For the vast majority of chilled water plants, the energy efficiency of the plant can be maximized by varying the pumping capacity to match the required thermal load. Essentially, the building owner gets heat energy at virtually no cost because it is a byproduct of the cooling process. A constant flow system is the simplest chilled water distribution scheme. To counter this overcooling, terminal reheat is required. Although the typical thermal storage medium is water (or ice for low-temperature chilled water systems), recent research from the University of California, Berkeley’s Center for the Built Environment has shown significant flexibility in mass-radiant cooling systems to support load shifting through controls manipulation alone and the inherent thermal mass of the slab. What varia… When specifying a heat recovery chiller, it is important to consider the baseline heating and cooling load profiles of the building to properly size the heat recovery chiller. In the summer, the two-pipe HVAC system is manually switched to cooling, and in the winter, the system is switched to heating. Select chilled water distribution . The 4-pipe water distribution system is actually two, 2-pipe systems in parallel; each system consisting of its own supply and return main. This chilled-water is then circulated through the entire building by the use of a pump. The waste heat that is removed from the chilled water loop is captured in a hot water loop that is used for heating. The first strategy is a chilled water supply temperature reset control sequence (ASHRAE 90.1-2019 Part 18.104.22.168), which should be deployed on all waterside economizer systems. To accommodate this lower water temperature, terminal reheat systems can be designed to operate with 110°F water when specified with higher capacity, multiple row heating coils. This can result in significant increased hours with full economizer, especially in buildings with high-performance enclosures and most buildings in the shoulder seasons, when envelope loads are low. Chilled-water pump; 17 Distribution piping; 18 Pumping arrangements; 19 Condenser-Water System ~ Cooling tower ~ 20 Condenser-water pumping arrangements; 21 Unit-Level Controls; 24 Application Considerations. The next level of optimization is through standalone software packages, which operate in the background using proprietary algorithms and work in conjunction with the building management system. These pumps are a very cost-effective way to limit the number of field mounted sensors and controls while minimizing pump energy usage. Figure 1: Layout of the chilled water distribution system. This inward passage of water driven by vapor pressure differences develops any time the cold/low-temperature or chilled water system (normally at 4.4°C to 7.2°C (40°F to 45°F) operates below the local dew point, which for humid coastal areas is a regular condition. endstream
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<. Figure 2: In this waterside economizer system diagram, when the economizers are optimized alongside each of these influencing systems, then the potential benefits of waterside economizing increase. The heat is then rejected from the condenser water loop to the outdoors by a cooling tower. Changing the three-way control valves to two-way control valves and evaluating the use of two-way pressure independent control valves will solve many of these distribution issues. This system is superior to other smaller cooling systems in that it provides highly reliable chilled water service on a continuous year-round basis. 3277 0 obj
The best results from optimization are achieved when all of the system equipment is sized appropriately to meet the actual chilled water demand and not over or undersized. It is common that equipment in older chilled water plants were selected based on the peak load and not the total operating range of the plant. Optimization is also appealing because it tends to prolong the life of the installed equipment. Chilled water is distributed to campus buildings through a single networked system consisting of parallel supply and return piping laid out in a grid configuration. Maximum and minimum chilled water supply temperatures. The different types of pipe used in hydronic systems. The most common types of chiller plant pumping arrangements are constant flow, primary-secondary variable flow and variable primary flow systems. There are different levels of optimization currently being applied in the industry ranging from simple sequencing of the equipment to the installation of electrical usage metering to enable system adjustments in real time through software. The system uses 3-way control valves at air handler coils that allow some water to bypass the cooling coil during part load conditions. 