Produced in Association with


SERIES 22 / Module 05 Ventilation


Figure 1: A typical mechanical ventilation balanced supply and extract system air handling unit (AHU)


Mechanical Ventilation in Commercial Buildings


Paul Bennett of BSSEC V


entilation in commercial buildings is crucial for maintaining indoor air quality, ensuring occupancy comfort,


and supporting the overall efficiency of the HVAC system. Commercial building ventilation systems can consume as much as 20%1 of a building’s total energy consumption and therefore ventilation energy savings is becoming a major focus of energy saving campaigns, owing to its large potential to save energy. The requirement for ventilation


systems in commercial buildings varies considerably between sectors. For example, an office building requires ventilation to provide minimum fresh air rates for occupant health and comfort (e.g. 8 litres of fresh air per second per person) where a swimming pool requires ventilation for occupant health, comfort and building fabric protection in minimising humidity levels at a rate of 15 litres of fresh air per second per square metre of pool wet area2. There is no one size fits all ventilation system in buildings, and the energy engineer can expect to find a multiple of ventilation systems installed in practice. The role of ventilation in more recent


times has also become a very important health & safety consideration, especially when considering the COVID-19 pandemic and how ventilation systems can be used to reduce the risk of contamination to its occupants.


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Types of Ventilation The 3 basic types of ventilation systems in commercial buildings includes:


1. NATURAL VENTILATION This relies on natural forces like wind and buoyancy (stack effect) to move air through the building. Components include windows, vents, louvers, and skylights strategically placed to allow fresh air to enter and stale air to exit. Advantages: Energy-efficient and


cost-effective with no mechanical systems required, e.g. electrically driven fans. Disadvantages: Dependent on


outdoor weather conditions and may not provide consistent ventilation. Energy losses occur as heated air is lost and not recovered when released through windows and vents.


2. MECHANICAL VENTILATION Uses fans and ductwork to control and distribute air movement to provide supply, extract or balanced ventilation as: ● Supply Ventilation: Introduces fresh air into the building using supply fans, creating a positive pressure environment. ● Exhaust Ventilation: Removes stale air from the building using exhaust fans, typically in areas like toilets and kitchens. ● Balanced Ventilation: Combines both supply and exhaust systems to maintain a balance between incoming and outgoing air, ensuring controlled ventilation rates. Advantages: Fully controllable and


independent of outdoor conditions. Can include components such as air filters and heat recovery devices to improve air quality and energy efficiency. Disadvantages: The use of fans


consume higher levels of energy as compared with naturally ventilated solutions.


3. MIXED�MODE VENTILATION Combines natural and mechanical ventilation systems, allowing the building to switch between the two depending on conditions. Natural ventilation is used when outdoor conditions are favourable for energy efficient operation, and mechanical ventilation takes over when additional control is required.


VENTILATION STRATEGIES ADOPTED IN COVID�19


1. Increase fresh air intake: Maximise the amount of outdoor air introduced into the ventilation system to dilute indoor air pollutants and pathogens.


2. Use high-efficiency filters: Install HEPA (High Efficiency Particle Air) filters to capture smaller particles including viruses.


3. Improve air distribution: Ensure that air is evenly distributed throughout spaces to avoid stagnant areas where airborne particles can accumulate.


4. Consider UVC (Ultraviolet-C) lighting: Incorporate ultraviolet lamps to help disinfect air in ventilation systems.


5. Zoning: Create separate ventilation zones to minimise air mixing between different areas, reducing the risk of cross-contamination.


6. Educate occupants: Encourage practices such as keeping windows open when possible and maintaining physical distance in shared spaces.


Table 1: Ventilation strategies adopted as a result of the COVID-19 pandemic to reduce contamination


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