Page 4 - Preface; The
© 20 09 Trane All rights reserved Chiller System Design and Control SYS-APM001-EN Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsib...
Page 5 - iii; Contents; Low
SYS-APM001-EN Chiller System Design and Control iii Contents Preface .................................................................................................. i Primary System Components ................................................... 1 Chiller .............................................
Page 6 - iv; System Controls
iv Chiller System Design and Control SYS-APM001-EN System Controls ........................................................................... 87 Chilled-Water System Control ........................................................ 87Condenser-Water System Control ......................................
Page 7 - Primary System Components; Chilled-water systems consist of these functional parts:; Chiller
SYS-APM001-EN Chiller System Design and Control 1 Primary System Components Chilled-water systems consist of these functional parts: • Chillers that cool the water or fluid • Loads, often satisfied by coils, that transfer heat from air to water • Chilled-water distribution pumps and pipes that send ...
Page 8 - Chiller evaporator
2 Chiller System Design and Control SYS-APM001-EN Primary System Components Figure 1. Typical vapor-compression chiller Water-cooled chillers are typically installed indoors; air-cooled chillers are typically installed outdoors—either on the roof or next to the building. In cold climates, air-cooled...
Page 9 - Effect of chilled-water temperature
Primary System Components SYS-APM001-EN Chiller System Design and Control 3 • In a direct-expansion (DX) shell-and-tube evaporator (Figure 3), warmer water fills the shell while the cool, lower-pressure liquid refrigerant flows through the tubes. Figure 3. Direct-expansion evaporator cut-away In eit...
Page 10 - Other, more sophisticated, chiller controls allow some; Water-cooled condenser; Effect of condenser-water temperature; tested a number of internally-enhanced
4 Chiller System Design and Control SYS-APM001-EN Primary System Components Some chiller controls can accommodate very little flow variation during machine operation. 2 Other, more sophisticated, chiller controls allow some flow variation. Some chillers can tolerate flow-rate variations—as much as 5...
Page 11 - While they found that some of the internally; Air-cooled versus water-cooled condensers; Maintenance
Primary System Components SYS-APM001-EN Chiller System Design and Control 5 While they found that some of the internally - enhanced tubes fouled in the long term, they concluded: Because of the high hardness and low water velocity used in these tests, we do not believe that the fouling experienced i...
Page 12 - Low-ambient operation; condenser relief
6 Chiller System Design and Control SYS-APM001-EN Primary System Components Low-ambient operation Air-cooled chillers are often selected for use in systems with year-round cooling requirements that cannot be met with an airside economizer. Air-cooled condensers have the ability to operate in below-f...
Page 13 - Loads; midnight
Primary System Components SYS-APM001-EN Chiller System Design and Control 7 Figure 4. Air-cooled or water-cooled efficiency Another advantage of an air-cooled chiller is its delivery as a “packaged system.” Reduced design time, simplified installation, higher reliability, and single-source responsib...
Page 14 - syndrome” discussed on page 79. Three-way; Two-way valve load control; all
8 Chiller System Design and Control SYS-APM001-EN Primary System Components Heat transferred from the loads can be controlled in a number of ways: • Three-way valve • Two-way valve • Variable-speed pump • Face-and-bypass dampers Three-way valve load control A three-way control valve (Figure 5) regul...
Page 15 - Variable-speed pump load control
Primary System Components SYS-APM001-EN Chiller System Design and Control 9 Figure 6. Two-way valve Variable-speed pump load control By using a pump for each coil (Figure 7), the flow may be controlled by varying the pump speed. In such systems, there may be no control valves at the coil. This can r...
Page 16 - Chilled-Water Distribution System
10 Chiller System Design and Control SYS-APM001-EN Primary System Components pumped all the time; however, in systems with very small water pressure drops, this system arrangement may work economically. Figure 8. Uncontrolled water flow with bypass damper Chilled-Water Distribution System Chilled wa...
