Duct and Riser Leakage Testing
Duct pressure testing is carried out to achieve integrity within a design range that has been selected by the design engineer or appropriate standard.
The ductwork air tightness level is the airflow rate through ductwork leakages divided by the ductwork area. It is recommended to test at least 10% and 10 m2 of the duct surface including all duct types and a variety of sizes and components. The airflow rate through leakage can be measured by temporarily connecting a device called a duct leakage tester to pressurize the ductwork including duct-mounted components. Air flow through the pressurizing device creates an internal, uniform, static pressure within the ductwork.
The aim of this type of measurement is to relate the pressure differential across the ductwork to the air flow rate required to produce it. Generally, the higher the air flow rate required to produce a given pressure difference, the less airtight the ductwork.
Airtight ductwork is one of the keys to a quality heating and cooling system. It helps to make the building healthy, comfortable and energy efficient. Although sealing up ductwork sounds simple, leakage problems are major concern in todays duct construction market. Leaky ducts can significantly increase energy bills, dramatically reduce system capacity and performance, as well as result in potentially dangerous indoor air quality problems. Duct leakage is often responsible for complaints about indoor comfort by building occupants.
Air leakage from sheet metal ducts occurs at the seams and joints and is therefore proportional to the total surface area of the ductwork and related to the air pressure in the system. As there is no direct relationship between the volume of air conveyed and the surface area of the ductwork system required to match the building configuration, it is difficult to express air leakage as a percentage of total air volume. Similarly, the operating pressure will vary throughout the system and, as leakage is related to pressure, the calculations are complex. It is generally accepted, however, that, in typical, good quality systems, the leakage under operating conditions will be in the region of six per cent for low pressure systems (class A), three per cent for medium pressure systems (Class B), two per cent for high pressure systems (Class C) and just 0.5 per cent for the highest pressure systems (Class D).
The only way to ensure that the ductwork is airtight is by testing it. Flow Balance can assess product performance and provide evidence that equipment is either fit or not for use on site. At the completion, certificates are issued with details of the joint ratings, material characteristics and the measured air leakage rate.
