Presentation on theme: "Retro-Commissioning: A Tool for Improving HVAC Systems and Energy Cost"— Presentation transcript:
1Retro-Commissioning: A Tool for Improving HVAC Systems and Energy Cost ReductionSpeaker:William McGuire, P.E.1
2AGENDA Retro-Commissioning of Existing Buildings Why Retro-Cx What is Retro-Cx ?How do you do it / what to look forCase StudiesTake-Away
3Why Retro-Cx Older bldgs. (Pre 1990) on average consume more energy Antiquated control systems that don’t workEnergy saving control strategies missed in designNeglected maintenance wasting energy and/or causing IAQ problemsSystem upgrades that miss the markBuilding usage / floor plans changed
4Why Retro-Cx Energy cost are only expected to rise Economic outlook may prevent new constructionEmployee / Community goodwill – “It’s the right thing to do”Owners learn more about their own facilitiesBenefits intended to be long lastingSimple payback typically less than two years
5Why Retro-Cx Leased Buildings LEED EB / ENERGY STAR buildings may become a differentiatorHigh energy costs translate into increased rent cost
6Why Retro-Cx Source: US Government Energy Information Administration Energy intensity 10% lessConsumption in Gross Energy by Year Constructed45% less energy consumedNew buildings 35% to 57% more efficient
7Why Retro-CxA study by Lawrence Berkeley National Laboratory (LBNL)Retro-Cx resultsWhole-building electricity savings range from 5% to 15%Gas savings range from 1% to 23%Payback ranged from 0.2 to 2.1 yearsThe bigger the building typically the better the payback periodSmall buildings have opportunity as wellSource: A RetroCommissioning Guide for Building Owners - PECI
8Why Retro-Cx Lawrence Berkeley National Laboratory (LBNL) – 2004 Value of Energy Savings $ $0.72/ft2Value of Non Energy Savings $ $0.45/ft2Non Energy: Equip Life, thermal comfort, IAQ, productivity, liability, etc.
9Sensors not operating properly Why Retro-Cx1996 PECI/EPA/DOE Study of 60 Commercial Buildings:15%33%40%HVAC ProblemsSensors not operating properlyMissing Equipment
10Why Retro-Cx Retro-Commissioning X-nth Examples Energy Savings $/sfBuildingSq.Ft.Annual SavingsSavings $/sf% Energy SavingsHospital185,000$100,000$0.5418%Healthcare100,000$135,000$1.3530%190,000$75,000$0.3913%150,000$80,000$0.53Office Bldg54,000$38,500$0.7140%ROIBuildingAnnual Savings5 year ROIHospital in Orlando$200,0002,000 %University Research Bldg$114,000Aquarium350 %Casino$75,000400 %Hospital in Central Florida450 %
11Retro-commissioning is “GREENER” Green Moment If Retro-commissioning our existing buildings can save just 10% energy consumptionReduce oil imports by 50%.Almost meets Kyoto Protocol.Exploit our existing buildings, not the environment !
13DISCOM What is Retro-Cx RETRO-Commissioning is evaluating and performance testing an Existing building’s HVAC….DesignInstallationSet-up / TABControls / OptimizationOperationMaintenanceDISCOM
14What is Retro-CxReveals hidden deficiencies that could have been avoided by commissioning.Highlights O&M problems that could have been avoided through better training.Reveals hidden control system problems, lowering energy costs.
15What is Retro-Cx Retro-Cx is NOT an energy study! Energy studies leave the Owner with proof of what they already suspect , something is wrong.It provides no answers as to what to do or were to start.Skip all the paperwork and go find the MONEY
16What is Retro-CxRetro-Commissioning Defined: It’s a Tune-up, not just an ECM listPROCESS: An experienced commissioning team investigates the existing systems operation looking for equipment and systems that are not operating “properly”.RESULT: The most common HVAC discovery is even though the space temperatures are comfortable, the systems are consuming much more energy than necessary due to over-cooling, over-heating, over-ventilating. Reveals hidden problems in DISCO&M.COST: Retro-commissioning’s cost is a few weeks of time for the commissioning team. The cost savings discovered usually pay back the retro-commissioning cost in months.
