Plumbing Engineer August 2021/61 61/Plumbing Engineer August 2021
return piping that would have normally been installed from the distant mechanical room to the risers. The underlying theme of all these design decisions is to reduce the volume in the premise plumbing. Less stored water volume in the piping equals less Legionella risk, water waste and energy consumption. The end result is healthier buildings and increased customer satisfaction. Right-Sizing the Premise Plumbing Once the architectural decisions have been made, it is now time to use IAPMO's Water Demand Calculator (WDC) to right-size the premise plumbing. It is cur- rently able to be used for single-family and multifamily occupancies. The WDC brings Roy Hunter's work into the modern era for these two occupancies because there is data to support updating the probabilities of simultane- ous use. It allows plumbing designers to use modern flow rates and these updated probabilities to more accurately size plumbing systems while still leaving a good margin of safety in the design. What is the calculated savings on this project from right-sizing? Construction costs: $5,000 in first costs of the piping; $5,000 in the fittings, valves, pipe insulation and installing the smaller diameter pipe; $20,000 by reducing the water heating system by a factor of four; The service entrance was reduced from 3 to 1 1/2 inches, which meant a smaller water meter, lowering the first costs still further; $850 less per apartment to build this building. Operational costs: $2,500 per year projected operational savings in water, sewer and energy included. Every item discussed previously directly impacted Legionella risk. The volume of the water in the premise plumbing system was reduced by about half from the design used in Phase I. Once again, less volume = less water aging = less Legionella risk = healthier buildings, all while saving water and energy and increasing customer satisfaction. Gary and I have worked together on these issues for many years because we understand that Legionella risk management and water and energy conservation are objectives integral to each other. After more than 20 years of work in the Legionella field leading outbreak investigations and resolutions as well as performing building audits, I've found the two single most critical variables for controlling Legionella risk are temperature and water age (time-to-tap). If the temperature at the fixture is more than 120 F and the time to tap is less than 1 minute, then the likelihood of any Legionella issues is very low. And if the temperature at the fixture is less than 130 F, then the likelihood of scalding is very low. The next article in the series will go into more detail on temperature, temperature control and temperature impacts related to Legionella risk in plumbing design. O Tim Keane is a consulting engineer with Legionella Risk Management. He was an original member of the ASHRAE 188 committee through the publication of ASHRAE 188 and ASHRAE Guideline 12 2020. He specializes in iden- tifying and cost-effectively resolving building water sys- tem design, operation and maintenance issues related to Legionella and other waterborne pathogens. Gary Klein, president of Gary Klein & Associates, is intimately involved in energy efficiency and renewable energy, with an emphasis on the water-energy-carbon connection.
Figure 2: Corner Apartments - Time-to-Tap. Figure: John MacArthur, Beardsley Architects + Engineers; Table: Gary Klein
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