Commissioning Instructions

Demand Control Ventilation
A6V12035398
Unrestricted
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Demand Control Ventilation
See 2019 nonresidential Compliance Manual section 4.3.7 for more information,
section 13.9 NA7.5.5 for acceptance criteria and NRCA-MCH-06-A for acceptance test
form.
Note: If this acceptance form is required (box checked on the Title 24 sheet), control
systems with DDC to the zone level are required to enable centralized demand shed at
non-critical control zones from either a single software or hardware point in the system.
The key aspect to determine whether DCV was specified properly is energy efficiency.
A VAV box with DCV should use less energy than the exact same VAV box
without DCV, even when the CO2 sensor has failed or drifted.
See 2019 nonresidential Compliance Manual section 4.3.4 for more information on
ventilation rates, typically for each space requiring mechanical ventilation the
ventilation rates must be the greater of either:
1. The conditioned floor area of the space, multiplied by the applicable minimum ventilation rate
for example 0.15 cfm/ft2. This provides dilution for the building-borne contaminants like off-
gassing of paints and carpets, or
2. 15 cfm per person, multiplied by the expected number of occupants. For spaces with fixed
seating (such as a theater or auditorium); the expected number of occupants is the number of
fixed seats. For spaces without fixed seating, the expected number of occupants is assumed to
be no less than one-half that determined for egress purposes in the California Building Code
(CBC). The Energy Standards specify the minimum outdoor ventilation rate to which the system
must be designed. If desired, the designer may, with documentation, elect to provide more ven-
tilation air. For example, the design outdoor ventilation rate may be determined using the pro-
cedures described in ASHRAE 62, provided the resulting outdoor air quantities are no less than
required by the Energy Standards.
Note that CO2 concentration only tracks indoor contaminants that are generated by occupants
themselves and, to a lesser extent, their activities. It will not track other pollutants, particularly
volatile organic compounds (VOCs) that off-gas from furnishings and building materials. Hence,
where permitted or required by the Energy Standards, demand controlled ventilation systems
cannot reduce the outdoor air ventilation rate below the floor rate listed in Energy Standards
Table 120.1-A (typically 0.15 cfm/ft²) during normally occupied times.
It is recommended that Demand Control Ventilation (DCV) be implemented using the
minimum/maximum airflow volumes based on the prescriptive airflow rates defined by
the EOR (engineer of record)
1. Determine the minimum airflow for the zone based on a Minimum ventilation air-
flow rate for the zone of 0.15 CFM/sq ft.
2. Determine the maximum airflow for the zone based on a Maximum ventilation air-
flow rate for the zone in DCV of 15 CFM/person.
3. The CO
2
set point should be OA_PPM + 600 ppm; where OA_PPM can be as-
sumed to be 400 ppm (ie, outdoor CO2 concentration (ppm).
Example for office area:
The design outdoor ventilation air is the larger of
• 12 people x 15 cfm/person = 180 cfm, or
• 1,000 ft² x 0.15 cfm/ft² = 150 cfm