17Retro-CommissioningHow do you do it?Uncovering the waste in DISCO&M
18HVAC Energy Cost Variation Show Me the Easy MoneyHVAC Energy Cost Can Vary Widely“Average” building = 46% HVAC“Wasteful” building = 2XEnergy Cost vs. HVAC Complexity$2.00/sf Light Commercial$3.00 Office/School$4.00 Institutional$ /7 Hospital$6.00 LaboratoryHVAC Energy Cost Variation$1-2 = Good$4-6 = Evil
19Where is the HVAC Energy Savings? Gas Pedal / Brake Pedal SyndromeImproper DISCO&M = energy savings opportunitiesHVAC systems have many combinations of gas pedal / brake pedals that could be affected by improper DISCO&M.
20Where to Start?Although each building and system is unique you can start with the following:Interview facility personnelReview construction documentsReview the controls workstationWalk the site
21Where to Start? Interview facility personnel They are a great resource as to why things are the way they are but not necessarily on how they should beKeep them informed on what you find, it may trigger additional thoughtsIf interested, train them on how the systems work
22Where to Start? Review construction documents Understand the design and how the systems are supposed to workUse the schedules and rules of thumbSum up connected loads (air and water)Compare design installation to installedCheck coil ∆Ts
23Where to Start? Review the Controls workstation and look for: Incorrect AHU leaving air temperature set pointsValve commands at 0% or 100%, or valves fightingOA Damper commandsControlling sensors like RH and CO2Pump / fan status on when command is off (in HAND?)Chilled water ∆T (secondary supply & primary return)Chilled water supply temperature / set pointGeneral space temperaturesSystem stability
24AHU Controls Interrogation Retro-Cx ExampleDehumidification SetpointSearch for ImproperSet pointsDevice OperationModesInput valuesOA damper positionUnit LAT SetpointSA SP SetpointCoil LATMost common discovery during Retro-Commissioning – CONTROLS not Optimized:GAS PEDAL is floored, but the BRAKES are used to control the speed of the systems.
25Things to look for Hidden DISCO&M Problems = High Energy Costs VFDDPOASATTVAVRAT“DIS” ProblemsImproper programming sequenceCoils piped backwardsOA damper occ. / unocc. set pointsVAV damper actuator / calibrationService access restrictedSpace thermostat calibrationSensors in wrong locationVFD / fan sheave sized for ‘max concurrent’“CO&M” ProblemsOverridden BAS temp space set pointsIncreased VAV airflow set pointsHigh duct static DP set pointDisabled duct static DP reset logicDecreased cooling coil setpointPreheat and Cooling coil fightingDisable supply air temp reset logicActual OA damper positionDirty filters
26Things to look for Chiller Plants Add / subtract logic Incorrect set points (chiller and system)Chillers / pumps / tower fans in manualCondenser water controlControlling sensor calibrationChiller isolation valves
27Use Your ExperienceDoes the number of operating chillers / boilers make sense?Add/subtract logicSensor calibrationDecoupler issuesDoes the duct static pressure set point seem right?Who’s set point is it?Sensor calibration?Does the number of pumps operating make sense?Do the differential water pressure set points make sense?Sensor location / calibration
28Where is the HVAC Energy Savings? BenchmarksAnnual Elec Cost1 hp motor = $5001 Ton cooling (MA unit) $750 = DX$400 = CHW1,000 CFM OA (8 tons) $10,000 = DX$5,000 = CHW1 degree Setpoint on AHU 7% of cooling capacity(10,000 cfm = 35 tons)CEP generation capacity = ‘Load’, Attack the Load first
29Retro-Commissioning Exercise Expose the ‘Evil’ in HVAC SystemsOne foot on the gas, one on the brakeTVFDDPVAVOne foot on the gasTVFDDPVAVIdentical air handling systems keep the space comfortable at 72F.One uses twice the energy.HOW? Systems sized for peak loads and operates in-between.
