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Weatherization Assistant: What’s New in Versions 8.4 and 8.5

This presentation discusses the field validation study of the Mobile Home Energy Auditor (MHEA) and the technical changes made in Version 8.4. It explores the validation results, comparisons with BESTEST and RESNET procedures, modifications made based on field validation, and the potential program impacts of the revised MHEA.

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Weatherization Assistant: What’s New in Versions 8.4 and 8.5

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  1. Weatherization Assistant: What’s New in Versions 8.4 and 8.5 Mark Ternes Mike Gettings Oak Ridge National Laboratory 2009 National Weatherization Training Conference July 22, 2009

  2. Purpose of This Presentation • Discuss MHEA field test and analyses results that led to important technical changes in Version 8.4 • MHEA field validation (overall performance) • BESTEST (UA values and space-heating load) • RESNET procedures (energy consumption) • True-up using the MHEA field validation homes (overall performance) • Summarize potential program impacts from use of the revised MHEA • Identify and discuss other changes that have been made in Version 8.4 and 8.5

  3. MHEA Field Validation Study • Validation performed at DOE request before full implementation of MHEA • Validation report published November 2007 (ORNL/CON-501) • Findings (86 homes) • MHEA over predicted space-heating energy savings of weatherization measures by ~200% on average per home • MHEA achieved an average realization rate of ~35% (actual savings divided by predicted savings)

  4. Home Energy Rating System (HERS) Building Energy Simulation Test (BESTEST) • Uses a basic single-family, site-built house that is simplistic enough to be modeled in MHEA • 10 different test configurations of this basic house • Insulation and infiltration levels • Glazing properties and orientation • Shading • Internal loads

  5. Comparison of UA Calculations

  6. Conclusions Regarding MHEA’s UA Calculations • Some deviations from BESTEST occur: • NOT because MHEA calculations are wrong • But because MHEA accurately reflects mobile home construction or for other explainable reasons • MHEA accurately calculates the UA-values of mobile home envelope components

  7. Space-Heating Load Analysis • MHEA UA-values made to equal BESTEST values to focus the analysis on the load calculation engine • BESTEST criteria are based on the results from three hourly simulation programs • DOE-2 • BLAST • SERI-RES • Loads calculated for a Denver climate • Space-cooling loads not examined

  8. Comparison of Space-Heating Loads

  9. Comparison of Change in Loads

  10. Conclusions Regarding MHEA’s Space-Heating Load Calculations • MHEA passes the BESTEST criteria for each of the 10 test configurations, usually falling near the midpoint of BESTEST’s allowable range • MHEA accurately calculates the space-heating load of a mobile home • MHEA’s loads essentially track BLAST and are about 3-9 MBtu higher than DOE-2

  11. RESNET Procedures • Tests space-heating energy consumption calculations for various heating systems using the BESTEST base case test configuration • Compares energy consumption of one heating system to another • 90% AFUE furnace to a 78% AFUE unit • 9.85 HSPF heat pump to a 6.8 HSPF unit • Electric resistance furnace to a 6.8 HSPF heat pump • RESNET results are based on the results of six hourly simulation programs • Two DOE-2.1 tools • Two DOE-2.2 tools • Micropas version 6.5 • TRNSYS version 15

  12. Results and Conclusions Regarding MHEA’s Space-Heating Energy Consumption Calculations • MHEA accurately calculates the space-heating energy consumptions of the tested systems

  13. So....... • MHEA found to accurately calculate: • UA-values • Space-heating loads (essentially equivalent to BLAST or DOE-2) • Space-heating energy consumptions • But re-analysis using the MHEA field validation mobile homes showed that: • MHEA still over predicted savings by 168% • MHEA still achieved a realization rate of only 37%

  14. Modifications to True-Up MHEA Predictions to Field Validation Results • Modeling of field validation homes in MHEA • Turned off programmable thermostat measure (12% of the homes) • Floor insulation levels of 0 in. changed to 0.5 in. (14% of the homes) • Engineering modifications to MHEA • Changed MHEA’s internal load assumptions to be more consistent with HERS and NEAT • Reduced MHEA’s infiltration loads by ~25% • Added an R-value of 1 to the ceiling, floor, and walls • Applied a 0.6 correction factor to MHEA’s energy savings calculations

  15. Results from True-Up Modifications • MHEA’s over prediction of energy savings reduced to just 28% • MHEA’s realization rate increased to 78% • Use of MHEA’s optional billing adjustment feature can further improve MHEA’s accuracy on individual homes • Over prediction of energy savings reduced to 16% • Realization rate increased to 87%

  16. Simulation of Program Impacts from Use of the Revised MHEA • Compared recommendations from the revised MHEA (Version 8.4) to the original (Version 8.3) • Frequency that measures are recommended • Average investment levels per home • 18 mobile homes in Ohio • 13 heated by natural gas • 5 electrically heated • Columbus weather (5723 HDD) • State-supplied fuel and installation costs • Included health & safety and repair items

  17. Program Impact Results and Conclusions • Use of the revised MHEA does NOT eliminate the recommendation of insulation measures • Roof: from 72% of the homes to 61% • Floor: from 89% of the homes to 61% • Wall: 17% for both versions of MHEA • Storm windows: 83% of the homes to 39% • Average investment levels remained high • Average investment per home dropped from $2832 to $2193 • Recommended investment level changed less than $130 in 39% of the homes

  18. MHEA Steering Committee Comments • MHEA is now more accurate • Estimated energy savings and SIRs are more reasonable • The changes made in the revised MHEA move the recommendations in the right direction • Measures with questionable economics – like storm windows or insulating a roof with a decent amount of insulation in it – are less likely to be recommended • Recommend issuing the revised MHEA once remaining programming issues are resolved

  19. Conclusions • MHEA’s basic engineering calculations were found to be accurate • Several adjustments had to be introduced into MHEA to make its energy estimates agree with measured field data • Recommendations appear to be reasonable • Program impacts compared to Version 8.3 appear to be reasonable and as expected • Final report published December 2008 (ORNL/CON-506) • Version 8.4 of the Weatherization Assistant with the revised MHEA was released November 14, 2008

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