Campus turns waste water vapor to heat for Tercero 3
January 25, 2013
Related story: UC's annual sustainability report shows a savings of $91 million in energy costs systemwide since 2004.
By Dave Jones
UC Davis is wringing energy — and hundreds of thousands of dollars in savings — from a former waste product: the water vapor often seen as a fluffy white plume coming out of the campus steam plant.
This bonus energy from a single, new piece of equipment called a condensing economizer will provide all the heat and hot water for the Tercero 3 residence halls, now under construction, and additional heat for campus boilers. All told, the university is saving 511,000 therms of natural gas annually.
Not only that, but Pacific Gas and Electric Co. is giving the university a one-time rebate of $511,000 (a dollar a therm). PG&E and Lockheed Martin, which validated the energy savings, presented the first installment last week; the rest will come when the 1,200-bed Tercero 3 opens next year. See separate story about the campus's $7.65 million in rebates and $4.63 million in net cost savings in UC’s Statewide Energy Partnership.
As he led a tour in advance of the check presentation, Pablo Orozco, assistant director of engineering in UC Davis Design and Construction Management, prepared his visitors for the “wow” of this energy-conservation project: the condensing economizer, one of the hottest technologies today in steam-plant efficiency.
With previous improvements to the steam plant, over the last 10 years, UC Davis had achieved fuel-to-steam efficiency in excess of 80 percent, a “state-of-the-art level for conventional boiler systems,” according to the Syska Hennessy Group’s feasibility study of the condensing economizer project.
The plant achieved 83 percent efficiency with the installation of boiler feed water economizers, for the preheating of water before it goes into the boilers.
Then Orozco, Utilities Director David Phillips and energy manager Joshua Morejohn of Facilities Management developed the condensing economizer project, and the New York-based Syska Hennessy did the engineering work to incorporate the technology and equipment into the steam plant.
Construction began last May (with Orozco as the project manager), the condensing economizer went online in mid-November — and today the plant’s fuel-to-steam efficiency is 91 percent.
Very simply, the condensing economizer is a vessel for heat transfer: Very hot water vapor comes in, cooler vapor (and former vapor, condensed all the way back to water) goes out — and the university saves fuel and money in the process.
Scavenging the ‘heat sink’
As Orozco explained the “wow” factor during the recent tour, the control panel showed the “heat sink” for an instant in time: water vapor with a temperature of 265 degrees Fahrenheit going into the condensing economizer, 104 degrees going out.
“That’s a lot of heat being scavenged off there,” said Matt O’Brien, a stationary engineer, reading the data on a computer screen in the monitoring room at the Central Heating and Cooling Plant on Dairy Road.
All that heat originated in the furnaces of campus boilers. They run on natural gas, and when it burns it throws off hydrogen, which bonds with oxygen to form — you guessed it — water, or water vapor in this case, owing to the heat.
This vapor is completely separate from the water in the boilers and from the steam that the boilers produce (for heating all around the campus).
Previously, the water vapor went directly into the atmosphere, through the boiler stacks. Now, the vapor is diverted by fan into the condensing economizer, where the vapor swirls around three coiled pipelines filled with water.
The water in the pipelines is cooler than the water vapor — and that sets up the heat transfer, from the swirling vapor to the water in the pipelines.
Two of the coiled pipelines in the condensing economizer carry water that eventually will end up in the boilers; the hotter the water when it enters the boilers, the less energy is needed to produce steam to heat the campus.
The water in the third coil is for Tercero 3, just south of the steam plant. Some of that water will stay in a closed loop that goes through a heat exchanger; this will heat the water in a closed-loop system that heats the residence halls. In each building, fans will blow air through coils of hot water — and this is the air that will keep students warm.
The rest of the hot water will be for domestic use, in sinks and showers. (For cooling, Tercero 3 will use the same chilled-water system that serves the rest of the campus.)
The impetus for the project? UC Davis’ commitment to sustainability and its goal of eliminating all waste from campus energy systems. The pathway? The campus’s collaborative spirit.
“We need innovative thinking and campuswide partnerships to make that happen,” Utilities Director Phillips said. “In this case, Student Housing’s support was critical, as construction of the Tercero dormitories provided an ideal new home for the recovered heat.”
Student Housing, in turn, cuts its costs: the hot-water heat system is cheaper to build and easier to maintain than a steam system, and hot water is cheaper to make — it doesn’t take as much gas.
And, by burning less gas, UC Davis estimates a reduction of 3,020 tons of carbon dioxide annually from the heating plant, or a 5.9 percent reduction from the emission levels of July 2009 to June 2010.
Mike Sheehan, director of Student Housing, said: “This is a great demonstration of a project’s triggering an innovation that will impact the entire campus.”
Indeed, when it opens in 2014, Tercero 3 will be the university’s first building project with heat that comes from a closed loop of hot water — and other Tercero buildings may not be far behind.
Anticipating the installation of another condensing economizer, Student Housing hopes to provide hot water for the future Tercero 4 and to substitute hot water for steam at the existing Tercero 1 and Tercero 2, and the Tercero Dining Commons (except for steam for kitchen equipment). In fact, while putting in the main hot water line to Tercero 3, the contractor stubbed out the pipeline for future connections.
UC Davis paid $716,407 for its first condensing economizer, included in the total project cost of $4.4 million for project development, design and construction.
The PG&E rebate cuts the university’s cost to $3.9 million, which will be paid off in 8.8 years (from energy cost savings estimated at $441,448 a year, based on a price of 88 cents per therm of gas and a price of 8.5 cents per kilowatt hour for electricity to run the condensing economizer).
Reach Dave Jones at firstname.lastname@example.org.
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