Lessons learned from designing “green” plumbing systems

By John A. Clark, PE

All plumbing projects under design/construction in today’s environment have some focus on saving energy, saving water, earning LEED points or just trying to make the world a better place. In my 40 years as a consulting engineer, designing and witnessing many “green” plumbing systems has made me aware of various problems that have occurred during green installations. For example, all the minor details that go along with fixture choices must match the goal of the original water saving design. The water temperature must be designed to be tempered or hot and cold (available as a choice); the soap must be acceptable for use with the selected flow rate; fixture and floor cleanliness near the urinals is essential, and odor control in the restroom is a priority.

Some design questions also need to be addressed: Is touch-free or paperless hand cleaning an objective? Is the long-term maintenance cost acceptable? Let’s break down some water conservation applications and their potential problems.

Toilets

Toilet selections have gone from 3.5 gallon per flush (gpf) units to 1.6 gpf units. Fixture manufacturers have redesigned their units to feature full solid waste removal. Some units use the “power flush” technology, which employs a bladder tank that uses air pressure to assist the flush. The downside of this type of unit is the noise factor. The flush noise is objectionable in multi-residential, health care and hotel projects.

Dual-flush units have been successful at saving water; they can be activated to remove either urine waste or solid waste. One problem with these fixtures is ensuring that the flush will also clean the bowl wall. When selecting a dual flush toilet, you need to make sure that the bowl wall is clean after a flush.

Another problem is the sensitivity adjustment of the toilet sensor flush valve. If the sensitivity adjustment is set too fine, slight user movement during fixture use will cause the flush to activate; there is then a delay time, during which, even though the user leaves the fixture, the unit will not flush again. This results in waste remaining in the fixture. Operations personnel should be aware of this problem and make the correct flush valve sensitivity adjustments.

Urinals

Water saving urinals available in the marketplace are 1gpf units, one-pint flush units and waterfree units. Using water for a flush is still a requirement in many local Codes, limiting the fixture choices to the 1gpf and one-pint flush units.

Waterfree units use either a liquid seal cartridge or a memory rubber seal trap to control the sewer gas odors. The cost of cartridge changes is a factor in the final cost analysis when compared to the cost savings of using less water. The memory rubber trap seal has the advantage of longer trap seal life than cartridge seal units have.

Restroom odor from urinals is also a topic of concern. The topic of urine odor control relates to the transition from wash-down urinals to those using siphon-jet technology. Wash-down urinals mix water with urine, resulting in residual urine odor. Siphon-jet urinals provide a clean flush and leave only pure water in the fixture bowl. When water is mixed with urine it has an objectionable odor. The pure urine flow into a waterfree fixture does not produce urine odor.

Fixture target size is also an important factor in restrooms having only one urinal mounted at the ADA height requirements. Often, urine winds up on top of the fixture, as well as on the floor in front of the fixture. Most of these units are small target-area, siphon-jet flush models. Although wash-down urinals have a larger target area, odor is still a problem with these fixtures.

One solution is to use wash-down type fixtures with low water usage and to use odor-control cakes in the fixture. Another solution is to select waterfree units that have a large target area and an extended front lip.

There are two different problems associated with urine flow. When urine and water are in the waste stream, mineral deposits form on the waste pipe walls and cause plugged lines. This condition is very common in restrooms with banks of urinals with high usage such as those in a shopping mall or a sports arena. The problem with waterfree urinals is that when the line has a flat pitch to the main, soft material forms on the waste line walls. This material eventually plugs the urinal branch line. Both problems require that the urinal branch line be cleaned or replaced.

Handwashing sinks

A 0.5 gallons per minute (gpm) flow restrictor nozzle is used in most handwashing sinks. One complaint is that, when liquid soap is used, it takes longer to remove the suds from the sinks. The solution is to use foam soap or to replace the 0.5 gpm flow nozzle with a 1.0 gpm flow nozzle.

Research has shown that refillable soap dispensers can become contaminated. The solution is to use disposable liquid and foam soap dispensers.

