REM v15.2 and the Duke Energy Progress RNC Program

Current RESNET guidelines require that HERS Raters begin using REM/Rate v15.2 on 1/1/2017. A full listing of the technical changes involved with v15 is available at Noteworthy items from the updates in v15 and later include:

  • RESNET Interpretations applied:
    • HPWH gains interact with the surrounding space
    • Water heater inlet temperature interpretation
  • Hot Water Addendum:
    • REM’s DHW tank temperature has been changed from 120°F to 125°F based on real-world data, gathered as part of RESNET’s household water efficiency analysis
    • Daily DHW usage reduced from 80 gallons to 60 gallons.
  • Weather data updated to include an additional 700 locations nationwide. This has the effect of potentially changing a home’s weather data and load calculations.

The RNC Program conducted a v15.2 analysis of over 600 RNC homes across NC climate zones. The average impact of the switch to 15.2 in this sample was -2% ( -52 kWh). The vast majority (over 90%) of homes saw savings impacts of less than +/- 10%. Additionally, 50% of homes in the sample were affected by less than +/- 5%.

As a group, HPWH homes were consistent negative outliers. Per the v15 updates, HPWHs now interact with the surrounding space (i.e. – a HPWH in conditioned space affects the space heating and cooling loads). When combined with the reduction in assumed DHW gallons per day, this lowers overall usage in the reference and as-built home, thereby lowering savings potentials from DHW. Impacts from v15.2 on HPWH savings are typically in the range of -400 to -550 kWh as compared to v14.6.3. Rebates for HPWH remain very much in line with the cost to builders, as is the Program’s intent.

Homes submitted to the program on or after 1/1/2017 will be processed in v15.2. v15.2-compatible UDRH files are now available on the Program website.