Green high-rise plumbing design
By Ron George
President, Ron George Design & Consulting Services
Recently, I was participating in a telephone conference call to discuss code and standard activities with a standards writing organization’s legislative committee. The discussion turned to LEED (Leadership in Energy and Environmental Design) and all of the green initiatives of various organizations and manufacturers. There seemed to be such a sufficient vagueness to the term “green” that each person had their own thoughts as to what being “green” really meant. Everyone chimed in to explain what they thought was “green” and not everyone had the same understanding of what a green product was or what a green design was. What does green mean? I am currently Chairman of the ASSE Plumbing Nomenclature Committee and we are in the process of collecting new terminology for the dictionary for the 7th edition of the “Plumbing Dictionary” published by the American Society of Sanitary Engineering. If you have a term that you would like to have considered for inclusion please send it to me at rgdc@rongeorgedesign.com.
You can purchase copies of the Plumbing Dictionary at: www.asse-plumbing.org.
Mentoring of green design
Many years ago I worked for a couple of engineering firms that had a Mechanical Electrical and Plumbing (MEP) departments. Not many architectural engineering or engineering firms have MEP departments anymore. MEP departments were great mentoring opportunities for young engineers. It was like an apprenticeship for engineers and designers. The MEP departments would have a senior engineer as the engineering department head to handle the administrative functions of the MEP department, and there were lead engineers for each discipline. The engineers for each discipline sat in the same area as the other department members and assisted with mentoring the younger engineers, and occasionally they were called into meetings with clients in a marketing effort. In the new age of marketing, a firm’s expertise with certain types of buildings, firms advertised that they have studios or design teams of highly skilled people that specialize in one type of building. (Hospitals, stadiums, labs, industrial facilities, etc.) The studio or design team all would sit together and work together. This caused the breaking up of the engineers and designers from their peers or mentors while they sat in isolation in a design studio. The fundamental flaw I saw with the studio or team concept is there was little or no mentoring for young engineers. Often there was one engineer assigned to sit with each design team and they were isolated in a design studio. In my opinion, the studio concept may sound appealing to a client, but it actually has hampered the mentoring and development of many young engineers and designers.
I started as a draftsman with an engineering firm in Texas in 1978. I was assigned to work in a very large MEP group. There were a lot of old gray-haired people with years of experience working in these firms. There were many elder statesmen in the engineering community that I worked with many years ago. One of those I was fortunate enough to work closely with was John Burgess of Carter & Burgess, Engineers, Planners Inc. When I worked at Carter & Burgess, I was assigned to work on a city park fountain project with John Burgess. He was a well-respected engineer in the industry and he had a personal interest in the park and the fountains. I remember a discussion Gene Carter and John Burgess had at my desk one day when the company was about to celebrate its 50th anniversary. I congratulated them on their upcoming 50th anniversary celebration. John then turned to me and said, “Ron, You may not realize it, but I am just a temporary employee here.” I laughed and said, “What do you mean? You guys have been in business together for almost 50 years.”
John smiled and said that when he got out of school he was looking for a job, and he saw that Gene had a small one-man engineering firm so he called him up and offered his services. Gene interviewed John and said that since he was just starting his business and he might need some help for a mechanical project. John told me, “Gene said my job would only be temporary and he was not sure if he had enough work to keep me on.” He went on to say, “He has never told me anything different.” They both chuckled. Their company had well over 360 employees at the time. Mr. Burgess spent a lot of time at my desk explaining things, mentoring me and taking a personal interest in each project. He loved what he was doing and he wanted to share it with others, including me. I was honored to have been able to work with him. There were many other engineers over the years at other companies that loved what they were doing. They took the time to explain how systems should be designed and they explained why the systems were designed that way, and what could go wrong if it was not designed properly. Other lessons included: how to draw and letter in the days of drafting on velum and Mylar; how to use the code books; reference standards; and where to find the design information and reference materials. These mentoring sessions included how to set up a project file and how to record important information in the project file. Over the years, I worked closely with many other senior engineers and designers; they would tell stories of their experiences and show me the proper way to design plumbing systems to save energy and materials, and provide a safe and sanitary plumbing system. We didn’t call it “green” or “LEED” back then, but that’s what it was.