Page 17 - outlet; Pump per chiller; is the number of chillers; Distribution piping
Primary System Components SYS-APM001-EN Chiller System Design and Control 11 • accommodates the total pressure (static head plus dynamic head) on system components such as the chiller’s evaporator, valves, etc. Note that the pump heat is added to the water and must be absorbed by the chiller. Genera...
Page 18 - Pumping arrangements; Constant flow system
12 Chiller System Design and Control SYS-APM001-EN Primary System Components valves may be either three-way or two-way. As previously discussed, three-way valves require constant water flow, while two-way valves allow the water flow in the system to vary. As flow varies, the pump may simply ride its...
Page 19 - Primary-secondary system; Condenser-Water System; Cooling tower
Primary System Components SYS-APM001-EN Chiller System Design and Control 13 the series, or another pumping arrangement can be considered. Reducing the flow rate affects this system type’s energy use all the time, so careful attention to flow rates and temperature is critical (refer to “System Desig...
Page 20 - Effect of load on cooling tower performance; increases; Condenser-water pumping arrangements; Single tower per chiller; Pumping redundancy
14 Chiller System Design and Control SYS-APM001-EN Primary System Components water entering and leaving the cooling tower is the range. The temperature difference between the leaving water temperature and the entering wet-bulb temperature is the approach. Effect of load on cooling tower performance ...
Page 21 - Chiller control
Primary System Components SYS-APM001-EN Chiller System Design and Control 15 Unit-Level Controls The chilled-water supply temperature is usually controlled by the chiller. Most commonly, supply water temperature is used as the sensed variable to permit control of chiller capacity to meet system load...
Page 22 - Centrifugal chiller capacity control
16 Chiller System Design and Control SYS-APM001-EN Primary System Components In addition to monitoring data, it is vital that the chiller controls alert operators to possible problems. Diagnostic messages are necessary for the operator to respond to safety issues and data points that are outside nor...
Page 23 - Chilled-water reset control
Primary System Components SYS-APM001-EN Chiller System Design and Control 17 by reducing motor speed at “low-lift” conditions, when cooler condenser water is available. Certain system characteristics favor the application of an AFD, including: • A substantial number of part-load operating hours (for...
Page 24 - Application Considerations; T reduces flow rates, which in turn reduces pipe and
18 Chiller System Design and Control SYS-APM001-EN Application Considerations Chiller system size affects design and control considerations. Each size comes with its own set of advantages and challenges. Small Chilled-Water Systems (1-2 chillers) Figure 17. Small chilled-water system schematic A com...
Page 25 - Constant flow; T is applied to; Variable flow
Application Considerations SYS-APM001-EN Chiller System Design and Control 19 Constant flow Constant flow is simple and often applied to small systems up to 200 tons—as long as the system pressure drop is fairly low and a wider T is applied to reduce the system flow rate. In constant flow systems,...
Page 26 - enabling the second chiller,; Parallel or series; Ts, because the maximum flow through the chillers; Part load system operation
20 Chiller System Design and Control SYS-APM001-EN Application Considerations part of those jobs. See “Energy and economic analysis of alternatives” on page 26. Number of chillers The number of chillers to install is a function of redundancy requirements and first cost. In general, the more chillers...
Page 27 - Managing control complexity
Application Considerations SYS-APM001-EN Chiller System Design and Control 21 than at full load. Variable frequency drives for unloading tower fans and chilled-water pumps may provide benefits, depending on the costs, system operating hours, system type, and outdoor air conditions. (See “System Cont...
Page 29 - Individual; Pipe size; Ts; Water
Application Considerations SYS-APM001-EN Chiller System Design and Control 23 Creating one centralized chilled-water system takes significant foresight, initial investment, and building development with a multi-year master plan. If the initial plant is built to accommodate many future buildings or l...
Page 30 - Chiller Plant System Performance; Chiller performance testing; can be performed at the factory; Limitations of field performance testing; and
24 Chiller System Design and Control SYS-APM001-EN Application Considerations To minimize power, large systems must be very efficient. The upside of a large system is the amplification of energy savings. A relatively small percentage of energy saved becomes more valuable. For this reason, the highly...
