The condenser is located after the compressor and before the expansion valve. These consensus standards and guidelines are developed by industry leaders with a wide variety of practical and technical/research experience, and published to define minimum values or to encourage acceptable and enhanced performance. The chiller is charged with a refrigerant that circulates throughout these components. An uncovered chilled water system will use more energy to maintain a cool temperature, as the outside air constantly warms it. Typically, towers are constructed of steel, fiber-glass reinforced plastic (FRP), wood or concrete. This in turn reduces the plant’s cooling output capacity and wastes energy. Heat exchangers are used to isolate different loops and are used in economizer systems. This delta T will affect building equipment (air handling or fan coil units) coil sizes, distribution system pumping costs, and chiller sizing and costs with associated energy costs required to produce the differential. Evaporator: Enables heat to move from the exterior water to be cooled into the refrigerant inside the component. Water loops require treatment for the prevention and control of corrosion, scale presence, and biological growth. By Randy Schrecengost, PE, CEM, Stanley Consultants, Austin, Texas, Air Conditioning, Heating, and Refrigeration Institute (AHRI), American Society of Mechanical Engineers (ASME), Building Officials Code Administrators International, ANSI/ASHRAE Standard 15-2013: Safety Standard for Refrigeration Systems, ANSI/ASHRAE Standard 34-2013, Designation and Safety Classification of Refrigerants, Guideline 22-2012: Instrumentation for Monitoring Central Chilled-Water Plant Efficiency. The chiller consists of three major components: the compressor, the condenser, and the evaporator (or heat exchanger). Groups such as ASHRAE, Air Conditioning, Heating, and Refrigeration Institute (AHRI), the American Society of Mechanical Engineers (ASME), and NFPA all have standards to review for systems, equipment, and testing requirements. Decisions regarding constant and variable system flows dictate designs typically referred to as primary/secondary (PS) and variable primary (VP) system designs. 1.Low return water temperatures. Most chilled water systems have water-cooled condensers that use the cooling tower to lower temperatures in the condenser. For the planned system, designers need to vary their selections of CHW supply temperatures along with the CHW delta T ranges to determine the best balance for each. He is a member of the Consulting-Specifying Engineer editorial advisory board. Finally, the building or buildings may not have any chillers or cooling towers, but only CHW distribution piping systems connected to a larger thermal utility network from a remote CHW central plant (CP) arrangement. All of the related building system codes—Building Officials Code Administrators International (BOCA) and International Building Code (IBC )—and system components such as piping (ASME B31), ductwork (SMACNA), motors and generators (IEEE, NEMA, UL), and other codes and standards are listed for reference. For more information, visit www.daikinapplied.com. Selecting a CF versus a VF system requires many considerations during the design effort. Pressure that’s too low may prevent circulation to high level air handler coils or pump cavitation. A complete optimization of a plant must evaluate the efficiency of the entire CHW system and operate all the individual components (chillers, cooling towers, pumps) at various levels to optimize the overall CHW system operation. Older pneumatic systems employ air compressor/driers, which require specific routine service. Chilled water systems are frequently installed in large buildings, stadiums or facilities, where fire safety is always a key requirement. as well as the pressure class of all the distribution piping, fittings, and valves within the system. To sustain efficient and reliable operation, a building owner who relies on a chilled water system would benefit from a professional service technician’s advice and eye. What Are the Components of an HVAC Chiller? Developing and executing a service schedule plan will help minimize unscheduled and costly shutdowns, while safeguarding the investment in equipment. The building’s piping distribution systems may or may not have a pump (typically identified as a secondary or tertiary building pump depending on the system) within its structure. A typical chiller uses the process of refrigeration to chill water in a chiller barrel. (Figure 5 is a parallel chiller arrangement.). Chilled Water Air-conditioning System :-Systems that employ water chillers are commonly called chilled water systems. ANSI/ASHRAE Standard 34-2013: Designation and Safety Classification of Refrigerants. The type of CHW system designed and installed and the amount of the CHW required for these cooling loads will be a major component in the overall building energy usage. All