Consulting-Specifying Engineer - January 2008 - (Page 17) M/E Roundtable PARTICIPANTS Water storage heats up What are the ideal applications for tankless and storage water heaters? Learn what CSE’s panel of experts say about both systems in terms of hot water, retrofits, design, and more. BY MELISSA HILLEBRAND, Associate Editor CSE : When considering tankless, when might a decentralized—point-of-use— approach be more ideal than a centralized—one tankless heater—approach? MELODY LUTZ: When a water-heating system is decentralized, it may eliminate the necessity for long or multiple hot water piping runs. This provides thermal efficiency by reducing temperature drop common in long pluming runs, reduces water consumption by decreasing time of delivery, and simplifies plumbing installation. Only cold water lines must be run near the point of hot water consumption. It is necessary to consider the needs at each point of use for sizing. It may necessitate a higher amperage electrical circuit if care is given to achieve higher temperatures at maximum fixture draw. JOHN ALFORD: A small project with just a few plumbing fixtures requiring hot water would qualify. Here in our area, the code doesn’t require hot water at public restroom lavatories. Sometimes when the building owner decides to forgo hot water at the restroom lavatories, small point-of-use heaters are provided at the janitor closets. Occasionally, a project may have a breakroom sink located remotely from the remainder of the project fixtures. It is possible to supply cold water to the sink and a small point-of-use water heater under the counter. WILLIAM HOOVER: While point-of-use heaters appear to be a good idea, the cost of the equipment and installation usually makes this approach cost prohibitive. Unless the distances are exceptionally long, the most cost-effective solution usually would be a whole house water heater and an on-demand recirculation system, which will provide hot water at all fixtures without water waste. CSE: What are ways to reduce hot water loads to make systems smaller? For example, is providing only cold water to restrooms an option? HOOVER: I don’t believe that most health code officials would approve providing just cold water in restrooms. The hot water load can be reduced by using an on-demand recirculation system, by washing clothes in cold water, by the use of low-flow fixtures, and by limiting the duration of hot water usages. ALFORD: As I mentioned before, our code doesn’t require hot water at hand washing lavatories in the public restrooms. We limit this application to the public restrooms. Eliminating hot water to most other fixtures would be an inconvenience to the building occupants. LUTZ: On-demand systems with accurate temperature control permit lower settings of water temperatures for lavatory applications. Temperatures of 90 to 100 F are more than adequate for hand washing. On-demand systems that activate as low as 0.15 gpm or 0.25 gpm allow the use of 0.5 gpm aerators for lavatory faucets, which reduces total consumption. Modulating controls to lower temperatures also permits service of multiple lavatory sinks with a smaller single unit, reducing utility requirements. Anytime systems modulate to desired consumption temperatures energy is saved by eliminating the need to cool incoming water for usage, thereby wasting heat energy. John Alford, PE, LEED AP Senior Plumbing and Fire Protection Engineer, TLC Engineering, Orlando, Fla. William R. Hoover Director-at-Large A. O. Smith Corp. Milwaukee Melody Lutz Vice President for Technical Sales Keltech Inc. Delton, Mich. Consulting-Specifying Engineer • JANUARY 2008 17
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