Finding the Right Chiller for the Job
Fuel availability, efficiency, and compressor type all play roles in buyers’ decisions
Chillers come in many shapes, sizes, capacities, and efficiencies in order to accommodate a wide array of commercial applications. For building owners looking to install new chillers or replace an existing system, the options can be daunting, but selecting the most appropriate chiller for an individual application does not have to be complicated.
Chris Opie, marketing director, Carrier Commercial, said the company offers a wide range of both air- and water-cooled chillers in 10- to 5,000-ton sizes that are either manufactured or assembled in Carrier’s Leadership in Energy and Environmental Design (LEED)-certified Charlotte, North Carolina, facility. Opie said air-cooled chillers offer a complete package with relatively easy installation at a competitive price.
“Customers have a wide variety of compression and efficiency types. Water is not needed on the condenser side, which could have been lost through evaporation in a cooling tower. The result is water savings and no need for water treatment on that loop. Customers do not need to set aside as much space for an internal mechanical room,” he said, adding that drawbacks are minimal. “It will not have the same level of efficiency as a water-cooled system, and air-cooled chillers are outside, so consideration should be applied in sound-sensitive environments.”
Climacool Corp. offers water-cooled and air-cooled modular chillers for cooling, heat recovery, and simultaneous heating and cooling (SHC) applications, said Tom McDermott, director of sales, Climacool. “Benefits [of air-cooled chillers] include not using internal building real estate and eliminating cooling tower maintenance costs,” he said. “Drawbacks include making sure the chiller is quiet enough for the outdoor location and the possible use of glycol in colder climates.”
Daikin Applied also offers a complete line of air- and water-cooled chillers for the commercial market, including the Pathfinder, Trailblazer, Magnitude, WTS Centrifugal, and Templifier lines. “The choice between air- and water-cooled chillers is dependent on space constraints, the availability and cost of water, and maintenance staffing,” said Robert Landes, product manager, positive displacement chillers, Daikin Applied. “In general, air-cooled chillers have lower installation and maintenance costs and offer higher efficiencies in certain scenarios.
While water-cooled centrifugal chillers have historically dominated the chiller market, air-cooled chiller popularity is rising as these systems have become more efficient, Landes said.
“Air-cooled chillers have a higher electrical draw, leading to higher electrical costs, but these expenses can be offset by the pump energy and water costs of the water-cooled system,” he said, adding that “the latest generation of air-cooled chillers presents an undeniable alternative in the 300- to 1,000-ton range, where larger water-cooled systems once reigned.”
Larry Kouma, director of global chiller application engineering, building efficiency, Johnson Controls Inc., said JCI offers a wide range of chiller solutions, from small air-cooled scroll chillers to large 6,000-ton water-cooled centrifugal chillers, as well as free-cooling air-cooled screw chillers to simultaneous heating and cooling centrifugal heat pumps.
“When considering air- or water-cooled chillers, there are many factors that need to be analyzed for the specific application,” Kouma said. “Sound is a draw between air- and water-cooled chillers, with air-cooled chillers typically having a higher sound but sometimes a lower impact because of their location outside.”
Benjamin Locke, co-CEO of Tecogen, said the company manufactures a range of natural-gas-engine-driven (GED) chillers primarily for commercial and industrial customers. Tecogen’s chiller products include the TECOCHILL® air-cooled RT-Series and water-cooled STx and DTx series.
“Air-cooled chillers — electric and GED — are less efficient than water-cooled types,” Locke said. “Their main benefits are that they are typically less costly to install because the cooling tower and related equipment is unnecessary, water usage is negligible, and chemical water treatment of the tower system is unnecessary.
“The pros and cons would favor the air-cooled chillers in smaller installations where building maintenance staff is less available for tower maintenance, and electricity usage is not a major factor,” he continued. “Larger chilled-water systems, where electric bills are substantial and more sophisticated operation and maintenance processes would be in place, overwhelmingly favor water-cooled chillers.”
Trane’s extensive chiller product line includes air-cooled, water-cooled, and compressor chillers, said Jeff Moe, product business leader, applied commercial HVAC, Trane, a brand of Ingersoll Rand. “Air-cooled chillers provide a lower first cost and simpler maintenance,” he said. “They also simplify the system without the need for a mechanical room, a cooling tower, or condenser pumps.”
While air-cooled chillers certainly have their place, water-cooled chillers have traditionally been more popular.
“Globally, [JCI’s] most popular chiller is the flagship water-cooled single centrifugal chiller, the [York] YK,” Kouma said. “This chiller offers a cooling capacity range of 250-3,000 ton and can be applied to many applications, from comfort cooling to process cooling.”
One of the biggest differences between air- and water-cooled chillers is their physical installation location, Kouma added. “Air-cooled chillers typically have larger footprints than water-cooled chillers, but they are located on the rooftop, where there is usually space available. Water-cooled chillers require a mechanical room somewhere inside the building and utilize space that could potentially be used for the building’s industry. Water-cooled chiller systems also require a cooling tower, condenser pumps, additional components, and a water-treatment strategy. However, because they are located inside, water-cooled chillers are safe from the outside environment and have a longer life span.”
“Water-cooled chillers are installed inside a building and are protected against the elements, which increases the life of the chiller,” Moe added. “Water-cooled chillers also provide exceptional energy efficiency. Installing a low-pressure water-cooled chiller can result in significant reduction in lifetime emissions compared to higher-pressure centrifugal chillers.”