Page 31 - Guidelines for system efficiency monitoring; Instrumentation for Monitoring Central Chilled-Water
Application Considerations SYS-APM001-EN Chiller System Design and Control 25 Guidelines for system efficiency monitoring ASHRAE Guideline 22 Instrumentation for Monitoring Central Chilled-Water Plant Efficiency 6 was first published in June 2008. It states: Guideline 22 was developed by ASHRAE to p...
Page 32 - Full year analysis
26 Chiller System Design and Control SYS-APM001-EN Application Considerations Energy and economic analysis of alternatives The process of making decisions between multiple, competing alternatives is simplified with the assistance of simulation software. Many packages are available for this purpose (...
Page 33 - System Design Options; for vapor compression; Guidance for Chilled- and Condenser-Water Flow Rates
SYS-APM001-EN Chiller System Design and Control 27 System Design Options There are many chilled-water-system design options; however, in a basic sense, each option is a function of flow, temperature, system configuration, and control. This section discusses the effect of flow rate and temperature de...
Page 34 - Chilled-Water Temperatures
28 Chiller System Design and Control SYS-APM001-EN System Design Options recommends a design method that starts with condenser-water temperature difference of 12°F to 18°F [7°C to 10°C]. Standard rating temperatures Currently, the standard rating condition temperatures in ARI 550/590 5 and ARI 560 9...
Page 35 - Condenser-Water Temperatures; and Nordeen; Standard rating flow conditions; Absorption chillers are rated using ARI Standard 560–2000,
System Design Options SYS-APM001-EN Chiller System Design and Control 29 Condenser-Water Temperatures Today’s chillers can run at various entering condenser-water temperatures, from design temperature to the lowest-allowable temperature for that particular chiller design. However, many existing olde...
Page 36 - Designers may use the standard
30 Chiller System Design and Control SYS-APM001-EN System Design Options Selecting flow rates Designers may use the standard rating conditions to compare manufacturers’ performances at exactly the same conditions. However, these standards allow any flow rates to be used and certified comparisons to ...
Page 38 - The total system power is now as follows:; The condenser-water pump remains at constant power.
32 Chiller System Design and Control SYS-APM001-EN System Design Options The total system power is now as follows: * Low-flow conditions represented in Table 5 through Table 8 are 1.5 gpm/ton [0.027 L/s/kW] chilled water and 2.0 gpm/ton [0.036 L/s/kW] condenser water. Figure 20. System summary at fu...
Page 39 - Coil response to decreased entering water temperature
System Design Options SYS-APM001-EN Chiller System Design and Control 33 Figure 21. Chilled water system performance at part load While the magnitude of the benefit of low-flow changes depends on the chiller type used (centrifugal, absorption, helical-rotary, scroll), all chilled-water systems can b...
Page 40 - Smaller tower
34 Chiller System Design and Control SYS-APM001-EN System Design Options performance of this coil when it is selected with a 44°F [6.7°C] entering fluid temperature and a 10°F [5.6°C] fluid temperature rise ( T). To provide the required 525 MBh [154 kW] of cooling capacity, the coil requires 105 g...
Page 41 - Same tower, smaller approach
System Design Options SYS-APM001-EN Chiller System Design and Control 35 Q = U x A 1 x T 1 , where A = area,U = coefficient of heat transfer, and T = temperature difference so, for a roughly equivalent heat rejection, U x A 1 x T 1 = U x A 2 x T 2 and for a constant coefficient of heat tra...
Page 42 - Same tower, larger chiller
36 Chiller System Design and Control SYS-APM001-EN System Design Options Same tower, larger chiller One retrofit option that benefits many building owners is installing a new, larger chiller selected for a lower flow rating and re-using the existing cooling tower, condenser-water pump, and condenser...
Page 43 - Retrofit opportunities
System Design Options SYS-APM001-EN Chiller System Design and Control 37 It quickly becomes evident that the same cooling tower and flow rate are adequate to reject more heat—in this case, approximately 50 percent more heat. Figure 22. Cooling tower re-selection with different chiller capacities Ret...