I attend every training seminar that I can. I have been a student for more than 31 years. There were classes on plumbing design, product seminars, HVAC design and fire protection system design. There were also local and national industry meetings with design seminars for organizations like ASPE, ASSE, ASME, ASTM, IAPMO, ICC, PHCC, MCA and many other inspector and manufacturer’s seminars and meetings. These organizations provide educational seminars and technical programs that have helped train plumbing engineers and designers in new and innovative concepts. It is important for senior level people to pass on the wisdom so that the next generation can understand why they do something.
In the last few years, I have attended seminars and technical presentations where good engineering practices seem to have been thrown out the window in favor of showing people how contractors or developers design plumbing systems. The call it “value engineering” or “cost cutting.” The term “value engineering” seems to have been abused to the point that the term is often used as an excuse to cut first-costs and use inferior materials with no real consideration for the increased life-cycle costs such as: decreased product life expectancy; increased maintenance costs; and significantly increased energy consumption costs.
The gray-haired guys showed me the proper way, or the “green” way, to design a high-rise building without pressure reducing valves. I often review drawings of high-rise buildings where there have been problems with the plumbing systems and I rarely see a proper plumbing system design. Most high-rise buildings have been designed by a design-build team, with a contractor hiring an engineer. This causes a bit of a conflict when the engineer wants to design the building right and the contractor is often looking for the cheapest way to build the building. I can say there are some good developers and contractors out there that have a good reputation and they provide buildings that perform well. The best developers and contractors are usually not the low bidder and they usually have impressive lists of project experience. The old saying “you get what you pay for” is true in this case. That is why an owner needs to understand who he has hired to design and build his building. Is it a low bidder or is it someone who truly has the experience and knowledge to build the building right without maintenance and energy bill headaches?
Common high-rise plumbing problems
Over the years, I have been involved in the design of numerous building types, including high-rise buildings. I get asked to investigate problems with high-rise buildings on a regular basis and there always seems to be a very poor plumbing design. This can probably be attributed to the fact that developers often build high-rise buildings and want to build them for as little money as possible, sell them and run with the money, leaving all of the plumbing system maintenance problems and high energy bills to the new owner with which to deal. I’m sure this is what drives engineers to design, contractors to build or building developer/owners to use such poor designs. Someone once told me that using pressure reducing valves on a domestic water booster system is like driving down the street with your foot all the way on the accelerator and controlling your speed with the brake. It is a senseless way to drive a car; it will wear out the components very fast and cost a small fortune in fuel bills. Yet, LEED apparently does not address pressure zones and PRVs.
Green high-rise plumbing design
Good high-rise plumbing design is “green design,” and one of the biggest clues to me if it is a green or sustainable design is if the building is designed with pressure zones for the domestic water systems that are each served by an independent booster pump system through express risers. This design keeps the building free from pressure reducing valves in a domestic water distribution system, which is a huge energy saver and maintenance headache. Pressure reducing valves can be noisy and they must be maintained on a regular basis. By having a booster pump for each zone, the energy savings are huge. I have seen developers build high-rise buildings with a single duplex pump that has two pumps at 100 percent capacity serving the entire building. In other cases there were two pumps at 80 percent each and in a low budget project there were two pumps sized at 50 percent with no back-up if one pump is down for repairs. The total energy consumption is equal to 100 percent to 200 percent of the peak design flow. For lower floors they install pressure reducing valves. (Brakes) The biggest challenge in high-rise plumbing design is addressing the elevation pressure change from the top to the bottom of the building. In buildings where the developers use one booster pump package for the entire height of the building, they fall on their face when it comes to the hot water system. This is where I often find they start small repressureization pumps on each floor for circulation or they add small heaters and circulators for recirculating downstream of a pressure reducing valve. Some of the basic plumbing design that was taught by the gray-haired guys was that for every foot of elevation change in a water riser there is 0.433 pounds per square inch (PSI) of elevation pressure loss or if you measure the pressure in feet of water column it is called elevation head pressure or head loss and it is expressed in feet of head.
If your building has a floor-to-floor height of 10 feet there will be an elevation pressure loss of 4.33 PSI per floor.
If the building has a floor-to-floor height of 12 feet there will be an elevation pressure loss of 5.19 PSI per floor.
