FILTRATION & DIRT REMOVAL FOR CLOSED CIRCUIT HEATING & CHILLED WATER SYSTEMS

THE PROBLEM

Dirt, debris, swarf, welding splatter and mill-scale are all incorporated into closed circuit water systems during construction. The complexity of pipework design in modern buildings means that it is often impossible to remove all this contamination by pre-commission cleaning and flushing.

Suspended solids and sludge continue to accumulate in systems during their working life due to corrosion, hard water, system modification etc. Corrosion of mild steel typically produces sediment volumes of 10 to 100 times the volume of the original metal removed.

Heating systems typically make up at 1.5 to 2.5% of the system volume per week. For a 10,000 litre volume system in a hard water area this will lead to more than 3 kg of solids per year accumulating in the system.

Closed circuit systems rarely fail due to corrosion and leakage most failures are due to accumulation of sediment causing blockages, poor heat distribution or dissipation, boiler failure and valve failure.

TYPICAL PROBLEMS CAUSED BY DIRT AND DEBRIS

New Buildings Difficulty in establishing and maintaining system balance Valves jamming and blocking Noise Pump seal failure		Existing Buildings Poor heat distribution Blockages & lack of flow Pump seal failure Control valve failure Noise Boiler failure

THE SOLUTION Filtration using cyclone separatorsto remove suspended solids and debris from the system down to less than 20 micron ensures systems achieve and maintain design performance with the minimum of maintenance throughout their working life. Clean conditions internally enable chemical corrosion inhibitors and biocides to work effectively, maintaining system integrity ensuring reliable and trouble free operation of controls. Although frequently described as filters, cyclones are technically dirt separators using centrifugal action to remove suspended solids or dirt.

FEATURES AND BENEFITS

• High flow Continuous Filtration with no change in pressure loss - can be used in mainstream flow. No variation in pressure loss or flow rate as dirt is collected.

• No Backwash Required - filtered dirt is purged to drain with minimum water loss whilst service flow is maintained.

• Zero Water Loss Option - when fitted with closed recovery dirt collector the unit will operate with no water loss from system, ideally suited to glycol and brine systems. Allows visual inspection of dirt removed.

• Compact Easily Installed - can normally be fitted as sidestream filter using existing connections, minimal installation cost. High filtration with minimal plant room area required.

• Easily Integrated into System Design - fixed flow and pressure loss characteristics and continuous flow capability allow units to be easily integrated into systems at the design stage.

• Filtration to less than 20 micron - progressive removal of particulates down to 5 micron on recirculating systems.

• Prevents Valve and Control Problems - installed for at least 3 months following commissioning of new installations, cyclone systems will remove any remaining silt and debris following pre-commissioned cleaning preventing problems with control equipment and valves. Especially applicable to sensitive fan coil systems which are difficult to flush and which incorporate complex and sensitive control valves.

INSTALLATION OPTIONS

1. Mainstream or Full Flow Filtration

Cyclone filter installed in flow line to provide filtration of full flow. Provides maximum filtration and system protection. Differential pressure across cyclone remains constant irrespective of dirt loading. No risk of flow reduction or stoppage due to blockage of cyclone.

Can be used on main flow or flow to sub circuit.

Recommended for:-

• Systems subject to fouling or dirt ingress i.e. engine test beds.
• Sensitive or critical subcircuits subject to risk of fouling from main circuit i.e. District heating or chilled water, computer cooling etc.
• Heating and chilled water systems
• Fan coil systems with multiport modulating control valves.
• Versatemp or similar systems incorporating heat pump units.
• Systems with plate heat exchangers
• Old systems being renovated or upgraded and fitted with replacement boilers etc.
• Glycol and Brine systems.

Equipment required: -

• Cyclone filter sized to suit system flow
• Mounting bracket or stand
• Auto purge valve and timer or dirt collector system
• Inlet and outlet pressure gauges on filter using Differential pressure to confirm flow within filter design parameters

For:-

• Maximum filtration and system protection
• Simple installation, no additional pumps required

Against:-

• Cost for equipment and installation
• System pump must have capacity required to overcome differential pressure of 0.4 to 0.8 bar of filter

Recommended for new installations, problem systems or system refurbishments. Not considered practical as a retrofit in view of disruption required to install.

2. Sidestream Filtration (click here to see sizing selection for sidestream flow)

2.1 Sidestream filtration using system pumps

Cyclone connected in sidestream bypass across main circulation pump flow and return. Typically 5% to 10% sidestream flow.

Recommended for new installations, refurbishments where additional pump capacity required can be incorporated or is known to exist and sidestream flow will not affect system balance or performance. In addition there must be sufficient differential pressure for cyclone to operate correctly (i.e. system differential pressure is greater than DP of cyclone at design flow).


