Chiller units are refrigerant systems that aid in cooling residential/commercial spaces, machines, industrial operations, and industrial chemicals. These units are energy efficient, cost-efficient, and time-efficient. Without these systems, production objectives often cannot be achieved.
Chillers fall under two main categories: vapor compression and vapor absorption chillers. vapor compression chillers use an electrically driven mechanical compressor to force a refrigerant around the system while vapor absorption chillers use heat to move the refrigerant around the system.
Vapor compression chillers are the most commonly used and fit into two subcategories: air chillers and water chillers. Let’s take a quick look at how each of these work, their applications, and the pros and cons of each.
Types of Chillers
As described, two different cooling mediums (air or water) can facilitate the transfer of the latent heat given up as the refrigerant changes from vapor to liquid. Thus, chillers can use two different types of condensers, air-cooled and water-cooled.
- Air-cooled condensers resemble the “radiators” that cool automobile engines. They use a motorized blower to force air across a grid of refrigerant lines. Unless they are specially designed for high-ambient conditions, air-cooled condensers require ambient temperatures of 95°F (35°C) or below to operate effectively.
- Water-cooled condensers perform the same function as air-cooled condensers, but require two steps to complete the heat transfer. First, heat moves from refrigerant vapor into the condenser water. Then, the warm condenser water is pumped to a cooling tower where the process heat is ultimately discharged to the atmosphere.
Water-cooled chillers feature a water-cooled condenser connected with a cooling tower. They have commonly been used for medium and large installations that have a sufficient water supply. Water-cooled chillers can produce more constant performance for commercial and industrial air conditioning because of the relative independence to fluctuations of the ambient temperature. Water-cooled chillers range in size from small 20-ton capacity models to several thousand-ton models that cool the world’s largest facilities such as airports, shopping malls and other facilities.
A typical water-cooled chiller uses recirculating condenser water from a cooling tower to condense the refrigerant. A water-cooled chiller contains a refrigerant dependent on the entering condenser water temperature (and flow rate), which functions in relation to the ambient wet-bulb temperature. Since the wet-bulb temperature is always lower than the dry-bulb temperature, the refrigerant condensing temperature (and pressure) in a water-cooled chiller can often operate significantly lower than an air-cooled chiller. Thus, water-cooled chillers can operate more efficiently.
Water-cooled chillers typically reside indoors in an environment protected from the elements. Hence, water-cooled chiller can offer a longer lifespan. Water-cooled chillers typically represent the only option for larger installations. The additional cooling tower system will require additional installation expense and maintenance as compared to air-cooled chillers.
Air-cooled chillers rely on a condenser cooled by the environment air. Thus, air-cooled chillers may find common application in smaller or medium installations where space constraints may exist. An air-cooled chiller can represent the most practical choice in scenarios where water represents a scarce resource.
A typical air-cooled chiller can feature propeller fans or mechanical refrigeration cycles to draw ambient air over a finned coil to condense the refrigerant. The condensation of the refrigerant vapor in the air-cooled condenser enables the transfer of heat to the atmosphere.
Air-cooled chillers offer the significant advantage of lower installation costs. Simpler maintenance also results due to their relative simplicity as compared to water-cooled chillers. Air-cooled chillers will occupy less space, but will mostly reside outside a facility. Thus, the outdoor elements will compromise their functional lifespan.
The all-inclusive nature of air-cooled chillers reduces maintenance costs. Their relative simplicity coupled with reduced space requirements produces great advantages in many types of installations.
How Air Cooled and Water Chillers Work?
Both air and water chillers have the same components: an evaporator, a compressor, a condenser and an expansion valve. Furthermore, the mechanics for both are very similar. The compressor pushes a refrigerant around the inside of the chiller through the condenser, the expansion valve, the evaporator, and back to the compressor.
The primary difference between air and water chillers is how the unwanted heat is ejected. Air chillers us air to remove heat while water chillers use, you guessed it, water.
Air cooled chillers use air to remove heat by using fans to force air across the exposed tubes of the condenser. While air chillers require more energy than water-cooled chillers, they can be a great option when it comes to stationary cooling. Air chillers are easy to instal and typically can be installed outside a building (no extra space requirements). Compared to water chillers, air chillers are more prone to blockages and recirculation issues.
Water chillers remove heat by pumping water through a sealed condenser and dispersing it through the cooling tower. Water-cooled chillers are typically more efficient than air-cooled chillers. Using water evaporation to dissipate heat uses significantly less energy than blowing air across a hot surface. This is thanks to water’s high heat capacity. Additionally, water chillers tend to last longer than air-cooled chillers.