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A startup builder in the San Francisco Bay Area has a goal of producing factory built/modular houses with net zero energy performance. Their first prototype was a two-story, two bedroom, urban infill townhouse design. It has been in operation for roughly a year, and has been extensively measured and monitored, providing information about its net zero performance. Some technologies incorporated into this prototype include higher R value walls than typically used in this mild climate, high performance windows, excellent airtightness, a heat pump water heater, drainwater heat recovery, and a residential-scale economizer. The data collected to date indicate that the building is on track to achieve net zero performance. Several obstacles arose during the construction and commissioning of the building, which provided some useful lessons on integrating advanced technologies. Another design constraint was that the builder wished to have an all-electric house: both for 'perceived net zero performance' (all measured in electricity), and due to restrictions of California net metering laws. An analysis was conducted to assess the relative cost-effectiveness of various building enclosure and mechanical measures. The monitored data has provided a wealth of information, including submetered energy consumption for various end uses; photovoltaic system output; heat pump water heater performance, and effectiveness of the drainwater heat recovery system. It has already been used to remotely diagnose malfunctioning or improperly operated equipment. [ABSTRACT FROM AUTHOR]

A homebuilder working in the New England area has been building net zero energy single family homes since circa 2008, and is currently continuing with multiple small-scale subdivisions of 20 or more homes. This builder specializes in net zero affordable homes and sustainable net zero communities, while retaining houses with a familiar local vernacular appearance. Some of the key features of these houses include solar orientation, superinsulated double-stud above grade walls (R-45+ nominal), triple glazed low emissivity krypton-filled windows, and exceptional airtightness. The mechanical design takes advantage of the reduction in enclosure-based heating loads by using single-point (or one point per floor) heating, in the form of mini-split or ductless split air source heat pumps. This modification substantially reduces installed HVAC system costs relative to a conventional ducted system. The effects of this single-point distribution in superinsulated housing are a matter of further measurement in this study. In addition, the ability of an air source heat pump to meet heating loads in a cold climate is a matter of concern; the ability to maintain setpoint (and dependence on backup heat) is another research topic. The renewable energy component is a roof-mounted photovoltaic system, sized to meet the modeled loads; a PVT system (combined photovoltaic-solar thermal) was also used in some cases. Controlled mechanical ventilation options have included heat recovery ventilators and simplified supply-only systems. When combining the factors of the installed cost of HRVs, the ventilation rates used, and the increased electrical (fan) energy of HRVs, the cost-benefit relationship of heat recovery appear to be not as advantageous as originally thought. The builder also has been concentrating on cost control for these houses, given the shift into full-scale production, and has been actively involved in monitoring of the effectiveness of various measures. Energy modeling and analysis have also been used to examine the cost-effectiveness of various options. Avenues examined have included various solar domestic hot water systems, building-integrated photovoltaics, modifications to the wall construction, and modified foundations. [ABSTRACT FROM AUTHOR]