A heat recovery chiller that is sized to provide the terminal reheat load during summer operation can offset the reheat load entirely while also providing chilled water and reducing the demand on the main chiller plant. There is the obvious reduction in energy usage, which directly translates to dollars saved with the utility company. Maximum and minimum chilled water supply temperatures. 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. 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). 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. 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. 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. To help with infection control, clinical spaces within health care facilities are required to have minimum air change rates. A holistic approach to optimizing chilled water and air distribution systems. Chilled water distribution. 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. 6. %%EOF Select cooling tower type, speed control option, efficiency, approach . The chilled water distribution system includes more than 6 miles of are direct-buried, ductile iron pipes up to 30 inches in diameter. The chilled water distribution system must be evaluated before a new chiller plant design or existing chiller plant upgrade can be finalized. While six-pipe, dual-condenser heat recovery chillers are available, this discussion focuses on four-pipe, single-condenser heat recovery chiller applications. In this scenario, the BMS monitors all cooling valve positions. 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. 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. 7.4 Chilled Water Distribution System . Understanding the actual building load so that equipment can be right-sized is critical. 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. As a result, reheat energy has historically been one of the largest end uses of energy in a hospital, representing 25% to 30% of the total annual energy usage depending on the climate zone. 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 J ��@����*�;��� (������L�(�W����>��X�@�n�lx���`�@`[�̅�9W��$�~=�aa���Đ�`� ����Y[��+3,��2�=��l&7�t7����``���X���K��+�B� ^��I Strategies such as chiller plant optimization, water side economizer and heat recovery chillers can create positive results by improving overall plant efficiency and reducing energy costs. Equipment manufacturers are also starting to include aspects of optimization into their onboard controls as well. The components of closed and open hydronic systems. The district cooling system is comprised of four major subsystems; the production system, the distribution system, the building bridge system, and the building cooling system. The chilled water produced reduces the load on the central chillers. Typically, heat recovery chillers are designed to provide hot water for space heating at 105°F to 110°F. The next level of optimization is through standalone software packages, which operate in the background using proprietary algorithms and work in conjunction with the building management system. h�bbd``b`I��A���H0�� "$�H���"���hJe`b���&��` �u How centrifugal pumps operate. 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. 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. 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. The distribution system piping ranges in size from 6 inch up to 36 inch. These plants produce flow chilled water which is distributed to the campus via an underground distribution system. Existing or proposed design delta T, or lower water return temperatures. The most common types of chiller plant pumping arrangements are constant flow, primary-secondary variable flow and variable primary flow systems. 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. This allows the software to sequence the equipment so it can operate most efficiently for longer periods of time throughout the year, thus providing a greater overall percent reduction in energy usage. Once the chilled water distribution parameters are understood, the chilled water pumping arrangement can be designed. Great for Condos, Apartments an… Understand how and when to consider a waterside economizer. 4. The 4-pipe water distribution system is actually two, 2-pipe systems in parallel; each system consisting of its own supply and return main. When considering a heat recovery application, always select the lowest practical heating temperature to meet the needs. �@�:�Y\7)M�p�PR����ɦ�](h�cF�S���B�m-��]~;8:=�()��Dp4)�,r�XrtJKX0�PС� l@�qG��H�dlii��@U�i �,B�@�0�Aʘ ���"@m�L Pressure drop is overcome by the use of a chilled-water pump. 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. To counter this overcooling, terminal reheat is required. 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. One pipe is used for the water loop, and the other pipe is used for the condenser loop. A heat recovery chiller is designed to provide both heating hot water and chilled water. Figure 3: In Oakland, Calif., a 100% waterside economizer system can produce 55°F chilled water without the chiller operating. What varia… Courtesy: SmithGroup. 3300 0 obj <>stream 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. Currently, some controls manufacturers integrate plant optimization into their standard control package. 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. 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. Piping is sized to meet a project’s pressure loss, water velocity, and construction cost parameters. Chilled Water Cooling Systems 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. Additionally, waterside economizer systems pair well with thermal energy storage systems, especially mild temperature systems serving sensible only cooling systems. This would happen because three pumps operating at a lower frequency may use less energy that two pumps operating at 60 hertz. So, the elevated chilled water temperatures are ideal. At each building the chill… The system uses 3-way control valves at air handler coils that allow some water to bypass the cooling coil during part load conditions. 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. Next, we’ll talk about a couple of different chilled water system configurations. 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. This brings the total hours available for full economizer up over 80% of hours in Oakland, Calif. (see Figure 4). 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. This system is superior to other smaller cooling systems in that it provides highly reliable chilled water service on a continuous year-round basis. Chiller plant design can have a significant impact on the ongoing operating costs of a building. 5. For maintenance personnel, this often means adhering to specific switch-over dates on the calendar. 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. Select condenser water tempera-tures, flow rate, and primary pipe sizes; 5. Selecting the lowest practical heating temperature reduces the chiller lift and results in the chiller operating more efficiently. 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. The waste heat that is removed from the chilled water loop is captured in a hot water loop that is used for heating. If the flow rate In the secondary side is low then some chilled water will flow into the secondary and some will recirculate back to the chillers. For many buildings, the chilled water system provides tremendous potential for creating energy savings. 