When you are learning about cooling systems, you may have heard the terms “cooling tower” and “chiller” before.
But how do these two systems operate, and what are the differences between them?
Keep reading to find out.
What do Cooling Towers and Chillers Do?
Both cooling towers and chillers are used for larger scale cooling, such as in multi-unit residential buildings or in commercial buildings. In spite of slight differences between the two systems, they produce similar results. You may see cooling towers in applications such as thermal power stations, and you may see chillers in applications such as microbreweries and wineries.
If you are looking to install one of the two options in your building, it is important to learn the difference so that you may find which application is better suited for your building. The better option for your building can help you save money on energy costs and ensure the unit is functioning optimally.
What is the Difference Between Cooling Towers and Chillers?
Let us first take a look at chillers.
A chiller removes heat directly from coolant and transfers it into the surrounding air. A pumping system circulates a water/glycol mixture or cool water from the chiller, removing heat in the process before returning the warm fluid back to the chiller.
Chillers use the refrigeration cycle, which is the process of changing the refrigerant from a gas to a liquid and back again by applying heat. Refrigerants are generally chemical compounds, and the exact refrigerant can vary depending on the heat application. For example, your vehicle’s air conditioning unit likely uses a refrigerant called R-134a.
The refrigeration cycle starts when a low-pressure liquid/gas mix enters the evaporator. In the evaporator, heat from the water or water/glycol solution boils the refrigerant, changing it from a to a low-pressure gas from a low-pressure liquid. The low-pressure gas then enters the compressor, where it is compressed to high-pressure gas. From there, the high-pressure gas enters the condenser where ambient air or condenser water removes heat and cools it to a high-pressure liquid. The high-pressure liquid now travels to the expansion valve, controlling how much refrigerant enters the evaporator, beginning the process all over again.
Let us now take a look at cooling towers.
A cooling tower works by maximizing evaporation of water, removing heat from water that is discharged from the system’s condenser or heat exchanger. They achieve this by containing materials (such as PVC plastic sheets) that create large surface areas for water evaporation to occur.
Most cooling towers use natural air flow through the cooling tower, but very large cooling towers use an electrical fan motor to generate airflow.
In general, cooling towers are more energy efficient than chillers and have a better energy ROI, though this may vary depending on application.
What Types of Chillers Are There?
There are two main types of chillers: air-cooled and water-cooled.
Using water as their method of heat transfer, water-cooled condensers use water from a cooling tower which cools and condenses the refrigerant. Water cooled chillers are best suited for large capacity cooling tasks. The downside of these systems is that they may produce excess heat.
Air-cooled chillers use air for the transfer of heat. An air-cooled condenser uses ambient air to cool and condense the hot refrigerant gas, bringing it back down to a liquid. The condenser can either be within the chiller or remotely located outside the chiller. They are less effective for large operations, especially those which emit a lot of heat, but they are more cost-effective and maintenance costs are low.
What Types of Cooling Towers Are There?
While chillers come in two basic types, there are many types of cooling towers available.
With crossflow cooling towers, the air is cooled by blowing across the hot water stream. The process water is pumped to the top of the tower into a hot water distribution basin. The distribution basin is gravity fed and does not interfere with the airstream. It is easily accessible from the outside of the cooling tower, and therefore is easier to clean and maintain.
With counterflow cooling towers, air is blown in the opposite direction of the water flow and process water is pumped into a sealed header box. The header box then distributes the water into branch arms and nozzles, which creates a pressurized water distribution system. Unlike a crossflow cooling tower, a counterflow tower’s water distribution system requires pumps to be shut off for cleaning, making them more difficult to maintain.
Forced draft cooling towers use a counterflow of water and air, resulting in a heat transfer. These are one of the two types of towers mentioned earlier in the article that use a fan to generate airflow.
Induced draft cooling towers pull the air upwards, pulling out the hot and moist air. This is the other type of tower that uses a fan to generate airflow.
There are also factory assembled cooling towers available that can be custom fit for a specific building’s needs.
How Much Do They Cost to Replace?
Whether you opt for a cooling tower or chiller, replacement costs will be high. Heat removal is a demanding and important task, especially in hotter climates.
With chillers, air-cooled is generally the more affordable option, although it may not be suitable for larger applications and hotter buildings. Equipment costs can be anywhere between $188,000-$250,000.
With so many cooling tower types available, the cost can vary widely. Depending on the style it can be anywhere between $50,000-$200,000, but many require additional tools such as sand filters or water treatment systems.
In conclusion, while they may achieve the same goal of cooling a large building, there are situations best suited for both cooling towers and chillers. If you are looking to upgrade or install one of the options in your building, it is best to consult with a commercial HVAC professional for guidance on which option will best suit your needs.