The 7th Emerging Water Technology Symposium (EWTS) was held in San Antonio the second week of May. The Symposium is sponsored by the leading plumbing groups: IAPMO, ASPE, PMI, World Plumbing Council, and the Alliance for Water Efficiency. This two day Symposium always has some interesting presentations.
With the emphasis on water and water efficiency, there were presentations on water pipe sizing. Gary Klein spoke on the use of the IAPMO Water Demand Calculator. This was followed up by Prof. Steve Buchberger addressing the further evolution of the calculator. This included an evaluation of sizing water piping for large arenas and stadiums.
Prof. Buchberger was the researcher and original developer of the IAPMO Water Demand Calculator. Having been a peer reviewer during the development of the calculator, Prof. Buchberger and I have become good friends. Like typical engineering nerds, we love discussing the ins and out of water pipe sizing. Large arenas and stadiums have become one of our favorite topics to discuss.
Since I redesigned a water piping system for a 60,000-plus-seat stadium, I presented my design approach used for peak demand. This approach is significantly different than both the Hunter method and the IAPMO Calculator. Thus, stadiums and large arenas became good candidates for further research.
As a professor at the University of Cincinnati, Prof. Buchberger had his postdoc researchers monitor the water use at the Fifth Third Arena located on their campus. The arena seats 12,000 fans of the Bearcats.
Plumbing engineers have often struggled to properly size the water distribution system for stadiums and large arenas. When I first entered the engineering profession, there were many new football stadiums about to open. Articles appeared in magazines claiming that the acceptance of the stadium rested on the final water test. That water test was nicknamed the “Big Flush.” This particular football stadium was located on the East Coast.
The article identified the procedures they would follow to perform the Big Flush. Workers would be stationed throughout the stadium, all connected by radio (this was before cell phones were invented). At the signal, every water closet and urinal would be flushed at the same time. If the plumbing system worked, the stadium was acceptable.
That particular stadium has since been demolished, with a new stadium constructed next door. Sure enough, I saw mention of the Big Flush for the new stadium.
The problem with the Big Flush is that it is a big joke. If an engineer designed a water distribution system to handle a big flush, they just grossly oversized the piping system. How grossly oversized you may ask? How about five times what is required under a worst case condition!
Just think about halftime use in a football stadium. What is the probability of every water closet and urinal flushing at exactly the same time? The answer is zero. A 1.6 gpf water closet flushes in 4 seconds with a flush valve. A 1 gpf urinal flushes in 7 seconds. Hence, for a big flush to actually occur, you would have a 4-second envelope for flushing.
Hunter never envisioned plumbing fixture use during the halftime of a football game, soccer match or basketball game when developing his water pipe sizing method. If anything, he may have considered the inning breaks in a baseball game, but that is doubtful.
When determining the number of fixtures required by the Plumbing Code, stadiums were based on a somewhat worst case condition. It was decided to use a college football stadium. Halftime during college games is 20 minutes, as opposed to 12 minutes for the NFL. The other assumption made is that 25% of the attendees will use the plumbing fixtures. If you do the math, you will understand how the code derived the fixture count numbers.
The water use will always be based on the number of fixtures used during peak demand. It is already established that peak demand would be halftime. For some college stadiums, pregame is as bad as halftime, based on tailgating habits.
If a football stadium holds 60,000 fans, halftime use assumes 15,000 people will flush either a water closet or urinal. Normally, two-thirds of the population will use a urinal rather than a water closet. That means that there will be 10,000 flushes of urinals and 5,000 flushes of water closets. However, this is over a 20-minute period of time. If equally divided, which it will not be, that means 500 urinal flushes a minute and 250 water closet flushes a minute. Playing with those numbers, you just blew Hunter’s method out of the water.
Getting back to Prof. Buchberger’s research, his EWTS presentation identified sizing the water mains based solely on the use of water closets and urinals. These are the two demanding fixtures in a stadium or large arena. A water closet flushes at a rate of 25 gpm, while a urinal ranges from 10 to 12 gpm. Thus, if 100 water closets flush at the same time, the water demand would be 2,500 gpm, a rather high number.
Remember the stadium with the Big Flush? Assume that stadium has 600 water closets and 300 urinals. If you used the lower values for the urinal flush rate, the big flush would flow 18,000 gpm. Research has shown that the actual flow rate is closer to 3,000 to 3,300 gpm. If the stadium had a single water supply (which they never do) this would mean the difference between a 12-inch water service versus a 30-inch water service. If you ran Hunter’s method, you would have a 5-inch water service, or grossly undersized.
The research presented by Prof. Buchberger showed an actual use closer to 20% of the total use of all of the water closets and urinals. Even with other fixtures using water during halftime, by applying a multiplier to the water closet and urinal use, there is still excess water flow available. As Prof. Buchberger noted, this is only the start of research on water use in stadiums and large arenas. The research will continue.
The views expressed here are strictly those of the author and do not necessarily represent PM Engineer or BNP Media.
