Buildings Guide

Mechanical Ventilation

Key Message

Studies report 60% thermal energy savings in the cooling demand related to ventilation loss by replacing natural ventilation with mechanical ventilation with self-adjustment by special extracts (ATEE 2006). In addition, adding heat recovery devices to mechanical ventilation systems can further increase these savings (ventilation component of heating and cooling energy) to 90% though at a higher capital cost but with recurring energy cost savings on the premium. Further, through the use of sensors-based variable air volume systems usually 30 to 40% of electricity for mechanical ventilation (especially, energy consumption of fans) can be saved compared to traditional constant air volume systems. All of these figures relate to buildings operated in closed mode, e.g. with cold or hot outside temperatures. In mild weather conditions or appropriate warm and arid climates, however, natural ventilation may use less energy than mechanical ventilation.


Ventilation in buildings will ensure optimized exchange of fresh air and thereby contribute to comfort and hygiene of occupants. Controlled mechanical ventilation found increased application in modern centrally air-conditioned buildings for its merits over natural ventilation. For example, mechanical ventilation with heat recovery mechanism ensures thermal energy savings during peak heating and cooling seasons (ATEE 2006). Ventilation is the process of letting in fresh air into a building while removing accumulated stale air within. Mechanical ventilation in buildings is done by three popular strategies. They are supply, exhaust and balanced ventilation. Exhaust and supply ventilation systems work on the principle of pressurizing or de pressurizing the space using a fan to aid the process. A balanced system is a combination of both supply and exhaust systems and offers to include more energy saving features such as heat recovery ventilation compared to exhaust and supply systems.


Different types of mechanical ventilation

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Mechanical ventilation of dwellings is common in some developed countries, while in most of the developing nations, natural ventilation is by far the most common method of ventilating residential buildings. Mechanical ventilation in commercial sector has become the norm in most of the modern centrally air conditioned buildings all over the world.  The increase in the market is attributed to increasing awareness about energy efficiency and simultaneously driven by energy code compliance requirements.

AHU by region value (%), 2012
BSRIA, 2012


In modern buildings mechanical ventilation is often integrated with cooling/heating systems. Central air conditioning refers to systems in which a central cooling/heating plant and a ventilation unit serves all conditioned areas of a single building or serves multiple buildings. The majority of commercial buildings certified under various green building and energy rating systems all over the world uses some form of mechanical ventilation systems. Central air conditioning and ventilation is divided into two broad categories.


Central air conditioning refers to systems, in which a central cooling/heating plant and a central ventilation unit serves all conditioned areas of a single building or serves multiple buildings. Read the document for more information on mechanical ventilation systems.

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Air water systems are in general more energy efficient compared to all air systems for comparable applications. Air water systems can effectively divide latent and sensible cooling load compared to All air systems. In air water systems cooling/heating is done through radiant systems/zone terminal units rather than forced air convection (central) and fresh air is circulated separately. This results in the reduction of required airflow, thus reducing the fan size and fan energy consumption leading to the down sizing of the ducts. In addition, cooling/heating energy is also reduced in Air water systems compared to All air systems due to the latter’s requirement of low supply temperature (of chilled water/refrigerant).


The following tables summarise various technological improvements leading to more efficient ventilation systems.


Sriraj Gokarakonda
Christopher Moore


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