IAPMO’s Newest Green Growth Spurt — Pipe Sizing
By Daniel P. Cole
What is new in green plumbing? Since the release of IAPMO’s Green Plumbing and Mechanical Code Supplement (GPMCS) in February 2010, the cities of Los Angeles and Houston, the states of New Mexico, Georgia and South Dakota, and the nations of Abu Dhabi and India have adopted all or portions of the document (others are on their way). If we are witnessing a growing interest, it is because the GPMCS is a living document, always growing and maturing. The newest growth spurt has begun to show itself in the foreword of the GPMCS under the Green Technical Committee (GTC) task group titled “Pipe Sizing Task Group.”
How did the Pipe Sizing Task Group originate and what is its mission? What may we anticipate seeing in the Green Supplement? The question of pipe sizing originated with the hot water task group chaired by Gary Klein (Affiliated International Management LLC). The problem at hand was the efficient and timely delivery of hot water to the end user. Reducing the hot water pipe size would increase the rate of flow, reduce the volume of water and, hence, deliver the hot water to the user more quickly and with less waste. What reduction were they considering? Investigations were under way for 3/8-inch tubing for a fixture supply branch. The deliberation continues.
In August 2008, at the International Emerging Technology Symposium held in Chicago (hosted by IAPMO), I made contact with Mary Ann Dickinson and Tom Pape (Alliance for Water Efficiency) to discuss research work that was underway regarding the revision of Hunter’s Curve. They requested a copy of the research document and, in turn, handed it over to the GTC.
Because of this document, the committee decided to separate the pipe sizing matter from the Hot Water Task Group and to make pipe sizing an independent task group. In the months following, the Pipe Sizing Task Group emerged, with the following members: Larry Galowin, NIST; Dick Wagner, Emcor Group and chairman of the National Standard Plumbing Code; Ron George, Ron George Design and Consulting Services; Phil Campbell, UA; Gary Klein, AIM; John Koeller, P.E., Koeller and Company; C.J. Lagan, American Standard; Jim Lutz, Lawrence Berkeley National; Larry Oliver, LEED AP, Glumac Engineering; Sally Remedios, Delta Faucet Company; Craig Selover, Masco Corporation; April Trafton, Donald Dickerson Associates; John Watson, Sloan Valve Company and Bill Erickson, C.J. Erickson Plumbing Company. I was appointed chairman of this task group. Yanda Zhang from the Heschong Mahone Group has recently come on board in support of our efforts.
With the varied interests of the stakeholders involved, a mission statement for the task group was established as follows: “The IAPMO Pipe Sizing Task Group is charged with investigating if significant water, energy and/or construction cost efficiencies can be achieved by revising the method of estimating the water demand load to be provided for the water distribution system comprising the water service, cold water and hot water distribution and to accordingly re-evaluate the minimum required pipe sizes. If so, this task group will work toward the development of code change proposals to the Uniform Plumbing Code that will help to achieve these efficiencies while ensuring continued
The first action item for the task group was to revise the method of estimating the water demand load. Since the publication of BMS65, Methods of Estimating Loads in Plumbing Systems, in 1940 and BMS79, Water-Distributing Systems for Buildings, in 1941 by Roy B. Hunter, a physicist for the National Bureau of Standards, Hunter’s Curve has been adopted by every model code, as well as by state-adopted plumbing codes, in the United States and other countries. Regardless of the recent criticism it has received, it is an ingenious method and has withstood the trial of time in successful plumbing systems.
The criticism of Hunter’s Curve over-estimating the water demand is not because of the mathematical probability used in his computations. Rather, it is because the variables have changed over time. Plumbing fixtures have changed. Toilet performance no longer requires four to five gallons of water per flush, and toilet-flushing curves now display one maxima rather than two. Showers are used more frequently than bathtubs. Faucets and showerheads have flow restrictions. Since Hunter’s day, clothes washers have placed a significant impact on water demand.
Toilet behavioral practices have changed. In residential applications, the bathroom has taken on a completely new dimension as compared to what it was in Hunter’s day. More time is spent in the bathroom, for all kinds of cosmetic and therapeutic purposes. The master bathroom, for two-plus occupants, would have been a novel concept to the NBS investigations. The rush-hour concept in public buildings and factories, where the clock regulated people’s toilet breaks, has changed over the years.
