The city of Chandler, Ariz., may be famous for its annual ostrich festival, but when it came to its new city hall, the city did not want an HVAC engineering firm that was going to bury its head in the sand. Thanks to heads-up work by the team at Phoenix-based SmithGroupJJR, led by Project Engineer Jonathan Silhol, PE, LEED AP BD+C, Chandler’s new city hall showcases some of the HVAC industry’s latest technologies and stands as an example of outstanding HVAC design work.
Chandler’s city hall is a five-story, 178,000-sq-ft, mid-rise government complex located in downtown Chandler. The complex houses city departments, council chambers, and a television studio. The overall design responds to the harsh desert climate and at the same time provides for appropriate outdoor spaces that introduced much-needed green space to the heart of the city’s downtown. The project is tracking Gold certification under the U.S. Green Buildings Council’s Leadership in Energy and Environmental Design (LEED) Version 2.2 program.
The Background
Prior to construction of the new city hall, Chandler had been leasing several facilities for a number of years. Ten years ago, the city made a commitment to build its own facility. The city did not borrow money for the construction. Instead, it saved a portion of the development fees from other projects built within city limits. Total project cost was $70 million, with $47 million devoted to construction and $5.8 million to the mechanical and plumbing systems. A portion of the additional funds were used to buy property, to demolish abandoned and deteriorating buildings around the project site, and for cleanup.
From the start, the client and design team worked closely together to establish the foundation for a successful project. Through community meetings, executive-committee meetings, and information-gathering sessions with various employees, the goals and vision of the project were established. SmithGroupJJR took these varied (and sometimes disparate) ideas, created a vision for the project, and articulated that vision into a cohesive design that was endorsed by all. Throughout the project, this vision was revisited to make sure it was being met. Additionally, the use of building-information-modeling software ensured a high level of design accuracy and coordination among the trades throughout the design process.
Cooperation from the start was very good between the general contractor, mechanical contractor, and electrical contractor.
Beating the Heat
Situated in an environment that is cooling-dominated, the first line of defense from the desert heat is the building exterior envelope. Passive shading strategies along with a high-performance window glazing were utilized to reduce as much solar heat gain as possible. This allowed the mechanical systems to be sized appropriately and varied depending on building function.
The complex’s office tower is a multistory building oriented on an east/west axis that maximizes northern and southern exposures. Passive shading strategies were used on the east, south, and west facades to block direct heat gain during summer, and allow for some penetration during winter. The western facade of the office tower features an intricate and artistic shading system, including a hinged structure with 1,800 perforated stainless-steel panels connecting the environment in a tangible, kinetic way by moving with the wind.
The central plant houses two 300-ton high-efficiency variable-speed chillers. The chilled-water system also utilizes a plate-and-frame heat exchanger that takes advantage of water-side free cooling when ambient conditions are appropriate. Chilled water produced by the central plant is distributed to 20 air-handling units (AHUs) located throughout the facility. Many of these AHUs serve the underfloor-air-distribution systems. The underfloor system minimizes fan-energy consumption, allows employees control of their thermal environments, and improves air quality. The AHUs also operate under a demand-control-ventilation strategy that assists in energy conservation.
The Chandler City Hall complex complies with ANSI/ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, and ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality. The interior spaces are provided with manually adjustable floor diffusers, and the perimeter spaces are provided with terminal units that automatically adjust to changing perimeter loads.
Dedicated-outside-air units are located in the tower to pre-condition outside air before it is delivered to the building. The building owner requires the electrical and data rooms to be conditioned by supplemental systems. A variable-refrigerant, air-cooled system was utilized to reduce the number of condensing units and increase the efficiency of the system. A direct-digital-control-based building-management system (BMS) was provided to control and monitor the mechanical systems and the lighting-control system. The project’s BMS was integrated into the owner’s campus enterprise control system to provide control at the existing front-end system.
