Below is a previously submitted credit interpretation that was accepted. Our project is almost identical to the situation that is outlined. The primary difference between our project and the one described, is that we don't expect specific approval from the Jurisdiction per the exception to 5.1. The question is whether GBCI will approve the method described below without any additional approval documentation from the Jurisdiction? The Jurisdiction will most certainly approve our ventilation to meet local code requirements, but we do not believe that is the intention of the exception to 5.1. Your thoughts would be appreciated.

11/12/2008 - Credit Interpretation Request

This is a (4) story multifamily residential project. We would like an interpretation on the requirements of EQ prerequisite 1 as it relates to naturally ventilated spaces that are not within 25 feet of an operable opening to the outdoors.

According to the CIR dated 5/15/2007, the question was asked whether or not naturally ventilated spaces with air transfer to mechanically ventilated spaces are considered mixed mode. The response stated "these spaces will be considered naturally ventilated, if they meet the criteria outlined in section 5.1 of ASHRAE 62.1-2004. This CIR allows the outside air being delivered to the corridors be used for transfer air to the living units.

In our proposed design, the living units are conditioned using DX split system air handling units. Per Table E-2, "ventilation is normally satisfied by infiltration and natural ventilation." Most spaces in the living units satisfy the requirements of natural ventilation thru operable doors and windows per the natural ventilation section of ASHRAE 62.1-2004, Section 5.1.1. However, there are some units where a portion of the naturally ventilated space (interior den and entry corridor) is not within 8 m (25 feet) of the operable wall opening to the outdoors. These spaces will be ventilated by means of air infiltrating via the unit entry doors from the pressurized, conditioned and outdoor air-ventilated corridors.

The reasoning behind this approach is that the unit entry doors serve as a means for uncontrolled inward air leakage to the units caused by pressure difference between the corridors (positively pressurized) and the units. The corridors are mechanically conditioned and ventilated via split systems with ducted outside air at a rate of 0.075 cfm/ft2; exceeding the corridor ventilation requirement of 0.06 cfm/ft2. Based on this, the entry doors to the living units will provide additional outdoor air each time the occupant enters and leaves the unit.

Further, this approach has been accepted by the local code authorities having jurisdiction over this project.

Question 1: Based on the referenced CIR, the definitions of infiltration and transfer air, does the design approach of using air infiltrating to the units from the conditioned corridor via the unit entry doors satisfy the minimum ventilation requirements? Please note this will be only for small portions of naturally ventilated spaces (less than 20 sf) that are not within 25 feet of operable wall opening to the outdoors.

Question 2: If not, then what is an acceptable approach to meet the minimum ventilation requirements for spaces that are not within 25 feet of operable wall or roof opening to the outdoors?

1/13/2009 - Ruling

Per ASHRAE Standard 62.1-2004, “Exception to 5.1: An engineered natural ventilation system when approved by the authority having jurisdiction need not meet the requirements of 5.1.1 and 5.1.2.“ Given the design approach described, as well as the fact that the local authority having jurisdiction has accepted this approach, this is acceptable. Please include documentation to this effect when submitting for certification.