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Energy Conservation Potential of Displacement Ventilation in Minnesota

Traditional ventilation (or mixed-flow) systems in commercial building are designed to uniformly dilute the entire volume of air in a room or space. By contrast, displacement ventilation (DV) systems rely on the concept of air stratification. A DV system delivers fresh, cooled air at low velocities close to the floor of the room. As this air both heats and becomes polluted by internal sources, it gradually rises to the top of the room where it is extracted.

DV purports to reduce power and energy use as well as significantly improve indoor air quality. More specifically:

  • Lower supply velocities result in lower pressure drops, potentially allowing the use of smaller fans and correspondingly less energy required to operate those fans;
  • By introducing the supply air at the floor level, accumulated contaminants are reduced in the area where people tend to be located, improving indoor air quality;
  • DV has been shown to have a higher ventilation effectiveness than traditional mixed-flow systems;
  • Economizer hours may be expanded since supply air temperatures tend to be higher with DV systems, potentially allowing for more free cooling.

Unfortunately, the majority of studies on DV are based on computer simulations with varying results. For example, reported energy savings from one group of studies range from a reduction in total energy use of up to 60 percent to an increase of up to 12 percent (Emmerich and McDowell). As a result, knowledge of the true energy benefits of DV suffers from a striking lack of field-based research on actual buildings, especially in heating dominated climates.

The goal of this CARD grant awarded to Sustainable Engineering Group LLC in 2013 is to conduct a field study to evaluate the power and energy savings potential of DV technology in Minnesota climate conditions, and to determine the significant impediments to its acceptance in the marketplace. To accomplish this, the grantee will identify existing Minnesota commercial buildings with DV systems, conduct surveys of building owners, and analyze the energy and performance data from these buildings. A total of 15 to 30 buildings will be included in the study. In addition, Sustainable Engineering will conduct a second survey among at least 30 local architects and engineers to determine attitudes and market awareness towards DV.

This CARD study will be conducted through January 2016. For further information, contact project manager Mark Garofano or CARD grant program administrator Mary Sue Lobenstein.