Evaluation of Passive Vents in New Construction Multifamily Buildings
In an effort to improve indoor air quality in high-performance new construction multifamily buildings, dedicated sources of outdoor air are being implemented. Passive vents are being selected by some design teams over other strategies, due to their lower first costs and operating costs. However, a lack of clear design guidance is resulting in poor performance of these systems despite the best intentions. With funding from the Department of Energy’s Building America Program, SWA measured the performance of these systems in several newly constructed multifamily buildings.
Passive vents, such as trickle vents and airlets, rely on a pressure differential created by an exhaust system to provide outdoor air to apartments. SWA’s field research focused on whether these negative pressures prevail through a variety of environmental conditions. The data from the evaluation of three buildings showed that the passive vents did not perform as expected. The average airflow through the passive vents fell short of providing the ASHRAE 62.2-2010 whole-house ventilation requirements. A majority of the exhaust make-up air still came from unintentional sources, either from leaks in the exterior envelope, neighboring apartments, or the corridor. It was also determined that exhaust flow rates necessary to create the pressure differential needed to induce flow through the vents often exceeded the continuous local exhaust rates required by ASHRAE 62.2-2010 by more than 50%. This results in higher fan energy.
Following the field assessment and lessons learned, SWA created a Measure Guideline for the proper design and installation of passive vents. The size and number of passive vents, the exhaust flow rates, the airtightness of the apartment and its entry door, all have significant impact on performance.
A brief summary of this Guideline may be found here