Construction workers install BlueDuct underground ductwork at Saints Anne & Joachim Catholic Church in Fargo, N.D. The underfloor ductwork was chosen as part of a displacement-ventilation system.

When church officials at Saints Anne & Joachim Catholic Church in Fargo, N.D., added a sanctuary as part of the final part of a multiphase building plan, they requested an HVAC system that churchgoers would not see, hear or feel.

The building system engineers decided the best solution would feature a displacement-ventilation system with completely hidden displacement diffusers integrated into the architecture of the building. This included air supplied under the floor by BlueDuct underground ductwork.

“Churches have unique heating and cooling needs,” said Jeremiah Christenson, managing principal and mechanical engineer from Obermiller Nelson Engineering Inc. of Fargo. “The HVAC system needs to respond quickly to accommodate a large congregation of people within a short period of time. To meet this and other requirements, we needed to combine innovative technology without impacting the beauty of the traditional architecture.”

Different from traditional ventilation, displacement ventilation requires multiple strategically located diffusers at floor level to spill the air, at a very low velocity, across the floor. BlueDuct provides the air supply to the diffusers.

The engineers explained that displacement ventilation allows air to stratify rather than mix, resulting in a very efficient system. As the air comes in contact with a heat source, such as people and equipment, the air is warmed and rises. This allows the occupied zone to be conditioned to the proper temperature. The air above the occupied zone can be a higher temperature without impacting occupant comfort or efficiency.

The BlueDuct’s low-velocity underground air ducts, manufactured by AQC Industries, allowed for arrangement of displacement diffusers near church occupants and spaced evenly throughout the interior area. AQC Industries worked with Obermiller Nelson Engineering to provide proper duct sizing and created CAD drawings to map the ideal duct placement.

The manufacturer said the low velocity of the system offers quiet operation and prevents airflow from being felt when people are sitting in close proximity to the outlets. Displacement diffusers were concealed in the stone pilasters, prayer kneelers and pews. The return-air system was installed in the attic to pull the return air from the top of the 45-foot-tall room. This further reduced any potential noise issues, minimized the effects of stratification, and increased system efficiency.

The BlueDuct direct-burial underground air ducts were selected by engineers for the church because of the product’s insulation value, and its watertight and airtight properties. The products are made from advanced high-density polyethylene (HDPE) and have a low-friction, smooth surface, which also resists mold, mildew and radon.