Grounded resources

The team marketing the Monarch Loft condominiums on the Merrimack River in Lawrence emphasizes the 13-foot-high windows with 48 panes, brick-and-beam interiors, 12-inch-diameter wood columns, 16-foot ceilings, and maple floors. They also brag about easy access to Interstate 495 and the new MBTA commuter-rail station across the street.

What some of the potential buyers like most, though, is the monthly heating and air-conditioning bills, which are projected to be $50 a month for a 1,200-square-foot unit. That's an estimated 9 percent savings over a typical air-conditioning bill and 32 percent less than it costs to run the average furnace in the winter.

The 50 bucks a month is not for oil or gas or coal. It's the cost of electricity to run a heat pump on a geothermal system the developer is installing to draw heat from the ground and to warm living space in the winter or to extract heat from humid air in the warmer months and send it through pipes buried deep in the earth, cooling the building's interior.

"We're not putting any pollution into the earth," said Mike Zimmerman, principal of Allied Consulting Engineering Services Inc. of Sudbury, which designed the extensive geothermal system for the huge Monarch on the Merrimack project in a converted mill building. "That's a gift to the planet."

Although it is not frequently used, geothermal energy is the most efficient, cheapest, and cleanest heating and cooling technology, the US Environmental Protection Agency said back in 1993.

The developer of the Lawrence project -- MassInnovation LLC, which is owned by Robert D. Ansin of Fitchburg -- has already redeveloped a large, historic mill building in his hometown using geothermal energy.

Monarch on the Merrimack -- named, Ansin says, because a butterfly signifies change and renewal of the historic textile district -- would be the largest private residential project in the United States relying on geothermal energy. The first phase has 202 residential units, and the total would rise to 800 if two later phases are completed as planned, according to the developer.

It could be the biggest geothermal system anywhere. According to "The Citizen-Powered Energy Handbook: Community Solutions to a Global Crisis," a new book by Greg Pahl, the world's largest system is in a Louisville, Ky., hotel and office building complex covering 750,000 square feet. The Monarch Lofts will have about 1.3 million square feet.

In 2003, Ansin said, a real estate broker took him to see the former Wood Worsted Mill, a six-story brick structure a third of a mile long. The American Woolen Co., which built and owned the 101-year-old mill, once produced 20 percent of all American textile products, Ansin said.

He took a look around and said, "This is too good to be true."

The mill produced a lot of military clothing during World War II, but shut down in 1954. Honeywell International Inc. later used the mill for manufacturing, and Malden Mills Industries Inc. moved its distribution operations there after a devastating fire and still uses a portion of the building.

Ansin and his redevelopment company bought the mill in 2003 for $4.4 million. They plan to build and sell a first phase of 202 condominiums and then two more phases of 300 units each at the site in Lawrence, which unlike its sister mill town Lowell has yet to enjoy a renaissance.

Monarch will feature a fitness center, meeting rooms with wireless Web access, art galleries, roof terraces for top-floor units, 10 acres of green space, and both underground and surface parking. The developers plan about 90,000 square feet of office and retail space, where tenants will include a cafe, restaurants, and a jazz club.

The building will use so little energy, Ansin said, that it isn't required to have the same levels of insulation that are required of most new construction in Massachusetts. That saves on construction costs and allows thick exterior brick walls to remain exposed on the interior.

Except for penthouses and two exceptionally large units on top, the residences will sell for between $200,000 and $350,000, higher-priced units being on higher floors and on the river side.

The remaining half of the original mill is 500 feet longer than the Empire State Building is high and has 2,100 windows, which are being replaced with historically accurate but thermally insulated ones.

The old mill had a separate 5-acre power-generating complex next door. There two tall stacks once belched smoke from the coal and later oil burned to keep the operations going and employ 10,000 people in three shifts at the mill's peak.

Those buildings remain, and they, too, could be renovated for new uses, Ansin said. But the heating and cooling exchange equipment connected to the 1,500-foot-deep wells for Monarch Lofts will be located on the first floor of the building, high enough above ground to avoid damage in times of major flooding, as happened last year, when the overflowing Merrimack River filled below-grade spaces.

The geothermal heating and cooling systems take water from wells drilled deep into bedrock that is 50 to 55 degrees year-round and transfer its heat to a closed-loop system of pipes that circulates water in the building. In each residential unit, the heat in that water is transferred to a chemical in pipes that are part of a heat-pump system. Through compression like that in an air conditioner, that heat is concentrated and the temperature is raised.

In the summer, no compression stage is needed, because the water from the wells is at around 50 degrees, considerably cooler than the air in the residences.

In the final stage of the process, the heat pump makes use of as much of the warming or cooling effect as the occupant desires. A duct system with a fan delivers the heated or cooled air to the living space, controlled by a thermostat.

Ansin said he is duplicating what he built in Fitchburg, but on a larger scale.

"We're redoing a building built in an entirely different time, for uses in demand today and for uses in the future," he said.

"If you can build something that's sustainable, regardless of what people want to use it for, you've got a winner."

Thomas C. Palmer Jr. can be reached at tpalmer@globe.com.