The Glycol Correction Calculator is an engineering and HVAC tool that helps determine the correct adjustments when a heating or cooling system uses a glycol-water mixture instead of pure water. This type of calculator belongs to the fluid dynamics and HVAC system optimization category. It is widely used in refrigeration systems, chilled water loops, and hydronic heating systems, where glycol is added to prevent freezing in low-temperature conditions.
Using glycol changes fluid properties like density, viscosity, and heat capacity. This affects system performance, including flow rate and pressure drop. The Glycol Correction Calculator ensures accurate system design and operation by applying manufacturer-specific correction factors and fluid property data.
formula
Formula for Glycol Percentage
Required Glycol % = Value from Manufacturer's Table based on Desired Freeze Point
This is a lookup process rather than a mathematical calculation. To determine the glycol percentage, you refer to the manufacturer’s glycol data sheet, find the desired freeze protection temperature, and read the corresponding percentage.
Formula for Corrected Flow Rate
Corrected Flow Rate = Original Flow Rate (for water) / Heat Transfer Correction Factor
Heat Transfer Correction Factor
Heat Transfer Correction Factor = Specific Gravity of Glycol Solution x Specific Heat of Glycol Solution
Where:
Original Flow Rate (for water) = System’s designed water flow rate
Specific Gravity of Glycol Solution = From data tables based on glycol type, concentration, and temperature
Specific Heat of Glycol Solution = From data tables based on glycol type, concentration, and temperature
Formula for Corrected Pressure Drop
Corrected Pressure Drop = Original Pressure Drop (for water) x Viscosity Correction Factor
Where:
Original Pressure Drop (for water) = Pressure drop calculated for pure water
Viscosity Correction Factor = Manufacturer’s factor based on glycol type, concentration, and temperature
Quick Reference Table for Glycol Freeze Protection
| Glycol Type | Glycol % by Volume | Freeze Point (°C) | Specific Gravity | Specific Heat (Btu/lb·°F) | Viscosity Factor |
|---|---|---|---|---|---|
| Propylene Glycol | 20% | -7 | 1.02 | 0.97 | 1.15 |
| Propylene Glycol | 30% | -12 | 1.04 | 0.94 | 1.25 |
| Propylene Glycol | 40% | -23 | 1.05 | 0.91 | 1.40 |
| Ethylene Glycol | 20% | -10 | 1.02 | 0.98 | 1.10 |
| Ethylene Glycol | 30% | -15 | 1.04 | 0.96 | 1.18 |
| Ethylene Glycol | 40% | -25 | 1.05 | 0.93 | 1.30 |
This table provides a quick guide for selecting the right glycol concentration and understanding its physical properties.
Example
A hydronic heating system is designed for pure water with an original flow rate of 200 gallons per minute (GPM) and a pressure drop of 15 psi. The system will use 30% propylene glycol at 10°C.
From the manufacturer’s table:
Specific Gravity = 1.04
Specific Heat = 0.94
Viscosity Factor = 1.25
Step 1: Find Heat Transfer Correction Factor
Heat Transfer Correction Factor = 1.04 × 0.94 = 0.9776
Step 2: Calculate Corrected Flow Rate
Corrected Flow Rate = 200 / 0.9776 ≈ 204.6 GPM
Step 3: Calculate Corrected Pressure Drop
Corrected Pressure Drop = 15 × 1.25 = 18.75 psi
Result: The system must pump approximately 204.6 GPM, and the pressure drop will increase to 18.75 psi when using 30% propylene glycol.
Most Common FAQs
Glycol prevents freezing in systems operating at low temperatures, protecting pipes and equipment from damage. It also provides corrosion resistance when using inhibitors.
Yes, glycol has lower heat transfer capacity and higher viscosity than water, which slightly reduces system efficiency. The Glycol Correction Calculator helps adjust the system to compensate for these changes.
No, mixing different glycol types can cause chemical incompatibilities, reduced freeze protection, and corrosion inhibitor failure. Always use the type specified by the manufacturer.