chillers have an internal sequence they use to run, and a series of safety sequences to prevent inadvertent damage while starting or running. connecting the chiller to the airhandlers, and the seawater system. Some buildings may have more than one CHW loop inside its walls. In both single-chiller and multiple-chiller arrangements, the CHW loop can be either constant flow or variable flow (which must remain above manufacturer required minimum flows). Coils are part of an air handler unit, which also contains air filters, fans, mixing boxes/dampers, and other air handling devices. The CHW portion of the system circulates and flows between the chiller and the building loads through pumping by the CHW pump (although dependent upon the system, usually referred to as the primary pump), and can be operated as constant flow or variable flow. Colder supply water means higher compressor horsepower costs. Chillers – Main components Condenser:. Furthermore, ASHRAE 90.1 requires various efforts such as pump pressure optimization where pump control setpoints are varied due to control valve positions in the system, and CHW temperature reset, which uses feedback from the building control valves and outside air temperatures to reset the CHW supply temperature upward when available to reduce chiller loads. Low delta T syndrome occurs when a design CHW temperature range is not maintained. In addition, ASHRAE also published Guideline 22-2012: Instrumentation for Monitoring Central Chilled-Water Plant Efficiency, which helps designers better understand how to control CHW plants, and has recently developed a District Cooling Guide – 2013 under the auspices of ASHRAE Technical Committee 6.2, District Energy, which does an excellent job of covering items mentioned later in this article. In both arrangements, one or both chillers may be on variable speed drives (VSDs) and the CHW, and even the condenser water, loop can be either constant flow or variable flow. Condenser water transfers the unwanted heat load removed by the chiller and the chiller’s compressor work (heat of compression) to the cooling towers. Regardless of whether the design is for a new chilled water (CHW) system or a modification to an existing system, an early review of codes, standards, and regulations is necessary to allow for an expedient design and avoid conflicts that will cost time and money to resolve. For reference, the typical condenser water system is considered an open loop, but it can be closed dependent on the heat rejection equipment used. Table 6-1 Chilled Water Distribution System ..... 6-3 Table 6-2 Advantages and Disadvantages of Primary-only vs. Primary-secondary ..... 6-5 Table 6-3 Impact on First Costs and Energy Costs of Chilled Water The plant room comprises of all the important components of the chilled water air conditioning plant. Pressure regulator stations maintain water loop pressure and air separators remove unwanted air from the chilled water. Another term for this type of arrangement that is becoming more common is a district cooling plant (DCP) that also serves a localized campus, whether in a college or university setting, an industrial complex, or large urban mixed-use site. A chiller provides consistent temperature and pressure to your industrial process. Typically these central CHW plants serve multiple buildings of various types ranging in function or use, size, construction materials, age, and cooling loads. The water absorbs heat from the condenser and the temperatures rise to 35°C or 95°F. ily chilled water and condenser water system piping system design, it is important to understand the evolution from 1-pipe into the other three systems, all of which are used for heating as well as cooling. Key system components include chilled and condenser water pumps, cooling towers, heat exchangers, and hydronic specialties including water pressure regulators, air separators, and chemical feed pots. Vapor-compression chillers have four main components: Compressor: Pumps refrigerant. Every CHW plant will experience low delta T at some point during its continued operation. Local, state, and federal codes and regulations will dictate permitting requirements that affect the location of buildings and equipment (central plants, cooling towers, buried piping systems), fuel handling and storage, environmental emissions and noise, water quality, and safety items. As its name suggest, this system makes use of water as its secondary refrigerant. The fluid circuit is typically comprised of a fluid reservoir, a pump, filters, and a heat … At the cooling tower, the cooled water enters the condenser at 29°C or 85°F. In a series chiller arrangement, the CHW flow will go through both chillers in series and the water pressure drop is additive. In this case, the CHW will flow in parallel paths through both chillers and will generally experience similar pressure drops. This chilled-water is then circulated through the entire building by the use of a