HEATING AND VENTILATION
An adiabatic system with low noise attenuators fitted to keep footprint to a minimum.
climate. Technology which leverages our cooler temperatures can reduce their reliance on high-risk evaporative cooling.
Reliance on evaporative cooling As a general rule, cooling towers rely on evaporative cooling 100% of the time, no matter what the temperature, while hybrid cooling plant uses evaporative cooling methods for around 50% of the year, only switching to dry mode in temperatures lower than 9.6˚C, most commonly between January and April, and then again in November and December. Most impressively, adiabatic technology can work efficiently in dry cooling mode for 97% of the year when operating in colder climates like the UK, only switching to evaporative cooling when temperatures exceed 21-23˚C, which, in mission-critical environments which work around the clock, equates to a tiny 3% of the year. It is also important to remember that cooling equipment which stores water or has a heat exchange surface which is directly wetted is notifiable to the local authority under the ‘Notification of Cooling Towers and Evaporative Condensers Regulations 1992’ Act.
Out of the three technologies explained here, the only one exempt from this admin-intensive registration process is adiabatic cooling equipment, such as Transtherm’s adiabatic cooler range, which was designed around direct advice from the British Health and Safety Executive’s leading Legionella risk assessors. It is important to note that the adiabatic technology marketplace varies greatly in terms of equipment quality and performance; specifiers should confirm with their manufacturer of choice that the plant they are purchasing is indeed exempt.
Modern cooling methods’ benefits Maintaining a cooling tower to a standard which is adequate for the prevention of dangerous bacteria requires considerable ongoing financial investment and a stringent maintenance programme, combining costly and environmentally damaging chemicals and weekly manpower on site. Weekly dip slide tests
46 Health Estate Journal October 2018
Transtherm’s BSE-approved adiabatic solutions include integrated safety functions to combat Legionella risk.
and chemical dosing, plus commissioning the complete strip-down and rebuild of the cooling tower structure on a bi-annual basis, are all basic requirements in the maintenance of this ageing equipment. Opting for a cooling system which is more technologically advanced can deliver numerous maintenance, risk-assessment, and remote monitoring benefits. Let’s look at class-leading adiabatic technology, for example, which inherently prevents the production and transmission of Legionella through a pre-commissioned UV system fitted as standard. While it is imperative to ensure that the mains water feed supplied to an adiabatic system is clean and free from contamination, an integral UV system is extremely effective at killing Legionella (99.99+ %). By administering a 30 mL/cm2
UV dosage,
the system can be categorised as 99.999% effective at killing Legionella, assuming that the water has a UV transmission of more than 95% in a 10 mm cell at 254 nm.
UV system failsafes
Harnessing the power of technically advanced industrial controls, market- leading adiabatic coolers will also automatically operate a number of UV system failsafes to further protect environments such as hospitals from dangerous nosocomial outbreaks. These failsafes typically include raising alarms via remote monitoring systems in the event of a UV failure. Remember, these systems have a trigger point of around 23˚C, which means that the adiabatic spraying function is only in operation around 3 per cent of the year. With long periods of inactivity, these failsafe modes are vital to ensure that the correct UV treatment is administered in the warmest months of the year, when the plant is operating at temperatures which are most conducive to the cultivation of Legionella. Should the UV system not respond adequately when adiabatic mode is triggered, the controls will either switch off the adiabatic system pending repair, or switch to a standby UV system if one has been installed. Either way, the alarm is raised through the centralised remote monitoring system so that adequate
manual intervention or maintenance can be arranged.
Lowering risk through product design
According to the British Health and Safety Executive (HSE), there are a number of product design considerations which would help a cooling system to meet all relevant parts of HSE and ASHRAE guidance on the control of Legionella bacteria in water systems.
These include avoiding materials such as rubber in piping, because it can form a natural breeding ground for Legionella. Copper is cited by the HSE and many industry-leading private risk assessors as the most suitable alternative, because it actively repels bacteria.
Avoiding dead-end piping, low spots, and other areas in the water distribution system where water may stagnate during shutdown, is another key design consideration, with automatic drain-down features a popular addition in more high- spec equipment.
As previously discussed, avoiding wetted media cooling, like the method used by hybrid systems, is also advantageous to prevent the accumulation of dirt, scale, or biological matter, which all facilitate the growth of potentially dangerous bacteria. In contrast, adiabatic cooling means that most of the moisture is evaporated into the air prior to the air reaching the coil or air inlet filters.
Water droplet sizes
Similarly, creating a system which does not emit water droplet sizes of between 1 and 5 microns in size will also dramatically reduce the potential for Legionella transportation. Droplet size can be adequately controlled with carefully designed spray outlet nozzles. which can ensure much safer sizes of between 50 and 100 microns.
Energy and water efficiency Understanding that cooling towers and hybrid systems rely heavily on evaporative cooling methods, it will be no surprise to learn that adiabatic coolers consume around 1% of the water used by traditional
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