The performance of a building’s duct system is critical to the efficiency and comfort of the occupants. This article discusses the factors that impact duct system performance and explains how to document and sample to assess the conditions in the system.
1. Building Size and Type
Duct systems can be designed for any building; however, each building has a unique set of problems that must be addressed in the design. The size and type of the building are essential factors in determining how much air is needed for heating and cooling, how to route ducts from one place to another, and whether or not electrical noise will be a problem.
In large, open buildings with much-uncontrolled sunlight, shadows may affect the duct system. Shadows result when large pieces of metal or other equipment cast a shadow on the inside of the ducts. To reduce the effects of shadows, especially in rooms with no windows, keeping all major equipment outside of the duct system is advisable. Large open buildings are also subject to temperature stratification; that is, rooms at different heights will be heated or cooled to different temperatures.
2. Design Practices
From the design standpoint of duct installation, the size and building significantly impact how ducts are routed outside, where they enter the building, and even whether they are insulated. The orientation of the building concerning heating/cooling requirements can also affect the duct system design.
3. Content of the Duct System
Because most heating and cooling equipment are located outdoors, it is not unusual for the outdoor air supply to have a significant amount of dust in it. Outdoor air intakes are frequently situated near roadways where exhaust fumes can be drawn into the building. If this is the case, unique materials may need to be installed to reduce the dirt entering the system.
4. Electrical Equipment
Duct systems are at risk for electrical noise problems. Since most ductwork is located under raised floors, it is subject to EMC problems associated with electrical equipment on raised floors. This may result in humming or ticking noises in the ducts or even equipment shutdowns.
5. Humidity and Condensation
Duct systems that carry supply air from outdoors can accumulate a significant amount of moisture in a short period, especially if the outside humidity is very high. This results in higher levels of moisture inside the building and wet insulation and other damp materials that could lead to microbial growth. The life of duct systems in humid climates is significantly shorter than similar ducts in dry climates.
6. Presence of Airborne Contaminants
Some climate zones, such as mold and pollen-prone areas, tend to generate large quantities of dust from building materials accumulated in the duct system. Dust creates potential fire hazards and shortens the service life of HVAC equipment.
7. Conditions in the Duct System
The next step is to inspect and sample the duct system to determine its conditions. It is important to take samples from inside and outside of each building separately since problems can vary significantly between buildings due to differences in climate, humidity levels, location on the site, etc.
When doing the visual inspection, consider that metals are more difficult to clean than other surfaces. This means ducts with metal components will require longer cleaning times and be more likely to accumulate dust than those without them.
8. Materials Used in Construction
Most duct system materials, such as galvanized sheet metal, fiberglass insulation, and duct board, can be cleaned when tested and found to be dust-free. When tested, the materials that cannot be adequately cleaned include fabric-backed insulation, aluminum foil-faced insulation, and fireproofing/soundproofing materials such as masonry block and cinder block.
These materials should only be cleaned when they are found to contain no measurable amounts of dust.
9. Temperature in the Ducts
The HVAC system is designed to cool or heat air through the ductwork, so it is vital to keep the thermal insulation on the ducts intact during cleaning. If there are areas where the insulation has deteriorated, repair them before proceeding with testing and cleaning. You can also opt for pex insulation sleeve that provides the best insulation with no loss of cool or heat air.
10. Length of Duct Runs
The length of duct runs can affect the time needed for cleaning. If ducts are very long, it will require more time to clean them. In some cases, you may consider using a mobile system mounted on a truck with a telescoping arm to shorten the required run while keeping the suction power constant. This way, more ducts can be serviced in a shorter period.
There are many reasons why a duct system can be inefficient and cause poor indoor air quality. We hope this article has helped you identify some of the most common causes for concern. How have these factors impacted your performance in the past? Let us know!
Ronald is a business editor who writes about various topics such as technology, health and finance. He works along with the colourful folks that build a nation through tech startups. He is also a professional football player and video games enthusiast.