City College of New York: Novel HVAC System Doubles Solar Roof Pod Energy Efficiency

January 23, 2012

A novel heating and cooling system designed by faculty and students of the Grove School of Engineering for the Solar Roof Pod, The City College of New York entry in the recent U.S. Department of Energy Solar Decathlon, delivers twice the energy efficiency of conventional units. The innovative system and its thermal storage tank capture the sun’s heat to both warm and cool the building.  It combines a novel design for heat exchange and storage with a heating and cooling system driven by solar heat and gravity alone.

“The difference that we propose is the idea of using heat to transport heat,” said Professor of Mechanical Engineering Jorge Gonzalez, the faculty lead advisor on the HVAC system. In a standard cooling system, a warm building is exposed to a chilled fluid called a refrigerant, which turns into a vapor.  In order to make it cool again, the refrigerant is compressed mechanically, an energy intensive process.

“Half of the energy used by traditional buildings is for cooling and 90 percent of that is used by the compressor,” Professor Gonzalez points out. The new system cools with no moving parts, aside from a few small pumps and little added energy.  The liquid carrying heat from the building rises as a vapor.  Instead of going to a compressor, the vapor moves into a saturated salt solution of lithium bromide.  The solution is warmed with solar heat, evaporating the vapor, which moves into the condenser and cools, restarting the process.