Ventilation Efficiencies of a Desk-edge-mounted Task Ventilation System

In chamber experiments, we investigated the effectiveness of a task ventilation system with an air supply nozzle located underneath the front edge of a desk and directing air toward a heated mannequin seated at the desk. The task ventilation system provided outside air, while another ventilation system provided additional space cooling but no outside air. Test variables included the vertical angle of air supply (-15 to 45 from horizontal), and the supply flow rate of (3.5 to 6.5 L s). Using the tracer gas step-up and step-down procedures, the measured air change effectiveness (i.e., exhaust air age divided by age of air at the mannequin’s face) ranged from 1.4 to 2.7, which is higher than typically reported for commercially available task ventilation or displacement ventilation systems. INDEX TERMS Ventilation rates and strategies, Offices, Improved IAQ practices and technologies, Perceived air quality INTRODUCTION Numerous studies have found that increased outside air ventilation rates in buildings are associated with reduced sick-building syndrome (SBS) health symptoms and with improvements in perceived air quality (Seppanen et al., 1999). Laboratory studies suggest that worker performance may improve with higher ventilation rates (Wargocki et al., 2000). In general, increased ventilation rates will increase building energy use; therefore, technologies or practices that bring about the benefits of increased ventilation rates without energy penalties are highly desirable. One general approach for obtaining the benefits of increased ventilation rates without actually increasing the quantity of outside air supply or the associated energy use is to supply outside air in a manner that preferentially ventilates the breathing zone. To quantify the benefits of such air supply methods, we use the air change effectiveness (ACE). The ACE is a measurable parameter used to compare the effective ventilation rate at the breathing zone to the effective ventilation rate that would occur throughout the building with thoroughly mixed indoor air at the same rate of outside air supply. ASHRAE (1997), defines the ACE based on ages of air as follows