© Copyright CalCERTS, Inc. 2019
Code Cycle: 2019 Non-Residential Standards
Reference: 2019 CalCERTS Non-Residential Training Manual Chapter 5
Mechanical Ventilation System Types
Reference: NRCM 184.108.40.206
There are generally three system types available for meeting the dwelling unit ventilation requirement (refer to Residential Compliance Manual Section 4.6.2 for descriptions of the system types identified below):
1. Exhaust Ventilation – Air is exhausted from the dwelling unit and replaced by infiltration.
2. Supply Ventilation – Outdoor air is supplied directly to the dwelling unit after being filtered.
3. Balanced Ventilation – may be a single packaged unit containing supply and exhaust fans that moves approximately the same airflow through a heat or energy recovery core, or may utilize separate fans without heat exchange. In both cases air supplied from outdoors must be filtered (see NRCM 4.3.1 for air filter requirements).
Multifamily Ventilation Systems:
- Exhaust and balanced systems are most frequently used in multifamily buildings, but supply ventilation may also be used.
- Exhaust (or supply) systems in low-rise buildings typically use individual fans located in the dwelling units that exhaust directly to outdoors.
- Central ventilation shafts and fans that are shared with multiple dwelling units in the building are more common in mid-rise and high-rise buildings.
When a supply or exhaust system provides dwelling unit ventilation to more than one dwelling unit:
- The airflow's must be balanced to provide ventilation airflow for each dwelling unit served at a rate equal to or greater than the required ventilation rate.
- The airflow's for each dwelling unit must also be balanced to be no more than twenty percent greater than the required rate (see Standards Section 150.0(o)1F).
Mechanical Ventilation Airflow Rate Verification
Supply and Exhaust Ventilation Systems
2. Measure and record the ventilation airflow(s).
3. If the measured airflow is greater than or equal to the ventilation airflow rate required by the Standards or the Certificate of Compliance, the mechanical system complies. Otherwise, the mechanical ventilation system does not comply, and corrective action shall be taken.
Balanced Ventilation Systems
1. A flow measuring device that meets the applicable instrumentation requirements given in Section NA220.127.116.11 and NA18.104.22.168 shall be used to measure the ventilation airflow's.
2. Confirm that both the supply side and the exhaust side of the balanced system operate simultaneously in response to a shared system control.
3. Measure the airflow rate for the exhaust side of the system.
4. Measure the airflow rate for the supply side of the system.
5. Calculate the percent difference between exhaust and supply airflow rates.
6. Calculate the average of the exhaust and the supply airflow rates.
7. If the exhaust and supply airflow rates are within 20% of each other, and the average of the exhaust and supply airflow rates is greater than or equal to the airflow rate required by the Standards or the Certificate of Compliance, the balanced ventilation system complies. Otherwise, the system does not comply, and corrective action shall be taken.
See attachment for balanced ventilation example
Multifamily Building Central Shaft Ventilation Systems
Reference: NRCM 22.214.171.124.1.15
Use of central ventilation fans/shafts that are shared with multiple dwelling units in the building are more common in mid-rise and high-rise buildings. When a supply or exhaust system provides dwelling unit ventilation to more than one dwelling unit, the airflow's in each dwelling unit must be equal to or greater than the required (minimum) ventilation rate, and the airflow's for each dwelling unit must also be balanced to be no more than 20 percent greater than the specified rate. The specified rate for the systems that share a common fan/shaft may be the minimum rate required for compliance, in which case each of the dwellings receiving airflow from a common fan/shaft must have ventilation airflow no more than 20 percent greater than the minimum dwelling unit ventilation airflow required by Equation 120.1-B. If the lowest airflow provided to any of the dwellings served by the common fan/shaft is a specific percent value greater than the minimum required for compliance, then the each of the dwellings receiving airflow from that common fan/shaft must have ventilation airflow no more than 20 percent greater than that lowest dwelling unit ventilation airflow.
If the lowest ventilation airflow among all dwellings served by the common fan/shaft is 2 percent greater than the minimum required for compliance, then all dwellings served by the common fan/shaft must be balanced to have ventilation airflow that is no more than 22 percent greater than the
minimum ventilation airflow required for compliance.