“…In the U.S., simulation optimization engines have been used to generate near-neutral-cost retrofit packages (on a cash-flow basis, assuming retrofit costs are financed) in varied U.S. climate zones, with average source energy savings varying from 43% to 74%, depending on the assumed interest rates for a 30-year loan (Fairey & Parker, 2012;Polly et al, 2011). Consistent with past research and current demonstration efforts, a 50% savings target represents a reasonable, achievable definition of the minimum requirements for a Deep Energy Retrofit (DER), though greater savings levels are desirable and have been used as a benchmark in some programs and studies (Affordable Comfort, Inc., 2010;Boudreaux, Hendrick, Christian, & Jackson, 2012;Less, Fisher, & Walker, 2012).…”