Glycol Cooled draft beer dispensing systems are typically used in commercial applications such as bars, restaurants, and stadiums.
These systems use a secondary refrigeration unit (called a power pack or glycol chiller) to maintain draft beer at the proper temperature all the way from the walk-in cooler to the point of dispense. This is done by the power pack chilling and constantly circulating a water and a food grade anti-freeze (glycol) solution next to the beer tubing all the way from the walk-in cooler to the point of dispense.
The tubing used is called trunkline, or also known as python. In it the beer and coolant tubing are wrapped with a plastic moisture barrier, a foil wrap to transfer cooling, closed cell insulation, and some type of outside jacket to protect the insulation.
A glycol bath can maintain a consistent product temperature, however it can not additionally cool the beer if the walk-in temperature is too warm. This system is great for longer distances, up to 500 feet. Multiple dispense stations can be linked to one system.
For a understanding of how Glycol Cooled systems work, and the different components involved, below is a link to a diagram of a typical Glycol Cooled system. Simply click on the diagram, and another window will open which will allow you to zoom in and scroll around the diagram to see all aspects of the system in great detail.