As energy deregulation and skyrocketing prices continue to roil the California market, the decision to retrofit two 1,000-ton chillers with variable-frequency drives at San Diego's One America Plaza office tower last year was either sheer genius, or amazingly lucky -- or both. With prices now ranging to 30 cents per kilowatt/hour (versus 9 cents in '99-early '00), the payback period on the two 1,000 hp VFDs from ABB has decreased from the original projection of 2.5 years to 1.5 years (after only nine months of production), and the number is getting lower with each passing week.

"On this kind of project, your savings are there," says Paul Wolf, former chief engineer of the building. "It would be a very good project for any building, even if energy prices were not increasing."

A Million Square Feet of Comfort for Tenants

Built in 1991, and overlooking the waterfront from the downtown business district, the 506 ft tall Class A building -- owned by Shimizu America Corp -- is 98% occupied and was planned as part of a two-tower facility connected to a 12-story hotel. There are 19 elevators -- six high-rise and six low-rise, plus those for freight and parking garages; and two executive shuttle elevators serve the top four floors. Adjacent to the 34-story tower is the Museum of Contemporary Arts building; together, the office and retail space total a million square feet of built-out space. The city's main trolley stop, which passes through the arcade next to the tower, brings in additional building users, as does the Santa Fe train depot, located next door.

Being on site ahead of construction has helped tremendously in the design, installation, and successful operation of the HVAC and building systems, according to Wolf. "I was able to work with construction, electrical, mechanical, and plumbing contractors, review all the plans, and make comments and corrections as the building was constructed," he noted. The advantage, he points out, is that now, tenant complaints or requests related to HVAC average three to four a week -- or less, an extremely low number.

"There's no school, really, for chief engineers and building engineers," according to Wolf. "If there are unhappy tenants, there's got to be a reason. Engineering designs usually work well if they're taken care of properly and not tweaked."

$500K in Energy Savings

While Wolf began pitching Shimizu almost immediately on the energy savings benefits and availability of utility incentives for a drives retrofit of the Trane chillers, the building owners concentrated expenditures on attracting occupants.

Meantime, Wolf implemented other retrofit projects to conserve energy and costs. These included: full lighting retrofits (to electronic ballasts) of the tower and underground garages, which dropped wattage consumption in half per fixture and reduced light replacement costs dramatically; addition of LEDs on all exit signs; installation of window filming to resist radiant heat gains; and addition of VFDs to the cooling tower fans. These changes saved One America Plaza $500K in energy costs annually, before the retrofit of the chiller.

The calculated payback periods for each of these improvements have been shortened by the energy crunch, as well. "They are paid off because they have paid us back," notes Wolf. These changes also reduced significantly the cooling demands made on the chillers -- from one and a half units needed to only one, even on the hottest days.

Demand Side Management

Adding VFD control to the chillers, which consumed 50% of the building's total energy draw, advanced Wolf's objective of using only the energy required based on the actual cooling demands of the building (heat is provided via electric strips on VAV boxes).

"Motor drives make it possible to operate compressor pump motors at the speed needed for the capacity required," observes Mike McMahan, the senior engineer from Control Technology, the local systems integrator that installed the drives for the chillers on a turnkey basis. Without the ability to turn down, or up, the speed and horsepower of the compressor in parallel to the variances in outside temperatures, the chiller runs at a constant -- often excessive -- speed, said McMahan, wasting a lot of expensive energy.

Unobtrusive Installation Yields Major Benefits

Wolf ordered the chiller retrofit in January 2000, following budget approval from Shimizu and qualification for incentive money from the Public Utilities Commission.

Installation of the ABB 1,000 hp ACS 600 series drives, among the largest of their kind for HVAC applications in southern California, required Control Technology to add structural support underneath the garage floor adjacent to the chiller and water pump room. Both drives were installed, commissioned, and fully operational by August.

"This was and is an extremely unobtrusive installation," notes McMahan. "The chillers function, from the operator's standpoint, as they did before. Operators are not required to make any special setups or changes; all of their existing building management controls are still active. We just add this electrical equipment piece between the utility and the starter that allows operators to change the speed of the pump motors."

Comparatively, temperature variations in desert-locked San Diego are relatively narrow, ranging from freezing to 77ºF. While one of the chillers will operate at its full 1000-ton capacity on an extremely hot day, 800 tons is the general operational requirement in summer, and 500-600 tons in winter. Both chillers are used in alternating one-week stints; changeovers, early AM every Tuesday, are seamless. And the capacity freed up through the earlier energy improvements means one of the chillers can accommodate property expansion, Wolf said: a high-rise condominium, now in the planning stages, that will be built in the space of the second office tower originally planned for the site.

Both the ABB drives and chillers are operated from the existing Trane Summit building management controls. "The retrofit retains full functionality of all systems on the chillers," said McMahan, and that includes operation of the inlet guide vanes. The microprocessor control provided through VFD technology, noted ABB experts, excels at precise control of vanes to prevent surge.

In addition to the chillers and cooling tower fans, VFDs are also installed on the building's chilled water pumps, as well as on the supply and return fans that handle floors 31-34. Air supply fans for the first 30 floors work in tandem with an open plenum return system and run at constant speed.

Master of Own Energy Fate

With energy costs from the local utility, San Diego Gas & Electric, doubling in the first four months of 2001 alone, One America Plaza has taken as much control of its energy-consumption fate as possible. "Optimal energy usage without sacrificing comfort for occupants is the mantra," said Wolf.

Smart energy usage also does not set off high or erratic consumption patterns that trigger surcharges from the utility. SDG & E levies incidental charges for the highest energy usage in a 15-minute window between the hours of 11:00 AM and 6:00 PM -- a charge that the chiller drives neither affect nor save. But the VFDs do save the building non-coincidental charges, those high-energy-use charges within every 24-hour period. In the event of a chiller shutdown, the VFDs also provide a soft start (slow ramp up), minimizing any chance of demand charges.

Minimized Mechanical Wear, Too

Slow ramp-up compressor motor starts decrease the heat mode on windings and extend bearing life. This, in turn, saves wear and tear on the chiller.

Quantifying true mechanical benefits and their payback should be done over time, 10 years minimum, according to McMahan. "The real comparison is to operate identical chillers over time, one via a VFD and the other without," he said.

Interest from other building engineers in One America Plaza's retrofit was immediate, following startup of the motor controllers. "Interest continues to grow as the energy companies deregulate," said Wolf. Both the local BOMA and ASHRAE offices set up tours to see the installation.

A 1,000 hp HVAC VFD installation is a little novel in the San Diego area, Wolf noted, but given the challenges chief engineers and building engineers now face to utilize energy wisely and contain costs, such installations have the potential to become common, he said.