Adding glycol protects exposed cooling circuits from freezing, but it also changes how much heat the fluid carries, how readily it moves through piping, and how well it transfers heat inside equipment. A loop that performs well on water may deliver less cooling after conversion—even with the same pump speed and temperature setpoint.
The practical answer is to treat glycol as a system change, not just a chemical addition. Check the heat load, fluid concentration, cold-start conditions, pump operating point, and heat exchanger performance before filling the loop.
For Tennessee, Arkansas, and Mississippi facilities, winter protection also has a summer consequence: the glycol generally stays in the system when outdoor temperatures and cooling loads climb.
What Glycol Changes Compared With Water
Understanding glycol process cooling loop performance starts with four fluid properties. Use data for the actual glycol formulation, concentration, and operating temperature—not a generic correction factor.
Specific heat decreases. Each pound of solution generally carries less heat per degree of temperature rise than water.
Thermal conductivity decreases. Heat moves through the fluid less readily, affecting heat transfer at exchanger surfaces.
Viscosity increases. The mixture resists flow more strongly, particularly during cold starts.
Density generally increases. This changes the relationship between volumetric flow, mass flow, pressure, and pumping power.
These effects interact. Higher density partly offsets lower specific heat when evaluating heat carried per gallon, but it doesn’t eliminate the cooling penalty. Higher viscosity can increase circuit resistance while reducing turbulence and heat transfer inside an exchanger.
The penalties depend heavily on temperature and concentration. A mixture circulating through a warm process loop behaves differently from that same mixture sitting overnight in an outdoor dry cooler.
Choose the Protection Requirement Before the Concentration
Freeze protection and burst protection are different
Freeze protection keeps the fluid from beginning to form ice at the selected design temperature. Burst protection may allow ice or slush formation while limiting damaging expansion under the conditions defined by the fluid supplier.
A burst-protected circuit isn’t necessarily pumpable or capable of cooling production equipment. If the plant must restart during freezing weather, a burst rating alone is not an adequate operating specification. Equipment manufacturers may also require freeze protection regardless of whether the circuit normally runs in winter.
Base the requirement on the lowest credible fluid temperature, including shutdowns, exposed piping, idle branches, and power outages. Normal winter operating temperature isn’t enough. Circulation and heat tracing should not be assumed available during a loss of power.
More glycol is not automatically better
Select concentration from the fluid supplier’s freeze-protection data, with an appropriate design margin and the equipment manufacturer’s requirements. Stay within the formulation’s permitted concentration range, including any minimum needed for corrosion-inhibitor performance.
Excess concentration adds viscosity and heat-transfer penalties without necessarily providing useful protection. Also confirm whether the specified percentage is by volume or by weight. Those values are not interchangeable.
Ethylene Glycol or Propylene Glycol?
Ethylene glycol generally offers lower viscosity and better heat-transfer performance than propylene glycol at comparable concentrations and temperatures. Its toxicity requires careful consideration of exposure, containment, and possible cross-contamination.
Propylene glycol is often selected where lower toxicity is a priority. That does not make every propylene glycol product suitable for food-related applications or unrestricted discharge. The complete formulation, inhibitor package, and applicable facility requirements still matter.
Use an inhibited heat-transfer fluid approved for the equipment and service. Automotive antifreeze is not a substitute unless the equipment manufacturer explicitly approves it. Confirm compatibility with piping, exchanger metals, mechanical seals, gaskets, and elastomers. Don’t assume different inhibitor packages can be mixed.
Recalculate Heat Transport and Exchanger Capacity
The basic heat balance is:
Heat load = mass flow × specific heat × fluid temperature rise
For volumetric flow, mass flow equals volumetric flow multiplied by density. Use consistent units and fluid properties at the relevant operating temperature.
This calculation tells you how much heat the circulating fluid can transport. For the same load and allowable supply-to-return temperature rise, glycol will commonly require more volumetric flow than water. Alternatively, the loop must accept a larger temperature rise or a lower load.
But transporting heat is only part of the job. Heat exchangers must still move that heat across their surfaces. Lower thermal conductivity and higher viscosity can reduce the fluid-side heat-transfer coefficient. Increasing flow may help, but it also raises pressure drop and may exceed equipment limits.
