AIR HANDLING
Solving the problem of hot, stuff y rooms without an AHU
In this article Ian Thomas, Product Manager, Trox UK, reviews ways of cooling, heating and ventilating spaces where air handling units are not feasible or desirable.
"Decentralised ventilation units can minimise
planning and loss of space, whilst ranges designed for installation in multiple locations within the space off er greater fl exibility and design freedom."
T
he record temperatures experienced this May have brought problems of hot, stuff y rooms into sharp focus. In many buildings there are readily available
methods for creating cool, well-ventilated spaces with the use of air handling units (AHUs) and variable air volume (VAV) ventilation systems. But what about those buildings and spaces where an AHU-based system cannot be employed, is too expensive, or is simply not desirable? Very often it is the spaces at greatest risk of poor air quality and uncomfortable conditions that face the greatest obstacles. High-occupancy sites such as schools, care homes, offi ces and gyms may have the most urgent need for eff ective and energy-effi cient cooling, heating and ventilation. But very often, traditional air-conditioning systems, which might be found in modern offi ce blocks and high-rise buildings, are simply not an option. Even where air conditioning is installed, many buildings have specifi c zones in which inadequate cooling and poor air quality continue to cause complaints, and solutions cannot be achieved with the existing system. In reality, people improvise when rooms are stuff y by opening windows or doors and bringing in standalone fans. Inadequate heating in colder weather can see the arrival of ineffi cient space heaters. Each of these measures can have a dramatic eff ect on the energy costs and carbon impact for the space. And in buildings with existing (but insuffi cient) air conditioning or heating, these ad hoc attempts to improve air quality or comfort conditions in problem areas can destroy any attempt to manage energy usage. For building services engineers, estates managers and facilities managers, this can result in a complete loss of control over the carbon and fi nancial impacts of buildings for which they are responsible and held accountable. In today’s more airtight buildings,
the problems are likely to be worse rather than better in spaces that cannot be ventilated using traditional air conditioning, due to the reduced
levels of fresh air escaping into the building from outside. Furthermore, many buildings in use today are modular, and are best suited to plug-and-play HVAC systems
rather than site-wide centralised systems. Last but 30 July 2026 •
www.acr-news.com
not least, when upgrading air quality in heritage and listed buildings, the alterations to the fabric of the building that would be needed to accommodate traditional air conditioning systems may simply not be acceptable or allowable.
Decentralised ventilation: an overview In many of the ‘problem spaces’ discussed above, decentralised ventilation could be an extremely eff ective alternative to air quality issues, whilst also off ering free cooling in summer and the opportunity to reduce heating bills in winter. Importantly, this approach does not require the use of a central AHU, or connection to a building-wide ventilation system. The decentralised units, for example, deliver 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-effi ciency EC fans to move air energy effi ciently. Most importantly, the units have integrated cross-fl ow 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.
Product selection and benefi ts When selecting decentralised ventilation units for a building, it is important to fi nd 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 fi tted into the suspended ceiling. Figure 1 illustrates the various installation options. There are a number of benefi ts. Thermal management: Decentralised ventilation units make heat recovery available all year round, enabling heating from other sources to be reduced during the winter, and creating a cooler indoor environment in warmer weather. The technology enabling these improvements in the Trox models, for example, is the use of rotary heat exchangers. The
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