32Retro-Commissioning DISCO&M Case Study #1 University Biological Science Building“CO&M”HVAC System operators and the Controls vendor were not familiar with the basis of design.
33University Biological Science Bldg: Fan Frame Problems Two parallel AHUs headered together30,000 CFM variable speed fans4 Different stories of how the ‘system’ was supposed to operate ??Fan motor frame that kept breaking requiring re-welding
34Fan Curve #2: Unoccupied Conditions Fan Curve #1: Occupied Conditions University Biological Science Bldg: – Fan Operation in Surge60 Hz45 Hz30 HzTurbulent ‘surge’ zone of fan curveDesignAdjusted operating point, 49Hz..Fan Curve #2: Unoccupied ConditionsFan Curve #1: Occupied ConditionsVAV Differential Pressure Setpoint: Set too high by untrained staffSavings: $15,000How: Fans allowed to back off from 60Hz to 30Hz at night
35University Biological Science Building Hidden Discoveries Static pressure setpoint set too high at 2.2” , instead of 1.0”.Fan always at 60Hz.VFDDPOASATRe-heat coil required to heat the overcooled air.TVAVRATPre-heat Coil improperly on. Heating summer air from 84F up to 104F.2-position VAV box closing more than necessary to ‘eat’ excess static pressure.Cooling Coil actuator broken. Overcooling the air to 49F instead of 55F.Water SideGas: pre-heat coilBrakes: cooling coilGas: re-heat coilAir SideGas: Supply fanBrakes: VAV damper
36University Biological Science Bldg: Retro-Cx Results PROBLEM SAVINGS DISCO&MAHU 1-1 Low Leaving Air Temp – Re-heating by VAV: $15,000 C,OAHU 1-1 Low Leaving Air Temp – Over-cooling: $30,000 MAHU 1-1 Pre-heat Coil Operation – Pre-heating: $27,000 MAHU 1-1 Pre-heat Coil Operation – Re-cooling: $25,000 MAHU Excess Fan Speed: $17,000 C,O,MTotal: $114,000 per year.Baseline Savings: $114,000 /yr ($0.90 / sf)Prevention: Training Legacy
37Retro-Commissioning DISCO&M Case Study #2 CA Research Laboratory “DSCO&M”Corporate Mandate: 10% energy savings.HVAC operators did not understand where the ‘optimized’ operating points were.
38BAS Interrogation - Observed Problems Improper Technician set-up of Drives. Release 60hz ceiling for direct drive fans.Should be <100% at part load1.5” ???Overflowing = extra pumping
39BAS Interrogation - VAV w/ Reheat Optimization Opportunities from Base DesignMin airflow, max heating, still over-cooling the space?Room is 2 deg lower than setpoint.
40Technician said lower CW temp. BAS Interrogation - Cooling TowersBad Operating Advice from TechnicianTechnician said lower CW temp.When OA is 65ºF WB, you cant get less than 71ºF regardless of tower speed.(6F approach)
41BAS Interrogation - CHW Installation Defects, Bad DataHow did the CHWS go from 44ºF to 50ºF ?“Short Decoupler Effect”
42BAS Interrogation - HW Boilers Improper Base Sequence of OperationsDesign coil delta-T is 40ºFThe boilers are dying from short cycling at 20% loading.