If the building has a floor-to-floor height of 15 feet there will be an elevation pressure loss of 6.49 PSI per floor.
Given a 50-story office building with 15 feet floor-to-floor elevation difference, and a required minimum of 25 PSI residual pressure at the top floor for flush valves and allowing for 10 PSI of friction loss in the distribution piping we can estimate the required pressure at the bottom of the water riser for the highest pressure zone as follows:
(50 floors x 6.49 PSI/floor = 324.5 PSI + 25 governing pressure + 10 PSI friction loss = 359.5 PSI. The pressure at the base of the riser with 15 foot floor to floor heights would need to be 359.5 PSI at the base of the riser. Note: Most standard piping systems and valves are not rated for these high pressures so high pressure rated pipes, valves and fittings must be used for the lower floors where the pressures will exceed about 125 to 175 PSI.
50-story example
Given a 50-story office building with 10 feet floor-to-floor elevation difference with a requirement for 25 PSI residual pressure at the top floor and allowing for 10 PSI of friction loss in the distribution piping, we can estimate the required pressure at the bottom of the water riser for the highest pressure zone as follows:
(50 floors 5 4.33 PSI/floor = 216.5 PSI + 25 governing pressure + 10 PSI friction loss = 251.5 PSI.) The pressure at the base of the riser with 10-foot floor-to-floor heights would need to be 251.5 PSI at the base of the riser.
Tri-plex vs quadra-plex booster pump packages
In my opinion, if I was giving out LEED points for booster pump systems a duplex pump would be deducted 25 points. A tri-plex pump would be awarded 50 points and a quadra-plex pump system would get 100 points. A good high-rise domestic water system design would have at least a tri-plex domestic water booster pump package for each pressure zone in the building with each pump sized at 33 to 50 percent of the load. If the pumps are sized at 50 percent capacity and one pump is down for service the pressure zone will still have 100 percent of flow capacity. At low flows a tri-plex pump system will utilize about 33 to 50 percent of the required energy depending on if one pump is a stand-by pump. A hydro-pneumatic tank can be utilized to allow the booster pumps to completely shut down when there are long periods on no water use at night. An even better high-rise domestic water system design utilizes quadra-plex domestic water booster pump package systems for each pressure zone for each pressure zone in the building with each pump sized at about 25 to 33 percent of the load If the pumps are sized at 50 percent capacity and one pump is down for service the pressure zone will still have 100 percent of flow capacity. At low flows a quadra-plex pump system will utilize about 25 to 33 percent of the required energy depending on if one pump is a stand-by pump. If the quadra-plex pumps are sized at 33 percent capacity and one pump is down for service it will still have full capacity. Hydro-pneumatic tanks should be used on all types of booster pump systems to save energy. We should give 50 points for having a properly sized hydro-pneumatic tank near the top of the system. A well-designed building is usually divided into pressure zones between eight to 10 floors per pressure zone depending on the floor-to-floor height. Given a 50-story building, the 50th floor usually has a governing pressure around 25 to 30 PSI and each story height of 10 feet adds 4.33 PSI to the pressure as you go down in the building from the top. If there is 25 PSI on the top floor, and there are 10 floors in the pressure zone below, the elevation pressure is 43.33 PSI. If we add the pressures, governing pressure = 25 PSI + 43.33 PSI elevation pressure + 10 PSI for friction loss = 78.33 PSI at the 41st floor. The maximum allowable pressure in a plumbing system is 80 PSI. From the 41th floor down to the basement, there would be an express riser to the basement 40 floors x 4.33 = 173.2 PSI. The water riser would terminate at a tri-plex or quadra-plex booster pump package sized for 20 percent of the flow (10 of the 50 floors) with 100 percent of the total 50 floors of elevation pressure of 216.5 + 10 PSI for friction loss + 25 PSI for the governing fixture = 251.53 PSI at the discharge header of the booster pump package.
