In the heat driven air conditioners, most of the energy used in the cooling operation is thermal for the removal of water from the desiccant. Off-peak electrical power can be used for this purpose. The desiccant may be stored at ambient temperature in a single plastic container as stratification maintains the dilute desiccant in the upper portion. The quantity of desiccant required is a one-time charge of 29 pounds per one ton (12,000 Btu) of cooling per hour. A recent price of concentrated liquid desiccant (1.55 specific gravity) was $1.13 per pound. The first large installation was a five-story building in Beijing with the desiccant storage on the first floor.