Evaporative Cooling. Terminology. Date: February 28, Concepts

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1 Evaporative Cooling Date: February 28, 2012 P R E S E N T E D B Y R O B E R T P A D G E T E 3 M S E N G I N E E R E D M E C H A N I C A L S Y S T E M S Concepts 1. Evaporation is a cooling process. Using evaporation in relatively dry climates, building owners can produce cooling with less energy than is typically required by direct expansion/refrigerant cooling. 2. Evaporative cooling technology is an old process that is being renewed, and reconfigured, to minimize negative impacts while taking full advantage of the opportunities for energy savings. 3. Varying the type of equipment and process used, plus combinations and order of placement of various components, yield different results for cooling efficiency. Terminology Direct Evaporative Cooling - passes incoming fresh air over the evaporation medium, directly cooling the incoming fresh air stream. Direct evaporative cooling is the most efficient. Indirect Evaporative Cooling - isolates the incoming fresh air from the outside air used to generate cooling. Indirect evaporative cooling is somewhat less efficient due to the need to exchange heat between the incoming supply air and the chilled water. Dry-Bulb Temperature (DBT) Commonly considered air temperature unaffected by moisture and direct radiation, and forming the X axis of the psychrometric chart Wet Bulb Temperature (WBT) The temperature of air that has been cooled to saturation, and the theoretical lowest temperature that can be achieved by evaporative cooling Wet Bulb Depression the difference in temperature between dry air (DBT) and saturated air (WBT), the amount of temperature drop available through the process of evaporation Psychrometric chart An evaluation tool that relates the parameters of air, including DBT, WBT, humidity, pressure, and other factors to present ranges of human comfort dependent upon these variables

Evaporative cooling technology is an old process that is being renewed, and reconfigured, to minimize negative impacts while taking full advantage of the opportunities for energy savings. 3.

2 EVAPORATIVE COOLING PAGE 2 Diagram of the cooling process Evaporation for Space Cooling Evaporative cooling is a very effective and economical strategy for space cooling in less humid environments such as the front range of Colorado. One can potentially achieve up to 85% reduction in the cost of energy used for cooling over standard DX cooling configured as a VAV system. Cooling is created by wetting a transfer medium with water and passing fresh air through the medium. As the warm, relatively dry air passes through the medium, vaporization of some of the water occurs, lowering the temperature of the air while also increasing the humidity. We have all likely experienced this effect. Simply becoming immersed in a cool pool on a hot summer day reveals the process of evaporative cooling our body being cooled as the water on our skin vaporizes into the surrounding air. The effect is enhanced when the surrounding air is set in motion as a light breeze may, resulting in displacement of cool air in the vicinity being replaces by drier air. Psychrometrics The method used to predict evaporative cooling performance is psychrometrics, and the tool used is the psychrometric chart, shown at the right. Environmental variables that affect human comfort are indexed on the chart, including a curved dew point temperature (green, indicating the lowest temperature achievable by a volume of air at constant pressure), Dry bulb temperature (blue, horizontal axis), absolute humidity, wet bulb temperature (red, angled axis) and others. Using the three main variables of DBT, Absolute Humidity, and air pressure, the anticipated effect of direct evaporative cooling and indirect evaporative cooling can be determined by inspection of the

Cooling is created by wetting a transfer medium with water and passing fresh air through the medium.

3 EVAPORATIVE COOLING PAGE 3 Evaporative Cooling in Colorado regions with warm/dry and particularly hot/dry air can utilize evaporative cooling more effectively. These climate conditions are typical of the front range of Colorado. These regions exhibit dominate climate conditions that trend towards the orange zone shown above. As humidity rises along with temperature, the effectiveness of evaporative cooling decreases. Two general system designs: There are two types of evaporative cooling strategies Direct Evaporative and Indirect Evaporative cooling. A comparison of these two types is shown in the chart below: Direct Evaporative Cooling Direct evaporative cooling adjusts wet bulb temperature, which has the effect of moving air temperature lower along the axis shown by the red arrow in the psychrometric chart Incoming fresh air is passed directly through the saturated media, and that air is delivered to the interior of the building The incoming air picks up considerable humidity, which can be beneficial or detrimental depending upon the occupants Indirect Evaporative Cooling Indirect evaporative cooling adjusts dry bulb temperature, which has the effect of moving air temperature lower along the axis shown by the blue arrow in the psychrometric chart Air is passed through the saturated media, but not allowed to enter the building. Fresh air is drawn into the building through a separate intake and directed through a heat exchanger No effect upon the humidity of incoming fresh air. 100% Outside Air 100% Outside air or recirculating interior air Move a significant volume of air to the interior Pressurized interior air needs an escape route through dampers or through the cooling unit Lower air flows are necessary for fresh air Air can be recirculated or exhausted through the cooling unit Do not function well in high wet-bulb environments (about 150 hours per year) Simple systems and controls Water is used in cooling media Very efficient cooling per input energy More complex systems Relatively higher water use is required Efficient, but not as high as Direct Cooling

