Consulting-Specifying Engineer - December 2008 - (Page 27)

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// years ago, Olson studied sustainable practices in the United Kingdom. It was during that stay that Dunham learned about thermal displacement ventilation, an energy-saving concept that is commonly used across Europe. In a traditional air system, overhead diffusers use cooler air than a displacement ventilation system, and then mix the air in the room to a certain temperature, typically 72 F. “Ninety percent of buildings in America use this,” said Olson, who has worked at Dunham since 1996. With thermal displacement ventilation, cool air circulates in the floor, supplying 64 F air instead of the traditional 55 F air, which eliminates the need for very cold water in the coolant coils. Because heat rises, it creates a naturally self-balancing system that provides as much heat as needed. Olson likens the system to a sweaty runner: “If you ran 3 miles and I was standing next to you, a lot more heat would come off your head. As that happens, cooler air would naturally be attracted to the heat to balance everything.” An 18-in. raised floor assists with airflow and allows enough space for current electrical distribution and for future technology advancements. Two outside air units contain energy recovery wheels that recover latent and sensible energy from building relief and toilet exhaust. An air-to-air plate exchanger provides free cooling and free reheat of supply air during dehumidification mode, but allows bypass when not dehumidifying to reduce fan static pressure. The beauty of the system is its ability to allow 30% more outside air to enter the building than required by code. Thermal displacement ventilation is an energy-saving concept. In traditional geothermal systems, vertical wells typically 200 ft deep are used to exchange energy with the earth. But Dunham noticed the 6-acre lake on Great River Energy’s property and thought about using that instead. Even though the lake was large, Olson didn’t know its depth or temperature. To see if the lake could be used as a possible energy source, Lonnie Vande Kamp, Dunham’s engineer of record, paddled a canoe to the middle of it in mid-August. He dropped a depth finder and thermometer for preliminary readings. “It wasn’t a very scientific starting point,” Olson said with a laugh. “But we had to see what we were dealing with.” After discovering the lake’s depth of 32 ft, Dunham commissioned a lake study to create a month-by-month temperature profile. The study showed the lake remained near 39 F during the winter and peaked at 60 F during the summer. Dunham considered a ground loop system but ultimately opted to use the lake since the study showed it offered hundreds of hours of free cooling from October through June, and the overall lake temperature would change only by a half degree. Two heat transfer methods were then considered: metallic heat exchangers and polyethylene tubing. Ultimately, Dunham used more than 30 miles of rugged-yet-flexible polyethylene tubing instead of metallic heat exchangers, which have a limited history and raise concerns about maintenance and long-term performance. Since the flexible coils don’t have joints and fittings, the ¾-in. coils were placed on top of a pallet. Twelve-inch concrete cinder blocks were attached under the pallet to elevate the piping slightly above the bottom of the lake, minimizing the lake bottom contact area to less than 1,200 sq ft. The 39 heat exchanger bundles were inflated with air and floated in raft-like fashion to Daylighting in occupied spaces, expansive views to the outside, and displacement ventilation provide superior indoor environmental quality. Photo: Don F. Wong These are roof-mounted photovoltaic fixed arrays, with the 200 kW wind turbine in the background. The arrays are connected to a series of dc-ac converters. Photo: Lucie Marusin Consulting-Specifying Engineer • DECEMBER 2008 27

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Consulting-Specifying Engineer - December 2008 Contents Viewpoint News M/E Roundtable ARC Awards New Construction Gold New Construction Silver New Construction Bronze Renovation Gold Renovation Silver A Green Approach to Air Conditioning Systems Turning Down the Lights Case Study New Products Equipment Lifecycles Advertiser Index Green Space Gas Technology Pure Power Supplement

Consulting-Specifying Engineer - December 2008

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