Five designers from HOK’s Los Angeles office – Jessica Ginther, Frank Cauthen, Jamila Valero, Zach Capehart and Kris Surichamorn – competed in the firm-wide Net Zero Design Competition as the team “soLAr.”

The net-zero competition challenged HOK’s teams to create a conceptual net-zero energy design for a building on a site in their local communities. Teams were required to use HOK’s Sustainable Analysis Tool to obtain climate data, set energy use intensity (EUI) targets and estimate the size of on-site renewable energy systems required to reach net-zero energy.

The soLAr team designed a mixed-use building on a site in downtown Los Angeles. The team’s design won first place in the internal HOK competition.

Tell us about your building. What major factors impacted the design?

Our project site is located amid many recently redeveloped medium- and high-rise commercial and multifamily projects. We proposed a mixed-use building to integrate into the neighborhood by matching existing uses, demographics and densities. Our building incorporates offices on the first-floor retail level, three stories of class B offices and 10 stories of apartments configured along single-loaded corridors.

The site is surrounded by existing buildings that interrupt access to the full skydome. To address this constraint, we rotated the residential floors to maximize solar access. We used a highly efficient solar generation technology to maximize the energy conversion of the daylight.

Adjacent construction also influenced our decisions about placement of occupied spaces that would benefit from natural ventilation and daylighting.

What kind of renewable energy did you design the building to use? How did your HOK Sustainable Analysis report impact that decision?

Being in Los Angeles, solar panels were an obvious place to start. But the HOK Sustainable Analysis tool showed that a conventional system would not provide the yield we needed.

To maximize the area available for solar collection, we designed a freeform veil with jewel-like concentrated photovoltaic (CPV) collectors oriented toward maximum sun exposure and contoured to minimize shelf shading and obstruction by neighboring buildings. As a semi-porous surface, the veil directs water runoff to filtration terraces on the building’s roof podium, where it is diverted for use in the CPV heating loop.

Multi-junction receivers operate at 40 percent efficiency by reflecting solar energy to a small area on each collector. To sustain that efficiency, large amounts of heat must be shed by the receiver. Instead of dissipating the heat to the ambient air, soLAr’s veil captures it in a water-coolant loop and routes the energy for use in absorption chillers for cooling individual apartments and retail and office spaces.

For each kW of electricity, an additional 2 kW of heat energy is made available for cooling or water treatment and desalination. Heat shed by the collectors that cannot be recaptured drives a convection stack effect on one side of the residential tower, enhancing the natural through-ventilation of each apartment.

How else did the HOK Sustainable Analysis report impact the design?   

Our HOK Sustainable Analysis report showed that the local climate was favorable to certain strategies and not others. The report showed that, even with a reduction in energy use and covering the entire site with a conventional PV installation, the building would not produce enough energy to achieve net zero. We then worked to find strategies to reduce our project’s EUI and considered alternative power generation strategies to not only be net zero, but net positive. The need to reduce the building’s energy use led us to explore how the different water, power and ventilation systems could integrate and benefit from each other.