Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.2

Inquiry

This CIR is a follow-up to the 2/26/2007 ruling for our 120,000 sq. ft. laboratory project. The EAc1 ruling dated 2/26/2007 indicates "the project may opt to model the VAV system as energy neutral". Does this include the exhaust fan system? G3.1.2.9 indicates the baseline "System fan electrical power for supply, return, exhaust and relief (excluding power to fan powered VAV boxes) shall be calculated using the following formulas". This formula listed may be suitable for determining baseline fan power in an office, but it seems like the fan power for any lab building would significantly exceed this number because of the exhaust fan requirements, pressure drop through fume hoods and exhaust air valves, etc. For example, a typical lab could have 0.01 to 0.05 inches of room differential pressure, plus 0.5 inches drop through the fume hood, plus 0.2 to 0.6 inches through the exhaust air valve, and plus 0.75 to 1.5 inches through the exhaust HEPA filter. This totals to about 1.46 to 2.65 inches of additional pressure drop for a lab exhaust system vs. office exhaust. The lab exhaust may also have about 0.5 inches of additional pressure drop associated with generating stack velocity on the discharge of the fan. Lab exhaust will have a slight pressure drop reduction from office exhaust since the lab system will not have fire dampers (0.2 to 0.3 inches), but this is not enough to offset all the other lab system pressure drops. For our specific project, we have modeled both the baseline and proposed case as VAV systems per the 2/26/2007 ruling. When we use G3.1.2.9 to calculate the supply and exhaust fan power in the base case and we model the proposed case with our actual supply and exhaust fans, the proposed case fan power is more then double the base case due to the exhaust fans. The proposed case fan power is greater then 500,000 kwh per year while the base case is closer to 200,000 kwh per year. For our proposed model, both the supply and exhaust are variable speed with high efficiency motors, but we are still penalized on fan power when comparing to the base case using G3.1.2.9. Can the VAV exhaust in a lab be modeled as energy neutral?