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Evaporative Condensed Chillers
Evaporative condensed chillers are an efficient alternative to air or water condensed chillers. Cooling Technology offers evaporative condensed chillers from 15 to 200+ tons and can select a system best suited for the specific application.Principle of Cooling by Evaporation
Evaporation has long been used to transfer heat to the atmosphere. Our own bodies benefit from this cooling effect when we sweat. For each pound of water that evaporates, it removes somewhere near 1,000BTU’s from the water that remains. The more evaporation that takes place, the more heat that is removed.
The amount of evaporation that can take place is determined by the amount of moisture already in the air. This “wet bulb” temperature can be measured using a sling psychometer. The lower the wet bulb, the drier the air, the more moisture it will accept and the more heat a given evaporative condenser is capable of rejecting.
Evaporative Condensed Refrigeration
The key to evaporative condensing is maximizing heat rejection efficiently. This is achieved by using a recirculating water system to provide continuous wetting of the bare condenser tubes while fans draw air over them, evaporating the water and rejecting heat to the atmosphere. The rate of evaporation is a function of the wet bulb temperature.
A lower wet bulb temperature reduces the condensing temperature and increases the overall thermal efficiency of the system. Evaporative condensers also require less coil surface and airflow compared to air-cooled condensers, further improving performance and lowering sound levels.
An air-cooled condenser is less effective because it draws ambient air over the condensing surface and rejects heat to the ambient air at the dry bulb temperature.
That temperature is typically 95 F, but can reach upward of 125 F on a building’s roof.
Evaporative condensers reduce the water pumping requirements associated with water-cooled condensers, which generally operate at 3 gpm per ton. Typically, evaporative condensers circulate water at 1 to 1.25 gpm per ton.
Generating Cost Savings
Let’s compare the energy efficiency ratio of a “typical” air, water and evaporative condensed chiller that provide approximately 30 tons capacity at a 45F leaving water temperature:
Air-condensed
EER = 380kBTU/h / 41.98kW = 9.05
(Based on 95F Ambient, 120F SCT, Includes condenser fans)
Water-condensed
EER = 365kBTU/h / 32.42kW = 11.25
(85F CWT 105F SCT, Includes condenser pump & tower fan)
Evaporative-condensed
EER = 365kBTU/h / 26.84kW = 13.59
(74F WB 95F SCT, Includes condenser water pump & fan motor)
As you can see, the evaporative condensed chiller is 33% more efficient than the air condensed model and 17% more efficient than the water condensed model. With electricity costing between 4.77 to 16.70 Cts/kWh (Energy Users News 5/02/02 statistics), an evaporative condensed chiller can save enough in operating costs to pay for itself in just a few years!
Although this example is based on a 95F ambient and 74F wet bulb, as ambient temperatures increase and wet bulb temperatures decrease, an evaporative condensed chiller can be up to 40% more efficient.
Conclusion
There are many areas of the country where using an evaporative condensed chiller can relieve the load from the utilities' straining electric distribution network. Many electrical utilities offer rebates to customers who buy premium efficiency equipment.
- Lower compressor kW draw reduces demand charges, which can account for 40 percent of a typical utility bill.
- Lower compressor amp draw reduces component and wiring sizes, resulting in lower installed costs.
- Lower compressor head pressure increases compressor life.
- Factory prefabrication reduces expensive field labor and installation costs.
Average summer conditions of selected U.S. cities
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