Evaporative Cooling Applications
Evaporative cooling can be used for increasing humidity or lowering the temperature in many contexts. Read about some of the applications below or go to www.evapcool.co.za for more information.
Spraybooths and Sanding Operations
In spraybooths, ambient temperature and humidity can influence productivity both indirectly and directly. Indirectly, hot and dry conditions will reduce productivity through their influence on worker comfort and morale if they are not improved with adequate cooling. Since the surface to be painted has often been in an oven recently, heat stress can be considerable, the more so with inspection lights.
The direct influence that temperature and humidity can have on productivity depends on the circumstances, particularly the coating that is being applied and the external environment. Some spraybooths require humidity control, while in others only cooling is necessary.
One example of the importance of humidity concerns the increasing use of water-based polyurethanes to reduce the amount of toxic solvents in the environment. This can lead to increased costs if the air in a spraybooth is too dry, because the paint can evaporate before reaching the surface being sprayed. Keeping the relative humidity level at about 72% RH prevents such evaporation for optimum paint transfer. Adequate control of the relative humidity also helps produce an improved finish on car bodywork, reducing the amount of time taken by sanding operations.
Evaporative cooling in spraybooths helps to reduce ambient temperature and also has a positive effect on humidity. In-duct evaporative cooling units have become a widely-used solution, as their operating costs are lower than those of spray washers, condensers, cooling towers and other mechanical cooling systems. They are also a more hygienic option.
Apart from spraybooths, sanding areas can benefit from evaporative cooling. If humidity in these areas is kept at 55%, it reduces or eliminates static problems or dust adhesion on paint. This is because the static charge on the dust is altered so that it is the same as that of the bodywork, eliminating the force attracting dust to the surface.
Modern computer equipment is energy intensive, and much of this energy is converted into heat which can cause problems in hot periods. CRAC (computer room air conditioning) for server rooms, UPS rooms, IT rooms and data centres typically consume large amounts of electricity. Modern computer systems are less sensitive to changes in ambient conditions. Equipment from most manufacturers is specified for operating in temperatures ranging from 10 °C to 35 °C, and high relative humidity is less of a problem because of the lack of tape and paper in modern rooms for computer equipment.
This has opened up the possibility of using evaporative cooling systems, reducing energy use and the impact on the environment. These systems can be backed up with refrigeration systems for periods of extreme temperatures.
A thermostat and humidistat can be used to automate the evaporative cooling system and whatever additional climate control equipment is needed. More complex control systems can be implemented for environments that require it.
Manufacturing industries frequently require cooling because of the heat produced by equipment. Sufficient cooling improves worker morale, the functioning of equipment, and product quality, resulting in higher and more consistent productivity. Food production is one area in which this is true.
Evaporative cooling systems provide an economical and effective solution. The costs associated with evaporative coolers are many times smaller than those of refrigeration air conditioning systems. In conjunction with a well-designed ventilation system that CFW can design and install, positive pressure, excellent humidity, temperature and airflow control, and conformity to environmental and hygiene regulations can be maintained.
Insect screens can be fitted for hygiene control.
Note that evaporative cooling is not sufficient to keep products and raw materials chilled.
Teaching and learning become unpleasant and unproductive when it is too hot. In places where equipment is operating, such as IT rooms, temperatures can be even higher. Air condition units are often installed to deal with this problem. However, evaporative cooling units are much more cost effective and environmentally friendly in dry conditions.
The comfort of office occupants often suffers because of the density of people in the space, as well as the amount of electronic equipment and insulation in modern buildings.
In hot ambient conditions, warehouses may require cooling for the comfort of workers and to protect products stored in them. Evaporative cooling systems designed to work with the ventilation system of the building can help to accomplish this at low cost, and have relatively low airflow requirements.
Air Compressor Rooms and Plant Rooms
In very high temperatures, many compressors will shut down automatically. This occurs when the oil that is used as a heat transfer medium heats up too much, causing it to degrade faster and to solidify. This can lead to blockages in the heat exchanger. Since this heat is eventually dispersed into the air by fans in typical compressors, the problem will be more severe when there is inadequate ventilation or air is merely recirculated.
With an easily installed evaporative cooler, the temperature of plant rooms can be controlled with one thermostat. In a properly ventilated and humidity controlled environment, the cooled air should not cause problems with the drying or compression.
To maximise the shelf life of bread, rusks and other baked goods, the cooling rate must be controlled. If the product cools too slowly, it can succumb to mould earlier than expected. Evaporative cooling can be used to control the cooling rate to optimise the product’s quality.
Restaurants and Bars
In restaurants and bars, proper heating and cooling is important to create a pleasant environment for patrons and staff. Refrigeration air conditioning systems are expensive to purchase and operate, and it is preferable not to recirculate air where food preparation is taking place or where occupancy levels are high.
The costs of evaporative cooling are much lower. Energy use is comparatively low, fresh air is introduced into the space, and entrances can be left open if required to welcome customers.
The environment for storing most pharmaceutical products should not reach temperatures of above 25 °C. In some countries, storage is regulated and wholesalers must demonstrate that they have complied with legislation. Regulations might set an absolute maximum temperature as well as mean temperatures over a period.
The expense of refrigeration has led many managers to prefer ventilation for temperature control. However, during heat waves, ventilation may not be sufficient. Evaporative cooling is often the ideal solution to this problem, especially in dry climates.
Power Turbine Cooling
Combustion turbines (CTs) are commonly used for peak demand power generation because they can start and stop more quickly than commonly used alternatives.
Turbine power output decreases with higher temperatures and fuel efficiency. The total thermal energy available in CT exhaust gases for systems using it for applications such as heating and cooling also decreases. The extent of this effect depends on CT design, with designs using aeroderivative technology (increasingly used for improved performance even in industrial/frame CT design) being especially sensitive to temperature variations. The challenge is exacerbated because the peak-demand power generation that CTs are typically used for is often needed when ambient temperatures are high.
This has led to the use of CTIC (combustion turbine inlet cooling), particularly in areas with hot and dry climates where a proportion of energy use is spent on ventilation and cooling.
CTIC has the following advantages:
- Maximises power output when the demand for and value of electricity is high
- Better fuel efficiency
- Reduces the use of less efficient turbines, reducing costs to consumers
- Reduces the marginal capital costs of additions to capacity.
- Environmentally responsible, reducing fuel use and emissions
Evaporative systems are an ideal solution for CTIC applications, as they are best suited to the environments in which CTIC is most needed. The contact of water with the air passing through the system also helps to reduce particulates, reducing the load on downstream filters and scrubbers.
They are the norm for CTIC as they have the lowest capital cost. They consume considerable amounts of water (which may need to be treated for pad systems) and their effect is dependent on the wet-bulb temperature.
Both wetted media and fogging systems are used. For wetted media, a need for higher saturation means that more media are required and pressure drops increase. This is an established technology. Media may need replacement every 5-10 years depending on water and air quality and hours of use. Proper maintenance is crucial.
Fogging uses a spray of fine water droplets. High-pressure systems can produce droplets of various sizes depending on ambient conditions and desired evaporation rates. They require high-quality water (reverse-osmosis or demineralized water is typical). Nozzles need replacement in 5-10 years due to erosion, and high-pressure pumps need annual servicing or better.
So-called wet-compression/over-fogging/overspray/high-fogging systems spray more water than can evaporate at the inlet, and the water is taken into the CT. This achieves maximal evaporative cooling and also cools the compressor because the additional water is taken into it, reducing the load on the compressor. Total flow rate (by mass) of gas into the CT is increased, further increasing power output.
For more information, visit www.evapcool.co.za
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