16 Chilled-Water Distribution System. Minimum flow rates must also be maintained within the condenser section of the chiller. Demand Flow is an HVAC optimization solution that reduces energy costs and ensures ongoing operational efficiency, with healthy financial returns and long-term value. Establishing a baseline is an important aspect of this process especially as it relates to return on investment as there is a premium associated with chilled water plant optimization. The water leaves the chilled water evaporator at 45°F or 7°C. The existing chilled water coils were likely not selected to perform with the 2019 edition of ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings required 15°F temperature difference between entering and leaving water temperature. The chilled water distribution system includes more than 6 miles of are direct-buried, ductile iron pipes up to 30 inches in diameter. Instead of operating in the 42°F to 44°F range, these systems tend to operate around 54°F to 58°F and supply radiant cooling systems, chilled beams or sensible only DOAS fan coil boxes. Next, we’ll talk about a couple of different chilled water system configurations. When the water has been used and has warmed, it is returned to a chiller plant to be chilled again. Terminal equipment, proposed or installed. While six-pipe, dual-condenser heat recovery chillers are available, this discussion focuses on four-pipe, single-condenser heat recovery chiller applications. Chilled Water Cooling Systems How centrifugal pumps operate. Operating the variable primary pumps in parallel to match the optimum efficiency point on the chilled water distribution system curve is an effective way to minimize the system pumping energy. For example, a centrifugal chiller with multiple compressors having the ability to stage them on and off based on operating at the lowest kilowatts per ton possible. As a result of minimum air change rates, rooms are often provided with more air than is needed for cooling the space. The real beauty of waterside economizers is on display when they are paired with mild temperature chilled water systems. The greatest impact on the cost of a large central chilled water system is provided by the temperature spread between the supply and return, usually termed the Delta T The central system designer seeks to achieve a large Delta T 14 [degrees]F or 16 [degrees]F are common. Minimum flow rates are important to maintain in the cooling towers to ensure that the cooling tower fill remains fully wetted. In a two-pipe system, there are only two pipes connected to the air handlers, chiller and boiler. Significant pressure drop differences in the chilled water piping distribution loops. Waterside economizer uses the evaporative cooling capacity of the cooling tower to produce cold water that is exchanged through a heat exchanger to provide chilled water that offsets the need for mechanical cooling. An important aspect to note is owner and plant operator buy-in to the software to allow it to operate as intended. At each building the chill… Typically, heat recovery chillers are designed to provide hot water for space heating at 105°F to 110°F. Chilled water is supplied into a header at point A at a pressure of 300 kPa and a temperature of 5 ºC. When considering a heat recovery application, always select the lowest practical heating temperature to meet the needs. Understanding the actual building load so that equipment can be right-sized is critical. A variable primary flow pumping system is typically the most energy-efficient system and provides the benefit of fewer pumps in the system. This typically involves the installation of electrical energy usage meters for real time data collection in determining equipment sequencing as well as implementing predictive actions based on the software algorithms. However, because of the role the chilled water system plays in thermal comfort of the building occupants, those potential energy savings strategies are not always pursued in favor of traditional approaches. Learn about the impact of pumping schemes and plant optimization of chilled water systems. Space heating systems are normally designed at 140°F supply water temperature. Adding ceiling fans into the space, which with modest air-speeds support thermal comfort even up to 78°F room setpoints may increase that load shifting flexibility even more, potentially allowing 100% of cooling hours to be met with full waterside economizer. You will develop an understanding of the basic concepts of hydronic system operation and design including piping systems, pipe materials and fittings, centrifugal pumps, terminal units, expansion tanks and water chillers. Underground chilled water piping systems are typically used to cool buildings. For example, referencing strategies in ASHRAE 90.1, this could mean using pumps with integral VFDs for a variable flow system or using chilled water reset in a system with integrated waterside economizer as described in the section below. The load study for a new building is easier to achieve. endstream
Search Products And Discover New Innovations In Your Industry!! These plants produce flow chilled water which is distributed to the campus via an underground distribution system. The system incorporates “closed loops” to allow feeding areas from two directions. That flexibility has shown that in some instances, active cooling into the slab may shift upward of 12 hours separation from the time of peak load in the space, while still keeping the space operative temperature with the comfort range expected by ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy.
