Select chilled water temperatures, flow rate, and primary pipe sizes; 3. For both options, the distribution sys- tem is variable flow using two-way valves at cooling coils. Providing a variable flow chilled water plant that is connected to a chilled water distribution piping network with two or more substantially different pressure drops could result in significantly less pump energy savings and the potential for the existing control valves leaking by in the lower pressure drop chilled water loop. 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. 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. Chilled water is centrally produced and distributed throughout the campus, and this district cooling system shall be utilized wherever possible. How Chilled Water Air Conditioning Works. My firm has successfully designed for 20 [degrees]F. Bypass line … This may leave the system able to operate at 100% economizer mode only when wetbulb temperatures are at or below 36°F. A variable primary flow pumping system is typically the most energy-efficient system and provides the benefit of fewer pumps in the 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. 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). Figure 1: Layout of the chilled water distribution system. 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 components of closed and open hydronic 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. 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. Equipment manufacturers are also starting to include aspects of optimization into their onboard controls as well. Here, a set of constant speed pumps distributes fixed quantity of water at all times and the temperature varies to meet the load. 3300 0 obj
Select chilled water distribution . Next, we’ll talk about a couple of different chilled water system configurations. Minimum flow rates are important to maintain in the cooling towers to ensure that the cooling tower fill remains fully wetted. 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. Another application such as service water preheating normally uses heat recovery water temperatures of 85°F to 95°F. The real beauty of waterside economizers is on display when they are paired with mild temperature chilled water systems. This increases the number of full economizer hours and will further reduce the operating hours on the chillers and their corresponding energy use. The header supplies four pipelines that go down the mine with draw-off points at depths of 1000 m and 2000 m. 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. 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 In the remaining hours, the close approach can provide a significant reduction in cooling load on the chillers. 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. Significant pressure drop differences in the chilled water piping distribution loops. 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. 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. 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. 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. 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. 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. When you pair these systems with close approach towers, you can see dramatic increase in hours of full economizer mode. Scenarios like this can be difficult for operators to accept after operating in a more traditional way for many years. Demand Flow is an HVAC optimization solution that reduces energy costs and ensures ongoing operational efficiency, with healthy financial returns and long-term value. 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. Total chilled water distribution system volume is 1.5 million gallons +. 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 waste heat that is removed from the chilled water loop is captured in a hot water loop that is used for heating. 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. 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.
The distribution system piping ranges in size from 6 inch up to 36 inch. 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. Select cooling tower type, speed control option, efficiency, approach . When considering a heat recovery application, always select the lowest practical heating temperature to meet the needs. Essentially, the building owner gets heat energy at virtually no cost because it is a byproduct of the cooling process. Pressure drop is overcome by the use of a chilled-water pump. This would happen because three pumps operating at a lower frequency may use less energy that two pumps operating at 60 hertz. Typically, heat recovery chillers are designed to provide hot water for space heating at 105°F to 110°F. 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. The system incorporates “closed loops” to allow feeding areas from two directions. temperature. Once the chilled water distribution parameters are understood, the chilled water pumping arrangement can be designed. This chilled-water is then circulated through the entire building by the use of a pump. Chilled water distribution. 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. 6. 5. Currently, some controls manufacturers integrate plant optimization into their standard control package. 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. 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. Additionally, waterside economizer systems pair well with thermal energy storage systems, especially mild temperature systems serving sensible only cooling systems. 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. 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. 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. 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. 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. Courtesy: SmithGroup. This 400-ton system includes two water-cooled chillers piped in parallel. 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. 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. Space heating systems are normally designed at 140°F supply water temperature. The heat is then rejected from the condenser water loop to the outdoors by a cooling tower. In the summer, the two-pipe HVAC system is manually switched to cooling, and in the winter, the system is switched to heating. 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. The centralized cooling distribution system consists of three central plants with a total of 38,000 tons of centrifugal cooling capacity connected to 4.5 miles of chilled water distribution system piping. 7.4 Chilled Water Distribution System . How to match pumps to systems. At the point that system flow rate exceeds chiller flow rate, deficit flow. As system load and flow increase, the excess flow rate (from supply to return) in the bypass line decreases. The chilled water distribution system must be evaluated before a new chiller plant design or existing chiller plant upgrade can be finalized. 3277 0 obj
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Optimization is the action of making the best or most effective use of a situation or resource. 0
So, the elevated chilled water temperatures are ideal. 3. The different types of pipe used in hydronic systems. The type of building, climate and load profile are contributing factors into whether one or all of those strategies should be considered. 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. Two-pipe HVAC chilled water systemsare reasonably energy efficient. endstream
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