HEATING AND VENTILATION
Could it be ‘curtains’ for cooling towers?
Cooling towers have been used to dissipate heat from ventilation, air-conditioning, and heating systems in hospital applications for decades, but change is afoot. Here, Matthew Griffin, adiabatic cooling specialist for Transtherm Cooling Industries, explains the shift change towards dry/wet evaporative cooling methods for NHS Trusts and private healthcare environments, exploring the key concerns of Legionella control, energy and water efficiency, noise reduction, and retrofitting.
Better energy efficiency standards, water conservation, noise reduction and, most importantly, the risk assessment and control of Legionella and other waterborne pathogens, have shrouded resource and OPEX-hungry cooling towers in an evolving stream of HSE compliance and expansive maintenance and local authority reporting procedures. In recent years, many Trust specifiers, working on both new construction projects and rolling refurbishment programmes, have moved in favour of more efficient cooling technologies. Some opt for hybrid coolers, which combine a small amount of dry cooling, using oversized heat exchange coils, with the evaporative cooling methods of a traditional cooling tower, while many are waking up to the superior capabilities of adiabatic cooling technologies. Adiabatic coolers are capable of minimising the growth of dangerous pathogens, eradicating the use of costly and environmentally harmful chemicals, and considerably reducing the labour-intensive maintenance and reporting procedures associated with less advanced cooling tower technology. To better understand this significant specification shift change, let us examine those key drivers.
Controlling Legionella risk Cooling towers are a known source for potential nosocomial Legionella outbreaks, with additional risk factors affecting neighbouring communities situated downwind from a poorly maintained system. Dissipating heat through a process of conduction between water and air, cooling towers, by design, break water droplets into smaller particles in order to multiply the amount of water surface in contact with the air to speed up evaporation and the overall cooling effect. It is a recognised fact that particles of below five microns in size can be introduced to the human body through microaspiration or inhalation, and contaminated water droplets can cause Legionellosis in both healthy people and
Transtherm Cooling says adiabatic cooling ‘outperforms cooling towers and hybrid systems to deliver substantial cost and energy savings’.
vulnerable patient profiles. Legionellosis typically manifests in those with weakened immune systems as the severe and potentially fatal Legionella pneumonia, also known as Legionnaires’ disease. The same bacterium can also cause Pontiac fever, manifesting as ‘flu- like symptoms even in young, otherwise healthy individuals.
Cooling towers
Many may argue that cooling towers situated away from hospital buildings are free from patient contamination risk, but outbreaks of Legionella have been traced back to poorly maintained cooling towers situated up to 150 metres from the contraction site. As the air and contaminated water droplets are drawn up through the top of the cooling tower, they create a visible plume of moist air (depending on the humidity). Once ejected from the cooling tower, wind or even gentle air currents can transport contaminated water droplets through open windows into neighbouring residential or office areas, or, most worryingly, straight into the inlet of the hospital’s air conditioning system.
Modern technologies reduce evaporative cooling
While there are a number of variables which will affect whether biofilm forms and dangerous pathogens grow, it is true to say that evaporative cooling is more dangerous. Put simply, the more evaporative cooling, the higher the risk of Legionella. Alternative, more modern, technologies, such as wetted surface hybrid coolers and adiabatic cooling systems, reduce a hospital’s reliance on evaporative cooling methods, instantly reducing the risk of contaminated water being transported through the air. Finding the most effective cooling method depends largely on regional weather conditions, with cooler climates such as that in the UK being ideal for dry cooling, or even free cooling, to reduce energy consumption and risk of Legionella growth. Average daily temperatures for the UK range from 5˚C in January to 16.4˚C in August, giving an average temperature across the year of around 10.3˚C. Using this as a threshold, specifiers can make an informed choice for the selection of cooling technology that performs the most efficiently for our
October 2018 Health Estate Journal 45
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