HVAC system designs must address both high indoor air quality as well as energy efficiency as the awareness of and demand for proper air quality increases. Economic considerations such as installation and operating costs have impaired many conventional system designs to the point of compromised indoor air quality. This paper discusses many HVAC design parameters that arc critical to achieving adequate indoor air quality.

To evaluate the health risk posed by particles emitted from sound absorbent materials used in ventilation channels, the number, size, shape and composition of fibers and other particles must be characterized. A method of studying those particle characteristics has been developed. The number concentration of small particles in the testing chamber was measured with a condensation nucleus counter. Both scanning electron microscopical and optical microscopical analyses were possible for filter samples because of the low particle concentration of background particles in the testing chamber.

As active noise control systems begin to penetrate the market place, are the days of the passive attenuator numbered? Andrew Brister looks at the likely future for anti-noise.

An intensive review indicates that among the existing formulae on the sound attenuation in long enclosures, only the geometrical reflection model seems relatively practical. Computations with this model show the following for rectangular long enclosures: with a larger cross-sectional size the relative attenuation from a given section is less but the absolute attenuation with reference to the source power is greater; the efficiency of absorbers is higher when there is less absorption; and obtain a higher attenuation, the absorbers should be evenly arranged in a section.

The term "buffer room" refers in this context to spaces built between thermally, visually, and acoustically "controlled" indoor rooms and the "no controllable" outdoor environment. Examples of buffer rooms are sunrooms, atria, (enclosed) staircases, and air locks. In a long-term research effort carried out in Austria, buffer rooms were studied with regard to their hygrothermal and acoustical performance within a human-ecological framework.

The acoustic environment was investigated in an office building with a history of occupant complaints. A scoring system was developed for rating occupants' sick building symptoms. High scores were associated with the occurrence of high levels of infrasound (< 20 Hz) in the rooms, und low levels with low scores. The infrasound came from the ventilation system as airborne noise, rather than structural-borne vibration. Levels of infrasound were often amplified in the tightly sealed rooms, and could be higher at work stations than at supply grilles.

Office noise affects the productivity of every person in every office. Companies have woken up to the detrimental effects on productivity of stale air pumped out by air-conditioning systems, and they are replacing these with natural ventilation systems. However, air-conditioning provides a useful by-product: the steady masking of background noise. Tom. Dawn considers the options for creating a better acoustical environment.