Have the exchanger, dry cooler, or chiller checked at the proposed mixture, flow, inlet temperatures, and design ambient conditions. A water-based capacity rating doesn’t establish glycol capacity. For chillers, review evaporator pressure drop, minimum flow, freeze controls, and manufacturer glycol corrections.
If only the outdoor circuit needs protection, a separate glycol loop and isolation heat exchanger may be worth evaluating. That limits glycol exposure elsewhere but adds another pump circuit, exchanger pressure drop, and an additional temperature approach—the temperature difference needed to transfer heat.
Check the Pump at Both Normal Operation and Cold Start
A centrifugal pump doesn’t maintain its previous flow simply because its motor still runs at the same speed. Glycol changes the system resistance, and sufficiently high viscosity also changes pump performance.
Review the pump and system together:
System head: Recalculate losses through piping, fittings, strainers, valves, and exchangers using the mixture’s properties.
Pump curve: Apply appropriate viscosity corrections where required, rather than relying solely on a water curve.
Motor loading: Check power across expected operating conditions. Higher density and lower pump efficiency can affect the requirement.
Suction conditions: Review cold-fluid suction losses, available net positive suction head, loop pressure, and air removal.
Speed control: Confirm that variable frequency drives have usable range without exceeding pump, motor, or equipment limits.
In a filled closed loop, the pump primarily overcomes circuit friction; it doesn’t continuously lift fluid through the building’s full elevation. Static fill pressure still matters for keeping upper piping pressurized and maintaining suitable suction conditions.
Don’t raise speed until flow, differential pressure, motor load, and equipment limits have been checked. A larger pump may not solve an undersized exchanger or excessive glycol concentration.
A Mid-South Scenario: Winter Protection, Summer Shortfall
Consider a hypothetical Memphis facility with an outdoor dry cooler serving indoor production equipment. Maintenance adds glycol before winter, but no one rechecks the water-based equipment selection.
The loop starts and circulates. During summer production, process temperatures climb even though the pump sounds normal and the cooler fans operate.
Possible contributors include reduced heat transport, lower exchanger performance, and reduced flow from increased resistance. Fouled surfaces, trapped air, or control problems could produce similar symptoms.
The useful next step is measurement—not immediately replacing the pump. Compare actual concentration, supply and return temperatures, verified flow, exchanger differential pressure, ambient temperature, and production load with the revised equipment ratings.
Commissioning and Maintenance After the Change
Record a water-loop baseline before conversion if practical. After filling, document the fluid product, concentration basis, measured protection level, operating temperatures, flow, pressures, and pump speed.
Pay particular attention to these items:
Dilution water: Follow the fluid supplier’s water-quality limits or use an approved premix. Hardness and contaminants can contribute to deposits or corrosion.
Concentration testing: Use a calibrated instrument and the correct product-specific scale or conversion. A refractometer does not measure inhibitor condition.
Fluid condition: Track pH, inhibitor condition, and contamination using supplier-recommended testing and intervals.
Makeup: Repeated water additions dilute protection. Track additions and investigate leaks rather than repeatedly adjusting concentration without records.
Instrumentation and expansion: Check flowmeter settings for the new fluid and review expansion-tank sizing, precharge, and fill pressure.
Sample and service the loop under facility chemical-handling, pressure-isolation, and lockout/tagout procedures. Don’t open a hot or pressurized circuit to obtain a reading.
Bottom Line
Specify the protection temperature first, then verify thermal capacity and hydraulics at both cold startup and peak summer load. Buying glycol by percentage alone leaves too much unanswered.
For an application review, bring the fluid specification, equipment schedules, pump curves, piping information, operating measurements, and required process temperatures. Process & Power can help facilities throughout Tennessee, Arkansas, and Mississippi review process cooling equipment and the surrounding system before a conversion or capacity change.
Contact us to discuss your glycol loop and cooling requirements. Call Process & Power, Inc. at 901-362-5500 or visit us at 1721 Corporate Avenue, Memphis, TN 38132 for help with industrial air compressors, pumps, blowers, vacuum systems, and compressed air equipment and service throughout Memphis and the surrounding area.
