Which chiller type is best for data centers: air cooled, or water cooled? There&#;s no single answer. HVAC system designers need to ask a lot of questions before advocating one type of chiller over another. The obvious equipment choice is sometimes over-ruled by unique project factors including the available square footage, backup power strategies, local regulations limiting power and water use, or the owner&#;s sustainability priorities.
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Ideally, data centers will consult with the HVAC company on the front end of the design process to make sure the solution meets short- and long-term objectives. If you&#;re the one making the decision on behalf of a data center, it helps to understand the pros and cons that are inherent to each type of chiller.
Capacity: Packaged air-cooled chillers are typically available in sizes ranging from 7.5 to 500 tons [25 to 1,580 kW]. Packaged water-cooled chillers are typically available from 10 to 4,000 tons [35 to 14,000 kW]. In other words, water-cooled chillers can deliver higher cooling capacity with fewer units and a smaller footprint.
Maintenance: Air-cooled chillers eliminate the need for cooling towers. Water-cooled chillers require cooling towers, which have critical maintenance demands: water treatment, chiller condenser-tube cleaning, tower mechanical maintenance, and freeze protection. Systems that use open cooling towers must have a water treatment program to prevent contaminants such as bacteria and algae. Cooling towers also evaporate water so you will need access to a large supply of make-up water to replace the evaporated volume.
Location: The pursuit of cheap power and lower taxes is changing the face of the data center industry, placing huge facilities in remote locations far removed from the users. If placed in location where temperature drop below freezing, air-cooled chillers can be easier to operate , because they eliminate the problems associated with operating a cooling tower in severe winter conditions. Cooling towers may require special control sequences, basin heaters, or even an indoor sump for safe operation in freezing weather.
Energy efficiency: Water-cooled chillers are typically more energy efficient than air-cooled chillers. The refrigerant condensing temperature in an air-cooled chiller is dependent on the ambient dry-bulb temperature. The condensing temperature in a water-cooled chiller is dependent on the condenser-water temperature, which is dependent on the ambient wet-bulb temperature. Since the wet-bulb temperature is often significantly lower than the dry-bulb temperature, the refrigerant condensing temperature (and pressure) in a water-cooled chiller can be lower than in an air-cooled chiller. The lower condensing temperature, and therefore lower condensing pressure, means that the compressor needs to do less work and, subsequently, consumes less energy. This efficiency advantage may lessen during nighttime operation because the dry-bulb temperature tends to drop faster than the wet-bulb temperature when the sun goes down.
Delivery & Installation: Most air-cooled chillers are &#;packed systems.&#; The system, including the condenser, compressor, and evaporator, is designed and configured at the factory for optimal performance and reliability, which reduces design and delivery time and simplifies installation. Water-cooled chillers have the added complexities of condenser-water piping, pumps, cooling towers, and controls.
Longevity: With the continued technology advances and growth in more data processing, the data center infrastructure needs to be able to support these advancements while delivering consistent performance. In general, air-cooled chillers last 15 to 20 years while water-cooled chillers last 20 to 30 years.
Partially, it&#;s because water-cooled chillers are typically installed indoors and operate at lower condenser fluid pressure, while air-cooled chillers operate outdoors, at higher condenser pressure.
Water conservation: Water availability, cost, treatment requirements as well as potential additional construction complexity all play a role in system selection. Since air-cooled chiller do not require water, they are often a preferred choice especially in locations where there is a water shortage, or the water is very expensive.
Water is one of two major resources data centers consume [1] . Combined, US data centers were responsible for consumption of 626 billion liters of water in , which includes both water consumed directly at data center sites and water used to generate the electricity that powered them that year. However, as the report points out, far more water is used to generate electricity that powers data centers than to cool them so chiller efficiency again comes back into consideration.
In summary, air-cooled chiller advantages include lower maintenance costs, a prepackaged system for easier design and installation, and better performance in freezing temperature. Water-cooled chiller advantages include greater energy efficiency, larger capacities, and longer equipment life. Yet, the best choice for the project may also depend on an entirely different set of decisions criterial. It&#;s important for data centers and system designers to take all factors into consideration to make sure the chiller that ultimately gets specified balances all the objectives over the long term.
[1] Sverdlik, Yevgeniy, DataCenter Knowledge, July , &#;Here&#;s How Much Water All US Data Centers Consume.&#; https://www.datacenterknowledge.com/archives//07/12/heres-how-much-water-all-us-data-centers-consume
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.
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:
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- 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!
Energy cost remains a major consideration in any powered equipment. Energy-saving measures are being implemented everywhere. While the chiller has direct impact on energy usage, there are other factors to consider. While the water-cooled chiller may be more energy-efficient, it receives stiff competition from air-cooled chiller in terms of installation cost, maintenance cost, number of equipment, and several other aspects. Most importantly, air-cooled chillers avoid water consumption so they are the ideal alternatives in areas with water scarcity or areas with cheap energy but costly water fees. Have you made your choice already? Give us a call today for the most specialized and customized attention. If you enjoyed this post, you maybe want to know different heat rejection condensing technologies.
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