A diagram of the Stantec’s design for using a plenum with filter modules to purify the outdoor air for the Surgical Day Care Center’s three existing air handlers. Instead of retrofitting three large air handlers with their own respective filter solutions, the engineer, Desmond Pattrick of Stantec Consulting, designed a mixing box setup (the large plenum on top) with one filter solution. All three existing air handlers draw outside air from this mixing box. (Photos courtesy of StrionAir Inc., Louisville, Colo.)
VANCOUVER, British Columbia - It can be difficult enough for a hospital to work around building construction in the facility; dealing with external construction too can make it much more complicated. Add unexpected problems and the process needs to be thought out very carefully indeed.

Vancouver General Hospital (VGH) anticipated elevated mold counts from upcoming demolition projects. The primary area of concern was the surgical center's outdoor air supply.

"We identified the need to improve existing filtration to ensure air quality was maintained inside the SDCC building independent of outside air conditions," said Con Buzunis, executive director of facility planning at the 955-bed VGH.

As often happens, however, when the professionals started looking to solve one set of issues (protection from the upcoming demolition), they found existing, unexpected problems with the mechanical system.

According to project manager Desmond Pattrick of Stantec Consulting Ltd., Vancouver, the VGH Surgical Day Care Centre (SDCC), "We were challenged with outside contaminants that would be released on three sides of this existing building due to construction and deconstruction. This raised tremendous issues for IAQ itself: Dust particles, spores, mold spores, etc., all of these have to be controlled."

Correcting and controlling these circumstances required work on two fronts - making sure the building was working at positive pressure to keep pushing air out, and using well-planned filtration systems to ensure intake air was as clean as possible. When air balancing contractor K.D. Engineering, Vancouver, tested the building, it found the building was actually at negative pressure, sucking in air.

"Over the years, some exhaust systems had been added and nobody had noticed that the building had become negative," said Pattrick. "When we investigated the systems, we measured the total volume of air going into the building and the amount being exhausted and measured air pressure." Among other system corrections, Stantec added a Skyline 4,000-cfm makeup air handler to return the building to its original positive pressure.

Then they could move on to the filtration challenge.

Rooftop plenum built by Advanced Sheet Metal, Vancouver, and designed by Stantec Consulting, Vancouver, for the project. It houses a new filtration system.

Thinking Through The New Filtration

Pattrick said costs and budgets are major considerations when a company is working with a hospital. It affected some decisions regarding the filtration upgrade; the SDCC is still operational but is slated for demolition itself in a few years.

With a heavy particle load anticipated from the surrounding area's construction and deconstruction, it was apparent that the 95 percent efficient filter media in the building's three original air handlers would not meet the health care facility outdoor air standard published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). However, HEPA filters would not be cost-effective for the building. Their use would increase airflow resistance up to 300 percent, requiring upgraded supply air fans and motors - not cost effective for a building that won't be around much longer.

"HEPA filters are very effective in filtering out particulates," commented Pattrick.

"However, the bacteria can stay alive in the system, producing gaseous toxins that can also cause problems. We would also have to create another centralized pre-air handler with 95 percent filters, carbon-charcoal filters, and then the HEPA filters. That's a dramatically expensive solution for a system that is only needed for a few years."

Ultraviolet germicidal irradiation (UVGI) effectiveness is not easily measurable, he pointed out; "therefore you are not able to determine the filtration efficiency of the airstream." It was important to be able to quantify results based on regular measurement and monitoring.

Stantec decided upon a method that uses mechanical filtration to capture particulates from 0.01 to 2 microns in size, then kills bacteria passing through the supply air side with a combination of electrostatics and ionization. Pattrick verified manufacturer StrionAir's claims by reviewing independent lab test results before presenting it to VGH officials.

"An independent lab test is the selling point for me, because typically I don't accept manufacturer's internal test claims," he said.

Instead of retrofitting all three air handlers with the filtration system, Stantec designed a universal galvanized sheet metal plenum to serve the three existing air handlers. An 18-unit filter bank purifies air drawn through louvers on two sides of the plenum. The four supply ducts come out of the plenum's remaining two walls to deliver supply air to the three air handlers and the added makeup air unit.

Advanced Sheet Metal, Vancouver, fabricated and installed the plenum, ducts, and connections in just three weeks.

Inside the 10- by 10- by 13-foot plenum Stantec Consulting designed for Vancouver General Hospital’s Surgical Day Car Centre’s outdoor air intake retrofit, an 18-unit StrionAir filter bank filters and kills mold and other organic particles via a combination of electrostatics, ionization, and mechanical filtration.

Hospital System's Health

When a doctor takes on a new patient, he or she likes to get baseline measurements of the patient's health so that positive or negative changes can be tracked. This is the way Stantec's several branches prefer to work with its hospital/institutional clients.

"We employed an outside air quality measuring agent for this baseline," said Pattrick. "Theodor Sterling Associates (Vancouver) took several samples. Then we started ongoing monitoring. We chose to start monitoring every two weeks to construct a historical database of the type of air we had in this building before construction started in the building.

"It gives you a clear picture of how efficient and effective the filtration system is," he continued, measuring levels of CO, CO2, respirable suspended particles (RSPs, a measure of airborne particulate capable of reaching the lungs when inhaled) volatile organic compounds (VOCs), etc.

"We didn't know if we had a healthy ‘patient' and it turned out that we did. The final stage was to implement the filtration system to prevent infiltration due to construction and deconstruction."

Theodor Sterling Associates' testing revealed an existing RSP reading of 17 micrograms per cubic meter (µg/cu m) was reduced to 2 µg/cu m after passing through the filtration system.

Pattrick also was able to avoid the necessity of creating an interface between the filtration system and the SDCC's pneumatic building controls. The filtration system's electronics have been connected to a nearby VGH building's DDC system manufactured by Delta Controls, Surrey, B.C.; power outages will activate an alarm through that system. Controls contractor ESC Automation, Vancouver, installed and interfaced the two systems.

Although the new filtration system is a necessity for the VGH building, short- and long-term costs had to be considered carefully. Working together, the HVAC professionals on this project came up with a real working solution.

Publication date: 11/07/2005