Volume 17, Number 4, December 2012
Research by NRC Construction has shown that displacement ventilation systems can potentially work well in the heating season when the supply air temperature is lower than room temperature (set point) coupled with controlled supplemental perimeter heating systems to offset effects of perimeter heat losses (through the skin of the building).
A displacement ventilation (DV) system introduces air at low velocities through outlets, usually located at or near the floor. The system utilizes buoyancy (generated by heat sources such as people and equipment) in a room to move contaminants and heat from the occupied zone into a higher stratified region, where they can be exhausted. As a result, the air quality in the occupied zone is generally superior to that achieved with mixing ventilation.
The NRC research team studied the heating season performance of displacement ventilation in several schools and in laboratory tests at their Indoor Environment Research Facility. Volunteers participating in the latter were satisfied with the thermal conditions supplied by DV. However, in the majority of the school studies, it was clear that further efficiency gains could be made with these systems. The most common problem was that the outdoor air flow rates were based on mixing ventilation, without taking into account the improved efficiency of displacement ventilation.
The Canadian context
DV is considered a suitable system for cooling-dominated climates but is seeing increased attention in Canada where cooling is often required year round in core areas of buildings. Even though stratified ventilation systems (UFAD and DV) are installed in North American buildings (presently less than 5% of commercial buildings), a better understanding of their performance is needed, especially in the Canadian context.
The rate of installation of these types of ventilation system is rapidly increasing, so good design is important to achieving energy savings and good performance. A key issue for the use of DV in Canada is the interaction of the core and perimeter conditioning systems, in particular integrating radiant heating and cooling systems.
Participants in a recent NRC-sponsored workshop on DV confirmed the need for research into overall system integration and for improved guidelines and standards. NRC researchers, in reporting the results of their findings, confirmed the experience of many of the participants, all of whom had experience with these systems.
The consensus among industry representatives and researchers was that examining the interaction of displacement ventilation and radiant heating/cooling systems was the next step in efforts to enhance efficiency and performance. Participants highlighted the need for detailed methodical research of the type offered by NRC, as they do not have the means to do this on their own.
NRC is currently seeking partners for the next stage of research, so that new DV designs can be implemented with significantly improved performance. This will assist industry to reach consensus regarding the design process and operational requirements of DV.
For more information
Contact Iain Macdonald at firstname.lastname@example.org 613-993-9676.