Presentation on theme: "Retro-Commissioning: A Tool for Improving HVAC Systems and Energy Cost Reduction Speaker: William McGuire, P.E."— Presentation transcript:
Retro-Commissioning: A Tool for Improving HVAC Systems and Energy Cost Reduction Speaker: William McGuire, P.E.
Retro-Commissioning of Existing Buildings Why Retro-Cx What is Retro-Cx ? How do you do it / what to look for Case Studies Take-Away AGENDA
Why Retro-Cx Older bldgs. (Pre 1990) on average consume more energy Antiquated control systems that dont work Energy saving control strategies missed in design Neglected maintenance wasting energy and/or causing IAQ problems System upgrades that miss the mark Building usage / floor plans changed
Why Retro-Cx Energy cost are only expected to rise Economic outlook may prevent new construction Employee / Community goodwill – Its the right thing to do Owners learn more about their own facilities Benefits intended to be long lasting Simple payback typically less than two years
Why Retro-Cx Leased Buildings LEED EB / ENERGY STAR buildings may become a differentiator High energy costs translate into increased rent cost
Why Retro-Cx Source: US Government Energy Information Administration Consumption in Gross Energy by Year Constructed - 2003 45% less energy consumed New buildings 35% to 57% more efficient Energy intensity 10% less
Why Retro-Cx A study by Lawrence Berkeley National Laboratory (LBNL) - 2004 Retro-Cx results Whole-building electricity savings range from 5% to 15% Gas savings range from 1% to 23% Payback ranged from 0.2 to 2.1 years The bigger the building typically the better the payback period Small buildings have opportunity as well Source: A RetroCommissioning Guide for Building Owners - PECI
Why Retro-Cx Lawrence Berkeley National Laboratory (LBNL) – 2004 Value of Energy Savings$0.11 - $0.72/ft 2 Value of Non Energy Savings$0.10 - $0.45/ft 2 Non Energy: Equip Life, thermal comfort, IAQ, productivity, liability, etc.
1996 PECI/EPA/DOE Study of 60 Commercial Buildings: 40% 33% 15% HVAC Problems Sensors not operating properly Missing Equipment Why Retro-Cx
Why Retro-Cx Retro-Commissioning X-nth Examples Energy Savings $/sf BuildingSq.Ft.Annual SavingsSavings $/sf% Energy Savings Hospital185,000$100,000$0.5418% Healthcare100,000$135,000$1.3530% Hospital190,000$75,000$0.3913% Hospital150,000$80,000$0.5318% Office Bldg54,000$38,500$0.7140% ROI BuildingAnnual Savings5 year ROI Hospital in Orlando$200,0002,000 % University Research Bldg$114,0002,000 % Aquarium$200,000350 % Casino$75,000400 % Hospital in Central Florida$200,000450 %
Retro-commissioning is GREENER If Retro-commissioning our existing buildings can save just 10% energy consumption Reduce oil imports by 50%. Almost meets Kyoto Protocol. Exploit our existing buildings, not the environment !
What is Retro- Commissioning?
DISCOM What is Retro-Cx Design Installation Set-up / TAB Controls / Optimization Operation Maintenance RETRO-Commissioning is evaluating and performance testing an Existing buildings HVAC….
Reveals 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. What 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
What is Retro-Cx PROCESS: 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-commissionings cost is a few weeks of time for the commissioning team. The cost savings discovered usually pay back the retro-commissioning cost in months. Retro-Commissioning Defined: Its a Tune-up, not just an ECM list
Retro- Commissioning How do you do it? Uncovering the waste in DISCO&M
Show Me the Easy Money HVAC Energy Cost Can Vary Widely HVAC Energy Cost Variation $1-2 = Good $4-6 = Evil Energy Cost vs. HVAC Complexity $2.00/sf Light Commercial $3.00Office/School $4.00Institutional $5.0024/7 Hospital $6.00Laboratory Average building = 46% HVAC Wasteful building = 2X
Where is the HVAC Energy Savings? Gas Pedal / Brake Pedal Syndrome Improper DISCO&M = energy savings opportunities HVAC systems have many combinations of gas pedal / brake pedals that could be affected by improper DISCO&M.
