Scale build-up weighs on HVAC efficiency

Preventative maintenance helps control energy costs, prevent premature failure
Thursday, March 8, 2018
By Tim Fregeau

Scale build-up can be present throughout an HVAC system, including in condensers, chillers, cooling towers, boilers, plate exchangers, piping and more. It can occur in any piece of equipment that uses water as a heating or cooling medium and, without proper care, can gradually corrode equipment, putting it out of service.

HVAC systems also account for a significant portion of annual energy expenses, making preventative maintenance even more critical. Chemical descaling can help improve the efficiency of these systems and thereby lower energy costs.

Operational impact

Imagine trying to cool down while wearing a winter coat when it’s 90 degrees Fahrenheit (around 30 degrees Celsius). That’s what HVAC equipment experiences with scale. Scale acts as an insulation barrier on any heat transfer surface, reducing that equipment’s ability to exchange temperature. This results in the equipment running harder to maintain the required output, triggering increased energy consumption and costs, as well as potential long-term damage to the equipment.

Once scale forms on boiler surfaces, both fuel and efficiency losses quickly ramp up. According to the U.S. Department of Energy, even “normal” scale of 1/32-inch thickness, produced by low-pressure applications, leads to a two-per-cent fuel loss.

Two per cent may not sound like much without more context. The U.S. Environmental Protection Agency offers a helpful example: A firetube boiler using 450,000 million British thermal units (MMBtu) of fuel (at USD $8 per MMBtu) over 8,000 hours per year, with 1/32 inch of normal scale, spikes yearly operating costs by more than USD $70,000.

Even worse, in high-pressure applications where iron and silica deposits exist, fuel losses can be as high as seven per cent. Operational costs jump up exponentially as scale thickness increases, so ignoring or delaying cleanings will only compound equipment’s energy consumption.

Considering how much of a facility’s overall energy consumption is expended by its heating and cooling system, it’s apparent scale has an immense impact on the bottom line.

Scale is also detrimental to the equipment’s overall integrity. When equipment is forced to work harder to keep up, it’s going to cause wear and tear that could result in the need for repairs or even replacement. If scale is not consistently removed from equipment, it can also cause under-deposit corrosion, which decreases the equipment’s expected longevity.

Scale can develop in a matter of weeks, so imagine what can happen to equipment such as a boiler that has been offline during the summer, or even just neglected, for months.

Early detection

One of the best ways to identify scale, and other potential issues, is to keep a daily operational log for every piece of heating and cooling equipment. This helps to track the equipment’s operating parameters and conditions, and becomes an invaluable source of information about its performance.

Operational logs make it possible to identify operational abnormalities early on and avoid downstream issues or, worse, unplanned shutdowns. While the measuring factor may differ between various pieces of equipment, most systems will have some form of an efficiency indicator that can be monitored. Not only can it raise a red flag for inefficiencies caused by scale, but it can also indicate other issues that may require repair or replacement.

Depending on the source of water and water treatment process, a facility may be susceptible to increased amounts of scale deposits. For example, if a facility relies on raw untreated water for cooling, expect frequent scaling issues resulting from the large traces of minerals.

Hard water, which has a higher mineral content, is the main source of scale buildup. The higher the mineral content of a water source, as measured in parts per million, or PPM, the faster scaling issues are likely to occur.

Water temperature is another major factor in scale buildup. The higher the temperature of water, the easier it is for the mineral deposit to fall out of suspension. Scale occurs when minerals within a water source fall out of suspension and stick to surfaces including walls, tubes and any other parts of heating and cooling equipment.

Long-term prevention

The best way to prevent scale is to implement a preventative maintenance program that includes periodic equipment descaling in its schedule.

Chemical descaling is a clean-in-place solution that does not require equipment to be disassembled. Industrial descalers work quickly to dissolve calcium, lime, rust, and other types of deposits from passages in water-cooled or heated equipment. While the most common type of scale is calcium carbonite, other particulate may also be a component of the overall deposit composition.

A variety of industrial descalers are available for different applications. These descalers comprise base ingredients that penetrate the deposit and dissolve it into liquid suspension so it can be removed from the piece of equipment being cleaned. The best solution depends on the specific equipment. Often, a good first step is to take a sample of the deposit and conduct a simple bench test to make sure the descaler completely dissolves the deposit.

Don’t forget to measure the impact of this cleaning on cost savings. Take the time to compare energy consumption before and after the descaling to be able to share successes in improving HVAC efficiency.

Investing in preventive maintenance aimed at scale build-up in heating and cooling systems will help keep operational costs down and equipment running smoothly.

Tim Fregeau is director of sales in the liquid solutions division at Goodway Technologies. In this role, he is responsible for the direction and go-to-market strategy for Goodway’s chemical product, which includes solutions for industrial descaling, coil cleaning and cooling tower cleaning.

2 thoughts on “Scale build-up weighs on HVAC efficiency

  1. Thanks for this insightful article! I agree the best way to prevent this is a regular preventative maintenance program.

    Maintenance and cleaning are really important and a lot of times it can save a lot of money for the companies who have these boilers

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