ASHRAE-Standard-55 - Page 046

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a. Comfort: conditioning with cooled air inherently covers large areas that may have multiple occupants,

some of whom are not experiencing the thermal transient and do not need the cooling. Air movement, in contrast, can be directed into smaller areas that do not overcool longer-term sedentary residents of the space. b. Energy: transition spaces at the indoor/outdoor boundary (stores, lobbies, transit stations) inevitably leak

their cooled air to the outdoors, and the colder that these spaces are maintained, the greater the energy loss. c. Cooling occupants by air movement provides equivalent comfort at warmer interior temperatures, so less

energy is lost from leaked air. Also, air movement cooling is inherently less energy intensive than the equivalent cooling from lowering a space’s air temperature or humidity level.

It is possible to quantify the combinations of air movement and air temperature that are most effective at keeping people comfortable during the time they are in lobbies, stores, and other transition spaces. One can also quantify the combinations needed by newly arrived occupants once they arrive in long-term sedentary spaces, such as their workstations, conference rooms, classrooms, waiting rooms, and restaurants. E8.2 Design Approach for Cooling Transition. Translating these environmental conditions into design, transition zones should be able to provide sufficient elevated air movement within the space that an occupant’s travel through it is comfortable throughout. The indoor destination (for example, an office workplace) should have personally controlled air movement sources available to deal with the transition to sedentary in spaces whose temperatures are not under the control of the occupant. The operational goal should be to avoid overcooling the space temperature, and to maintain it at an appropriately warm level (not below 25°C

[77°F]) to allow the most effective draft-free convective cooling. Here are example strategies based on current research results:

a. Transition zones: Maintain indoor operative temperature between 26°C to 28°C (78.8 to 82.4 °F) (for

humidities around 50% rh) with a continuous ambient air speed of 0.6 to 0.8 m/s (118 to 157 fpm) in the parts of the space occupied by people in transition. The most common source of room-wide air speed is ceiling fans, though large horizontally oriented fans are also used. b. Destination workstations: Make available a personally controlled fan capable of 1.2 m/s (236 fpm) on

the upper body while maintaining an operative temperature between 25°C to 28°C (77°F to 82.4°F) and ambient air speed of at least 0.3 m/s (59 fpm).

For sedentary long-term occupants in the transition zone, (sales clerks, receptionists, etc.), provide the ability to reduce air speed in their locations.

44 ANSI/ASHRAE Standard 55-2023