What Happens to Pump Coolers When Temperatures Drop Below Freezing?

Winter has a way of finding every shortcut you took in summer. The valve that was never quite closed, the pipe run that nobody insulated, the standby unit sitting full of water in an unheated corner. Cooling equipment is especially exposed, because it’s full of water by design and water has one nasty habit. It expands when it freezes. If you run a CPK heat exchanger, or you’re comparing it with a plate fin heat exchanger for a cold site, it’s worth understanding exactly what freezing does and how to avoid it. The damage can be sudden, expensive, and completely preventable. So let’s go through it plainly, from what physically happens inside the unit to what you should do before the first hard frost arrives.

Why winter is rough on cooling equipment

Most cooling loops are designed around summer. That’s when the heat load is worst, the cooling water is warmest, and the argument for the equipment is easiest to make. Winter gets less attention because the problem flips. Instead of too much heat, you’ve got a risk of too little.

Think about what changes. Ambient temperatures fall, and any water sitting in exposed pipework, outdoor equipment or unheated buildings starts to cool toward the air temperature. Cooling tower basins and outdoor lines are the obvious victims. But even indoors, areas near doors, vents or poorly insulated walls can drop below freezing in a cold snap.

Flow matters too. Moving water resists freezing far better than still water, because it keeps carrying heat from warmer parts of the system. A loop that’s running is fairly safe. A loop that’s stopped, or running at very low flow, is where ice forms. That’s why freeze damage so often appears after a shutdown, a power cut, or a night when a pump tripped.

There’s also the human factor. Winter shutdowns, holiday breaks and standby equipment all create situations where water sits idle in cold spaces. Plenty of freeze failures happen simply because nobody thought about a unit that wasn’t in use.

What actually happens when water freezes in an exchanger

Here’s the physics, kept short. When water turns to ice it expands by roughly nine percent. That doesn’t sound like much until you remember the water is trapped inside narrow passages with rigid walls and nowhere to go.

Ice forms first at the coldest, slowest moving spots, often along tube walls or in corners. As it grows, it squeezes remaining liquid, which can’t escape if both ends are blocked by ice or closed valves. Pressure builds rapidly, far beyond what thin walls are designed for. Something has to give.

In a tube bundle, tubes can split along their length, flatten, or bulge. Tube joints can loosen. In a plate type unit, plates can deform or crack, and brazed joints can open. Headers and end covers can crack too. The damage might be obvious, a visible split with water spraying everywhere, or it might be hidden, a hairline crack that only starts leaking after the ice melts.

And that’s the sneaky part. A frozen unit can look fine while frozen, because the ice is plugging the crack. The leak shows up when it thaws, sometimes hours later, sometimes after the unit is back in service and one fluid starts crossing into the other. Cross contamination between circuits is a serious consequence, depending on what the fluids are.

Where freeze damage likes to hide

Freeze failures follow patterns, and knowing the usual hiding places helps you protect against them.

Dead legs are the classic. A branch of pipe with no flow, a capped stub, a bypass line that’s normally closed, all hold stagnant water that freezes first. Low points are next. Water drains to the lowest part of a system and sits there, so low point pockets and drain traps are vulnerable.

Outdoor or exposed pipework tops the list for obvious reasons, particularly small bore lines, instrument tubing, and sensor pockets, which have little thermal mass and freeze quickly. Valve bodies and strainers can freeze and crack as well.

Standby and spare units deserve special mention. A second cooler that’s valved off and full of water might sit unnoticed all winter. Because there’s no flow, it’s the first to freeze. Same for equipment that’s been shut down for maintenance and left filled.

Then there’s the cold spot nobody expected. A draught under a door, a broken window, a ventilation fan pulling frigid air across one section of pipe. Local conditions matter more than the weather forecast. Walk the plant on a cold night with a thermometer, or an infrared gun, and you’ll find surprising chilly corners.

Glycol, and what it does to your numbers

The most common protection for loops that can’t be kept warm is antifreeze, typically a glycol and water mix. Glycol lowers the freezing point of the fluid, and in stronger mixtures it turns to a slush before becoming solid, which is much gentler on equipment than hard ice.

But it isn’t free. Glycol changes how the fluid behaves. It has a lower specific heat than water, so it carries less heat per unit of flow. It’s more viscous, especially when cold, so it resists flow more and raises pressure drop. Heat transfer coefficients fall as well. The net effect is that a cooler sized for plain water may need more area, or more flow, to do the same job with glycol.

Concentration matters. Too little and you don’t get the protection you think you have. Too much and you pay a performance penalty for no extra benefit. Choose the concentration based on the lowest temperature you expect, with a safety margin, and test it, with a refractometer or similar, instead of guessing. Concentrations drift over time with leaks and top ups.

Quality counts. Use inhibited glycol suited to your system and materials, because uninhibited glycol can become corrosive, and some types are toxic or environmentally sensitive. Check compatibility with gaskets, seals and metals, and follow the maker’s guidance. If you switch to glycol, tell whoever sizes your cooler, because it changes the calculation.

How a CPK heat exchanger fits a cold weather plan

I’m not going to quote ratings for the CPK heat exchanger. They depend on the version and conditions, and the current datasheet is where numbers belong. What I can do is outline how to think about cold weather with it.

Start with where it’s installed. Indoors in a heated space is safest. Outdoors or in an unheated building, it needs protection, insulation, heat tracing, or a plan to drain it when it isn’t running. Check the datasheet and manual for the maker’s guidance on minimum temperatures, freeze protection and drain-down procedures.

Check both circuits. The cooling water side usually gets the attention, but the process or seal liquid side might also contain water. If both sides can freeze, both need a plan.

