The Glycol Flow Rate Calculator is an HVAC and fluid engineering tool used to determine the correct flow rate for a glycol-water mixture in heating or cooling systems. This calculator belongs to the fluid dynamics and thermal system optimization category. It ensures that a system delivers the intended heating or cooling capacity while accounting for the changes in fluid properties caused by adding glycol.
When glycol is mixed with water, it changes the fluid’s density, viscosity, and heat capacity. These changes affect how efficiently heat is transferred. Using the correct flow rate ensures that the system operates effectively without underperforming or wasting energy. The Glycol Flow Rate Calculator adjusts the calculations to account for glycol’s lower heat transfer capability compared to pure water.
formula
Glycol Flow Rate (GPM)
Glycol Flow Rate (GPM) = Heat Load (BTU/hr) / (500 × ΔT × Heat Transfer Correction Factor)
Where:
Heat Load (BTU/hr) = The total amount of heat the system must move per hour
ΔT (°F) = The temperature difference between the supply and return fluid
Heat Transfer Correction Factor = A multiplier that accounts for glycol’s reduced heat transfer efficiency. It is found from manufacturer data tables based on glycol type, concentration, and fluid temperature
The constant 500 is used for water-based systems and comes from the product of the density of water (8.33 lb/gal) and 60 minutes in an hour.
Quick Reference Table for Common Glycol Flow Rate Factors
| Glycol Type | Glycol % by Volume | Fluid Temp (°F) | Heat Transfer Correction Factor |
|---|---|---|---|
| Propylene Glycol | 20% | 100 | 1.06 |
| Propylene Glycol | 30% | 100 | 1.09 |
| Propylene Glycol | 40% | 100 | 1.13 |
| Ethylene Glycol | 20% | 100 | 1.04 |
| Ethylene Glycol | 30% | 100 | 1.07 |
| Ethylene Glycol | 40% | 100 | 1.10 |
This table helps quickly find the correction factor without doing repeated data lookups.
Example
A chilled water system needs to move 1,000,000 BTU/hr using 30% propylene glycol at a ΔT of 12°F. From the manufacturer’s table, the Heat Transfer Correction Factor is 1.09.
Step 1: Insert values into the formula
Glycol Flow Rate = 1,000,000 / (500 × 12 × 1.09)
Step 2: Multiply the denominator
500 × 12 = 6000
6000 × 1.09 = 6540
Step 3: Divide
1,000,000 / 6540 ≈ 152.9 GPM
Result: The system must pump approximately 152.9 gallons per minute to meet the heat load with 30% propylene glycol.
Most Common FAQs
Glycol solutions have different heat transfer properties than water. Using the water-only formula would result in an incorrect flow rate and possible underperformance.
Yes, generally. Higher glycol concentrations reduce heat transfer efficiency, which means you need to move more fluid to achieve the same heat transfer.
No, correction factors depend on glycol type, concentration, and operating temperature. Always use data from the glycol manufacturer for accurate results.