AIR CONDITIONING


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Decentralised ventilation: is it the best option for your project?


Ian Thomas, product manager, TROX UK discusses the benefits of decentralised ventilation for commercial buildings where there is a significant need for effective and energy efficient ventilation


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raditional air conditioning systems, incorporating air handling units (AHUs) and variable air volume ventilation (VAV),


can deliver the required levels of air quality in most applications. But what about those buildings and spaces where an AHU-based system cannot be employed, or is simply not feasible? Very often it is the spaces at greatest risk of poor air quality that face the greatest obstacles. Schools, care homes and gyms, for example, may have the most urgent need for effective and energy-efficient ventilation, as well as heating and cooling, but are not ideally suited (or able to afford) the traditional air-conditioning systems that might be found in modern office blocks and high-rise buildings. Even where air conditioning is installed, many buildings have specific areas in which poor air quality continues to cause complaints, and solutions cannot be achieved with the existing system. In many of the ‘problem spaces’ discussed above,


decentralised ventilation could be an effective alternative. This approach does not require the use of a central AHU, or connection to a building-wide ventilation system. Decentralised units work by delivering fresh air, heating, cooling, and heat recovery directly within the room - eliminating the need for long duct runs or central air handling plant. Unlike localised ventilation driven from a central point, decentralised ventilation units are completely self-contained. Fresh air is delivered into the space by the unit, from the perimeter or fascia of the building, or from the ceiling void. The units incorporate high-efficiency EC fans to move air energy efficiently. Most importantly the units have integrated cross-flow or rotary heat exchangers which prevent the heat from the room air being conducted outside without being used. Heat is recovered via the heat exchangers as the air passes through the units, providing free heating of the air in winter or free cooling in summer. As decentralised ventilation units require a fresh


air source, it is important to find products suitable for installation in a wide range of physical locations. The TROX range, for example, includes units for


Left: Ian Thomas, product manager, TROX UK


vertical or horizontal installation next to windows, for placement under window sills of external walls, or for installation directly under the ceiling or actually fitted into the suspended ceiling. See Figure 1.


Benefits of decentralised ventilation


So what benefits might decentralised ventilation have for your project? Firstly, air quality levels are measured by the unit


itself, enabling fresh air supply to adapt automatically to demands, as levels of occupancy, and types of usage of the room, change during the day. An integrated air quality sensor in the TROX units, for example, calculates and adjusts to demand. Filters (of at least ISO ePM1 60%, formerly F7, in the case of TROX units) reduce fine dust, pollen and pathogens in the room air for better health and hygiene. Secondly, decentralised ventilation units have


practical advantages. For example, they can minimise planning and loss of space. In addition, all


12 May 2026


components for filtration, heat recovery, thermal treatment of the air and control are already integrated in the units. Even though the units are perfectly capable of operating independently, they can also be connected to the central building management system. Lastly, there could also be valuable energy efficiency advantages of decentralised ventilation. Heat recovery is available all year round, enabling heating from other sources to be reduced during the winter, and creating a cooler indoor environment in warmer weather. Best-in-class units are those incorporating rotary heat exchangers which operate regeneratively. The thermal energy is temporarily stored in the storage mass, a solid, slowly rotating wheel, and then, as the wheel comes into contact with the other airflow, is transferred to this other airflow. This process results in much higher efficiency levels. To conclude, there are many buildings and spaces


for which traditional systems involving AHUs are simply not feasible or desirable, but that does not mean that occupants have to suffer poor levels of air quality.


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