Patent ID: 6993918

Claim:
The method of controlling the temperature of a process tool with a thermal transfer fluid to maintain the tool at a selectable temperature in the range of −80° C. to +60° C., comprising the steps of: compressing and then condensing a first refrigerant having a first boiling point such that it is liquid at ambient temperature and pressure; expanding the condensed first refrigerant to a liquid-vapor mixture at a first refrigeration energy rate; compressing a second refrigerant having a second boiling point such that it is a gas at ambient temperature and pressure; effecting a first thermal energy transfer between the expanded first refrigerant and compressed second refrigerant while condensing the compressed first refrigerant; condensing the compressed second refrigerant with the expanded first refrigerant to effect a second thermal energy transfer, and expanding the condensed second refrigerant to provide a second refrigeration energy rate selectively related to the first for a cumulative refrigeration energy rate to achieve a desired thermal exchange rate with a thermal transfer fluid.