A growing number of colleges and universities are using deep underground pipes to heat and cool their buildings without burning fossil fuels. By Cara Buckley , The New York Times OriginalArticle here When administrators at Princeton University decided to cut the carbon emissions that came from heating and cooling their campus, they opted for a method that is gaining popularity among colleges and universities. They began drilling holes deep into the ground. The university is using the earth beneath its campus to create a new system that will keep buildings at comfortable temperatures without burning fossil fuels. The multimillion dollar project, using a process known as geoexchange, marks a significant shift in how Princeton gets its energy, and is key to the university’s plan to stop adding greenhouse gases to the atmosphere by 2046. The drilling makes an almighty muddy mess, but when all is said and done, the more than 2,000 boreholes planned for the campus will be undetectable, de