Improving Performance of Controlled-Environment Agriculture

Urban agriculture is attracting more and more interest because it offers a solution to several current societal issues: urban densification, increased food demand, promotion of the local economy, transportation reduction, etc. When carried out in a controlled environment, either in a greenhouse, a vertical farm, a shipping container or a Building Integrated Agriculture (BIA) space, this type of agriculture can yield up to a hundred times more than field crops, all year round. However, controlled-environment agriculture (CEA) requires high energy use to maintain optimal indoor conditions, such as temperature, humidity, carbon dioxide (CO₂) concentration and lighting.

Members of the Laboratory of Thermal and Building Science (LTBS) research team have set themselves the objective of improving the performance of these controlled-environment agriculture spaces to reduce their ecological footprint. Heating, ventilation, and air conditioning (HVAC) systems are at the heart of their energy consumption.

Complex HVAC Systems Sizing

HVAC systems must essentially maintain indoor conditions by providing sufficient air at conditions that allow the absorption of water and plant-produced energy. To date, there is little data available to assess the HVAC load of a BIA space. This load varies according to time of day (photosynthesis periods or dark periods, without light), crop growth, and their spatial configuration (vertical stacking).

Figure 1 Ventilation system in a greenhouse

These difficulties are compounded by the importance of maintaining constant air speed around the leaves to ensure CO₂ absorption and preventing the crops from growing in a non-homogeneous way within the BIA space.

Research Objectives

The growing interest in integrating agricultural spaces into buildings designed for other uses requires a deeper understanding of the design requirements and potential interactions of different spaces. To do this, the LTBS research team members will pursue three short-term objectives:

• Modelling crops to evaluate their influence on the indoor conditions of agricultural spaces.
• Developing sizing guidelines for HVAC systems.
• Evaluating, among other things, potential synergies between agricultural and other spaces in a building and their impact on HVAC demand.

Crop Modelling

A generalized model, taking into account energy and CO₂ exchanges between crops and their environment will be developed and validated by experimental measurements obtained with the controlled environment test bench (BE2C).

Figure 2: Controlled environment test bench

HVAC System Sizing

A numerical approach will be proposed to evaluate the effect of crops on indoor conditions and to propose air distribution strategies using computational fluid dynamics analysis to reduce the energy demand of the HVAC system. This analysis will take into account energy, moisture, and CO₂ exchange occurring at the crop leaf level. The simulations will be validated by experimental data measured inside the test bench.

Synergies Between Spaces with Different Purposes

Finally, the influence of crop density on indoor conditions of different building types will be determined. The possibility of recovering heat and CO₂ released by the cultivation of mushrooms to grow other crops will also be evaluated.

Enormous Potential

Controlled-environment agriculture offers great advantages for a country like Canada, where the climate is harsh and the cost of electricity can be fairly low. It can help meet the demand for locally grown, pesticide-free food and stimulate local economies.

Members of the LTBS research team are working to reduce the environmental footprint of this approach while maximizing yields.