1. 1 Recirculating Residential Water Heating Systems Do Such Systems of Potential Savings September 16, 2003

2. 2 What Is The Issue? City of Port Angeles requested that the RTF review the a recirculating hot water system for use in residential buildings to determine: – 1) Whether it could qualify for C&RD and – 2) What the potential savings might be from such a system.

3. 3 Available Data “Economic Operating Cost Analysis Summary for Laing Instant Hot Water Recirculating Systems (October 2001) Sub-metered water use from AWWA Sub-meter water heating use from multiple utility studies ( ELCAP, RSDP, RCPD, etc.) LBNL Water and Water Heating Use Study (LBL-35475)

4. 4 Laing Report Assumptions/Assertions Calculations based on 4 persons/household Hot Water wasted without recirculating systems = 14,087 gals/yr (38 gals/day) Hot Water savings with recirculating = 12,320 gals/yr (33.8 gals/day) Gross Electricity savings = 3,007 kWh/yr – –Pumping energy use @ 289 kWh/yr –Piping losses @ 3080 kWh/yr - 362 kWh/yrNet Electricity savings = - 362 kWh/yr

5. 5 Other Reports Average hot water use for US (1993 data) = 60 gal/day/household with 2.6 persons/household - (LBNL) 57.4 gal/day/household for 2.8 person/household) of which 48.2 was used in sinks, bath or showers – Seattle Water Department sub-metering study Average “baseline” DHW use in PNW is 3,800 kWh/yr/household (2.6 occupants)

6. 6 Breakeven Case Assumptions Total hot water use = 55.4 gal/day/household With EF 90 water heater (Fed. Std Jan ‘04) annual DHW = 3,604 kWh/yr Pumping use w/autostat = 1 hr/day * 33 watts = 12 kWh/yr (pump only runs when returning hot water temp drops below 120 F) Piping losses = 60 ft*10 Btu/hr/ft*16hrs/day/350 days/3414 Btu/kWh = 985 kWh/yr (R3 insulation)

7. 7 Conclusions Baseline DHW electricity use for typical homes is significantly lower than Laing assumptions Piping losses increase as a percent of total water heating use as household hot water use decreases (I.e., things get worse as the number of occupants decrease) In order to break-even, the recirculating system must reduce daily total hot water use by 17 gals (30%) and average faucet and shower use by 45%

8. 8 Recommendation Decline request to make recirculating hot water systems in single family buildings eligible for C&RD due to lack of demonstrable savings as well as high probability that such systems would actually increased energy use.