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.
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Both cooling towers and chillers are used for large-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 to find which system 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.
The main purpose of a cooling tower is to reject excess or unwanted heat from a system or building. Cooling towers can be classified as Direct Contact or Indirect Contact.
Indirect Contact cooling towers are also known as:
This system operates with internal and external flow systems. The internal flow system includes the entering hot water stream to be cooled and air flow. The entering hot water runs through a series of tubes that are designed to achieve maximum surface area. At the end of these tubes is the outlet of cooled water. The external flow system includes the cooling water that is pumped into a set of nozzles that spray over the tube system to achieve cooling [1].
A fraction of the sprayed cooling water condenses at the bottom of the tower and is recirculated. The other portion of water that evaporates leaves the system through the top of the tower as warm humid air. Cooling is achieved through indirect interaction between ambient air and cooling water inside the tower [1] [2].
The following diagram shows the operation of an Indirect Contact cooling tower:
Direct Contact cooling towers are also known as:
These are called Direct Contact because the water and air come into direct contact through processes within the tower. These cooling towers can be recognised by the large boxes on top of buildings with large fans expelling air from the building.
The cooling water is pumped into a set of nozzles that spray over the fill packing material to achieve cooling. The fill packing is a labyrinth type structure that provides a means for evaporation. The sprayed cooling water condenses at the bottom of the tower and is recirculated. Air enters the base of the tower and flows through the falling water. The hot water that flows into the tower to be cooled enters the fill packing to be exposed to the cooling water under specific air flow conditions. Air flow can be upwards (counter-flow) or horizontal (crossflow) [1].
Direct Contact cooling towers can be further classified by the air flow mechanism used. These include forced and induced draft systems that can create crossflow, counter-flow and mixed-flow conditions depending on the design [1].
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The following diagram shows the operation of a Direct Contact cooling tower:
There are several types of chillers that have a variety of uses in large scale cooling. The two main categories of chillers are Vapour Compression and Vapour Absorption. Vapour Compression systems use a mechanical compressor to drive the flow of a refrigerant within the system. Vapour Absorption systems use a heat source (steam or hot water) to drive the flow of a refrigerant within the system [3].
We will be looking at the most commonly used Vapour Compression chillers, air cooled, and water cooled. The operating principle is the same for both systems where a compressor drives the flow of the refrigerant between a condenser, an expansion valve, an evaporator and back to the compressor again. Water cooled chillers have a sealed condenser and require a pump to deliver the water to a cooling tower. Air cooled chillers use fans to induce air flow over the exposed condenser tubes to reject heat from the system [3].
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.
Here is a list of some of the resources that we have used in combination with Connected Sensors industry expertise to produce this post:
[1] Singham, JR, 1990, Hemisphere Handbook of Heat Exchanger Design, Section 3.12 (Cooling Towers), Hemisphere Publishing Corporation, New York.
[2] Buecker, B, 2010, Cooling Tower Heat Transfer 101, Power Engineering, Available at: https://www.power-eng.com/coal/cooling-tower-heat-transfer-101/ [Accessed January 2023]
[3] Evans, P, 2018, Chiller Types and Application Guide, The Engineering Mindset – Guide to Chillers, Available at: https://theengineeringmindset.com/chiller-types-and-application-guide/ [Accessed January 2023]
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