New thinking has emerged on using the earth’s own heat. Experts say geothermal systems can be installed just about anywhere since the earth is about 55 or so degrees near the top of its crust. Heat pumps run by electric motors can tap this non- polluting and virtually inexhaustible supply of energy and use it to heat and cool buildings just about anywhere, including the heart of Manhattan. Neal Rauch reports from the east side of Central Park.