EXHIBIT A-2
REVIEW OF URINAL SAVINGS CALCULATIONS FOR THE PRESIDIO
By
PMCL@CDM
November 18, 2003
Water savings from the replacement of urinals are calculated as the difference in gallons per flush between the old fixture and the new fixture times the frequency of use (i.e., number of flushes per day, or per year). The flush volume of the old and new fixtures can be measured. However, the frequency of use must be assumed. This document provides a review of frequency of use assumptions regarding urinal use found in the general literature, and the frequency of assumptions used in water savings estimates for the Presidio of Monterey.
Summary
The calculation of water savings from the installation of waterless urinals requires knowing the frequency of fixture use. This information is difficult to obtain and thus water savings are typically based on assumed values for the frequency of urinal use. Such assumptions vary widely and are generally undocumented.
The assumed frequency of urinal use determined by Black & Veatch for the Presidio of Monterey is well documented and is calculated from rational assumptions. The subsequent calculation by PMCL of frequency of urinal use at the Presidio of Monterey improves upon the information used by Black & Veatch to provide a reasonable (although conservative) estimate of the average rate of urinal fixture use. The level of detail provided in these calculations is more advanced than the assumptions found in the general literature regarding the frequency of urinal use.
|
Source |
Number of
Uses per Hour per Fixture |
|
PMCL |
3.39 flushes/hour |
|
Black & Veatch |
2.6 flushes/hour |
|
DOE – FEMP |
2.14 – 3.75 flushes/hour |
|
New Mexico State Engineer |
12.3 – 25.0 flushes/hour |
|
Waterless Company |
8.6 – 15.0 flushes/hour |
|
Falcon Company |
8.3 – 20.3 flushes/hour |
Had the estimate of urinal water savings at the POM been based on general standards recommended by the manufacturers, rather than the PMCL-calculated frequency of use, the estimated savings would have been significantly higher.
1) The U.S. Department of Energy, Federal Energy Management Program (FEMP) brochure How to Buy a Water-Saving Replacement Urinal compares the average water use of a 3.0 gallon per flush (gpf) fixture, 1.0 gpf fixture, and 0.0 gpf fixture.
|
Gallons per Flush |
3.0 gpf |
1.0 gpf |
0.0 gpf |
|
Annual Water Use |
23,400 gallons |
7,800 gallons |
0 gallons |
“Savings estimates are based on the flush rate for an existing unit of 3.0 gpf. Urinal use is assumed to be 30 flushes per day, 260 days per year.” – FEMP November 2000. (www.eere.energy.gov/femp/procurement/pdfs/urinal.pdf)
Note that the assumption that a urinal is flushed an average of 30 times per day can be divided by the number of hours per day that a building is open to provide an estimate of the average number of flushes per hour.
|
Flushes per Day |
Hours of Operation |
Flushes per Hour |
|
30 |
14 |
2.14 |
|
30 |
12 |
2.5 |
|
30 |
10 |
3.0 |
|
30 |
8 |
3.75 |
2) The New Mexico Office of the State Engineer published A Water Conservation Guide for Commercial, Institutional and Industrial Users (July 1999). Regarding the installation of waterless urinals, the report states:
“Replacing a 2.0 gpf urinal with a waterless variety in a typical office building can save 44,000 gallons per year (assuming urinal was used 200 times a day for 220 days per year).” – page 36. The source of these assumptions is not identified.
Note that the math in this statement is incorrect. Water savings of 44,000 gallons per year divided by 220 days equals savings of 200 gallons per day. Dividing this by 2.0 gpf is equal to 100 flushes per day, not 200. Conversely, water savings of 2.0 gallons per flush times 200 uses per day is 400 gallons per day, times 220 days per year equals 88,000 gallons per year.
Using the assumed value of 200 flushes per day to calculate an hourly frequency of use produces a high rate of use such as might occur in high traffic location (12.3 flushes per hour is equal to one flush every five minutes) not likely to be sustained throughout the day.
|
Flushes per Day |
Hours of Operation |
Flushes per Hour |
|
200 |
14 |
12.3 |
|
200 |
12 |
16.7 |
|
200 |
10 |
20.0 |
|
200 |
8 |
25.0 |
This calculation probably represents the frequency of use for all urinals in a typical office building, rather than the frequency per urinal. Dividing the assumed 200 flushes per day by the FEMP assumption of 30 flushes per day per urinal suggests an average of 6.7 urinals per typical office building.
3) The Waterless Company is the purveyor of the Waterless® urinal. Their literature states: “A typical office building rest room with 3 urinals and 120 men equals a yearly water use of 237,000 gallons of potable water flushed down the drain. This assumes 3 uses per person per day and only 220 working days.” (http://www.waterless.com/conserva.htm)
This calculation assumes that the replaced fixtures use 3.0 gallons per flush. The calculation of 120 men times 3 uses per day equals 360 uses per day, times 220 days equals 79,200 uses per year. This number divided into the annual savings of 237,000 gallons means 3.0 gallons per use.
