Creating the best movie-going experience for film lovers is critical for a movie theater complex located north of Los Angeles in Universal City. Nineteen screens create an amazing movie-viewing experience, with digital surround sound and stadium-style rocker seats. Because comfort is so critical, the theater worked with Los Angeles-based Air Treatment Corporation to install a Multistack MagLev™ water-cooled centrifugal chiller that uses Danfoss Turbocor oil-free, variable speed, magnetic bearing compressors to deliver reliable, efficient, precise temperature control under any conditions.

“The Multistack chiller looked like it would be a real efficient workhorse,” said the complex’s director of technical services. “We needed something that would perform over a wide range of loads as they vary during the day and week. We were looking for problem-free performance – a system that runs perfectly – plus a control system that takes care of the chiller and corrects any problems out in the system. The Multistack chiller proved to be a much smarter solution than the previous system.”

This chiller has never missed a beat. It can run smoothly from 400 tons all the way down to 10 to 15 tons capacity when operating on one compressor.

"The theater complex requires reliable, efficient cooling 365 days a year," says Bruce Lumbattis, systems specialist for Air Treatment Corporation, who oversaw the project. "Nobody wants to refund tickets for uncomfortable customers. The old system was a massive thermal storage system using two large screw compressors. It initially made sense to use a thermal storage system because, at that time, Southern California Edison provided incentives to use electricity during the off-peak hours of midnight to 6:00 a.m. During the night the system would build ice, and then melt it during the day to provide cooling to avoid paying peak demand charges for electricity.

"But when the complex installed their own 12 KV switchgear to distribute power for a new solar photovoltaic (PV) array, it changed their operating plan. They were no longer dependent on the local utility for 480 VAC power and could generate their own electricity, so peak charges were no longer an issue.

Multistack Chiller Brings Sound and Efficiency Benefits
Lumbattis talked to an engineer about replacing the thermal storage system, which was configured with three 970-ton/hour thermal storage tanks and two screw compressors in a sub-basement. The chillers were connected by a six-inch discharge line and a 4 1/8-in. liquid line with two evaporative condensers on a roof 70 feet above the basement. The engineer suggested replacing the screw chillers with a standard, water-cooled centrifugal chiller and replacing the evaporative condensers with cooling towers. Ten- or 12-in. diameter piping and pumps would circulate condenser water from the basement to the rooftop.

"I had just installed those evaporative condensers in 2006," said Lumbattis. "They were in good shape. I suggested that we keep using them. Evaporative condensers in hot, dry climates like southern California deliver lower condensing temperatures, which can significantly reduce chiller energy consumption. I pointed out that Multistack offers a condenserless flooded centrifugal chiller design that could use the existing evaporative condensers. It would eliminate the need for a recirculation system using cooling tower, large piping, condenser water pumps and water treatment system.

"We tore out the screw chillers and tanks, and installed a Multistack MS450FL MagLev water-cooled flooded chiller with 450-ton capacity at a 42-degree design leaving water temperature. It has revolutionized our operations. We gained an unbelievable amount of space in the mechanical room. And the chiller’s sound and efficiency benefits are the direct result of the Danfoss Turbocor compressors."

Compressors Drive Outstanding Chiller Performance
As a unique condenserless flooded design, the Multistack chiller employs innovative magnetic levitation bearing, or MagLev, technology – in this case, four Danfoss Turbocor variable speed compressors.

Because the complex has 19 theaters, theater occupancy can vary throughout the week — and even throughout the day. A conventional centrifugal chiller would constantly need to throttle capacity to meet the changing load.

"A conventional centrifugal chiller is designed to operate efficiently at full-load conditions," says Lumbattis. "But that's typically only about five percent of the time. For the other 95 percent, we don't need all that cooling capacity. To lower capacity, centrifugal chillers typically employ inlet guide vanes and speed controls to reduce refrigerant flow. Hot gas bypass is another technique used to keep the chiller from surging or stalling at low-load condition. But these techniques really hurt efficiency."

Because the complex has 19 theaters, theater occupancy can vary throughout the week — and even throughout the day. A conventional centrifugal chiller would constantly need to throttle capacity to meet the changing load.

Lumbattis explains that, "one of the other reasons I like Danfoss Turbocor variable speed compressors is they can easily reduce speed and reduce capacity to meet part-load conditions."

The complex’s director of technical services adds, “This chiller has never missed a beat. It can run smoothly from 400 tons all the way down to 10 to 15 tons capacity when operating on one compressor. The efficiency is amazing. The previous system had two 450-hp motors that were either on or off.”

