Chilled Water Plant Design American Standard Inc.

Transcription

1 Chilled Water Plant Design 2003 American Standard Inc.

2 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

3 Goal: Minimize Capital & Operating Costs Improve: Reliability, Efficiency, & Comfort

4 First Cost Energy Consumption

5 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

6 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

7 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 Pumps are working.

8 Chiller technology improvements kw/ton 0.90 Cataloged at standard ARI conditions Year

9 Affect of reduced flow on pumps Pump is smaller (lower cost) Pump uses less power % Full load power % Waterflow

10 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

11 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 = LMTD41 F = LMTD = TD2 - TD1 Ln (TD2 / TD1)

12 How about Tower? Condenser side opportunity Q=U A1 delta T1 = U A2 delta T2 Delta T1 = = 16.2F ( = 9 C) Delta T2 = = 21.1F ( = 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

13 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) Chilled water pump Chiller 0 41/16 42/14 43/12 44/10 Chilled water supply temperature/deltat

14 Chilled Water System Optimization Decoupled Systems Variable Flow Systems Series Chiller Configuration 2003 American Standard Inc.

15 Decoupled Systems moving to Variable Flow Systems

16 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

17 Primary-secondary and VPF comparison Design Conditions : CHW system type Primary/ secondary Variable primary flow Cooling load, tons Total CHW flow rate 1,000 1,000 Primary pump head, feet Secondary pump head, feet NA ARTI-21CR/

18 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, 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

19 VPF System Minimum flow and control P P P P bypass line VFD modulating control valve for minimum chiller flow control valve

20 VPF system - when to use? Flows vary Chillers with adaptive controls Operator understands plant operation Retrofits - even small jobs

21 Why consider VPF now? Chiller control sophistication First cost savings Pump space Pump wiring Piping and connection Operating cost savings Pumps Cooling Tower

22 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.

23 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

24 UCP 2 UCP2 Feedback?? º 42 º CH 530 Feedforward CH 530 Feedback Σ?? º 42 º

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26 Water Temp [degf] Water Flow [gpm] 50% Flow Reduction Capacity Control w/o Water Flow Compensation 1, , , Evaporator Water Flow Evap Entering Water Temp Evap Leaving Water Temp Chiller off Chiller 30 off :00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00 Time (hour:min:sec) Chiller on

27 Water Temp [degf] Water Flow [gpm] With Compensation Capacity Control with Water Flow Compensation 1, , , Evaporator Water Flow Evap Entering Water Temp Evap Leaving Water Temp :00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00 Time (hour:min:sec)

28 variable primary flow Advantages Reduces capital investment Saves mechanical-room space Improves system reliability

29 VPF advantages Lower Capital Cost Fewer Pumps Motors Pump bases Starters and wiring Fittings and piping Less labor

30 VPF advantages More Available Space Opportunity to Add other equipment Select larger, more efficient chillers Improve service access

31 VPF advantages Improved Reliability Provides system with Fewer pumps and accessories Better balance between pumps and chillers online

32 VPF advantages Greater Flexibility any flow rate any T

33 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

34 chiller selection considerations Evaporator Flow Limits flooded or falling-film evaporators water velocity, fps minimum maximum traditional limits revised limits: standard 1.5 tubes high- 2.0 performance tubes

35 1.9-to-1 turndown variable flow Selection 4.6-to-1 turndown

36 chiller selection considerations Evaporator Flow Limits Purpose: Lower limit Upper limit refrigerant carryover controller stability heat transfer erosion affordable pressure drop

37 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

38 What are other s saying??? Variable Primary Flow Chilled Water Plant Design

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41 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.

42 VPF System More information /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

43 Parallel VPF Systems moving to Series Configuration Systems 58 F 50 F 42 F

44 Series configuration - when should I use it? Gas/electric (hybrid) fuel mix Mixed chillers Low-flow systems

45 Series configuration - benefits Fuel flexibility Control flexibility Low distribution costs

46 VPF system configurations Series arrangement Simple loading of either chiller More efficient upstream Chiller can be Absorption, Screw, etc. VFD

47 VPF system configurations Series-Parallel Flow F 89.6 F F F 89.6 F 570/730 Tons Simplex 45/55 split 57 F F 89.6 F F 89.6 F 41 F VFD

48 VPF system configurations Series-Counter Flow F F F 89.6 F 650 Tons * 2 Simplex 50/50 split 57 F F F 89.6 F 41 F VFD

49 VPF system configurations Series-Parallel Flow F F F Single Compressor Chiller Lift F 41 F Upstream Chiller Downstream Chiller Lift F 41 F Lift F F Upstream chiller: = Series-Parallel flow Arrangement Downstream chiller: = Average lift: (vs for single compressor)

