URBAN LAND MAGAZINE — In 2017, California passed the first net-zero building code in the United States. New York City; Washington, D.C.; and other cities have made net-zero building commitments as well, including both new and existing buildings.
Construction is now fully underway on The American Geophysical Union’s (AGU) headquarters renovation in Dupont Circle. As part of its mission of “science for the benefit of humanity,” AGU seeks to lead by example and is striving to create the first-ever “net zero energy” renovation of an existing commercial building in the District.
In order to realize this goal, particular strategies had to be devised and technological advances realized. We would like to present just a few of them from the architects’ perspective:
Solar Photovoltaic (PV) Array
This solar PV array includes 720 solar panels making up a 250 kilowatt system. It includes 24 panels on a vertical, south-facing surface and 696 panels laid out horizontally and elevated above the penthouse roof. The panels are from manufacturer Sunpower, and at just over 22% efficiency, they are some of the most efficient on the market.
Dedicated Outdoor Air System (DOAS) with Exhaust Air Heat Recovery
The DOAS will provide a dedicated means of ventilation for the building. This system will condition the air prior to delivering it inside, while at the same time recovering the outgoing exhaust air’s heat to help raise the temperature of the incoming fresh air for space heating needs.
Hydroponic Phytoremediation (Hy Phy) Wall
While this wall looks like a standard green wall or vertical garden, it will actually work a little harder. When installed it will be an active rather than passive wall, and function as part of the building’s ventilation system. In conjunction with the DOAS, the wall will filter and improve indoor air quality, all while reducing the amount of outside air necessary. The plants, their roots, and the water filtration system will scrub air of unwanted toxins and VOCs before it recirculates throughout the building.
Municipal Sewer Heat Exchange System
This system will tap into a combined sewer line in front of the building, which was built in the 1890s, to maximize the efficiency of the building’s mechanical systems. It will essentially function the same way a geothermal system does—as a heat sink/source—but it will be the first of its kind in the United States. The system operates by:
- Diverting wastewater to a settling tank located just outside of the building.
- Circulating the then debris-less water into a sewer heat exchanger in the underground garage.
- While in the garage, separately piped in radiant fluid will be pre-heated or cooled before being circulated throughout the building.
Fear not, it is a closed loop system, no sewage contamination will take place. Read more about how sewer heat exchange works here.
Stormwater Collection and Re-use
Rainwater will be captured from the roof and PV array and collected in a large cistern also located in the building’s garage. After filtration and treatment this greywater will be reused for all flushing fixtures and the irrigation of the green roof and hy phy wall. The cistern’s capacity is 11,300 gallons.
Enhanced Dynamic Glazing System
The existing windows at AGU will soon be removed and replaced with dynamic glass. The curtainwall glazing will be made up of triple-pane, air-filled, 1-3/4” thick windows. The added 3rd pane gives the windows a lower U-value and solar heat gain coefficient to help reduce the transmission of heat and cold. This glazing will also utilize an electrochromic film to tint the windows on-demand. This tint twill take the place of traditional blinds as well as reduce glare and heat transmission while still allowing natural light in and views out.
DC Powered Workspace and Lighting
The US electrical grid is wired for alternating current, or AC, power distribution. However, direct current, or DC, power is used by computers, appliances, and LED lighting. Conveniently, DC power is also what will be produced by the large PV array on AGU’s roof. Creating an energy distribution microgrid which relies on direct DC to DC power will reduce the energy efficiency loss caused by power conversion.
Enhanced Envelope Insulation
The existing building envelope is brick on a CMU backup wall separated by an air gap. The exterior walls do not currently contain insulation or an air/weather barrier. 6” studs have been added along the interior of the perimeter wall which will provide space to:
- Install 8” of closed-cell spray-applied insulation to achieve an R-value of 53. The new insulation will also act as an air barrier.
- Anchor new windows which will now be in-line with the insulation, creating a continuous thermal barrier.
Radiant Ceiling Cooling System
In a radiant ceiling system temperature is controlled by radiation, a more efficient way to condition space than forced-air. Decoupling the building conditioning system from the DOAS provides the opportunity to reduce the overall energy needed to move air through the building since it’s now only needed for ventilation, not for space cooling.
“The renovation of the existing AGU headquarters provides an unprecedented opportunity to challenge ourselves to lead by example and demonstrate that we, and the Earth and space science community we represent, can be a model for sustainable design, reducing the carbon and environmental impacts of business operations in a cost-effective and replicable way.”
– American Geophysical Union
Be sure to follow the latest construction updates at Building AGU.