The cooling is typically obtained through a refrigeration cycle, but from time to time evaporation or cost-free cooling is used. Air conditioning methods may also be designed based on desiccants (chemical substances which clear away moisture in the air). Some AC programs reject or shop heat in subterranean pipes.[2] Clinic https://docs.google.com/spreadsheets/d/14Zqd0FEGkdjJlcohp4SFWeSZ9M4AIBFQpIDlHrjqztI