Proper Inspection of HVAC Systems

May 14, 2007
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There are many reasons why HVAC ducts should be inspected as part of the building maintenance procedure, and proper inspection tools and techniques are required for professional companies to maintain a competitive edge and avoid unnecessary liability.

According to the World Health Organization, 30 percent of buildings experience a form of sick building syndrome. Causes may be related to mold, mold-spores, mildew, fungi, poor ventilation, microbes, bacteria, particles, stale air, odors or a combination thereof. For the building’s occupants, various medical issues may arise, and even their ability to function optimally may be severely affected. The source of these problems is very often related to the improper design, installation, operation, and maintenance of the Heating, Ventilation, and Air-Conditioning (HVAC) system.

There exist some standards for required HVAC duct inspection for the building commissioning process. The Sheet Metal and Air Conditioning Contractors’ National Association issues guidelines for inspections that primarily focus on duct materials, reinforcement, construction, and the installation of fire dampers, whereas the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and Associated Air Balance Council (AABC) issues standards for required pressure test and air balancing that is executed to ensure system verification and performance.

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However, due to the difficulty and cost of correcting duct leakage in a finished building, it is common practice to just increase fan speed to compensate. This hypothesis is supported by Lawrence Berkeley National Laboratory findings where, on average, commercial building duct leakage exceeds the ASHRAE recommended leakage by roughly a factor of 20. This finding corresponds well with reports from other researchers who report that, on average, between 10 percent and 20 percent of the total air provided by the supply fan is lost to leaks in commercial buildings. Considering that the annual spending of HVAC energy in the U.S. alone is in the order of $55 billion, finding and solving problems from the inside can have an enormous effect on energy savings and the health of building occupants.

The required inspections and testing mentioned above are all executed from the outside of the duct, at diffusers or access openings. This only gives a small window into the overall condition of the system. There is no required visual inspection inside the ductwork for new construction or retrofits to ensure that turning vanes and dampers are properly installed and working. There is nothing to ensure debris and construction dust has been properly removed to prevent turbulent airflow and contamination of the occupied space, nor are there any requirements to ensure that the internal fiberglass lining is not damaged, or that all the seams are properly sealed to prevent insulation fibers from being released into the air. Thus, there is really no complete quality assurance in place between the design phase and when the building is occupied. With such a lack of quality standards, the building owners or professional contractor firms may bridge this gap by some basic inspections to prevent many HVAC problems from occurring or getting worse and to limit the tremendous amounts of wasted energy. Such a move will change the industry, from being reactive to incidences, to a proactive mode where the possibilities of future problems are eliminated ahead of time.

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In the past, inspections consisted of an access opening and a flashlight or mirror. A major drawback to this technique is the inability to record or document for future reference. Also, if an access opening did not exist where you needed to inspect, a new one must be cut. Every time a new opening is cut in the duct, especially if lined with fiberglass, it has the potential to become a problem area.

Even the cutting of the sheet metal is a safety hazard to the worker if proper tools are not used. Considering the expense of labor and materials, and the damage to the duct, it is no wonder that proper inspections are almost nonexistent. A typical commercial building, with an average of 150 to 200 lineal feet of duct for every 1,000 square feet of floor space, would need hundreds of openings to properly inspect the entire system.

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Video inspection systems are available that are portable, battery operated, and have cameras that will fit in a 1-inch opening and can digitally record to small memory cards. As cutting bits and airtight plugs are readily available for 1-inch-diameter holes, which cause minimal damage to the duct’s integrity, it is important to consider the size of the camera. These entry points may be used to check for construction dust and debris, or even the proper installation and operation of turning vanes and dampers during air balancing. Furthermore, the same holes may be used for routine maintenance inspections, including dirt buildup and deteriorating fiberglass liner, or to simply verify that the ducts have been properly cleaned by a duct-cleaning contractor. These small openings provide an inexpensive and easy access to locate, diagnose and document problems in the HVAC systems.

Inspection of cooling coils and the condensation drain pan is sometimes difficult because of access panel location. As particles build up, organic growth often occurs due to moisture on the cooling coils. It is good practice to inspect these every time the filters are changed. If particles and organic growth block the cooling coils, the airflow in the system can become severely restricted, causing poor ventilation and increased energy usage. Bacterial and mold growth can occur because the condensation pan does not have proper drainage. All of these inspection tasks listed above may be easily completed using a camera system (Image 1). Video recording capability is highly recommended so that any problems can be properly documented.

A few problems detected in ductwork with this type of camera are shown in the following two images. Image 2 was from an inspection executed after a registered duct cleaning company had completed cleaning without using video-assisted cleaning procedures. It is no wonder the EPA does not endorse duct cleaning unconditionally. Image 3 was taken at a new construction site where the contractor failed to seal the fiberglass seams, leaving them exposed to high-velocity airflow for fiber shedding. Internal duct liner is still listed as a carcinogenic for animals, despite the fact that it was taken off the list of human carcinogens very recently.

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Whereas handheld camera systems are a must for spot-checking certain areas inside duct, robotic cameras may be necessary for longer distance inspections from a single access opening. Due to various types of duct construction over hard-to-access ceilings, there are many times a robotic inspection system will be the better choice. Many buildings have very difficult access to the HVAC system. In buildings with high ceilings, there are worker safety issues and the costs of setting up scaffolding to consider. Or it may be that the contractor or building owner desires to limit the amount of access openings to maintain duct integrity. When larger inspection openings are cut in duct, as needed for a robot, they should be replaced with an approved access door that can be used in the future.

A robotic inspection provides large amounts of information about the duct system in regards to finding dampers, turning vanes, improper construction, debris, damage, or locations of organic growth. If inspecting an HVAC system for the purpose of cleaning, the robot will help you to avoid missing areas that would be costly if discovered after the bid was submitted. Also, the video images can be utilized for a more professional image when submitted along with the bid.

Many times a robotic system will be necessary because of difficult access and the fact that no drawings or blueprints exist for the building. For this type of inspection there are video recording robots that can drive 200 feet with the ability to negotiate 45-degree climbs within galvanized and lined ducts. This capability enables the contractor or building owner to inspect the duct using the fire damper access doors as prime access for the desired inspection. As with handheld camera units, battery operation and easy setup and use, along with digital recording make a robotic system (Image 4) much more efficient to use than some of the older bulkier units. Image 5 shows how well a robot can document the need for cleaning in a residential trunk line.

Much of the inspection equipment today allows for a more professional and complete job. With the increased awareness of improved IAQ in today’s society, proper inspection equipment and procedures are necessary to solve the needs of your customers.

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