Adiabatic Cooling Systems & Legionnaires’ Disease
In this article our cooling tower specialists consider the selection of adiabatic cooling systems over the more traditional evaporative cooling towers, and how their use can impact the risks associated with Legionella bacteria and Legionnaires’ disease.
The article outlines how adiabatic or hybrid coolers work, how they compare to the more traditional evaporative systems, whether they offer a safer alternative, the requirements for registering them with the Local Authority; and the importance of a thorough legionella risk assessment and effective scheme of control.
Cooling towers and the risks from Legionnaires’ disease
If you have responsibility for the control of legionella and Legionnaires’ disease at your workplace, you may already know that many outbreaks of the disease have been linked to cooling towers.
While cooling towers are not in themselves a significant risk factor, inadequate treatment of the cooling water, poor cleaning, maintenance and disinfection can easily lead the towers to experience raised levels of bacteria, including the potentially dangerous Legionella bacteria. These bacteria can then make their way into the atmosphere by contaminating small droplets of water (aerosol) created by the cooling tower processes. This contaminated aerosol can disperse in to the atmosphere and potentially affect people in the area along with those working on the site.
Adiabatic cooling as an alternative to wet cooling
An alternative to a wet or evaporative cooling tower is an adiabatic cooler, sometimes referred to as a “dry/wet” or “hybrid” cooling system.
Adiabatic coolers are designed to operate both in dry air cooling, and wet evaporative cooling formats
Adiabatic systems are designed to operate both in dry air cooling, and wet evaporative cooling modes. There are different types of adiabatic cooling system, and these can have a wide range of risk profiles so it’s important to do your homework before any decisions are made.
They are ideal for companies wanting to reduce water use. Typically, an adiabatic cooler only requires 10% or even less of the water a traditional wet cooling tower would use in the same circumstances.
So…. does this also mean the risk from Legionella bacteria is lower? Let’s find out.
Is adiabatic cooling safer than a traditional evaporative cooling tower?
Any water system carries a potential risk of legionella being present within that system. If proper measures are taken to contain this risk, there is no reason why the system should pose any danger to those using it or anyone nearby. Even a cooling tower, which is considered to be a higher risk system, can be safely run if proper water treatment, maintenance, cleaning and disinfection procedures are conducted in accordance with the manufacturer’s instructions; and the Health and Safety Executives ACOP L8 and HSG274 Part 1 (Cooling Systems).
However, adiabatic systems can be safer than cooling towers when the two are compared side-by-side. The open nature of a wet cooling tower and the amount of evaporation that can occur when in use means the risk of legionella escaping via a contaminated aerosol, into the atmosphere is higher than that of an adiabatic system.
Do you need to register adiabatic cooling systems?
If your business uses an evaporative cooling tower and you are thinking of switching to an adiabatic system, you may wonder whether you’ll need to register the new system with your local authority. This is an important and necessary step for all those using cooling towers. However, at the present time, this is not required for adiabatic cooling systems unless they create a spray of water that goes straight onto a heat exchanger. There are several adiabatic designs in use, so this is a consideration worth thinking about if you have yet to switch from wet cooling towers to this type of cooler.
That said, don’t make the mistake of thinking you don’t need to worry about the control of legionella at all. Certainly, there is a lower risk of legionella causing issues within this type of system. With 90%+ less water in use, this makes sense. However, there will still be water used throughout the system, so you must still consider where the potential risks lie with a detailed legionella risk assessment and effective scheme of control.
Comparing evaporative cooling towers with adiabatic systems
It’s reassuring to know you can potentially lower the risk of an outbreak of Legionnaires’ disease simply by choosing an adiabatic alternative to a regular evaporative cooling tower. However, you’ll still have aerosolised water present which can present a danger that needs to be managed. If Legionella bacteria is present in that spray, anyone nearby could inhale it into their lungs, with the corresponding potential to develop Legionnaires’ disease.
So, just as you would conduct a legionella risk assessment for a cooling tower, so you need to do the same with an adiabatic cooling system. One key difference to highlight is that cooling towers recirculate the water they use, whereas adiabatic systems do not. This means a lower risk for the adiabatic alternative, as nothing is recirculated. If bacteria entered the water at any stage, it would remain within the system in a traditional cooling tower. This means it has a chance to multiply and create risk issues within the water system, while this is less likely to happen in the alternative “once-through” adiabatic system.
Other areas to look at include the positioning of the adiabatic cooler when in use. Are there windows that allow sunlight to come through onto the system, therefore raising the temperature of the water inside it? Are there any dead legs of runs of pipework that are not always in use? Could these be removed to create a more efficient system? If not, can they be flushed through regularly to help reduce the risk of stagnation, a situation that allows Legionella bacteria to multiply?
Making sure you have the knowledge to maintain your adiabatic system
You may be familiar with a traditional cooling tower – how it operates, how to maintain it, and how it should be cleaned and disinfected to comply with the law. Changing over to an adiabatic cooler presents a promising alternative, yet it is one you need to know more about before switching.
Clearly, a legionella risk assessment is just as important in this situation as it is with a cooling tower. You may find that calling in an expert, such as Legionella Control International, to conduct a legionella assessment and to engage an experienced and competent water treatment company to carry out ongoing cleaning, maintenance and disinfection services is the best path to take.
Saving water is one clear advantage of an adiabatic cooler. The reduced risk of legionella is certainly another – but you must take adequate steps to ensure this reduced risk is always managed correctly. Do this, and you may be glad you switched.
Legionella and water safety specialists
Our teams of legionella and water safety specialists support those responsible for the control of legionella in cooling towers and other water systems, helping them to protect people and meet their health and safety obligations in this specialist area.
We deliver professional water safety risk assessments for legionella and other waterborne pathogens, water testing, independent compliance auditing, City & Guilds training and other environmental risk management services that help keep employees, guests and others safe.
To speak with one of our legionella cooling tower specialists’ call us today on 0330 223 36 86 or contact us here …