SUSTAINABLE ENERGY Thermal analysis of north wall insulated greenhouse dryer at different bed conditions operating under natural convection mode Asim Ahmad | Om Prakash Department of Mechanical Engineering, Birla Institute of Technology, Ranchi, India Correspondence Asim Ahmad, Department of Mechanical Engineering, Birla Institute of Technology, Mesra, Ranchi 835215, India. Email: asimlife91@gmail.com Funding information Department of Mechanical Engineering, Birla Institute of Technology Abstract An experimental investigation has been carried out on the modified greenhouse dryer with insulated north wall operating under natural convection mode of heat transfer for different floor conditions, namely ground floor, concrete floor, gravel floor, and black painted gravel floor. The terms like coefficient of diffusivity, coefficient of performance, overall heat transfer coefficient, heat loss factor, and heat utilization factor has been calculated for dif- ferent floor conditions. The maximum difference between room temperature and ambient temperature was found to be 32.4  C at 13 O'clock for black painted gravel floor, followed by gravel floor, concrete floor, and ground floor which are 27, 14.1, and 11.5  C, respec- tively. It has been observed that the rise in the percentage of maximum room temperature in comparison to maximum ambient temperature for black painted gravel floor, gravel floor, concrete floor, and the ground floor was 50.31, 46.15, 30.1, and 26.6%, respectively at 13 O'clock. It has been found that the maximum temperature absorbed by black painted gravel bed. Hence, this type of floor condition is highly recommended for drying of low and medium moisture content type vegetables and fruits. The thermal parameters of the result obtain from the present setup was compared with the published literature, and it was found that all parameters show the similar trends; however, the present setup shows the superior performance compared to other research work. KEYWORDS greenhouse dryer, heat loss, natural convection, no-load, thermal performance 1 | INTRODUCTION Among all developing countries, India is the second largest country for producing vegetables and fruits. The yearly financial damage in post- harvest loss is 104.0 million USD because of inadequate handling, stor- age facilities and deprived protection techniques. 1 As per global estima- tion, the annual production of fruits and vegetables were found to be 392 and 486 million tons, respectively. About 30 to 40% of the entire crop production gets damaged mainly due to an inappropriate post- harvest methodology. The spoilage occurs by the attacks of microor- ganisms in high moisture content fruits and vegetables. 2,3 Drying is the most economical way to minimize post-harvest loss. In this process, the crop is being dried up to safer moisture limit which enhances the life of the crops. Drying may be done by the use of mechanical dryer but because the demand and consumption of energy in the developing country is very high; therefore, the use of non- renewable energy for drying is not a good idea. Solar energy is an abundant source of energy, and the heat comes from solar radiation can be used for drying purpose. 4 Solar drying is being classified as controlled drying and uncon- trolled drying. Solar drying is always considered as cheap and the best method of drying fruits and vegetables. The solar drying in an uncon- trolled process is also known as open sun drying which completely Received: 13 November 2018 Revised: 3 April 2019 Accepted: 29 April 2019 DOI: 10.1002/ep.13257 Environ Prog Sustainable Energy. 2019;e13257. wileyonlinelibrary.com/journal/ep © 2019 American Institute of Chemical Engineers 1 of 12 https://doi.org/10.1002/ep.13257