pump. When designing new or retrofitting existing CHW systems, the interaction between all building loads as related to outdoor air (OA) ventilation requirements, and the energy needed to condition that amount of airflow, along with the internal building’s return air (RA) loads and any other process heat loads, should be part of the system considerations so all the equipment can be sized and controlled properly to account for all the energy impacts, including the energy transfer for hydronic system preheat or precool opportunities. These chillers can be designed to operate in series or parallel modes. Water is cooled to a predetermined set-point that is set within the chiller itself. For water-cooled chillers, a condenser water loop is necessary, and always operates when the chiller is energized to operate. The designer should become aware of the various advantages and disadvantages for either scheme, which include: central plant operators’ familiarity with their different operational modes, different size pump motor requirements, different capital investment requirements for infrastructure, and “low delta T syndrome.” See Figure 5 for a schematic that shows a proposed PS CHW system; Figure 6 is a schematic that shows a possible VP CHW system. 4. Motor-pump shaft alignment is important and should be checked periodically as heavy piping and supports may shift over time. Learn design basics for CHW systems to meet a distribution loop’s load requirements. A chiller uses a vapor compression mechanical refrigeration system that connects to the process water system through a device called an evaporator. While they require minimal attention, a regular check of expansion tanks and air separators is wise. Most chiller control sequences are straightforward and easy to use for the operation of one or more chillers within a plant. In large building and facilities, chilled water-cooling systems can yield many advantages, including refrigerant and maintenance containment, energy efficiency, and low installed cost. Two of these handbooks, Fundamentals – 2013 and HVAC Systems and Equipment – 2012, contain several chapters filled with information and basic criteria needed to design CHW systems. Chilled water systems are refrigeration units. He has extensive experience in design and project and program management at all levels of engineering, energy consulting, and facilities engineering. This water is pumped through chilled water piping throughout the building where it will pass through a coil. This is very valuable for any designer or engineer beginning a new project, as these resources are updated every 3 or 4 years. The larger CHW central plant that provides the buildings with CHW may have chillers in a parallel or series arrangement, and may have pumps (primary and/or secondary) located within the CP building. There are still some older systems where the secondary loop is also constant volume. Chillers can be considered the heart of the chilled water system. Fan motors, gear or belt drives, and water make-up float assemblies all require routine maintenance and inspection. Chiller designs differ, depending on the building or industry they are installed in, and the temperatures required. Controls are also critical to the system because they operate water valves, control set points and schedule equipment. Emphasis is often placed on the chiller since it is the most visible and typically the highest energy element of a chilled water system. A CHW plant’s output capacity can be defined by the following equation for a water-only system: Because load is directly proportional to flow rate and delta T, a change in delta T will require a change in flow rate for the same load. There are two common configurations for CHW plant pumping schemes that will work with the selected CHW equipment to deliver the CHW to a building or group of buildings: In the PS scheme, the primary CHW loop is typically constant volume flow while the secondary loop is variable volume flow. In large building and facilities, chilled water-cooling systems can yield many advantages, including refrigerant and maintenance containment, energy efficiency, and low installed cost. Chillers have many uses, from bringing the temperature down in an ice hockey rink, to cooling large buildings where low temperatures are essential, such as food processing plants and petrochemical factories. Water is chilled and sent out through the chilled water pipes to … Because cooling towers evaporate large amounts of water with some drift to the atmosphere, control of biological matter is also an important health issue. ANSI/ASHRAE Standard 15-2013: Safety Standard for Refrigeration Systems is the reference standard for “machinery rooms” that typically house the larger equipment (i.e., chillers, pumps) necessary for a CHW system. Search Products And Discover New Innovations In Your Industry!! 