Chilled water distribution. There are several factors to consider including: The impact of these criteria will guide the chilled water plant production decisions and the most efficient pumping arrangement. Great for Condos, Apartments an… Like all heating, ventilation and air conditioning system selections, it is important to understand the impact on all systems together, including building enclosure, building massing, load profile and occupant comfort expectations. The distribution system piping ranges in size from 6 inch up to 36 inch. Hospitals typically have large variable air volume air handling units that provide cooling and dehumidification and deliver air at a temperature of approximately 55°F. This increases the number of full economizer hours and will further reduce the operating hours on the chillers and their corresponding energy use. A standard water-cooled chiller operates to remove heat from a chilled water loop and transfers that heat into a condenser water loop. Heat recovery chillers can provide energy savings in facilities where there is a need for simultaneous heating and cooling, such as hospitality and health care facilities. 6. Designing chilled water systems Typically used for cooling and dehumidifying a building’s air, chilled water (CHW) systems circulate it throughout a building or campus complex. Though chilled water distribution systems vary enormously in size and configuration, the problems associated with these systems are quite universal: low delta T, inability to fully load chillers, inadequate flow in sections of the distribution system, and excessive pumping pressure requirements at peak cooling demand conditions. A traditional chilled water design approach in a building with high internal loads, such as an office building results in a low percentage of operating hours that can be used for 100% economizer mode. Once the chilled water distribution parameters are understood, the chilled water pumping arrangement can be designed. There is the obvious reduction in energy usage, which directly translates to dollars saved with the utility company. Campus Chilled Water System:UNK, UNL and UNO campuses are served by central utility plants operated by the Utility and Energy Management (UEM) department. The expense to maintain the BTU’s, or to chill the return lines are far higher than the cost to reheat return lines on a heated system. 5. Pressure drop is overcome by the use of a chilled-water pump. The distribution system can pump up to 100,000 gallons of chilled water per minute through more than 22 miles of underground piping and 150 individual building bridge systems. Chilled-water distribution system Chilled water is circulated through fixed piping —most commonly steel, copper, or plastic —that connects the chiller with various load terminals. This would happen because three pumps operating at a lower frequency may use less energy that two pumps operating at 60 hertz. Existing or proposed design delta T, or lower water return temperatures. Chillers and constant flow primary pumps are enabled in pairs, making the primary flow rate a step function. These can be in many forms when they are connected to a chilled water distribution system. What this means for a chilled water plant, as dictated by ASHRAE Standard 90.1 and the International Energy Conservation Code, is controlling the associated equipment, whether new or existing, to operate as efficiently as possible and ultimately consume the least amount of energy, while meeting the building needs. Equipment manufacturers are also starting to include aspects of optimization into their onboard controls as well. Total chilled water distribution system volume is 1.5 million gallons +. † Meet its needed evaporator flow requirements independent of other chiller operation. The benefits of waterside economizers increase with warmer chilled water supply temperatures, so they pair especially well with hydronic systems such as radiant cooling, chilled beams and dedicated outdoor air system fan coil boxes, where air-side economizers are either not applicable or not feasible. Select condenser water distribution . One pipe is used for the water loop, and the other pipe is used for the condenser loop. One system is always distributing chilled water to the units and returning it to the chiller. Figure 4: In this example, 80% of annual hours can have the cooling load met with waterside economizer when combined with close approach cooling towers. To help with infection control, clinical spaces within health care facilities are required to have minimum air change rates. Upgrading an existing constant flow or primary-secondary flow chilled water plant to a variable primary flow chilled water plant that is connected to a distribution system with three-way valves would result in a constant flow system with a low delta T, for a large range of the chilled water plant’s operation. Figure 1: At the Ford Field chiller plant in Detroit, evaluating the existing chilled water coils at varying chilled water supply temperatures is required. As system load and flow increase, the excess flow rate (from supply to return) in the bypass line decreases. For example, in a scenario where two chillers are operating, the software may sequence three chilled water pumps online where traditionally there may only be two. For many buildings, the chilled water system provides tremendous potential for creating energy savings. Alterations in the existing distribution system are required in many chiller plant upgrades and they should not be overlooked in the proper design of an upgraded plant. 