Heat pump the brand name Freon, a trademark of DuPont. Its manufacture is now banned or severely restricted by the Montreal Protocol of August 1987 because of the damage that CFCs cause to the ozone layer if released into the atmosphere. One widely adopted replacement refrigerant is the hydrofluorocarbon (HFC) known as R-134a (1,1,1,2-tetrafluoroethane). Heat pumps using R-134a replaced R-12 (dichlorodifluoromethane) and have similar thermodynamic properties but with insignificant ozone depletion potential and a somewhat lower global warming potential. Other substances such as liquid R-717 ammonia are widely used in large-scale systems, or occasionally the less corrosive but more flammable propane or
Full-service community schools in the United States magnet schools, and alternative schools, the full-service community school model is one of many educational reform efforts that are intended to increase student achievement, but the full-service community school model specifically focuses on the development of the community as a whole. A charter school receives public funds but is not subject to all of the rules, regulations, and statutes public schools must adhere to. A charter school is accountable to what is sent forth in its individual charter. A school voucher is a certificate issued by the government to allow families to apply it the cover the tuition at a