Compressors Provide Fantastic Turndown Capacities
The Multistack MS0450FL MagLev™ chiller uses four Danfoss Turbocor TT400 oil-free, variable-speed, magnetic bearing compressors. Each compressor incorporates an integrated variable speed drive (inverter) to change output voltages to regulate motor speed. Slower compressor speed reduces refrigerant flow, which reduces cooling capacity, thereby reducing energy consumption.

Precise, individual control of each compressor assures optimum chiller and system energy efficiency – and complies with the new 2015 standards for chiller efficiency.

The speed of each TT400 compressor can be reduced from 100 percent to 30 percent, or slower. That allows precise reductions in capacity to match cooling requirements across the range. Plus, with Multistack’s MagLev™ FlexSys™ control system, the chiller provides fast control response and can unload from full load to minimum flow in one minute, run at reduced flow for a minute, then reload to full load a minute later.

According to Ken Koehler, key account manager, Danfoss Turbocor Compressors, "in addition to the variable speed control, the Danfoss Turbocor TT compressor family employs built-in inlet guide vanes (IGVs) to trim the compressor capacity at low loads. The blades of the impeller inside centrifugal compressors are like airplane wings – when speed slows down, the wings experience turbulence. Just like an aircraft can stall at low speeds, so can a centrifugal compressor. The vanes control the amount of gas flowing to keep the compressor trimmed to maintain system stability."

In the Multistack chiller, the four Danfoss Turbocor compressors are configured in parallel. That allows each compressor to turn on and off to handle extremely low loads. For example, the Multistack FlexSys™ controls use a timing sequence that compares chilled water set point and inlet guide vane position. The controller is able to determine a decrease in inlet guide vane position and can begin monitoring kW consumption. When the cooling load can be more efficiently carried by one or two compressors instead of two or three, a compressor is shut off and the remaining operating compressor(s) carry the cooling load. The fourth compressor serves as a redundant backup if one of the compressors goes off line and cannot operate.

Precise, individual control of each compressor assures optimum chiller and system energy efficiency – and complies with the new 2015 standards for chiller efficiency. The oil-free compressor technology also means there is no refrigerant-entrained oil to hinder heat transfer and reduce efficiency as can happen in traditional chillers with oil lubrication systems. It also means fewer parts, greater reliability, and lower maintenance costs. All MagLev™ chillers are run-tested on Multistack’s AHRI Certified test loop.

"Thanks to four Danfoss Turbocor TT variable speed compressors, Multistack’s chiller has the air conditioning industry’s best unloading capability without the need for condenser water temperature relief. This chiller lets me turn down capacity to just 10 tons when running with one compressor," says Lumbattis. "That's amazing – a nominal 450-ton machine running in a stable condition at 10 tons. Technologically, that's really a big deal. It's a big deal economically, too. It is saving us a lot of electricity."

Although the use of a solar photovoltaic (PV) array makes a comparison of before-and-after installation electric use and costs difficult, the system with the new Multistack chiller now consumes about 10 percent less energy than before – which translates to huge energy cost savings for the theater. The new chiller also helped the complex qualify for a nearly $96,000 rebate from Southern California Edison Business Incentives.

Other benefits include the Danfoss Turbocor compressor's inverter that enables a "soft start." Unlike a conventional chiller that can pull as much as 800 to 1,000 amps when starting, each Danfoss Turbocor compressor draws only two amps at start-up, which avoids start-up demand spikes, smooths out the system load and reduces thermal stress on internal motor components. Because the chiller is wired into the utility, the Danfoss Turbocor compressor's inverter maintains the correct output voltage and phase to minimize voltage and harmonic problems if grid power is ever lost.

Lumbattis also appreciates the definite reduction in noise. "It's night and day," he says. "The loudest thing in the mechanical room is the chilled water pumps. You can have a normal conversation in here. That would have been impossible before."

The peak sound level of a Danfoss Turbocor compressor is only 71 Dba – about the sound level of a typical conversation. The low noise is a result of a compressor shaft with twin impellers formed as a single assembly that rotates on magnetic bearings. This design not only eliminates compressor friction and vibration, it also eliminates the need for an oil lubrication system.

The combination of oil-free operation, quietness, and part-load operating efficiency is so attractive that Lumbattis notes a second phase of the project is underway.

"Both the theater and the complex are very proud of what this condenserless, flooded chiller has accomplished," notes Lumbattis. "The complex even put red and gray tile on the mechanical room floor and painted the room an elegant grey with a red stripe. The Multistack MagLev chiller and Danfoss Turbocor compressors are getting real star treatment. And they've performed a sequel by installing two similar Multistack chillers in the building next door."