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Radiant temperature asymmetry between ceiling and floor, and air and walls must be limited to reduce discomfort. To reduce draft risk at temperatures below 22.5 °C (72.5 °F), air speed due to the HVAC system must be 0.15 m/s (30 ft/min) or below.
ASHRAE 55-2017 defines the Cooling Effect (CE) at elevated air speed (above 0.2 metres per second (0.66 ft/s)) as the value that, when subtracted from both the air temperature and the mean radiant temperature, yields the same SET value under still air (0.1 m/s) as in the first SET calculation under elevated air speed.
Research completed in 1984 revealed some factors which were not accounted for in the original publication of the method; these findings were a result of the ASHRAE research project 359. In 1988 ASHRAE Research Project 472 worked to correct these oversights with the introduction of a classification system for walls, roofs, and zones ...
In a stratified building, temperature differentials of up to 1.5°C per vertical foot is common, and the higher a building's ceiling, the more extreme this temperature differential can be. [2] In extreme cases, temperature differentials of 10°C have been found over a height of 1 meter.
The norm ISO 7730 and the ASHRAE 55 standard give the predicted percentage of dissatisfied occupants (PPD) as a function of the radiant temperature asymmetry and specify the acceptable limits. In general, people are more sensitive to asymmetric radiation caused by a warm ceiling than that caused by hot and cold vertical surfaces.
Sol-air temperature (T sol-air) is a variable used to calculate cooling load of a building and determine the total heat gain through exterior surfaces. It is an improvement over: It is an improvement over:
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Operative temperature is used in heat transfer and thermal comfort analysis in transportation and buildings. [10] Most psychrometric charts used in HVAC design only show the dry bulb temperature on the x-axis(abscissa), however, it is the operative temperature which is specified on the x-axis of the psychrometric chart illustrated in ANSI/ASHRAE Standard 55 – Thermal Environmental Conditions ...