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April 24, 2003
Photo courtesy of CDi Engineers
The new Seattle Justice Center features several sustainable energy designs — including specialized air-flow modulators — that should help the project become the city’s first large LEED-certified building.
Sustainable design was a key goal for the new Seattle Justice Center. So engineers went the extra mile to incorporate innovative mechanical systems throughout the project — helping to make this among the first buildings in Seattle to seek a prestigious LEED silver standard.
Special mechanical features include energy-conserving devices built into the heating and ventilation systems, airflow handling on a floor-by-floor basis, and submeters on utility systems. These and other design elements cut energy costs by 32 percent. And they made it possible for the city to receive utility incentives and credits to save taxpayers money on the $92 million project.
The Justice Center is one of the first buildings in the state with variable-flow chillers in its cooling system. Most systems maintain a constant flow of chilled water for air conditioning, to avoid the possibility of water freezing inside the chillers. But new control systems can prevent freezing, so that flow rates can be decreased when not needed. This saves as much as 67 percent of pumping energy costs.
Another important feature in the cooling system, essential given the variable-flow chillers, involved installation of pressure-independent valves. These “smart” valves constantly self-tune and modulate flow no matter how high or low pressure might be, ensuring that the correct flow of chilled water is delivered throughout the system. This minimizes pump energy consumption and simplifies system maintenance.
Fresh air flow
How much fresh air is needed in a room? It depends. A crowded courtroom clearly needs more air than an office that’s only partially occupied.
Until recently, fresh air flow was maintained at constant levels in most buildings. The new Justice Center, however, uses dozens of sensors to monitor carbon dioxide levels and control the amount of fresh air being brought into the building. By controlling the amount of outside air to meet the actual needs of the building at any given time, the Justice Center realizes savings of about 5 percent on total heating and cooling costs.
Fan-powered VAV boxes powered by fans do something similar for air flow within rooms at the Justice Center. In older buildings, cold air falls out of diffusers in an icy blast. A few feet away, people may be sweltering.
Fan-powered boxes prevent hot and cold spots by maintaining room air circulation while supply-air temperature is modulated to match load. While they are doing this they save energy by recirculating warm air from zones that have less heating requirements to zones with greater heating requirements.
This requires that an electrically powered fan be provided at each VAV box. Seattle Justice Center has high-efficiency motors on these fans that consume only 70 percent of the energy that conventional fan motors would use.
Being right next to Interstate 5 is a mixed blessing for the Justice Center. The location provides easy access for drivers, but complicates air quality issues. Contaminated air is a major health concern for employees, jail inmates, and others who must spend long hours in the building.
The city of Seattle deserves praise for putting in high-efficiency filters in the Justice Center’s air handling units. These filters were not mandatory and represented an additional expense — illustrating the city’s commitment to high-air quality for its staff and visitors.
Air on demand
The 13 floors of the new Justice Center include offices, courtrooms, a jail, police headquarters and public areas. Usage tends to vary by floor, with some levels used only during business hours and others occupied around the clock.
So the city opted for individual air-handling systems on each floor, allowing them to shut off air flow on unoccupied floors. Although this required less ductwork, it also required a greater number of air-handling units. The additional expense is well justified, as the system concept will pay for itself in just a few years.
Submeters were installed within the building to track gas, water and electricity usage. Submeters are tied directly to the building control system, where graphical displays show utility demand and consumption.
The benefit here is that city employees can monitor utility usage in real time, spotting potential trouble spots and fixing them before they turn into big energy wasters. The meters will indicate when energy consumption departs from normal values, alerting maintenance personnel to look for things like malfunctioning valve operators or chiller controls.
Without submeters, facility managers would have no choice but to wait for end-of-month bills from the utilities — and risk the discovery of overconsumption after precious resources had already been wasted.
Paybacks and partnerships
The city of Seattle is realizing two significant financial benefits from choosing a sustainable design for the Justice Center’s mechanical systems. The first derives from the cost-savings of the systems themselves. Initial costs will be easily recovered in three to five years. After that, energy bills will run a mere 50 percent of what similarly sized but less-sustainable buildings would expect to pay.
The second benefit comes from partnering with Seattle City Light, which offers considerable financial incentives for building energy-efficient structures. Utilities are concerned about growth in demand for power and water, and are looking for ways to curb usage among major users — and avoid building new power-generating facilities.
The city’s mechanical-design consultants conducted an “Energy Smart” analysis to qualify the project for City Light programs. By evaluating the cost effectiveness of various energy-conserving measures and working with City Light staff, they were able to help the city to procure hundreds of thousands of dollars in utility rebates.
The result is a proud accomplishment — what is expected to become Seattle’s first large LEED-certified building, and a silver rating indicating better than baseline achievement. The project was already in design when the city decided to move toward all new buildings being LEED-certified. It can therefore now use the Justice Center as a model, showcasing sustainable design practices for other large public facilities throughout the region.
Joe Llona is an associate with CDi Engineers, a Lynnwood-based mechanical engineering firm that was one of the first in the state to join the LEED movement. For more information, see www.cdiengineers.com.