6 Factors to Consider in Choosing Direct Evaporative Cooling

Direct evaporative cooling is a technology that has been used since ancient times to help control temperature, evidenced by ancient Egypt frescos from around 2500 B.C. that show slaves fanning urns of water in order to cool the rooms used by royalty. In the 16th century, Leonardo Da Vinci sketched designs for the first mechanical evaporative cooler. Of course, much has changed with direct evaporative cooling since these times and it is important to have a thorough understanding of the function of direct evaporative cooling equipment before making the decision to incorporate one into your project.

If you dip your fingers into a glass of water and then blow air onto your fingers you will feel a sensation of cold as the water evaporates. In doing this, you have experienced direct evaporative cooling. Direct evaporative coolers use this principal by circulating water over a saturated cooling media. The hot air is passed across the cooling media where it absorbs the moisture, resulting in reduction of the dry bulb air temperature. The dry bulb temperature achieved through direct evaporative cooling should come within 2 to 3 °F of the wet bulb temperature under the right circumstances. A water pump with a control and distribution system ensures that water is spread evenly over the surface of the cooling media, maximizing efficiency and life of the fluted cellulose cooling media pads which Titan Air utilizes. Fans are then used to create a negative pressure that causes air to be drawn through these pads and distribute the resulting cool air. Titan Air direct evaporative coolers can reach efficiencies of 89%.

Direct evaporative coolers, which are commonly referred to as swamp coolers, are a simple, environmentally friendly and relatively inexpensive method for cooling an indoor area. You should carefully consider the following prior to making a decision to incorporate a direct evaporative cooler.

1. Will a direct evaporative cooler be effective in the local climate?
   • Direct evaporative cooling is most effective in climates of hot, dry air such as in the southwestern United States. They are also most effective at the hottest time of day and when relative humidity is less than 50%. In warm, moist climates direct evaporative coolers are ineffective due to the higher humidity levels in the air.
2. Are cooling costs a concern?
   • The original equipment cost of direct evaporative cooling is less than other cooling options due to its simple design, which also results in easier maintenance and quicker installation. Power consumption is limited to the water pump and fan(s). Water vapor is not recycled so a compressor is not needed as with closed-cycle refrigeration, resulting in direct evaporative cooler operating costs estimated to be 1/8 that of refrigerated air. Due to the large quantity of water required in direct evaporative cooling, the local water cost should be considered. While this may not be a problem in an area where water is inexpensive, this may be problematic in a drought stricken area. The amount of water required can be estimated prior to purchasing a direct evaporative cooler.
3. Is environmental impact a decision making factor?
   • Only water is required, no refrigerants like ammonia or CFCs are used that can be toxic or contribute to ozone depletion. Lower energy expenditures will also reduce the carbon footprint of direct evaporative coolers compared to other cooling methods.
4. Is the added humidity from direct evaporative cooling an issue?
   • Direct evaporative cooling works best in dry climates where the added humidity can be beneficial to increasing comfort by preventing dry eyes or skin, and can also help alleviate allergies and asthma. However, excessive humidity can also cause the following issues:
     • High humidity can cause corrosion damage to items such as electronics and mechanical equipment. This can be compounded by high levels of dust in the air.
     • Condensation of water due to high humidity can also damage delicate items such as paper products. Wood building materials and other commonly found items in industrial settings may also be susceptible.
     • As the air from direct evaporative coolers is usually 80-90% relative humidity, it can reduce comfort in humid environments as higher humidity lessens the rate of moisture evaporation from the body.
5. Can the building be ventilated during cooling?
   • Direct evaporative systems cannot function properly without continuously exhausting the supply of air from the conditioned area to the outside, otherwise there will be a build-up of moisture in the area. This means that they can be used while windows/doors are open as opposed to standard air conditioners which require an enclosed space in order to operate properly and efficiently. This open ventilation required by direct evaporative coolers results in “fresher” air than that of a closed air conditioning system as air pollutants and germs are removed from the building.
6. Have you considered the unique maintenance requirements of direct evaporative cooling?
   • As mentioned earlier, direct evaporative coolers have greater ease of maintenance compared to other cooling systems but there are some specific maintenance factors to consider prior to choosing a direct evaporative cooler:
     • The sump and water distribution header should be cleaned and flushed periodically in order to remove any built up debris. The cooling media should also be flushed periodically and brushed off to remove any mineral deposits that have accumulated due to water hardness. Depending on maintenance and water quality, the cooling media can last from several months to several years.
     • Proper water treatment is necessary when it comes to direct evaporative coolers. The water quality at the job site will determine the type of treatments needed. The treatment could be as simple as setting the proper water flow/bleed off rates and doing regular flushing/drying of media. However, in areas where poor water quality exists or where biological fouling particulates are present a more stringent approach is needed. That is when a water treatment specialist is recommended to help determine the best treatment options.

Direct evaporative coolers can be shipped as loose accessories or built into an air handler and are available in custom sizes. Incorporating direct evaporative cooling can be a simple and relatively inexpensive method to cool an area. Be sure to choose a manufacturer that offers the highest quality construction and components and is also able to assist you with any questions that you may have. This will ensure that you receive the best possible equipment for your project.