5.Chiller performance is reduced. Drain pans and lines also need to be cleaned of accumulated biological growth and dirt to sustain proper indoor air quality. How Chilled Water Air Conditioning Works. While designing a chilled-water system, a myriad of decisions must be made. (See Figures 3 and 4 for schematic arrangements of a larger central plant.). And the selected delta T will also affect a building’s air handler coils regarding flow rates and supply air temperatures. Purpose of a chilled water system The purpose of a chilled water system is to provide cold water to air-handler equipment for the purpose of cooling supply air to control space temperature. An independent, stand-alone single chiller system type is relatively easy to design and operate, but even though the first cost is less, this system is typically the least energy-efficient design for buildings. The coolant is then pumped through the process, extracting heat out of one area of a facility (e.g., machinery, process equipment, etc.) To read similar Cooling System Assessment articles, please visit www.coolingbestpractices.com/system-assessments. Maintenance issues for the larger chilled water system, including those at the component level, may indeed originate at the chiller. 1-Pipe Systems A 1-pipe water distribution system is a system that has a one main pipe looping around the building and then returning. Coils are commonly constructed of copper tubes and aluminum fins requiring routine service such as air filter replacement and fin cleaning. Fouled water and scaled pipes inhibit heat transfer at the chiller and cooling coils. Randy Schrecengost is a project manager/senior mechanical engineer with Stanley Consultants. CHW systems are all designed for a differential temperature or delta T between the CHW supply and return water between the chiller and the building loads. In a very broad sense, a CHW system consists of the following components: A heat absorption component such as a chiller (or evaporator) A compressor in a refrigerant cycle A heat rejection component such as a cooling tower (or radiator) … it—have to do with chilled water systems? The design of these DCPs must take into account the diversity of all loads throughout the area they serve including when the different peak loads will occur. SPX Appoints Executive Officer and President – Global Cooling, Carrier AquaEdge 19DV Chiller Line Expanded to 350 Tons, Vaisala Introduces HUMICAP Humidity & Temperature Probe, Delta T Systems Introduces the Compact Eco Series TCU. Yet, if you look beyond the flanges, there’s an opportunity to improve delivery of chilled water to the airside or process loads and maximize system efficiency. The extensive support system can often impact the chiller’s operation and are not always immediately apparent without digging deeper. The system’s CHW flow can be controlled from static pressure, which provides some reliability but has limited flexibility for operational changes, and can waste energy in over pumping. This standard illustrates minimum efficiency and control systems requirements along with commissioning for building envelope, HVAC, power, lighting, and other equipment, all of which is included in a CHW system design. ASHRAE Standard 90.1-2013: Energy Standard for Buildings Except Low-Rise Residential Buildings, The world’s largest CHW plant: Pearl of Qatar, Answers, details about ASHRAE 90.1 Addendum ch. Control sequences are a key element in achieving any energy management and savings goals. The compressor is of open type and can be driven by the motor directly or by the belt via pulley arrangement connected to the motor. The use of two or more chillers with part load capacity will provide more opportunities to improve the CHW system part-load performance and help reduce energy consumption, and can greatly assist in providing redundancy in the design. As with any design, the designers of a CHW system should consider various options and equipment through discussions with the owner, and recommend one or more of these options to meet the project goals and performance requirements. From the early years of HVAC design, the use of CHW to transfer heat from areas of higher loads (e.g., building loads at air handler coils, or industrial equipment loads at heat exchangers) to a condensing water loop or a refrigeration system for heat rejection has been successful. The first steps to operating a highly efficient chilled water system is understanding what’s installed, how it operates, and what the right service plan approach is to optimize performance over the full life of the equipment. Designers should select a chiller at a higher part load efficiency to maximize energy savings based on the larger run hours at part load. The CHW pumps will increase pressure by raising the suction pressure at the pump by the total dynamic head of the system. Tower Tech is a cooling tower manufacturer based in Oklahoma City. Service requirements across all types of cooling towers are consistent. It is not as easy if the chiller plant is part of a campus environment, although