Page 44 - Cost Implications; In new systems, reduced pipe sizes
38 Chiller System Design and Control SYS-APM001-EN System Design Options In both cases, either reusing an existing tower, or reusing existing chilled water piping, the design engineer can often help reduce total project costs using the existing infrastructure by selecting a chiller with a higher tem...
Page 45 - Misconceptions about Low-Flow Rates
System Design Options SYS-APM001-EN Chiller System Design and Control 39 Figure 23. Annual system operating costs (absorption chillers) Kelly and Chan 10 compare the operational costs of chilled-water system designs in site locations. Their summary states: In conclusion, there are times you can ’hav...
Page 46 - plant; no
40 Chiller System Design and Control SYS-APM001-EN System Design Options and a more conservative zero condenser-water-pipe pressure drop, we can examine the effect of reducing flow rates. Figure 24. System energy consumption (no pipes) Energy consumption for the chiller, condenser-water pump, and co...
Page 47 - Demirchian and Maragareci
System Design Options SYS-APM001-EN Chiller System Design and Control 41 Misconception 2—Low flow only works for specific manufacturers’ chillers. Demirchian and Maragareci 12 , Eley 13 , and Schwedler and Nordeen 11 independently showed that system energy consumption can be reduced by reducing flow...
Page 48 - System Configurations; This section examines:; Parallel Chillers
42 Chiller System Design and Control SYS-APM001-EN System Configurations Multiple chilled-water systems are more common than single chilled-water systems for the same reason that most commercial airplanes have more than one engine—the balance of reliability and cost. The most typical system configur...
Page 50 - Series Chillers
44 Chiller System Design and Control SYS-APM001-EN System Configurations Series Chillers If chillers are piped in series, as in Figure 27, the mixing problem disappears and the starving coils problem (when one of the pumps in a parallel arrangement is not running) is resolved. Series flow presents a...
Page 51 - Hydraulic decoupling
System Configurations SYS-APM001-EN Chiller System Design and Control 45 percent of the system load. At system loads greater than 50 percent, the upstream chiller is preferentially loaded because it will attempt to produce the design leaving chilled-water temperature. Any portion of the load that re...
Page 53 - Production
System Configurations SYS-APM001-EN Chiller System Design and Control 47 Production An individual production (chiller) pump need only pump water from the return bypass tee (point A in Figure 29), through its chiller, and into the tee at the supply-end of the bypass line (point B in Figure 29). This ...
Page 54 - P across the system,; Distribution-loop benefits of decoupled system arrangement; T syndrome” on page 79.
48 Chiller System Design and Control SYS-APM001-EN System Configurations Distribution Distribution pumps take water from the supply water tee (point B in Figure 29), push it through all the distribution piping and load terminals, and then on to the return water tee (point A in Figure 29). This pump ...
Page 55 - Because unused chilled water does not; Common
System Configurations SYS-APM001-EN Chiller System Design and Control 49 Elevated return-water temperatures. Because unused chilled water does not bypass the cooling coils (two-way, rather than three-way, control valves), all water that is returned accomplishes some cooling. Theoretically, the retur...
Page 56 - Decoupled system–principle of operation
50 Chiller System Design and Control SYS-APM001-EN System Configurations Figure 33. Tertiary pumping arrangement Decoupled system–principle of operation At the tee connecting the supply and bypass lines, a supply–demand relationship exists, as shown in Figure 34. Think of the total flow rate from al...
Page 57 - surplus
System Configurations SYS-APM001-EN Chiller System Design and Control 51 show a deficit and the pump will be cycled on again. The amount of surplus flow necessary depends on the size of the chiller to be shut off. The surplus flow must exceed a certain quantity before shutting off a chiller–pump pai...
Page 58 - Adding a chiller; deficit; Multiple chilled-water plants on a distribution loop
52 Chiller System Design and Control SYS-APM001-EN System Configurations Chiller sequencing in decoupled systems Given the amount and direction of flow in the bypass line, chillers can be added or subtracted. Adding a chiller When there is deficit flow in the bypass line, the system is receiving wat...
