Many regions in the world are grappling with water scarcity. Numerous efforts to desalinate and trade in water are evidence of the magnitude of the problem. The World Bank puts the number of people living with absolute water scarcity at 2bn, a number that could hit the 4.6bn mark within the next 65 years. The water energy nexus has been a regular subject in recent years. Power plants that feed most nations consume a lot of water, either directly or indirectly. When it comes to the feasibility study of a cooling plant, the debate of consuming water or not is very important. Depending on the results of this study, water-cooled or air-cooled chillers will be selected.
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What is a chiller?
This device removes heat from a load and transfers it to the environment using a refrigeration system. This heat transfer device is the preferable cooling machine in power plants and other large-scale facilities. It is simply a system consisting of ethylene + water or water reservoir and circulation components. The cooling fluid is circulated from the reservoir to the equipment undercooling. There are also air-cooled chillers, which disperse heat-using fans. These are more recent and common in power plants. In this post, we review the difference between the two technologies, leaving the choice of which one to pick to you. ARANER would be happy to help you in the decision making process.
Water-Cooled Chiller
Water cooled chiller systems have a cooling tower, thus they feature higher efficiency than air-cooled chillers. Water cooled chiller is more efficient because it condense depending on the ambient temperature bulb temperature, which is lower than the ambient dry bulb temperature. The lower a chiller condenses, the more efficient it is. This system has several essential components including:
- Cooling towers
- Condenser water pumps
- Make-up water pumps
- Chillers
- TES reservoirs
What are the benefits of a water-cooled chiller? Some users may prefer these chillers because of the smaller size they occupy as compared to air-cooled chillers. These chillers also feature higher efficiency and last longer than the mentioned alternative. Those who would like the equipment to be placed indoors may find the water-cooled machine desirable.
Discover: Chilled Water System on your next project: save up to 40% of energy
In The Evaporator
The role of the evaporator is to produce chilled water. The device releases the water at about 6°C (42.8°F) and pushes it throughout the facility with the help of a pump. A network of pipes passes the chilled water through every necessary section of the building. After exchanging coldness with room air, which blows across the Air Handling Units (AHU’s) and fan coil units (FCU’s), the water is now warmer at about 12°C (53.6°F). It returns to the evaporator where the refrigerant absorbs the unwanted heat and directs it to the condenser. The chilled water is cool once again and it can now continue to cool the facility. Note how this is called “chilled water” throughout no matter the temperature.
In The Condenser
A refrigerant brings unwanted heat from the evaporator and passes through the condenser. There is another loop connected to the condenser- the condenser water loop, which is between the cooling tower and the condenser. After entering the condenser at about 27°C (80.6°F), the water leaves at 32°C (89.6°F) and heads to the cooling tower. Note that at no time do the refrigerant and the condenser contact directly. Heat exchange is only through a pipe wall. The condenser water, with the unwanted heat, goes to the cooling tower for further heat rejection.
In The Cooling Towers
This is where the unwanted heat in a facility ends up. A large fan feeds the unit with air. The air meets with the oncoming condenser water. From the direct contact, the condenser water loses heat to the air. The condenser water goes back to the condenser the cycle continues. These open-topped devices come in many designs depending on many factors. Examples are cross flow, counter flow, natural draft and mechanical draft. Stay with us for coverage of these designs in upcoming posts. This is a good way of settling the cooling tower vs. chiller confusion. However, if you still need more details about the water-cooled chiller components and operation, reach out to our team and you will get help. Now, compare it to the air-cooled chiller discussed below.
Air-Cooled Chiller
Where aesthetics and environmental conditions or water access restrictions exist, the air-cooled chiller may be applied. Both air-cooled chiller and water cooled chiller depend on an air stream as a means of heat transfer. The difference is that the water-cooled chillers or rather the cooling towers use a humid air stream (ambient air stream + water spray) while the air-cooled chillers use a current of ambient air. Normally water-cooled chiller is cheaper and more efficient, with the disadvantage of high water consumption. ARANER has found a way of combining modern manufacturing methods and advanced technology to achieve highly effective and efficient air-cooled chillers. Owing to that, the company’s chiller plants are very competitive to water chilled chillers in different aspects. For example, these plants are very impressive in terms of footprint, efficiency, and noise. Unfortunately, some people still believe that air-cooled chillers cannot offer quite good efficiencies. What such people only need to check is the performance of these chillers two decades ago is the progressive increase in NPLV rating of air-cooled chillers over the years. Already, many chiller plants in the Middle East and elsewhere have adopted ARANER’s air-cooled designs and have expressed satisfaction. When used in part-load applications, these chillers are very reliable. In summary, here are the benefits of using air-cooled chillers:
- No cooling towers
- Better environmental stability-no water wastage
- Low maintenance costs
- Easier to operate and control-tower freezing and tower bypass absent
- Chemical costs avoided
- Water costs avoided, especially in cities
- No water problems to deal with in case of disaster
Fig 1: Air-Cooled Chilled Alongside Water Cooled (Traditional) Chiller
How do I choose between the two?
