The climate-change approach to air distribution
The terminal products associated with displacement-ventilation systems can be compatible with the architectural design of buildings.
The impact of climate change offers new opportunities for displacement ventilation says KOE WIECKOWSKI.Manufacturers are facing tough challenges — not least the requirement to design products that do not exacerbate the effects of climate change. For some, the task is less arduous — particularly when they are already using tried and tested technology that has been eco-friendly long before climate change and energy efficiency became part of everyday vocabulary. Very effective
Displacement ventilation is one such technology. It is an under-rated and misunderstood, but a very effective method of producing and maintaining indoor air quality. Thanks to climate change, it has come of age and being looked at in a new light. A well planned system can cut energy costs and address environmental concerns by creating opportunities for using fresh-air to provide free cooling for a large proportion of the year — which is exactly what displacement ventilation offers. Originally developed for industrial buildings, displacement ventilation enjoys a steadily increasing percentage of market share for many air-conditioning applications throughout the world. Scandinavian countries have used displacement ventilation systems for over 30 years. The uptake in Europe has been slow but steady; our friends across the pond have yet to embrace it enthusiastically. Displacement ventilation relies on using the natural buoyancy (thermal convection) of warm air to deliver improved ventilation and comfort. Fresh, filtered air is introduced at low velocity and low levels at a temperature of 3 to 6 K below the desired room temperature. The cooler supply air displaces the warmer room air, creating a zone of cool fresh air at the occupied level. Heat generated by a person, lighting, machinery and/or equipment will generate a buoyant thermal plume, which will rise to ceiling level, where it will be extracted. Any contaminants produced by activities in the area will also be transported upwards and out of the space. Simple but clever. Applications
Displacement ventilation systems are ideal for a variety of premises and environments with high ventilation requirements. These are preferably where contaminants are warmer and/or lighter than the surrounding air, where the supply air is cooler than the ambient air and where the room heights are more than 3 m. As well as industrial environments, applications include classrooms, airports, atria, retail, food service areas, concert halls and lecture theatres; systems are also used in offices. In many cases the reduced air-volume requirements of displacement systems means that the costs compare very favourably with a mixing system. Displacement ventilation systems tend to be less efficient where ceiling heights are lower than 3 m, where disturbances to room air flows are strong and where contaminants are colder and denser than the ambient air. Much research has been carried out by BRE (Building Research Establishment) to determine if displacement ventilation is an effective method for producing low-cost energy-efficient cooling. Results show that displacement ventilation on its own using appropriate diffusers could deal with heat loads of around 60 to 80W/m2 in typical office environments without causing thermal discomfort outside the near zone area. This enables a reduction in energy by using fresh-air free cooling for much of the year. Very discreet
A key feature of displacement-ventilation systems is that the methods and locations of supplying and extracting air can be very discreet and aesthetically compatible with the architectural design of the building and any critical noise level requirements. Terminal products are designed and built to suit many environments; occupants are often completely unaware of their presence. The market offers many types of units that include wall, floor or, in special cases. ceiling mounted to high-volume panels designed for high airflow rates in industrial premises to fully adjustable panels designed for areas with low supply-air temperature. With building fabric and architectural considerations to address, manufacturers offer standard and customised solutions. Some are being incredibly creative and keeping pace with trends in building design. Circular, half-round and quarter-round panels are often seen and used in an innovative manner. Examples include decorative panels behind bars, doubling as a support beneath tables in airport lounges, as integrated wall panels in corridors. In many stepped applications for example in cinemas and lecture theatres, air is supplied through floor plenums between each tread, and lighting is used to make a feature of the design. At Birmingham International Airport, Repus air displacement units discharge clean, filtered, cool air into the open area on the ground floor via perforations in round units. Distribution is at low velocity, the cooler air supply spreading at low level throughout the area and gently displacing the warm, stale air as it does so. Noise levels are very low, and the units are unobtrusive. Benefits
There’s no doubting the many advantages of displacement systems.
• Economical to run.
• Operational efficiency.
• Can be concealed with architecturally designed fascia.
• Quiet operation.
• Greater compatibility with architectural/ building requirement.
• Improved air quality in occupied space.
• Opportunities for customised designs of terminal equipment to suit aesthetic requirements.
• Draught free. There is no doubt that displacement ventilation is an environmentally friendly solution for indoor-air-quality and comfort issues. But as Robin Aston, a consultant in displacement ventilation points out: ‘Air quality is a key strand in the climate-change debate. Manufacturers have an opportunity to shape ventilation requirements of future buildings, they need to be pro-active and clearly demonstrate the benefits if they are not to miss out.’ Wieckowski is general manager of Colman Moducel, Oldfields Business Park, Birrell Street, Fenton, Stoke-on-Trent, Staffs ST4 3ES.