Page 59 - Pump control in a double-ended decoupled system
System Configurations SYS-APM001-EN Chiller System Design and Control 53 Figure 36. Double-ended decoupled system One of the benefits of decoupled water systems is that they are simple to control. The distribution pump flow is determined by a pressure transducer located at the furthest load. Flow in...
Page 60 - Chiller sequencing in a double-ended decoupled system; When deficit flow is detected at a chilled-water plant, a
54 Chiller System Design and Control SYS-APM001-EN System Configurations When more than one chiller plant is operating, finding the right location for the differential pressure sensor can be difficult. The point of lowest pressure in the system shifts depending on which loads are using the most wate...
Page 61 - Other plant designs; eliminates the; water flow varies throughout the entire system
System Configurations SYS-APM001-EN Chiller System Design and Control 55 with a surplus that may, or may not, be large enough to indicate stopping a chiller in that plant. Other plant designs There are many other ways to connect chillers to distributed loops and each provides its own challenges and ...
Page 62 - The VPF design can separate pump; Advantages of variable primary flow
56 Chiller System Design and Control SYS-APM001-EN System Configurations • The bypass can be positioned either upstream or downstream of the cooling coils. • A control valve in the bypass ensures that the amount of flow through the operating chiller(s) never falls below the minimum limit, but remain...
Page 63 - Chiller selection requirements; Evaporator flow limits; One benefit of VPF systems is reduced pumping energy. To
System Configurations SYS-APM001-EN Chiller System Design and Control 57 secondary systems. The pressure drops previously satisfied by the distribution pumps are instead satisfied by the now larger primary-only pumps, permitting selection of larger, more efficient pumps (with efficiencies similar to...
Page 64 - To deter vibration and tube erosion (maximum flow limit)
58 Chiller System Design and Control SYS-APM001-EN System Configurations Experience with actual VPF plants indicates that a minimum evaporator-flow limit of 60 percent for packaged chillers and 40 percent or less for configured chillers work well. Chiller manufacturers specify minimum and maximum li...
Page 65 - Managing transient water flows; T. Chiller 1’s controller will unload the machine; Select for the greatest tolerance to large changes in flow rate.; The objective
System Configurations SYS-APM001-EN Chiller System Design and Control 59 Small packaged chillers typically offer less design flexibility than larger machines. It may not be possible to select a small packaged chiller with a minimum flow rate of less than 60 percent of the design system flow… but don...
Page 66 - Estimate the expected flow-rate changes and
60 Chiller System Design and Control SYS-APM001-EN System Configurations rate changes (Table 14). Selecting chillers with these characteristics improves the likelihood of stable, uninterrupted operation. Estimate the expected flow-rate changes and make sure that the chillers you select can adapt to ...
Page 67 - System design and control requirements; early in the design process
System Configurations SYS-APM001-EN Chiller System Design and Control 61 evaporator because its selection pressure drop is lower than that of Chiller 2. Load is proportional to flow rate and temperature difference, tons = (gpm × T) / 24. Because Chiller 1 is asked to satisfy a load that exceeds it...
Page 68 - Accurate flow measurement; accurate and repeatable; Bypass locations
62 Chiller System Design and Control SYS-APM001-EN System Configurations Accurate flow measurement The success of a variable-primary-flow installation depends on the quality of the flow-measuring device that controls the system bypass valve (and perhaps also indicates the plant load). Some practitio...
Page 69 - Bypass flow control; or; Chiller sequencing in VPF systems; entire
System Configurations SYS-APM001-EN Chiller System Design and Control 63 • Locate a bypass line and valve near the end of the piping run. The bypass control valve sees a lower operating pressure and may provide more stable control. Some operating cost savings may be sacrificed to maintain the pump-o...
Page 70 - Adding a chiller in a VPF system; almost
64 Chiller System Design and Control SYS-APM001-EN System Configurations flow nears the maximum limit for the operating chiller(s), another machine must be brought online. Similarly, as the system load and flow decrease, chillers must be shut down to reduce the need for bypass water flow. Adding a c...
