“Mr. [Steven] Hilton is very focused on the environment; he really wanted to create a campus that was highly sustainable,” says Ted Hyman, FAIA, LEED AP, managing partner of ZGF Architects, LLP in Los Angeles, CA.
ZGF was hired to carry out the Hilton Foundation’s vision, first with a campus master plan, then by completing the first of four planned phases. The first: a building featuring a unique passive downdraft system, photovoltaics (PV), thermal solar hot water tubes, and extensive water-saving elements.
The Hilton Foundation building, designed to exceed the US Green Building Council’s Leadership in Energy & Environmental Design (LEED) Platinum certification, is significantly more efficient in its use of energy and water than most LEED Platinum office buildings. A large contributor toward achieving net-zero energy is the design of the building’s integrated envelope and building cooling and heating systems.
The Foundation was located in Century City in a corporate office environment when Steven Hilton was contemplating where he would establish his organization’s new home. The Foundation ultimately purchased land in Agoura Hills, because they wanted to move the staff into a place that would enhance the organization’s culture. The 66-acre Agoura Hills site is situated at the bottom of Ladyface Mountain.
“There is stormwater runoff from the Santa Monica Mountains that was flowing into large catchment basins,” says Hyman. “Every time it rained the runoff was going into Santa Monica Bay, so, as part of the new building project, the goal was to help improve the erosion issues. It was also about building an office environment that was an incredible place for the staff to work.”
ZGF put together a master plan for the Hilton Foundation headquarters that encompassed four phases on the 44-acre site. Because of a reduction in the Foundation’s size in 2008, the decision was to proceed with a smaller building at the bottom of the hill in order to contain initial costs. With growth in the economy, the endowment has increased again, which opens the door for considering future phases.
Unique Heating and Cooling System
As for how the building envelope’s cooling and heating system is designed, Hyman says, “Staff members are essentially working inside an air handler. There are no mechanical fans for moving air within the building. Agoura Hills is a location where, in the summer, it will hit 105 degrees [Fahrenheit], and there are days it’s 110 degrees for a week at a time. And in the winter, it will dip down below freezing for a week at a time.”
Given those temperature fluctuations, the building could not rely solely on passive ventilation. The architects and engineers considered a variety of options and chose a passive downdraft buoyancy system that takes advantage of the change in the density of air as it is cooled and heated to effectively move air in the building without requiring the need for energy to drive the fans.
The solution was achieved through chimneys.
“The building is straightforward,” says Hyman. “There are offices on the perimeter surrounding a two-story high atrium space. Two offices on each floor share a chimney along the façades of the building, and at the top of the chimney is a cooling coil.”
The idea dates back hundreds of years to its use in the Middle East. In warm weather, air enters the top of the chimney and is cooled by the chilled water in the cooling coils. The volume of air coming into the chimneys and the amount of air leaving the building through the louvers in the atrium is controlled by a sophisticated building management system, which also senses wind and sun direction.
In cooler months, when perimeter heating is required, the air coming in through the chimneys is heated by coils near the plenum space to cause it to rise within the offices. In addition, there are rooftop solar hot water tubes that can provide all the hot water needs for the project.
“Because the air that flows over those cooling coils relies on physics instead of fan energy, it tends to move more slowly than conventional systems; and as it gets cooler, and denser, and falls down the chimney, it induces the air movement,” says Hyman. “Then it comes up through the raised floor into the offices. As air in the offices heats up because of the people and computers, it rises and is released into the atrium through a vent at the top of the partition.”
At the top of the atrium a series of operable clerestory windows and louvers are tied to the building system. As the atrium space heats up, the louvers open and draw the warmer air out of the building.
“The principal idea is the introduction of air movement without any fans in the building,” says Hyman. “The challenge becomes direct sunlight reaching interior surfaces causing heat gain. Because it’s such a sensitive system, you can’t just turn up the fan up when you’ve got a large heat load in the building. The building systems need more time to react and to adjust the temperature.”
In designing the building envelope to ensure the heating/cooling systems work, “it became critical that we protected the building from direct solar radiation within the building, as it could generate heat loads that we couldn’t overcome with the system,” says Hyman. There is a dynamic shading system on the windows on the south exposures, which incorporates a micro blade that is shaped to allow natural light and views out without allowing solar radiation to enter the building. It features an override, so if someone sitting in the office finds it to be too cool and they want it warmer, they can override the blinds and leave them up until the space is heated up to the occupant’s preference.
