Rating System

LEED BD+C: New Construction

Rating System Version

v3 - LEED 2009, v2 - LEED 2.2

Inquiry

We are trying to determine the correct baseline HVAC system type for a new 9 story, 400,000 ft2 hospital in San Francisco. Per 90.1-2004 section G3.1.1 exception C, the baseline should be System Type 3 (packaged single zone systems with DX cooling) in ".any zones having special pressurization relationships, cross contamination requirements, or code required minimum circulation rates." This exception is vague but appears to require System 3 in almost all hospital zones since almost all hospital zones have "special pressurization relationships, cross contamination requirements, or code required minimum circulation rates." We are not aware of any large, multi-story hospitals in the U.S. that use packaged single zone systems. Such systems are simply not practical or even possible for most zones in a large hospital. For example, it would probably be impossible to find enough roof or shaft space to serve a 9 story hospital with rooftop packaged single zone units. A few exceptional hospitals are using variable air volume (VAV) reheat in some zones with special pressurization requirements but the majority of hospitals being built today use constant volume (CV) reheat in such zones. The 90.1 baseline is intended to represent the industry standard of care and constant volume reheat (not packaged single zone) is the current standard of care where pressurization is required. Constant volume is the industry standard because it is simpler and considerably less expensive and less maintenance than variable volume. Constant volume systems in hospitals either have no terminal units or have standard CV terminal units on the supply side but not on the return/exhaust side. VAV systems, on the other hand, require terminal units on both the supply and return/exhaust sides. Furthermore, terminal units in VAV systems in California are typically not standard VAV terminal units (e.g. butterfly damper type) but are special airflow control devices (e.g. Phoenix valves) due to the local oversight agency\'s (OSHPD\'s) stringent room relative pressure requirements and lint issues for standard VAV terminals on the exhaust side. Such control devices are considerably more expensive than standard VAV terminal units. Therefore we request confirmation that the following clarification (for hospitals only) of 90.1-2004 section G3.1.1 exception C provides a suitable baseline in accordance with the intent of LEED