Page 50 - 2018_IMC

VENTILATION

With the exception of smoking lounges, the ventila- b.“Warm air” is air warmer than space temperature.
tion rates in Table 403.3.1.1 are based on the absence c. “Ceiling” includes any point above the breathing zone.
of smoking in occupiable spaces. Where smoking is d. “Floor” includes any point below the breathing zone.
anticipated in a space other than a smoking lounge, the e. Zone air distribution effectiveness of 1.2 shall be permitted for systems
with a floor supply of cool air and ceiling return, provided that low-
ventilation system serving the space shall be designed
velocity displacement ventilation achieves unidirectional flow and
to provide ventilation over and above that required by thermal stratification.
Table 403.3.1.1 in accordance with accepted engineer- f. Zone air distribution effectiveness of 1.0 shall be permitted for systems
ing practice. with a ceiling supply of warm air, provided that supply air temperature is
less than 15°F above space temperature and provided that the 150-foot-
Exception: The occupant load is not required to be
1
per-minute supply air jet reaches to within 4 / 2 feet of floor level.
determined based on the estimated maximum occu-
pant load rate indicated in Table 403.3.1.1 where 403.3.1.1.1.3 Zone outdoor airflow. The zone
approved statistical data document the accuracy of outdoor airflow rate (V ), shall be determined in
oz
an alternate anticipated occupant density. accordance with Equation 4-2.
403.3.1.1.1 Zone outdoor airflow. The minimum V = V bz (Equation 4-2)
-------
outdoor airflow required to be supplied to each zone oz E z
shall be determined as a function of occupancy clas-
sification and space air distribution effectiveness in 403.3.1.1.2 System outdoor airflow. The outdoor
accordance with Sections 403.3.1.1.1.1 through air required to be supplied by each ventilation sys-
403.3.1.1.1.3. tem shall be determined in accordance with Sections
403.3.1.1.1.1 Breathing zone outdoor airflow. 403.3.1.1.2.1 through 403.3.1.1.2.3.4 as a function
The outdoor airflow rate required in the breath- of system type and zone outdoor airflow rates.
ing zone (V ) of the occupiable space or spaces 403.3.1.1.2.1 Single zone systems. Where one
bz
in a zone shall be determined in accordance with air handler supplies a mixture of outdoor air and
Equation 4-1. recirculated return air to only one zone, the sys-
tem outdoor air intake flow rate (V ) shall be
ot
V bz = R P + R A z (Equation 4-1) determined in accordance with Equation 4-3.
z
a
p
V = V (Equation 4-3)
where: ot oz
A = Zone floor area: the net occupiable floor
z
area of the space or spaces in the zone. 403.3.1.1.2.2 100-percent outdoor air systems.
Where one air handler supplies only outdoor air
P = Zone population: the number of people in to one or more zones, the system outdoor air
z
the space or spaces in the zone. intake flow rate (V ) shall be determined using
ot
R = People outdoor air rate: the outdoor Equation 4-4.
p
airflow rate required per person from
Table 403.3.1.1. V ot = Σ all zones V oz (Equation 4-4)
R = Area outdoor air rate: the outdoor airflow
a
rate required per unit area from Table 403.3.1.1.2.3 Multiple zone recirculating sys-
403.3.1.1. tems. Where one air handler supplies a mixture
403.3.1.1.1.2 Zone air distribution effective- of outdoor air and recirculated return air to more
ness. The zone air distribution effectiveness (E ) than one zone, the system outdoor air intake flow
z
shall be determined using Table 403.3.1.1.1.2. rate (V ) shall be determined in accordance with
ot
Sections 403.3.1.1.2.3.1 through 403.3.1.1.2.3.4.
TABLE 403.3.1.1.1.2
ZONE AIR DISTRIBUTION EFFECTIVENESS a,b,c,d 403.3.1.1.2.3.1 Primary outdoor air frac-
AIR DISTRIBUTION CONFIGURATION E z tion. The primary outdoor air fraction (Z )
p
shall be determined for each zone in accor-
Ceiling or floor supply of cool air 1.0 e
dance with Equation 4-5.
Ceiling or floor supply of warm air and floor return 1.0 V
oz
Ceiling supply of warm air and ceiling return 0.8 f Z = ------- (Equation 4-5)
p
V
Floor supply of warm air and ceiling return 0.7 pz
where:
Makeup air drawn in on the opposite side of the room 0.8
from the exhaust or return V = Primary airflow: The airflow rate
pz
supplied to the zone from the air-
Makeup air drawn in near to the exhaust or return loca- 0.5 handling unit at which the outdoor air
tion
intake is located. It includes outdoor
For SI: 1 foot = 304.8 mm, 1 foot per minute = 0.00506 m/s, intake air and recirculated air from that
°C = [(°F) – 32]/1.8. air-handling unit but does not include
a. “Cool air” is air cooler than space temperature. air transferred or air recirculated to the
2018 INTERNATIONAL MECHANICAL CODE  33
Copyrighted © 2017 by, or licensed to, ICC (ALL RIGHTS RESERVED); licensed to UL, LLC pursuant to License Agreement with ICC. No further reproductions authorized or distribution authorized.
ANY UNAUTHROIZED REPRODUCTION OR DISTRIBUTION IS A VIOLATION OF THE FEDERAL COPYRIGHT ACT AND THE LICENSE AGREEMENT; AND SUBJECT TO CIVIL AND CRIMINAL PENALTIES THEREUNDER.