Page 51 - 2018_IMC

VENTILATION

zone by other means. For design 403.3.1.2 Exhaust ventilation. Exhaust airflow rate
purposes, V shall be the zone design shall be provided in accordance with the requirements
pz
primary airflow rate, except for zones of Table 403.3.1.1. Outdoor air introduced into a space
with variable air volume supply and V pz by an exhaust system shall be considered as contribut-
shall be the lowest expected primary ing to the outdoor airflow required by Table 403.3.1.1.
airflow rate to the zone when it is fully 403.3.1.3 System operation. The minimum flow rate
occupied. of outdoor air that the ventilation system must be capa-
403.3.1.1.2.3.2 System ventilation efficiency. ble of supplying during its operation shall be permitted
The system ventilation efficiency (E ) shall be to be based on the rate per person indicated in Table
v
determined using Table 403.3.1.1.2.3.2 or 403.3.1.1 and the actual number of occupants present.
Appendix A of ASHRAE 62.1.
403.3.1.4 Variable air volume system control. Vari-
TABLE 403.3.1.1.2.3.2 able air volume air distribution systems, other than
SYSTEM VENTILATION EFFICIENCY a,b
those designed to supply only 100-percent outdoor air,
Max (Z p ) E v
shall be provided with controls to regulate the flow of
 0.15 1 outdoor air. Such control system shall be designed to
 0.25 0.9 maintain the flow rate of outdoor air at a rate of not less
than that required by Section 403.3 over the entire
 0.35 0.8
range of supply air operating rates.
 0.45 0.7
403.3.1.5 Balancing. The ventilation air distribution
 0.55 0.6
system shall be provided with means to adjust the sys-
 0.65 0.5 tem to achieve not less than the minimum ventilation
 0.75 0.4 airflow rate as required by Sections 403.3 and
403.3.1.2. Ventilation systems shall be balanced by an
> 0.75 0.3
approved method. Such balancing shall verify that the
a. Max (Z ) is the largest value of Z calculated using Equation 4-5 among all
p
p ventilation system is capable of supplying and exhaust-
the zones served by the system.
ing the airflow rates required by Sections 403.3 and
b. Interpolating between table values shall be permitted.
403.3.1.1.2.3.3 Uncorrected outdoor air 403.3.1.2.
intake. The uncorrected outdoor air intake 403.3.2 Group R-2, R-3 and R-4 occupancies, three sto-
flow rate (V ) shall be determined in accor- ries and less. The design of local exhaust systems and
ou
dance with Equation 4-6. ventilation systems for outdoor air in Group R-2, R-3 and
V ou = D all zones R P +  all zones R A z R-4 occupancies three stories and less in height above
z
a
p
grade plane shall comply with Sections 403.3.2.1 through
(Equation 4-6) 403.3.2.5.
403.3.2.1 Outdoor air for dwelling units. An outdoor
air ventilation system consisting of a mechanical
where:
exhaust system, supply system or combination thereof
D = Occupant diversity: the ratio of the shall be installed for each dwelling unit. Local exhaust
system population to the sum of the or supply systems, including outdoor air ducts con-
zone populations, determined in nected to the return side of an air handler, are permitted
accordance with Equation 4-7.
to serve as such a system. The outdoor air ventilation
P system shall be designed to provide the required rate of
s
D = ------------------------ (Equation 4-7) outdoor air continuously during the period that the
 all zones P z building is occupied. The minimum continuous outdoor
where: airflow rate shall be determined in accordance with
Equation 4-9.
P = System population: The total number of
s
occupants in the area served by the
system. For design purposes, P shall be Q OA = 0.01A floor 7.5 N + + br 1 (Equation 4-9)
s
the maximum number of occupants
expected to be concurrently in all zones where:
served by the system. Q
403.3.1.1.2.3.4 Outdoor air intake flow rate. OA = outdoor airflow rate, cfm
The outdoor air intake flow rate (V ) shall be A floor = floor area, ft 2
ot
determined in accordance with Equation 4-8. N br = number of bedrooms; not to be less than one
V Exception: The outdoor air ventilation system is not
ou
V ot = -------- (Equation 4-8) required to operate continuously where the system
E
v
has controls that enable operation for not less than 1
hour of each 4-hour period. The average outdoor air-
34 2018 INTERNATIONAL MECHANICAL CODE 
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