A glycol runaround system circulates a water-glycol mixture through two coils to transfer heat between separated air streams, preventing freeze-up in cold climates while achieving 40-65% sensible heat recovery. The glycol solution, typically 20-50% propylene glycol or ethylene glycol by volume, maintains fluidity at temperatures below 0°C. This configuration allows reliable heat recovery operation in northern climates where pure water systems would freeze.
Technical Details
Glycol solutions are circulated at 0.5-2.0 gallons per minute through small aluminum or copper coils rated for 250-500 kPa pressure. Standard glycol concentrations of 30-40% provide freeze protection to -15°C to -25°C depending on formulation. The mixture has specific heat of 3.2-3.5 kJ/kg°C and thermal conductivity of 0.38-0.42 W/m°C. Circulating pump power consumption ranges from 15-40 watts. Annual fluid analysis ensures proper inhibitor concentration and freeze protection.
Applications and Practical Significance
Glycol runaround systems are essential for cold climate applications including northern facilities, cold storage operations, and outdoor intake air systems. They maintain continuous heat recovery operation through winter months when water-based systems would fail. Glycol solutions cost 3-5 times more than water but eliminate freeze damage risk. Proper disposal procedures are required when replacing glycol at 5-10 year intervals.