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Intent:
To provide capacity for
ventilation system monitoring to help
promote occupant comfort and well-being.
Requirements:
Install permanent
monitoring systems to ensure that
ventilation systems maintain design minimum
requirements. Configure all monitoring
equipment to generate an alarm when the
airflow values or carbon dioxide (CO2)
levels vary by 10% or more from the design
values via either a building automation
system alarm to the building operator or a
visual or audible alert to the building
occupants.
AND
Mechanically Ventilated Spaces -
Monitor CO2 concentrations within
all densely occupied spaces (those with a
design occupant density of 25 people or more
per 1,000 square feet). CO2
monitors must be between 3 and 6 feet above
the floor.
Provide a direct outdoor airflow measurement
device capable of measuring the minimum
outdoor air intake flow with an accuracy of
plus or minus 15% of the design minimum
outdoor air rate, as defined by ASHRAE
62.1-2007 (with errata but without addenda)
for mechanical ventilation systems where 20%
or more of the design supply airflow serves
nondensely occupied spaces.
Naturally Ventilated Spaces - Monitor
CO2 concentrations within all
naturally ventilated spaces. CO2
monitors must be between 3 and 6 feet above
the floor. One CO2 sensor may be
used to monitor multiple spaces if the
natural ventilation design uses passive
stack(s) or other means to induce airflow
through those spaces equally and
simultaneously without intervention by
building occupants.
Implementation:
Building HVAC systems
are designed to flush out indoor airborne
contaminants by exhausting old air and
replacing it with outdoor air. The rate of
ventilation air exchange is usually
determined during the design phase, and is
based on density and type of occupancy. Many
conventional ventilation systems do not
directly measure the amount of indoor air
that is delivered. Implementation of the
following strategies is recommended to
achieve this credit.
Outdoor Air Flow Monitoring -
Monitoring the outdoor air flow rate
confirms that the HVAC equipment is
providing the required ventilation rate. Air
balance control methodologies, such as
fan-tracking and measuring
building-pressurization, do not directly
prove that appropriate ventilation air is
being provided and do not satisfy the credit
requirement. The ventilation rate can be
measured at the outdoor air intake of an air
distribution system using a variety of
airflow devices, including Pitot tubes,
Venturi meters, rotating vane anemometers,
and mass air flow sensors. These sensors
must be installed according to the
manufacturer's best practices guidelines.
The ventilation rate for a particular HVAC
system can be accurately determined from a
mass balance calculation if both supply air
flow and return air flow are directly
measured with air flow monitoring devices.
To satisfy the requirements of this credit,
the measurement devices must detect when the
system is 15% below the design minimum
outdoor air rate. When the ventilation
system fails to provide the required levels
of outside air, the monitoring system should
be configured to deliver a visible or
audible alert to the system operator to
indicate that operational adjustments might
be necessary.
The minimum outdoor air rate might change
based on the design and modes of the HVAC
system. Constant volume systems with a
steady-state design occupancy conditions
usually have different outdoor air rates for
weekdays and nighttime or off-peak
conditions. In variable air volume systems,
the rate of outdoor air needs to stay above
the design minimum, even when supply air
flow is decreased because of reduced thermal
load conditions.
CO2 Monitoring - CO2
monitors can also measure the
effectiveness of the ventilation system in
delivering outdoor air. Properly placed CO2
monitors can confirm that a
ventilation system is functioning properly.
There are 2 typical system configurations
that generally meet the requirements of this
credit.
The first approach involves CO2
sensors that use measured concentration to
provide an alert if the ventilation system
is not functioning properly. An indoor
concentration of 1,000 parts per million (ppm)
was commonly used in the past as the set
point for the alarm, but a higher alarm
concentration may be appropriate when the
design complies with Standard 62.1-2007,
because the effective ventilation rate per
person has been reduced significantly for
some zones.
Locate CO2 monitors so that they
provide accurate representative readings of
the CO2 concentrations in
occupied spaces. Multiple CO2
monitoring stations throughout occupied
spaces provide better information and
control than a single CO2 monitor
for the entire system. A single CO2
monitor, typically installed in the
return air duct, is less expensive and
easier to use than providing multiple
sensors, but it may not be able to identify
underventilated areas in the building.
The second approach for buildings with HVAC
systems that have limited airflow monitoring
capabilities (small capacity air handling
units or split systems) is to use
differential CO2 monitoring to
satisfy the credit requirements. This
approach requires CO2 monitors in
all occupied spaces, an outdoor CO2
monitor, and a means by which the air
handling units can provide a greater amount
of outside air if the CO2 delta
between the spaces reaches or exceeds 530
ppm.
For outdoor CO2 sensors, use
reliable measurement data to determine
conservative set points based on an ambient
CO2 concentration. Alternatively,
use 400 ppm for the assumed constant outdoor
CO2 value, because it is a
conservative assumption and supported in
California's Title 24 energy code. |