As humidity rises along with temperature, the effectiveness of evaporative cooling decreases.

4 EVAPORATIVE COOLING PAGE 4 Two stage evaporative cooling systems Combining both types of evaporative cooling strategies is a strategy used to maximize the cooling benefit with minimal energy requirements. Indirect/Direct space cooling systems are configured such that incoming fresh air is first cooled and dried by passing it through an indirect cooling heat exchanger. In psychrometrics, this has the effect of moving the air temperature horizontally to the left. Then, incoming air passes through a direct evaporative cooler, further extracting heat, and adding a small amount of humidity. In an example, outside air in Denver Colorado is cooled from 93 F to 59 F in the indirect portion of the air handler, and the n f u r t h e r cooled from 59 F to 52 F in direct portion, creating suitable dry bulb air temperature for commercial cooling without sign ifican tly increasing the humidity. A similar process undertaken in Los Angeles (a more humid environment) finds a total reduction from 93 F to only 67 F DBT, demonstrating the reduced system performance with more humid outside air conditions. Hybrid evaporative / cooling coil systems Combining both types of evaporative cooling strategies is a strategy used to maximize the cooling benefit with minimal energy requirements. Indirect/Direct space cooling systems are configured such that incoming fresh air is first cooled and dried by passing it through an indirect cooling heat exchanger. In psychrometrics, this has the effect of moving the air temperature horizontally to the left. Then, incoming air passes through a direct evaporative cooler, further extracting heat, and adding a small amount of humidity. In an example, outside air in Denver Colorado is cooled from 93 F to 59 F in the indirect portion of the air handler, and th e n f ur t h e r cooled from 59 F to 52 F in direct portion, creating suitable dry bulb air temperature for commercial cooling without sign ifica ntly increasing the humidity. A similar process undertaken in Los Angeles (a more humid environment) finds a total reduction from 93 F to only 67 F DBT, demonstrating the reduced system performance with more humid outside air conditions. Case Study The new Green Valley Ranch Library, near Denver, was evaluated for the potential to use 4 different types of hybrid heating and cooling systems. The base case for evaluation was a system employing electric heat and DX cooling. The selected system utilizes hot water heat with a boiler fed system and an Indirect/Direct Evaporative cooler. This selected system was shown to be 47% more cost effective in operations than the base case, with 28% lower GHG emissions.

In psychrometrics, this has the effect of moving the air temperature horizontally to the left.

5 EVAPORATIVE COOLING PAGE 5 System maintenance tips For increased durability and higher system performance, the presenter offered the following suggestions for system design and specifications: 1. Install an air dam to prevent incoming fresh air from bypassing the saturation media 2. Ensure that the media is properly installed 3. Ensure that all pumps, hardware and supports are fabricated with Stainless Steel 4. Allow media to dry out at night and other underused periods 5. Do not allow the media to rest in standing water C O N T A C T I N F O R M A T I O N : R O B E R T P A D G E T E 3 M S L A W R E N C E S T R E E T D E N V E R, C O L O R A D O B O E 3 M S. C O M This information was presented at a Boulder County Energy Smart and Denver Energy Challenge Contractor Training Event and was funded by the American Recovery and Reinvestment Act

Ensure that all pumps, hardware and supports are fabricated with Stainless Steel 4. Allow media to dry out at night and other underused periods 5.

SIMULATION OF RADIANT COOLING PERFORMANCE WITH

SUMMARY REPORT MAY 2008 SIMULATION OF RADIANT COOLING PERFORMANCE WITH EVAPORATIVE COOLING SOURCES Timothy Moore Center for the Built Environment (CBE) University of California, Berkeley May 2008 EXECUTIVE