Cathedral Poses Hvac Design, Installation Challenges
What has historically taken centuries to construct is being built in Los Angeles, CA, in three years. Construction began in May 1999 on the $163 million Cathedral of Our Lady of the Angels, scheduled for completion in spring 2002.
As the first Roman Catholic cathedral erected in the western United States in 30 years, it is expected to serve not only as a sacred space but as a major tourist attraction.
“The dynamic, contemporary design has virtually no right angles, and many of the floor surfaces are sloped or ramped,” says project manager Nick Roberts of Leo A. Daly, the Los Angeles-based firm serving as executive architect. “This geometry contributes to the cathedral’s feeling of mystery, but [also] presents challenges for the construction documents.
“Instead of working with 2-D plans, we developed critical areas of the design using 3-D CAD models, and provided 3-D coordinates to the contractors instead of conventional dimensions.”
Mortar In The Cathedral“The effect of the exterior environment on the interior will be minimal,” says John Gautrey, senior associate of London-based Ove Arup and Partners, which designed the project’s hvac, electrical, and plumbing components.
“Just as in medieval cathedrals, we’re utilizing the mass of the building to keep it cool in summer and warm in winter.”
Insulation is provided by the 40,000 cu yards of architectural and structural concrete that is 4-ft thick in some places. This configuration “creates very stable conditions,” according to Gautrey. “With no people and no lights, the cathedral would maintain a year-round temperature of 60Â°F.”
That, however, will not be the case, since a cathedral in downtown Los Angeles “is meant to be a focal point for visitors,” Gautrey says, “and the lights will always be on. We’ve calculated that the surface temperature will be 70Â° to 74Â° most of the time.
“We’ll basically be using lights and people to keep the building warm.”
HVAC Out of SightAny heat that is needed will be introduced through the air system, with the bride’s room and other side rooms having their own hvac systems.
The archdiocese wants the cathedral to last 500 years — well beyond the 30- to 50-year lifecycle of most high-use buildings — “but the hvac system is not going to last 500 years,” says Gautrey. “We had to design a system that doesn’t impact the architecture, but is easy to replace without tearing everything up.
“We’ve had to work out routes and supply points that are not seen. The air comes up through grilles that fit within the stone floor finishes, with floor diffusers below the pews. Unless you get down on your hands and knees and look under the pews, you won’t see the supply points.”
No chilled water is generated on site because the cathedral will be tapping into the supply system that connects county buildings in downtown Los Angeles. This connected load is 720 tons, according to Kent Williams, sales engineer and project manager for Anaheim, CA-headquartered Thermalair, the hvac contractor.
Since the cathedral is directly across the street from the central plant, it is the first building to tap into the supply. “We’re at the highest pressure point — 210 psi,” says Williams. “Normally you see 75 to 100 psi, so we needed a pressure-reducing system. We’re letting the county push the water into our buildings, and we’re using our pumping system to return the water to the county. This is sure an unusual way to provide chilled water.
“We didn’t find this out until we were well into the project. We had to put our thinking caps on. We have never done anything like this before.”
A/C Load Lower Than NormalBecause the sheer mass of the building maintains a stable interior temperature, the air conditioning load is “much lower than you’d normally expect,” says Gautrey.
“The cathedral is similar to a large theater that would perhaps operate at 20 to 30 cfm per person. In contrast, the cathedral will run at about 15 cfm, since we only need to condition the bottom 10 feet, the occupied area of the space.
“Fifteen cfm just happens to be the code minimum for fresh air per person, so we can use 100% outside air, thereby keeping the air quality very clean.”
Building codes also allow for control of outside air based on ppm of CO2. Since this is a huge volume, with peak occupancy of 3,000 people occurring only three or four times a year, outside air can be taken down to 5 cfm/person while monitoring CO2, making for a very energy-efficient system.
“I tried to persuade the architect that we didn’t need air conditioning at all,” Gautrey says, “but if we don’t move air when the cathedral is at full capacity, it will get a bit stagnant.”
Gautrey used computational fluid dynamics (cfd) to computer model airflow over a projected week’s load and thereby optimize the system. “Historically, buildings have too much a/c and never use it. Cfd allows for planning in large spaces that are difficult to calculate otherwise.”
Despite the many challenges of such a large and complex project, everyone involved echoes the sentiments of Terry Dooley, senior vice president of Santa Monica, CA-based Morley Construction Co., the general contractor: “I have been in construction for more than 40 years, and this is one of the few thrilling projects I’ve been a part of in all that time!”
Sidebar: Earthquakes, Alabaster, and the Test of TimeA cathedral built in Los Angeles to stand 500-plus years is one that must withstand major earthquakes. To this end, the Cathedral of Our Lady of the Angels will simply “go with the flow”: A system comprised of 196, 3-ft-thick, rubber isolator pads and sliders will isolate the cathedral from its foundation in the event of a temblor.
Oversized ball joints will allow the building to move up to 54 in. along any horizontal axis. In short, the cathedral will “float” through the “Big One” — a magnitude 8.3 on the San Andreas Fault or a 7.0 or higher on the faults that run through downtown L.A.
A 10- by 10- by 15-ft room was built to house the ball joints so that the piping can move with the cathedral. “They can bend around in a 3-D space so they don’t break,” says John Gautrey, who designed the system.
Another challenge Gautrey faced was that of 24,000 sq ft of 5/8-in.-thick alabaster windows. “They’re semi-transparent,” he says; “when backlit, they’re really beautiful. You can see the veins in the alabaster.”
As with most things that are beautiful, the alabaster windows are also delicate. When they reach a surface temperature of 115Â° to 120Â°F, they decompose into gypsum, which is chalky, opaque, and crumbly — not what you want for windows.
“We had to work out a system to keep the surface temperature below 100Â°,” Gautrey says. At first he tried laminating glass onto the alabaster, but the high temperature required for lamination degraded it.
“Protecting the alabaster windows — a major feature of the church — was accomplished by moving them inside the conditioned air space and building an exterior membrane of fritted glass,” says Terry Dooley, senior vice president of Morley Construction Co., the general contractor.
“The quality of the exterior glazing helped,” says Gautrey; so did the creation of a 75-ft-high cavity between the outer windows and the alabaster. “The resulting stack effect is used to move internal air through that space and keep the alabaster from overheating. We needed to do this without mechanical assistance, so that 150 years from now, someone won’t come along and turn off the fans.
“Think of it as a double-paned window with six feet of airflow between the panes.”
Facts, Figures, and EquipmentSite and structure
Publication date: 12/18/2000