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
Wiley protocol at separate times throughout the period. The protocol is promoted as differing from conventional hormone replacement therapy in several ways: The protocol also includes a follow-up program to monitor the serum of the bioidentical hormones. Wiley has stated that in her opinion, the most important aspect of the protocol is the specific schedule and levels of the hormone doses rather than their bioidentical nature. A patent was granted for the protocol in 2011 for the specific blend of hormones and dosing method. Concerns have been raised that serum levels may not be an acceptable marker for transdermally administered hormones, that