10.2 Enclosed Parking Garages

10.2.1  Overview

Garages exhaust systems are sized to dilute the auto exhaust at peak conditions to an acceptable level for human health and safety. EMCS trends of garage CO levels show that in a typical enclosed garage there are only two or three short periods of concern: in the morning when cars enter the garage; during the lunch break when cars enter and leave and at the end of the day. This prescriptive measure requires modulating ventilation airflow in large enclosed parking garages based on pollutant concentrations. By modulating airflow based on need rather than running constant volume, the system will save energy and maintain a safe environment.

Figure 10-1 – Garage CO Trends


10.2.2  Mandatory Measures

For garage exhaust systems with a total design exhaust rate ≥10,000 cfm, §120.6(c) mandates automatic controls to modulate airflow to ≤50% of design based on measurements of the contaminant levels.  This includes:

      Minimum fan power reduction of the exhaust fan energy to ≤ 30% of design wattage at 50% of design flow.  A two speed or variable speed motor can be used to meet this requirement.

      CO concentration shall be measured with at least on sensor per 5,000 ft2 with  each sensor located where the highest concentrations of CO are expected.

      CO concentration of ≤25 ppm or less as control set point at all times.

      A minimum ventilation of ≥0.15 cfm/ft2 whenever the garage is "occupied"

      Controls or design to ensure that the garage is maintained at neutral or negative pressure with respect to adjacent occupiable areas when the garage is scheduled to be occupied.

      CO sensors shall be certified to the minimum performance requirements listed under section §120.6(c) of the standards

      Acceptance testing of the ventilation system per NA7.12.


A.   Minimum Fan Power Reduction §120.6(c)2

Where required, the fan control must be designed to provide ≤30% of the design fan wattage at 50% of the fan flow.  This can be achieved by either a two speed motor or a variable speed drive.

B.   CO Sensor Number and Location §120.6(c)3

CO sensors (or sampling points) must be located so that each unique sensor serves an area no more than 5,000 ft2.  Furthermore, the standard requires a minimum of two sensors per "proximity zone."  A proximity zone is defined as areas that are separated by obstructions including floors or walls. 

The typical design for garage exhaust is to have the exhaust pickups located on the other side of the parking areas from the source of make-up air.  The ventilation air sweeps across the parking areas and towards the exhaust drops.  Good practice dictates that you'd locate sensors close to the exhaust registers or in dead zones where air is not between the supply and exhaust.  Separate floor and rooms separated by walls should be treated as separate proximity zones.

C.   CO Sensor Minimum Requirements  §120.6(c)7

To comply, each sensor must meet all of the following requirements:

      Certified by the manufacturer to be accurate to +/- 5% with less than 5% drift per year.

      Be factory calibrated

      Be monitored by the control system for faults:

      Alarm if any sensor (or sensing zone) is more than 15 ppm above or below the average of all zones form more than 4 hours.

      Alarm if during unoccupied periods if the reading of sensors in the same proximity zone differ by more than 15 ppm using 30 minute rolling averages.

10.2.3  Prescriptive Measures

There are no prescriptive measures for enclosed garage exhaust.

10.2.4  Additions and Alterations

There are no separate requirements for additions and alterations.

10.2.5  Compliance Documentation

The exhaust system must be tested per NA7.12.

Mandatory Measures Note Block

The person with overall responsibility must ensure that the Mandatory Measures that apply to the project are checked and listed on with reference to plans as noted under Notes 4 of this Compliance Form.

Project Description

PROJECT NAME is the title of the project, as shown on the plans and known to the enforcement agency.

DATE is the last revision date of the plans.  If the plans are revised after this date, it may be necessary to re-submit the compliance documentation to reflect the altered design.  Note that it is the enforcement agency’s discretion whether or not to require new compliance documentation.

Documentation Author’s Declaration Statement

The CERTIFICATE of COMPLIANCE is signed by both the Documentation Author and the Principal (Enclosed Parking Garage) Designer who is responsible for preparation of the plans of building.  This latter person is also responsible for this compliance documentation, even if the actual work is delegated to a different person acting as Documentation Author.  It is necessary that the compliance documentation be consistent with the plans.

DOCUMENTATION AUTHOR is the person who prepared the compliance forms and who signs the Declaration Statement.  The person’s telephone number is given to facilitate response to any questions that arise.  A Documentation Author may have additional certifications such as an Energy Analyst or a Certified Energy Plans Examiner certification number.  Enter number in the EA# or CEPE# box.

Principal Designer’s Declaration Statement

The Declaration Statement is signed by the person responsible for preparation of the plans for the building.  This principal designer is also responsible for this compliance form, even if the actual work is delegated to someone else (the Documentation Author as described above).  It is necessary that the compliance documentation be consistent with the plans.  The Business and Professions Code governs who is qualified to prepare plans and therefore to sign this statement.  See Section 2.2.2 Permit Application for applicable text from the Business and Professions Code.