Bacteria in Closed Heating and Chilled Water Systems

With the increasing complexity of building services installations in modern, highly serviced offices, commercial buildings and other work spaces, the need to manage and control bacteria in closed heating and chilled water systems is becoming ever more important.

Bacteria in closed heating & chilled water systems

Here we consider the main problems caused by bacteria in closed heating and chilled water systems, we look at how to carry our simple water tests to identify the contaminating bacteria, and the types of bacteria that are commonly found to contaminate closed systems.

The many problems associated with the bacterial contamination of open circuit pipework systems, especially open evaporative cooling water systems and cooling towers is now well recognised, particularly where waterborne pathogens such as Legionella bacteria can present safety critical issues.

Approved codes of practice, detailed guidance notes and tried and tested management and control procedures now exist for dealing effectively with microbial contamination in such open circuit systems.

However, the issues associated with the growth and proliferation of bacteria in closed heating and chilled water systems is still less understood although there are a number of key guides now available to assist building services engineers, water treatment companies and facilities management specialists in this important area including:

BSRIA Guide BG 50/2013
BSRIA Guide BG 50/2013 – Water Treatment for Closed Heating and Cooling Systems.
British Standards
British Standards BG 29/2012 – Pre-Commission Cleaning of Pipework Systems.
CIBSE AM14
CIBSE AM14 – Non-Domestic Hot Water Heating Systems.
BS 8552:2012
BS 8552:2012 – Sampling and monitoring of water from building services closed systems. Code of practice.

What problems are caused by bacteria in closed systems?

The presence of unwanted bacteria in closed heating and chilled systems can cause a number of potentially serious problems including:

Accelerated corrosion of the system
Accelerated corrosion of the closed circuit system can occur resulting in increased maintenance costs, reduced performance and premature system failure.

The corrosion tends to result from the formation of organic acids, hydrogen sulphide, ammonia etc. within the closed system.
System blockages
The closed system and its components can become blocked by a build-up of bacteria and microbial slimes.

These cause blockages of the strainers, control valves and pipework.
Reduced system efficiency
Microbial fouling of the internal closed circuit surfaces, in particular heat exchange surfaces reduces system efficiency and leads to increased costs.
Poor commissioning data
The build-up of bacteria and generation of internal gases with in the closed circuit system can affect the accuracy of commissioning data leading to poorly configured systems.

How to test for closed system bacterial contamination

Typical bacterial contamination of closed heating and chilled water systems can include pseudomonas, sulphate reducing bacteria, nitrite reducing bacteria and other slime forming bacteria.

Avoiding contamination of closed circuit water systems should be your primary objective, however if you suspect problematic microbial contamination has occurred then there are a number of simple tests you can perform on a water sample taken from the system to confirm this. The tests include:

Smell
If the water sample is contaminated with bacteria it is likely to have a distinct, usually unpleasant smell. A strong smell of stagnant water will be a good indication that microbial contamination is present.
Colour
If the water sample is contaminated with bacteria it is likely to have a distinctive brown or green colour. This colour change would tend to indicate the presence of algae or other bacteria contamination.
Clarity
If the water sample is contaminated with bacteria it is likely to have a distinctive cloudy appearance.

Cloudy water will be a good indication that microbial contamination is present and is often caused by organics produced by the bacteria.
Dip slide test
A simple test using a dip slide which is then incubated will often be sufficient to identify the general level of microbial contamination.

If you need to identify the type of bacteria causing the contamination then a more extensive laboratory water test will be required.

Closed Systems Testing

Types of bacteria commonly found to contaminate closed heating & chilled water systems

Types of bacteria commonly found to contaminate closed heating and chilled water systems
Bacteria	Typical Characteristics	Temp	pH
Pseudomonas Bacteria	Pseudomonas Aeruginosa – slime forming aerobic bacteria	20 – 40 °C	4 – 8
Sulphate Reducing Bacteria (SRB)	Desulfovibrio – anaerobic bacteria that forms hydrogen sulphide	20 – 40 °C	4 – 8
Sulphur Bacteria	Thiobaciullus – sulphuric acid forming aerobic bacteria	20 – 40 °C	1 – 6
Iron Bacteria	Leptothrix – slime forming aerobic bacteria	20 – 40 °C	7.4 – 9.5

Expert closed system engineering solutions

Water Treatment Services are a leading independent UK water management company offering expert water management solutions including the management of closed heating and chilled water systems, water disinfection, cleaning and chlorination of water systems, pre-commission cleaning, boiler and cooling water treatment, energy efficiency and engineering support services..

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 engineers, site service specialists and technical experts we can offer water management treatment services including the management of closed heating and chilled water systems across the whole of the UK.

Contact us today to learn how our water management solutions can ensure your building services installations are maintained to achieve optimum performance… contact us →