The impact of passive ventilation strategies on thermal comfort in large church buildings in hot-humid climate of Abuja, Nigeria

In Nigeria's hot and humid climate, large naturally ventilated church buildings often fail to provide thermal comfort during densely attended services. This ongoing discomfort arises from a key design paradox: massive internal volumes and high heat loads are mismatched with inadequate and ineffective passive ventilation strategies. Compounded by unreliable electricity and the high cost of mechanical cooling, this creates a widespread challenge to occupant well-being and energy resilience. This study therefore investigates practical, low-energy passive retrofit strategies to convert these high-occupancy spaces into thermally comfortable environments without over dependence on mechanical systems. A pragmatic mixed-methods approach was adopted to develop and implement a replicable retrofit evaluation framework. Following a pilot study, four large churches in Abuja were assessed during peak services across different seasons. Thermal comfort surveys collected over 1,300 subjective responses, while simultaneous environmental measurements at heights relevant to occupants (0.6–1.5m) recorded air temperature, mean radiant temperature, relative humidity and air velocity. Results revealed widespread thermal dissatisfaction and a strong preference for increased air movement. Field measurements confirmed operative temperatures often exceeding 32°C, with patterns indicative of weak cross-ventilation and buoyancy-driven stratification. To evaluate retrofit options, a representative building was modelled in DesignBuilder/EnergyPlus. The baseline model validation against in situ measurements achieved hourly CVRMSE of 4.75 to 11.20% and NMBE of -0.09 to -9.33% (combined CVRMSE 6.20%, NMBE -5.96%), satisfying ASHRAE Guideline 14 hourly calibration thresholds. The validated model was then used within the developed framework to explore passive retrofit strategies, including enhanced opening placement, high-level heat relief and external shading. Scenario assessments explicitly considered thermal comfort, gender, behavioural adaptations and energy consumption. A steadystate CFD layer, having achieved solver convergence and a mass balance check (<1%), provided highresolution airflow analysis to diagnose stratification and validate ventilation mechanisms. The study therefore provides and demonstrates a robust, framework that links occupant perception, field measurements and validated simulation for high-occupancy buildings in hot-humid climates. Findings show that passive interventions aimed at improving airflow effectiveness and stratification can significantly reduce occupied overheating hours by over 60% and improve perceived comfort, offering a credible low-energy solution for large assembly spaces where mechanical cooling is unsustainable.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

De Montfort University

Year dc:date.issued

2025

Author dc:creator

• Lar, Ponzing Emmanuel

Licence

• https://dora.dmu.ac.uk/bitstreams/bae9a841-a2f7-4b7e-bcfb-19d7defc1b14/download