Factoring also into the equation was energy efficiency and comfort. The campus, which was completed and occupied by Edwards’ 2,500 Denver-based employees by November 1999, has many energy-saving features. For instance, incorporated into Building One is a central chiller plant on the roof with central air handlers then use a proprietary vertical fan discharge arrangement.

Improvements and cost savings were incorporated into the three remaining buildings, which prompted Southland Industries (SI) Colorado Division, the design-build contractor for the mechanical plant, to enter its project into the prestigious ASHRAE Technology Awards for 2000. It finished in second place in New Commercial Buildings category.

BACKGROUND

The Denver firm, Fentress Bradburn Architects, Ltd. designed the four facilities with extensive project planning from J.D. Edwards. Each of the four buildings encompasses 185,000 sq ft and the site also includes three large parking structures, as well as extensive surface parking areas. The buildings are all six stories.

According to David Peters, SI’s Colorado Division engineer, the building height maximizes building efficiency while staying under Denver’s high-rise building codes. Additionally, this size kept the buildings to a more marketable size, should the company need to vacate a facility at any time in the future.

The general contractor for the entire project was Hensel Phelps Construction Co., of Greeley, CO. In order to meet the extremely aggressive schedule and tight budget, the owners, architect, and contractors worked as a tightly knit team, all participating in critical timing and design decisions. The buildings are all the same general size and design, but have subtle differences in exterior architectural details and interior workspace designs.

The look of the buildings is contemporary but conservative, and they are intended to stand up well with changing architectural styles.

“We didn’t want people in the future to look at a building and say, ‘Oh, that must have been built in the 90s,” said Taylor.

Each of the four buildings cost approximately $40 million to build, furnish, and occupy. It must be noted here that knowledge learned from the construction of Building One, which was completed in 1997, was incorporated in the remaining three buildings. Within the buildings, a strategy of logical segmentation was again followed, allowing possible future building owners to subdivide the facility in units as small as half a floor.

CHILLERS SUPPLY DISPERSED AIR HANDLERS

For Buildings Two, Three, and Four, SI deviated from Building One, which used a central chiller plant on the roof with central air handlers. Instead, these buildings were designed with a proprietary vertical fan discharge arrangement. While the system satisfied the building’s needs, the result was a large penthouse, and the building did not offer the future flexibility that the ownership wanted.

It was decided to try for a lower cost on the subsequent buildings by issuing a design-build RFP, calling for two custom rooftop units. It was also felt this approach would offer some degree of additional flexibility. This system did meet a new, lower budget. But, at their interview, SI was able to establish that what the ownership really wanted was a central chiller plant with air handlers on each floor. However, Edwards realized that this system would be outside its budget.

SI accepted the challenge to provide such a system, if possible, and took the approach of using a cold air 45¿F (7.2¿C) primary supply air system, with secondary fan-powered terminals used as air blenders to supply 55¿F (12.8¿C) air to the spaces. This resulted in smaller ducts, air handlers, and terminals and, coupled with the use of a low-flow/high delta T chilled-water system, operating at 38¿F (3.3¿C) to 56¿ (13.3¿C), smaller piping distribution and pumps.

The chillers are two Trane Series R™ Model RTHB water-cooled screw chillers, each rated at 250 tons, operating at a low 0.58 kW/ton at full load (considering the low supply chilled-water temperature) taking advantage of Denver’s dry climate and supplying 72¿F (22.2¿C) water from the cooling towers at design. The net result was a first-cost savings compared to the custom rooftop system of $63,000 — or about 33 cents per square foot.

“To say that the client was delighted is an understatement!” said Peters.

DRY CLIMATE ALLOWS FREE COOLING

Joe Buttermore, SI’s project manager, noted that, “With this approach, not only does the owner save money and time during construction, they also gain significant energy savings once the system is in use.”

The lower airflow [about 30% less than a 55¿F] [12.8¿C] system also means about 30% lower fan horsepower. Because of this, and because of Denver’s dry climate, the owner achieves reduced operating costs. The design also included a “free cooling” feature, allowing the dedicated rooftop cooling towers to provide chilled water without chiller compressor operation during many months of the year. This design even provided some free cooling on the design day.

SI’s design featured chilled water being pumped to the six individual floor air handlers in each building. These are Trane Modular Climate Changer™ units rated at 22,000 cfm, with a seventh unit dedicated to providing 35,000 cfm of tempered outdoor air to Trane constant-volume terminals in each air-handler room. The units are equipped with a prefilter section, a high-efficiency filter, dedicated precooling coils, chilled-water coils, and plug-type centrifugal fan, equipped with a variable-frequency drive (vfd). The vfd allows the air handler to accommodate a wide range of loads, depending on weather conditions and building heat loads.

According to Taylor, the dispersed air-handler approach was taken to reduce the amount of floor space taken by ductwork and to enhance the concept of half-floors as independent units of real estate.

“Acoustics were a part of the decision, too,” said Taylor. “We needed to satisfy ourselves that the mechanical rooms would not be intrusive. We are very pleased with their quiet operation.”

The air handlers are used in a horizontal configuration and feature a double-wall design in the plug fan section and numerous access doors to facilitate inspection and cleaning. Acoustics were further enhanced using a special “deep treatment,” ultra-low pressure drop silencer fabricated in SI’s shop for each air handler. Each air handler supplies approximately 30 VariTrane™ parallel-type fan-powered vav terminal units.

INDIVIDUAL BUILDING CONTROL SYSTEMS

The individual campus buildings are equipped with a Trane Tracer Summit™ building management system. The building management systems can all be monitored from a central location by Edwards operations manager, Tony Alfano and his staff. “Because of varying types of work being done and individual preferences, we have set local temperature zones that can vary by four to five degrees,” said Alfano. “The Tracer Summit system allows us to accommodate these requests, as well as to continuously monitor system performance.” Peter noted that, “The entire combined Trane equipment package, including the Tracer Summit system — which was icing on the cake — allowed us to obtain a significant cost savings. We were able to pass this on to the owner and it helped us to give him the central chiller plant and distributed air handlers that he wanted.” Since moving into their new work areas, employees have adapted well and appreciated the comfort level in the new buildings. According to Alfano, the number of comfort calls to individual areas has diminished and most can be handled by changing local setpoints with the building management system. Taylor said there is potential for further expansion by J.D. Edwards on the site. “We are sold on this design approach and I would expect the same results, both in terms of construction and operating efficiency, and the final level of building comfort.”

Publication date: 11/26/2001