Comparative Analysis of Passive Cooling in Subtropical Housing Regions

Thesis Abstract

In subtropical housing regions, buildings often rely on mechanical cooling to achieve thermal comfort, yet energy-intensive cooling poses environmental and economic challenges in developing urban contexts. This study examines the comparative effectiveness of passive cooling strategies across residential typologies representative of distinct subtropical climates, to identify design configurations that reduce cooling loads while maintaining occupant comfort. The aim is to develop an evidence-based framework that guides integrated architectural design decisions for energy-efficient housing. Specific objectives include (1) inventorying passive cooling techniques—natural ventilation, thermal mass, shading, insulation, and landscape integration—across three representative subtropical cities; (2) evaluating the performance of these techniques under typical seasonal meteorological variations using a mixed-methods approach; (3) quantifying energy savings and indoor thermal comfort implications through calibrated simulations and field measurements; and (4) formulating design guidelines and a decision-support model for architects and policymakers. The methodology adopts a convergent parallel mixed-methods design. The population comprises 180 built residential units across three subtropical cities with diverse climatic signatures. A stratified random sample of 90 dwellings is selected, with 30 units per city, ensuring representation of detached houses, townhouses, and apartment typologies. Data collection instruments include (i) on-site thermal performance monitoring over 12 months using data loggers to capture ambient temperature, relative humidity, solar radiation, and operative comfort indices; (ii) occupant surveys and time-activity diaries to gauge perceived comfort and behavioral responses; (iii) architectural drawings and material specifications to document passive design features; and (iv) climate data from municipal meteorological stations for contextual analysis. Validity and reliability are ensured through pilot testing, instrument calibration, and inter-rater reliability checks for qualitative components. Data analysis employs regression-based energy modeling (EnergyPlus) to simulate hypothetical scenarios, complemented by ANOVA to compare performance across housing types and cities. Qualitative data from occupant interviews are analyzed via thematic analysis, supported by a conceptual framework grounded in the Theory of Planned Behavior and the Passive Cooling Theory, with triangulation to bolster interpretive validity. A holistic performance metric—comprising thermal comfort days, cooling degree hours reduced, and peak load offset—binds quantitative results with qualitative insights. A sensitivity analysis examines the robustness of results under variations in occupancy, micro-climate conditions, and building orientation. Expected findings indicate that well-integrated passive strategies—including cross-ventilation optimized by window placement, high-thermal-mmass walls combined with night flushing, strategic shading with vegetation, and envelope airtightness balanced with ventilation—yield measurable reductions in cooling loads (minimum 18–35%) and enhanced occupant comfort scores, with variability linked to microclimate and urban density. The study anticipates that shading effectiveness and ventilation efficacy are climate-sensitive, with sun-control and nocturnal cooling contributing most significantly in hot-humid versus hot-dry subtropical subregions. Cross-city comparisons are expected to reveal context-specific design configurations—such as verandah-based shading in high solar gain cities and elevated thermal mass strategies in moderate humidity contexts—while identifying universal principles for passive cooling integration. The study contributes to knowledge by empirically validating a cross-regional framework for passive cooling in subtropical housing, bridging architectural design, energy performance modeling, and occupant behavior. It advances a decision-support model that combines empirical performance data with a set of design guidelines and a scoring rubric to assist early-stage design decisions in architectural practice and urban policy. The main conclusion posits that a context-aware assemblage of passive cooling measures—prioritizing occupant-centered ventilation, shade-driven solar control, and appropriate thermal mass—can achieve substantial energy savings without compromising indoor air quality or comfort. Recommendations include adopting region-specific guidelines for passive cooling at the urban design stage, incorporating dynamic shading strategies in building envelopes, enhancing fabric energy performance through material selection and detailing, and promoting occupant education to optimize behavioral cooling opportunities. Further research should explore long-term climate resilience of passive cooling strategies under evolving subtropical climate scenarios and extend analyses to include retrofit feasibility in existing housing stock.