Work is underway on an 1800-lot subdivision in Louisville, Kentucky, that according to its developers will be the largest community in the country that insists that every house must have a ground-source heat pump.Builders who buy lots in the North Village of Norton Commons will have a free hand on what kind of houses they build, as long as they meet general architectural guidelines, but a ground-source heat pump for heating and cooling will be a requirement.The project is a Traditional Neighborhood Development, a type of development which includes a variety of housing types and commercial buildings and is designed so people who live there can walk to many of their destinations.Marilyn Patterson, director of marketing and general counsel for the development, said by telephone that there are a variety of advantages to requiring ground-source heat pumps, including better heating and cooling performance, greater efficiency than other options, and reduced environmental impact. A big part of the appeal is that no one living there will have to listen to a noisy outdoor compressor belonging to a neighbor with a conventional air-source heat pump. In a news release, developers said well drilling has started for heat exchange tubing on the first 50 lots, and another 75 lots will be drilled in the spring. Construction could begin any time.It will take 12 to 15 years to build out the entire North Village, she said. The 600-acre development already includes the South Village, with about 1,000 residential units, where ground-source heat pumps were not a requirement.Houses will range in size and costHouses in the South Village range in size from 1,200 square feet to 8,000 square feet, and cost between $360,000 and $2 million, Patterson said. She expected the range to be similar in the North Village, but the first group of houses would probably be in the 2,200- to 2,500-square-foot range.Requiring ground-source heat pumps makes the houses more expensive, adding from $4,500 for a smaller unit to as much as $15,000 for a large house, she said, but the 30 percent federal tax credit, good through the end of 2016, will take away some of the sting.Builders will not be required to build to any particular efficiency level, Patterson said, although upgraded insulation packages and Energy Star appliances would probably be the norm. “The market demands they build efficient housing,” she said.Developers also promote the idea that people who live in Norton Commons have a lot of what they need nearby: local stores, schools, and playgrounds in addition to housing. So driving won’t be as essential to life there as it is in many suburban settings.“What could be greener than that?” she asked.