Make sure it can actually be drained. Are there drain points at the low spots and vents at the high ones, so the unit empties fully? Water trapped in pockets defeats the whole point of draining. If the existing installation can’t be drained properly, fix that before winter, not during it.

Think about flow control. Keep some flow going on cold nights if you can, with a bypass or recirculation arrangement, so water never sits still in a cold place. And consider alarms on low temperature or low flow, so someone knows early if something’s going wrong.

How a plate fin heat exchanger behaves differently

Now the other contender. A plate fin heat exchanger is built from flat plates with thin corrugated fins brazed between them, creating a compact block with a lot of surface area. In many designs it’s aluminium, and aluminium has a useful property. It stays strong and tough at very low temperatures, which is why these units are common in cryogenic and gas processing work.

That doesn’t make them immune to freezing water, though. Quite the opposite. The passages are narrow, the walls thin, and the structure rigid and brazed. If water freezes inside, the expansion has nowhere to go, and the damage can be severe. Because the block is sealed and compact, repair is rarely practical, so a frozen unit often means a replaced unit.

Moisture is a bigger concern in low temperature gas service. Water vapor in the stream can freeze on cold surfaces and block passages, a problem called icing or freeze out, which is why gas is usually dried before it enters such units. Check that drying is adequate for your temperatures.

Cleaner fluids and careful procedures matter more here. Drain thoroughly where water is involved, purge with dry air or nitrogen if the maker recommends it, and avoid sudden temperature swings. A plate fin heat exchanger can handle extreme cold well when it’s dry and clean, and badly when it’s wet and forgotten.

Shutdown and drain-down habits that actually work

Procedures only help if people follow them, so keep them simple and visible.

Before a planned shutdown in cold weather, decide whether to keep the loop running, protect it, or drain it. Each is valid, depending on how long the shutdown is and how cold it’ll get. For short stops, maintaining flow or heat is often easiest. For long ones, draining is safest.

Draining properly means more than opening one valve. Open drains at all low points and vents at high points, so air can replace the water. Check for pockets that don’t drain, such as U bends, dead legs and horizontal sections with no slope. Blowing through with compressed air, where the maker allows it, clears stubborn water. Leave drain and vent valves open afterwards, so any residual moisture can’t pressurise.

Label things. A tag on a closed unit that says it’s drained and when saves somebody from guessing. A simple checklist on the wall, with steps and initials, prevents the classic mistake of draining the main unit and forgetting the spare.

For units that stay in service, check insulation and heat tracing before winter starts. Test the tracing, replace damaged lagging, and make sure thermostats and alarms work. Boring jobs, but they’re the ones that prevent flooded plant rooms.

After a freeze, before you restart

Sometimes the cold wins anyway. A power cut, a failed heater, an unexpected plunge. If you suspect water froze in your cooling equipment, don’t just switch everything back on.

First, let it thaw gradually and naturally, or with gentle controlled warming. Avoid blasting a frozen unit with hot water or flame, because rapid heating creates thermal stress. While it thaws, keep isolation valves in a safe state and watch for leaks.

Then inspect. Look for visible damage, bulges, cracks, weeping joints, damaged insulation, split valves and strainers. Check the whole system, not only the exchanger. Small bore lines and instrument connections often fail first.

Test before returning to service. A pressure test of each circuit, following your site procedures and the maker’s limits, reveals leaks that were hidden by ice. For equipment where cross contamination between fluids would be a problem, check carefully for signs of leakage between circuits, such as unexpected changes in levels, water quality or composition.

Record what happened and what you found. That record helps you improve protection for next winter, and helps decide whether a questionable unit should stay in service. If damage is suspected and can’t be ruled out, replacement is usually cheaper than a failure later.

Conclusion

So, what happens to pump coolers when temperatures drop below freezing? If water freezes inside them, it expands, splits tubes or plates, and often shows the damage only after the thaw. A CPK heat exchanger, a plate fin heat exchanger or any other design can suffer if it’s left wet, still and cold. The risk is highest in dead legs, low points, outdoor pipework and idle standby units.

Know where your system is exposed. Keep flow going where you can. Use properly inhibited glycol at the right concentration, and remember it changes your heat transfer numbers. Drain thoroughly when shutting down, with open drains and vents. Keep insulation, tracing and alarms in working order. And after any suspected freeze, thaw gently and test before restarting. Do that and winter becomes a routine season, instead of the one that wrecks your equipment.

FAQs

Can a CPK heat exchanger be damaged by freezing?

Yes, if water freezes inside it. Expanding ice can split tubes, loosen joints or crack headers, and the damage may only show after thawing. Check the maker’s guidance on minimum temperatures and drain-down, and protect both circuits if both contain water.

Is a plate fin heat exchanger better in cold conditions?

Aluminium plate fin units stay tough at very low temperatures, which suits cryogenic and gas processing duties. But water freezing inside narrow passages can still cause severe damage, and repair is rarely practical, so keep it dry and protected.

How does glycol affect heat exchanger performance?

Glycol lowers the freezing point but has lower specific heat and higher viscosity than water, so it raises pressure drop and reduces heat transfer. Cooler sizing should account for it, and concentration should be tested instead of guessed.

What is the best way to protect a cooler during a winter shutdown?

Either keep flow or heat going so water never sits still in the cold, or drain the unit fully with open drains and vents, blowing out residual water where the maker allows it. Tag the unit so everyone knows its state.

Where does freeze damage usually happen first?

In dead legs, low points, outdoor and small bore pipework, instrument lines, valves, strainers and idle standby units, because stagnant water in those places freezes first.

What should I do after a suspected freeze?

Let the equipment thaw gradually, inspect for visible damage, pressure test each circuit before restarting, and check for signs of leakage between circuits. If damage can’t be ruled out, replacement is often the safer choice.