A more detailed look at the layout of a recirculating chiller uncovers a few key points. The primary circulating fluid circuit is self-contained, or closed, and interacts with the refrigeration circuit through a heat exchanger. In the case of the vapor-compression version, this heat exchanger is the evaporator of the refrigeration circuit. In the thermoelectric-based system, the heat exchanger is directly coupled to the thermoelectric, or Peltier devices. Also to be noted are the many sensors, both pressure and temperature, that allow the control of the primary circuit to deliver the temperature control needed for the process needs.