Where to Start? Although each building and system is unique you can start with the following: Interview facility personnel Review construction documents Review the controls workstation Walk the site
Where 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 be Keep them informed on what you find, it may trigger additional thoughts If interested, train them on how the systems work
Where to Start? Review construction documents Understand the design and how the systems are supposed to work –Use the schedules and rules of thumb –Sum up connected loads (air and water) –Compare design installation to installed –Check coil Ts
Where to Start? Review the Controls workstation and look for: –Incorrect AHU leaving air temperature set points –Valve commands at 0% or 100%, or valves fighting –OA Damper commands –Controlling sensors like RH and CO2 –Pump / fan status on when command is off (in HAND?) –Chilled water T (secondary supply & primary return) – Chilled water supply temperature / set point – General space temperatures –System stability
AHU Controls Interrogation Retro-Cx Example Coil LAT Most common discovery during Retro-Commissioning – CONTROLS not Optimized: GAS PEDAL is floored, but the BRAKES are used to control the speed of the systems. Unit LAT Setpoint Dehumidification Setpoint SA SP Setpoint OA damper position Search for Improper Set points Device Operation Modes Input values
DIS Problems Improper programming sequence Coils piped backwards OA damper occ. / unocc. set points VAV damper actuator / calibration Service access restricted Space thermostat calibration Sensors in wrong location VFD / fan sheave sized for max concurrent CO&M Problems Overridden BAS temp space set points Increased VAV airflow set points High duct static DP set point Disabled duct static DP reset logic Decreased cooling coil setpoint Preheat and Cooling coil fighting Disable supply air temp reset logic Actual OA damper position Dirty filters T T VFD OA RA SA DP VAV T Things to look for Hidden DISCO&M Problems = High Energy Costs
Things to look for Chiller Plants Add / subtract logic Incorrect set points (chiller and system) Chillers / pumps / tower fans in manual Condenser water control Controlling sensor calibration Chiller isolation valves
Use Your Experience Does the number of operating chillers / boilers make sense? –Add/subtract logic –Sensor calibration –Decoupler issues Does the duct static pressure set point seem right? –Whos 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
Where is the HVAC Energy Savings? Benchmarks Annual Elec Cost 1 hp motor = $500 1 Ton cooling (MA unit)$750 = DX $400 = CHW 1,000 CFM OA (8 tons)$10,000 = DX $5,000 = CHW 1 degree Setpoint on AHU7% of cooling capacity (10,000 cfm = 35 tons) CEP generation capacity = Load, Attack the Load first
Retro-Commissioning Exercise Expose the Evil in HVAC Systems Identical air handling systems keep the space comfortable at 72F. One uses twice the energy. HOW? Systems sized for peak loads and operates in- between. One foot on the gas, one on the brake One foot on the gas T T VFD DP VAV T T T VFD DP VAV T
System Component Performance Performance Cost (6 summer months) = $12,000 (62 kW, $.07) $25,000 (129 kW) Fan 7,500 cfm = 5 kW10 kW OA 2,500 cfm (95F/78F) = 33 tons (52 LAT)45 tons (50F LAT, +OA) Preheat coil = 0 kW23 kW Reheat coils 20% = 9.5 kW23 kW (50%) Chilled water 45F = 47 kW (45F)72 kW (42F) Both set-ups have comfortable 72F space temps !! Retro-Commissioning Exercise Evil Performance = 2 x Groovy T T VFD DP VAV T The Good! The Bad!
Retro- Commissioning 4 Case Studies
Retro- 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.
University Biological Science Bldg: Fan Frame Problems Two parallel AHUs headered together Fan motor frame that kept breaking requiring re- welding 30,000 CFM variable speed fans 4 Different stories of how the system was supposed to operate ??
Fan Curve #1: Occupied Conditions Design Adjusted operating point, 49Hz. 60 Hz 45 Hz 30 Hz Turbulent surge zone of fan curve Fan Curve #2: Unoccupied Conditions VAV Differential Pressure Setpoint: Set too high by untrained staff Savings: $15,000 How: Fans allowed to back off from 60Hz to 30Hz at night University Biological Science Bldg: – Fan Operation in Surge
T T VFD OA RA SA DP VAV T Pre-heat Coil improperly on. Heating summer air from 84F up to 104F. Cooling Coil actuator broken. Overcooling the air to 49F instead of 55F. Static pressure setpoint set too high at 2.2, instead of 1.0. Fan always at 60Hz. 2-position VAV box closing more than necessary to eat excess static pressure. Re-heat coil required to heat the overcooled air. Water Side Gas: pre-heat coil Brakes: cooling coil Gas: re-heat coil Air Side Gas: Supply fan Brakes: VAV damper University Biological Science Building Hidden Discoveries
PROBLEMSAVINGS DISCO&M AHU 1-1 Low Leaving Air Temp – Re-heating by VAV:$15,000C,O AHU 1-1 Low Leaving Air Temp – Over-cooling:$30,000M AHU 1-1 Pre-heat Coil Operation – Pre-heating:$27,000M AHU 1-1 Pre-heat Coil Operation – Re-cooling:$25,000M AHU Excess Fan Speed:$17,000C,O,M Total:$114,000 per year. Baseline Savings: $114,000 /yr ($0.90 / sf) University Biological Science Bldg: Retro-Cx Results Prevention: Training Legacy
Retro- 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.
