VENTILATION & AIR HANDLING ◀A decentralised ventilation system offers various installation options
▼Decentralised ventilation units are completely self-contained, thereby minimising planning and loss of space
Alternative approach to improve air quality Decentralised ventilation offers an efficient way to improve indoor conditions where traditional HVAC is impractical – so says Ian Thomas.
Ian Thomas
www.troxuk.co.uk
P
Product manager Trox UK
meaning that plug and play HVAC systems could actually be preferable to site-wide centralised systems in many projects.
oor air quality is known to reduce cognitive performance and attention levels, with CO₂ emissions
from room occupants being a strong contributory factor. Spaces containing higher concentrations of people, from offices to classrooms, theatres and gymnasiums, can be particularly vulnerable. Unfortunately, many of these spaces are difficult to ventilate efficiently and cost- effectively. Traditional ventilation systems involving AHUs (Air Handling Units) and VAV (Variable Air Volume) systems, are not always feasible or affordable, and even in sites where AHUs are installed, there can still be ‘problem spots’ that lead to complaints from room occupants. Ad hoc attempts to improve air
quality or comfort conditions, made by room occupants, such as opening windows or bringing in standalone fans, can destroy any attempt to manage energy usage. Furthermore, in today’s more airtight buildings, the air quality problems can be even more acute, due to the reduced levels of fresh air escaping into the building from outside. In heritage and listed buildings, traditional air conditioning systems may simply not be acceptable or allowable. Lastly, many buildings in use today are modular,
EIBI | MAY 2026
Decentralised ventilation 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 deliver fresh air, heating, cooling, and heat recovery directly to 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, they 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. When selecting decentralised
ventilation units for a building it is important to find products suitable for installation in a wide range of physical locations, to make best possible use of the available sources of fresh air. The TROX range, for example, includes units for 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.
Traditional ventilation systems involving AHUs… are not always feasible or affordable
The key benefi ts Improvements in air quality: Integrated measurement of air quality, within the decentralised ventilation unit, ensures that fresh air supply adapts automatically, in line with changing levels of occupancy and usage of the room throughout the day. An integrated air quality sensor in the TROX units, for example, calculate and adjusts to demand. Risk of infection is also reduced compared to dry air. The TROX units have integrated fine dust filters of at least ISO ePM1 60% (formerly F7) for fresh air, resulting in a definite reduction of fine dust, pollen and pathogens in the room air for better health and hygiene. The improved comfort levels and quiet operation of the units (with the help of patented sound attenuators) aids concentration, for higher performance of room occupants. Practical benefits: Decentralised
ventilation units can minimise planning and loss of space, whilst
ranges designed for installation in multiple locations within the space offer greater flexibility and design freedom. All 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, the TROX range, for example, can also be connected to the central building management system due to the integrated FSL Control III, for management and monitoring. These practical benefits also make the units suitable for small spaces requiring improvements in air quality, such as classrooms. Just two TROX units with a rated performance of 400 m³/h, for example, provide a standard classroom with the required fresh air in order to achieve and ensure an average CO₂ concentration of less than 1000 ppm.
Energy effi ciency Heat recovery is available all year round, enabling heating 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, in projects where it is simply not feasible or affordable to install an AHU, optimum air quality can still be achieved effectively. ■
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