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Waterside energy-recovery hourlong-chicago_ashrae


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Waterside energy-recovery hourlong-chicago_ashrae

  1. 1. WatersideEnergy RecoveryRequirements, Design andApplication Mick Schwedler, PE manager Trane applications engineering © 2011 Ingersoll Rand
  2. 2. reasons to useEnergy Recovery Required by code or standard Availability of simultaneous heating and cooling loads Economically justified  Reduces heating load  Reduces ancillary power Environmentally responsible  Reduces emissions  Eligible for “green” benefits (energy, water usage)
  3. 3. ASHRAE 90.1-2010 (since 1999)Waterside Energy RecoveryIF … Facility operates 24 hours per day  Heat rejection exceeds 6 million Btu/hr (~ 450 tons)  Design service water heating load exceeds 1 million Btu/hrTHEN Required energy recovery is (smaller of):  60% of design heat rejection  Preheating water to 85°F
  4. 4. types ofHeat-Recovery Chillers Single condenser (“bundle”) Dual condenser heat- standard  Equally sized condenser = recovery condenser bundles Auxiliary condenser heat-  Unequally sized standard condenser > recovery condenser bundles
  5. 5. heat-recovery chillersSingle Condenserhelical-rotary (screw)compressor scroll compressor centrifugal compressor
  6. 6. heat-recovery chillersDual Condenserheat-recovery leaving capacity chillercondenser water control? efficiencyFull capacity hot yes decreasesPartial capacity warm no increases heat-recovery condenser standard condenser evaporator water-cooled chiller with centrifugal compressor
  7. 7. heat-recovery chillersComparison of Options Chiller condenser optionCharacteristic Dual Auxiliary “Heat pump”Configuration Second, Second, No extra full-size smaller condenser condenser condenserApplication Large Preheating Large base- heating loads heating loads loads or continuous operationLeaving water Hot Warm HotCapacity control? Yes No YesChiller efficiency Decreases Increases Acceptable
  8. 8. variable air volumeTempering Supply AirWhen required supply/primary airflow isless than minimum setting:  Reduce primary airflow to minimum  Let space temperature drift downward  Add heat to avoid overcooling 105°F (40.6°C) water often is sufficient Supply air is always dehumidified
  9. 9. waterside heat recoveryTemperaturesService-water 85°F to 95°Fpreheating (29.4°C to 35°C)Space heating 105°F to 110F (40.6°C to 43.3C) source: 2008 ASHRAE Systems and Equipment Handbook
  10. 10. tempering VAV supply airHeating Coil Selectionselection parameter 1-row coil 2-row coilEntering water 113°F 105°FCoil flow rate 4.33 gpm 1.75 gpmFluid delta-T 6.02°F 14.91°FCoil fluid pressure drop 10.3 ft H2O 0.21 ft H2OAir pressure drop: design cooling airflow 0.45 in. wg 0.79 in. wg minimum airflow (est) 0.04 in. wg 0.07 in. wgLeaving-coil (primary) air 75°F 75°F Effectively balances heat-recovery temperatures and system pressure drops
  11. 11. waterside heat recoveryEffect on Chillers Compressor work is proportional to lift  “Lift” is pressure difference between evaporator and condenser  Warmer condenser water (for heat recovery) raises condenser pressure Changes in lift affect different compressors differently  Positive displacement  Centrifugal (full load vs. part load)
  12. 12. positive-displacement water chillerRefrigeration Cycle heat recovery 5 condenser 2 4 3 pressure expansion liquid/vapor compressor device separator 7 1 evaporator 6 enthalpy
  13. 13. positive-displacement water chiller Capacity 100 compressor type: 80 scrollchiller capacity, % screw 60 40 20 0 0° 10° 20° 30° 40° temperature rise (leaving-condenser water)
  14. 14. positive-displacement water chiller Efficiency 100 compressor type:power increase, % kW/ton 80 scroll screw (S) screw (M) 60 screw (L) 40 20 0 0° 10° 20° 30° 40° temperature rise (leaving-condenser water)
  15. 15. centrifugal chiller performance Power Increase Heat recovery 40 Chiller 85-105 F 32power increase, % kW/ton impeller diameter, inches compressor change 30 30 power increase 20 28 10 impeller diameter 0 26 85 87 89 91 93 95 97 99 condenser water temperature, °F
  16. 16. centrifugal chiller comparisonEfficiency Operating modeChiller type Cooling Heat recoveryCooling only 0.57 kW/ton Not applicable (6.2 COP)Heat recovery 0.60 kW/ton 0.69 kW/ton (5.9 COP) (5.1 COP) Entering to leaving water temperatures:Evaporator 54°F to 44°F 54°F to 44°F (12.2°C to 6.7°C) (12.2°C to 6.7°C)Condenser 85°F to 95°F 85°F to 105°F (29.4°C to 35.0°C) (29.4°C to 40.6°C)
  17. 17. heat-recovery chiller controlCondensing Temperature unloading with constant % maximum pressure differential leaving hot-water temperature C A unloading with constant B entering hot-water temperature % load
