About Cooling Towers
Introduction
Cooling towers have been with us for a long time. The evaporative cooling tower was originally developed as a water conservation device, designed to reduce dependence on ‘once through’ cooling systems and successfully replaced many such systems. The development of the cooling tower also expanded the ability of designers to provide efficient cooling in areas without large water supplies. Cooling towers are now applied widely across a range of industries in Australia and New Zealand; however they are not always applied efficiently or optimally.
Traditionally, in the building and HVAC&R industries, lowest first cost as opposed to whole of life costs, has been the primary driver for equipment and system selection, design and construction. Even designs that incorporated energy or water efficiency features were often simplified or rationalised during the competitive tendering and building construction process. Designs whose energy efficient or sustainability features did survive the construction process were then rarely commissioned, controlled or operated so that the anticipated efficiencies were rarely realised in practice. In the days of relatively cheap energy and water abundance any industry concern over these issues was minimal. Times have changed.
With the advent of green buildings and green HVAC&R systems and, with the growing interest in and requirement for efficient buildings and building services, attitudes in the HVAC&R industry have changed. Now designs have to be energy efficient to comply with building regulations or voluntary building and system performance rating schemes. Systems have to be commissioned, finetuned and periodically recommissioned under most rating schemes. Owners want sustainable building systems to provide safe, healthy, comfortable and productive environments. Owners and operators also want optimised and integrated systems that reduce operating and compliance costs. Green leases are now including water and energy targets and requirements for optimised building operation.
The benefits from optimising designs have never been truer than in the case of cooling tower systems. The opportunities for improved energy and water consumption are undeniable and tower and component manufacturers have risen to the challenge. New designs and innovations, new materials and methods of manufacture have led to considerable improvements in performance and environmental impacts. New methods of system control and new system configurations are also achieving significant operational benefits.
Drift is reduced, fan efficiency is improved, fill and tower effectiveness is increased, towers are smaller, lighter and more corrosion resistant than ever before. Previously visible plumes can be made to disappear, water consumption can be reduced, and system energy consumption can be reduced. Advances in cooling tower engineering and design means that towers can be constructed on site faster and cheaper than was previously possible.
The relationship between cooling towers and public health issues, particularly the potentially deadly Legionnaires’ disease is also changing. Health authorities, building owners and system maintainers realise that risks can be mitigated by appropriate management strategies and that these strategies are generally well understood by the industry. Risk assessment, water treatment and management, system monitoring and maintenance, are all applied to better manage the health risk. Compliance costs fall with a better informed and educated industry properly managing the risk.
The benefits that cooling towers offer over competing heat rejection systems, in terms of energy savings, space and capital costs continue to be a significant driver for their inclusion in HVAC&R systems.
Standards
The primary design standard for cooling towers and cooling water systems is AS/NZS 3666.1. Its primary focus is the control of microbes such as Legionella in building water and air handling systems, particularly cooling water systems and cooling towers.
AS/NZS 3666.2 is a sister standard and is concerned with the operation and maintenance of air-handling and water systems. Again microbial control within such systems is the main focus.
Both AS/NZS 3666 part 1 and part 2 are called up in the Building Code of Australia as primary referenced standards and both are mandatory in all states and territories of Australia. Apart from building legislation there is individual state specific legislation and regulations relating to cooling towers which should be complied with as they are relevant to both installation and maintenance.
AS/NZS 3666.3 is the third standard of the series and deals with a performance based approach to the maintenance of a cooling water system with respect to the control of microorganisms. The approach outlined in this standard combines an automatically monitored water treatment system with prescribed monitoring, assessment and control strategies to maintain a low risk environment within the cooling water system.
The AS/NZS 3666 standards reference a series of associated documents and standards which also form requirements of the standards.
AS 5059 is a risk management standard specific to the design and operation of cooling towers associated with power stations.
There are no cooling tower product standards developed for the Australian/New Zealand application; however there are standards for components and materials used in the manufacture of towers.
Drift eliminators are assessed by the laboratory test method AS 4180.1. Industry certification standards and schemes do exist for cooling tower products and performance. However their adoption in Australia and New Zealand has been limited to date.