It is estimated that HVAC systems account for approximately 40 percent of the energy used in commercial buildings, which is why many building owners and managers are looking for ways to cut these costs. One way to do that may be to utilize evaporative cooling systems, which can be relatively inexpensive to purchase and often require much less energy than other forms of cooling.
Evaporative cooling technology is already becoming more integrated in data centers, thanks to revised design guidelines from ASHRAE, but coolers have commonly been used in other types of commercial facilities for years. Commercial kitchens, laundries, dry cleaners, greenhouses, loading docks, warehouses, factories, construction sites, workshops, and kennels are just a few of the applications that can utilize evaporative cooling, said Anne Wood, director of marketing, Phoenix Mfg. Inc. (PMI). “Anywhere large volumes of air exchange are needed and DX refrigeration is cost prohibitive, evaporative cooling is beneficial.”
There are multiple types of evaporative systems available, including direct, indirect, and hybrid systems.
“Direct evaporative systems are excellent for applications that have large heat-load removal needs and those that are open to using outside air to accomplish this,” said Harold Simmons, global director of strategy, United Metal Products, which manufactures a full line of indirect evaporative solutions as well as indirect-direct evaporative systems and multi-mode systems.
In a direct evaporative cooling system, outside air is mixed with hot return air from the building to achieve the desired supply temperature. When the outdoor air is too warm for the desired supply temperature, media in the airsteam is wetted to reduce the air temperature toward wet bulb temperature. Direct evaporative cooling units are often among the least expensive evaporative cooling systems available, and they work well in open environments, such as warehouses.
PMI manufactures direct evaporative coolers — both forward-curve blower systems and fan systems — with airflow capacities of 5,500-24,000 cfm.
“Blower systems are used where static pressure is a prime consideration,” said Wood. “When the air is being dumped directly into a building or space and very little static pressure is created, then the fan cooler can produce the same airflow with a substantially smaller motor, thus eliminating energy use for the building.”
Indirect evaporative cooling systems keep the moisture separate from the application’s airstream. This takes advantage of the properties of evaporation as well as the difference between dry bulb and wet bulb temperatures, said Simmons. “Indirect systems are great for facilities that want to benefit from the energy-efficient cooling that evaporative technology provides without adding moisture to the air being delivered into the facility.”
Indirect evaporative cooling systems are ideal for medium to large commercial and industrial applications, said Matt Sculley, vice president (Americas), Seeley Intl. “Our indirect evaporative product is the Climate Wizard, which delivers 100 percent dry, fresh, cool outside air for a number of different applications. These can include stand-alone or primary cooling, pre-cooling the outside air, supplementary cooling to traditional HVAC systems, and hybrid cooling — for example, together with variable refrigerant flow [VRF] or with a heating system.”
The company also manufactures the Breezair line of direct evaporative coolers, which uses up to 80 percent less energy than refrigerated cooling systems.
While evaporative cooling systems can be beneficial in many applications, there are certain factors that need to be considered when designing and installing these systems. For example, evaporative cooling often works best in areas with low relative humidity levels, such as Phoenix, Las Vegas, and Denver.
“Evaporative cooling also raises the internal humidity level, which desert inhabitants may appreciate as the moist air rehydrates dry skin and sinuses,” said Wood. “However, the cooling potential for evaporative cooling is dependent on the wet bulb depression; therefore, assessing typical climate data is an essential procedure to determine the potential of evaporative cooling strategies for a building.”
Simmons agrees, noting that evaporative cooling is not the right solution for every building application; however, building owners in high and/or dry climates who are looking for ways to reduce energy costs should consider evaporative cooling solutions.
“Energy savings is dependent upon multiple variables and design criteria, but it is not uncommon to see evaporative cooling systems provide 50 percent or more energy savings for building owners when applied appropriately,” Wood said.
