Two-pipe HVAC chilled water systemsare reasonably energy efficient. 4. Variable flow condenser water systems are also a way to reduce the total pump energy used in the chilled water plant. 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. 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. What varia… Heat recovery chillers can be very effective in health care facilities. 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. 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. Courtesy: SmithGroup. 3300 0 obj <>stream Underground chilled water piping systems are typically used to cool buildings. Bypass line … Optimization is also appealing because it tends to prolong the life of the installed equipment. 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 When considering a heat recovery application, always select the lowest practical heating temperature to meet the needs. 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. 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. Search Products And Discover New Innovations In Your Industry, Scott Battles, Jonathan Hulke and Stet Sanborn. The Designer 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. For both options, the distribution sys- tem is variable flow using two-way valves at cooling coils. Courtesy: SmithGroup. Select chilled water temperatures, flow rate, and primary pipe sizes; 3. 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. Significant pressure drop differences in the chilled water piping distribution loops. 2. While six-pipe, dual-condenser heat recovery chillers are available, this discussion focuses on four-pipe, single-condenser heat recovery chiller applications. Once the chilled water distribution parameters are understood, the chilled water pumping arrangement can be designed. 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. For maintenance personnel, this often means adhering to specific switch-over dates on the calendar. endstream endobj 3278 0 obj <. How Chilled Water Air Conditioning Works. 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. Learn about the impact of pumping schemes and plant optimization of chilled water systems. 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. 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. This 400-ton system includes two water-cooled chillers piped in parallel. One pipe is used for the water loop, and the other pipe is used for the condenser loop. Type of chilled water system control valves, installed or proposed (three-way or two-way valves). Chilled Water Cooling Systems In the summer, the two-pipe HVAC system is manually switched to cooling, and in the winter, the system is switched to heating. 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. 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. 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. 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. 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. Care must be taken when reducing the flow in a condenser water system to avoid suspended solids from settling out in 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. 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. Figure 1: At the Ford Field chiller plant in Detroit, evaluating the existing chilled water coils at varying chilled water supply temperatures is required. Figure 3: In Oakland, Calif., a 100% waterside economizer system can produce 55°F chilled water without the chiller operating. One system is always distributing chilled water to the units and returning it to the chiller. The distribution system piping ranges in size from 6 inch up to 36 inch. Space heating systems are normally designed at 140°F supply water temperature. Chilled Water Distribution System. 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. 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. So, the elevated chilled water temperatures are ideal. The chilled water distribution system must be evaluated before a new chiller plant design or existing chiller plant upgrade can be finalized. Total chilled water distribution system volume is 1.5 million gallons +. At the point that system flow rate exceeds chiller flow rate, deficit flow. The 4-pipe water distribution system is actually two, 2-pipe systems in parallel; each system consisting of its own supply and return main. Essentially, the building owner gets heat energy at virtually no cost because it is a byproduct of the cooling process. When the pumping capacity matches the thermal load, it increases the temperature difference between the chilled water supply temperature and chilled water return temperature. The type of building, climate and load profile are contributing factors into whether one or all of those strategies should be considered. 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. When the water has been used and has warmed, it is returned to a chiller plant to be chilled again. system; 4. 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. Minimum flow rates are important to maintain in the cooling towers to ensure that the cooling tower fill remains fully wetted. 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. 0 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. 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 components of closed and open hydronic systems. 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. In this scenario, the BMS monitors all cooling valve positions. 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. This system is superior to other smaller cooling systems in that it provides highly reliable chilled water service on a continuous year-round basis. Select cooling tower type, speed control option, efficiency, approach . Maximum and minimum chilled water supply temperatures. A holistic approach to optimizing chilled water and air distribution systems. 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. �@�:�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 There is the obvious reduction in energy usage, which directly translates to dollars saved with the utility company. 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. Chillers and constant flow primary pumps are enabled in pairs, making the primary flow rate a step function. 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 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. 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. J ��@����*�;��� (������L�(�W����>��X�@�n�lx���`�@`[�̅�9W��$�~=�aa���Đ�`� ����Y[��+3,��2�=��l&7�t7����``���X���K��+�B� ^��I 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. 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). 3. 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. As a result of minimum air change rates, rooms are often provided with more air than is needed for cooling the space. The other is distributing hot water to the units and return- ing the water to the boiler. 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. 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. 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 known as the chilled water system delta T, and the higher the delta T, the lower the pumping energy required for the system. 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. 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. 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. Additionally, waterside economizer systems pair well with thermal energy storage systems, especially mild temperature systems serving sensible only cooling systems. Minimum flow rates must also be maintained within the condenser section of the chiller. 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. The chilled water produced reduces the load on the central chillers. Currently, some controls manufacturers integrate plant optimization into their standard control package. 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. Pressure drop is overcome by the use of a chilled-water pump. Select condenser water tempera-tures, flow rate, and primary pipe sizes; 5. After completing the course, you should know: 1. Campus Chilled Water System:UNK, UNL and UNO campuses are served by central utility plants operated by the Utility and Energy Management (UEM) department. 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. Limit the number of field mounted sensors and controls while minimizing pump energy usage distribution sys- tem variable. Chilled again to remove heat from a chilled water without the chiller the is! Typically the most energy-efficient system and provides the benefit of fewer pumps in the chiller lift and results the... 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