city lights

A California city taps its natural resources to make green, reliable energy.

By Barbara Wolcott

The rolling blackouts of two years ago have not been forgotten in California. The northeastern states and southern Canada aren't likely to forget their more recent blackout, either. And even where energy is reliable from a homeowner's or office worker's point of view, small dips and spikes in the power supply can ruin batches of very fine products—microchips, for instance.

Blackouts and commercial losses are only a couple of the motivators driving the development of distributed generation.

There are also green concerns, the intention of producing at least some of the energy one uses from environmentally benign sources. Generating your own, however, can cost more than buying power from the utility.

In some instances, though, systems can take advantage of natural resources at hand, to produce energy or to conserve it, and in either case can save money.

It is along these lines that several county and municipal energy projects coming together have turned a small California city into a testbed for schemes designed to cut the power bill. San Luis Obispo, with a population of 50,000, is putting in small-scale energy systems ranging from hydroelectric generation to geothermal climate control.

San Luis Obispo's primary water source is above La Cuesta Summit, which rises more than 1,500 feet in the Santa Lucia Mountain Range. The water falls 740 feet from the source to the city's old water treatment plant. It was relatively easy as well as profitable to put in a small hydroelectric system a generation ago. The city sold power to the grid and offset some of the water department's electricity costs.

The hydroelectric plant, behind San Luis Obispo's old water treatment facility, will once again run on water falling from the Santa Lucia mountains.

A single turbine and a generator rated at 640 kilowatts were purchased from Shinko Electric Company Ltd. of Japan and installed in 1985 adjacent to the water treatment plant. Nine years after the plant went online, it was shut down, partly because a new water filtration plant was built a short distance downstream, but mainly because water coming into the system changed.

It had flowed freely through an 8-foot-high tunnel from the mountains. The hydraulics changed when the California State Water Project ran piping through the same tunnel. The pipe was laid within the flow, and state engineers installed a concrete cover on it. While the addition did not impede the flow of water to San Luis Obispo, it changed the hydraulics of the stream.

Taking the Full Advantage

Recent events in the power industry deregulation have made retrofitting cost effective.

Dean Rubinson, an engineer with Black & Veach Consultants in Concord, Calif., ran a feasibility study for the restart of the hydroelectric plant. He reported that the best option was for the city to use the plant as it stands, but with new electronic controls.

Rubinson said the plan "takes full advantage of the hydroelectric generation potential of the raw water system at a minimum of capital expense." San Luis Obispo city engineers agreed.

According to the city's water division manager, Gary Henderson, "The water treatment facility takes a great deal of electricity to run. The city spends $260,000 a year to do it, and we estimate that with the hydro plant we can sell $52,000 worth of electricity to the grid during that same period. That's an attractive payback, especially since the system is expandable for future growth."

The $2 million cost of restarting the hydroelectric plant will be amortized over 20 years.

The retrofitted hydroelectric system will use a large open clarifier tank at the decommissioned old filtration plant to store water, essentially creating a small lake for steady inflow of water to the turbine.

This is not the only project where the city expects to save on power bills. Copeland Sports Corp., a private company, is building a parking garage in the downtown area that will be purchased by the city when it is finished. One floor of the garage will contain offices with heating and cooling needs assisted by geothermal technology. Pumps will circulate tap water through a system of looped piping placed in 50 vertically drilled boreholes 300 feet deep. The pipe and fittings are made of high-density polyethylene, or HDPE.

Steve Best, owner of David's Plumbing, Heating & Air Inc., is a local specialty subcontractor for the job. He said, "For flexibility, resistance to corrosion, and expandability, HDPE for this application is preferred to steel."

Best added that the piping is sealed in each borehole with a special thermally enhanced betonite grout. This allows for full contact between the pipe and the surrounding surface to optimize thermal conductivity.

Dusty but still in place: A Black & Veatch engineer recommended using the old hardware, updated with new controls, when the city restarts its hydroelectric plant. The generator is rated at 640 kilowatts.

The circulating water, moderated by a consistent 62°F temperature underground, will moderate the temperatures in the offices of the new building all year long. Sixteen pumps will move energy to or from the Earth by way of the ground loop heat exchanger.

The new system will use power, but for every one Btu equivalent of electricity consumed, it will draw four to five Btu out of the ground. According to Best, "Day after day, Btu will be absorbed from the Earth and rejected into the Earth to meet the heating and cooling needs of these offices."

