AnswerD
ExplanationDuct leakage in HVAC systems can significantly increase energy losses, particularly when ducts are poorly sealed or located in areas that exacerbate the impact of leakage. This issue is addressed in the LEED for Homes Rating System (v4) under the Energy and Atmosphere (EA) category, specifically in credits related to Heating and Cooling Distribution Systems.
According to the LEED Reference Guide for Homes Design and Construction (v4), the location of ducts plays a critical role in energy losses due to leakage:
EA Credit: Heating and Cooling Distribution Systems
To minimize energy losses, locate all heating and cooling ducts and air handlers within the conditioned envelope of the building. Ducts located in unconditioned spaces, such as attics, basements, or exterior walls, are more likely to lose energy due to leakage, as air escaping from ducts in these areas is lost to the outside or unconditioned zones, increasing heating and cooling loads.
Source: LEED Reference Guide for Homes Design and Construction, v4, Energy and Atmosphere Credit: Heating and Cooling Distribution Systems, p. 126.
The LEED v4.1 Residential BD+C rating system further clarifies this:
EA Credit: Optimize Energy Performance
Ducts located in unconditioned spaces (e.g., attics, unconditioned basements, or exterior walls) contribute to significant energy losses when leakage occurs, as conditioned air escapes to areas outside the thermal envelope. Sealing ducts and locating them within conditioned spaces are best practices to minimize losses.
Source: LEED v4.1 Residential BD+C, Credit Library, accessed via USGBC LEED Online.
Ducts in unconditioned attics, basements, or exterior walls are particularly problematic because any leakage results in conditioned air being lost to spaces that are not temperature-controlled, requiring the HVAC system to work harder to maintain indoor comfort. This scenario maximizes energy losses compared to ducts within the conditioned envelope.
Why not the other options?
A . Interior wall cavities are used to conduct return air: Using interior wall cavities for return air is not a best practice and may cause pressure imbalances or air quality issues, but it is less likely to cause significant energy losses due to supply duct leakage. Return air systems are typically within conditioned spaces, and the primary concern is airflow efficiency, not energy loss to unconditioned areas.
B . Duct layout includes multiple 90-degree bends on a single branch: Multiple 90-degree bends increase airflow resistance, reducing system efficiency, but they do not directly cause duct leakage. Leakage is related to unsealed joints or poor duct construction, not the geometry of the duct layout.
C . Ducts are located within conditioned envelope but joints are unsealed: While unsealed joints cause leakage, ducts within the conditioned envelope leak into spaces that are already temperature-controlled. This reduces the energy impact compared to leakage in unconditioned spaces, as the conditioned air remains within the thermal envelope.
The LEED AP Homes Candidate Handbook confirms that the exam tests knowledge of EA credits, including duct system design and energy performance, referencing the LEED Reference Guide for Homes Design and Construction as a primary resource. The handbook ensures that the exam is based on LEED v4, aligning with the focus on duct location and sealing.
References:
LEED Reference Guide for Homes Design and Construction, v4, USGBC, Energy and Atmosphere Credit: Heating and Cooling Distribution Systems, p. 126--127.
LEED v4.1 Residential BD+C, USGBC LEED Credit Library, accessed via LEED Online (https://www.usgbc.org/credits).
LEED AP Homes Candidate Handbook, GBCI, October 2024, p. 12 (references study resources and exam scope based on LEED v4).
USGBC LEED for Homes Rating System (v4), available via USGBC website (https://www.usgbc.org/resources/leed-homes-design-and-construction-v4).
LEED v4.1 for Homes, USGBC, accessed via LEED Online, confirming duct location impacts.
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