Small Changes Yield Large Results at NIST's Net-Zero Energy Residential Test Facility

The Net-Zero Energy Residential Test Facility (NZERTF) was designed to be approximately 60% more energy efficient than homes meeting the 2012 International Energy Conservation Code requirements. The thermal envelope minimizes heat loss/gain through the use of advanced framing and enhanced insulation. A continuous air/moisture barrier resulted in an air exchange rate of 0.6 air changes per hour at 50 Pa. The home incorporates a vast array of extensively monitored renewable and energy efficient technologies including an air-to-air heat pump system with a dedicated dehumidification cycle; a ducted heat-recovery ventilation (HRV) system; a whole house dehumidifier; a photovoltaic system; and a solar domestic hot water system. During its first year of operation, the NZERTF produced an energy surplus of 1023 kWh. Based on observations during the first year, changes were made to determine if further improvements in energy performance could be obtained. The changes consisted of installing a thermostat that incorporated control logic to minimize the use of auxiliary heat, using a whole house dehumidifier in lieu of the heat pump's dedicated dehumidification cycle, and reducing the ventilation rate to a value that met but did not exceed code requirements. During the second year of operation, the NZERTF produced an energy surplus of 2241 kWh. This paper describes the facility, compares the performance data for the 2 years, and quantifies the energy impact of the weather conditions and operational changes.