Each pressure zone would be designed in the same manner with the total head for each booster pump package being about 43.3 PSI less. I have seen many buildings with one giant duplex pump and pressure reducing valves on all of the lower floors and no hydro-pneumatic tank. It saved the developer and the contractor a lot of money but it will cost the owner many times more money in increased energy costs and maintenance costs. This type of design wastes a great amount of energy and in my opinion any building over 15 stories that utilizes this type of design should have 100 points deducted from the LEED certification ratings for every 10 floors of the building or 10 points per floor if they exceed 10 floors in a pressure zone and if they do not locate the water heaters within the pressure zone. The ideal plumbing design does not require pressure reducing valves at each floor.
Other high-rise plumbing design tips
When a design utilizes pressure reducing valves, there in not an easy way to recirculate hot water within a pressure zones unless the water heater is located within the pressure zone. This should be a code requirement because in most cases it does not happen because developers and owners typically don’t know the water heater must be located within the 10 floor pressure zone in order for the water heater to work properly.
If the water heaters are all located in the basement, as I have seen some in several wayward designs, the PRVs will blow off constantly. This usually results in a revelation moment for the engineer when they realize their folly, and they typically try to compensate for it by replacing the pressure relief valves on the water heaters with ones that are set at higher pressures. Now they have voided the warranty on the heater and created a potential bomb.
The next boo-boo I see engineers make on a regular basis is that they put the water heaters at the top of the building. Now the hot water starts out at 25 PSI or so at the top of the building but as it flows down in a downfeed riser it gains pressure and you end up with hot water at about 250 PSI near the bottom of the building. The engineers or designer typically starts adding pressure reducing valves at this point, and if they are lucky, they will last a year. Most don’t last that long at that pressure on a hot water system. When the hot water pressure reducing valve fails you have 250 PSI hot water and 80 PSI cold water. The hot water can overwhelm the cold water where it crosses over in shower valves and faucets and you get toilets flushing with hot water and you can have other problems associated with excessively high hot water pressures in the piping system. The high-pressure hot water will likely create scalding and thermal shock hazards throughout the building within a few short years.
The water heaters should be located within the 10-floor pressure zone and then circulation can be done without passing through pressure reducing valves and then repressurization pumps
I also have seen where CPVC piping was substituted for copper piping in the risers of a building about 50 stories tall. Don’t forget CPVC pipe will expand about five times as much as copper. The expansion must be controlled with offsets in the riser every five to eight floors. Failure to do so will cause the CPVC riser to expand linearly and push out firestopping and snap off branch pipes. CPVC pipe and PEX pipe are good for branch piping in high rise applications within office spaces, apartments or condos. I recently have submitted a code change for requiring the engineer to submit calculations addressing thermal expansion in straight runs of piping over 100 feet long in risers.
Siphonic roof drains are not recommended for high-rise buildings. They work great for large roof areas up to a couple of floors. When you exceed two floors, many manufacturers do not recommend the siphonic systems because of the potential for significant pressure surges and movement in the piping.
Pipe materials and hanger designs should be selected to minimize noise transmission to the building from flowing water or vibration from connected pumps elsewhere in the building.
Cost savings can be realized for domestic cold water branches utilizing galvanized piping, or in some cases, stainless steel with local code approval for the risers; and utilizing cross linked polyethylene or PEX piping for branch piping after a manifold and valve assembly.
When you get to the basement of the building, often there are multiple basement levels below the sewer level. This usually requires the installation of sewage ejectors and sump pumps. Try to design the system where anything that can go to the sewer by gravity is routed by gravity. Make sure the sewage ejectors are designed to handle the potential discharge of a broken water pipe or a reduced pressure backflow preventer discharging under pressure. Consider adding the sewage ejector pumps to the emergency generator load in the event of a power failure. Make sure the main domestic water shut-off valves are located in an accessible location where they can be easily shut off if there is a problem and the entire basement floods.
Ron George is President of Ron George Design & Consulting Services. He has served as Chairman of the International Residential Plumbing & Mechanical Code Committee. He is active in plumbing code and plumbing product standard development committees with ICC, IAPMO, ASSE, ASME, ISEA and ASTM. His company specializes in plumbing, piping, fire protection and HVAC system design and consulting services. He also provides plumbing and mechanical code consulting services and he provides investigations of mechanical system failures and litigation support. His company also provides 3D cad services and Building Information Modeling (BIM) services.
To contact Ron, w-mail: rgdc@rongeorgedesign.com. Web site: www.rongeorgedesign.com.