Building America Expert Meeting Highlights Opportunities for Hot Water Energy Savings

July 2004

High-performance homes have reduced energy use by leaps and bounds, but the findings of a recent Building America Expert Meeting in Pittsburgh, Pennsylvania, suggest that even more improvements are possible. Typically, energy savings in high-performance homes are achieved through improvements in space conditioning. Domestic hot-water systems, which have been largely overlooked until now, could lead to more savings—with better research and industry participation.

At a Building America-funded meeting in early April, experts met at the facilities of IBACOS (Integrated Building and Construction Solutions, Inc.) in Pittsburgh where they discussed the relationship between domestic hot water systems and energy savings. Currently, hot water accounts for 21% to 32% of the energy consumed by high-performance homes. Through further research, the experts would like to advance domestic hot water production, heat recovery, and distribution with the goal of reducing energy, water use, or both. Attendees included representatives from national laboratories, manufacturers, and Building America teams, including Oak Ridge National Laboratory, CARB, Aspen Systems Corporation, Davis Energy Group, Lawrence Berkeley National Laboratory, and National Renewable Energy Laboratory.

A highlight of the meeting was a series of presentations by industry representatives, who offered analysis and proposed solutions. Researcher William Rittelmann of IBACOS presented the misuse of hot water recirculation systems on passive solar hot water systems in a residential community in Tucson, Arizona.

"While trying to fix one problem, the community ended up with another. They were wasting energy for the sake of conserving water," said Rittelmann, who stressed the importance of working toward efficiency in both water and energy use.

Nearly a dozen presentations and several group discussions took place. Through their findings, the experts came to the following conclusions on domestic hot water systems:

Heat Pump Water Heaters

• In home use, the operational efficiency of heat pump water heaters is significantly less than the listed Energy Factor. Future studies should evaluate the impact of water use schedules versus environmental factors in order to give more accurate estimates.
• Although heat pump water heaters are promoted as producing collateral dehumidification and space cooling as byproducts, they do not always produce them. When they do, the benefits are insignificant. There have not been studies to characterize the effects of heat pump water heaters on space conditioning.
• Product cost still appears to be the most significant market barrier to the widespread use of heat pump water heaters.

Distribution Systems

• Studies indicate that hot water distribution efficiency can be as low as 61% for a typical home with piping in the attic; however, more field studies are needed before making recommendations to change benchmark or building codes.
• Current trends-larger homes, more plumbing fixtures, piping outside of the conditioned area-contribute to an increase in hot water distribution losses.
• Hot water recirculation systems contribute to large energy loss if not adequately controlled. Energy codes that require these systems should be changed to also define acceptable methods of control.
• Pipe sizing and water heater sizing methods are based on fixture flow rates from the 1940s and should be updated to reflect current Federal Minimum Standards.
• California's energy code is the first to require hourly energy calculations for domestic hot water systems. This requirement will need better equipment efficiency and capacity ratings over a wide range of conditions, as well as additional equipment test procedures and better predictive analysis tools.

The Expert Meeting brought new insight but few immediate action items. For research to eventually benefit the homeowner, more studies and participation by other industry members will be needed. Meeting participants hoped that future gatherings would include code representatives and professional societies, such as the American Society of Plumbing Engineering.

The meeting may have raised more questions than answers, but it stood to promote improved energy use by domestic hot water systems, which in itself represents another step along the road towards building better homes.

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