The Benefits of Using Evaporative Condenser

1.     Introduction:

The objective of a mechanical refrigeration system is to remove heat from a space or product, and to reject that heat to the environment in some acceptable manner. Evaporative condensers are frequently used to reject heat from mechanical refrigeration systems. The evaporative condenser is essentially a combination of a water-cooled condenser and an air-cooled condenser, Evaporative condensers offer important cost-saving benefits for most refrigeration and air-conditioning systems.

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This paper presents brief description of evaporative condenser, its advantages and dis-advantages.

2.     Overview:

Conventional air-cooled condensers are simple refrigerant to air heat exchangers where refrigerant heat is transferred sensibly from the condensing high pressure/temperature refrigerant to a working ambient stream of air. This heat transfer mechanism is dependent on the ambient air stream’s DB temperature. In an Evaporative Condenser-type Air Conditioner (ECAC), refrigerant heat rejection is primarily driven by the latent heat of vaporization of water into a working ambient air stream. This latent heat transfer is dependent on the WB temperature of the ambient air stream.

In the most severe hot and dry climate condition of 115° Fahrenheit (F) DB and 74°F wet-bulb (WB), the ECAC had an EER which was 51% higher than that of the air-cooled condenser technology under similar conditions, and reduce compressor electricity requirement by up to 30%.

3.     Energy Efficiency Ratio for ECAC and Standard Air-Cooled Condenser:

The ECAC EER is consistently higher than that of the air-cooled unit across the entire range of tested ambient conditions; According to The series of laboratory tests conducted at the TTC followed the test protocol outlined in the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) 37-

And indoor condition was maintained at 80°F/67°F as per AHRI 210/240.

At low DB temperatures (83°F-85°F) the EER of the ECAC is approximately 9% higher than the standard air-cooled EER; EER for ECAC is 14 while EER for standard air-cooled is 13. At 115°F, the EER of the ECAC is approximately 51% higher than the standard air-cooled EER; EER for ECAC is 13.1 while EER for standard air-cooled is 8.7.

4.     Water consumption in evaporative condenser:

Makeup supply water must be provided to serve purge, drift and evaporation, In order to mitigate effects of water fouling, water must be routinely purged. In order for the ECAC to function properly, sufficient water must be provided for the evaporative effect.

Purge: The amount of purged water is independent of climate zone variations. The amount of water purged per interval is relatively constant at approximately 1.8 gallons (gal) per one interval.

Evaporation: The increase is approximately 27% from the lowest usage of 5gal/hr. for the mild condition of 83°F (DB)/ 69°F (WB) to the highest usage of almost 7gal/hr. for the extreme conditions in 108°F (DB)/ 69°F (WB), and 111°F (DB)/ 73°F (WB), as well as the 115°F (DB)/ 74°F (WB) condition.

Total water usage for evaporation and the hourly purge of water in the sump over all climate zones was in the 6.5 gal/hr. to 8.5gal/hr., for air conditioning unit of capacity of 3-ton. This is equivalent to about 2.1 gal/hr. to 2.8 gal/hr. per ton.

5.     Reducing consumption of water for evaporative condenser:

The major dis-advantage of evaporation condenser is high water consumption, so this consumption must be reduced to overcome this issue.

To overcome this dis-advantage some evaporative condenser can use recycled water like storm water or gray water if the concentration ratio is maintained conservatively low. Similarly, blow down water may be reused elsewhere on-site, but using gray water may need additional treatment to reduce concentration of impurities.

Reducing water consumption in evaporative condensers can save more than the value of the water alone. This includes pre-treated before use and chemicals added to it to.  

First step in reducing water consumption start with monitoring the amount of water used in each step of the process enables the water efficiency of the evaporative condenser installations to be determined. It also allows malfunctions or reductions in efficiency to be identified.

·        Blow down or Purge:

Optimizing blow down is often the greatest opportunity to reduce water consumption in evaporative condenser installations. Blow down can be minimized if the concentration ratio (CR) or cycle of concentration (COC) is high.

Concentration ratios of around 3:1 – 5:1 are typical for many evaporative condenser installations.

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And the best way to reduce the concentration of TDS in make-up water and increase cycle of concentration is by water treatment.

Water treatment:

Effective water treatment is necessary for reliable and efficient operation of refrigeration systems by reducing energy and water use, effective water treatment also helps reduce the negative environmental impact and carbon dioxide emissions associated with a facility and to reduce the risks associated with waterborne pathogens.

