June 28, 2011


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.