Nebraska’s first ‘geo’ neighborhood a bridge to the future 

 

The Bridges housing development near Lincoln, Neb., is quickly becoming one of the “greenest” neighborhoods in America. It’s not a marketing ploy by Miracle Grow. Rather, the state’s first all-geothermal development is a study in back-to-the-future energy reduction. But it didn’t start out that way. 

 

“I just like to create stuff that looks good,” said Gary Pickering, Bridges developer and president of Lincoln-based Pickering Creative Group, a marketing firm. “My initial vision was purely aesthetic. I wanted to make a gorgeous environment with lots of water that would include a variety of unique bridges, all set like gems within the green living space. It wasn’t about energy efficiency.”

 

Pickering’s all-things-green approach evolved many months before the first of 70 planned homes was constructed at the 181-acre space. The development’s landscaping is well under way as big machines sculpt the property, adding small lakes, roads, miles of paved walkway and entry points for a multitude of bridges.

 

“Each bridge is distinctly different,” said Pickering. “At the development’s entry point is an 80-foot-long covered bridge built with heavy timbers with a floor surface that deliberately rumbles under the weight of a car. Other bridges are made of cedar, stone and bowed metal.” One bridge will have an ornate cupola in its center.

 

The green landscape/green energy approach stems from a conversation Pickering had with Mike Rezac, president of Rezac Construction Inc., a partner in the Bridges project, when they first reviewed the plan for so many bodies of water. A decade ago — before green-build was cool — Rezac focused his firm on sustainable home construction.

 

“I’ve had experience with geothermal before,” said Pickering. “So, when Mike and I looked at the landscape plan, he brought up the idea of tapping the abundance of btus in the water.”

 

The lakes at Bridges, some of which measure 500 feet long and 70 feet wide, are about 12 feet deep. “They’re deep enough for a bunch of stainless steel, 4-by-6-foot, or 4-by-8-foot “Slim Jim” heat exchangers, one dedicated to each of the 58 homes planned for the development on property bordering any of the seven lakes,” said Doug Kreifels, president of Action Plumbing & Heating, tapped by Rezac to do the mechanical work.

 

Rezac, who builds eight to 12 homes a year, built the first three homes in the Bridges development. Each home is a Nebraska state-certified “green build” home (see www.nebraskagreenbuilders.com), recognizing deliberate steps Rezac has taken to manage a home’s design, construction, energy use, water efficiency and lot development.

 

Lake loops

 

According to Kreifels, the lakes are the key source of energy savings. During the development’s very early stage, geothermal pipes were horizontally bored from each of the initial lake-bordering home sites to the water’s edge.

“We went down about six feet and, from that point, pointed the drill toward the lake,” said Kreifels. After inserting the geothermal tubing underground, the last 10 feet of borehole was grouted, sealing it to eliminate the risk of water penetration from the pond.

 

“This way, most of the underground work and tubing to and from the home is ready to go. When a buyer presents a home plan, determination can then be made about the size of the lake-loop heat exchanger: the larger the home, the larger the ‘Slim Jim,’” added Kreifels.

 

Up to 30 EER

 

“With the tubing already in place to complete the system, and buried, there’s little exterior work involved,” said Rezac. The 12 homes not bordering a lake will tap the earth’s thermal energy through more traditional geo-exchange – with closed loop pipes inserted into deeply-drilled boreholes.

 

All homes will include either a Carrier gt-px geothermal unit or a ClimateMaster Tranquility 27 system. Some homes are served by a four-, five- or six-ton heating and cooling systems; others may require two units to meet a total of seven tons. According to Steve Wilkey, geothermal division manager for Comfort Products Distributing, involved in the project as the manufacturer’s rep for Carrier and ClimateMaster, all are two-stage systems with variable-speed blowers for maximum heating and cooling comfort and efficiency. Factory-installed hot water generators will provide about 50% of the heat for all domestic water needs.

 

“The Nebraska State Department of Energy asked me to go a step further with one of the homes, hoping that we’d be willing to take it to a net-zero energy level,” added Rezac.

 

And so they did. The third home in the development has achieved total energy independence. One of the surprising things Rezac discovered in monitoring energy performance so closely for the DoE home is that, coupled with the underwater heat exchangers, they pushed the efficiency of the geothermal systems from an expected efficiency of 27 eer to 30 eer because of the superb thermal transfer they achieved with the lake water plates.

 

Rezac explained that they researched the effectiveness of wind and photovoltaic (pv) energy production for the net-zero home. “But we wanted the home to be mainstream and to side-step all the code restrictions on wind turbines, so we went with pv and also incorporated other active and passive solar design facets — such as a longer roof overhang, and optimal orientation of the home for winter solar gain.

 

According to Rezac, each geothermal system — which requires no combustion process — avoids the release of about one ton of greenhouse gas each year.

 

The Norris Public Power District based in Beatrice, Neb. estimates, depending on the size of the home, that residents will save between $500 and $1,500 per year on their utility bills. “We’re partnering with local utilities, Carrier and ClimateMaster on this project,” continued Rezac. “They’ve helped immensely, working closely with us in designing the systems.”

 

“There’s really no limit to what we can do, or at least attempt to accomplish, with the combination of geothermal energy at this development,” said Wilkey. “There’s been a sense of exploration and discovery from the beginning. Ultimately, the homeowners will reap the benefit, and beyond this development we hope we’re making some contribution to a larger, broader good for the building industry and the environment.”

 

Heat exchanger fisheries

 

Utility experts have closely monitored exchange temperatures at the submerged heat exchangers, both in the heating and cooling modes. “The surprise came when we discovered that exchange levels exceeded those of ground loops. We’ve achieved a 20-degree differential, well above design standards.”

 

Rezac went on to explain that one surface acre of water with an average depth of 10 feet could serve 20 tons (240,000 btus) of heating and cooling without significantly influencing ambient temperatures in the body of water.

 

“The lakes have an average temperature of 60 degrees in the heat of summer,” added Rezac. Monitoring lake temperatures before and after insertion of the lake plate heat exchangers has been especially important because each of the lakes is a unique and carefully-controlled ecosystem. “Each body of water is home to one specific fish,” said Rezac. Species include yellow perch, small or largemouth bass, and catfish. Each lake is tended carefully by an expert dedicated to the task.”

 

“No doubt, we’ll be building homes at the development for several years,” concluded Pickering. “We’re taking it at a realistic pace with time to enjoy accomplishment at each new stage. It’s not every day that you can be involved in something like this.”