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26 November 2014

HOK Net-Zero Energy Design Competition Winner: soLAr


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.

elevation - east1 - 300Tell 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.

HEATTRASFER303Multi-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.

How did you design the building to be more efficient?

Water 300We looked to design for efficiency in a number of ways:

  • A mechanical parking system allowed us to offer parking for all the residential units, while eliminating emissions typically generated from car movements in conventional garage layouts. The system also eliminates the need to mechanically ventilate large volumes of below-grade parking.
  • Elevator use is minimized by locating offices within a walkable height of entry level.
  • Bi-level apartments have access to daylight and natural ventilation on opposing sides. The three occupancy types have distinct daily energy use patterns that surge at different times, moderating peak demand for resources. Basic conservation measures, including occupancy sensors, automatic faucets and low-flow fixtures minimize electricity and water consumption.

What was a main takeaway from the design process?

As architects and designers, our learning curve related to advanced energy building systems was steep. We spent many hours doing research to find examples and statistics related to the potential systems we could integrate to develop a highly efficient design. Though finding and internalizing the information was not a quick process, it allowed us to focus on the most promising systems.

What is your favorite aspect of soLAr’s design?

Our favorite part of the design process was the discovery of synergies between systems. We found, for example, that a byproduct that had the potential to act as a disadvantage of a system could be repurposed and incorporated into a different system to provide efficiency.


It is exciting to now have soLAr as a conceptual starting point that scrapes the surface of the possibilities to bring renewable energy technology from an industrial scale to an architectural design.

Logical next steps in developing the veil strategy are to study the freeform shape relative to optimal convection effects and other wind inputs. Elaborating on the structural support system may bring a different dimension or “texture” to the surface and expose more opportunities for synergies.

These topics are naturally at the intersection of BIM and our buildingSMART goals for a data-driven design process that uses digital tools to achieve measurable performance improvements in HOK’s projects.

View all of the project images on Flickr.