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 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. 16 Chilled-Water Distribution System. Courtesy: SmithGroup. There is the obvious reduction in energy usage, which directly translates to dollars saved with the utility company. %PDF-1.6 %���� 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. 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. One pipe is used for the water loop, and the other pipe is used for the condenser loop. 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. Chiller plant design can have a significant impact on the ongoing operating costs of a building. My firm has successfully designed for 20 [degrees]F. 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 pumping capacity matches the thermal load, it increases the temperature difference between the chilled water supply temperature and chilled water return temperature. In this scenario, the BMS monitors all cooling valve positions. Courtesy: SmithGroup. Terminal equipment, proposed or installed. 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. 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. After completing the course, you should know: 1. 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. Care must be taken when reducing the flow in a condenser water system to avoid suspended solids from settling out in the system. Existing or proposed design delta T, or lower water return temperatures. Currently, some controls manufacturers integrate plant optimization into their standard control package. Figure 3: In Oakland, Calif., a 100% waterside economizer system can produce 55°F chilled water without the chiller operating. The 4-pipe water distribution system is actually two, 2-pipe systems in parallel; each system consisting of its own supply and return main. 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. 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. 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. system; 2. Typically, heat recovery chillers are designed to provide hot water for space heating at 105°F to 110°F. The distribution system piping ranges in size from 6 inch up to 36 inch. The basic concepts of piping system design. 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. Pressure drop is overcome by the use of a chilled-water pump. Heat recovery chillers can be very effective in health care facilities. 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. 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). 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. 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. 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. Next, we’ll talk about a couple of different chilled water system configurations. As a result of minimum air change rates, rooms are often provided with more air than is needed for cooling the space. 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. 7.4 Chilled Water Distribution System . 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. 0 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. Two-pipe HVAC chilled water systemsare reasonably energy efficient. The system incorporates “closed loops” to allow feeding areas from two directions. 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. The waste heat that is removed from the chilled water loop is captured in a hot water loop that is used for heating. temperature, and make cooling tower A variable primary flow pumping system is typically the most energy-efficient system and provides the benefit of fewer pumps in the system. Learn about the impact of pumping schemes and plant optimization of chilled water systems. 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. 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. 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. 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. Chilled water distribution. The other is distributing hot water to the units and return- ing the water to the boiler. Case 3: Conversion of a Parallel-piped System to Series, and from “Conventional” to Increased ΔT. Chilled water is supplied into a header at point A at a pressure of 300 kPa and a temperature of 5 ºC. 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. The chilled water produced reduces the load on the central chillers. 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 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. temperature. For maintenance personnel, this often means adhering to specific switch-over dates on the calendar. The real beauty of waterside economizers is on display when they are paired with mild temperature chilled water systems. 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. 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. 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. 3277 0 obj <> endobj The water leaves the chilled water evaporator at 45°F or 7°C. These pumps are a very cost-effective way to limit the number of field mounted sensors and controls while minimizing pump energy usage. 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. Understanding the actual building load so that equipment can be right-sized is critical. 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. 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. Search Products And Discover New Innovations In Your Industry, Scott Battles, Jonathan Hulke and Stet Sanborn. 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