Closed System Filters – Equipment Selection Guide
This equipment selection guide reviews the use of closed system filters in closed heating and cooling water systems. The guide looks at the different types of filtration system available, why you should be using one, how they work, understanding temperature and pressure considerations, and the benefits this type of closed loop filtration can deliver.
Why use closed system filters?
When it comes to the treatment of engineered water systems, closed recirculating heating and cooling systems are often ignored, or at least not commissioned or managed to ensure optimum performance is achieved.
While such closed systems should still be treated chemically in an attempt to control both bacteria and corrosion, it’s also important to incorporate some form of in-line or side-stream filtration to help remove unwanted sludge, fine debris and suspended solids from the system.
How can filtration of a closed system help?
Even though as the name suggests, closed systems are in theory sealed or closed to the atmosphere, that doesn’t mean that solid matter can’t build up through the effects of corrosion, alterations, leaks, poor commissioning or inadequate maintenance.
One of the main signals that solids have become a problem in a system is the presence of cloudy or discoloured water.
If you don’t do anything to address these problems, then a build-up of solids in the system could cause a number of potentially damaging (and costly) conditions including:
If you introduce an effective closed system filter system, you can help avoid many, if not all of these issues.
The primary aim of this type of filter is to remove any contaminants including suspended solids, from the closed system and so prevent the problems they cause.
The most commonly recommended closed system filter solution is a side-stream filter.
This type of system has the benefit that the flow of water through the main stream will remain unaffected if the filter itself becomes clogged or develops a flow problem.
Selecting a closed system filter
The type of filtration you select for a closed heating or cooling system will typically be determined by the type and size of the solids contaminating the water.
Some of the issues to be considered when selecting a closed system filter system include:
- Capital cost of the closed system filter installation
- The size of the particles to be removed
- Operating temperature and pressure of the system – heating or cooling
- Impact of solid build-up on the filter
- Operational costs
- Whether the system is manual or automatic
- Reliability
- Ease of operation
What are the different types of closed system filtration?
Here we look at the different types of closed system filtration:
Bag and cartridge filters for closed systems
Bag and cartridge filters are one of the most common ways of removing suspended solids from a closed system and they are the ideal choice for smaller heating and chilled water systems often found in commercial office buildings.
They tend to be manual systems and typically incorporate a pressure gauge to monitor the pressure differential between the inlet and outlet. As the pressure begins to rise it will alert users that the filter bag or cartridge needs to be changed or flushed.
This type of filter is available in a range of filtration sizes typically between 0.35 and 0.5 microns.
When you first start using bag and cartridge filters, you may find that you have to use a series of progressively finer filters as you begin to clean-up the system… for example, you might start with a larger 50 micron filter to remove the largest particles from the system.
As the water quality improves this larger filter can be replaced with a smaller gauge filter and so on, until you reach your desired filter size and the water quality target is achieved.
Although they are simple and easy to use, bag and cartridge filters aren’t always the most efficient option.
The filtration system depends on manual operation to be effective.
When the filter needs to be changed, the closed system may need to be shut down, drained and flushed out.
It can also be expensive to maintain this type of system. You should also think about chemical treatment costs and water lost during this changeover when looking at whether this type of closed system filter is suitable for your operation.
High performance closed system filters
High performance filters are designed to remove suspended solids as small as 5 microns.
They use a special high-surface media which allows particles to enter the filter bed but can still be easily backwashed.
This style of closed system filter is typically self-cleaning, and the backwashing process is automatic.
A high performance filter is efficient when taking particles out of closed systems operating at lower water temperatures, and with a maximum pressure of 100 psig.
High performance filters can often run for longer before they need back-washing, which saves on water consumption.
Most can also be set to backwash automatically, giving operators the control to select the pressure.
High performance filters also use fresh makeup water in the backwashing process.
If your system operates at higher temperatures or higher pressures, then you can also install a hot water filter.
These can operate at higher temperatures and pressures (typically to 250 psig).
A hot water filter of this type will have usually incorporate a three way motorised valve to allow flow rate monitoring and ports for taking water samples.
Super performance filters
As the name suggests a super performance filter can remove very fine solids from a closed system, as small as 0.5 microns.
This type of filter uses sand and other filters along the surface and is designed to operate at higher flow rates.
They are designed for closed systems operating at higher water temperatures and pressures up to 100 psig.
If you want to use a super performance filter in a closed system with particles larger than 5 microns, this will usually lead to a loss of water from the system and more frequent back-washes.
These filter systems also use fresh water during back-washing which helps to keep water lost from the system to a minimum.
Sand filtration for closed loops
One of the main benefits of sand filters is that they come in a wide range of sizes and designs.
The closed system water being treated passes through the sand filter and the suspended solids become trapped, with clean water emerging from the bottom.
If a sand filter is properly installed and managed, it can be used to remove fine particles as small as 5 microns.
Sand filters do require to be back-washed frequently to get rid of accumulated solids and this process is typically automated by either a timer or activated by using inlet-outlet pressure differentials.
When using inlet-outlet pressure differentials it’s usually a good idea to incorporate a back-up timer which will start the back-washing after a set period.
This stops hard or matted deposits from accumulating.
Additionally, if you backwash sand filters with makeup water instead of water from the closed system itself, this should keep your water and treatment chemical costs down too.
The case for closed system filters is clear
Using some form of filtration in a closed heating or cooling system is essential to ensure optimum performance is achieved.
The installation of this type of equipment can bring with it a number of benefits including:
Specialist engineering and industrial water management solutions
Water Treatment Services offer a comprehensive range of innovative engineering and water management solutions including the design and installation of closed system filter systems, and the management of closed heating and cooling installations to optimise performance.
Our experts can provide advice and support to help you identify the most appropriate strategies for the management of your heating and cooling water systems.
With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained water treatment engineers and equipment specialists we offer cost effective engineering and environmental support solutions across the whole of the UK and internationally.
Contact us today to learn how our industrial water management solutions can help you.
Further reading…
More information about our specialist closed system water treatment solutions
