A presentation to the 2009 National Weatherization Training Conference this year by Michael Blasnik, of M. Blasnik & Associates looked at why energy modeling always overestimates energy savings in retrofits and highlighted some common strategies that deliver little or no energy savings.
The tool used in the WAP program is the Weatherization Assistant and effective measures are based on Savings to Investment Ratio greater than 1. Most energy auditors I know believe actual performance of buildings never lives up to the modeling, regardless of the tool used, including NEAT and Rem/Rate.
Blame for this shortfall is usually placed on the occupants of the building, but Mr. Blasnik say the energy modeling software is based on poor assumptions and algorithms that are not tested and calibrated to actual performance. His assessment, based on several evaluations, is that actual energy savings are generally 50-70% of the modeled projections for the most effective measures such as air sealing and insulation. He goes on to list a number of measures with only marginal savings:
10 simple things that don’t do much
Furnace Tune-ups — Savings potential too rare to be worthwhile as general advice
Furnace “Right-Sizing” — Modern Furnaces show little part load degradation and Over-sizing gives quicker recovery from setback
Basement Duct Sealing — Studies in Ohio and Penn. pegged heating savings at less than 3% . Basement duct sealing may be worthwhile if costs are low or targeted to big leaks, but generally basements are connected to the conditioned space.
Floor Insulation — Wx evaluations findings Savings (therms/yr): OH=0, IA=6, NJ=21, CO=39, OR=28
Basements - Same reasons as basement ducts , connected to inside the thermal boundary, so heat loss regained. Colorado WX found perimeter insulation cheaper, same savings (39 therms).
Window Replacement — Savings ~ 2-3 th/yr/window, 100+ year payback unless existing windows are very inefficient single-pane, so storm windows more cost-effective.
Tankless Gas Water Heaters – Offer gas savings 35-75 th/yr, but often very expensive — $2000+ retrofit for gas, resulting in 30-40 year payback and likely to increase water usage with “endless” showers and efficiency may be overstated.
Save on A/C by Cooling Your Attic? — A cooler attic in the summer won’t save much if ceiling is well insulated, unless ducts are in attic, then may save 15% of cooling load
Cool Roofs - Are an expensive retrofit with long payback and not recommended in heating climates anyway. Cool roof lasts longer, esp. white coatings on flat roofs
Energy Feedback Devices — 10+% savings often touted from Power Cost
Monitor, TED, but new studies are finding much lower savings, although these devices are inexpensive investments. (And the TED 5000 with Google Powermeter has a big WOW factor that may help sell other, more effective upgrades)
Change furnace filters monthly - Blasnik say there is no evidence of savings by changing more than once per season.
His presentation also discounts emphasizing air mixing, closing drapes at night, cleaning refrigerator coils, and energy efficiency kit programs.