Page 71 - Subtracting a chiller in a VPF system
System Configurations SYS-APM001-EN Chiller System Design and Control 65 Controlling transient flows is mandatory, regardless of plant size. The number of chillers in the plant will not alter the degree of care needed to properly manage transient flow-rate changes because the transition from one ope...
Page 72 - not; Other VPF control considerations; Select slow-acting valves to control the airside coils.
66 Chiller System Design and Control SYS-APM001-EN System Configurations A more conservative approach might be to wait to turn off the chiller until it would result in no higher than 80 percent capacity for the remaining operating chillers. Going back to the example, if the desired (n-1) chiller cap...
Page 73 - Plant configuration; Consider a series arrangement for small VPF applications.; When the plant consists of only two chillers; Assess the economic feasibility of VPF for single-chiller plants.; did
System Configurations SYS-APM001-EN Chiller System Design and Control 67 Plant configuration Consider a series arrangement for small VPF applications. When the plant consists of only two chillers and expansion is unlikely, you can simplify control by piping the evaporators in series. Doing so avoids...
Page 74 - Moderate “low; syndrome” it merely reduces the adverse effect of low; Guidelines for a successful VPF system; Chiller selection
68 Chiller System Design and Control SYS-APM001-EN System Configurations Figure 39. Example of operating-cost savings for a VPF, single-chiller plant Analysis results are based on a 50-ton scroll chiller and a 5-hp chilled water pump for two-story office building in St. Louis, Missouri. Moderate “lo...
Page 75 - Bypass flow; slowly
System Configurations SYS-APM001-EN Chiller System Design and Control 69 • Understand the specific loading/unloading characteristics of the chiller controller Bypass flow • Select a high-quality control valve with linear-flow characteristics • Select flow-sensing devices that deliver precise, repeat...
Page 76 - Chilled-Water System Variations; Heat Recovery; requires heat recovery in specific
70 Chiller System Design and Control SYS-APM001-EN Chilled-Water System Variations A number of chilled-water system variations can and should be used when appropriate. Each configuration offers specific advantages to solve problems and add value to the system. Heat Recovery ASHRAE/IESNA Standard 90....
Page 77 - Refrigerant migration
Chilled-Water System Variations SYS-APM001-EN Chiller System Design and Control 71 load. The details of operation are discussed in “Sidestream plate-and-frame heat exchanger” on page 74. Plate-and-frame heat exchangers isolate the building loop from the water in the open cooling tower loop, but they...
Page 79 - Preferential Loading; Preferential loading - parallel arrangement
Chilled-Water System Variations SYS-APM001-EN Chiller System Design and Control 73 body of water. Flow rates need to be carefully selected to balance the economic and environmental requirements. Preferential Loading Preferential loading is desirable for systems that use heat recovery or free cooling...
Page 80 - Sidestream plate-and-frame heat exchanger; A free-cooling heat exchanger
74 Chiller System Design and Control SYS-APM001-EN Chilled-Water System Variations One caveat when applying this arrangement is that chillers on the production side of the bypass line will run more often at low part-load conditions. Older chillers or newer chillers with a high cycle point may not ha...
Page 81 - Sidestream heat recovery; Sidestream with alternative fuels or absorption
Chilled-Water System Variations SYS-APM001-EN Chiller System Design and Control 75 Sidestream heat recovery A similar situation occurs if a heat-recovery chiller is placed in this sidestream position 24 (see Figure 46). This chiller may be equipped with a heat recovery condenser or it could be a sta...
Page 82 - Sidestream system control; Preferential loading – series arrangement
76 Chiller System Design and Control SYS-APM001-EN Chilled-Water System Variations Sidestream system control The flexibility of sidestream applications is increased by the fact that the devices are used to pre-cool return water, not to produce the system chilled-water temperature. This means that th...
Page 83 - Series–Counterflow Application; Series-series counterflow
Chilled-Water System Variations SYS-APM001-EN Chiller System Design and Control 77 Series–Counterflow Application Another system configuration that can be very energy efficient incorporates the previously described series application, but does so for both the chilled water and condenser water. Figur...
