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Quotes - Engineering - SalesHYDRONIC AND PROCESS
Glycol Loop
Separation
The number that catches people out is the glycol derate. Propylene glycol is more viscous than water and carries less heat per unit mass, so both the coefficient and the pressure drop move against the selection.
AHRI certification now covers propylene and ethylene glycol as well as water, which means certified performance data exists rather than a rule-of-thumb derating factor.
A 50 percent mix behaves very differently from a 30 percent one, and neither behaves like water.
Request a QuoteGlycol degrades performance in two directions at once, which is why guessing at it goes wrong.
What the derate actually does to a selection
Specific heat falls, so a given flow carries less heat and you need more of it for the same duty. Viscosity rises, so that increased flow costs disproportionately more pressure drop. The two effects compound rather than cancel.
The practical result is that a frame sized on water and then 'derated by ten percent' is usually short on surface and over on pressure drop simultaneously. Neither error is visible until commissioning.
Give us the glycol type and concentration with the duty. Certified data exists for both common glycols now, and using it is free.
- Propylene or ethylene matters. - They are not interchangeable in a calculation, even at the same concentration.
Sizing This Duty
Name the glycol and its concentration, then give the flow and the entering and leaving temperatures for the glycol loop and for the water loop. Mention any code requirement. The selection lists frame, plates and pressure class, quoted.
Request a glycol loop separation quotePractical Questions on Glycol Loop Separation
At the coldest temperature the glycol will actually reach in service, as well as at the design point. Glycol thickens sharply as it cools, so a unit that meets its pressure drop at the nominal condition can be well over it on a cold start, and the pump may not make flow until the loop warms.
Give us the minimum glycol temperature along with the concentration. If the cold-start case governs, the selection shifts toward more plates or a larger port, and it is far better to learn that on paper.
The water freezes in the channels. If the glycol arrives below the freezing point of water and the water pump trips or a valve closes, there is nothing to carry heat in, and ice forms between the plates quickly. Ice can split a brazed pack.
It shows up afterward as glycol in the water loop, a falling glycol level, or a visibly bulged unit. Interlock the glycol flow to proof of water flow and fit a low-temperature cutout on the water outlet. Freeze Protection covers the arrangement.
It is enough to build the same exchanger. It is not enough to know the same exchanger is still right.
Loops get refilled. An ethylene glycol system changed to propylene, or a mix topped up to a stronger concentration than the original design, leaves the old selection short on surface and high on pressure drop without any change to the hardware. Send the designation together with the glycol type and a measured concentration - a refractometer reading, not the figure on the drawing - and we will rate the old build against today's fluid before quoting it.
Partly. An H plate, the obtuse chevron, gives high heat transfer and high pressure drop; an L plate gives low and low; M sits between. On a viscous glycol side, moving from H toward M or L relieves the pump, but the lost heat transfer has to be bought back with more plates.
So the trade is pump energy against plate count, and it is worth pricing both ways. What does not work is keeping the water selection and hoping. Glycol and Fluid Properties explains how the two effects interact.
Frames for This Duty
