A typical single-stage housing has multiple sections and components: The first is a bioseal damper and decon port; the second is the aerosol injection and test section to ensure even distribution of the dioctylphthalate (DOP) or poly-alpha-olefin (PAO); the third is the HEPA filter; the fourth is the the scan section, which allows in-place testing of the first HEPA filter; followed by the second injection port, decon port and final bioseal damper. Each unit measures 5 to 6 feet in length, is 30 inches square, and costs about $18,000.

Two years ago a CamContain housing model was developed that is lighter and cheaper to ship, and costs $15,500. It has an automated scan section, which allows operators to automatically scan the face of the filter using an external cart, and then maintain the scan records electronically.

Certek developed a model called SAFEMOD, an aluminum housing that is somewhat less expensive to build, costs $10,700, and is designed to be completely disposable: The module between the bioseal dampers is removed intact, incinerated, and replaced. As an alternative the HEPA filter could be removed from the housing and replaced, although this is a more involved process than a typical HEPA filter arrangement.

A third option currently in R&D is a room-side replaceable HEPA filter, much like a cleanroom filter but made to test in the direction of airflow. That model costs approximately $7,500.

Another component to consider is the type of damper on the ductwork, which could vary depending on the life cycle and use of the filter unit.

The flat blade damper, for example, is just that: a flat blade that turns on an axle, closes, and seals with a gasket. It can last through 2,000 cycles, has an operating torque of 75 foot-pounds, and costs about $2,000.

The dish style pulls out and twists, and does the same thing when it goes back, so it doesn’t wear the gasket material, giving it a 10,000-cycle life. It has an operating torque of 45 foot-pounds, and costs about $2,400.

The linear damper, which currently is available only on the CamContain filter housing, simply pulls out off the housing itself, and unseats the gasket, with a comb to distribute the airflow. It has an operating torque of 20 foot-pounds, and costs $2,650.

To make the selection even more complicated, each of these damper options also is available with either manual, pneumatic, and electric actuators. With a flat-blade damper, upgrading to pneumatic adds $900 to the cost, and $2,300 for electric. The dish-style damper is also $900 more expensive with a pneumatic actuator, and $1,900 more for electric. The linear damper increases by $700 when operated pneumatically, and by $1,700 electrically.

Location is Everything

Once you have decided on the filter, housing, and components, the next step is to decide on their orientation within the building.

Chris Kiley, biocontainment mechanical engineer at Merrick & Company in Atlanta, Ga., gave as an example a generic BSL-3 lab configuration with three 200-sf animal rooms and three adjacent 100-sf procedure rooms. The traditional arrangement has six HEPA filters—one for each spacemdash;located in the interstitial space above. This provides a minimal amount of contaminated ductwork, maintenance is performed outside the space, and operations and maintenance personnel are not exposed to contaminated HVAC components. On the downside, the costs are high for equipment, construction, and maintenance. There are six filter units to purchase and maintain, and they require large interstitial space. In addition, there is no redundancy, so when the filter is down, the room is out of commission.

The CamContain housing option uses the same configuration, so the benefits are the same as the traditional example, but the units are smaller. That alone can shave $16,500 off the shipping and constructions costs, though despite their smaller profile, they still require substantial interstitial space to allow access for operations and maintenance personnel.

Certek housings are installed in the same configuration but can save $50,000 because they are made of aluminum instead of stainless steel. They also are significantly smaller. In the long run, they can be costly to maintain because the entire housing can be incinerated instead of just the filter. The built-in scan section makes it cumbersome to replace or repair the filter.

Room-side replaceable HEPA filter housings cost about $75,000 less than the traditional units. Maintenance for HVAC is still done outside the space, but testing of the filters themselves occurs within the lab and could be disruptive to the research. Also, the technology is not yet proven.

“This has been on a test bench for a year and a half or so,” says Kiley. “Nobody wants to be first in these things, so it is still out there, and I think there are some European installations coming up.”

“Ganging” the HEPA filters—grouping them together in one space rather than locating them individually above each lab or ante-room—would save between $130,000 and $165,000 in this example, depending on the specific orientation of the filters.

Ganging the filters saves on construction cost because they require less square footage as a group than they do individually, and they are cheaper to operate and maintain because fewer filters are required.

“You could put these in a closet somewhere,” says Kiley. “You could put them in a mechanical space. You can duct it pretty far away. We had one facility where we ducted it three stories up to a mechanical room.”

On the downside, they generate a lot more contaminated ductwork, which needs to be decontaminated prior to maintenance work on the HVAC components located on the dirty side. In addition, they don’t appear to meet new BMBL guidelines for working with high risk agricultural agents that require pressure decay testing.

“There is another downside,” says Kiley. “If you are doing work in one of these labs and generating a lot of dust or aerosol, you could clog up all the filters and lose the entire suite.”

One configuration saving about $130,000 includes four filters operating at 250 fpm when only three are required. That redundancy permits the labs to keep operating while the filters are tested and maintained one at a time. By bumping the capacity to 500 fpm and installing three filters, the labs can function on two units and have one for redundancy, at a savings of $155,000. The savings increase to $165,000 if you gang CamContain filter housings.

Taking into account all the variables—including filter type, housing, dampers, seals, configuration—there are nearly 13,000 possible solutions.

“Here is our real world application,” says Kiley. “We had a BSL-3/4 facility that bid in January of last year. The initial cost for the 145 filters alone was just over $3 million. After going through a value engineering process with the mechanical subcontractor and the vendors, we realized an $800,000 savings just by changing the filter housing. The risk associated with everything else stayed the same; the redundancy stayed the same.

“The important thing to remember is, there is no single solution that fits all the applications,” he says.

By Lisa Wesel

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