BAS Interrogation - Observed Problems Overflowing = extra pumping 1.5 ??? Should be <100% at part load Improper Technician set-up of Drives. Release 60hz ceiling for direct drive fans.
BAS Interrogation - VAV w/ Reheat Optimization Opportunities from Base Design Min airflow, max heating, still over-cooling the space? Room is 2 deg lower than setpoint.
BAS Interrogation - Cooling Towers Bad Operating Advice from Technician Technician said lower CW temp. When OA is 65ºF WB, you cant get less than 71ºF regardless of tower speed. (6F approach)
BAS Interrogation - CHW Installation Defects, Bad Data How did the CHWS go from 44ºF to 50ºF ? Short Decoupler Effect
BAS Interrogation - HW Boilers Improper Base Sequence of Operations Design coil delta-T is 40ºF The boilers are dying from short cycling at 20% loading.
Retro-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 = $24,000 Hot Water Boiler Sequence – Revise controls to turn off lag boiler properly. Save boiler fuel from eliminating pre- and post-purge heat loss. +/- $20,000 Fix CHW Low Delta-T Problem – save secondary pump energy by pumping less colder water. Save 40kw for ½ year =$80,000 AHU Static Pressure 1.5 Setpoint – Optimize SPs lower to save fan energy. Assume 5% savings of 475 bhp fan motors = $50,000 Secondary Items CHW – Constant speed pumps with variable 2-way valves; design oversight? Can save pump energy by going variable primary (add drives). $20,000 VAV with Reheat – many are reheating. Min cfm setting could be lowered to avoid reheating. And SATR logic can be implemented. Save +/- $big
PROBLEMSAVINGS DISCO&M Cooling Tower Operation:$24,000 O Hot Water Boiler Sequence:$20,000 IS Chilled Water: Low Delta-T Syndrome$80,000 D or I AHU Static Pressure Setpoint Optimization:$50,000 S Constant pump CHW system with 2-way valves :$20,000 D VAV re-heating setpoints:$ big S Total:$200,000 per year. Baseline Savings: $200,000 /yr ($0.50 / sf) Retro-Commissioning Results
Retro- Commissioning DISCO&M Case Study #3 Not-For-Profit Hospital O&M Looking for HIDDEN CAPACITY resulting from possible improper operation.
Hospital BAS Interrogation - Typical Air Handling Unit 1. Chilled Water Valve – failed open, making 49.6ºF air. 5.4ºF colder than set point 2. Supply Fan VFD – is at 100%, no spare capacity for filter loading 3. Outdoor air damper – Software Override (SWO), changed from design setpoint
Hospital 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.
6 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) Retro-Commissioning Case Study #3: Summary Not-for-profit Hospital
Retro- Commissioning DISCO&M Case Study #4 For-Profit Hospital DISCO&M 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.
Hospital BAS Interrogation - Chiller Plant Logic Problems Improper Chiller OFF Logic – Operating more pumps & towers than necessary Building Load 1000 tons. (2 chillers needed) Three 550 ton chillers ON. (1650 tons)
For-Profit Hospital: Improper Constant Volume Pump Set-up Circuit Setter – 80% Closed. Should have trimmed impeller
For-Profit Hospital: AHU Investigation – Improper Design Original Design / Construction Problems: Low first cost solutions = high long term operating costs
PROBLEMSAVINGS DISCO&M AHU Supply Air Temp Reset Logic$72,000 D Condenser Water Reset Temp Reset Logic$33,000 D Chiller ON/OFF Logic$10,000 D Pump Valve Adjustment$26,000S AHU Device Tune-up$58,000 O&M Modify AHU Re-heat coil retro-fit$186,000 DIS Total:$385,000 Implementation Cost:$150,000 Baseline Savings: $385,000 /yr ($1.50 / sf) Retro-Cx Investment: 5 month Retro-Commissioning Case Study #4: Summary For-Profit Hospital Prevention: Design review, Performance Testing Training
WHAT TO LOOK FOR: Variable systems and their set points Gas/Brake systems – pre/re-heat, humidity, VAV, parallel equip Starters in Hand mode because a control device isnt working HVAC loads. CEPs can only meet loads. BAS Computer Screens = anything at 100% capacity Take-Away Retro-Commissioning Existing Buildings DISCO&M