Night Flushing and Heavy Walls Could Cut Cooling Loads in Tropical Campus Buildings, Review Finds

University campuses in the tropics are among the most punishing environments for buildings. Lecture theatres packed with students, deep floor plans that trap heat in core zones, and constant internal gains from lighting and equipment combine to push cooling demand ever higher, straining local electrical grids and undermining decarbonization goals. A new systematic review published in Frontiers in Energy Research examines whether one of the oldest tricks in the passive design playbook, combining heavyweight construction with natural ventilation, can meaningfully reduce cooling loads in these high-occupancy institutional buildings, and it arrives at an answer that is promising but carefully qualified.

The review, conducted by Anthony B. Sholanke and David Agbetoye of Covenant University in Nigeria, followed a PRISMA-informed search, screening, and thematic synthesis process. The authors identified 71 records, removed duplicates and off-topic entries, and settled on 37 studies published between 2020 and 2026, drawn from Google Scholar, the Covenant University Repository, the Multidisciplinary Digital Publishing Institute, and ResearchGate. Because the included studies varied so widely in building type, climate, and method, the authors judged a quantitative meta-analysis statistically indefensible and instead organized the evidence around three recurring themes: natural ventilation as a thermal purge mechanism, the strategic placement of thermal mass, and the integration of both with phase change materials.

The core physical logic of the strategy is straightforward. Thermal mass, in the form of concrete slabs, masonry walls, or earth-based construction, absorbs excess heat during occupied daytime hours, delaying the rise of indoor air temperature. Then, overnight, natural ventilation flushes cool outside air across those surfaces, extracting the stored heat and recharging the mass for the next day’s cycle. The review describes this as a thermal purge: the building’s fabric acts as a heat sink by day and is reset by night, potentially lowering the starting temperature of the interior each morning and reducing the burden on any mechanical cooling system.

Several mechanisms drive the purge. Cross-ventilation exploits pressure differentials between windward and leeward facades, while the stack effect, buoyancy-driven flow through solar chimneys, atria, and high-level clerestory openings, sustains airflow even on windless days. Courtyards and atria can act as the building’s lungs, breaking up deep plans and, when landscaped with vegetation or water features, pre-cooling incoming air. The authors note that institutional buildings, with their elongated plans and repetitive spatial modules, may be particularly well suited to such strategies, provided internal partitions do not obstruct the flow.

Placement of the mass matters as much as its quantity. The review emphasizes that unshaded external mass walls exposed to intense tropical sun can become heat reservoirs that radiate warmth into interiors well into the evening, increasing rather than reducing cooling loads. The recommended pattern is therefore to concentrate mass in internal partitions, floor slabs, and structural cores, kept exposed to indoor air rather than buried behind gypsum board or insulation, while external envelopes rely on shading devices, overhangs, ventilated cavities, and double-skin facades to limit solar gain before it reaches the heavy layers.

One of the most striking technical findings comes from a single simulation study included in the review, which modeled internal thermal mass under idealized cyclical design-day conditions. That study found the relationship between mass thickness and peak cooling-load reduction is nonlinear: beyond an optimum of roughly 28 to 45 millimeters for the internal mass layer, additional mass became counterproductive, presumably because the material could not be fully discharged overnight. The same study reported that granite as an internal mass material was about three times more effective than concrete of comparable thickness, and that pairing a lightweight envelope with internal mass cut peak cooling load by a further 35.9 percent. The review’s authors are explicit that this figure is an illustrative, single-study benchmark, dependent on one material, one modeling method, and one set of climate assumptions, and should not be read as a universal design rule.

Phase change materials add a modern twist to the old heavy-wall approach. Rather than storing sensible heat through high density, PCMs absorb large amounts of latent heat as they melt, offering far higher energy storage density in thin layers that can be integrated into ceiling tiles, wallboards, or floor slabs. Materials with transition temperatures near the desired indoor comfort range, around 24 to 26 degrees Celsius, can moderate the temperature spikes that would otherwise trigger air conditioning. But the review stresses that PCMs only work if they fully re-solidify overnight, a regeneration cycle that depends entirely on effective night flushing directed across the PCM-enhanced surfaces. Without that purge, the material saturates and stops performing.

The review is notably candid about the limits and contradictions in the evidence. Only 10 of the 37 included studies, about 27 percent, are directly institutional or tropical in context; the remainder are mechanistically informative but require local validation before prescriptive application. The authors also flag genuine disagreement in the wider literature about whether thermal mass works at all in climates with a narrow diurnal temperature range, a condition common in humid-equatorial settings. A field study of vernacular earth buildings in Costa Rica recorded peak-temperature damping of roughly 5 degrees Celsius in heavyweight construction, moderating but not eliminating that concern. More troubling, a Scopus- and Web of Science-indexed review found that in terraced houses in Johor Bahru, Malaysia, night flushing with high thermal mass reduced peak indoor temperature by about 2.5 degrees Celsius but did not meaningfully improve daytime comfort at 65 to 77 percent relative humidity; ceiling fans were needed to recover an additional 4 degrees of Standard Effective Temperature reduction. In other words, night flushing reliably removes stored heat, but translating that into occupant-perceived comfort in hot-humid climates may require pairing with fan-assisted air movement.

Practical barriers also loom large. Night flushing requires vents or windows to remain open and unobstructed overnight in buildings that may be unattended, raising concerns about security, weather ingress, and insects, which points toward lockable, screened ventilation hardware rather than fully open windows. Effective operation also depends on consistent control, opening vents at the right time and closing them before daytime heat begins, something the review says is poorly served by the heuristic, rule-based scheduling still common in tropical buildings. The authors point to predictive, potentially AI-driven ventilation control as a promising alternative to static schedules.

For architects and campus administrators, the review’s recommendations are framed as evidence-informed starting points rather than validated specifications: concentrate thermal mass in internal partitions and cores, keep heavy elements exposed to indoor air, use mixed-mode ventilation with night flushing to reset thermal inertia before occupancy, and deploy solar chimneys or atria to sustain buoyancy-driven purges during still periods. The authors call for longitudinal field monitoring of tropical institutional buildings integrating PCMs with night ventilation, research into bio-based phase change materials from local resources, and future systematic reviews with registered protocols, full database coverage, and formal quality appraisal. The overall message is that thermal mass and natural ventilation function best as a synergistic, context-dependent pair, a strategy whose benefits are real but whose magnitude depends heavily on climate, humidity, building type, and the discipline of the nightly purge.

Subject of Research: Integration of thermal mass and natural ventilation for passive cooling in tropical institutional buildings

Article Title: Thermal mass and natural ventilation integration for passive cooling in tropical institutional buildings: a systematic literature review

Article References: Sholanke, A. B., & Agbetoye, D. (2026). Thermal mass and natural ventilation integration for passive cooling in tropical institutional buildings: a systematic literature review. Frontiers in Energy Research, 14, Article 1974826. https://doi.org/10.3389/fenrg.2026.1974826

Image Credits: AI Generated

DOI: 10.3389/fenrg.2026.1974826

Keywords: thermal mass, natural ventilation, passive cooling, tropical climate, institutional buildings, night flushing, phase change materials, systematic review, building energy efficiency, sustainable architecture, solar chimney, thermal comfort