(click diagram to enlarge)

2.2 Sidestream Filtration Using standalone Packaged Units

Cyclone filtration units are packaged skid mounted units incorporating a cyclone filter complete with sidestream pump and automatic or manual purge system.

Operation

A sidestream flow of water (Typically 5% to 10% of system flow), drawn from the system pipework by the sidestream circulation pump incorporated in the unit is pumped through the cyclone filter where suspended solids and silt are separated by centrifugal force. The cleaned filtered water is returned to the system. The suspended solids or dirt collected by the filter is periodically purged to drain manually or automatically with minimal water loss.

Recommended for:-

• Retro-fit on existing installations to ensure no impact on system flow or balance
• New installations, refurbishments to ensure no impact on system flow or balance.
• Temporary or mobile installation for system clean-up

Equipment required

• Sidestream Filtration unit Cyclone filter sized to suit sidestream flow
• Option of dirt collector system where applicable

For:-

• Simple installation, units incorporate sidestream pump and controls etc. all on stainless steel skid

Against:-

• Can affect system balance and operation if the system pumps do not have the additional capacity required to allow for sidestream bypass flow. This is why we supply the unit with an integrated pump.

Applications

• All heating and chilled water systems especially those incorporating fan coil units and multi port valves.
• Glycol Systems – used in conjunction with zero liquid loss dirt collector
• Brine Systems – used in conjunction with zero liquid loss dirt collector
• Thermal Fluid systems – used in conjunction with zero liquid loss dirt collector
• High pressure Hot Water Systems – used in conjunction with zero liquid loss dirt collector
• Versatemp Systems
  

3. Closed Recovery Dirt Collection units (CRS)

Used in conjunction with cyclone filtration systems, these units collect the filtered dirt from the filter purge discharge allowing purge fluid to be returned to the system thereby eliminating any water or fluid loss from the system. The filtered dirt is collected in re-usable fabric bags for disposal.

Closed recovery systems are recommended for systems where fluid loss from filter purge needs to be avoided such as :-

• Brine systems,
• Glycol systems,
• Thermal fluid systems,
• Chemically treated systems
• Medium and High Temperature hot water systems

Two sizes of closed recovery units are available:- CRS 8/16 with a collection bag 8” diameter and 16” deep and CRS 8/30 with a collection bag 8” diameter and 30” deep.

Collection bags must be manually removed for disposal normally at monthly or quarterly intervals. More frequent attention is however required where heavily fouled systems are being cleaned up.

Bag full alarm option provides volt free contact for remote monitoring (BMS).

Benefits of Closed recovery system units

• Enables inspection and assessment of the removed dirt providing direct indicator of progress of any cleaning or monitoring of water treatment and system integrity.
  
• Continuous high performance filtration with no risk to integrity of system through water loss, equipment fault etc.
  
• CRS unit can be used for addition of chemical treatment.

FILTER SIZING SELECTION

Cyclone separators only perform effectively when the flow rate is within the design parameters for the unit. If the flow rate drops below the minimum design flow, filtration performance will be affected.

Mainstream or Full Flow – Size unit to water flow rate not pipe size. See selection chart in literature or catalogue.

Sidestream flow - Where system volumes are known, sidestream filtration units should be selected on the basis of filtering the full system volume every 2 – 4 hours.

For new clean systems filtering the volume every 4-hour (i.e. sidestream flow 25% of system volume per hour) would be sufficient

For older systems, which are known to be fouled, filtering the volume every 2 hours (i.e. sidestream flow 50% of system volume per hour) is recommended.

Where system volume is not known, sidestream flow can be based on a percentage of system flow:

• For new clean systems use 2.5 to 5% of system flow
• For older systems known to be fouled use 5 to 10% of system flow.

Where existing system connections are used, this will often dictate the size of sidestream filter selected, as this will dictate the flow rate. Installing a 1” cyclone filter on ¾” or ½” connections will give poor or negligible filtration, as the flow velocity through the cyclone will not be sufficient to effectively separate the suspended solids.

CONNECTION POINTS

Location of connection points on the system can be critical to the performance of any sidestream filtration.

Remember, the sidestream filter can only remove dirt that reaches the filter. If the take-off point for water flow to the filter is from the top of a pipe or a position where water is relatively clean, the performance of the filter will be compromised.

The take off point for flow to the sidestream filter must be from the bottom of pipework or outside of a bend, the take off should never be taken from the top or side of the pipework, inside of a bend or dead leg of pipework not subject to flow.

Where units are being fitted, connection and return points should be from similar areas of pressure i.e. both on suction side or discharge side of pump. If the unit is connected across the main pump flow and return this could affect either the balance of the system or performance of the cyclone.

(click diagram to enlarge)