GRILLES & DIFFUSERS
THE BASIC UNIT OF A
CENTRAL HVAC SYSTEM
Supply air outlets and diffusing equipment introduce air into a conditioned space to obtain a desired indoor atmospheric environment from the floor to 1.8 m above the floor level.
Return and exhaust air is removed from a space through return and exhaust inlets.
To obtain comfort conditions within this zone, standard limits have been established for acceptable effective draft temperature, which combines the effects of air temperature and air movement in terms of their physiological effects on a human body with humidity and radiation considered as constant. Variation from accepted standards causes occupant discomfort.
EFFECTIVE DRAFT TEMPRATURE
θ = (tx - tc) - 8 (Vx - 0.15) ....(1)
θ = effective draft temperature, K
tx = local airstream dry-bulb temperature, °C
tc = average (control) room dry-bulb temperature, °C
Vx = local airstream centreline velocity, m/s
A high percentage of people are comfortable where the effective draft temperature , as defined in Equation (1), is between -1.5 and +1 K and the air velocity is less than 0.35 m/s.
If several measurements of air velocity and air temperature are made throughout the occupied zone of an office, the ADPI is the percentage of locations where measurements were taken that meet these specifications for effective draft temperature and air velocity. If the ADPI is maximum (approaching 100%), the most desirable conditions are achieved.