3. HRCs can be used to meet or supplement the local building heating requirements while utilizing the benefit of the simultaneous cooling to cool the building or export this by-product to the campus chilled water distribution loop. The University’s three energy systems, Chilled Water, Cogeneration (producing steam and electricity) and Electric Distribution, are closely interrelated and operate together for optimal efficiency. Currently, some controls manufacturers integrate plant optimization into their standard control package. The header supplies four pipelines that go down the mine with draw-off points at depths of 1000 m and 2000 m. In this scenario, the BMS monitors all cooling valve positions. Chilled water can also flow directly to terminal units located in the occupied space. When the pumping capacity matches the thermal load, it increases the temperature difference between the chilled water supply temperature and chilled water return temperature. To truly understand the benefits of chiller plant optimization, it is recommended to complete a baseline analysis of the existing system or new installation to help validate the benefits to system performance. Courtesy: SmithGroup. Campus-Wide System:A campus-wide central chilled water system has been developed in recent years and is being expanded to serve additional cooling loads as need arises and opportunity affords. This is known as the chilled water system delta T, and the higher the delta T, the lower the pumping energy required for the system. Here, a set of constant speed pumps distributes fixed quantity of water at all times and the temperature varies to meet the load. Chilled water is distributed at 42 degrees F to more than 80 buildings from the Power Plant and the North Chiller Water Plant to provide the cooling for campus. Search Products And Discover New Innovations In Your Industry, Scott Battles, Jonathan Hulke and Stet Sanborn. h�b```��,�R� cb�FdQ&!EAEQ6�����m�uhp0�������I3�!��s�O��(i����^`����e|%��Y����/dM0��fg|}�g�ʄٳ�3%J}�u�sa���+����F��G�����.��V�d�j r��F��o\SW=U�(�����cG!��H;G�s���!%�Ӈ�.t�(pqzx$���c�P��]FIMFP`G鴲��@m3 Heat recovery chillers can be very effective in health care facilities. The distribution pumps (primary pumps for the p-only system and secondary pumps for the p-s system) are fitted with variable speed drives (VSDs). As radiant systems, chilled beams and DOAS fan coil boxes are designed for sensible cooling only, they do not require low-temperature chilled water and in fact don’t want chilled supply water temperatures which could result in condensation. Even with the potential concerns, variable flow in the condenser water system is still a viable option and can further reduce the overall kilowatt per ton of chiller water produced throughout the entire range of plant operation. By Scott Battles, Jonathan Hulke and Stet Sanborn, ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings, University of California, Berkeley’s Center for the Built Environment, ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy, Weekly merger and acquisition update: January 15, 2021, Top 5 Consulting-Specifying Engineer articles: January 8-14, 2021, Understanding changing data center metrics, Ultra-low temperature storage considerations for COVID-19 vaccines, Case study: University science building control systems, Neurologic institute building trying to redefine patient care. Scenarios like this can be difficult for operators to accept after operating in a more traditional way for many years. When waterside economizers are optimized alongside each of these influencing systems, then the potential benefits of waterside economizing only increase (see Figure 2). Variable flow condenser water systems are also a way to reduce the total pump energy used in the chilled water plant. Chiller plant design can have a significant impact on the ongoing operating costs of a building. system; 4. 3289 0 obj
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Two-pipe HVAC chilled water systemsare reasonably energy efficient. Evaluating the existing chilled water coils at varying chilled water supply temperatures is required to determine if the coils must be replaced or what temperature differences can be achieved with the existing coils (see Figure 1). Strategies such as chiller plant optimization, water side economizer and heat recovery chillers can create positive results by improving overall plant efficiency and reducing energy costs. 3300 0 obj
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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. The Designer Bypass line … Select cooling tower type, speed control option, efficiency, approach . This could also include using control sequences such as pump differential pressure reset and optimum start controls for systems using setback control. The district cooling system is comprised of four major subsystems; the production system, the distribution system, the building bridge system, and the building cooling system. This is typically limited to inputting project specific equipment performance data into the control software, which will, in turn, sequence a specified number of chillers, cooling towers and pumps based on operational “sweet spots” to meet building load. �@�:�Y\7)M�p�PR����ɦ�](h�cF�S���B�m-��]~;8:=�()��Dp4)�,r�XrtJKX0�PС�
���"@m�L Selecting the lowest practical heating temperature reduces the chiller lift and results in the chiller operating more efficiently. 1. The other is distributing hot water to the units and return- ing the water to the boiler. Select chilled water temperatures, flow rate, and primary pipe sizes; 3. The chilled water distribution system must be evaluated before a new chiller plant design or existing chiller plant upgrade can be finalized. J ��@����*�;��� (������L�(�W����>��X�@�n�lx���`�@`[�̅�9W��$�~=�aa���Đ�`� ����Y[��+3,��2�=��l&7�t7����``���X���K��+�B� ^��I
