Experimental measurements of Ventilation rates in concurrent mixed mode buildings
Standards have largely focused on sequential and change over mixed mode ventilation up till now. Even though concurrent mixed mode ventilation has been in use for some time, no standards exist. Concurrent mixed mode was recently mentioned for the first time in 6.4.3 of the recently published ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) Standard 241-2023, as an applicability of equation 6.1, which requires that the total air flow rates from mechanical ventilation (MV), air cleaning systems, and natural ventilation (NV) be greater than the minimal equivalent clean airflow rate required within the breathing zone. According to 6.4.3, the combined influence of natural and mechanical ventilation systems must meet Equation 6-1. However, the standard makes no mention of calculating the combined effect of this concurrent system. It's uncertain if the airflow rates from both modes should be additive or if one mode should take precedence, creating a different resultant effect. This DRP focuses on measuring this resultant or combined effect occurring from using both the systems (NV and MV) simultaneously in the same space. Concurrent systems raise the common concern that opening windows when air conditioning is turned on may increase energy consumption because building operators will have to pay to condition outside air entering through open windows (Brager et al., 2007). Concurrent systems may fail to meet required energy savings because of frequent concerns such as excessive door openings or insufficient airflow due to limited window access. This research will close the knowledge gap on effective utilization of both systems in tandem, allowing more users to switch to these systems for increased comfort and energy savings.
