Introduction
Among the many water quality parameters that affect HVAC system performance, electrical conductivity and sulfate concentration are two of the most overlooked yet impactful. These values offer insight into the chemical makeup of the water and are direct indicators of potential scaling and corrosion. When not monitored and controlled, elevated conductivity or sulfates can compromise heat exchanger performance, corrode piping, and significantly increase operating costs. Understanding these parameters allows mechanical engineers and facility managers to take early action, preventing long-term system damage.
Understanding Electrical Conductivity in HVAC Water
Electrical conductivity (EC) measures the water’s ability to conduct an electrical current, which is directly proportional to the concentration of dissolved salts and ions. The more ions—such as sodium, calcium, chloride, or sulfate—the higher the conductivity.
Acceptable Range for HVAC Systems: 10–500 µS/cm
Why it matters: Elevated conductivity suggests a high level of ionic content, which increases the potential for galvanic corrosion, especially in systems with dissimilar metals. It also indicates the likelihood of scale formation, particularly in heat exchangers where temperature differences promote precipitation.
High conductivity also points to poor system flushing, leaking exchangers, or inappropriate make-up water. A sudden spike in conductivity is often the first warning sign of system contamination.
How to Monitor and Control Conductivity?
Continuous Monitoring: Use in-line conductivity sensors for real-time data.
Periodic Testing: Utilize portable EC meters or send water samples to a certified lab.
Control Measures: Implement blowdown protocols in open systems and use deionized or softened water to reduce ionic load in closed loops.
Sulfates and Their Role in Corrosion
Sulfates (SO₄²⁻) are a specific group of anions found in many water sources. While not harmful at low concentrations, they can significantly increase the risk of pitting corrosion, especially when combined with other aggressive ions like chlorides.
Recommended Limit for HVAC Water: <70 ppm
Corrosion Mechanism: Sulfates accelerate electrochemical reactions and weaken protective oxide layers on metals, especially steel and copper. This is particularly dangerous in stagnant areas or systems with inconsistent water flow.
Additional Risk: Sulfates may serve as a nutrient source for sulfate-reducing bacteria (SRB), which contribute to microbiologically influenced corrosion (MIC).
Monitoring Strategy for Sulfates
Sampling Frequency: At least quarterly in closed-loop systems; monthly in open systems or those using well or untreated water.
Testing Methods: Ion chromatography or photometric sulfate tests are most accurate.
When to Act: Levels exceeding 70 ppm require immediate mitigation to prevent long-term material degradation.
How Conductivity and Sulfates Work Together
Although different in nature, conductivity and sulfate levels are often interconnected. A high conductivity reading may indicate high sulfate presence, along with other corrosive ions. Controlling one typically requires a comprehensive view of overall water chemistry.
Key Impacts on HVAC Systems
Increased Scaling: From dissolved solids precipitating out due to temperature changes.
Pitting and Localized Corrosion: Especially on welds, joints, or thin-walled components.
Inhibitor Failure: Corrosion inhibitors are less effective in high ionic environments.
Treatment Solutions and Best Practices
Deionization or Reverse Osmosis: To lower total dissolved solids (TDS) and thus conductivity.
Chemical Treatment: Use of blended corrosion inhibitors and sulfate binders.
Filtration and Flushing: Regular system flushing can prevent sulfate build-up.
Water Source Control: Always use treated or conditioned water for make-up supply.
Routine Documentation and Response
Logging conductivity and sulfate levels over time can help establish trends and catch early signs of system imbalance. Combine these readings with other parameters like pH, hardness, and microbial content for a full-picture diagnostic.
Final Recommendations
Electrical conductivity and sulfate concentration are critical markers for corrosion control in HVAC systems. Mechanical engineers and maintenance teams must include them in every water quality assessment. Ignoring these parameters may lead to hidden corrosion, unexpected leaks, and a sharp decline in energy efficiency.
Collaborate with a trusted environmental testing laboratory that specializes in HVAC applications. The right lab can offer not just raw numbers, but expert guidance on interpreting results, selecting treatment options, and developing a preventive maintenance program tailored to your system.