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Efficient Chilled Water System for Commercial Buildings

Learn about the components and characteristics of a chilled water system in commercial buildings, including constant volume distribution, 3-way valve zoning, and system performance.

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Efficient Chilled Water System for Commercial Buildings

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  1. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Chilled Water SystemPresentation

  2. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Constant VolumeDistribution

  3. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Air-conditioning SystemComponents

  4. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Constant Volume SystemComponents

  5. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Typical 3-way Valve Zone

  6. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Full Load Condition

  7. FLOWTHINKING Fully LoadedCoil COMMERCIAL BUILDINGSERVICES • Supply watertemperature • Design return watertemp. • Coil designflow • Coil design pressuredrop • Load (flow x 10Fx500) • Coil P @ designflow • Bypassflow • BypassP • 3-way valve pressuredrop • Pump flow andhead • Actual return watertemp 45F 55F 100GPM 20FT 500,000Btuh 20FT 0GPM 3-way valveclosed 10FT 100 GPM @ 30FT 55F

  8. FLOWTHINKING COMMERCIAL BUILDINGSERVICES UnloadedCondition

  9. FLOWTHINKING UnloadedCoil COMMERCIAL BUILDINGSERVICES • Supply watertemperature • Design return watertemp. • Coil design flow • Coil design pressuredrop • Load (flow x 10Fx500) • Coil P @ designflow • Bypass flow • Bypass P • 3-way valve pressuredrop • Pump flow andhead • Actual return water temp 45F 55F 0GPM 3-way valveclosed 0.0 Btuh 0 FT 100GPM 20FT 10FT 100 GPM @ 30FT 45F

  10. FLOWTHINKING COMMERCIAL BUILDINGSERVICES So What? • When the load on the coil is zero, the valve is returning “unused” chilled water at essentially supplytemperature. • Cold return water “unloads” the chillers, causing them to operate inefficiently.

  11. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Part LoadCondition

  12. FLOWTHINKING Partially LoadedCoil COMMERCIAL BUILDINGSERVICES • Supply watertemperature • Design return watertemp. • Coil designflow • Coil design pressuredrop • Load (flow x 10Fx500) • Coil P @ designflow • Bypassflow • BypassP • 3-way valve pressuredrop • Pump flow andhead • Actual return watertemp 45F 55F 50GPM 20FT 250,000Btuh 5FT ???GPM 3-way partially closed 10FT ??? GPM @ 30FT ??F

  13. FLOWTHINKING COMMERCIAL BUILDINGSERVICES 3-way Valve Characteristic 1/2 Through Coil 1/2 ThroughBypass 125 100 75 50 25 0 FullFlow ThroughBypass FullFlow ThroughCoil %Flow 25 5075100 % ValveStroke

  14. FLOWTHINKING COMMERCIAL BUILDINGSERVICES What’s Really Happening?

  15. FLOWTHINKING Coil with 3-way Valve atMid-position COMMERCIAL BUILDINGSERVICES • Supply watertemperature • Design return watertemp. • Load (flow x 10Fx500) 45F 55F 250,000Btuh 20FT 62.5GPM 7.8FT 53F 62.5GPM 7.8FT 10FT 125 GPM @ 30FT 49 F (62.5 GPM @ 53F+ 62.5 GPM @ 45F) • Coil design pressuredrop • Coilflow • Coil P @ 62.5%flow • Coil leaving watertemp • Bypassflow • BypassP • 3-way valve pressuredrop • Pump flow andhead • Actual return watertemp

  16. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Head2 = Head1(Flow2/Flow1)2 Head2 = 20(.625/1)2 Head2 = 20(.3906) Head2 =7.8

  17. FLOWTHINKING COMMERCIAL BUILDINGSERVICES T = Load/ Flow X500 T = 250,000/62.5 X500 T =8 Therefore, LWTcoil = 45 + 8 =53

  18. FLOWTHINKING COMMERCIAL BUILDINGSERVICES RWT = (Flow1 X EWT + Flow2 X LWT)/ Flow1 +2 RWT = (62.5 X 45 + 62.5 X53)/125 RWT =49

  19. FLOWTHINKING COMMERCIAL BUILDINGSERVICES 3-way Valve in MidPosition

  20. FLOWTHINKING COMMERCIAL BUILDINGSERVICES 3-way Valve SystemDeficiencies Low return water temperatures. Robs chilled water from other coils at part loadconditions. Increases flow in primary piping. 4.Adds additional chillers online. 5.Chiller performance isreduced.

