Beyond AC
Harnessing nature to build resilience
How natural ventilation helps future- proof buildings and control costs In a warming world, innovative businesses and urban planners are rediscovering the value of an old idea: Let nature do the cooling. Natural ventilation – the science of moving air through buildings to maintain thermal comfort without the use of air conditioning systems – is emerging as a cornerstone of intelligent climate resilience planning. Extreme heat is becoming the new normal, and it’s putting more strain on power grids. By incorporating natural ventilation into building design, organisations can reduce energy costs and carbon emissions, keep employees comfortable and protect against the costs of future climate extremes. It can also help businesses stay ahead of compliance demands as climate resilience and carbon emissions attract closer attention from regulators and governments. Builders relied on natural ventilation methods for most of human history, until the introduction of air conditioning in the early 20th century. Today’s versions use sophisticated, tech-enabled design and engineering techniques to harness thermal buoyancy (the tendency of hot air to rise) and wind effects to ventilate indoor spaces efficiently. Perhaps the most compelling argument for natural ventilation? It’s free to run, and at a time when temperatures are rising along with the costs of keeping cool with air conditioning. What’s more, the upfront investments in designing and building natural ventilation systems are often less than those for complex HVAC systems.
Integrating natural ventilation into projects not only saves money now, but also helps protect buildings and businesses against future challenges, such as climate change and rising energy costs. In GHD’s recent work on the Ontario Line subway station project in Toronto, for example, we modelled the building’s thermal comfort not only on current weather conditions but also on several global warming scenarios. This ensures the station will remain within temperature thresholds even under extreme heat, removing the need for costly retrofits in the future. As part of the design, several hundred square metres of automated louvers (angled slats), positioned in various locations, are programmed to open when the indoor temperature reaches a certain level. This allows hot air to escape through the top of the building. Permanent openings, such as escalator shafts, also help by drawing in cooler air indoors and allowing warmer air to exit through the louvers. In hot climates, louvers are typically designed to be resistant to heat and sand, and are often equipped with seals to prevent dust and debris from entering the building. Another key benefit of louvers is their seasonal flexibility: They can be closed in winter to retain heat within the building and opened in summer to enhance ventilation. Louvers can also provide acoustic insulation, which can be tailored to meet specific noise control requirements. Another building envelope cooling strategy is glazing, which was also deployed in the Ontario Line project. Glazing, a protective layer applied to a surface, plays a key role in limiting direct sunlight and, therefore, heat from entering a building. High-performance double or triple glazing with low-emissivity (Low-E) coatings and a low solar heat gain coefficient (SHGC) is commonly used to reduce solar radiation while maintaining sufficient daytime lighting. Glazing systems are often complemented by solar- reflective coatings and architectural elements, such as sunshades or brise-soleils, which help deflect solar rays and further reduce thermal loads. Sun breakers support thermal comfort by intercepting sunlight before it reaches building façades, while still allowing for natural airflow. Common materials include aluminium, perforated metal or treated wood, and are selected based on performance and aesthetics. The most effective natural ventilation projects are designed to leverage local climate and weather conditions. The 18-story San Francisco Federal Building, which opened in 2007, is a prime example. Instead of louvers, remote-controlled windows in optimal locations create cross ventilation by leveraging wind exposure. The building’s management system monitors temperature, wind speeds and carbon dioxide levels, and automatically opens windows during favourable conditions.
Ali Rezghi, Junior Energy & Computational Fluid Dynamics
Modeling Specialist
16 | GHD | Nexus Magazine
Nexus Magazine | GHD | 17
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