Handwashing sinks in healthcare facilities do not require an overflow opening; therefore, drain stops cannot be used in these type fixtures; the drain opening must have a grid strainer.

Sensor-controlled faucets

Most sensor-controlled faucets supply tempered warm water rather than having a water temperature adjusting device as part of the faucet assembly. The user expects the warm tempered water to be delivered the moment the flow begins. This has led to increased use of “point of use electric water heaters” or storage heaters at or near the faucet. Sensor faucets that do have a temperature adjustment feature need to have some indication as to which position is for hot water delivery and which is for cold water.

Sensitivity of the control is a factor that is dependent on the maintenance knowledge of the client’s operational staff. We have all been frustrated by doing the “wave” under the spout to try to get the water to flow.

Tubs and showers

Most new hotels and motels only provide showers, a trend that is also being seen in the housing market. Shower nozzles use a 1.75 gpm flow control device; when a hose-type body spray attachment is added, the flow rate jumps to 3 gpm flow. Providing an in-line flow control to the hose body spray connection will make the necessary correction.

Waste line sizing in low water flow buildings

Water flow in the piping is still the transport source for all liquid and solid waste. When less water is provided, stoppages tend to occur in the sewer mains. One solution is to provide smaller pipes in order to increase the liquid flow velocity. This solution requires the approval of the local Code Authority. Another option is to increase the pipe pitch to the building sewer invert. This will, however, increase excavation costs.

Smaller waste piping can be sized by using modified fixture unit values based on material developed by the Stevens Institute of Technology. The National Plumbing Code includes the Stevens Method. The International Plumbing Code and the Uniform Plumbing Code include some provisions from the Stevens Method. All plumbing codes allow the use of accepted engineering methods to size a system.

Hand drying

The designer needs to determine the client’s goal: Is the goal to reduce paper usage or is it to provide a touchless facility? A paperless restroom requires an electric hand dryer. The mounting height of the dryer unit is critical to avoid the complaint that the unit “blows your skin off.” When mounted at the recommended height, the user’s hand will activate the unit away from the nozzle, minimizing the high velocity factor. Paperless restrooms also need to have a touch-free exit path, so that recontamination does not occur when the user has to touch a doorknob or handle in order to leave the space.

Touch-free paper towel dispensers should be available in all restrooms that have a “pull handle to open” exit door. Paper should be available in rooms with diaper changing tables, and a waste container should be located near the exit door for disposal of the paper towel used to grasp the door handle.

Restroom odor

Most public restrooms have a floor drain that gathers any flooding from clogged fixtures. Over time, however, the trap goes dry, and sewer gas contributes to restroom odor complaints. Some possible solutions are to train the maintenance staff to add water to the trap, to add mineral oil to the trap to minimize the water evaporation, to design the drains with trap primers or to use memory rubber trap seals.

Restrooms with urinals that mix water and urine will have urine smell; therefore, you must check to be sure that the room’s exhaust system is working. A simple test for a working exhaust system is to see whether the exhaust grille will hold a small piece of toilet paper to its surface. Many times, although you can hear fan noise, the drive belt may have either come off, or it may be broken.

Electric water coolers

Provide a triple filter -- taste, odor, mineral removal -- on all water supplies to water coolers. In a multi-story building, provide a filtered, dedicated supply riser to all of the stacked units. Place a sign on the wall explaining that the water in the unit is filtered. Also, provide a bottle filler unit on coolers, so that the occupants can bring their water bottles back to their workstations.

Conditions when low water flow is “bad”

In the therapy areas of healthcare facilities, turn-around time for draining and filling the hydro tanks requires larger fill lines, greater capacity mixing valves and larger drain lines from the floor sinks.

Conclusion

Low water usage fixtures are available for use in “green” designs. However, all of the minor details that go along with fixture choices must match the goal of the original water saving design.                   

John A. Clark, P.E. is senior quality assurance engineer with Karges-Faulconbridge Inc. (KFI), Saint Paul, Minn. He is an experienced engineer with more than 40 years as a design mechanical engineer for both commercial and industrial projects. He has authored many articles and papers on plumbing, fire protection and HVAC coordination topics.