Sidestream Filtration

Side Stream Filtration: Enhancing HVAC Performance

Optimising HVAC filtration is essential to safeguard cooling tower systems, protect boilers, and maintain overall water circuit health. Side stream filtration units target metal oxides, magnetite, and other suspended solids that cause corrosion, reduce efficiency, and increase operational costs. Below, we compare cyclone filters, bag filters, and cartridge filters to help you choose the ideal method for your specific needs.

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BSRIA: Why Side Stream Filters Are Best Practice

According to BSRIA guidelines (BG 50/2021), incorporating sidestream filters into closed-loop water systems larger than 2,500 litres helps maintain cleaner pipework and extend equipment life. Treating just a fraction of the circulating water (5–15%) continuously removes fouling particles, aligns your system with industry standards, and prevents costly downtime.

Understanding Metal Oxides, Magnetite, and Corrosion

Metal Oxides: Form when metals (e.g., iron or steel) react with oxygen in water. Common forms include rust and magnetite.

Magnetite (Fe₃O₄): A dense, magnetic iron oxide frequently found in closed chilled & heating loops which easily settles out in low velocity pipe sections.

Why Removal Matters

When metal oxides and magnetite build up, they reduce heat transfer, block flow, and accelerate corrosion mechanisms, including:

Microbiologically Influenced Corrosion (MIC)
- Cause: Bacteria (e.g., sulfate-reducing bacteria) create corrosive biofilms on metal surfaces.
- Role of Solids: Particles embed in biofilms, intensifying localised corrosion attacks.
Galvanic Corrosion
- Cause: Two dissimilar metals in the same electrolyte (water) form anodic and cathodic sites.
- Role of Solids: Suspended solids settle and create uneven metal contact points, hastening corrosion.
Differential Aeration Cells
- Cause: Oxygen level variations on metal surfaces create anodic (low O₂) and cathodic (high O₂) zones.
- Role of Solids: Particles coat certain areas, depleting local oxygen and increasing corrosive activity.

By using side stream filtration, you maintain cleaner circuits, minimise corrosion risks, and improve overall system reliability.

Filtration Technologies: Cyclone, Bag, and Cartridge Filters

Cyclone Filters

How They Work -

Cyclone filters use centrifugal forces to separate denser particles from the water flow. Heavier contaminants, like magnetite or larger debris, spin to the chamber walls and collect at the bottom for easy purge.

Advantages

High Flow Capacity: Excellent for large volumes with minimal pressure loss.
Low Maintenance: No disposable media.
Ideal for Heavier Solids: Particularly effective if contaminants have a higher specific gravity than water.

Drawbacks

Less Effective for Fine Particles (<5 microns): Multiple passes may be needed for thorough removal.
Not Suitable for All Densities: Particles close to the density of water may not separate effectively in one pass.

Bag Filters

How They Work -

Water passes through a permeable bag that traps particles at or above the chosen micron rating.

Advantages

Higher Flow Rates vs. Cartridge Filters: Can handle moderately high volumes and hold more dirt before replacement.
Magnetic Rods: Bag filter systems can include a high-gauss magnetic rod, greatly enhancing magnetite removal.
Micron Ratings: Choose from a range of pore sizes to tailor filtration levels. 1 to 100 micron.
Filter housings generally only need one cost effective bag, however multiple bag housings are available for higher flow rates.

Drawbacks

Consumable Media: Bags require periodic replacement once they’re loaded with debris.
Lower Flowrate: Compared to Cyclone Filters

Cartridge Filters

How They Work -

Water passes through multiple cylindrical cartridges with a defined pore size. These can remove contaminants at extremely high efficiencies—up to 99% in a single pass.

Advantages

High Removal Efficiency: Excellent for polishing water to a very fine degree (sub-5 microns).
Precision Filtration: Numerous filtration micron ratings available.

Drawbacks

Lower Flow Capacity & Less Dirt-Holding: Cartridges typically need more frequent replacements if contaminants are abundant.
Cartridges are more expensive than bags
Multiple cartridges required at lengths up to 40" to meet flow demand

Key Applications: Cooling Tower Filtration and Boiler Protection

Cooling Tower Filtration

Open-loop systems exposed to ambient air often pull in debris, organic matter, and dust. Sidestream filters help manage these contaminants while minimising biocide use and extending the life of heat exchangers.

Boiler Protection

Closed-loop boiler systems are prone to magnetite formation due to elevated temperatures. A well-chosen side stream filtration system prevents sludge accumulation and maintains steady heat transfer.

Optimise Your HVAC Filtration with Side Stream Filtration

By adopting side stream filtration, you’ll adhere to BSRIA best practices, ensure boiler protection, and keep cooling tower filtration at peak performance. From cyclone filters to bag and magnetic filters to cartridge filters, we provide tailored solutions to keep your systems free from metal oxides, magnetite, and other harmful suspended solids.

Ready to enhance efficiency and reduce maintenance costs?Contact us today to explore the ideal side stream filtration approach for your operations. Ensure cleaner water circuits, lower energy bills, and a longer service life for your critical HVAC equipment.

Frequently Asked Questions (FAQs)

Q: Do I still need chemicals if I install sidestream filters? A: Yes. Side stream filtration tackles physical contaminants, but chemical treatments help control scale, corrosion, and microbial growth.

Q: Which filtration method is best for magnetite removal? A: All three—cyclone filters, bag filters, and cartridge filters—can remove magnetite. However, installing filtration incorporating magnetic rods are particularly efficient at trapping ferrous particles in a single pass.

Q: How much flow is diverted for sidestream filtration? A: Typically, 5–15% of the total system flow goes through the sidestream filters, leaving the main loop largely unaffected.

Q: Can filter systems handle large industrial applications? A: Absolutely. Our filter solutions scale from small commercial buildings to large industrial facilities, depending on flow requirements and contaminant loads.

Q: How does BSRIA define Water Treatment? A: Any processes that improve the quality of water to make it appropriate for its intended use and reduce the risk of damage to the system. Which includes Solids removal and filtration and chemical water treatment.

Can a Filtration System Help Reduce Microbiological Growth and Prevent Issues Like MIC in My Closed-Loop System? Yes, installing a sidestream filtration system can effectively reduce microbiological growth and prevent microbiologically influenced corrosion (MIC) in closed-loop heating and chilled water systems. By continuously removing suspended solids, organic debris, and corrosion byproducts, a sidestream filter helps control bacterial contamination and minimises the risk of biofilm formation—a key contributor to MIC and system fouling. A high-performance sidestream filter improves water quality, enhances heat exchanger efficiency, and extends HVAC system lifespan by preventing sludge buildup and maintaining optimal closed-loop water treatment conditions. Regular filtration for closed-loop HVAC systems reduces reliance on chemical dosing, lowers maintenance costs, and supports energy-efficient system operation. By integrating sidestream filtration as part of a comprehensive closed-loop water treatment plan, facilities managers can prevent costly corrosion-related failures, maintain system performance, and ensure long-term protection of their heating and cooling water loops.