Evaporative cooling systems do utilize water, which may lead some to be concerned that it adds to operating costs, but water usage really needs to be looked at from a holistic standpoint, taking into account the entire hydro-footprint, said Simmons. “In certain areas of the country, the amount of water used to generate electricity at the power plant is high, therefore any kWh saved on-site due to the application of energy-efficient systems can actually use less water.”
Simmons referenced Arizona as an example, where it takes approximately 7.85 gallons of water to produce 1 kWh of electricity at the power generation source.
“This means that for every kWh that is saved at the facility level from applying energy-efficient systems, a significant amount of water can be saved,” Simmons said. “It is not as simple as saying the DX system uses no on-site water and the evaporative system uses X number of gallons on-site, therefore it uses more water. In actuality, the DX system may have a larger hydro-footprint.”
Ultimately, in drier climates, evaporative cooling can usually reduce energy consumption and total equipment costs compared to compressor-based cooling, said Wood. “Even in climates not considered arid, indirect evaporative cooling can still take advantage of the evaporative cooling process without increasing humidity. And in very humid environments, an evaporative cooler will still lower the temperatures more than the ambient temp, usually by 8°-12°F.”
As an example, Sculley points to hot and humid Queensland, Australia, where his company’s Climate Wizard units have been used to great success in McDonald’s restaurants.
“The technology easily copes with excessive air humidity outside while inside there are continual peaks in heat loads from the kitchen and patrons,” Sculley said. “The results have been outstanding with indoor comfort levels for both customers and workers maintained. The low energy use has been recognized by consultants and specifiers who are looking at other installations in Queensland rather than refrigerated systems.”
Evaporative cooling is also becoming more popular, because the systems are relatively simple to design and maintain. On the service side, basically all that needs to be done is to keep the pads clean, oil the motor, and make sure the belt tension is accurate, said Wood.
“However, one of the more important issues that is overlooked when designing these types of systems is determining where the spent air will be exhausted,” she said.
That’s because exhaust ducts and/or open windows must be used at all times with an evaporative cooling system in order to allow air to continually escape the conditioned area, said Wood.
“The evaporative cooling system cannot function without exhausting the continuous supply of air from the air conditioned area to the outside. It is also necessary to determine wind direction, as a strong, hot, southerly wind will slow or restrict the exhausted air from a south facing window or opening.”
As with any HVAC equipment, there is an art and science to the application of evaporative solutions, said Simmons, but the end result is that this technology can save money for building owners and managers.
“There has definitely been an uptick in interest in evaporative systems over the last 10 years as owners of large scale facilities are becoming more environmentally conscious as well as financially aware of how evaporative systems can play a role in reducing costs,” he said.
Evaporative Cooling Towers Save Money, Too
Cooling towers are another form of evaporative technology, only these are used to reject heat from a building.
Open-circuit towers use direct cooling and provide the most efficient means of heat rejection with regard to footprint and fan motor horsepower. While this greatly influences energy consumption, it requires continuous access to water for cooling, explained Adam Radford, global product manager – closed circuit coolers, Evapco Inc.
Closed-circuit coolers use indirect cooling by cooling the working fluid through evaporation from the coil.
“The primary benefits of closed-circuit cooler technologies are closing the loop — or keeping the process fluid free from outside contamination — increasing the operating efficiencies of other process equipment, reducing water consumption, its dry operation, and built-in redundancy for critical chilled water applications,” said Radford. “Closed-circuit coolers are the ideal solution for most applications, where reduced operating expenses and green building is of highest concern.”
Excessive water use can be a concern when using cooling towers, but manufacturers are offering new technology to limit its use.
“Evapco offers several new hybrid closed-circuit cooler designs that utilize finned coil technology and only use water at peak load conditions,” said Radford. “The finned technology offers end users the ability to run the units completely dry at full load when ambient conditions are favorable — typically from October through May in most regions — and at even higher switchover temperatures during partial load conditions. Evaporative cooling still provides very efficient means of heat rejection in terms of both installed cost and operating costs.'