Proposed Changes Related to Combustion Safety, Infiltration
March 29, 2012 | By HPAC Magazine
Public comment is being sought on proposed changes to ASHRAE’s residential indoor air quality standard regarding combustion safety in existing homes and default infiltration in new construction. ANSI/ASHRAE Standard 62.2-2010, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings, is the only nationally recognized indoor air quality standard developed solely for residences. It defines the roles of and minimum requirements for mechanical and natural ventilation systems and the building envelope intended to provide acceptable indoor air quality in low-rise residential buildings. Five proposed addenda to Standard 62.2-2010 currently are open for public review. For more information, visit www.ashrae.org/publicreviews. Proposed addendum p applies primarily to existing homes. The standard as written addresses combustion safety mainly in a prescriptive manner, with the assumptions that went into determining the requirements based on typical construction for new homes. Given the characteristics in older homes, especially leakage levels, following these requirements precisely often could have resulted in requiring replacement of equipment that in practice works fine. Also open for public comment is addendum r, which has a larger impact on new construction. Historically, Standard 62.2 has allowed all homes to have a default infiltration credit that can be taken without any knowledge about how leaky the house really is, according to Paul Francisco, vice chair of the Standard 62.2 committee. As houses have gotten tighter, the assumed infiltration may be substantially higher than actually exists in many homes, notes Francisco.
“This addendum removes the default credit, and allows infiltration to be credited only if infiltration is measured,” he said. “This has the effect in new construction of requiring sufficient mechanical ventilation to provide the entire intended air exchange, thereby ensuring that the intended overall rates are achieved, or that a test is done to measure infiltration. Without that test, the installed mechanical ventilation will increase. With the test there will be little change in installed mechanical ventilation rates.”
Addenda p and r are open for public review from March 23 until May 7.
Three additional addenda are open for public review from March 23 until April 22. They are:
• Addendum a would remove Method A of ASTM E1554 as an option for the duct tightness testing in the newly proposed Section A4.1.
• Addendum o clarifies that a system must be operated in order to achieve the stated purpose of the standard to define minimum requirements for acceptable indoor air quality. Currently the standard is being interpreted by some to say that a system could be installed and turned off and still be in compliance.
• Addendum q – Historically, local exhaust fans have been permitted to serve the dual function of providing whole-house ventilation and local exhaust. When serving as dual-duty fans, the whole-house rate and the local exhaust rate have not been required to be additive. This proposed change is needed to clarify that the whole building ventilation rate can be credited towards the local exhaust rate, and that the rates are not required to be additive, according to Francisco.