Points out that awareness of low-frequency noise generated by heating, ventilation and air conditioning systems has been a serious and increasing problem for many years. Reports that ASHRAE is currently funding research into aspects of the problem that involve the measurement and assessment of low-frequency noise because present test procedures and rating methods are inadequate for evaluating this class of problem. Focuses on more basic questions such as what are the sources of these low-frequency problems and why they have become so prevalent in recent years. States it is becoming obvious that packaged air-handling equipment using direct drive systems and variable-frequency power are the least likely to create problems with low-frequency fan noise.

KEYWORDS: Heating, ventilation, air conditioning, noise, fans, frequency.