The Optimal Tuning, within Carbon Limits, of Thermal Mass in Naturally Ventilated Buildings

Abstract

What proportions should a thermally massive building have? How should the thermal mass be distributed? Should the "massing" change with the choice of material? This paper shows how to optimize the physical proportions of a building so that it synchronizes ambient heat exchanges in a natural feedback cycle. An internal mass is thermally coupled with buoyancy ventilation; the cycle is driven by the daily swing of outdoor temperature. Tripling up functions in this way—so that structural materials can reliably cool and power the ventilation for buildings—could help decarbonize the construction industry and provide an effective strategy for adapting to life-threatening heatwaves. Based on harmonic analysis, the method allows designers to thermally tune the form and mass of a building to meet chosen targets for temperature and ventilation in free-running mode. Once the optimal balance of exchange rates is known, design teams can proportionally vary the building height and ventilation openings against the surface area and thickness of an internal thermal mass. The possible permutations are infinite but parametrically constrained, allowing teams to fairly compare the functional and environmental credentials of different construction materials while they produce and evaluate preliminary options for organizing the exterior form and interior spaces of a building. An example study suggests that thin-shell structures of minimum weight, and even timber buildings, may be optimally tuned to produce ample ventilation and temperature attenuation.

Dynamic metrics of natural ventilation cooling effectiveness for interactive modeling

“…For example, two identical buildings in a hot and humid climate could lead to different thermal environments depending on heat capacities of building materials [6]. Thermal mass is known to have significant impact on natural ventilation's cooling potential [7][8][9], and alternating cooling modes, namely mixed-mode, is an effective way to utilize natural ventilation [10][11][12][13]. Window operation controlling the timing of the use of natural ventilation is another significant element in natural ventilation [14][15][16].…”