The 360 uses per day divided by the number of urinals equals 120 flushes per urinal per day.
|
Flushes per Day |
Hours of Operation |
Flushes per Hour |
|
120 |
14 |
8.6 |
|
120 |
12 |
10.0 |
|
120 |
10 |
12.0 |
|
120 |
8 |
15.0 |
These calculations are all contingent upon the
assumed number of men (120) in the building.
4) Falcon Waterfree Technologies, LLC is the purveyor of the Waterfree® urinal. Their literature cites the following case study:
In September 2000, Falcon Waterfree
Technologies, LLC. (FWT) arranged with the University of California Los Angeles
(UCLA) to install a Falcon Waterfree urinal in a men's restroom in Boelter Hall
(classroom building) on campus for the purpose of: (a) measuring usage, (b)
comparing bacterial growth rates and odors with traditional flush urinals and
(c) performing lifecycle cost analysis modeling of waterfree urinal
installation within typical educational institutions. The assignment was
performed by the UCLA Department of Civil and Environmental Engineering under
the leadership of Professor Birgitte K. Ahring, Ph.D. Measured over a period of
six weeks, the Falcon Waterfree urinal averaged 814 uses per week. (http://www.falconwaterfree.com/ucla.htm)
Water savings are not reported, nor are any other statistics related to
the frequency of use. The reported 814 uses per week could translate into a
range from 8.3 uses per hour (based on 7 days per week and 14 hours per day) to
20.3 uses per hour (based on 5 days per week and 8 hours per day).
5) Peter Mayer, vice president of Aquacraft, Inc., has conducted numerous studies pertaining to the end uses of water use. Aquacraft and PMCL co-authored studies for the American Water Works Association Research Foundation on residential end uses of water, and well as commercial and institutional end uses of water. Mr. Mayer is also active in the AWWA water use efficiency committee and is familiar with current research projects on water use efficiency. Mr. Mayer is not aware of any studies that have specifically measured the frequency of use for urinals. Primarily, measurement of frequency of use requires the installation of metering devices on individual fixtures, which is expensive and as yet no one has been willing to fund such a study. His recommended estimate is to assume four restroom visits in an eight hour day (once every two hours, or 0.5 visits per hour) and for males assume that 3 out of 4 visits are urinal uses (Personal communication, November 6, 2003).
Black & Veatch conducted a survey of water use fixtures in buildings at the Presidio of Monterey (POM) in 1998. Their analysis estimated the potential for water conservation at the POM. Black & Veatch calculated average urinal use in non-housing facilities as follows:
· 4,300 student/teacher/employee population
· 4 restroom visits per day per person (in 8 hour work day)
· 50 percent male
· 50 percent male restroom visits use urinal
· Therefore, 4,300 total urinal uses per day for non-housing facilities
· 347 urinals at POM (138 in housing, and 209 in non-housing facilities)
· Therefore, (4300/209) 20.6 flushes per day per urinal in non-housing facilities
The estimated 20.6 flushes per day per urinal divided by the assumed eight-hour day equals an average use rate of 2.6 flushes per hour per urinal. The Black & Veatch analysis assumed 250 days per year of operation at POM non-housing facilities. This assumption indicates that facilities are closed on weekends and holidays.
PMCL Assumptions for the
Presidio of Monterey
The PMCL estimate of frequency of urinal use began with the Black & Veatch assumptions. The assumption that student, faculty and employee population is 50 percent male was revised to 66 percent male based on information from the POM administrative office. Furthermore, the Black & Veatch assumptions that buildings were in operation 8 hours per day for 250 days per year were updated. POM staff provided the hours of operation and number of days per year of operation for each building in which waterless urinals were installed. This information is shown by building in Table V-2 of the Technical Memorandum.
Since the POM non-housing facilities have different hours of operation per day, it was necessary to calculate the average urinal flushes per hour. The hourly rate of use is calculated as follows:
· 4,300 student/teacher/employee population
· 66 percent male
· 0.5 restroom visits per hour (i.e., once per two hours)
· 50 percent male restroom visits use urinal
· Therefore, 709.5 total urinal uses per hour for non-housing facilities
· 209 urinals in non-housing facilities
· Therefore, 3.39 flushes per hour per urinal in non-housing facilities
Note that the proportion of urinal use per restroom visit for males is conservative (i.e., low) relative to the recommendation by Mr. Mayer. Using his recommendation that 75 percent of male restroom visits are urinal uses would result in an hourly urinal use rate of 5.09 uses per hour per urinal at the POM non-housing facilities.
This hourly rate of urinal use (3.39) is multiplied by the hours of operation of each building, the number of replaced urinals, and the flush volume of the replaced to determine the average gallons saved per day per building. The daily savings per building is multiplied by the annual number of days of operation for each building to estimate annual water savings, as shown in Table V-2 of the Technical Memorandum.
Water savings for the gym are calculated as the average daily traffic flow (1,093 persons per day), the percent males (80 percent), and an assumed value of one urinal use per male visitor, as also shown in Table V-2.
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