Abstract
In light of climate change and the rise of urbanisation, it is anticipated that by 2050, more than two-thirds of the world’s population will be living in cities. Despite concerns from certain experts about the biosphere’s ability to provide sufficient food for the growing population, decision-makers have renewed their focus on local production as a means to enhance urban food systems. Urban agriculture is expected to grow as a source of food, income, and employment.
A greenhouse offers optimal conditions for the intensive cultivation of a variety of crops. It also decreases air movement which is crucial for plant development and is commonly used to limit the transmission of diseases in plants. The aim of this research was to evaluate the indoor climate of a commercial rooftop greenhouse with an attempt to investigate and possibly improve its structure by using experimental testing and numerical modelling.
The literature review covers different greenhouse designs and parameters significantly affecting crop development. The experimental programme consists of dependent and independent variables and includes an experimental design. The experimental testing took place over a period of two days in hot outdoor climate conditions during the afternoon.
Two cases were experimentally investigated; in Case 1, the greenhouse doors were kept open, and in Case 2, the greenhouse doors were closed. The experimental method and procedure outline all the apparatus used as well as the necessary steps involved to successfully carry out the investigation of the indoor climate.
The experimental results include the graphical analysis of the data obtained during experimental testing for Case 1 and Case 2 outside and inside of the greenhouse. The temperatures for the experimental tests were consistently higher than the forecasted weather temperature for the particular day.
The numerical model for the greenhouse was generated in StarCCM+ software. The numerical results include plane sections that highlight the temperature and velocity profiles accordingly. The temperature and airflow velocity profiles for the numerical and experimental results displayed a similar trend. For Case 1, the temperature values ranged from 28°C to 36°C and the airflow velocities ranged from 0.01 m/s to 0.35 m/s. For Case 2, the temperature values ranged from 33°C to 40°C and the airflow velocities ranged from 0.01 m/s to 0.2 m/s.
Comparing the numerical results with the experimental results obtained, the experimental results were higher than the numerical results for maximum indoor temperatures with an average difference of 2.86% for Case 1 and 6.73% for Case 2. For maximum indoor airflow, the experimental results were higher than the numerical results with an average difference of 0.60% for Case 1 and 0.04% for Case 2.
Furthermore, both experimental and numerical results indicated that openable doors were insufficient when left open to remove all the warm airflow generated inside the greenhouse. When the doors were closed, it adds to the thermal discomfort altogether.