This project, supported by the U.S. Department of Energy’s Building America Program, is a case study in reaching zero energy within the affordable housing sector in cold climates. The design of the 1200 square foot, 3 bedroom 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.
From April 2006 through March 2007 the home’s 4kW PV system produced 5127 kWh of AC electricity. Only 3585 kWh of electricity and 57 therms of natural gas were used in the home during this period. On a source energy basis, the home produced 24% more energy than it used. The energy used for space heating, water heating, and lighting have been dramatically reduced through superinsulation, passive solar tempering, solar water heating, compact florescent lights and other efficiency measures. The energy used in the home is now dominated by appliance and plug loads determined by occupant choices and behavior. These loads constitute 58% of all the source energy used in the home. Because these loads are generally outside of the control of the home designer and vary considerably with different occupants, sizing a PV system to achieve zero net energy performance is challenging.
This case study demonstrates that it is possible to build efficient affordable zero energy homes in cold climates with standard building techniques and materials, simple mechanical systems, and off-the-shelf equipment.