The intent of WEp1 is to "Maximize fixture water efficiency within buildings to reduce the burden on potable water supply and wastewater systems." Meeting this prerequisite requires fixture potable water use over the performance period to be equal to or less than the baseline. Our confidential client, heretofore referred to as CC, is an existing 2 million s.f. mixed use building that consists of commercial office space and a convention class hotel. A water meter gauges the hotel's water use, but because hotels typically measure water (as well as energy use, supplies, etc.) by dividing total water use by the number of occupied rooms per year, they sometimes lack robust submetering. The challenge we face is multifaceted: The LEED-EB model for baseline calculations does not include an Occupancy Type that captures hotel guest usage patterns, which are inherently different from the closest model provided by LEED, residential use. Hotel guests may overuse water since they are not being directly metered. Also, daily housekeeping further increases water use per room. Since the current LEED-EB model does not readily incorporate hotel guest use patterns, the fixture use model is insufficient to demonstrate that fixture potable water use is less than the baseline, unless we can 1) adjust the baseline to more closely align with hotel guest usage patterns, and 2) apply the values from published reports about the hotel industry to CC's meter data. (These values suggest that CC's hotel falls within the average water use per day per occupied room for hotels of its size: 254 gallons. Importantly, whereas LEED measures water use per person, the hotel industry measures water use per room; this figure includes domestic and process water used by employees, such as bathroom breaks and food preparation.) Thus, we seek a ruling as to whether: 1) We may adjust LEED values (for duration and frequency of fixture use) so that the baseline more accurately reflects the guest water usage documented in published reports. For instance, based on a survey of hotel customers prepared for the Los Angeles Dept. of Power and Water, average daily shower duration per room is 16.2 min. Assuming 2.1 guests per room, the shower duration per person would be 8.1 min. Additionally, hotel housekeeping protocol of cleaning occupied guestrooms once per day, results in at least one additional toilet flush per room per day. 2) To calculate the hotel's fixture potable water use, we may disaggregate the metered water by applying figures found in industry studies that break down percentages of total water use by volume according to various usage sectors, including guest room and kitchen. For instance, guest rooms constitute as much as 62% of a hotel's total water use. Because CC's hotel's metered water usage falls neatly within the daily average of 254 gallons per occupied room for hotels of its size, the next step is to apply such industry percentages of total water by usage sector to calculate fixture potable water use. To truly comply with WEp1's intent, CC must be able to accurately measure its fixture potable water use against the calculated baseline. Achieving these measurements for mixed use commercial properties hotels - a building type which has not yet been standardized by LEED - requires adjustments to both the method of measuring potable water use and calculating the baseline so that buildings containing hotels may strive toward LEED certification. CC is dedicated to the LEED process and has already installed one submeter to monitor the exterior hose bibs of the property and another to monitor makeup water in a vacuum pump system. CC understands that the mixed-use nature of its building constitutes groundbreaking work under the LEED-EB standard and is willing to install additional submeters in order to further refine water use within the hotel building.
The project team seeks to a) use alternative usage patterns to the default fixture use values presented in the LEED for Existing Buildings: Operations & Maintenance Reference Guide to accommodate hotel occupants, and b) manipulate the facility's meter data for comparison with the baseline using industry figures. a) In the event that special circumstances exist in the project building that make the LEED default fixture use values inappropriate, the project team may modify these values. The altered fixture use values must be consistently applied to both the baseline case and installed case calculations, and the project team must explain in the certification application the unique circumstances that warrant the use of these values, as well as justification for the values used. Altering the average daily shower duration based on Los Angeles Dept. of Power and Water data, for example, qualifies as a valid justification for deviating from the LEED default shower duration figure. With respect to cooling tower makeup, the project team should list the number of tons, the evaporation rate and number of cycles to be used based upon the proposed condenser water treatment, thereby calculating the amount of makeup required for the cooling tower. Based upon the estimated full load hours, the annual makeup rate for the tower can be calculated. Using similar parameters and calculation technique, the revised makeup could be calculated taking into account new water treatment increasing the number of cycles and providing more efficient drift eliminators at the tower. A similar calculation could be performed utilizing baseline kitchen fixtures and equipment and assumed hours of operation and comparing the new water usage based upon the new types of fixtures and equipment and the same hours of operation as in the baseline case. b) Because WE Prerequisite 1 and WE Credit 2 are not awarded based on comparing metered data to the calculated baseline, it is not necessary nor appropriate to apply industry percentages of water use by sector to meter data to estimate fixture potable water use in the project building. The project team must assess prerequisite and credit compliance through the calculation methodology outlined in the Reference Guide and using the submittal template calculator. The percent reduction is derived by comparing a calculation of the baseline and the installed case using the same calculation methodology to estimate water consumption for both, and is based wholly on the flow and flush rate of installed fixtures, occupancy, and assumed fixture use patterns. Thus, there is no need to manipulate meter data or account for process water used by employees.
Related Addenda (Corrections & Interpretations)