February 2012
Greetings,
This time, I have three subjects for this article. All com-ments are greatly appreciated.
Tankless Water Heater: The attractive advertising of the tankless water heater are giving the engineers a major chal-lenge. Engineers as consultant must provide recommenda-tions to what they believe in to their clients. And if the client requests such a demand, as long as it is not against the code, the engineer must comply. However, the client is not an en-gineer, and is only motivated based on color brochure, fancy spokesman and prime time advertisements. This issue will be on the table for a while. The engineering facts are still there for a good debate.
Is the plan checker always right? The street water pressure ranges from 75 to 85 psi, then you are obligated to install multistage pressure regulator. The engineer must design the system with 75 psi, with PRV pressure drop, the pipe sizes will increase accordingly. However, if the pressure is at 85 psi, there are two pressure drops at zero flow. First as in Ber-noulli’s energy equation, the hydrostatic pressure drop based on the height difference of the street and the fixture heights at the space. Of course each psi is equal to 2.3 ft head pres-sure drop, therefore for every 4 psi equals 9.2 ft of head. Se-cond pressure drop is not controversial, it is only misunder-stood. The backflow devices have documented and verified pressure drops at zero flow. The check valves are not silent and create static friction and also reduce the hydrostatic pressure. Zurn sent information on two of their backflow devices. These documents clearly show the pressure drop at zero flow is near 9 to 10 psi.
treet Pressure - Static Height Pressure (2.33 psi/ft) - Pres-sure Drop at Backflow =
If it is less that 80 psi- Therefore you do not need pressure regulators
As they say, if you do not need headache, why do you take aspirin?
Why would you want to install a system that you do not need?
This will be an excellent code modification request.
Water Piping Design: One of the difficulties of the engi-neers is the piping design for the facility, especially when you have only one urinal fixture. Here is the issue.
The engineer identifies that the street pressure is low and he is obligated to go for tank type water closet. With one Urinal in the mix, the engineer is obligated to use the flush valve curve. However, by communicating with every valve compa-ny, the required valve pressures are only 10 psi, lower than the 15 psi code required. The water flow through the urinal does not need they dynamics required in water closets. Therefore, why would we need the fixture unit for the urinals in the code and punish the entire building. The increase in pipe size is not a green act.
This will be an excellent code modification request.
Sewer Backflow Device: Recent avalanche of sewer back-flow device requests on plan check for an existing two story buildings for small T.I on the first floor. Placement of this device on the outside is very difficult.
Who goes to the city to identify the rim elevation of the man-holes on the street and compare to elevation of the building?
How is the building going to modify the sewer piping and separate the second floor with first floor?
These are practical questions that may require to completely modify the building sewer system. The sad issue is that this code is very old and the elevations of the manholes and building were there from the beginning. Building plan check-er, the original civil engineer and plumbing engineers miss the boat and now is a headache for small T.I. years after the fact.
How do you resolve this? Who pays for this: Landlord or the T.I. Tenant?
Respectfully Submitted,
Dr. Saum K. Nour , PE*3, Ph.D., CPD, CFPE, LEED AP
Vice President - Legislative