Page 84 - Unequal Chiller Sizing; There are benefits to using unequally-sized chillers
78 Chiller System Design and Control SYS-APM001-EN Chilled-Water System Variations series. The left half of Figure 50 shows a modularized configuration where series chiller modules are placed in parallel with each other, so that any upstream chiller’s valves could be “paired” with virtually any down...
Page 85 - System Issues and Challenges; Required Volume = Flow Rate × Loop Time
SYS-APM001-EN Chiller System Design and Control 79 System Issues and Challenges Low T Syndrome For many years the “low T syndrome” debate has raged. 27, 28 The symptom of the problem is that, in large systems, return-water temperature is too low, thus not allowing the chillers to fully load. Man...
Page 86 - allowing for stable system operation; Chiller response to changing conditions; Example; mix
80 Chiller System Design and Control SYS-APM001-EN System Issues and Challenges • Flow Rate = the system flow rate, in gpm [L/s] • Loop Time = the time it takes for fluid to leave the chiller, move through the system, and return to the chiller, allowing for stable system operation , in minutes [seco...
Page 87 - Contingency; Minimum capacity required; Electrical requirements
System Issues and Challenges SYS-APM001-EN Chiller System Design and Control 81 Contingency Today, many organizations have contingency plans for critical areas of their business. Some deal with natural disasters and others with the loss of power in critical areas. However, few have actually taken th...
Page 88 - Alternative Energy Sources; Electricity generation
82 Chiller System Design and Control SYS-APM001-EN System Issues and Challenges Location of equipment Location can be a major factor in contingency planning. When selecting the location of the temporary equipment, it is important to consider: • Water and electrical connections location • Sound sensi...
Page 89 - Alternative fuel; , allow the owner to take advantage; Thermal storage; Engineers; Plant Expansion; is one way of handling this
System Issues and Challenges SYS-APM001-EN Chiller System Design and Control 83 situation. Electrical generation can be outsourced to avoid internal capitalization. A variation of electrical generation uses an engine indirectly- or directly-coupled to a chiller. Either variation produces chilled wat...
Page 90 - Retrofit Opportunities; system; Flow rate out of range
84 Chiller System Design and Control SYS-APM001-EN System Issues and Challenges Retrofit Opportunities A tremendous retrofit opportunity can be realized if the low-flow concepts discussed in the chapter “System Design Options” on page 27 are utilized. Building owners may need to increase the capacit...
Page 91 - Temperatures out of range; Precise temperature control
System Issues and Challenges SYS-APM001-EN Chiller System Design and Control 85 Temperatures out of range A laboratory load requires 120 gpm [7.6 L/s] of water entering the process at 85°F [29.4°C] and returning at 95°F [35°C]. The accuracy required is more precise than the cooling tower can provide...
Page 93 - Chilled-Water System Control; Chilled water reset—raising and lowering; chiller; Chilled-water pump control
SYS-APM001-EN Chiller System Design and Control 87 System Controls Chilled-Water System Control Chilled water reset—raising and lowering Many chilled-water plants use chilled water reset, that is, the chiller’s leaving-water temperature setpoint, in an effort to reduce chiller energy consumption. Th...
Page 94 - Critical valve reset (pump pressure optimization); Number of chillers to operate
88 Chiller System Design and Control SYS-APM001-EN System Controls high. The control point is selected to minimize over-pressurizing the system and to assure adequate flow at all critical loads. Critical valve reset (pump pressure optimization) Often, pumps are controlled to maintain a constant-pres...
Page 95 - entire plant; Condenser-Water System Control; Minimum refrigerant pressure differential
System Controls SYS-APM001-EN Chiller System Design and Control 89 If the chiller and tower capabilities are conducive to this strategy, the location and load profile determine if, when, and for how long the right conditions might occur. Determine the optimum control sequence for the entire plant by...
Page 96 - Cycling a single fan.
90 Chiller System Design and Control SYS-APM001-EN System Controls The flow reduction options include: • Cooling tower bypass • Chiller bypass • One or two throttling valves in the condenser-water pipe with the pump riding its curve • A variable-speed condenser water pump After the minimum-pressure ...
