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A better way to predict comfort: the new ASHRAE standard 55-2004


Substantial progress in our understanding of human response to thermal environments has been made since Standard 55- 1992, including the amendment 55-95a. Incorporating many of these advances, Standard 55-2004, Thermal Environmental Conditions for Human Occupancy, was recently published after completingfour public reviews and receiving approval by both ASHRAEand the American National Standards Institute (ANSI).

The standard specifies conditions of the indoor thermal environment that occupants will find acceptable. It is intended for use in design, commissioning, and testing of buildings and other occupied spaces and their HVAC systems, and for the evaluation of existing thermal environments. Because of the inherent variations in occupants’ metabolic rates and clothing levels, and because it is not possible to prescribe or enforce what these should be, this standard cannot practically mandate operating setpoints for buildings.

The two most important additions included in this new standard are an analytical method based on the PMV-PPD indices and introduction of the concept of adaptation with a separate method for naturally conditioned buildings. The adaptive model and several other changes are based on various ASHRAE sponsored research projects. This article provides an overview of the key features and limits of applicability of Standard 55-2004.

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