The cooling is usually reached through a refrigeration cycle, but sometimes evaporation or free of charge cooling is used. Air conditioning programs can also be built according to desiccants (chemical substances which clear away moisture from the air). Some AC systems reject or keep warmth in subterranean pipes.[2] Air conditioners https://docs.google.com/spreadsheets/d/12u7rJLrjSWIMoTyNzJz1omJPJnoZX4A_U0YLwoyEYUk