At the same time, the HVAC industry is faced with new responsibilities and opportunities. Buildings' HVAC systems stand as the greatest contributors to occupant comfort, safety, and health, and are one of the prime lines of defense against emergencies and hazards.

Building safety and health have long been addressed. We deal with Legionnaires' disease, mold, indoor air quality (IAQ), and Sick Building Syndrome (SBS), for example. Now, however, there are new concerns.

Since the HVAC system is designed to circulate air throughout the building, toxic material fed into an outside air intake will spread quickly through the entire building. Terrorists also can take advantage of any duct that is accessible to spread contaminants.

According to the International Code Council, April 4-10 is Building Safety Week. It is time to make sure HVAC systems in buildings are safe from potential attacks.

Key to maintaining the safety and security of an HVAC system is a periodic walk-through of the building by a team of building personnel and HVAC professionals. The team would list all observed security and safety risks and recommend retrofit measures and changed procedures. The HVAC professional can evaluate the recommendations. The building owner would decide which measures are to be performed. The advantages to the building owner are many, including meeting obligations of security and safety to the building occupants; reducing energy usage in most cases; and longer equipment life.

The HVAC contractor also can realize some advantages, including developing a relationship with the building owner that could lead to future projects; opportunities for retrofit work; opportunities for IAQ, test and balancing (TAB), and energy management surveys; and making HVAC systems safer and more effective.

Figure 1. Suggested checklist for rooftop units.

High-Risk Areas

A walk-through team is likely to discover some common problems, including dirty filters, clogged coils, inoperative dampers, an outside air intake vulnerable to deliberate contamination, contaminated water in the cooling tower basin, and outside air intakes and rooftop units within 25 feet of potential contamination sources.

More unusual problems have been discovered, including gasoline stored in the boiler room, a pipe running through a fire damper so it cannot close, the outside air intake picking up car and bus exhaust fumes, and a school custodian shaking dust mops next to a return air intake.

Figure 2. An intake at ground level.

Evaluating Retrofit Measures

Some changes require little or no cost, such as removing hazardous materials including paint, cleaners, fuel, and thinners from mechanical and boiler rooms; making mechanical rooms and rooftop units accessible only to authorized personnel; and establishing a schedule for replacing filters.

Of course, many retrofit items will require capital outlay. These have to be evaluated either in terms of reducing high-risk areas or in terms of long-term savings. A typical retrofit to reduce risk makes the outside air intake safer. If an air intake is at ground level (see Figure 2), it is very easy for a terrorist to introduce toxic material into the entire duct system. To make the intake less accessible, ductwork can be installed to raise the intake at least 12 feet above the ground (see Figure 3).

Figure 3. Duct installed to raise intake at least 12 feet off the ground.

Filters

Filters can never provide protection from all toxic materials. However, proper filter selection and a reasonable replacement program can provide cleaner and healthier air in the conditioned spaces. They also provide savings in longer equipment life and lower maintenance costs from such things as dirt-loaded fan blades, restricted coils, and dirty ducts.

Frequently, especially in older buildings, filters were selected for low first cost, rather than for indoor air quality or lower long-term costs. As everyone in the industry knows, the common throw-away filter usually found in residential units does little more than filter out dust. It does not provide protection from toxic materials that could be introduced into the system. (Figure 4 is a general summary of the filtering ability of the different types of filters.)

The HVAC professional is qualified to determine whether installing more efficient filters is feasible. Installing more efficient filters generally means more resistance to the system and possible problems such as reduced airflow and overloading of motors and fans.

In many buildings, air bypassing the filter cells is an unrecognized problem. It can be caused by air leakage around the rack, old or missing gasket material against the filter's cells, or leakage between filter cells. Air leakage means that a percentage of the conditioned air is not filtered.

Ideally, a filter rack will have a differential pressure gauge installed. The accurate way to tell if filters need changing is by the pressure drop across the filters, as recommended by the filter manufacturer. Building personnel tend to change filters (if they think of it) on a calendar basis. However, experience has shown that filters load not by the calendar but by the seasons (spring and pollens, summer and dust, etc.). The HVAC professional should guide the person responsible to maintain a log that will indicate when filters need to be checked.

Figure 4. Sizes of common particles and the filters that can capture them.

Training And Safety

Building owners and supervisors need to be educated that having properly trained operators of HVAC systems means more occupant comfort, greater energy savings, lower repair costs, and longer equipment life. The HVAC professional is the person qualified to provide this training.

There's an old saying that "People don't do what you expect - only what you inspect." But, many building operators don't know what to inspect in an HVAC system. And some building personnel apparently haven't a basic concept of the function of an HVAC system. For example, in one building an inspection revealed that the vacuum cleaner was regularly emptied into a waste can located in the fan plenum.

Of course, the building owner and the building maintenance supervisor have the final responsibility for maintaining security and safety in the HVAC system. But it really requires someone with system understanding to set up the proper maintenance program - including checklists, time logs, and inspection and maintenance schedules.

In the end, a building security and safety plan needs to contain the following elements: