Thermal modeling of living walls: A review

Green (vegetative) building envelopes are widely recognized for their environmental benefits. They have a positive effect on the energy efficiency of buildings and improve the urban microclimate, e.g. by mitigating urban heat island effects and increasing living comfort in cities. Living walls are considered an emerging technology and thus lack widely implemented and established models of thermal response. Experimentally oriented studies of living walls currently prevail, while research on modeling is scarce. This study presents a detailed review of the modeling of heat and mass transfer, considering the individual mechanisms separately. The review demonstrates that existing models primarily adopt heat and mass transfer mechanisms from green roof models. However, the adjustments may be inadequate for dense urban environments due to the vertical layout of living walls. Most studies also assume the uniformity of properties, such as growing media moisture content throughout columns and rows of living wall modular elements, although these properties can vary and significantly affect the thermal response. It is also highlighted that the influence of an open-air gap on living wall thermal response (and modeling) might be underestimated. Identified modeling gaps serve as recommendations for further development of mathematical models. This includes expanding considered boundary conditions, adjustments of oversimplified assumptions, and emphasizing the need for further validation, that will stimulate the development of living wall technology towards a sustainable, energy efficient and reliable technology.