“They are programmed so that after a period of time they reset, so that even if somebody comes and opens their blinds all the way and leaves for the day, those blinds will go back to a protected position while the space is getting direct sun,” says Hyman. “It’s pretty amazing when you walk through the building that none of the lights are on during the day. They simply aren’t needed most days.”
The Ways of Light and Land
The building was sited to maximize the opportunities in reaching the goal of net-zero energy by its true north/south placement and narrow width, enabling the ability to capture natural light, thereby harvesting sufficient daylight for all of the workspaces.
To meet the demands for electric power, there are solar panels, which also provide covered parking over a portion of the parking lot, producing sufficient electricity to bring the building to a net-zero usage on an annual basis.
The site also is home to a number of Coast Live and Valley Oak trees. “Oak trees are protected in Agoura Hills, so the building was sited to minimize the number of oak tree relocations. For every tree that was removed, four new trees were required to be planted,” says Hyman. An endangered flowering plant in the phlox family, the Ojai navarretia, was discovered on the site and also had to be protected. Over a period of a few years prior to starting construction, seeds were collected and replanted. “They’re being tracked for a couple of years to ensure that they are ahead of where they were before we built the building,” says Hyman.
Hyman says one of the more interesting undertakings was a demonstration project to manage stormwater in a much more sustainable way. “Utilizing bioswales to filter and collect the stormwater allowed us to reduce sediment and pollution and conserve water for irrigation and other uses onsite,” says Hyman. “When the stormwater finally reaches the debris basins, the basins are set up with an overflow to filter the water so only clean water is flowing into the stormwater system.”
Even the plant material selected for the debris basins can survive when the desilting of the basins requires large bulldozers to scrape off the sediment. The plants will reseed themselves and regrow.
Other sustainable site features of the Foundation’s property include a green roof with native plants for insulation and to absorb rainfall, permeable paving, and substantial recycling of construction waste.
After Moving In
The Foundation has had a year to experience what it is like to live in a net-zero building with these kinds of systems. There has been a “learning curve” both in how to operate the building, as well as how to live “with” the building, says Hyman.
“It’s a very different kind of experience,” he adds. “The building uses 100% outside air, so it is very healthy, and because of the buoyancy approach, it also is unusually quiet. You just cannot go to the thermostat and dial up or down, and instantly hear the system ramp up.” The systems respond very slowly, Hyman points out.
“The control systems are everything in the building, and to get the controls to work right, to get that air flow and get the blinds and windows to all work together, has taken most of the year to get it really tuned to where it is optimized.”
It’s at a point now where in the morning the building is using electricity from the grid for power, but by 11 a.m. or noon, it’s actually netting out at zero, and, by the end of the day, the building is producing more energy than it has consumed. “When we say net-zero, the goal is not that we’re off the grid, but that the utility bill annually is zero dollars,” says Hyman. “It’s a realistic approach. It would have been far more costly to have the building “˜off the grid.'”
How occupants adjust to a net-zero energy building when they’re conditioned to live in other types of spaces is one of the most interesting facets of the project, says Hyman.
“Mr. Hilton was really passionate about the design,” he says. “Before they moved from Century City, he shared with the staff that this is a very different building and it’s going to change their culture, which is something they were very interested in. In their previous facility, everybody dressed very formally. When they were moved to the new space, they were going to be more connected to nature, and the staff was told they should start dressing accordingly for the temperature as it changes seasonally.”
Hyman says the leadership and staff at the Hilton Foundation have been “incredible” clients in trying to change their culture to live in this building differently. “You can’t walk into your office in the morning and say, “˜I want it three degrees warmer,’ turn the knob, hear the fan go on and you’re going to be warmer,” he says. “It’s a much slower reaction. The tradeoff obviously is that it is a far more healthy and sustainable work environment.”
Hyman says sick days and productivity is being measured to ascertain whether this proves out. “It certainly feels like it when you’re in the building,” he says. “There’s a Zen feeling to the spaces. Having a building that’s really connected to nature really changes the culture of the place.”
It is also notable that everything in the building serves more than one purpose, says Hyman.
“The chimneys are acting as the mechanism for moving air, but also are the main lateral system for the building as large concrete shear walls, but in addition, the concrete further improves building performance providing thermal mass,” he says.
