Making sense of leakage to the outside
Written by Stacie Bagnasco, July 26, 2017.
In California the California Energy Commission [CEC] aka Energy Standards, provide two basic methods for complying with low-rise residential energy budgets: the prescriptive approach and the performance approach. The mandatory measures must be installed with either of these approaches, but mandatory measures may be superseded by more stringent measures under either approach.
The prescriptive approach, composed of a climate zone dependent prescriptive package is less flexible but simpler than the performance approach. Each energy component of the proposed building must meet a prescribed minimum efficiency.
The performance approach is more complicated but offers considerable design flexibility. The performance approach requires an approved computer software program that models a proposed building, determines the allowed energy budget, calculates the energy use of the building, and determines when it complies with the budget. Compliance options such as window orientation, shading, thermal mass, zonal control, and house configuration are all considered in the performance approach. The approach is popular with production home builders because of the flexibility and because it provides a way to find the most cost-effective solutions for complying with the Energy Standards.
A proposed designed building is a proposed building being modeled using rules described in the Alternative Calculation Method Manual. In order for a building to comply with the standards, the proposed building energy use must be less than or equal to the Standard Design Building energy use and meet the mandatory requirements in the Title 24 Building Energy Efficiency Standards.
Compliance for certain energy efficiency measures, as specified by the CEC, requires field verification and diagnostic testing of dwelling units by a certified Home Energy Rating System (HERS) some of these measures are mandatory. In the performance approach, a number of these measures are to gain compliance credits to help your project meet or beat the proposed energy budget which is set by the “Standard Design” We are here to talk over the two instances when the diagnostic test and verification of “Leakage to the Outside” can be used or is required.
For new construction using the performance approach, here is a list of the HVAC distribution type and location descriptors that the compliance software shall allow the user to select from; Ducts located in attic (Ventilated and Unventilated),Ducts located in a crawl space, Ducts located in a garage, Ducts located within the conditioned space (except, 12 LF),Ducts located entirely in conditioned space, Distribution system without ducts (none),Ducts located in outdoor locations, Verified low leakage ducts located entirely in conditioned space, Ducts located in multiple places.
All of the distribution types listed, with the exception of “no ducts” in a newly constructed home, must be verified and registered in a HERS provider registry by a certified HERS Rater, no exemption, it is mandatory. The test compliance criteria is that any air distribution system in a Newly Constructed project must meet or beat ≤5% leakage (% of Air Handler Airflow).
In new construction when the energy consultant takes a compliance credit for VLLDCS (verified low leakage ducts in conditioned space) the Standards specify use of the procedures in Section RA126.96.36.199.8 to determine if space conditioning system ducts are located entirely in directly conditioned space, the duct system location is verified by diagnostic testing. Field Verification is required. Duct sealing is required. Verification of VLLDCS is a visual inspection to confirm space conditioning duct systems are located entirely in conditioned space. If any part of the space conditioning duct system is outside of conditioned space, the system does not pass. Additionally, ducts are to have ≤to 25 cfm” leakage to outside” when measured.
In a prescriptive approach for an alteration, as mentioned previously, the mandatory measures cannot be traded off. In “Altered” existing duct systems you are allowed ≤15% leakage (% of Air Handler Airflow) and if that test fails you are permitted to perform a “Duct Leakage to Outside” The objective of this test is to determine the amount of duct leakage to outside the air barrier for the conditioned space. This procedure is utilized to provide an alternate leakage measurement for situations when it is likely that a portion of the total duct leakage is inside the air barrier for the conditioned space (or indirectly conditioned space as defined by the CEC). The target for this particular test is ≤10% of the allowable target based on 15% of the Air Handler Airflow unit being tested. Those procedures can be found in RA188.8.131.52.4.
What we have found is that most HERS Raters opt out of performing a “leakage to the outside” test for an alteration project because they don’t own a blower door and miss opportunities to perform the “leakage to the outside” verification in new construction, when the energy consultant took a compliance credit for VLLDCS, for the same reason. By performing a “leakage to the outside” test in an alteration it presents an opportunity to show the homeowner other infiltration issues that may be going on which they may have otherwise, not known about. A picture paints a thousand words. By discovering infiltration issues and educating the homeowner, the opportunity presents itself to create revenue for your company. Working for the greater good at improving our homes health, comfort and environment is an admirable goal and one that we shouldn’t take lightly.
831 Conserve (dba Central Coast Energy Services)
BPI Building Analyst
Member of the Central Coast Greywater Alliance
HERS Whole House; Residential and Non Residential Compliance Rater