Where is Scale Likely Hiding in Your Facility’s HVAC Equipment?

If your facility’s machinery uses water as a heating or cooling medium, you likely know any water formed deposits will negatively impact energy efficiency and equipment life expectancy. When higher amounts of water and evaporation deposits settle, scale builds up. Keep in mind that a good portion of scale is hiding out and building up in difficult to reach places. Focusing in on all areas including these hidden spots will help keep operational costs down and equipment running smoothly.

So where are these scale hiding spots? Let’s break it down by equipment type.

Where to Find Scale?

  • Heat Exchangers/Condensers:  Heat exchangers in your facility may be shell & tube, plate & frame or they may be called coolers or condensers.  Regardless of the tag word to identify this piece of equipment, the primary function is to adjust temperature between two mediums.  During this function, elevated temperatures on the water side allow mineral deposits to fall out of suspension and plate onto the heat transfer surface.  This creates an insulating barrier minimizing the exchanger’s ability to function properly which correlates to loss of efficiency and higher operational costs.
  • Cooling Tower Fill:  Cooling towers utilize a plastic fill material which provides an expanded surface area designed to slow the descent of water.  On top of the cooling tower is a fan that pulls air through the fill material, thus cooling the water. The warm water generated from the process equipment descends within the fill material and the mineral deposit falls out of suspension and plates not just on the fill material, but also the other surfaces within the tower structure.  As scale builds up on the fill, the air flow created by the fan is minimized and does not properly cool the water. This action results in the fan drawing higher amperage and the process equipment not being sufficiently cooled.  The end result is loss of efficiency and higher operating costs.
  • Evaporative Condensers & Fluid Coolers:  These self-contained units encompass a tube bundle.  Inside the tubing may be a refrigerant, ammonia or water but it is the outer tubing that becomes scaled. As water cascades over the outer tube surfaces, the water is trying to re-condense the refrigerant, ammonia or water within the tubes.  The heat transfer taking place elevates the water temperature allowing the mineral deposit to fall out of suspension and plate onto the tube surface creating an insulating barrier.  This barrier minimizes the units ability to function properly, which correlates to loss of efficiency and higher operational costs.
  • Boilers:  Boilers function to elevate water temperature or create steam.  The heat exchange process facilitates mineral separation from the water, creating scale build-up.  These scale accumulations plate onto the tube surface and form an insulating barrier. As a result, more gas is needed to elevate the temperature or meet the required steam load. The end result is higher operating costs due to increased gas usage.
  • Pumps & Piping: These two areas of your HVAC system are the true hiding areas for scale because they cannot be visually inspected.  When pumps or pipes become scaled flow rates are minimized and the motor draws additional amperage. Scaling can also result in under-deposit corrosion.  

Knowing where to look is only half the battle. To fully remove this highly resilient thermal conductor, you need to carefully consider your tools and techniques.

How to Remove Scale?

  • Brushing: One method of mechanical scale removal is called brushing. These abrasive brushes are pulled or pushed through the tubing and scrape away hard build-up, scale, rust and debris, within tube surfaces.  Though brushes are an effective tool for removing deposits in tubing, they are not optimal for every cleaning situation.
  • Descaling Chemicals:  Chemical descaling solutions are designed to remove water formed deposits and dissolve the scale into a liquid suspension, allowing it to be flushed out of equipment. Chemical descaling is a clean-in-place solution requiring no disassembly of the equipment.  Industrial descalers work quickly to dissolve calcium, lime, rust, and other types of deposits from passages in water-cooled or heated equipment.  However, when scale deposits are primarily comprised of phosphates or silica’s, mechanical methods may be a better solution.

So what’s the best solution for you?  It depends on the specific equipment and deposit composition you are looking to remove.

Facility managers can effectively address scaling in their equipment by incorporating operational performance logbooks, visual inspections and thoroughly assessing system components most susceptible to build-up. These areas can then be the focus of their maintenance efforts. But careful consideration of a scale removal method is also crucial for effectively removing scale in its entirety. While removing some scale can improve efficiencies, the only way to optimize efficiency is to thoroughly descale the equipment and put preventive measures in place.

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