Optimal control of building integrated rooftop greenhouse for energy efficiency

Climate change and rapid population growth have intensified concerns over food security, driving the need for sustainable food production solutions. Urban agriculture has emerged as a key strategy, offering local and resilient food sources within city environments.

However, the energy consumption associated with urban agriculture presents a significant challenge, as maintaining suitable environmental conditions for crop growth often requires substantial energy resources. A promising solution to this issue is the implementation of building-integrated rooftop greenhouses (BiRTGs). Installing greenhouses on unused rooftop spaces in existing buildings can enhance passive effects through improved insulation, while active effects can be achieved by facilitating energy exchange between the building and the greenhouse for wasted heat utilization.

On the other hand, maintaining optimal conditions within a rooftop greenhouse requires precise control of various environmental factors, by manipulating the system such as shading and thermal screens, natural ventilation, and HVAC systems. These controls are crucial not only for promoting the optimal growth of crops but also for influencing the thermal performance of the underlying building.

In this regard, the interaction between greenhouse operations and the building’s energy dynamics calls for a comprehensive approach to control and optimization. Therefore, this study investigated an optimal control strategy for BiRTGs to maximize the benefits of heat exchanges between the building and the greenhouse. The energy behavior of the building and rooftop greenhouse was modeled using TRNSYS, while the optimal control algorithm for the greenhouse was developed using Matlab.

By employing a co-simulation that integrates TRNSYS with Matlab, the optimal control solutions for shading and thermal screens, natural ventilation, fan, and HVAC systems were found to minimize the combined heating and cooling thermal load of both the building and greenhouse. As a result, by optimally operating a greenhouse system in response to the time-varying outdoor conditions, the thermal load of the building and greenhouse was reduced by up to 25%. During the winter season, the introduction of solar radiation into rooftop greenhouses for crop cultivation and the operation of heating systems during nighttime significantly impacted the thermal load savings of the building below.

In contrast, during the summer season, the appropriate use of shading screens yielded favorable results on the thermal load of the underlying building. This research contributes to the growing field of urban agriculture by providing a viable solution for enhancing the energy efficiency of BiRTGs, offering a pathway towards more sustainable urban environments.