Evaluation study of a commercial gas boiler energy efficiency program

Robert Mowris and Ean Jones, Robert Mowris & Associates, USA
Kathleen Carlson, Verified, Inc, USA

Keywords

International Performance Measurement and Verification Protocol, monitoring, measurement, evaluation, commercial gas boilers, water heating, energy efficiency, combustion efficiency, boiler operating hours, ANSI

Abstract

This paper provides evaluation, measurement, and verification findings for a commercial gas boiler energy efficiency program in California. The program provided incentives for low, medium, and high efficiency natural gas boilers with output capacities ranging from 422 to 2,110 GJ/hour and rated efficiencies ranging from 82 to 98 percent. The evaluation adhered to the International Performance Measurement and Verification Protocol (IPMVP). Field measurements of boiler efficiencies were made using combustion efficiency analyzers. Hours of operation were monitored using motor loggers installed on the combustion supply-air fan. Ex-post energy savings were based on field measurements and customer billing data. Statistical sampling methods were used extrapolate mean savings estimates from sample measurements to the population and to evaluate precision.

Net ex-post program savings were 38,252 ± 4,357 GJ/year and 765,044 ± 34,662 GJ lifecycle. The first-year net realization rate was 0.87 ± 0.10. This was due to field-measured efficiencies and full-load operating hours being less than ex ante values. Field-measured boiler efficiencies were generally 4 to 12 % lower than manufacturers’ ratings due to higher inlet and lower outlet temperature conditions. Manufacturer ratings are based on 26.7 ± 1.67°C inlet and 82.2 ± 0.91°C outlet temperatures according to ANSI Z21.13-2000. The ANSI inlet and outlet temperatures are not typical of normal operation where average inlet temperatures are 46.1 ± 4.4°C and outlet temperatures are 63.3 ± 4.7°C. In-situ field measurements of old boilers found pre-retrofit combustion efficiencies of 75 % consistent with ex ante values.

The incentives offered by the program ranged from 20 to 30 % of the cost of the boilers. The program design was based on manufacturers’ reported performance data and product literature. Future programs should be based on field-verified boiler efficiency ratings rather than manufacturers’ ratings. Problems encountered during the evaluation included loss of equipment and data due to internal explosions on two boilers. The program cost was $ 1,142,857, and the evaluation study cost was $ 48,820.