  21. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Chiller Performance Curve 1.1 1.0 0.9 0.8 0.7 0.6 0.5 102030405060708090100 PercentLoad KW perTon

  22. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Pump Sizing • Select for full chillerflow • Head must be adequate for: • Chiller evaporator • Longestcircuit • Coil • Three wayvalve • Air separator

  23. FLOWTHINKING COMMERCIAL BUILDINGSERVICES SystemConfiguration ConstantVolume

  24. AnyQuestions?

  25. Variable Volume ConstantSpeed

  26. FLOWTHINKING Variable Volume ConstantSpeed COMMERCIAL BUILDINGSERVICES Primary – SecondarySystem Primary– Circuit Includes Chillers & Primary Pump. Constant water flow through the chiller is maintained and chilled water is produced Secondary – Chilled water is circulated tothe Circuit demand area (load) by using Secondary pumps.

  27. FLOWTHINKING COMMERCIAL BUILDINGSERVICES PRIMARY -SECONDARY

  28. FLOWTHINKING Other Famous Names of Primary- Secondary COMMERCIAL BUILDINGSERVICES Primary – ProductionLoop Secondary – DistributionLoop

  29. FLOWTHINKING COMMERCIAL BUILDINGSERVICES FundamentalIdea

  30. FLOWTHINKING COMMERCIAL BUILDINGSERVICES No Secondary Flow

  31. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Primary =Secondary

  32. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Primary >Secondary

  33. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Primary <Secondary

  34. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Control Valve in Secondary

  35. FLOWTHINKING COMMERCIAL BUILDINGSERVICES • Common Pipe DesignCriteria • Use the flow of the largestchiller • Chiller staging at half of this flow iscommon • Head loss in common <1 1/2ft • Distribution pipe size is often used where reductions would be inconvenient • Three pipe diameters betweentees • Excessive length increases total headloss • Low velocities in systempiping

  36. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Control Valve in Secondary Variable flow through coil Constant flow throughsystem Variable flow through coil Variable flow throughsystem Three WayValve Two WayValve

  37. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Variable Volume Constant Speed PRIMARY – SECONDARYCIRCUIT

  38. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Control Valves Change the Secondary SystemCurve H1 H2 H3 Head F1 F2 F3 Flow

  39. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Head Absorbed by 2-wayValves Pumpcurve TDH ofpump 150 125 Varyingdifferential pressure absorbed by controlvalve HD 100 75 50 Systemresistance 25 25 50 75 100 %Flow

  40. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Pump HorsepowerComparison 150 Constant Flow Primary Pumps,only 125 HP 100 75 SecondaryPumps+ 50 Primary Pumps =V/V 25 5075 % DesignFlow 25 100

  41. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Constant vsVariableVolume 150 140 Constant Flow, C/S Pump Pump Over-haded by 150% (3 W ayValve) C/S Pump (2 W ayValve) 130 120 110 100 Base Design HP% Pump HD M atched to System@ DesignFlow Constant Flow, C/S Pump (3 W ayValve) 90 80 70 C/S Pump (2 WayValve) 60 50 % Full Load (Design)HP 40 30 20 10 0 102030405060708090100 %Flow

  42. AnyQuestions?

  43. Step Function ofChillers

  44. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Production =Distribution

  45. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Distribution > Production

  46. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Production >Distribution

  47. FLOWTHINKING COMMERCIAL BUILDINGSERVICES “Loading” aChiller • A chiller is a heattransferdevice. Like most equipment, itis most efficient at fullload. • To “load” a chillermeans: • Supply it with its rated flow ofwater • Insure that water is warm enough to permit removal of rated Btu without freezing thewater

  48. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Chiller Performance Curve 1.1 1.0 0.9 0.8 0.7 0.6 0.5 102030405060708090100 PercentLoad KW perTon

  49. FLOWTHINKING COMMERCIAL BUILDINGSERVICES Check Valve inCommon?

  50. FLOWTHINKING COMMERCIAL BUILDINGSERVICES What can we do?

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