It is no accident that so many town squares in hot climates include a fountain, which provides welcome cooling to local residents as they gather to discuss the issues of the day.
Similarly, many Turkish houses are constructed with two chimneys. Water is sprayed into one of them, which causes the cooler, heavier, humid air to fall into the premises. This results in hot indoor air being ‘pushed’ up the other chimney, creating a positive airflow of cool air through the property. And, of course, there are many other similar examples around the world that make use of architectural or natural water features to provide cooling.
Though the users of these relatively simple cooling systems may not fully be aware of the underlying physics, they are enjoying what we now call adiabatic cooling. Adiabatic cooling occurs when liquid water evaporates (changes state) to form water vapour suspended in the air. Heat energy is taken from the surrounding air to provide the energy required for this change of state to take place.
The benefits of adiabatic cooling have been known for thousands of years. It still makes sense to apply them to the control of temperature and humidity in our buildings, John Barker
These same principles have also been applied in modern buildings to provide a degree of local cooling, though historically the results have tended to be disappointing. However, with the application of modern technologies, the latest generation of evaporative humidifiers offers a more sophisticated, controllable and highly effective solution. In doing so, they help to address the common problem of low relative humidity (RH) in UK workplaces, while also providing ‘free cooling’ to maintain comfortable temperatures and reducing the energy consumption of comfort cooling systems.
Evaporative Humidifiers and Bacterial Growth
In modern evaporative humidifiers, water is supplied to the top of the evaporative module and flows down wet media. Warm, dry air passes through the wet media, evaporates water and thus raises the humidity level and reduces the temperature.
Latest models offer up to 12°C cooling as a result of the transfer of energy when the water evaporates.
The medium used for this needs to be of inorganic fibreglass so it does not provide nutrients for bacterial growth and is also incombustible. This latter property was an important consideration in choosing a humidification solution for a project in the accommodation block on an offshore oil rig.
Such systems can also be supplied with a variety of different thicknesses of media to allow for different efficiencies of the system – the deeper the media, the greater the efficiency (higher humidity) that can be achieved.
Cost-effective and hygienic, evaporative humidifiers are therefore a solution for many low-energy buildings, particularly when humidification and cooling are both required in the space. Obvious examples include data centres and a wide range of industrial applications where process machinery produces excess heat and precise humidity control is required.
Fitting Adiabatic to Air Handling Units (AHU)
Despite the clear benefits of humidity control and adiabatic cooling, many air handling systems are not fitted with humidification when they are first installed. However, with the right equipment, retrofitting to an existing air handling plant is straightforward, assuming the psychrometrics of the system are suitable. For example, evaporative units are often added downstream of the air conditioning components within the AHU (see diagram below).
In such cases, the humidifiers can be supplied flat-packed or pre-assembled for fast and simple installation, with the ability to configure the system for easy maintenance from either side of the air handling units (AHUs). Similarly, when new AHUs are being installed, the evaporative humidifier can be installed during the factory assembly of the AHUs.
Improving AHU Energy Efficiency
In either case, the detail of the humidifier design is of great importance in ensuring optimum performance. For example, if the media matrix of the humidifier does not cover the full width of the AHU, blanking plates will be required, and this will increase pressure drops and associated energy consumption by the fans. Customising the matrix to the width of the AHU is therefore an obvious measure.
Air velocity through the matrix is also an important consideration. If this rises above 3.5m/s, a droplet separator will be required to prevent water droplets from coming off the face of the matrix. This again has the potential to increase both costs and pressure drop, but the correct sizing of the humidifier helps to address this issue.
The result of these factors is that when the humidification system is tailored to the specific dimensions and configuration of the AHUs, pressure drops are reduced so that smaller and cheaper fans can be used, or inverter-controlled fans will run at lower speeds and reduce energy consumption.
Evaporative Humidification Technology
Modern evaporative humidifiers also take advantage of the latest control technologies to deliver a range of features that certainly wouldn’t be available on a town square fountain. For example, microprocessor control allows field configuration, master/slave configuration of multiple modules, on/off or modulating performance, time control and optional links to a building management system.
Evaporative humidification and adiabatic cooling are based on ancient principles, enhanced by clever design, innovative manufacture and modern materials to create a highly energy-efficient and cost-effective way of introducing moisture into the air. As such, they deliver significant cost savings with a fast return on investment for a wide range of applications that require cooling as well as humidification.
Watch our evaporative humidifier video for an in-depth look at the technology, or get in touch with one of our humidity control experts to discuss your specific project requirement.
