Recirculating chillers are a closed loop system that uses heating and cooling to control the temperature of a process or tool. It is closed loop in that the fluid that circulates in the process loop is self contained in the unit and, typically, a reservoir of fluid is temperature controlled. A secondary loop is used to dissipate, or reject, excess heat to the ambient environment when the primary loop reservoir is being cooled. The primary loop temperature control can be accomplished with either a vapor-compression cycle, similar to most air conditioning, or using thermoelectric devices, also known as Peltier coolers. In many cases, heating elements are also used in combination with the cooling technologies to give more temperature control. The secondary loop for dissipation to the ambient can be air-cooled, using fans to move the excess heat to the surrounding air, or by liquid cooling using process or building water supplies that might be available.