The cooling capacity is the main guideline for the choice of the chiller. Equally crucial is the balance between operating costs and capital costs. Some clients will base their buying decision on initial costs. However, a value-based option considers both operational cost and initial cost. To determine the initial cost of each option, add the costs for both contractors and equipment. For the water-cooled chiller, remember to add cooling tower. When it comes to life cycle cost, you have to consider both purchase cost and operating cost. When you evaluate each of the two chillers this way, you are able to determine its total cost. What you must note is that water-cooled chillers normally appear more valuable if you ignore first cost and water cost. However, it is only after you look at the broader costs that the true picture appears clearly.
Other alternatives: hybrid chillers
Hybrid chillers are chillers that can operate as air-cooled chillers under certain conditions and water-cooled chillers under other conditions. They are an interesting alternative for areas with a predominantly dry climate and low water availability. Also, when water availability is not constant or reliable.
It might interest you: Environmental Consideration of Chillers for District Cooling Plants
Water-cooled chiller and air-cooled chiller, the main advantages!
Chiller Startup Procedures: Chapter 2
Air-cooled Chiller Startup Procedures
After making sure that everything is fine during preliminary checks, a qualified technician begins with startup procedures. In this module, we’ll look at how to startup an air-cooled chiller. By the end of this module, you’ll be able to operate an air-cooled chiller. Skip to quiz!
Introduction
The process to start a petrol car and an electric car is not the same. Likewise, startup procedures for all the chillers are not the same. There can be slight variations in the process.
Different manufacturers may vary the components and design of a chiller. Chiller startup procedures may slightly differ depending on the manufacturer. It also depends on what type of chiller we are operating.
Recall that air-cooled chiller’s condenser is cooled by air. Air-cooled chillers use fans to blow outside air over their condenser. By this process, heat is removed from the refrigerant inside the condenser.
To startup a chiller, we first need to switch on the chilled water pumps. Switching on water pumps makes the water circulate through the chiller.
Chilled Water Pumps
Recall that water pumps circulate cold water into a building. Centrifugal pumps are the most popular and commonly used for circulating water in chiller systems.
Chilled water pumping includes two sets of pumps:
Primary pumps and
Secondary pumps.
The set of pumps that return water from a building to the chiller are called primary pumps. The other set of pumps that supply cold water from the chiller to a building are called secondary pumps.
To switch on water pumps, we need to press the ‘green’ button in the respective pump panel. For some water pumps, we just need to flip the switch to turn on them. Switching on water pumps depends on how they are connected to a power source.
After switching on chilled water pumps, we’ve to ensure that water is flowing through the evaporator. Water pressure in the pipes reveals whether the water flows through them or not.
Chiller Startup Procedure
After making sure that water is flowing through the chiller’s evaporator, an operator needs to turn on the power supply to the chiller. For that, the operator has to locate the chiller’s electrical panel and flip the main circuit breaker to the ON position.
After turning on the power supply to the chiller, the operator has to press the power button in the HMI of the chiller. It takes a few minutes to load the display of HMI.
An operator has to set the temperature and turn the chiller on in HMI. Operation procedures of mobile may vary depending on the operating systems like Android, iOS, Windows, etc. In the same way, operation procedures for chiller HMI may vary depending on the manufacturer.
Log Sheet
A chiller takes over half an hour time to stabilize all the parameters like temperatures, pressures, current, and others. So a technician should not take the readings immediately after switching on the chiller.
Taking readings in the log sheet allows the operator to analyze chiller performance by comparing it with previous readings.
Shutdown Procedure
If a technician switches off a chiller before switching off water pumps, water in the evaporator can freeze out. This happens when there is no running water through the chiller. Frozen water can even damage the chiller. So an operator has to follow the correct shutdown procedure.
