Comparison of Air-Cooled and Water Cooled Industrial Chillers and How Do You Choose Which is Right for an Application

Industrial Chillers

Industrial chillers are refrigeration systems that cool any process fluid through a vapor-compression refrigeration cycle to provide an ambient environment for laboratory and manufacturing processes. They are widely used for controlled cooling of factory machinery, high-heat specialized lasers and MRI machines, printer rollers, welding equipment, as well as semiconductors. Chillers, available in refrigeration capacities from 100 to 3000 tons, find application in a wide range of industries, from aerospace and healthcare to power generation.

All industrial chillers operate according to the basic principles of refrigeration. Therefore, all chillers feature basic refrigeration components such as evaporators, compressors, condensers, and recirculation pumps. Typically, chillers are available as packaged closed-loop systems, containing all refrigeration components in a single unit, or as open-loop systems. Industrial chillers can also be classified based on whether the condenser is air-cooled or water-cooled. Application dictates which configuration is ideal for a given project. Both water-cooled and air-cooled chillers use a similar refrigeration cycle system; the only difference being the method of cooling used in the condensers.

Refrigeration Cycle:

A refrigerant cycle involves two significant processes, the evaporation of liquid refrigerant by the evaporator and the condensation of refrigerant vapor by the condenser. A chiller features a condenser, an evaporator consisting of coiled tubes, expansion devices, and a compressor. During a refrigeration cycle, the refrigerant liquid in the chiller alternatively goes through a change of state from liquid to vapor and vapor to liquid.

In a refrigeration cycle, the process fluid enters the low-pressure inlet of the evaporator, where the heat load from the warm process fluid is absorbed by the refrigerant liquid in the evaporator, thereby cooling it. As a result, the now cooled fluid cools the process load or space that needs to be cooled. After heat absorption, the refrigerant evaporates to a superheated vapor and enters the compressor connected to the evaporator.

In the compressor, the refrigerant is compressed to a high pressure, high temperature refrigerant gas and passed to the condenser. The hot gas is cooled to liquid in the condenser and the heat is absorbed by a cooling medium. The pressure and temperature of refrigerant liquid leaving the condenser is decreased by the expansion valve. After passing through the expansion valve, the low-pressure refrigerant again enters the evaporator to repeat the refrigeration cycle.

Air-Cooled Chillers

In air-cooled chillers, the condensers use the ambient atmosphere as the cooling medium to extract heat from the refrigerant. In many cases, a condenser fan is used to force air over the condensing coils to enhance the cooling effect of the ambient atmosphere. These chillers typically use R407C refrigerant that have replaced R-22 refrigerant, due to the latter's environmental impacts. Utilizing this refrigeration cycle, the air chillers produce cold refrigerant that can be transferred through pipes and pumps to hundreds of cooling zones. Industrial air-cooled chillers are available in small as well as large capacity models suitable for comfort cooling applications in buildings. Air-cooled condensers can operate in below-freezing conditions without freeze protection overheads. For process applications like computer data centers that warrant year-round cooling control, air-cooled chillers have a unique advantage over water-cooled systems. Furthermore, in industrial or commercial environment where water is corrosive or scarcely available, air-cooled chillers can be used as practical cooling solutions.

The primary advantages of this type of chiller are as follows:

  • They do not require mechanical room
  • They require less maintenance
  • No condenser pumps or cooling towers are required
  • Quicker availability
  • Low installation cost

Water-Cooled Chillers

Water-cooled chillers on the other hand use water, rather than air, to cool the refrigerant. The warmed water exiting the condensers is then cooled, in many cases via cooling towers. Water-cooled chillers use R134a and R407C as refrigerants, which have replaced R-12 CFC and R-22 respectively. These water-cooled chillers are available as either a closed loop system, which is contained in a single unit, or a split system. Both these systems are typically installed indoors. The cooled water then enters the condenser and the heat removal cycle is repeated. The large refrigerating capacities and high efficiencies achievable with water-cooled chillers make them an ideal choice for large industrial applications and commercial complexes requiring large air conditioning systems.

Advantages:

  • Long service life
  • Indoor chiller location
  • Large tonnage capabilities
  • Available in large sizes
  • High efficiency

Air-Cooled Versus Water-Cooled Chillers

Operating Cost:

When compared to water-cooled chillers, air-cooled systems that function without any condenser water pumps or water cooling towers require lower initial installation and maintenance costs. However, lower condensing temperature of water-cooled chillers can offset this high installation cost.

For instance, consider the following table depicting the energy efficiency and cost savings offered by a 250-ton water-cooled chiller as compared to a 100-ton air-cooled chiller.

100 Ton Air-Cooled Screw Chiller
250 Ton Water-Cooled Screw Chiller
IPLV Efficiency (kW/ton): 0.83
IPLV Efficiency (kW/ton): 0.46
(Based on the ASHRAE 90.1. standard)
(Based on the ASHRAE 90.1. standard)
Annual Energy Use: 166,000 kWh
Annual Energy Use: 230,000 kWh
Annual Energy Cost: $10,000
Annual Energy Cost: $13,800
Lifetime Energy Cost: $145,000
Lifetime Energy Cost: $195,000
Lifetime Energy Cost Savings: $74,000
Lifetime Energy Cost Savings: $135,000
(If the assumed life of the chiller is 23 years, Energy price trends and discount values based on federal guidelines)
(If the assumed life of the chiller is 23 years, Energy price trends and discount values based on federal guidelines)

Energy Efficiency:

Since wet surfaces transfer heat more efficiently than dry surfaces, air-cooled chillers consume about 10% more power than water-cooled units do. This makes water-cooled chillers an ideal choice for applications requiring a high efficiency chiller.

Capacity:

Air-cooled chiller packages are available with capacities up to 500 tons. Thus, for applications requiring high capacity cooling in excess of 500 tons, the options are limited compared to water-cooled chillers that have capacities ranging up to 3000 tons.

Maintenance:

For applications that warrant year-round mechanical cooling, air-cooled chillers are perfect options. Unlike water-cooled chillers, they do not require condenser water treatment, cooling tower services, condenser-tube cleaning, and tower freeze protection. In addition, water-cooled chillers require regular condenser water treatment programs that eliminate the growth of algae or bacteria.

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3 comments

prolix1001 5 years ago

I have enjoyed reading your articles. It is well written. It looks like you spend a large amount of time and effort in writing the blog. I am appreciating your effort. .

Refrigeration Equipment


RAMESH PATEL 4 years ago

what is differenec betwoo or adv and dis adv of air cooled and water cooled chiller


abdul ghaffar 4 years ago

how we measure chiller efficiencies according to its capacity

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