oning HFC-507A -0 3,900 Low-temperature refrigeration Natural Refrigerants I Carbon dioxide (CO2) 0 1.0 Ammonia (NH3) 0 0 Propane 0 3 District Energy Systems For projects with district energy systems, specific technical guidance can be found on USGBC's Registered Project Tools (http://v/ww.usgbc.org/proj