Ventilation Rate Design Procedure; Indoor Air Quality Design Procedure - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

VENTILATION RATE DESIGN PROCEDURE

The Ventilation Rate Procedure is deemed to provide acceptable
IAQ by providing an indirect solution to the control of IAQ.
Acceptable outdoor air is generally defined in terms of sulfur
dioxide, carbon monoxide, ozone, nitrogen dioxide, lead, and
particulate levels. If levels are too high the air "should" be
treated (BOCA says high levels shall be treated). Exceptions
allow recirculating air during rush hour traffic if treatment is
not possible. Minimum outdoor air airflow per person are listed
for each type of occupancy, for example 7.08 L/s for classrooms,
14.16 L/s for operating rooms, and 28.13 L/s for smoking
lounges. These rates are set on the assumption that they will
maintain CO levels below 1000 ppm and that this is a valid
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indicator of acceptable IAQ. Recirculation of air to reduce
quantities of outdoor air requires that air cleaning equipment
be used to lower the contaminant levels to those required for
Office Building
General office space
High density open office space
Reception areas
Telecommunications/data entry
Conference rooms
Main entry lobbies
Excerpt of Table 6.1b (Converted to S-I units) from ASHRAE Standard 62-1989

INDOOR AIR QUALITY DESIGN PROCEDURE

The Indoor Air Quality Procedure provides a direct solution
by restricting the concentration of all known contaminants of
concern to specified acceptable levels. This procedure lists
acceptable levels for CO , chlordane, ozone, and radon gas
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and references many other potential contaminants without
defined limits. The use of CO
inferred. The limit of 1000 ppm is recommended to satisfy
comfort and odor criteria. The use of subjective evaluation
implies an occupied building which further implies changes
after occupancy.
The requirements for recirculation are similar to the
Ventilation Rate Procedure.
Maintenance of acceptable IAQ is complicated by the use of
variable air volume systems. Some designers choose to utilize
ENGINEERING MANUAL OF AUTOMATIC CONTROL
Table 4. Minimum Ventilation Requirements
Prescriptive Requirements
People R
p
L/s per person
2.83
2.83
3.30
3.30
2.36
3.30
as an indicator of IAQ is
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INDOOR AIR QUALITY FUNDAMENTALS
outdoor air and that the Indoor Air Quality Procedure must be
used. The air cleaning equipment must be designed to reduce
particulates and where necessary and feasible, gaseous
contaminants.
Spaces with variable occupancy served by a common supply
may have their fraction of the outdoor air requirement adjusted
to match the occupancy. This requires additional sensors and
controls. This can done with CO
VAV flow readings, and measurement of the outdoor air airflow.
Table 6.1b in ASHRAE Standard 62-1989 provides minimum
ventilation requirements based on per person or square foot
and nonsmoking. The table has many references and is
excerpted and converted to SI units here as Table 4 with the
recommendation that the latest ASHRAE publication on
Ventilation For Acceptable Indoor Air Quality be consulted
before using any of the data.
Simple System Requirements
Building R Outside Air R
b
2
L/s per m L/s per m
0.356
0.356
0.356
0.356
0.356
0.305
dual duct constant volume HVAC systems to simplify IAQ
control. Use of direct drive variable geometry fans and
innovative outdoor air economizer designs allow designers to
provide both IAQ and energy efficiency.
Designers frequently use constant volume terminal boxes
in their designs. One adaptation of this technology applies a
constant volume terminal box to supply 100 percent
conditioned outdoor air to a conference room when a motion
sensor indicates that the room is occupied. This air is the
ventilation component. The conference room is also served
by a fan powered variable air volume box which cools and
heats the room with centrally supplied primary air and
recirculated air. Other designers apply constant volume
terminal boxes in the outdoor air intakes of smaller VAV fan
systems to ensure minimum outdoor air at all times. This may
supply too much outdoor air at light loads depending upon the
percentage of the load represented by occupants.
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sensors, occupancy sensors,
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Supply Air R
sb
2
L/s per m
0.660 0.660
0.660 0.813
0.914 1.321
2.490 6.096
1.625 5.080
0.610 0.610
ss
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