HVAC Systems Can Be Facilities' Achilles Heel
October 01, 2002
Appeared in Building Operating Management/FacilitiesNet
Whether it’s a high-rise, hospital or shopping mall, one area of the building often least protected has been the HVAC system — at least until now. Today there is a great deal of interest in cost-effective ways to protect HVAC systems.
The air intake is the number one potential HVAC risk, not only for attacks but also for pranks and vandals. Moving the air intakes is cost-prohibitive for most existing buildings. “Air intakes on new buildings will no longer be at street level for high-rises, but I have not heard of anyone making a case for moving existing ones,” says Bogle of Ernst and Young.
An alternative is to restrict access to outdoor air intakes if possible, says Jerry Packham, project manager with Affiliated Engineers Inc. Owners are turning to fences or grills to restrict access, and some are also installing CCTV.
Another way owners can protect their air supply is to make sure the highest MERV-rated (Minimum Efficiency Reporting Value) filters appropriate for the system are installed. A higher-security option is HEPA filters. “A HEPA filter will trap particles down to 1 micron in size, and that comprises the majority of weapons-grade biological contaminants,” says Gillick of Syska Hennessy Group.
Filtration isn’t the ultimate solution, however. HEPA filters do not trap all the particles, and if even a few get through, the system has failed. Also, most air handlers and rooftop units can’t easily accommodate larger, more efficient filters.
Another step some owners have taken is to make sure all mechanical rooms are secure. At minimum, rooms should be locked, Packham says.
More costly measures may be justified if the risk is there. For instance, some Fortune 500 companies have installed UV systems in air handling units that kill biological contaminants in the air stream, Gillick says.
Packham recommends dedicated exhaust systems for mailrooms. Some facilities are also providing negative pressure in mailrooms and labs.
A strategy often used in laboratories is to dilute any chemical agent that might get into the air stream with an emergency exhaust of the area, Packham says. Some owners have been talking about using that sort of an approach for an entire building, with HVAC systems that will automatically shut down when a chemical contaminant is identified. But it’s tricky to design a system like that without endangering occupants.
Systems now coming on the market purport to capture and identify biological contaminants quickly enough that the HVAC system can respond to the attack, but these systems aren’t well tested. There are concerns about how fast the systems can detect a contaminant and how many contaminants they can reliably detect.