The Food and Agriculture Organization reported that urban agriculture has attracted more than half a billion people worldwide. This has a global contribution of 15% of food production [
1]. In developed cities, urban agriculture is being reformed to produce food on a commercial scale [
1]. One common constraint faced by urban farming is land scarcity. The urban farms should be highly productive with minimum dependency on artificial resources for the land-scarce urban environment [
2]. According to Worldometer [
3], Singapore’s population has increased from 1 million in 1950 to 5.8 million in 2020, and it may reach 6.9 million by the end of 2030. Singapore is the second most densely populated country in the world with limited land resources. Its high-rise buildings offer large surface areas of walls and roofs [
4]. More than 90% of the food supply relies on overseas imports [
5]. The scarcity of agricultural land, high costs, and disruption of supply chains due to conflict and pandemics have highlighted the need to develop a reliable and eco-resilient farming module [
2]. With the aid of advanced technology, farming indoors is now possible; substituting sunlight with artificial LED lighting assists crops in making food through photosynthesis. Optimal Heat Ventilation and Air Conditioning (HVAC) systems promote crop growth and reduce the demand for water supply in controlled growth environments [
6]. Indoor farming includes vertical farming, which allows crops to be vertically stacked in layers, but this has high variable costs with electrical bills for ventilation and lighting. Another type of indoor farming is rooftop farming on buildings with the advantage of using natural sunlight. Both methods of farming maximize the crop output within limited land space [
7,
8]. Utilization of the rooftops of Housing & Development Board (HDB) buildings to produce crops would be an added advantage for urban farming. However, current urban rooftop spaces are used for mechanical and electrical (M&E) amenities such as air-conditioning cooling units and water tanks. Competitive needs will require that the vertical structure constructed be modular and easy to plug in and use. Vertical farming on the building façade also offers additional advantages for the occupants. Especially in Singapore, which has a tropical climate throughout the year, the vertical farming of crops on the façade and rooftop would protect the building from excessive heat gain, which places higher demands on air-conditioning cooling. The setting up of urban farming on a rooftop will provide shade to the roof as well as provide a trans-evaporation effect as the crops grow, filtering out fine dust and thus improving air quality. Polycarbonate materials are used instead of traditional glass for the vertical farm as it helps to diffuse light more evenly than glass greenhouses. This helps plants thrive and even grow faster. Polycarbonate protects plants from excessive sunlight or radiation as it naturally offers UV protection.
In addition, by farming in a controlled environment, the crops are not affected by any bad weather conditions in the open area, and the harvest quality is controlled. It improves the environment by reducing the carbon footprint [
1] during the transportation of food, as well as reducing crop damage that often happens during the logistical process [
9]. It provides chemical-free food with no risk of pests and diseases [
1]. However, with all the benefits it could bring to the country, indoor farming has some prominent challenges. One of them is the price of locally produced crops remaining competitive [
10]. This is due to the high demand for artificial lighting to replicate sunlight for photosynthesis, and for the cooling and ventilation required for healthy plant growth. The airflow is of great importance for the proper growth of plants [
11,
12]. As mentioned in previous studies, the airflow velocity has to be within the range of 0.3–1 m/s [
13] to provide sufficient ventilation for the crops. As mechanical ventilation might be required, the utilization of photovoltaic panels to produce electricity will be crucial to reduce energy consumption and improve the farming module efficiency [
14,
15]. Co-generative photovoltaic thermal modules of different geometrical and physical designs will provide an additional source of energy and preserve the architectural aspects of the farming module [
16]. Based on the current state of the art, urban farming has great potential to reshape the future of agriculture. It has several advantages and could be a reliable source of food for cities. However, there are many challenges that need to be solved. Crop cultivation in urban farming requires a sufficient amount of light, airflow, and nutrients. The present work proposes a methodology that assesses the natural ventilation and natural lighting for a farming module in the early design stages. This methodology can be adopted to understand the anticipated future performance for a farming module before its physical construction. This work aims to study the airflow and the Photosynthetic Photon Flux Density (PPFD) inside an urban-metabolic farming module (UmFm). In our study, the UmFm will be erected on the step terrain of an unused plot of land in SIT@Dover to model the space constraint on the rooftops of the buildings. A good assessment of local airflow and the PPFD with consideration of the surrounding buildings is essential. Based on the stereographic sun path diagram for Singapore, we can infer that there are a total of three different key directions that the sun will travel: 70° overhead from the north during the summer solstice, 70° overhead from the south during the winter solstice, and mostly between 80 to 90° overhead on other days. CFD simulations are also performed for the four prevailing wind scenarios in Singapore. The effect of the opening angle for the façade’s panels is discussed. The impact of installing mesh netting (insect-proof screens) on the air velocity is introduced through simulations and experiments. The obtained air velocity is explained in the light of the optimal conditions for crop growth.