Case study: Hospital uses displacement ventilation
A Canadian hospital addition provided efficient HVAC and reduced airborne infections
The Nanaimo Regional General Hospital in Nanaimo, B.C., emergency department and psychiatric emergency services addition included the addition of new emergency and psychiatric emergency services departments and a six-bed psychiatric intensive care unit. The U.S. Green Building Council LEED Gold project was intended to expand and improve service and enhance patient safety for the city and surrounding communities of Nanaimo with a total building area of 35,000 square feet.
The emergency department includes trauma, urgent care, triage, admitting, waiting, and nonurgent care; the psychiatric component includes secure holding, exam and observation rooms. The construction took place adjacent to the operating hospital and the new building was connected to the existing at two levels. Stantec provided multiple services including mechanical design of heating, ventilation and air conditioning, plumbing and fire protection systems.
Using evidence-based design, several mechanical systems were used:
- Displacement ventilation.
- Radiant panels.
- Earth energy exchange system for tempering fresh air.
- Active heat pump heat recovery system that recovers energy from the exhaust air.
- 24/7 cooling load heat recovery.
As one of the first projects in Canada to implement displacement ventilation in the acute care setting, lots of analysis and modeling went into making sure that everything was going to work as intended. Through computational fluid dynamics modeling of the patient space, it was shown that providing cool outside air at a low level and then allowing that to air to pool and then rise via natural buoyancy would result in reduced effective cooling loads within the space. It also improved infection control through the use of directional airflow and lowered initial capital and ongoing operational costs.
The building energy performance index is 524 kilowatt-hour/square meter/year. When compared to a baseline code-compliant building, the project provides an annual gas savings of 939 gigajoules, an annual electricity savings of 1.07 million kilowatt-hours and an annual electrical demand savings of 39 kilowatts for an overall energy cost savings of 47%. The electrical savings alone approximately equal to the amount of electricity used to power 100 homes annually.
On an infection control front, the new emergency department showed an overall decline of 68% in health care associated infections on a three-month rolling average.