Adherent deposit termed scale forms on the condenser tubes as a result of continuous evaporation which lead to increasingly concentrated of dissolved solids will reduce heat transfer efficiency. Deposits on the condensing coil surface significantly reduce the ability of an evaporative condenser to remove heat. For example, 1/32” of scale on the condenser tubes reduces its heat transfer capability by about 27%, increase the energy cost by 7% and decrease the available refrigeration capacity (tons) by 1%.

An effective water treatment program that provides scale control directly translates into lower energy use, operating costs and carbon dioxide emissions.  Based on U.S. national averages, each kWh reduction in electricity usage reduces carbon dioxide emissions by 1.55 lbs.

The potential for deposits to occur in an evaporative condenser is a direct function of makeup water quality, system design and operation, and maintenance practices.

Makeup water will have pre-treatment, which include:

• softening (changing the chemical composition of some of the dissolved salts) to reduce scaling; and
• Demineralization or reverse osmosis to remove the majority of TDS.

·         Drift:

Water, in the form of small droplets, is often lost in the airflow leaving evaporative condenser installations, and is called drift, water losses through drift  can be 0.05% – 0.2% of water flow through evaporative condensers.

Drift eliminators are often fitted to prevent this loss, Good construction and drift eliminator design may reduce this significantly. Losses on modern units are typically around 0.005% but can be as low as 0.001%.

·         Maintenance:

Maintenance the system periodically is very important to keep the system efficient, maintenance process include the following:

• Regularly inspect the spray nozzles and condenser tubes. Poor water flow over the condenser tubes reduces cooling efficiency and will cause deposits to form.
• Check heat exchange equipment for signs of fouling such as a high head pressure and/or approach temperature.
• Check water treatment controller readout for high/low conductivity reading daily.
• Check chemical feed equipment daily. Check chemical pumps for prime and operation.

6.     Conclusion:

We conclude that Evaporative Condenser Air Conditioner (EVAC) is efficient than standard air-cooled units but need high water supply, this make it useful to use in hot and dry areas with  abundant of water.

But in hot and dry countries suffering from scarcity in water, this option become un-useful even if re-using grey or storm water because it need additional treatment before reuse, which make other high efficient air conditioning systems more cost effective.  

The evaporative condenser is a critical component in various industrial applications, helping to effectively dissipate heat in cooling systems. With its ability to combine both air cooling and water evaporation, the evaporative condenser offers high performance in diverse sectors such as HVAC, refrigeration, and industrial cooling. Below, we discuss the key applications and benefits of using an evaporative condenser.

HVAC Systems

The evaporative condenser plays an essential role in HVAC systems, particularly in large-scale commercial and industrial buildings. It helps to manage heat produced by air conditioning units, ensuring the system operates efficiently. The evaporative condenser cools the refrigerant by utilizing both air and water, thus lowering energy consumption and improving system performance, especially in areas where water is readily available.

Refrigeration Systems

In refrigeration systems, an evaporative condenser is used to maintain the optimal operating temperature for refrigerants. By efficiently transferring heat from the refrigerant to the surrounding environment, the evaporative condenser ensures that refrigeration systems can function smoothly without excessive energy use. These condensers are commonly used in supermarkets, cold storage facilities, and food processing plants to maintain the required temperature levels.

Industrial Cooling

In industrial cooling processes, such as in chemical and manufacturing plants, the evaporative condenser is vital for maintaining temperature regulation. It allows large-scale cooling of machinery and processes, where heat dissipation is critical to prevent overheating and ensure optimal production. The evaporative condenser helps to maintain process stability, enhance efficiency, and reduce the likelihood of heat-related breakdowns.

Power Generation

The evaporative condenser is also widely used in power plants to condense steam and recover waste heat. In power generation systems, steam from turbines is cooled down by the evaporative condenser, which helps to convert steam back into water for reuse. This process is crucial for improving energy efficiency and reducing environmental impact by conserving water and energy.

ApplicationBenefitHVAC SystemsEfficient heat management for large-scale cooling.Refrigeration SystemsMaintains optimal refrigerant temperatures.Industrial CoolingPrevents overheating in machinery and processes.Power GenerationImproves energy efficiency by condensing steam.

The evaporative condenser is a versatile and efficient solution used across various industries to manage heat dissipation and improve overall system performance. Its application in HVAC, refrigeration, industrial cooling, and power generation provides numerous benefits, including enhanced efficiency, reduced energy consumption, and long-term reliability. With its advanced cooling capabilities, the evaporative condenser continues to play a critical role in modern cooling technology.