HOFFMANN coolers are designed as compression refrigeration systems. This version which can also be found in refrigerators, for example, has the best efficiency of all common cooling techniques in the room temperature range.
An electrically driven compressor sucks in the gaseous working fluid and compresses it. The compression heats up the gas. In the subsequent condenser, the gas is cooled by releasing the heat to the environment. The still pressurized working fluid (gas) liquefies in the course of it and flows to the expansion valve.
The working fluid is supplied to the evaporator via the expansion valve. In case of reduced pressure, the working fluid evaporates again and cools down in the course of it. The evaporator can thereby absorb heat from the environment. The compressor sucks the working fluid that is now gaseous again from the evaporator so that the cycle is complete.
The following diagram illustrates the function: