Chilled Water Plant Design 2003 American Standard Inc.
Agenda Earthwise System Variable Primary Flow Series Configuration Case Study 20,000RT Project Parallel, primary/secondary, low temp, YK Series-counter, primary/secondary, low temp, low flow YD Series-counter, primary/secondary, low temp, low flow CDHG Series-counter, VPF, low temp, low flow, CDHG
Goal: Minimize Capital & Operating Costs Improve: Reliability, Efficiency, & Comfort
First Cost Energy Consumption
EarthWise Chilled Water Systems: Good for Business... Offers lower first cost and lower operating cost. Good for the Environment: Reduced utility generated greenhouse gas emissions. Reduces pumping costs... A low flow, low temp, high efficiency system Leverages today s technology Equipment - Chillers, Controls System options $ control s +$ piping, pumps +$ chillers
Low Flow Chilled Water Plant Design A Paradigm Shift - New Rules of Thumb New rules of thumb 44 (6.7 ) Lower chilled water supply (such as 41 F = 5 C) Larger T across evaporator (such as 16 F= 8.9 C) that s at 1.5 gpm/ton Lower flows through condenser (such as 15 F = 8.4 C or 2 GPM/ton) that s something less than 3.0 gpm/ton
example chilled water plant Design Formulas Tons = gpm * t / 24 Chillers are working. t ( C) 11 (20 o F) 10 (18 o F) 8.9 (16 o F) 7.8 (14 o F) 6.7 (12 o F) 5.6 (10 o F) 4.4 (8 o F) 3.3 (6 o F) 2.2 (4 o F) gpm/ton 1.2 1.3 1.5 1.7 2.0 2.4 3.0 4.0 6.0 Pumps are working.
Chiller technology improvements kw/ton 0.90 Cataloged at standard ARI conditions 0.80 0.70 0.60 0.50 Year 1970 1975 1980 1985 1990 1995 2000
Affect of reduced flow on pumps Pump is smaller (lower cost) Pump uses less power % Full load power 100 80 60 40 20 0 0 20 40 60 80 100 % Waterflow
Summary : Earthwise TM Systems System Power tower tower pumps pumps Operating Cost chiller Traditional System chiller Low Flow Evaporator & Condenser First Cost Pump size Tower size Piping Size
distance How about Coil? Chilled water side temperature 80 F Coil It s a simple heat transfer device Reacts to colder entering water by returning it warmer TD2 57 F 54 F water air 41 F 55 F TD1 44 F LMTD44 F = 17.44 LMTD41 F = 18.13 LMTD = TD2 - TD1 Ln (TD2 / TD1)
How about Tower? Condenser side opportunity Q=U A1 delta T1 = U A2 delta T2 Delta T1 = 94.2-78 = 16.2F (34.6-25.6 = 9 C) Delta T2 = 99.1-78 = 21.1F (37.3-25.6 = 11.7 C) A1*16.2 = A2*21.1 A2 = 0.77 A1 Tower exchanges heat between the entering (warmest) water temp and the ambient wet bulb
kwh/ton/year Low Flow Chilled Water Plant Design What are other s saying??? Kelly and Chan (Vanderweil Engineering) HPAC January 1999: Optimizing Chilled Water Plants Chilled water T: 18 & Condenser water T: 14.2 F With the same cost chillers, at worst, the annual operating cost with lower flows be about equal to standard flows but still at a lower first cost PG&E: CoolTools Chilled water T: 12 F to 20 F Condenser water T: 12 F to 18 F (multi-stage) 600 400 200 Chilled water pump Chiller 0 41/16 42/14 43/12 44/10 Chilled water supply temperature/deltat
Chilled Water System Optimization Decoupled Systems Variable Flow Systems Series Chiller Configuration 2003 American Standard Inc.
Decoupled Systems moving to Variable Flow Systems
Primary-secondary and VPF comparison Primary-secondary VPF Primary pumps No secondary pumps Secondary pumps Chiller and primary pumps staged in pairs Chiller and pump staging not necessarily connected Bypass line and valve for minimum flow control Bypass line (no valve) allows constant evaporator water flow Reduced installed cost Reduced operating cost
Primary-secondary and VPF comparison Design Conditions : CHW system type Primary/ secondary Variable primary flow Cooling load, tons 500 500 Total CHW flow rate 1,000 1,000 Primary pump head, feet Secondary pump head, feet 50 120 70 NA ARTI-21CR/611-20070-01
Primary-secondary and VPF comparison CHW system type Primary/ secondary Variable primary flow CHW pump equip cost, $ 10,516 7,358 CHW pump installation cost, $ 2,857 1,486 Piping & fittings installed cost, $ 19,070 NA VFD / Starter installed cost, $ 9,860 14,550 Bypass / decoupler installed cost, $ 1,328 929 Bypass valve installed cost, $ NA 1,548 Flow meter installed cost, $ NA 1,800 Total installed cost, $ 43,631 27,671 Total installed cost, $ Base -15,960 Total installed cost, % Base -37
VPF System Minimum flow and control P P P P bypass line VFD modulating control valve for minimum chiller flow control valve
VPF system - when to use? Flows vary Chillers with adaptive controls Operator understands plant operation Retrofits - even small jobs
Why consider VPF now? Chiller control sophistication First cost savings Pump space Pump wiring Piping and connection Operating cost savings Pumps Cooling Tower
Feedforward Control Feedforward control is an open loop predictive control strategy that measures and compensates for load changes by using entering water temperature as an indication of load change. With feedforward control, the chiller can respond faster to load changes.
Feedforward Control Flow compensation works by calculating a new delta temperature as flow changes. Maintains stability at low flow rates Rejects disturbance caused by variable flow
UCP 2 UCP2 Feedback?? º 42 º CH 530 Feedforward CH 530 Feedback Σ?? º 42 º
Water Temp [degf] Water Flow [gpm] 50% Flow Reduction 130 120 Capacity Control w/o Water Flow Compensation 1,500.00 1,300.00 110 1,100.00 100 900.00 90 Evaporator Water Flow 700.00 80 500.00 70 300.00 60 Evap Entering Water Temp 100.00 50-100.00 40 Evap Leaving Water Temp Chiller off Chiller 30 off -500.00 0:00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00 Time (hour:min:sec) Chiller on -300.00
Water Temp [degf] Water Flow [gpm] With Compensation 130 120 Capacity Control with Water Flow Compensation 1,500.00 1,300.00 110 1,100.00 100 900.00 90 Evaporator Water Flow 700.00 80 500.00 70 300.00 60 Evap Entering Water Temp 100.00 50-100.00 40 Evap Leaving Water Temp -300.00 30-500.00 0:00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00 Time (hour:min:sec)
variable primary flow Advantages Reduces capital investment Saves mechanical-room space Improves system reliability
VPF advantages Lower Capital Cost Fewer Pumps Motors Pump bases Starters and wiring Fittings and piping Less labor
VPF advantages More Available Space Opportunity to Add other equipment Select larger, more efficient chillers Improve service access
VPF advantages Improved Reliability Provides system with Fewer pumps and accessories Better balance between pumps and chillers online
VPF advantages Greater Flexibility any flow rate any T
chiller selection Considerations Evaporator flow limits (consult manufacturer) Rate-of-change tolerance Flow range-ability Difference between design flow rate and evaporator s minimum flow limit
chiller selection considerations Evaporator Flow Limits flooded or falling-film evaporators water velocity, fps minimum maximum traditional limits 3.0 11 12 revised limits: standard 1.5 tubes high- 2.0 performance tubes
1.9-to-1 turndown variable flow Selection 4.6-to-1 turndown
chiller selection considerations Evaporator Flow Limits Purpose: Lower limit Upper limit refrigerant carryover controller stability heat transfer erosion affordable pressure drop
chiller selection considerations Rate-of-Change Tolerance chiller (compressor) type centrifugal helical-rotary scroll allowable flow-rate change* (% of design flow per minute) 10% for process cooling 30% for comfort cooling 10% for process cooling 30% for comfort cooling 10% for all applications * Tolerances pertain specifically to Trane chillers
What are other s saying??? Variable Primary Flow Chilled Water Plant Design
VFP systems: Reduces total annual plant energy 3-8% Reduces first cost 4-8% Reduces life-cycle cost 3-5%* *Relative to conventional Decoupled chilled-water systems.
VPF System More information Http:/trane.com/commercial /library/newsletters.asp (1999 and 2002) Don t Ignore Variable Flow, Waltz, Contracting Business, July 1997 Primary-Only vs. Primary-Secondary Variable Flow Systems, Taylor, ASHRAE Journal, February 2002 Comparative Analysis of Variable and Constant Primary-Flow Chilled-Water-Plant Performance, Bahnfleth and Peyer, HPAC Engineering, April 2001 Campus Cooling: Retrofitting Systems, Kreutzmann, HPAC Engineering, July 2002
Parallel VPF Systems moving to Series Configuration Systems 58 F 50 F 42 F
Series configuration - when should I use it? Gas/electric (hybrid) fuel mix Mixed chillers Low-flow systems
Series configuration - benefits Fuel flexibility Control flexibility Low distribution costs
VPF system configurations Series arrangement Simple loading of either chiller More efficient upstream Chiller can be Absorption, Screw, etc. VFD
VPF system configurations Series-Parallel Flow 103.85 F 89.6 F 47.98 F 103.85 F 89.6 F 570/730 Tons Simplex 45/55 split 57 F 103.85 F 89.6 F 103.85 F 89.6 F 41 F VFD
VPF system configurations Series-Counter Flow 103.82 F 96.63 F 48.96 F 89.6 F 650 Tons * 2 Simplex 50/50 split 57 F 103.82 F 96.63 F 89.6 F 41 F VFD
VPF system configurations Series-Parallel Flow 103.85 F 105.6 F 102.12 F Single Compressor Chiller Lift 62.85 F 41 F Upstream Chiller Downstream Chiller Lift 61.12 F 41 F Lift 57.62 F 47.98 F Upstream chiller: 105.6-47.98 = 57.62 Series-Parallel flow Arrangement Downstream chiller: 102.12-41 = 61.12 Average lift: 59.37 (vs. 62.85 for single compressor)
VPF system configurations Series-Counter Flow 103.82 F 103.82 F 96.63 F Single Compressor Chiller Lift 62.82 F 41 F Upstream Chiller Downstream Chiller Lift 55.63 F 41 F Lift 54.86 F 48.96 F Upstream chiller: 103.82-48.96 = 54.86 Series-Counter flow Arrangement Downstream chiller: 96.63-41 = 55.63 Average lift: 55.24 (vs. 62.82 for single compressor) (vs. 59.37 for series parallel flow (7%)) Better chiller efficiency, but high P
Example : Let s prove it from Topss Selection : 650-ton chiller 44.6 F chilled water with 9 F T 3 gpm/ton condenser water flow
initial selection condenser flow rate: 3 gpm/ton
Series-parallel Flow Downstream chiller: chilled water flow 1950 gpm (system) condenser water flow 1300 gpm (chiller) leaving chilled water 41 F chiller capacity 45% of system total
downstream chiller: Series-parallel Flow Bundle size : 630
Series-parallel Flow Upstream chiller: chilled water flow condenser water flow leaving chilled water chiller capacity 1950 gpm (system) 1300 gpm (chiller) 47.98 F 55% of system total
upstream chiller: Series-parallel Flow Selection #25
Series-counter Flow Downstream chiller: chilled water flow 1950 gpm (system) condenser water flow 2600 gpm (chiller) leaving chilled water 41 F chiller capacity 50% of system total
downstream chiller: Series-counter Flow Less pressure drop
Series-counter Flow Upstream chiller: chilled water flow condenser water flow leaving chilled water chiller capacity 1950 gpm (system) 2600 gpm (chiller) 48.96 F 50% of system total
upstream chiller: Series-counter Flow Selection #7
series system advantages: better price & ROI 44.6/53.9F; 89.6 F / 3gpm/ton 1. Series counter flow: Selection # 7 + 3 0.585Kw/ton, ave $307,366/chiller 2. Series parallel flow: Selection #41 + 25 0.615 kw/ton, ave $318,049/chiller 1 2
example chilled water plant Series-Series Counter flow Dubai 20,000 Tons Plant Base Case: 10 Chillers Evaporators and condensers piped in parallel Cooling towers Primary-Secondary chilled water system Condenser water pumps 0.780 kw/ton at specified conditions
Economics 5.43 cents / kwh $0.0068 / gallon of water
Base Case Layout 56 F 40 F Chilled water 56-40 F (16 T) Condenser flow rate of 3 gpm/ton (10 T)
Alternative 1 YD Chiller Four 5000 ton chiller modules Series-Counterflow Primary-Secondary 0.703 kw/ton Fewer pumps Reduced chilled water flow rate (increased T)
Alt 1: Series Counterflow 104.5 F 99.7 F 95 F Upstream chiller Downstream chiller 57.25 F 48.2 F 39.2 F
Compressor Lift 104.5 F 104.5 F 99.7 F Single Compressor Chiller Lift 65.3 F Upstream Chiller Downstream Chiller Lift 60.5 F Lift 56.3 F Series- Counterflow Arrangement 48.2 F 39.2 F 39.2 F Upstream chiller: 104.5-48.2 = 56.3 Downstream chiller: 99.7-39.2 = 60.5 Average lift: 58.4 (vs. 65.3 for single compressor) Better chiller efficiency
Alt 2: Decreased condenser rates, Trane Duplex chillers Increased T (reduced flow) of chilled and condenser water Reduced installed cost Pipes Pumps Cooling towers Chiller module is more efficient.650 kw/ton Duplex chillers lift
Base cooling tower conditions 104.4 F 3 gpm/ton range 10 F 95 F 87 F design wet bulb approach = 8 F
Base cooling tower conditions Base Flow rate (gpm) 6000 Design wet bulb (deg F) 87 Approach (deg F) 8 EWT (deg F) 104.4 LWT (deg F) 95 Fan power (kw) 96
Affect of reduced flow on cooling towers Reduce box size, or... Reduce fan power, or... Reduce approach temperature
Same cooling tower at reduced flow rate 105.1 F 2.42 gpm/ton range 12.1 F 93 F 87 F design wet bulb approach = 6 F
Same cooling tower at reduced flow rate Base Same tower lower flow Flow rate (gpm) 6000 4840 Design wet bulb (deg F) 87 87 Approach (deg F) 8 6 EWT (deg F) 104.4 105.1 LWT (deg F) 95 93 Fan power (hp) 96 96
Affect of temperatures on the chiller Decreased chilled water leaving temperature takes more power Increased condenser water leaving temperature takes more power
Alt 2: Trane Duplex Series Counterflow 102 F 96 F 105 F 99 F 93 F Upstream chiller Downstream chiller 57.25 F 48.2 F 39.2 F 52.7 F 43.7 F
Trane Duplex Series Counterflow, Average Lift Upstream chiller upstream circuit: 105-52.7 = 52.3 downstream circuit: 102-48.2 = 53.8 Downstream chiller upstream circuit: 99-43.7 = 55.3 downstream circuit: 96-39.2 = 56.8 Average lift: 54.5 vs. 65.3 for single compressor vs. 58.4 for other series counterflow (7%) Better chiller efficiency
Alt 2: Summary Reduced flows: installed cost savings Smaller condenser pipes Smaller chilled water pipes Smaller cooling towers Smaller condenser pumps Smaller chilled water pumps Operating cost savings Better chiller efficiency (reduced lift due to Trane Duplex modules) Reduced pumping power Reduced make-up water consumption
Alt 3: Variable Primary Flow Reduced number of pumps Fittings Piping Electrical connections Controls Responds to Low T Syndrome Reduced operating costs
Alternatives Base case: 10 parallel chillers, primary-secondary, 16 T Chilled water, 10 T condenser water 4 Chiller modules, series counterflow primary-secondary 18 T Chilled water, 10 T condenser water Trane Duplex modules, series counterflow, primary-secondary, 18 T Chilled water, 12 T condenser water Trane Duplex modules, series counterflow, variable primary flow 18 T Chilled water, 12 T condenser water
Analysis of Alternative 20,000 ton District Cooling Designs for the UAE (87WB) Chiller Pumps Case 1 (competitor) Case 2 (competitor) Case 3 TAS/Trane Case 4 TAS/Trane Parallel R-134a Chiller Design Series R-134a Chilling Design Series R-123 Chilling Design Series R123 Chilling Design Primary Secondary Pumping Primary Secondary Pumping Primary Secondary Pumping Variable Primary & Reduced Chw pipe Tabreed Type, York Chillers JBR, York/Stellar YD Chillers JBR, TAS/Trane Optimal, TAS/Trane Capacity-TR 20000 20000 20000 20000 Chiller kw 15600 14056 12994 12994 Number of chillers 10 4 4 4 kw/tr 0.78 0.703 0.650 0.650 Evaporator Water GPM 30000 26668 26668 26668 Evaporator Water T-In 55.94 57.25 57.25 57.25 Evaporator Water T-Out 39.92 39.2 39.2 39.2 Evaporator Water dt 16.02 18.05 18.05 18.05 Condenser Water GPM 60000 60000 48400 48400 Condenser Water T-In 95 95 93 93 Condenser Water T-Out 104.54 104.54 105.1 105.1 Evaporator Water bhp/pump 122 214 117 0 Evaporator Water kw 909 638 348 0 kw/pump 91 160 87 0 Condenser Water bhp/pump 136 341 293 293 Condenser Water kw 1016 1016 872 872 kw/pump 101.6 254 218 218 Distribution Pump bhp 1940 1362 1356 1823 Distribution Pump bhp 1445 1015 1010 1358 Cooling Tower Fan bhp 1293 1293 1293 1293 Fan kw 963 963 963 963 Fan kw/tr 0.0482 0.0482 0.0482 0.0482 Water Consuptiom GPM 879 879 852 852 Water Consumption gallons/ton-hour 2.64 2.64 2.56 2.56 Power Consumption Equipment Power 19933 17689 16187 16187 Misc Power 268 268 268 268 kw/tr 1.010 0.898 0.823 0.823 Financial Considerations Annual Full Load Operating Hours Water Rate $/gal 0.0068 0.0068 0.0068 0.0068 Energy Rate $/kw-hr 0.0543 0.0543 0.0543 0.0543 Annual Water Cost Total $ 1,738,216 $ 1,721,515 $ 1,634,278 $ 1,634,278 Annual Energy Cost $ 4,087,975 $ 3,858,686 $ 3,346,897 $ 3,316,355 Total Annual Operating Cost $ 5,826,191 $ 5,580,202 $ 4,981,175 $ 4,950,633 Savings Vs. Case 1 $ 245,989 $ 845,016 $ 875,558 Savings Vs. Case 2 $ 599,027 $ 629,568 Savings Vs. Case 3 $ 30,541
Base - 10 chillers 4 Modules - Primary/Secondary Trane Duplex modules, Primary/Secondary Trane Duplex modules, Variable Primary Flow Energy Use Dubai, 20,000 ton plant, Annual kwh 80,000,000 70,000,000 60,000,000 50,000,000 kwh 40,000,000 30,000,000 20,000,000 10,000,000 - Primary pumps Distribution pumps Condenser pumps Tower Fans Chillers
Base - 10 chillers 4 Modules - Primary/Secondary Trane Duplex modules, Primary/Secondary Trane Duplex modules, Variable Primary Flow Estimated operating cost Dubai, 20,000 ton plant, Estimated Annual Operating Cost $6,000,000 $5,000,000 $4,000,000 $3,000,000 $2,000,000 =$599,000 Annual Makeup water cost Annual Electric Cost $1,000,000 $-
Net Present Value utility savings only Dubai, 20,000 ton plant, Net Present Value $8,000,000 $7,000,000 $6,000,000 $5,000,000 $4,000,000 $3,000,000 $2,000,000 $1,000,000 $- Alt 2-1 Alt 3-1 Alt 4-1
Significant benefits available By Reducing condenser water flow Reducing chilled water flow Duplex series-counterflow arrangement Trane Duplex modules Save Both capital and operating costs VPF saves additional Capital costs Operating costs
example chilled water plant Series-Series Counter flow Washington D.C. 10,500 tons chilled water plant 98.9 o F 91.3 o F 85 o F 55 o F 45.1 o F 37 o F
Conclusion :
Greater Focus on System Efficiency and..
annual energy consumption, kwh Lower Operating & Installation Cost Low-Flow Systems 750,000 600,000 450,000 chiller 300,000 150,000 pumps 0 base case low flow cooling tower fans
Trend Toward Lower Flow Rates 95 F [35 C] 44 F [6.7 C] 100 F [37.8 C] 41 F [5 C] 85 F [29.4 C] 85 F [29.4 C] 54 F [12.2 C] 57 F [13.9 C] ARI conditions evaporator flow rate condenser flow rate 2.4 gpm/ton [0.043 L/s/kW] 3.0 gpm/ton [0.054 L/s/kW] low-flow conditions evaporator 1.5 gpm/ton flow rate [0.027 L/s/kW] condenser flow rate 2.0 gpm/ton [0.036 L/s/kW]
EarthWise Chilled Water Systems Exploit technology! Low flow Low temperature High efficiency Leverage: Optimized Controls Variable Primary Flow Series Evaporators First Cost Operating Cost
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