Executive SummaryThe design of this 1,280-square-foot, three-bedroom Habitat for Humanity of Metro Denver zero energy home carefully combines envelope efficiency, efficient equipment, appliances and lighting, and passive and active solar features to reach the zero energy goal. The home was designed with an early version (July 22, 2004) of the BEOpt building optimization software; DOE2 and TRNSYS were used to perform additional analysis. This engineering approach was tempered by regular discussions with Habitat construction staff and volunteers. These discussions weighed the applicability of the optimized solutions to the special needs and economics of a Habitat house-moving the design toward simple, easily maintained mechanical systems and volunteer-friendly construction techniques. A data acquisition system was installed in the completed home to monitor its performance.This report details the design of the home, presents detailed performance data from the first year of operation, and includes summary performance data from the second year of operation.Some overall conclusions from the project are listed below:• The NREL/Habitat ZEH exceeded its goal of zero net source energy and was a net energy producer for the first two years. The home produced 24% more energy than it consumed on a source energy basis in the first year of monitoring and 12% more energy than it consumed in the second year. • PV system sizing for ZEHs is challenging.o Total home energy use for a specific house becomes highly uncertain because of occupant choices and behaviors.o Meeting the ZEH design goal depends on occupant behaviors.o The economics of excess annual PV production depends on net metering agreements. • Zero energy does not necessarily mean a zero utility bill.o There are fixed monthly costs for NG and electricity service.o NG costs may not be displaced by net electricity production.• Efficient, affordable ZEHs can be built with standard construction techniques and off-the-shelf equipment. Meeting the BA goal of cost neutral ZEH in all housing sectors will require additional research on cost-effective efficiency options.ii
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* UA o is often referred to as the building loss coefficient. It represents the rate of heat loss or gain of a house as a function of temperature between the inside and outside under steady-state conditions. † DOE-2.2 is an hourly building energy simulation software tool.
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