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