decoupling the central plant control from any building-level control would allow the plant to operate as it needs to while the buildings all operate separately. The chiller is the section of the system where an exchange of heat occurred between the water that goes to the building and the evaporator. To arrive at a final design, the design team must solve many problems. Chiller. The 2013 ASHRAE Handbook-Fundamentals Chapters 18 and 19, and ASHRAE 90.1 provide methods and guidelines for developing HVAC load calculations and building energy modeling. As mentioned earlier, ASHRAE has developed numerous sources of information for CHW systems that can be used as resources for the designer. Fundamentally, the function of the chilled water system is to transport the cooling fluid from the chillers, to the load terminals and back to the chillers to maintain the thermal envelope. Chiller. Figure 6 shows a large 1450-ton chiller, which is one of three in a parallel arrangement. Instead of a wasteful, single-pass-through system, a chiller recirculates the cooling water. as it flows back to the return side of the process water system. Designers should research and become familiar with this phenomenon but realize low delta T is a symptom of problems on the load side at the buildings and possible overpumping at the plant on the CHW loop (see Table 3). Dirty coils can significantly curtail efficient heat transfer and hike energy use since operators typically must lower chilled water temperatures to overcome the reduction in heat transfer. Depending on the size of the building and the related cooling loads necessary to cool and dehumidify the building’s airstreams or other processes where some form of cooling is needed, the CHW system may have more than one of the larger components mentioned (chillers, cooling towers, pumps), and may be independent from nearby surrounding buildings. The VP scheme, sometimes called direct-primary, can be either a constant or a variable volume flow system. Chilled water pumps deliver the cold water to the building/process loads and then carry the heated water back to the chiller for re-cooling. Expansion tanks within a closed loop system will act as the point of constant pressure and be considered the reference pressure for the system, and will also allow for the expansion or contraction of the CHW due to thermal and volumetric changes in the closed system. Either condenser water (CW) piping (for a water-cooled system) or refrigerant based piping (for an air-cooled or evaporative-cooled distribution system) to move the separate fluid systems between the respective components. ASHRAE has numerous technical sources of information including a series of four handbooks that are updated every 4 years. These include the compressor, condenser, thermostatic expansion valve and the evaporator or the chiller. Larger heat exchangers are field cleanable, yet that can be a time-consuming task due to the complexity of the procedure. The typical system delivering CHW from a chiller or the entire central plant is a closed loop hydronic system, and this means that the starting point within the system is the same as the ending point within that system. Some form of hydraulic modeling of a building or thermal utility distribution CHW system should be completed for any design because of the relationship of the volumetric flow rate to the pressures that will be experienced in the system. ASHRAE’s various technical committees write standards and guidelines to establish consensus for such items as: methods of testing and classification, design, protocol, and ratings for systems and equipment components of those systems. Chillers can be either air- or water-cooled. Among the many important items to consider regarding these system designs are any system constructability and budgetary constraints, system operability, operations and maintenance costs, and energy consumption costs. However, these systems are commonly being replaced because the technology and efficiencies of the chillers have increased, as have the energy costs associated with operating the distribution system. article titled, “Evaluating Chilled Water Cooling System Components,” reviews water pumps, cooling towers, heat exchangers, controls and hydronic specialty components. ASHRAE Standard 90.1-2013: Energy Standard for Buildings Except Low-Rise Residential Buildings is the reference standard for energy efficiency. Closed chilled water system loops are not exposed to the atmosphere, but still need inhibiters to control corrosion. Understand key equipment and its integration to improve energy efficiency. This is because chillers are normally selected within a small percentage range of the calculated design process loads of the building (or buildings) they serve. They include many pieces of equipment and the piping required to connect them, including pumps, heat exchangers, compressors and tanks. 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