased from 4 to 10 W/m2.K.