One drawback is that water-cooled chillers can be more difficult to install than air-cooled units because they are located inside the building and require cooling towers, he said. “However, the versatility and higher capacities that water-cooled chillers deliver can provide multiple benefits to the entire HVAC system.”
In some situations, water-cooled chillers are the only option, Landes said. “They may be the only option for larger installations where there’s a lack of space or when sound requirements make outdoor air-cooled chillers unfavorable. Typically, water-cooled chillers are smaller than air-cooled units but also require additional support equipment, such as cooling towers and condenser pumps.”
Locke also said water-cooled chillers outperform air-cooled types with regard to efficiency by a wide margin, especially in larger applications. “As such, they are the preferred type — even mandated by building codes in larger buildings — in today’s carbon-conscious society.”
There are three primary types of compressors used in chillers — scroll, screw, and centrifugal.
“Scroll compressors are generally used in smaller packaged equipment, both air- and water-cooled,” Opie said. “They are relatively inexpensive but tend to be a bit less efficient than their screw compressor counterparts and generally won’t facilitate as high a capacity.”
Screw compressors fill the mid-level capacity range and are also found on both air- and water-cooled models. “They are generally more efficient than scroll compressors and are available in larger sizes,” Opie said. “The addition of variable-speed drives on screw chillers has increased chiller efficiency by a significant amount.”
Centrifugal compressors are the largest compressors, and [they] offer the highest capacity and efficiency. “They are generally only applied on water-cooled chillers,” Opie said. “Due to their capability to deliver high-capacity cooling, there is usually only one compressor per chiller. For the customer who has big, complex jobs where efficiency is important, centrifugal chillers are likely used.”
“Large centrifugal and screw compressors that are aided with VFDs [variable frequency drives] offer very good part-load efficiencies, yet do not offer redundancy,” McDermott said. “Smaller scroll compressors are now offered with VFDs to aid in efficiency and unloading. Multiple scroll compressors for chillers also aid in redundancy for the chiller.”
“In chiller applications, we are typically using positive-displacement compressors and centrifugal compressors, depending on the size and application,” Landes said. “Positive-displacement compressors are well-suited for air-cooled systems and other high-head applications. Higher-tonnage, lower head applications are ideal for centrifugal compressors.”
York chillers utilize all three main compressor types, Kouma said. “Similar to choosing between air-cooled and water-cooled chillers, the choice between the various compressor types depends on many factors, the greatest being application type. Centrifugals are more effective for medium to large cooling load requirements and complex applications. Screws are ideal for medium applications and facilities with critical temperature requirements. Finally, scrolls are most commonly used in small applications like residential.”
While compressors are a major component in chillers, Locke said chiller equipment should be selected based on the size of the load/chilling demand, efficiency, and total cost of ownership, including equipment cost, installation, ongoing maintenance, and savings generated.
“Our preference is to use the screw-type; it’s robust, highly efficient, and matches our engine speed range. This is a critical advantage for us because it allows incorporation of a variable-speed turndown strategy with a direct drive [no gears or transmission],” Locke said. “Variable-speed technology allows our products to reduce output by varying the engine/compressor rpm accordingly, which maximizes both engine and compressor efficiency.”
Moe also said building owners should focus on overall performance requirements and concentrate less on the specific type of compressor in the chiller. “It is important to remember that it is the chiller — not the compressor — that delivers the performance,” he said.
WEIGHING THE OPTIONS
When choosing a chiller — no matter what type — it’s important to take into consideration building application and location, first cost, energy efficiency, and life cycle cost in order to choose the chiller that best fits the customers’ needs, Moe said. “In the end, it’s the combination of total cost of ownership and which chiller best meets the needs of the customer’s application.”
Kouma listed many factors, including product application, building load and hours of operation, regional location, fuel source and costs, initial available investment, and annual operating cost expectations as things building owners should consider before deciding on a chiller product. Locke also listed several factors to consider, including the current cost of fuels. “Given the cost of electricity, the constraints of the electric grid, and the continuing trend of low natural gas prices, gas-engine-driven chillers present long-term economic savings for customers requiring industrial-sized chillers,” he said.
Opie said building owners need to take all factors into consideration, from deciding whether to go with air- or water-cooled systems to ensuring the equipment is installed correctly to ensure maximum efficiency and operation. “We go beyond just selecting the equipment but need to ask how they will be piped,” he said. “Parallel or series can have a big effect on overall system performance.”
McDermott said selecting a chiller that can also provide hot water for the building can help save tremendous amounts of energy. “A small footprint will enable additional building real estate to be used for income-generating operations,” he said. “Life cycle, along with total ownership costs, which include 20-plus years of servicing, should also be included when considering a chiller.”
Landes also recommended looking at the total length of ownership when selecting a chiller. “Length of ownership plays a big role, as total life cycle costs can only be determined by looking at the full length of the life cycle,” he said. “High upfront costs often result in benefits of efficiency over time, leading to a lower total cost of ownership, but that all depends on how long the chiller will be in operation at a given site. Available space, resources, and geographical locations should be considered, as well. Overall, it’s important for end users to select chillers that best align with the application at hand, based on how the chiller will operate within the system.”
Concentrating on efficiency and total cost of ownership benefits the owner and the environment, Moe said.
“According to a recent report from Navigant Research, commercial, residential, and industrial buildings are responsible for 47 percent of greenhouse gas [GHG] emissions and 49 percent of the world’s energy consumption,” Moe said. “HVAC systems are an important component in both cases, and a chiller’s environmental impact should always be considered.”
Publication date: 5/9/2016