Commercial Evaporative Cooling Unit Rooftop Install - Cambridge Engineering®

INDUSTRIAL & COMMERCIAL EVAPORATIVE COOLING SYSTEMS

Cambridge Engineering’s evaporative cooling systems provide industry-leading cooling solutions for commercial and industrial facilities. Improving indoor air quality is the driving force behind our evaporative cooling systems and does so while also reducing energy consumption and operational costs. The Cambridge Engineering ESC-Series indirect evaporative cooling units are best suited for industrial or commercial facilities in need of higher quality air without inflating operational costs. Similarly, our E-Series direct evaporative cooling units are best suited for facilities in hot, dry and arid climates in need of fresh and cool conditioned air.

WHAT IS EVAPORATIVE COOLING?

Evaporative coolers provide cool tempered air by converting hot dry air through a series of evaporative processes. This process works by pulling warm air through a series of dampened pads to draw out the air’s natural heat and inject a cooler air into your work space. While the concept has been used in residential applications like “swamp” coolers in the Southwest for decades, technology advances have made evaporative cooling a viable alternative to conventional cooling in commercial and industrial buildings in other areas of the country. Manufacturers have begun to offer two-stage (“indirect-direct”) evaporative cooling systems that offer greater cooling effectiveness, extending the geographic range where evaporative cooling can be used.

Types of Evaporative Cooling

WHAT IS DIRECT EVAPORATIVE COOLING?

Direct evaporative cooling is designed to cool the air by evaporating water which increases the moisture content of the air. Standard cooling systems use evaporative media of shredded aspen fibers, typically 1 to 2 inches thick. These systems have an effectiveness of 55 to 70 percent. (Effectiveness is a measure of how closely the supply air temperature leaving the evaporative cooler approaches the outdoor wet-bulb temperature.) Effectiveness is defined by:

Evaporative Cooling Effectiveness Equation – Cambridge Engineering®

TDB is the outdoor dry-bulb temperature while TWB is the outdoor wet-bulb temperature. SAT is the supply air temperature leaving the evaporative cooler.

The thickness of the media and air velocity contribute to the system effectiveness. More advanced evaporative cooling systems use a rigid medium 8 to 12 inches thick and have an effectiveness of 80% to 90%. Direct evaporative cooling systems are suitable for hot and dry climates where the design wet-bulb temperature is 68°F or lower. In other climates, outdoor humidity levels are too high to allow for sufficient cooling.

 

Direct Evaporative Cooling Applications & Building Types – Cambridge Engineering®

WHAT IS INDIRECT EVAPORATIVE COOLING?

Indirect evaporative cooling uses an air to air heat exchanger to remove heat from the primary air stream without adding moisture. Hot and dry outside air is passed through a series of horizontal tubes that are wetted on the outside. A secondary air stream blows over the outside of the coils and exhausts the warm, moist air to the outdoors. The outside air is then cooled without adding moisture as it passes through the tubes. Indirect evaporative cooling typically has an effectiveness of 75%.

While the greater number of air passes increases the pressure drop and the required fan power, the high effectiveness extends the geographic range where the indirect evaporative cooler can fully meet the cooling demand.

Direct Evaporative Cooling Applications & Building Types – Cambridge Engineering®

Evaporative Cooling Climate Zones – Cambridge Engineering®

WHAT ARE TWO STAGE EVAPORATIVE COOLING SYSTEMS?

Indirect cooling is often paired with a second direct evaporative cooling stage, to cool the supply air further while adding some moisture to the supply air. Two-stage systems (often referred to as indirect-direct or IDEC systems) can meet the entire cooling load for many industrial and commercial buildings in arid to semi-arid climates. IDEC systems provide cooler supply air at a lower relative humidity than direct evaporative cooling units. First, the indirect stage cools the supply air without increasing humidity. Since the air is cooled, it has a reduced capacity to hold moisture. Second, the supply air is then passed through a direct cooling stage, which cools the air further while adding additional moisture. IDEC systems typically have an effectiveness of 100% to 115%, cooling the air to a temperature slightly below the outdoor air wet-bulb temperature (see sidebar).

For commercial systems, indirect-direct systems can be coupled with a conventional DX cooling stage to meet cooling demand during hot and humid outdoor conditions (when outdoor air dry-bulb temperatures exceed 70°F). Since the systems use 100% outside air for cooling, they can also be paired with heat recovery to capture some of the energy that is lost in the exhaust air stream and reduce the ventilation cooling load.

IDEC systems used in arid climates (with a design wetbulb temperature of 66°F or lower) can have power consumption as low as 0.22 kW/ton, much lower than compressor-based cooling which can have power consumption on the order of 1 kW/ton. However, in more humid climates indirect-direct systems have less power reduction and energy savings than other cooling solutions.

DESIGN OA, INDIRECT EVAPORATIVE & DIRECT EVAPORATIVE BY CITY

Design OA, Indirect Evaporative & Direct Evaporative by City – Cambridge Engineering®

Rooftop Evaporative Cooling Unit Install-2 - Cambridge Engineering®
Rooftop Evaporative Cooling Unit Install-3 - Cambridge Engineering®
Evaporative Cooling Unit Drop Through Install - Cambridge Engineering®

EVAPORATIVE COOLER CONTROLS

Industrial and commercial evaporative cooling units recently introduced advanced features to the market like variable air volume control. Additionally, lower air velocity increases heat transfer effectiveness significantly reducing system fan power.

An advanced feature not commonly available on evaporative coolers would include the use of sensors to monitor system performance. Temperature and humidity measurements allow for an estimate of system effectiveness. Static pressure gauges measure pressure drops across the media can also be used to determine when media maintenance is required.

Due to the higher air temperatures than traditional air conditioning systems, more air is required to provide the necessary cooling. As it is generally 100% outside air evaporative units will match the existing mechanical exhaust loads of a building.

BENEFITS OF EVAPORATIVE COOLING

Industrial and commercial evaporative cooling systems have several benefits. These systems use only a fraction of the energy of typical compressor-based cooling systems. Highly-efficient evaporative cooling systems can reduce energy use by 70% (the actual savings will vary with the type of evaporative system and climate). For dry climates where evaporative cooling can meet the entire load, the units dramatically reduce peak-demand. When evaporative cooling is used with supplemental DX cooling it can reduce the DX cooling required. Moreover, since they use 100% outside air for cooling, the right evaporative cooling system can improve indoor air quality while reducing overall operating cost and energy consumption.

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Content Source: Energy Design Resources e-News April 2010

 

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