Construction begins in January 2019 on a new zero energy home for a challenging site in North Arlington, Virginia. A steeply sloping hill falls away to the east. The home will be placed along the north side of the site to take advantage of an existing plateau in the yard for the permaculture garden. This will also give maximum solar exposure for winter solar heating and rooftop photovoltaic panels. The home will have two entrances: one to the office located at street level, and one for the residence at the terrace level. The upper entrance will also serve as the wheelchair entrance for this fully accessible home.
We designed the home to the Passive House standard. The most challenging aspect of this was the large amount of south-facing glass. We compensated for this by keeping west and north glazing to a minimum and providing motorized shading and overhangs for all south-facing glass. We will be using double wall construction with an EIFS system at the exterior; similar to the approach used at the Fairfax zero energy home.
What makes this home unusual is its electrical system. The residence is equipped with an 11kW roof-mounted photovoltaic (PV) array sized to provide sufficient energy to achieve “net zero” status when calculated on an annual basis. The planned installation is among the first residential direct current (dc) installations to incorporate dc to dc power management and battery storage systems. With this approach, direct current power generated through the PV array, is fed directly to a common dc bus, and used to simultaneously satisfy ongoing residential power demands and charge an on-site 20kW battery bank. This configuration facilitates power production and consumption from the PV array under daylight conditions, with stored energy from the batteries powering loads after dark. The generation, consumption and storage of dc power, without the conversion to alternating current, eliminate the losses inherent in this conversion process.
The home makes extensive use of dc power produced from the PV array and stored in the on-site batteries for lighting, selected motor loads and strategically placed convenience receptacles. Circuits are also designed to adapt to next-generation dc appliances when time comes for replacement. The home is highly automated through an integrated Loxone direct current, low voltage control system for lighting, blinds, security and mechanical systems. The entire electrical system was designed by Interface Engineering, who recently completed the installation of a direct current lighting and power system for the American Geophysical Union building renovation in Washington, DC. To learn more about the developments in direct current, see this blog post.
- Date November 10, 2018
- Tags Aging in Place, New Homes, Passive Houses