A Reliable but Simplified Method for Measuring the Savings from Advanced RTU Control Retrofits February 13, 2013 Presentation to: RTF Commercial Rooftop Unit Working Group Presented by: Michael Baker, SBW Consulting, Inc. Bill Koran, NorthWrite, Inc.

Objective Obtain RTUG Recommendation for Approval of this simplified method for estimating savings from Advanced Rooftop Controls 2 February 13, 2015

Questions to Address Are fan savings well estimated by the simplified method? Can cooling and heating savings be estimated by the simplified method? Is the simplified method the simplest reliable method of verifying ARC Retrofit electrical savings? 3 February 13, 2015

Approach Compare best practice savings estimate with simplified savings estimate Compare total, program-level savings Understand unit-to-unit variations 4 February 13, 2015

Approach – Best Practice Method Research-level, best practice savings estimates completed by PNNL  Savings estimate based on regressions  True power measurements of baseline and post power of RTU  Roughly 1 year of data  Alternate between baseline and efficient modes, changing each day.  61 RTUs, of which 16 are Heat Pumps 5 February 13, 2015

Approach – Simplified Method Simplified savings estimates  Savings estimate based on regressions  Baseline and post power from VFD on fan  Same data periods  54 RTUs, including 16 Heat Pumps 6 February 13, 2015

Steps in the Simplified Method 1. Collect hourly average fan speed, fan power (VFD output) and OAT from the RTU that has advanced controls 2. Fit a power regression to fan power vs. speed, for all speeds occurring in the efficient mode of operation. 3. Calculate the 100% speed fan power using the fit curve 4. For each hour compute savings as the difference between the 100% speed fan power and the VFD input power. Input power is derived by dividing the output VFD power by Fit a model to fan savings vs. OAT (Outside Air Temperature) and use TMY (Typical Meteorological Year) OAT to extrapolate to annual fan savings. It is expected that time and outside air temperature will be the independent variables. Obviously, extrapolating to TMY weather includes the implied assumption that fan speed is weather-dependent. This may not be a good assumption for all applications. 7 February 13, 2015

Project Sites 8 February 13, 2015 Note: The number of RTUs in this table is greater than the number of RTUs listed in the prior slides because some RTUs were dropped from the analysis.

Comparison of Fan Savings Only 9 February 13, 2015

Comparison of Estimated Fan Power 10 February 13, 2015

Savings Comparison, All Units 11 February 13, 2015

Savings Comparison with Uncertainty in Best Practice Savings 12 February 13, 2015

Savings Comparison, Gas Packs and Heat Pumps 13 February 13, 2015

Deviation of Savings From Predicted is Associated with Cooling Deviations 14 February 13, 2015

Conclusions Fan savings are very well estimated by the simplified method. Cooling savings are well estimated, on average, by a multiplier on the fan savings. Cooling savings vary unit-to-unit, and estimation is uncertain even with a best practice method. The simplified method, using supply fan VFD power, is the simplest reliable method of verifying ARC Retrofit electrical savings. 15 February 13, 2015

Example Fan Savings Estimate 16 February 13, 2015

Example Fan Savings Estimate 17 February 13, 2015

Fan Savings Calculations 18 February 13, 2015 DateTime 375 FanSpeedAvg 375 FanPowerAvg 375 ESMModeHrs Sum of Hours 375 UnitPowerAvg Fan Post kW Fan Post kWh kW Savings kWh savings 5/3/13 4:00 PM /3/13 3:00 PM /3/13 2:00 PM /3/13 1:00 PM /3/13 12:00 PM /3/13 11:00 AM /3/13 10:00 AM /3/13 9:00 AM /3/13 8:00 AM /3/13 7:00 AM /3/13 6:00 AM /3/13 5:00 AM Fan Post kW = 1/VFDeffy*(multiplier* (IF(speed>90,(speed-90)/(100-90)*100+(1-(speed-90)/(100-90))*90,IF(speed>75,(speed- 75)/(90-75)*90+(1-(speed-75)/(90-75))*75,IF(speed>40,(speed-40)/(75-40)*75+(1-(speed- 40)/(75-40))*40,IF(speed>0,(speed-0)/(40-0)*40+(1-(speed-0)/(40-0))*0,0))))) ^exponent)

Outliers 19 February 13, 2015

Outliers and Deviation of Savings From Predicted 20 February 13, 2015

RTUG Recommendations to the RTF Does the RTUG agree that the simplified method is reliable and should be considered proven? Does the RTUG agree that a standard protocol should be developed based on this simplified method and presented for approval by the RTF? 21 February 13, 2015