At an operating temperature of 40 °C (104 °F) glycol has only:
88 % of the heat capacity
62 % of the heat conductivity
75 % of the heat-transfer coefficient
Up to 3.85 times higher pressure losses, and
3.8 times the viscosity of water.
Electrical costs associated with glycol systems are generally twice that of our systems. To prevent Thermal Stagnation, glycol systems require two means of protection.
The first is to undersize the system, but that leaves the owner paying for the installation labor and getting a smaller system than needed. The second is to require extra equipment designed to reject energy collected by the system in the summer, and further degrading the cost effectiveness of those systems.