Recent and current building practice has resulted in an increase in the number and severity of low-frequency noise problems at frequencies 250Hz and below (mainly due to the increasing usage of variable-air volume air distribution systems and the increased usage of floor-by-floor or roof-top package air handling equipment). Very little work, however, has focussed on the question of how people react to indoor noise in situations where the background sound at low frequencies (<250Hz) is established by the noise level of operating HVAC systems.

The objectives of the project were:
(a) To generate a practical philosophy and procedure(s) for the evaluation of the
acceptability of low-frequency HVAC sound;
(b) To provide the technical basis for development of low frequency design
criteria for future publications in ASHRAE handbooks.

The main areas covered in this investigation and reported are:  

 - Literature review
 - Noise sample measurement
 - Metric derivation and selection