Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.0

Inquiry

This project is a new approximately 4000 square foot Emergency Medical Services (EMS) station in Austin, which will be occupied 24/7. This question pertains to EA Credit 1 (Optimize Energy Performance) and relates to the determination of the baseline HVAC system. The two systems proposed by the mechanical engineer are: Option 1: One ductless split system heat pump per zone. Outside air will be provided to the zones by one central outside air unit with DX cooling and gas heating. (Single zone AC, multi-zone ventilation) Option 2: Ducted DX split systems serving multiple zones with gas heating. Outside air same as in #1 above. (Multi-zone AC, multi-zone ventilation) In our current baseline modeling, we selected the baseline system in accordance with ASHRAE 90.1-1999 section 11.4.3. This section offers three possible system type categories. The applicable category for baseline modeling is based on the type of system proposed in the actual design. The possible system categories are \'Single Zone Residential\', \'Single Zone Non-Residential\', and \'All Other\'. Given that ventilation outside air for either of the two proposed systems above is multi-zone, we categorized the proposed system as \'All Other\'. According to ASHRAE 90.1-1999 Figure 11.4.3 the baseline system is a Packaged VAV with parallel fan-powered boxes and VAV fan control. Question #1: Is this baseline system correct? Question #2: Does this system qualify for the exception (b) of ASHRAE 90.1-1999 6.3.2.1? ASHRAE 90.1-1999 allows for the baseline modeling of a constant-volume packaged unit with parallel fan-powered boxes in place of the packaged VAV system with parallel fan-powered boxes if a VAV system would be considered impractical for the subject project. Question #3: Since system #1 is single-zone, we would like to know if we can base our modeling of the baseline system chosen by the \'Single Zone Non-Residential\' category. Using this category will require a baseline system that is significantly different than the baseline system currently required under the \'All Other\' system category. In short, in our use of ASHRAE 90.1-1999 11.4.3, do we have flexiblity to treat the HVAC system as single-zone, although ventilation air is provided with a multi-zone system?