ID#2205 made on
WEc1 - Water efficient landscaping
LEED BD+C: New Construction, LEED O+M: Existing Buildings, LEED BD+C: Core and Shell, LEED BD+C: Schools
The project is a renovation of a part of a student residence hall, which is part of a large university campus facilities program. Thus, drip irrigation is not proposed due to its higher maintenance re...
The project is a renovation of a part of a student residence hall, which is part of a large university campus facilities program. Thus, drip irrigation is not proposed due to its higher maintenance requirements. The Reference Guide provides only two methods of irrigation in order to calculate efficiency: spray and drip. Spray irrigation is rated at 62.5% efficient while drip irrigation is rated at 90.0%. We feel there are more than just two options to calculate irrigation efficiency (IE) as it pertains to this credit. Not all at-grade irrigation equipment should be generalized as "spray" irrigation. There are fixed-arc spray heads, which have efficiencies as suggested by USGBC, and there are rotary heads that are more efficient. Rotary heads can provide a greater radius of coverage and dispense water at a lower precipitation rate. For the larger turf areas at this site, rotary heads provide higher uniformity. We can prove with credit submittal documentation that the IE of rotating sprinkler heads at a minimum is 75.0%. Rotary heads will not cover all turf areas; the remainder will have to be covered by fixed-arc spray heads. We are partitioning water consumption calculations in the design case by irrigation method and assigning the appropriate IE to each. Shrub areas are proposed with fixed-arc spray heads. The fixed-arc spray heads proposed have a pressure-regulating feature that reduces pressure at the nozzle to an optimum level. Fixed-arc spray head nozzles are designed to dispense a certain amount of water over a given area. A properly pressurized spray head and nozzle issues water droplets that are sized so as to not be affected by wind and sun and throw the proper distances. When pressure is too high, water droplets become finer (mist) and the spray patterns become distorted from slight breezes. This effect decreases efficiency, requiring longer irrigation times and more water to be dispensed in order to obtain the proper net result. Not all heads have the pressure-regulating feature. Heads that do contain this feature regulate pressure to their optimum of 30 psi. 60-psi pressure at the spray heads is available. Per the manufacturer's data (to be submitted), water consumption with pressure regulation is 71.0% of standard fixed-arc designs. Rotary heads do not have this feature and require the full 60-psi available. Irrigation controls are intended to automatically adjust watering times based on local climate conditions. Conventional controllers are set to turn irrigation on at the same time everyday for the same duration. The campus utilizes a central control system with weather station to manage irrigation duration. Evapotranspiration (ET)-based controllers receive central control signals and adjust irrigation times based on daily weather. Rain sensors enhance water savings further by suspending the daily irrigation cycle depending on how intense rainstorms are. The irrigation engineer calculates that an ET-based controller dispenses only 61.1% of the water used by a system with typical controls in the month of July at our location (to be submitted). In the spirit of controller efficiencies as suggested in the Reference Manual, we request that the USGBC allow us to expand the credit calculation analysis to include the efficiencies and reductions expected by specifying rotating heads, pressure-regulating heads, and ET-based controlling. Our project will have at least a 53.6% reduction in potable water consumption during the month of July compared to typical irrigation system with the same landscaping scheme.
The project is requesting clarification on whether or not efficiencies other than those associated with spray and drip irrigation heads (0.625 and 0.9 respectively) can be used in the calculations to determine total water applied. The use of alternate efficiencies for different types of irrigation heads is acceptable. However, similar to the percent reduction in water use attributed to ET-based controllers, the reported efficiencies of alternate irrigation head types must be supported by manufacturer documentation or detailed calculations by the landscape designer or irrigation engineer. The supporting calculations for the design irrigation head efficiency cannot simply be based on a comparison to the usage rate seen in a less efficient standard or baseline irrigation head as suggested by the CIR. The reported efficiency of any irrigation head type must be a measure of the amount of water that actually reaches and is used by the plant materials and must address both evaporation and drift losses. ET-based controllers are already accounted for in Equation 3 as detailed on page 121 of the LEED-NC v2.2 Reference Guide. Further, the percent reduction in water use attributed to any weather-based controller or moisture sensor-based systems must be supported by manufacturer documentation and detailed calculations by the landscape designer or irrigation engineer. Partitioning the project into areas by irrigation type is acceptable. However this does not exempt the project from demonstrating compliance with the water use calculation methods detailed in the Reference Guide. For example, the areas that are partitioned by irrigation type must obviously also take into account sub-areas with specific plant types, microclimates and densities. These sub-areas will have distinct evapotranspiration rates which should be calculated using the appropriate landscape coefficient (KL) for that area. Applicable Internationally.
Related Addenda (Corrections & Interpretations)