Page 97 - Chiller–tower energy balance; Gillespie, and Kammerud
System Controls SYS-APM001-EN Chiller System Design and Control 91 prevalent than either two-speed fans or pony motors. Using variable-speed drives on cooling-tower fans offers two distinct benefits. First, the tower-water-temperature control is extremely good. Second, the fan power varies with the ...
Page 98 - Condenser water pump:; Pump power is reduced because both the flow
92 Chiller System Design and Control SYS-APM001-EN System Controls Variable condenser water flow Chiller-tower-pump balance There are times when a system designer may choose to vary the condenser water flow in addition to, or instead of, the cooling-tower fan speed. This may be beneficial in systems...
Page 99 - Decoupled condenser-water system
System Controls SYS-APM001-EN Chiller System Design and Control 93 These three energy consumers must be balanced to minimize overall energy use. This makes varying condenser water flow complex, but the strategy below has been implemented on projects. Control of the condenser water pumps and cooling ...
Page 101 - Failure Recovery
System Controls SYS-APM001-EN Chiller System Design and Control 95 Failure Recovery With all the varied approaches available to potential customers, it sometimes seems that the main idea gets lost. People purchase chilled-water plants to reliably produce chilled water to satisfy another need, such a...
Page 102 - Conclusion
96 Chiller System Design and Control SYS-APM001-EN Conclusion It is vital to have a clear understanding of chilled-water system concepts and their application. There is nothing particularly complex about the principles involved. Instead, system design is simply a matter of exercising a few key rules...
Page 103 - Glossary; See
SYS-APM001-EN Chiller System Design and Control 97 Glossary ASHRAE. American Society of Heating, Refrigerating, and Air-Conditioning Engineers (www.ashrae.org). building automation system (BAS). A centralized control and monitoring system for a building. chilled water. Also known as leaving-chilled-...
Page 104 - direct digital control.
98 Chiller System Design and Control SYS-APM001-EN Glossary COP. Coefficient of Performance; cooling effect divided by heat input (dimensionless); the reciprocal of efficiency. direct digital control. Programming used by building control systems to control variable outputs, such as valves or actuato...
Page 105 - The temperature of the air surrounding the object
Glossary SYS-APM001-EN Chiller System Design and Control 99 temperature, ambient. The temperature of the air surrounding the object under consideration. temperature, wet-bulb. A measure of the degree of moisture in the air. It is the temperature of evaporation for an air sample, measured with a ther...
Page 106 - References; T at Logan International Airport Central Chilled-Water
100 Chiller System Design and Control SYS-APM001-EN References 1 Webb, R.L. and W. Li. “Fouling in Enhanced Tubes Using Cooling Tower Water, Part I: Long-Term Fouling Data.” International Journal of Heat and Mass Transfer 43, no. 19 (October 2000): 3567-3578. 2 Schwedler, M. and B. Bradley. “An Idea...
Page 107 - Trane Applications Engineering Group.
References SYS-APM001-EN Chiller System Design and Control 101 15 Bahnfleth, W. and E. Peyer. “Comparative Analysis of Variable and Constant Primary-Flow Chilled-Water-Plant Performance.” HPAC Engineering (April 2001). 16 Houghton, D. “Know Your Flow—A Market Survey of Liquid Flow Meters.” E SOURCE ...
Page 108 - Solberg, P. “Ice Storage as Part of a LEED® Building Design.”
102 Chiller System Design and Control SYS-APM001-EN References 32 Trane Applications Engineering Group. “Thermal Storage – Understanding the Choices.” Ice Storage Systems, Engineered Systems Clinics . Trane, 1991. ( ISS-CLC-2) 33 Trane Applications Engineering Group. “Thermal Storage – Understanding...
Page 109 - Index
SYS-APM001-EN Chiller System Design and Control 103 Index A absorption refrigeration 98 ASHRAE GreenGuide 27, 29, 33 Guideline 22 25 B bypass flow control 63 bypass locations 62 bypass valve 8 C campus pumping arrangements 49 centrifugal chiller capacity control 16 check valves 46 chilled water flow...