The ceiling designs are often dependent on factors such as the need to accommodate air distribution ducts and plenums, power and telecom wiring, fire safety equipment and security systems. The Ceilings and Interior Systems Construction Association (CISCA), USA, in its study, evaluated the performance benefits of suspended ceiling v/s open plenum (exposed) designs for office buildings.
The availability of many different suspended ceiling products, systems and designs today, such as floating ceilings, curved ceilings and transparent/translucent ceilings provides a great deal of flexibility for different applications. The study assesses construction cost, energy conservation and performance issues such as fire integrity, ease of maintenance, lighting and acoustic performance in case of exposed and suspended ceilings.
According to the CISCA study report, for a typical office, the initial construction cost of the suspended ceiling design can range from almost 15% to 22% more than for an open plenum design. However, the additional cost of the suspended ceiling, flexible ducts and cable tray is partially offset by the additional cost of a return fan, return air ductwork, and conduit for the open plenum design. Moreover, the open plenum ceilings require that HVAC, power and telecommunications systems have some architectural treatment or finish (e.g. metal or gypsum enclosure, painting, etc.) and be fire rated or enclosed in a fire rated assembly. In case of lighting fixtures, the cost of suspended ceiling recessed lights is relatively similar to the cost of pendant light fixtures in the open plenum design.
Suspended ceilings prevent dust and small leaks from reaching occupied spaces below and there are maintenance savings by not having to frequently clean pipes & raceways and paint or finish exposed equipment and systems. There is an estimated increase of 10% in the maintenance cost of cleaning and repainting an open plenum to maintain acceptable levels of indoor air quality (i.e. prevent dust buildup on surfaces of equipment, ductwork, etc.) and a clean appearance in general.
Suspended ceiling assemblies provide a flexible and accessible ceiling finish allowing ease of reconfiguring building systems to accommodate changing work and space requirements. In addition to operating cost savings, the reduced cost of modification including simple moves to and from existing workplaces, relocation of furniture and reconfiguration of offices and workstations can be significant. The open plenum ceilings require that HVAC, power and telecommunications systems have some architectural treatment or finish (e.g. metal or gypsum enclosure, painting, etc.), that they be fire rated or enclosed in a fire rated assembly. Also, fixed components such as rigid metal ductwork, conduit, hard wired power and telecommunications connections and fixed mounted light fixtures are more difficult and expensive to move and reconfigure.
The energy and maintenance savings justify the use of a suspended ceiling plenum, with extremely short simple paybacks of one to eight months. One reason is the use of a return air plenum with low static pressures and fan horsepower instead of a ducted air return with high static pressures and fan horsepower. A suspended ceiling with a return air plenum is also more effective in removing the heat generated by lighting, thereby reducing the air-conditioning load on the space.
The study noted that suspended ceilings typically have more uniform light reflectance than open plenums with layers of equipment. Open plenum designs with uneven and somewhat darker surfaces usually have a light reflectance around 50%, while suspended ceilings typically provide a reflectance of at least 70%. The higher reflectance of a ceiling reduces the total number of luminaires needed lowering the heat load on the cooling system as well.
A suspended ceiling can provide margin of fire safety as it offers a physical separation between the elements of the building services, such as the ductwork and piping, and the occupied room or space below. A fire resistant rated ceiling apart from separation also offers specified fire resistance period to the movement of smoke, fire gases, and spread of flame into the space above. In addition, building spaces where a suspended ceiling is not in place, the height of the space is greater which delays smoke detection and sprinkler system activation.
Exposed structure designs that use no ceiling and reveal the building service elements can cause acoustic problems due to reverberation. The use of suspended ceiling systems provides acoustical performance and sound absorption to control overall noise levels.
The environmental benefits of the suspended ceiling designs include reduced environmental emissions from lower energy use and better control of indoor air and lighting quality due to ease in reconfiguring of air distribution and lighting with the changing layout of workstations. The energy savings of 5.8-7.6% and acoustical separation & sound attenuation are also important indoor environmental issues for offices.