For shutting down a chiller, an operator has to follow the reverse order of the chiller startup procedure. An operator has to first turn off the chiller at HMI and shut off the power supply at the electrical panel. After a few minutes, he has to switch off the chilled water pumps connected to the chiller.
After preliminary checks, an operator begins with chiller startup procedures. There can be a slight variation in the startup procedures for different chillers. A technician has to start chilled water pumps and then switch on a chiller.
Water-cooled Chiller Startup Procedures
You know how to start an air-cooled chiller. The startup procedure for a water-cooled chiller is very similar to an air-cooled chiller. As a water-cooled chiller consists of condenser pumps and a cooling tower, you need to focus on them as well. By the end of this module, you should be able to operate a water-cooled chiller. Skip to quiz!
Introduction
Recall that the water-cooled chiller’s condenser is cooled by water. The chiller’s shell and tube condenser is cooled with water. Cooling towers and condenser water pumps are used to supply water to cool the refrigerant inside the condenser.
Condenser Water Cycle
After preliminary checks, we’ve to start the condenser water cycle. Recall that the condenser water cycle consists of
Recall that condenser water pumps are used to circulate from the cooling tower to the chiller’s condenser.
To start condenser water pumps, a chiller technician has to make sure that the suction and discharge valves are open. Then he has to press the ON button on the electrical panel of the water pumps.
The device used to cool hot water from the condenser is a cooling tower. Cooling towers are large boxes designed to remove heat from water by spraying it down through the tower.
To start cooling tower fans, a chiller technician has to press the ON in its electrical panel. He has to make sure that the cooling tower fans are rotating. Cooling tower fans do not rotate if the temperature of water in the basin is within specified limits.
The cooling tower fans only run when the temperature of water in the basin is more than the set point. So the fans cycle ON and OFF to maintain a water temperature of about 85°F.
Chilled Water Pumps
The chilled water cycle is the same for both air-cooled and water-cooled chillers. Water pumps are used to circulate water in this cycle. Chilled water pumping includes two sets of pumps:
Primary pumps and
Secondary pumps.
To switch on water pumps, we need to press the ‘green’ button in the respective pump panel. For some water pumps, we just need to flip the switch to turn on them. Switching on water pumps depends on how they are connected to a power source.
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Chiller Startup Procedure
After making sure that water is flowing through the chiller’s evaporator and condenser, an operator needs to turn on the supply to the chiller and start it.
Chiller Shutdown Procedure
For shutting down the chiller, a chiller technician has to follow ‘Last in first out.’ He has to follow the reverse order of the startup procedure.
For shutting down the water-cooled chiller, a technician has to press the power button in the HMI and disconnect the power supply to the chiller. Then he has to turn off cooling tower fans and chilled water, and condenser water pumps.
BMS
In some plants, all the chiller components are connected with BMS. BMS stands for ‘Building Management Systems.’ BMS are computer-based control systems that monitor and control connected chiller components.
An operator can control all the chiller operations through BMS.
For a water-cooled chiller startup, a technician has to start
Next, he has to start the chiller by pressing the power button in HMI.
Question #1: Startup procedures for all the chillers are the same.
TRUE
FALSE
Scroll down for the answer...
Answer: FALSE
Startup procedures for chillers may vary from one chiller to other.
Question #2: Which of the following is the procedure to switch on chilled water pumps?
Pressing 'Green' button in electrical panel
Flipping the switch in the electrical panel
Turning on through BMS system
Depends on how water pumps are connected to a power source
Scroll down for the answer...
Answer: Depends on how water pumps are connected to a power source
Switching on water pumps depends on how they are connected to a power source. All the chilled water pumps do not follow the same procedure.
Question #3: In air-cooled chillers, an operator has to switch on condenser water pumps before switching on evaporator water pumps.
True
False
Scroll down for the answer...
Answer: False
This is false. Air-cooled chillers do not contain condenser water pumps.
Question #4: Arrange the following steps in a sequence to turn off a water-cooled chiller?
Switch off the cooling tower fans
Switch off the chilled water pumps
Shutdown the chiller
Switch off the condenser water pumps
1. Shutdown the chiller
4. Switch off the chilled water pumps
Question #5: A technician can control the operation of a chiller through a Building Management System.
True
False
Scroll down for the answer...
Answer: True
This is true. A technician can control the operation of a chiller through a Building Management System.
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