Besant and Johnson (1995) discuss details of fluid glycol the use in a run-around system in Saskatchewan, Canada.
...the temperature difference between the air and coupling fluid is only a few degrees in a run-around system. This implies that the designer must not only specify the glycol concentration and flow rate for the coupling fluid but also the coil height, coil width, number of coil tube passes, coil tube size, thickness and spatial configuration and fin wavy pattern, spacing and thickness for each heat exchanger coil in the design. [In this example] the system operators, over the years, increased the ethylene glycol content of the coupling fluid to nearly 60% just to be sure there would be no freezing problems, a measure that would reduce the system effectiveness.
