>
Click here to read the full article
Chapter 1. Gold is Discovered in California - Again
| More than 160 years after its discovery at Sutter's Mill in Coloma, Calif., gold is again making headlines in the state, this time at the Leadership in Energy and Environmental Design (LEED) Gold NoHo III Office in North Hollywood. |
 |
| As the third and final phase of NoHo Commons, a live-work-play development located adjacent to the North Hollywood Red Line subway station and the entrance to the NoHo Arts District, the nine-story Class-A building boasts a number of innovative systems and technologies that contributed to the LEED Gold rating awarded by the United States Green Building Council (USGBC). Included among them is a builtup direct expansion cooling system that features eight Danfoss Turbocor two-stage, direct-drive, oil-free refrigerant compressors. |
 |
Designed as an extension of the NoHo Arts District by Los Angeles-based architecture and urban planning firm Jerde Partnership, the NoHo III Office, or 5250 Lankershim Plaza, is a 215,000-square-foot, glass-clad structure that includes 182,000 square feet of office space as well as retail and restaurant locations, a double-height, seven-theater cinema complex, a rooftop helipad and a parking structure. The building also enhances the pedestrian experience throughout the district, linking the adjacent metro station, Academy of Arts and Sciences and the larger surrounding area.
 |
During the design phase, the building's architectural firm and ownership tasked consulting engineers Levine/Seegel Associates (LSA), Santa Monica, Calif., with developing a heating, ventilation and air-conditioning (HVAC) system that could meet the demanding requirements for a LEED Gold building and exceed California's Title 24 energy efficiency standards by 20 percent.Based on the size and scope of the building, the initial HVAC design called for a central station chilled water system located in a rooftop mechanical room. The central plant would consist of a variable-frequency-drive (VFD) centrifugal chiller, a cooling tower with VFD fans, chilled water and condenser water pumps with VFDs on the chilled water side of the equation. The air handler was to be a central station chilled water variable volume fan system that would supply air to terminal direct digital controls/variable air volume (DDC/ VAV) zone boxes located throughout the occupied spaces, with hot water reheat along the building's perimeter. |
Although the initial system configuration established the basis for meeting LEED Gold standards, the construction costs carried a premium that could not be sustained throughout 2009 in the midst of what became the worst economic downturn since the Depression of the 1930s. In an effort to conserve both construction costs and energy, LSA teamed with design/build mechanical contractors ACCO Engineered Systems, Glendale, Calif., for a collaborative approach to a new cooling system.
The discussion soon focused on the possibility of moving from a chilled water to a central station built-up, direct expansion (BU-DX) cooling system made popular by ACCO and others throughout California in the late 1970s through the late 1980s. This approach would eliminate both the chilled water and condenser water pumps central to the operation of the original chilled water design.
Chapter 2. Energy Savings, Reduced Construction Costs
"Eliminating chilled and condenser water pumping represents a huge energy savings," said Jacob Coble, ACCO project manager. "At the same time, the system eliminated the transfer of heat from the refrigerant to the water and then the air. Instead, the heat transfers from the refrigerant directly to the air, which dramatically improves system efficiency." Most industry experts acknowledge BU-DX as potentially the most efficient cooling system. However, its application has traditionally been limited to buildings much smaller than NoHo III. In addition, compressor technology available in the past limited the true energy savings potential of the system.
| "The reason we were able to apply a BU-DX system to a building as large as this one is because Danfoss Turbocor offers compressor technology that is far more efficient than the reciprocating compressors typically used in older direct expansion systems," Coble explained. "They're small with good capacity for their size, giving you the ability to gang them together and build a larger capacity system to meet the demands of a building as large as NoHo III." |
 |
Intrigued by the Danfoss Turbocor-based BU/DX approach, LSA completed a performance assessment that, according to Anil Shenoy, LSA president, revealed, "The Danfoss Turbocor compressor was 24 to 28 percent more efficient than any other positive displacement compressor that we evaluated."
The Danfoss Turbocor compressor has one major moving component-the shaft-which is suspended as it rotates within a pair of electro-magnetic bearings in a nearly frictionless condition. "As a result, the compressor does not require any oil for lubrication, so you don't need to include oil design in your mechanical system," said Coble.
The compressors run at variable speeds ranging from 18,000 rpm to more than 30,000 rpm while adjusting the position of the shaft six million times per minute to keep it operating at the magnetic center. Available in capacities ranging from 60 to 150 tons, each of the eight 60-ton compressors in the NoHo III application, along with its mounting stand, weighs barely 300 pounds.
"Structurally, these compressors offer another important advantage," Coble noted. "Eight compressors were used to take full advantage of the part-load efficiency of this remarkable technology, and the total roof load of the refrigeration plant is approximately 2,400 pounds. That may sound like a lot, until you compare it to a conventional centrifugal chiller which can weigh as much as 15,000 pounds."
 |
Coble estimated the reduced roof load to be as much 30,000 to 40,000 pounds compared to the original chilled water system. "And the lighter roof load associated with the Danfoss Turbocor compressors means the building requires less structural support in the form of reinforced concrete and steel, which reduced construction costs." |
According to Chuck Richter, ACCO senior vice president, "The first discovery yielded by the move from chilled water to built-up direct expansion was an installed system cost savings of nearly 10 percent." This reduction was achieved while retaining the LEED Gold rating, breaking the conventional paradigm that the pursuit of a LEED rating adds to construction costs.
Coble highlighted a number of additional benefits that can be tied to the compressors and the BU-DX system, including: quiet, vibration free operation; low-cost maintenance requirements; built-in system redundancy with multiple compressors; the potential to offer low-cost off-hours operation to tenants; no parts within the compressor that are subject to frictional wear; and mitigated downtime risk and costs with multiple compressors.
In addition to the LEED Gold rating awarded by USGBC, the Los Angeles Department of Water and Power recognized the superior performance of NoHo III Office by rewarding the building's owners with a significant rebate.
| According to Shenoy, Danfoss Turbocor technology has opened the door to several other innovative air-conditioning options that LSA is considering for future projects. Coble is not surprised. "I have to think you're going to see more built-up direct expansion systems in the future," he predicted. "It just makes sense. The system offers cost savings, energy savings, less weight, less structural elements, no oil and better interfacing with today's technology. It's definitely a 21st century approach to energy efficiency and all the savings that go with it." |
 |