The essentials of water quality in heating and cooling systems
Clean water management for industrial applications that utilise brazed plate heat exchangers (BPHEs) is crucially important.
Water quality in a heating (or cooling) system, such as district heating, must be free from the formation of deposits and corrosion to optimise plant and operating efficiency. When water quality is impacted, there is a risk of fouling and scaling, also corrosion, with a direct effect on the efficiency and productivity of an incorporated brazed plate heat exchanger.
Cleaned tap water circuit
A brazed plate heat exchanger comprises of corrugated plates that combine to create channels through which a hot medium and a cold medium, typically water, can be distributed. They are used for various functions in a heating or cooling system, acting as condensers, evaporators, oil or gas coolers.
Fouling and scaling can occur from fluid flowing through a BPHE containing traces of dirt, oil, grease, or organic deposits, which can leave a coating on the heat transfer surface. A coating of limescale as thin as 1mm can decrease heat transfer efficiency by up to 8%. However, SWEP BPHEs have a form of self-cleaning through a high level of turbulence induced by their unique plate pattern, with the fluid performing a scouring action to keep the heat transfer surface clean.
Corrosive damage, from a chemical reaction between a metal and its environment, reduces the functionality of a material or the technical system of which the material is a part. Outcomes include blocked thermostat valves, jammed circulation pumps and clogged BPHEs, decreasing their performance and lowering system efficiency.
Different metals can be susceptible to corrosion damage in different ways. Generally, stainless steel, used in district energy systems, has good resistance but can be sensitive to high chloride content in water. Most SWEP heat exchangers use copper as the brazing material, which has good resistance to corrosion in most district energy water environments. However, if water quality is poor, copper can start to corrode or leach into the water.
Constant monitoring for possible corrosion is essential so that damage and product failure can be avoided. Electronic corrosion coupons are utilised to detect corrosion in water systems over set periods of time. This is done by permanently comparing mass measuring results to previous ones, thereby establishing a corrosion rate. Usually, an annual average is used to measure corrosion rate in a system. An average yearly corrosion rate below 7pm/year represents little risk of corrosion damage, 7pm/year to 21pm/year indicates corrosion damage is probable and >21pm/year shows a sizeable risk of system failure.
Such real-time monitoring can be used throughout a water-based system’s life – from pre-commissioning cleaning onwards – ensuring systems are handed over to end-users in the best possible condition, then subsequently to provide ongoing reassurance and an early warning system.
To learn more, visit our district energy applications page and download the brochure ‘Water management for brazed plate heat exchangers’