50 VPF system configurations Series-Counter Flow F F F Single Compressor Chiller Lift F 41 F Upstream Chiller Downstream Chiller Lift F 41 F Lift F F Upstream chiller: = Series-Counter flow Arrangement Downstream chiller: = Average lift: (vs for single compressor) (vs for series parallel flow (7%)) Better chiller efficiency, but high P

51 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

52 initial selection condenser flow rate: 3 gpm/ton

53 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

54 downstream chiller: Series-parallel Flow Bundle size : 630

55 Series-parallel Flow Upstream chiller: chilled water flow condenser water flow leaving chilled water chiller capacity 1950 gpm (system) 1300 gpm (chiller) F 55% of system total

56 upstream chiller: Series-parallel Flow Selection #25

57 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

58 downstream chiller: Series-counter Flow Less pressure drop

59 Series-counter Flow Upstream chiller: chilled water flow condenser water flow leaving chilled water chiller capacity 1950 gpm (system) 2600 gpm (chiller) F 50% of system total

60 upstream chiller: Series-counter Flow Selection #7

61 series system advantages: better price & ROI 44.6/53.9F; 89.6 F / 3gpm/ton 1. Series counter flow: Selection # Kw/ton, ave $307,366/chiller 2. Series parallel flow: Selection # kw/ton, ave $318,049/chiller 1 2

62 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 kw/ton at specified conditions

63 Economics 5.43 cents / kwh $ / gallon of water

64 Base Case Layout 56 F 40 F Chilled water F (16 T) Condenser flow rate of 3 gpm/ton (10 T)

65 Alternative 1 YD Chiller Four 5000 ton chiller modules Series-Counterflow Primary-Secondary kw/ton Fewer pumps Reduced chilled water flow rate (increased T)

66 Alt 1: Series Counterflow F 99.7 F 95 F Upstream chiller Downstream chiller F 48.2 F 39.2 F

67 Compressor Lift F 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: = 56.3 Downstream chiller: = 60.5 Average lift: 58.4 (vs for single compressor) Better chiller efficiency

68 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

69 Base cooling tower conditions F 3 gpm/ton range 10 F 95 F 87 F design wet bulb approach = 8 F

70 Base cooling tower conditions Base Flow rate (gpm) 6000 Design wet bulb (deg F) 87 Approach (deg F) 8 EWT (deg F) LWT (deg F) 95 Fan power (kw) 96

71 Affect of reduced flow on cooling towers Reduce box size, or... Reduce fan power, or... Reduce approach temperature

72 Same cooling tower at reduced flow rate F 2.42 gpm/ton range 12.1 F 93 F 87 F design wet bulb approach = 6 F

73 Same cooling tower at reduced flow rate Base Same tower lower flow Flow rate (gpm) Design wet bulb (deg F) Approach (deg F) 8 6 EWT (deg F) LWT (deg F) Fan power (hp) 96 96

74 Affect of temperatures on the chiller Decreased chilled water leaving temperature takes more power Increased condenser water leaving temperature takes more power

75 Alt 2: Trane Duplex Series Counterflow 102 F 96 F 105 F 99 F 93 F Upstream chiller Downstream chiller F 48.2 F 39.2 F 52.7 F 43.7 F

76 Trane Duplex Series Counterflow, Average Lift Upstream chiller upstream circuit: = 52.3 downstream circuit: = 53.8 Downstream chiller upstream circuit: = 55.3 downstream circuit: = 56.8 Average lift: 54.5 vs for single compressor vs for other series counterflow (7%) Better chiller efficiency

77 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

78 Alt 3: Variable Primary Flow Reduced number of pumps Fittings Piping Electrical connections Controls Responds to Low T Syndrome Reduced operating costs

79 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

80 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 Chiller kw Number of chillers kw/tr Evaporator Water GPM Evaporator Water T-In Evaporator Water T-Out Evaporator Water dt Condenser Water GPM Condenser Water T-In Condenser Water T-Out Evaporator Water bhp/pump Evaporator Water kw kw/pump Condenser Water bhp/pump Condenser Water kw kw/pump Distribution Pump bhp Distribution Pump bhp Cooling Tower Fan bhp Fan kw Fan kw/tr Water Consuptiom GPM Water Consumption gallons/ton-hour Power Consumption Equipment Power Misc Power kw/tr Financial Considerations Annual Full Load Operating Hours Water Rate $/gal Energy Rate $/kw-hr 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

81 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

82 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 $-

83 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

84 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

85 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

86 Conclusion :

87 Greater Focus on System Efficiency and..

88 annual energy consumption, kwh Lower Operating & Installation Cost Low-Flow Systems 750, , ,000 chiller 300, ,000 pumps 0 base case low flow cooling tower fans

89 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]

90 EarthWise Chilled Water Systems Exploit technology! Low flow Low temperature High efficiency Leverage: Optimized Controls Variable Primary Flow Series Evaporators First Cost Operating Cost

91 Questions or Comments?