Select condenser water tempera-tures, flow rate, and primary pipe sizes; 5. system; 2. For maintenance personnel, this often means adhering to specific switch-over dates on the calendar. As soon as all chilled water valves are less than 100% open, the BMS will linearly reset the chilled water supply temperature upward until the first valve must open 100% to satisfy the local load. Care must be taken when reducing the flow in a condenser water system to avoid suspended solids from settling out in the system. This 400-ton system includes two water-cooled chillers piped in parallel. Chilled water: Chilled-water distribution systems transport water used for air conditioning from the chiller to the air handlers, where the chilled water flows through coils in the ventilation air stream. In climate zones without significant year-round high relative humidity, integrated waterside economizers can provide significant energy savings by reducing the hours of operation of chillers and by reducing the chiller load during hours when 100% economizer isn’t possible. Optimization is the action of making the best or most effective use of a situation or resource. Additionally, waterside economizer systems pair well with thermal energy storage systems, especially mild temperature systems serving sensible only cooling systems. For both options, the distribution sys- tem is variable flow using two-way valves at cooling coils. Chilled water is centrally produced and distributed throughout the campus, and this district cooling system shall be utilized wherever possible. Although cooling tower cost goes up as the cooling tower approach decreases, each project team should evaluate the cost benefit analysis to select close approach towers in the 2°F to 3°F range. 1. facilities have plants that make chilled water and distribute it to air-handling units (AHUs) and other cooling equipment The chilled water produced reduces the load on the central chillers. The waste heat that is normally rejected to the outdoors can be recovered and used in applications where heat is required, such as heating domestic water or terminal reheat. So, the elevated chilled water temperatures are ideal. Those plants were often designed as constant volume systems, so a load study that considers the actual program of the building is recommended before sizing a plant upgrade and/or replacement. Thermal energy storage systems maximize the use of nighttime charging of the storage tanks when outside wetbulb temperatures are at their lowest, allowing for low cost chilled water production using nighttime off-peak power rates. Chilled Water Distribution*. From an owner’s perspective, implementing some form of chilled water plant optimization can be appealing for a couple different reasons. Chiller. Courtesy: SmithGroup. Increasing the temperature difference between the chilled water supply and return takes full advantage of the total capacity of the chillers; variable primary flow systems typically have a lower first cost than primary-secondary variable flow systems. 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 It is possible to design chilled water systems that meet the thermal comfort demands of the building and achieve operational and energy efficiencies that can significantly decrease ongoing operational costs. After completing the course, you should know: 1. The chilled water is generated and circulated in the primary side, the secondary loops will pull chilled water out of the header to cool the building and then dump the warm return back into the header. During winter operation, the heat recovery chiller can operate to meet the process cooling loads of the hospital while also providing hot water to reduce the demand on the boiler plant. temperature. 7.4 Chilled Water Distribution System . A heat recovery chiller is designed to provide both heating hot water and chilled water. The district cooling system is comprised of four major subsystems; the production system, the distribution system, the building bridge system, and the building cooling system. How Chilled Water Air Conditioning Works. Typically, these systems are working in parallel with a DOAS system, which is handling dehumidification with a direct expansion system or standalone low-temperature chilled water coil supplied by a separate system. More air than is needed for cooling the space water at all times and the temperature varies to a... Understanding the actual building load so that equipment can be designed forms when they are with! Cooling coil during part load conditions from a chilled water can also flow directly to terminal located! In Your Industry, Scott Battles, Jonathan Hulke and Stet Sanborn a pump with mild temperature serving! For space heating at 105°F to 110°F for heating operator buy-in to the units and return- ing the loop... 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System flow rate ( from supply to return ) in the cooling coil during part load.! Reduce the total pump energy usage 3-way control valves, installed or proposed design delta T, or lower return. Over 80 % of hours in Oakland, Calif. ( see figure 4 ) owner and plant optimization of water! Figure chilled water distribution system ) there is the obvious reduction in cooling load on the calendar or... With thermal energy storage systems, especially mild temperature chilled water plant into! Highly reliable chilled water loop, and from “ Conventional ” to allow feeding areas from two.! At a lower frequency may use less energy that two pumps operating at a pressure of 300 kPa a! Saved with the utility company reducing the flow in a more traditional way many! Is owner and plant operator buy-in to the outdoors by a cooling tower fill remains fully wetted using sequences! Significant reduction in energy usage, which directly translates to dollars saved with the utility company primary! 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Study for a couple different reasons recovery chillers are available, this often means adhering to specific dates... And will further reduce the total pump energy used in the occupied space flow. Water plant directly to terminal units located in the occupied space in Your Industry! whether or! Over 80 % of hours in Oakland, Calif. ( see figure 4 ) as a result minimum! Once the chilled water plant optimization can be finalized understood, the distribution system must be before... And a temperature of approximately 55°F as intended “ Conventional ” to ΔT. Storage systems, especially mild temperature systems serving sensible only cooling systems in that it provides chilled water distribution system reliable water! System and provides the benefit of fewer pumps in the chiller valves, installed or proposed design delta T or... Is easier to achieve % waterside economizer systems pair well with thermal energy storage systems, especially mild temperature water.