The one thing everyone can count on is that winter weather is unpredictable. Heavy snow, ice storms, unexpected freezes in warm weather climates; each of these things can cause disruption to services or cause damage to water-based systems.
Vacuum furnace water systems are no different.
Water often circulates from an exterior cooler, through the pipes within your factory, into your vacuum furnace, and then back out to the cooler. These systems are much easier to keep flowing in low temperatures when they’re circulating than when the system is shut down for holiday closures or winter storm outages.
Still water simply freezes faster.
It’s important to know how prepared your water systems are as a part of your maintenance schedule prior to holiday shutdowns throughout the winter months.
Taking three key steps to diagnose the status of the water in your circulation systems will help you make sure you don’t return from your holiday to burst pipes or ice in your furnace water jacket: Estimate, Test, Prepare.
Estimate the Unpredictable
Weather uncertainty makes it difficult to know exactly how much protection your water system will need each year.
That’s why it makes sense to start with the worst-case scenarios and work from there.
Review the coldest winter days in your community’s weather history. How many of them have happened within the last 25 years? If you’re seeing an increase in more extreme winter weather as a trend, use those low-temperature days as your guide. You should prepare for an extreme weather threshold that is 5 degrees colder than recent extreme lows. Never underestimate mother nature’s ability to surprise you.
Many times, extreme cold temperatures can be accompanied by ice storms or other severe weather events that could lead to power outages. Ensuring that your systems are able to withstand those severe temperatures until power systems return will help you avoid potential equipment damage and expensive production delays.
Test Your System Chemistry
To combat cold weather, maintenance teams often add anti-freeze chemicals (frequently some form of glycol*) to their closed-loop water systems. Some of those systems may have been running with glycol circulating since the previous winter.
Closed-loop water systems are sealed and should have the same volume of fluid all year long. Even in a closed system, however, the glycol partially loses its ability to protect the system at a given temperature over time. Balance testing should happen at a minimum every two years.
Open-loop water systems pump water up into a cooling tower that feeds back into the system using gravity. When these systems are turned off, all the circulating water remains inside the building. As a result, open loop water systems usually require rust and mold inhibitors, but don’t typically need glycol-based antifreeze.
Refractometers can be used to check the glycol levels within your systems. Knowing the concentration of glycol within your system can ensure that you can add enough volume of that same chemical to ensure your systems are protected.
Be careful not to add too much glycol to your system – overtreating your water may have a adverse effect on the quenching capabilities of your furnace.
*What’s the difference between Ethylene Glycol and Propylene Glycol?
ETHYLENE GLYCOL (EG)
Is the green liquid we used to have in our car radiators. It’s the least expensive, has the least impact on heat transfer, and effects pump performance the least. It is toxic so it’s falling out of general usage. It is very corrosive so a suitable inhibitor package must be used to protect your piping and equipment. Never use ethylene glycol for corrosion protection. Its only use is to prevent slushing and freezing of your coolant.
PROPYLENE GLYCOL (PG)
It’s the pink liquid we currently have in our car radiators. It’s about 20 percent higher in cost than EG, has some impact on heat transfer due to its high viscosity, can affect pump performance, and is needed in slightly higher concentrations than EG for equal freezing protection. Its appeal derives from its low toxicity. It is corrosive so a suitable inhibitor package must be used to protect your piping and equipment. Never use propylene glycol for corrosion protection. Its only use is to prevent slushing and freezing of your coolant.
DO NOT USE AUTOMOTIVE ANTI-FREEZE. Coolants for automobiles have inhibitors based on aluminum. Their inhibitor package is wrong for most industrial water-based cooling systems.
Source: Frequently Asked Questions – Dry Coolers
Prepare for Peak Performance
With severe low temperatures estimated and water system chemistry tested, the next step is to bring your glycol levels to the proper ratios to protect your systems.
There are two categories that users need to know about anti-freeze levels: Freeze and Burst.
Freeze protection requires the highest concentration of glycol, preventing the formation of ice crystals at the lowest temperatures. This is essential for systems where even a small amount of icy slush within a system could cause a blockage or breakdown.
Burst protection is a lower concentration of glycol, sufficient to keep pipes from bursting or other mechanical damage that could be caused by water freezing.
If your water systems typically remain on throughout the winter, freeze protection should be the threshold you are aiming to attain. Particularly if you are counting on them to deliver cold water to your vacuum furnace throughout winter operations. Other systems that remain dormant throughout the winter may only require burst protection levels of glycol.
Remember that when you are calculating the amount of glycol that you will need to order for your system, you should consider the volumes of not just the water within your furnace and within the cooling tower, but also the pipes that extend from the tower to the furnace.
With plenty of room in your reservoir tank, add about 80 percent of the glycol, based on your calculations, to a circulating system. Then using your refractometer to confirm your calculations are correct, slowly add the remaining amount to your reservoir until tests show that the proper percentage of glycol is circulating by volume.
| Freeze Protection | Burst Protection | |
Temperature  °F | DOWFROST | DOWFROST |
| 20 | 17% | 11% |
| 10 | 26% | 18% |
| 0 | 34% | 23% |
| -10 | 41% | 28% |
| -20 | 45% | 30% |
| -30 | 49% | 33% |
| -40 | 51% | 35% |
| -50 | 53% | 35% |
| -60 | 55% | 35% |
This table shows the protection from freeze damage provided by various concentrations of DOWFROST propylene glycol inhibited fluids. Source: Frequently Asked Questions – Dry Coolers
To determine the concentration required, select the lowest expected ambient temperature and decide whether the cooling system requires freeze protection to keep it pumpable, or burst protection to simply prevent damage from fluid expansion.
For more information about preparing your vacuum furnace systems for winter shutdown, check out this article in the Ipsen Knowledge Center: Essential Preparations for Winter Shutdown.