Building types have diversified; there are approximately eight different building classifications, along with sub-categories, required on architectural plans to determine occupant loads and egress necessities. Each requires different needs assessment for water usage. An assembly-type building will have different water demands than a business building. Residential needs are different from mercantile needs.
Occupant loads, fixture requirements and frequency of usage are all factors to consider for each building classification.
So, what has the Pipe Sizing Task Group done? First, as already indicated, we have determined not to fault the mathematical probability that Dr. Hunter created. We shall continue to use the binomial distribution method. In fact, we have re-created Hunter’s method, as published in BMS65, step-by-step, with corresponding tables and graphs in a computer program for the manipulation of the variables. We have gathered current fixture performance data from manufacturers to determine flow rates, amount of water used and the time the fixture is in service. These variables have been applied to derive new probability data points for a true curve revision.
We can also accurately weight the fixtures anew as we generate new curves for each fixture. To date, we have evaluated eleven different plumbing fixtures and have weighted them with new fixture units. The task group is looking for water-use specifications from manufacturers for clothes washers, dishwashers and tub fillers.
We are also mindful of the different building classifications and of the toilet behavioral practices of the occupants. Having the ability to generate new curves, we can weight the fixtures in varying ranges, according to the needs of the building classifications. In other words, we can weight the fixtures for residential applications on the low end of the curves, between 5 to 45 gallons per minute; whereas, for assembly type applications we can weight the fixtures on the high end of the curves. Thus, we can generate a family of curves, using the same probability data for fixture performance.
In this regard, though, there is a rub. The conundrum is in determining the frequency of use for each building type application. How often will the fixtures be used in a stadium? At “rush hour,” almost all fixtures are in use simultaneously. What about a residence? What about a place of business or a restaurant? Are there “peak” times in every building type? If so, what are they? Aquacraft data shows that there are two peak times in residences; one in the morning and one in the evening hours. One of the task group’s pressing needs is for field data showing peak values for various types of buildings, including the number and types of fixtures and occupancy levels in each building that is field-tested. We can then evaluate the data against the newly generated curves and fixture units for correspondence.
Finally, we are mindful of the revision efforts and re-evaluation of Hunter’s Curve that have occurred before our group worked on this issue. We have collected documents (and continue to do so) of our predecessors, namely French and Wyly, NBS 1946; Connor and Severo, Research Triangle Institute and University of Buffalo, 1962; the American Water Works Association, M22, 1975 ; Breese, James Breese and Company, 1980; Thomas Konen, Stevens Institute, 1980 – 1994; ASHRAE’s modified Hunter’s Curve,1987; Wistort, ASPE Convention, 1994; Larry Galowin, NIST and John Swaffield, Hariot Watt University, as well as many documents, old and current, from CIB (International Council for Building Research). CIB W-62 (the CIB Commission on Water Supply and Drainage) was specifically organized to address the need for an improved computational procedure for the design and evaluation of water service and distribution systems in buildings. This is now the leading international think tank on this question.
At the CIB W-62 36th international symposium, held in Sydney, Australia, in November 2010, Pete DeMarco of IAPMO, representing the United States, presented a paper co-authored by Larry Galowin and me titled, “Hunter Fixture Unit Probability/Uncertainty.” This paper introduced the improved computational methods initiated by IAPMO, and it gave preview of what may be coming, displaying the tentative revised curves, fixture performance table, a comparison chart with the original Hunter’s Curve and plotted data points from field data that fall closely within the range of the revised curve. DeMarco reported that the paper was well received.
The tenacious teamwork of IAPMO, partnering with industry experts who volunteer their time and effort, shows the world at large that the plumbing industry is alive and well and is committed to the health of the world in its green effort to conserve for all future generations. Dr. Hunter would truly be proud of IAPMO and its partners, as they are indebted to him.
Daniel P. Cole is the technical services supervisor for IAPMO. He is a licensed journeyman plumber in the state of Illinois and has had more than 20 years’ experience in the design and installation of plumbing systems as a journeyman plumber and as a plumbing contractor. In addition, he is a member of the American Society of Plumbing Engineers and the Illinois Plumbing Inspector’s Association. He can be reached at dan.cole@iapmo.org.