Energy-Saving Details
As part of the mechanical cooling system for the project, a water feature was designed at the southern end of the building’s courtyard. Part of the condenser-water system, it allows the water from the cooling towers to cascade down a wall into a pool. As the prevailing winds enter the courtyard, an evaporative-cooling effect is created. This effect, in combination with landscaping and shade structures around the courtyard, lowers the effective temperatures and creates a microclimate.
An ambient/task-lighting approach was utilized throughout the complex to reduce lighting-power densities. This was coupled with active photo-sensor controls along the perimeter in the office tower to harvest daylight to further reduce lighting energy. Daylighting-control strategies allow lights to be turned off for approximately 80 percent of daylight hours.
Single-story portions of the complex utilize a combination of perimeter glazing and tubular daylighting devices to bring in light. High-efficiency motors and variable-speed drives are utilized throughout the facility.
Providing on-site renewable energy has been a goal, and provisions have been made for a future installation of a 330-kw photovoltaic array on the upper deck of the parking structure. This would effectively lower the building’s energy-utilization index (EUI) to 33.6 kBtu per square foot per year and equates to a 63-percent reduction from a regional average meeting the current 2030 Challenge target.
Water Conservation Critical
As with any facility located in a desert, water conservation is critical. The Chandler City Hall complex has taken a comprehensive approach to reducing potable-water use. Both interior and exterior strategies were employed. The interior approach utilizes low-flow, water-conserving fixtures, while the exterior approach utilizes high-efficiency drip irrigation and low-water-use native plants. During summer, there is an excess of water generated, so no potable water is being used for the exterior systems and the majority of the interior fixtures are fed primarily from a greywater system. Less water is generated during winter and requires some potable water. A large portion of the water closets are fed from the grey-water system. The source of the greywater is the condenser-water system at the central plant, which uses non-chemical water treatment. Water is collected and stored in an underground storage tank and treated with ultraviolet light. In all, these strategies reduce domestic-water usage by 69.5 percent and wastewater usage by 81.4 percent.
“What really made this project enjoyable and interesting from a design standpoint was bringing all the elements together,” Silhol said. “We did a packaged central plant, an underfloor-air-distribution system, and a greywater system. Those are things that stand out from a mechanical-engineering perspective.”
The project wasn’t without its hurdles, however.
“We had a lot of meetings on the commissioning side,” Silhol said. “The owner has a LON-based campus system, and there were many proprietary controls on the job. We faced some challenges integrating the various pieces. It took some time and effort to integrate everything for the owner, but we’re pleased with the results.”
Performance and Proof
The building meets energy-modeling and minimum-energy-performance criteria set forth in ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings. The energy cost budgeted approach was modeled utilizing eQUEST (DOE2.2) software. The principal features of the baseline building model were compliant with Standard 90.1-2004. Improvements to this model then were made to reflect design improvements to the building envelope, lighting, and HVAC systems. The final analysis showed a 33.1-percent reduction, with a potential of 38.1 percent should the city install a 330-kw photovoltaic array. The facility net energy utilization index (EUI) is 43.1 kBtu per square foot per year, which is a 53-percent reduction from a regional average.
A third-party commissioning agent was hired by the owner to ensure the mechanical and electrical systems functioned properly. The project team worked with the agent and performed enhanced commissioning, measurement, and verification procedures. There was an extensive effort to ensure the various equipment control systems were integrated into a central system at the project site and then connected to the owner’s campus control system.
In addition to the good cooperation between SmithGroupJJR and the contractors, Silhol said a key to the successful project was the customer.
“The people at city hall were tremendous,” Silhol said. “They were very supportive throughout. They understood the design and understood the process. They were very pleasant to work with.”
There’s an old saying that “you can’t fight city hall.” However, fighting isn’t necessary, and staying cool is the name of the game—even in the desert—with an outstanding HVAC system design. Congratulations to SmithGroupJJR, Phoenix, as it receives the inaugural HPAC Engineering Design Award.