Dave Smith, the city's building maintenance supervisor, said the geothermal system will cost $218,000, and the annual savings are expected to make it a 16-year payback. According to Smith, whose office will be in the new building, the system will save putting 20,000 pounds of carbon dioxide in the air annually, and 18,000 pounds of sulfur dioxide. The closed loop circulation will save about 10,000 gallons of water a year that would have evaporated in traditional heating and cooling processes.

A stone's throw from the city's building complex site the San Luis Obispo County campus is undergoing its own energy makeover. When the county decided to put air conditioning in the old courthouse, which had none previously, design engineer Allen Crosby of Aircon Energy in Sacramento suggested it also look at long-term energy savings. He recommended replacing lamps in county buildings for higher efficiency and adding motion sensors to turn lights on and off.

In addition, Aircon recommended that the old boilers and chillers at the library and courthouse annex be retrofitted or replaced with new, more efficient ones.

County Campus Cogeneration

According to the county capital projects coordinator, Greg MacDougall, heating and cooling, even with the additional 42,000 square feet of area in the old courthouse, use less electricity than they did before.

"Everyone's looking for ways to save on electricity costs, especially government," MacDougall said. "Our budgets are getting whacked, but people still need the services, so we have to find ways to deliver those services cheaper. One way to do that is to lower operating costs."

The courthouse retrofit won an award from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

The county hired Aircon to look into energy efficiency options in other areas. The result is a new co-generation system to cut power costs at the county government campus. The system serves the old courthouse, the annex, and the library. Across the street, a new county administration building under construction will also be served by the new power plant.

The system, designed by consulting engineer Ron Blue of List Engineering in Monterey, Calif., has three co-generation units of 200 kilowatts apiece, fueled by natural gas. Exhaust heat will be recycled for hot water in all the buildings and to maintain comfortable temperatures in offices during winter. The system will cool the buildings in summer through an absorption chiller.

A compact panel monitors system that will provide much of the electricity and heat for a county building complex.

The production of power on-site is expected to provide 45 to 55 percent of all electricity needs for the county building complex. An incentive program through the Public Utilities Commission has already brought the county a half-million-dollar rebate. The payback for the capital expenditure is expected to take seven to nine years, even with fluctuating gas prices.

The system will end up costing $1.7 million, less a $502,000 rebate, and will save taxpayers about $200,000 annually. It is able to produce 600 kW of electricity, about half of what will be required to run the entire campus of the courthouse, the annex, the library, and new the 100,000-square-foot administration building.

Engineers are also looking at powering the jail with a similar system.

The new multistory county building being built across from the courthouse has energy consciousness built in. The floor consists of an airspace sandwiched between two 1 1/2-inch concrete slabs. A blower system that takes advantage of low nighttime temperatures, which often fall into the 50s in the summer, will circulate cool air at night through the space inside the floors. The cooling of the floors overnight will reduce some of the need for air conditioning during the day.

Louver covers will let in the winter sun, but keep the summer sunlight out.

The building will have the same kind of energy-efficient lighting and motion sensors that the courthouse annex uses to save electricity. According to some county workers, the sensors sometimes work too well. If everyone happens to sit still long enough in an office, the system will shut off the lights. That leaves a roomful of people waving their arms to bring the lights back on.

The city engineering staff is looking to put solar electric arrays on the roofs of two buildings. A city councilman, John Ewan, is a supporter of green energy systems. He is in the solar energy business, but is prohibited from bidding on projects because of his position on the council.

Also under consideration is a plan to offset the cost of electricity at the city sewer plant with by-product methane produced on-site to power microturbines. The elimination of fossil fuel from the process may qualify the project for a rebate from the Public Utilities Commission. Solar projects qualify for rebates in California, too.

A hundred years ago, electric power plants were small and scattered. That was before the emergence of today's vast energy infrastructure of power grids and fuel lines.

Demand was small, too, before today's ever-expanding need for light, heat, and fuel.

No one expects the grid to break up or demand to shrink. But spreading out part of the production and making better use of what we burn can take some of the burden off the central system. It can even save money.

Barbara Wolcott, a frequent contributor to Mechanical Engineering magazine, is a freelance writer based in San Luis Obispo, Calif.



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