Case study University of Waterloo Academic Building

An Introba project that exemplifies the “simple approach” is the University of Waterloo Academic Building in Ontario, Canada, designed by Moriyama Teshima Architects. With a total floor area of 12,500m2, roughly one quarter of the building will have natural ventilation as part of a mixed-mode system. The project is targeting completion in 2025. What makes the strategy simple is twofold. First, there are few moving parts; air enters via windows at the lower levels, and air exhausts via the solar chimney which illuminates the central, feature stair.

Second, only a ‘light touch’ was required to incorporate the system. Air movement is achieved through pressure generated by the architectural features - windows, corridors, atrium, and solar chimney - which were required in any case to provide views, daylight and circulation.

In other words, the strategy eschews costlier features such as double-skin facades or dedicated chimneys which are often specified as part of natural ventilation systems, but which can add significant cost and embodied carbon.

A key component of making the system economic is the utilisation of both wind and stack effect to generate airflow. Spaces which utilise natural ventilation are connected to the central atria and chimney, which collects warm, used air. Acoustic attenuators were included to allow air to transfer from the back of classrooms through to the chimney. A fire shutter is also used to maintain separation requirements while allowing free movement of air. The system will be automated, responding dynamically to internal and external conditions to ensure appropriate airflow for comfort, humidity and air quality.

Per Figure 1, Introba and Eckersley O’Callaghan carried out a whole life carbon (WLC) analysis of three alternate natural ventilation options over 50 years. The analysis compares natural ventilation strategies with different levels of architectural intervention and corresponding operational carbon savings, compared to a sealed baseline scenario.

At the simplest end, manually operated windows serve perimeter spaces only. The cooling savings are calculated to be 20% of annual cooling in the spaces served. This option represents the roposed strategy for the case study building.

The second option includes a central chimney for exhaust, and an automation system controlling the natural ventilation. The cooling savings are estimated to be 50% of annual cooling.

The most complex option includes a double-skin facade at naturally ventilated spaces only. The double-skin increases the hours of the year when natural ventilation can be used, by allowing pre-heat of air in suitable conditions. For this option, cooling savings are estimated at 50% and heating savings are estimated at 20%.

The analysis demonstrates that the option with a central exhaust chimney and automated control provides the greatest payback in terms of kgCO2e. The key takeaway is that while greater interventions such as double skin facades can save more energy, the additional savings don’t outweigh the carbon premiums. By contrast, over time, a simple, automated natural ventilation system pays off.

The whole life carbon savings of natural ventilatio has the potential to be far greater when it is used to extend the life or reduce the size of costly mechanical systems. This whole life carbon assessment approach also does not consider the many other benefits of natural ventilation such as increased occupant productivity.

Assumptions used in Natural Ventilation

Whole Life Carbon Calculation:

Cooling COP = 2.0, heating COP = 3.0

Grid carbon intensity based on 2023 = 0.09 kgCO2/ kWh

Glazing and curtain wall replacement period = 25 years

Natural ventilation hardware replacement = 12.5 years

Mechanical systems carbon excluded, conservatively

Life cycle stages included: A1-A5, B2-B7, C1-C4 and a third of D