noise

This article describes the physical mechanisms leading to broadband noise from axial fans. It gives the results of a literature survey about the semi-empirical correlations available to predict this noise and their application to two examples : a low pressure fan and a high pressure fan.

In this paper, a literature survey on rectangular and round ventilation ducts is presented. The comparison is based on two important aspects: pressure drop and noise radiation. The pressure losses in the ductwork should be kept as low as possible without jeopardizing proper control of the flow rates in the system. Pressure loss through a rectangular duct is significant higher than a volumetrically equal round one. The higher the aspect ratio, the higher-pressure loss in the rectangular system.

The main findings from the Probe occupant surveys are assessed. The emphasis is on the consequences for strategic thinking on how best to design and manage buildings to improve conditions for occupants and users, taking examples from the Probe studies. Comfort, health and productivity of occupants are positively associated statistically; and all are easily undermined by chronic, low-level problems.

Buildings located in noisy areas require a high degree of sound insulation. This will usually involve making the building envelope virtually airtight, and as a result losing the possibility of utilising natural ventilation. The solution is to employ a mechanical ventilation system, but such systems can themselves constitute a source of intrusive noise. Discontinuities in ducts result in the generation of flow noise and a loss of static pressure. The greater the discontinuity, the greater is the loss in static pressure and the greater is the sound power generated.

This paper summarizes baseline results from the U.S. Environmental Protection Agency's (EPA) school demonstration studies. Indoor pollutants of concern were formaldehyde, sum of targeted volatile organic compounds o:VOC), carbon monoxide (CO), particulate matter less than 2.5 microns (PM2.5), particulate matter less than 10 microns (PM10), and bioaerosols (bacteria, fungi, and thermophiles). The five schools presented here had no significant indoor air quality problems. Locations of these schools were distributed throughout various climate zones in the United States.