Volume 45 Number 1
Fixture Flow Rates: Wisconsin’s POE Water Treatment Device Sizing Requirements
Summary: In an attempt to assist water treatment dealers and buoyed by a study from the WQA among others, the state of Wisconsin's Department of Commerce has permitted an alternative method for the sizing of point-of-entry devices. Before, the state's universal plumbing code was the law. The following discusses what this means for affected dealers.
The Wisconsin Department of Commerce has formally approved a system for sizing point-of-entry (POE) water treatment devices such as softeners, iron filters, etc., that can be used as an alternative to current sizing requirements contained in the Wisconsin Uniform Plumbing Code. The approval is based on data taken from a study commissioned by the Water Quality Association (WQA), “Analysis of Indoor Peak Demands in 60 Selected Single-Family Homes," and conducted by Aquacraft Inc., Water Engineering & Management and the Wisconsin WQA, using an alternate sizing system application filed by the Wisconsin WQA. The funding for the study was a joint effort of the WQA and the Wisconsin WQA. The POE water treatment device alternate sizing method is valid through August 2007. In 2003-2004, the Wisconsin Plumbing Code Council may consider amendments to the Wisconsin Plumbing Code to permanently include the alternate sizing method.
Language in the current Wisconsin Uniform Plumbing Code requires plumbers and installers to size POE water treatment devices using traditional fixture unit value flow rate calculations. The code assigns a fixture unit value to plumbing fixtures such as baths, toilets, dishwashers, clothes washers, faucets, etc., and then converts the sum of the fixture unit values to a code design flow rate. That code design flow rate is then used to make sure that all fixtures will still operate after determining the difference between the incoming pressure and the pressure loss through plumbing pipes, and devices such as water heaters, water meters and water treatment devices. Many plumbing system designers design the plumbing system first and calculate the remaining pressure at the critical fixture without figuring in the pressure loss from any water treatment device(s) that may need to be installed. This often leads to designers asking for a water treatment device with a very high flow rate at a very low pressure loss. For example, if a code design, flow rate requires 16 gallons per minute (gpm) and the remaining pressure loss available through the water treatment system is only 3 pounds per square inch (psi), then the water treatment system must be able to produce 16 gpm at a 3 psi loss or less. When code designed flow rates are too high, oversized POE water treatment devices would be required by code. Yet, oversized POE water treatment devices operate inefficiently and are more expensive for the consumer to purchase.
The study's specifics
The Wisconsin Department of Commerce alternate approval applies statewide to sizing POE water treatment devices installed in single-family homes or individual dwelling units in multi-family dwellings. The Wisconsin Uniform Plumbing Code allows POE water treatment devices to be installed in parallel to meet the demand. Parallel installation of POE water treatment devices is sometimes used on private well applications where the well pump has a flow rate capacity lower than what's needed to appropriately backwash a single large POE water treatment device such as an iron removal system. If the POE water treatment device is installed to serve only interior fixtures, the resulting decreased flow rate sizing is dramatic (see Figure 1). For a single-family home with a count of 30 fixture unit values, the required code design flow rate for the POE water treatment device would be 20 gpm. Under the alternate sizing method the flow rate for the POE water treatment device would be 7.5 gpm. The pressure loss through the example POE water treatment device (see Figure 2) at 20 gpm is 20 psi. The pressure loss at 7.5 gpm is only 1.7 psi. The lower flow rate sizing method allows installers to use the POE water treatment device pressure loss at the lower flow rate sizing method in their sizing calculations for the water distribution system.
The data in the WQA/Aquacraft study analyzed interior flow rate water usage. As a result, if the water treatment device provides treated water for exterior wall hydrants, flow rates for exterior wall hydrants are calculated using existing code criteria and then added to the alternate sizing method flow rate to size the POE water treatment device. If the WQA desires to include the exterior flow rate data at some future date, the Wisconsin Department of Commerce will consider additional data. An example of the reduced design flow rates—showing both interior fixture uses only or interior fixture use plus exterior hose bibs—is shown in Table 1.
What to look for
Situations such as these may prompt the water treatment professional to specify a larger size POE water treatment device than what the code would require as a minimum. The goal is to meet the homeowner’s expectations at a cost the homeowner can afford.
About the authors
Loretta Trapp is the project manager for Clack Corp., of Windsor, Wis. Previously, she's been affiliated with NSF International's Drinking Water Treatment Unit Program and the Wisconsin Department of Commerce. She also was a member of WC&P's Technical Review Committee in 2001-2002. Trapp can be contacted at (608) 846-3010, (608) 846-2586 (fax) or email: email@example.com
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