Reducing duct leakage is an important part of what we do in the fabrication and installation of air distribution systems. We take special care to follow the SMACNA Duct Construction Guidelines and quality check each section of duct and fitting for assure it has been sealed before it goes out the door.
As each section of duct is installed it is sealed. Each rectangular section of duct and fitting has for corners and two perimeter edges. As pieces of ductwork go up the corners and edges can number in the thousands that require sealing.
Duct sealing and testing is required by the 2009 International Energy Code Council, ASHRAE Standard 90.1, ASHRAE Standard 189 and SMACNA.
Central HVAC systems in commercial buildings continuously supply heated or cooled air to conditioned spaces through a complex network of ductwork. Large fan pressure rises are needed to move the supply air through the typically long duct runs, and the associated fan power is a substantial fraction (35-50%) of HVAC energy use. This fan energy can be reduced by using tight ducts that deliver conditioned air to where it is needed.
There are three notable characteristics that affect the energy associated with ductwork:
1. There can be thousands of field-assembled joints between sections of ductwork and duct mounted accessories that create numerous opportunities for air to leak out.
2. For a hole in the duct to be a problem there must be a pressure difference for air to flow in or out. The higher this pressure is the higher the rate of leakage will be. Because this relationship is somewhere between a quadratic and cubic function of pressure and flow, fan energy must be substantially increased to compensate for the leakage.
3. The location of the ductwork leaking plays an important role in the energy relationship. Duct leakage that occurs in the conditioned space is of little importance. Ducts that leak into ceiling return air plenums short-circuit the conditioned air back to the fan causing the air flow to be increased to compensate for the loss.
Recent field measurements and studies indicate that supply air leakage can increase fan power requirements considerably: a leaky system (10% leakage upstream of VAV boxes, and 10% downstream at operating conditions) uses 25 to 35% more fan power than a tight system (2.5% leakage upstream and 2.5% downstream at operating conditions).
Air Masters also provides Duct Leakage Testing for existing commercial buildings that want to reduce unnecessary energy costs while regaining lost heating and cooling capacity at the same time.