“Though the city’s architectural guidelines called for a mission-style of architecture, Mr. Hilton felt we should make the building feel a little more natural,” says Hyman. “With the city’s support, we were able to incorporate a stone veneer on the concrete.”
Hyman points out this building is very much about its place. “It wouldn’t make sense in a cold climate,” he says.
Collaborative Excellence
When they began designing the Conrad N. Hilton Foundation, ZGF modeled a series of integrated strategies for the building’s systems. “Mr. Hilton brought in the Rocky Mountain Institute [RMI], a non-profit research and educational foundation, to review the alternatives,” says Hyman. “They challenged us in a very collaborative way to really design something special. The entire team, including engineers, contractor, and RMI, became an incredibly collaborative group.”
Cheech Huang, LEED GA, of the MATT Construction Corp. in Santa Fe Springs, CA, served as the project manager for the Conrad N. Hilton Foundation. He indicates that there were some challenges in doing the project.
“It is rare that one has to try to make a mechanical system beautiful,” he says. “One of the fascinating things about this project is that the entire building’s architecture plays a role in the mechanical system-the chimneys, the clerestory windows, open atriums, ceilings, flooring-every element is dialed in to the atmospheric controls, and important for the health and comfort of the occupants.
“The challenge was to build a complex, well-functioning mechanical system and, at the same time, detail it as an elegant piece of architecture,” he continues. “ZGF Architects figured out an ingenious way to integrate the building’s mechanical items as beautiful architectural elements, and even focal points of the building.”
Huang’s advice to others considering a similar project is to be patient post-occupancy.
“It is a dynamic building,” he points out. “There is adjustment and verification that goes on throughout the first year, as you “˜tune’ the building and learn how best to adjust the settings to optimize the user experience.”
It’s also critical to get the architectural, engineering and construction team as well as key subcontractors on-board early for collaborative meetings, he adds.
A project of this magnitude requires teamwork. In addition to the architectural work of ZGF Architects, others involved in the project include:
- The Cadmus Group of Irvine, CA: commissioning agent
- WSP Built Ecology, M/E/P Engineers of San Francisco, CA: security, energy, and passive design consultant
- KPFF Consulting Engineers, Calabasas, CA: structural engineers
- David Nelson & Associates, Littleton, CO: lighting designer
- Stantec Consulting Services, Irvine: civil engineer
- Van Atta Associates, Santa Barbara, CA: landscape architect
- Davis Langdon, Los Angeles, CA: cost estimator
- Rocky Mountain Institute, Snowmass, CO: sustainable consultant
- Alden, Fort Collins, CO: water resource engineer
- GeoSoils Consultants, Van Nuys, CA: geotechnical engineer
- Envicom Corporation, Agoura Hills, CA: environmental consultant
- PlanNet Consulting, Brea, CA: audio/visual, IT, security consultant
- Kaminski Kaneko Design, Los Angeles: signage consultant
- Bigelow Development Associates, Malibu, CA: construction manager
- MATT Construction, Santa Fe Springs, CA: general contractor
Importantly, the materials used in the building are critical to its long-term success.
The structural system features Washington Iron Works’ wide flanges and tube steel. Largo provided Cemex. The 1100-Clear concrete curing was provided by W. R. Meadows. Viracon was the source for the VNE24-63 insulating glass. Sarnafil’s G410 Energy Smart Roof membrane was used for the low-slope roofing. Flora Source’s LiveRoof was used for the green roof.
Focal Point’s Covelight 26 is used for interior ambient lighting. Pluris’ ICL-LED650/ICL-LED900 is used for downlights. Philips’ eW Profile Powercore provides the task lighting. Kim Lighting’s WP9SE-LED is used for exterior lighting. The lighting controls are provided by WattStopper and Lutron.
The SolarWorld 240 watt photovoltaics are provided by Martifer Solar USA. The building management system is provided by Climatec. Energy Labs provided the HVAC-passive cooling roof unit. Uponor is used for the radiant flooring. The HVAC solar hot water collectors are Sunda Seido 2-16s from Beijing Sunda Solar Energy Technology Co. The ceiling tile is Decoustic’s Ceilencio custom ceiling system. Nysan Solar Control S_enn shade is used for the exterior sunshades.