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. Another application such as service water preheating normally uses heat recovery water temperatures of 85°F to 95°F. Figure 1: At the Ford Field chiller plant in Detroit, evaluating the existing chilled water coils at varying chilled water supply temperatures is required. These can be in many forms when they are connected to a chilled water distribution system. 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. 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. 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. 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. 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. When the water has been used and has warmed, it is returned to a chiller plant to be chilled again. The different types of pipe used in hydronic systems. This chilled-water is then circulated through the entire building by the use of a pump. 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. 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. 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. Terminal equipment, proposed or installed. The heat is then rejected from the condenser water loop to the outdoors by a cooling tower. 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. Variable flow condenser water systems are also a way to reduce the total pump energy used in the chilled water plant. In other scenarios where traditional air-side economizers are not ideal, such as climate zones where an outside air economizer would introduce too much dehumidification load or mission critical data centers where excessive outside air may reduce the interior relative humidity too low, waterside economizers may be used to achieve significant savings. Select chilled water temperatures, flow rate, and primary pipe sizes; 3. 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 My firm has successfully designed for 20 [degrees]F. Optimization is also appealing because it tends to prolong the life of the installed equipment. Type of chilled water system control valves, installed or proposed (three-way or two-way valves). Space heating systems are normally designed at 140°F supply water temperature. %PDF-1.6 %���� Chilled water is centrally produced and distributed throughout the campus, and this district cooling system shall be utilized wherever possible. 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. † Meet its needed evaporator flow requirements independent of other chiller operation. As system load and flow increase, the excess flow rate (from supply to return) in the bypass line decreases. The load study for a new building is easier to achieve. How Chilled Water Air Conditioning Works. Chilled Water Distribution*. 3277 0 obj <> endobj 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. temperature, and make cooling tower How to match pumps to systems. Select chilled water distribution . Traditional chilled water systems producing 42°F to 44°F chilled water will be limited in how many hours they can take advantage of 100% waterside economizer, especially when the engineer has specified a traditional cooling tower approach of 6°F to 7°F and required a plate and frame heat exchanger with its 1°F to 2°F approach. These increased supply water temperatures greatly increase the available hours for 100% waterside economizer, showing economizer hours with a traditional approach cooling tower (see Figure 3). 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. Several pump manufacturers offer sensorless pumps with integral variable frequency drives that have the pump curves implanted in the pump VFD, and can operate single or multiple pumps at the most efficient point on the system curve. 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. The header supplies four pipelines that go down the mine with draw-off points at depths of 1000 m and 2000 m. Chilled water can also flow directly to terminal units located in the occupied space. temperature. Courtesy: SmithGroup. system; 2. Demand Flow is an HVAC optimization solution that reduces energy costs and ensures ongoing operational efficiency, with healthy financial returns and long-term value. Besides selecting close approach towers, there are several other strategies that can be deployed to increase waterside economizer hours, reduce chiller hours and possibly eliminate the need for compressor cooling all together. 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. The chilled water distribution system must be evaluated before a new chiller plant design or existing chiller plant upgrade can be finalized. 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. Chilled water is supplied into a header at point A at a pressure of 300 kPa and a temperature of 5 ºC. Select condenser water distribution . Search Products And Discover New Innovations In Your Industry!! 1. Figure 1: Layout of the chilled water distribution system. Bypass line … 1. 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. 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. 0 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. 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. 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. Review how and when to deploy a heat recovery chiller. 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. Heat recovery chillers can be very effective in health care facilities. 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. Chillers and constant flow primary pumps are enabled in pairs, making the primary flow rate a step function. One system is always distributing chilled water to the units and returning it to the chiller. A constant flow system is the simplest chilled water distribution scheme. 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. Learn about the impact of pumping schemes and plant optimization of chilled water systems. Courtesy: SmithGroup. When you pair these systems with close approach towers, you can see dramatic increase in hours of full economizer mode. The Designer The basic concepts of piping system design. 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 first strategy is a chilled water supply temperature reset control sequence (ASHRAE 90.1-2019 Part 6.5.4.4), which should be deployed on all waterside economizer systems. system; 4. 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. If the building has been designed to be a low-load, high-performance building, teams may be able to install sufficient thermal storage to remove the need for chillers altogether to meet the sensible building load. There are several factors to consider including: Existing or proposed design delta T, or lower water return temperatures. 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. 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. Scenarios like this can be difficult for operators to accept after operating in a more traditional way for many years. After completing the course, you should know: 1. A more complex chilled water cooling system configuration can consist of multiple chillers, multiple pumps, cooling towers, heat exchangers, and all sorts of valves to redirect flow according to the heat load inside of the building. Minimum flow rates must also be maintained within the condenser section of the chiller. 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. The type of building, climate and load profile are contributing factors into whether one or all of those strategies should be considered. 16 Chilled-Water Distribution System. endstream endobj 3278 0 obj <. 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