  18. 18. heat-recovery chiller controlCondensing TemperatureCompressor type Acceptable basis of controlPositive displacement Entering-condenser water temperature Leaving-condenser water temperature • Provides less capacity • Uses more powerCentrifugal Entering-condenser water temperature • Reduces likelihood of surge
  19. 19. Energy Recovery Topics Airside  Waterside  Outdoor air  Requirements  Types  Types  Requirements  Operation  System configurations  Supply air tempering  Operation  Requirements  Operation
  20. 20. system configurationPrimary–Secondary Available heat off = 150 × (52.6 – 40) 52.6°F 40°F = 1890 MBh Auxiliary heat required 750 gpm = 2000 – 1890 52.6°F 40°F = 110 MBh heat-recovery 300 gpm chiller production52.6°F (supply) 40°F distribution 225 gpm (demand) 40°F56°F 825 gpm
  21. 21. system configurationPreferential Loading Available heat off = 150 × (56 – 40) 51.2°F 40°F = 2400 MBh Rejected heat 750 gpm = 2400 – 2000 production51.2°F (supply) = 400 MBh 40°F525 gpm distribution 225 gpm (demand) 56.0°F 40°F heat-recovery 300 gpm chiller 40°F56°F 825 gpm
  22. 22. system configurationsSidestream Loading off Available heat = 150 × (56 – 42.7) 50.2°F 40°F = 2000 MBh 900 gpm production No rejected heat50.2°F (supply) No auxiliary heat51.2°F 40°F distribution 75 gpm (demand) 42.7°F 56°F heat-recovery 300 gpm chiller 40°F56°F 825 gpm
  23. 23. system configurationsSidestream LoadingControl strategies:  Satisfy heating requirements  Maintain leaving-condenser water temperature (positive-displacement compressors)
  24. 24. system configuration comparisonHeat Available/Required System configuration Primary–Characteristic secondary Preferential SidestreamCooling load:cooling-only units 393 tons 350 tons 383 tonsheat-recovery unit 157 tons 200 tons 167 tonsHeat-recovery 40°F 40°F 42.7°Fsupply temperatureAvailable heat 1890 MBh 2400 MBh 2000 MBhAuxiliary heat 110 MBh –400 MBh* 0 MBhrequired*Surplus recovered heat must be rejected
  25. 25. system configurations Variable Primary Flow Piping heat-recovery chiller in sidestream position may simplify control bypass line modulating control valveVFD for minimum chiller flow heat-recovery chiller control valve
  26. 26. system configurationsDistributed SidestreamTypical application:  Remote heating requirement  Chilled water load  Small chiller (or water-to-water heat pump) heating load heat-recovery chiller chilled water supply or return
  27. 27. airside system options Load-shedding economizer heat-recovery chiller heating load chilled water supply or return Control cooling load so heat rejection equals heating loadoutdoor-air controllertemperature sensor
  28. 28. airside system optionsLoading chiller withexhaust airstream Water from chiller Water to chiller EA RA C EA space T H T C HOA MA CA SA
  29. 29. single condenserHeat-Recovery Control controller V1 cooling tower heating T1 load V2 heat condenser exchanger P P water-cooled T2 chiller controller P evaporator cooling load
  30. 30. Dual-Condenser Chillersheat-recoverycondenserstandardcondenserpiped to cooling tower centrifugal heat-recovery chiller
  31. 31. dual condenserHeat-Recovery Controlcontroller cooling T2 tower P heating V2 controller load standard condenser T1 heat- P recovery P condenser auxiliary water-cooled heat P evaporator chiller Control based on entering-condenser water temperature cooling load
  32. 32. Analysis Toolstool applicationSystem Analyzer™ High-level scoping (< 1 hr)TRACE™ Chiller Plant Simplified building entriesAnalyzer Full analysis of chilled water plant, economic ratesEnergyPlus, HAP, TRACE Full energy simulation Hour-by-hour calculations of energy consumption, power demand, related costs
  33. 33. Waterside EnergyRecovery Steps Simultaneous heating  Place the chiller(s) in and cooling loads the appropriate system location Chiller HR capacity = Design heat recovery  Design the system with load the proper connections and controls Select lowest temperature that  Train the building meets requirements operators Select the proper  Operate the system chiller type properly Analyze the system
  34. 34. waterside heat recoveryReferencesFrom Trane: Waterside Heat Recovery in HVAC Systems SYS-APM005-EN 1991 Engineers Newsletter: “Two Good Old Ideas Combine to Form One New Great Idea” others: 2008 ASHRAE Handbook: HVAC Systems and Equipment chapter 8 2003 ASHRAE Journal: “Energy Efficiency for Semiconductor Manufacturing Facilities” Ralph M. Cohen, PE (August issue)
  35. 35. waterside heat recoveryReferences2008 ASHRAE Handbook: HVAC Systems and Equipmentchapter 82003 ASHRAE Journal: “Energy Efficiency for SemiconductorManufacturing Facilities”Ralph M. Cohen, PE (August issue)