NA7.5.3 Air Distribution Systems Acceptance

Use Form NRCA-MCH-04-A

Purpose of the Test

The purpose of this test is to verify all duct work associated with all non-exempt constant volume, single-zone, HVAC units (i.e. air conditioners, heat pumps, and furnaces) meet the material, installation, and insulation R-values per §120.4(a) and leakage requirements outlined in §140.4(l) for new duct systems or §141.0(b)2D for existing duct systems.

As detailed in the Standards, this test is only required for single-zone units serving less than 5,000 ft² of floor area where 25 percent or more of the duct surface area is in one of the following spaces:

•      Outdoors, or

•      In a space directly under a roof where the U-factor of the roof is greater than the U-factor of the ceiling, or

•      In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces, or

•      In an unconditioned crawlspace; or

•      In other unconditioned spaces.

Within this criteria, this test applies to both new duct systems and to existing duct systems which are either being extended per §141.0(b)2D or the space conditioning system is altered by the installation or replacement of space conditioning equipment per §141.0(b)2E, including: replacement of the air handler; outdoor condensing unit of a split system air conditioner or heat pump; cooling or heating coil; or the furnace heat exchanger. Existing duct systems do not have to be tested if they are insulated or sealed with asbestos.

Instrumentation

Performance of this test will require measuring duct leakage. Equipment used:

Fan flow meter (a fan with a calibrated orifice used to pressurize the ducts) accuracy within 3 percent of measured flow. Contact CalCERTS, USERA, or CHEERS for proper equipment.

Digital manometer (pressure meter) accuracy within 0.2 Pascals.

Duct leakage tests must be verified by a third party HERS rater who has been certified by a HERS provider that has been approved by the California Energy Commission. There are currently three companies that certify HERS raters. They can be found at http://www.CalCerts.com  http://www.usenergyraters.com/ or http://www.CHEERS.org.

Test Conditions

For new construction all ductwork must be accessible for visual inspection. Hence, visual inspection must be performed before the ceiling is installed.

All ductwork and grilles should be in place before performing the fan flow test to ensure system depicts normal operating configuration. Hence, testing must occur after visual inspection and installation of the diffusers.

HVAC system must be installed and ready for system operation, including completion of all start-up procedures, per manufacturer’s recommendations.

Estimated Time to Complete

Construction Inspection: 0.5 to 2 hours (depending on duct access for visual inspections and availability of construction material documentation (i.e. cut sheets, etc.)

Equipment Test: 3 to 6 hours (depending on how long it takes to seal all supply diffusers and return grills.

Acceptance Criteria

Flexible ducts are not compressed or constricted in any way.

Duct connections meet the requirements of §120.4 (new ducts only).

Joints and seams are properly sealed according to requirements of §120.4 (new ducts only).

Duct R-values meet the minimum requirements of §120.4(a) (new ducts only).

Insulation is protected from damage and suitable for outdoor usage per §120.4(f) (new ducts only).

The leakage fraction for new HVAC ducts does not exceed 6 percent per §140.4(l), where the leakage fraction is calculated by dividing total measured leakage flow rate by the total fan system flow rate.

The leakage fraction for existing HVAC ducts does not exceed either 15 percent or overall system leakage is reduced by a 60 percent per §141.0(b)2D. The leakage fraction is calculated by either dividing total measured leakage flow rate by the total fan system flow rate OR by comparing “pre-modification” and “post-modification” measured system leakage values.

Obtain HERS Rater field verification as described in Reference Nonresidential Appendix NA1.

Potential Issues and Cautions

If this test is to be applied to existing duct systems that are having alterations made to the ducts or the HVAC equipment attached to the ducts, test the system leakage before making the alterations.

Ensure all of the supply and return diffusers/grills are sealed tightly, all access panels are in place, and duct ends are sealed tightly prior to leakage testing.

After the test, remember to remove all blockages from the supply and return ducts (i.e., where the supply and return ducts at the HVAC unit were blanked off).Seal any holes drilled in the supply and return ducts for the static pressure probes.

Since a certified California HERS rater must also verify duct leakage performance, it may be prudent to coordinate this test with the HERS rater so that the HERS rater can witness/verify the test simultaneously.