43Retro-Commissioning Case Study #2: Summary Primary Items Cooling Tower Operation – Turn 1 off, and modify software for condenser water reset based upon wet bulb temp. Save $1200 /wk for 20 weeks = $24,000Hot Water Boiler Sequence – Revise controls to turn off lag boiler properly. Save boiler fuel from eliminating pre- and post-purge heat loss. +/- $20,000Fix CHW Low Delta-T Problem – save secondary pump energy by pumping less colder water. Save 40kw for ½ year = $80,000AHU Static Pressure 1.5” Setpoint – Optimize SP’s lower to save fan energy. Assume 5% savings of 475 bhp fan motors = $50,000Secondary ItemsCHW – Constant speed pumps with variable 2-way valves; design oversight? Can save pump energy by going variable primary (add drives). $20,000VAV with Reheat – many are reheating. Min cfm setting could be lowered to avoid reheating. And SATR logic can be implemented. Save +/- $big
44Retro-Commissioning Results PROBLEM SAVINGS DISCO&MCooling Tower Operation: $24, OHot Water Boiler Sequence: $20, ISChilled Water: Low Delta-T Syndrome $80, D or IAHU Static Pressure Setpoint Optimization: $50, SConstant pump CHW system with 2-way valves : $20, DVAV re-heating setpoints: $ big STotal: $200,000 per year.Baseline Savings: $200,000 /yr ($0.50 / sf)
45Retro-Commissioning DISCO&M Case Study #3 Not-For-Profit Hospital Looking for HIDDEN CAPACITY resulting from possible improper operation.
46Hospital BAS Interrogation - Typical Air Handling Unit 1. Chilled Water Valve – failed open, making 49.6ºF air. 5.4ºF colder than set point2. Supply Fan VFD – is at 100%, no spare capacity for filter loading3. Outdoor air damper – Software Override (SWO), changed from design setpoint
47Hospital BAS Interrogation - Chiller Plant Return Chilled water temperature is too low. The return temperature should be 58F. Too many chilled water coils are over-flowing, and producing low return water temperatures. Another LOW DELTA-T PROBLEM.The flow of 1149 gpm and the calculated tons of 359, calculate a flow rate of 3.2 gpm/ton. The secondary CHW is pumping over 50% more chilled water than it should be due to failed open AHU chilled water valves.
48Retro-Commissioning Baseline Savings: $200,000 /yr ($0.90 / sf) Case Study #3: Summary Not-for-profit Hospital6 of 30 Air Handling Units had hidden cooling coil valve problems.Heating boilers are re-heating the overcooled air.The spare central plant capacity that was ‘discovered’:Cooling: 142 Tons (new spare capacity)Heating: 1.7 million btuh (25% of one big boiler)Baseline Savings: $200,000 /yr ($0.90 / sf)Retro-Cx Investment: 1 day ( Incidental)Value: Defer new 1000 ton chiller ($1000/ton)
49Retro-Commissioning DISCO&M Case Study #4 For-Profit Hospital Administration wanted energy savings.Facilities Staff did not want anyone (us) to look at their system and find potential problems – it might make them look bad.
50Hospital BAS Interrogation - Chiller Plant Logic Problems Building Load 1000 tons.(2 chillers needed)Three 550 ton chillers ON.(1650 tons).Improper Chiller OFF Logic – Operating more pumps & towers than necessary
52For-Profit Hospital: AHU Investigation – Improper Design Original Design / Construction Problems: Low first cost solutions = high long term operating costs
53Retro-Commissioning Case Study #4: Summary For-Profit Hospital PROBLEM SAVINGS DISCO&MAHU Supply Air Temp Reset Logic $72,000 DCondenser Water Reset Temp Reset Logic $33,000 DChiller ON/OFF Logic $10,000 DPump Valve Adjustment $26,000 SAHU Device Tune-up $58,000 O&MModify AHU Re-heat coil retro-fit $186,000 DISTotal: $385,000Implementation Cost: $150,000Baseline Savings: $385,000 /yr ($1.50 / sf)Retro-Cx Investment: 5 monthPrevention:Design review ,Performance TestingTraining
54Take-Away Retro-Commissioning Existing Buildings WHAT TO LOOK FOR:“Variable” systems and their set pointsGas/Brake systems – pre/re-heat, humidity, VAV, parallel equipStarters in ‘Hand’ mode because a control device isn’t working‘HVAC loads’. CEP’s can only meet loads.BAS Computer Screens = anything at 100% capacityDISCO&M