The City of Tucson has a demonstrated commitment to the promotion of sustainable development practices, and is considered a leader in the area of energy efficiency. This case study will highlight a city effort - the construction of a new municipal facility - to practice and promote energy efficiency design principles and technologies in this desert community of nearly 500,000 people. The city's Department of Operations takes the lead in the design of city facilities, and played this same role in bringing this project to fruition. For additional information about the City of Tucson's energy efficiency programs, click here.
In April 1998, Tucson and Pima County jointly developed the Sustainable Energy Standard (SES), a building energy code that is 50 percent more efficient than the 1995 Council of American Building Officials Model Energy Code. It provides a quantifiable standard against which building plans can be measured to ensure that completed projects use substantially less energy than they otherwise would have under the Model Energy Code.
As new construction, the Southeast Service Center (SESC) was seen by Tucson as an ideal opportunity to achieve and go beyond the SES requirements. The City's main objectives in undertaking this project were to design and build a commercial office building using commercially available energy-efficient and renewable energy products, and to educate staff, consultants, and contractors about these measures. By pursuing the SES, the City would be leading by example and raising awareness in the general public of sustainable building practices.
Building and site design began in early 1998, with construction commencing through the following summer and completion in September 1999. Total project cost was $800,000 for the 3700 square foot facility, which houses Council Ward IV offices, a Department of Finance office, and offices for the Community Services Department.
The building is constructed with window-less insulated masonry walls to the east and west. Window wall construction was used for the north and south facades. South windows are shaded to block summer sun while allowing a moderate amount of direct sunlight in the lower windows for winter heating. Fins of white fabric reflect light into the north facing offices. Windows are high performance, low-e thermal break style, with a high degree of infrared reflectance.
The building also includes a 5kW solar photovoltaic (PV) system. The PV panels are located on the roof and grid-tied to the distribution system. Tubular solar skylights are used throughout the building. Although not required to meet the SES, daylighting is maximized through the use of light sensors and dimmer controls in fluorescent lighting located near windows. The mechanical system consists of high efficiency heat pumps controlled through an energy management system.
The following energy saving features were required for this project to meet the Sustainable Energy Standard:
- High efficiency HVAC system with setback controls and after-hours override;
- Insulation at R-38 for the roof, R-19 for the walls and R-3 for the glazing;
- Duct leakage control;
- Energy efficient lighting; and
- Air leakage control for the shell.
The estimated avoided energy cost due to the energy-efficient features is $3,100 per year. The incremental cost for these items, relative to the cost for a new building just meeting the building code, is estimated at $24,200, resulting in a simple payback period of just less than eight years (excluding the cost of the solar PV and daylighting systems). The average energy cost per square foot is $1.17, as compared to other similar City buildings, which range from $2.00 to $2.40 per square foot.
The SESC has set the standard for the design, construction and operation of future City buildings, and serves as a model for commercial design and construction for the community as a whole. The building has won awards from both the Southern Arizona Energy Award program and the Governor's Energy Awards program.
As a result of this project, the Mayor and City Council have mandated that all future City buildings (both new and renovated) be designed and constructed to the Sustainable Energy Standard. With approximately 50,000 square feet of new conditioned space and about 120 major renovation projects each year, the benefits of building to the SES are likely to be significant.