Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.0

Inquiry

Our project is a student recreation center in an urban location. We have proposed a rainwater harvesting system that will collect roof and site stormwater to be stored in two 8,000 gallon cisterns for irrigation use. Irrigation will not be required during several months of the year, so the irrigation season will start with full tanks. There is a backup system that uses potable water if the cisterns are empty. Our Design Case calculation shows that the irrigation water needed in July exceeds the 16,000 gallons that can be stored in the cisterns, pursuant to the required methodology and calculations. We calculate that we need 26,370 gallons of water based on mostly native vegetation with a small amount of sodded lawn (university requirement). The calculations and methodology presented in WEc1.2. assumes that all of the rainfall occurs at one time, fills the cisterns to their 16,000 gallon capacity and the rest bypasses to the municipal stormwater system. Is it possible to break the rainfall amount for July into four separate, smaller rainfall events that would occur throughout the month? (This is closer to naturally occurring events than one large monthly storm event.) By distributing the rainfall throughout July, the water in the cisterns would be used and replenished throughout the month. Any clarification you can provide on this issue is appreciated.