Natural ventilation systems may require a more robust and intense integrated design process, consisting of several focused workshops analyzing several alternatives. Computer modeling may be necessary to test various design alternatives to determine which is most effective and efficient.
Avoid oversizing mechanical equipment. Oversized equipment will often increase operating costs and reduce operational efficiency. The correct equipment size will depend on a number of factors, including local climate, total building area, insulation levels, air filtration medium, number of windows and doors, and occupant comfort preferences.
Implement energy recovery systems, economizers, low-pressure-drop design, and efficient fans as appropriate to support ventilation rates meeting or exceeding the referenced ASHRAE standard without compromising energy performance.
Continuing to use an integrated design approach among the mechanical engineer, architects, owners and end users will facilitate design decisions that impact the mechanical design. For example, space planning decisions will impact the architectural programming of the space as well as access to natural ventilation.
At the first integrated design meeting during schematic design, develop a detailed natural ventilation strategy that includes goals for windows, building orientation, space planning and other sources of natural ventilation. In larger buildings, consider using an atrium to use the “stack effect”—allowing air to enter the building through exterior windows, cycle through the building into the atrium space and out through the top of atrium, using the natural buoyancy of warm air. Fans can be added, if necessary, to assist with stack-effect exhaust.
For mixed-mode and naturally ventilated spaces, it is up to the mechanical engineer to calculate the outdoor airflow rate and communicate with the architect on application of CIBSE guide for naturally ventilated spaces.
