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Retro-Commissioning:
A Tool for Improving HVAC
Systems and Energy Cost
Reduction
Speaker: William McGuire, P.E.
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Retro-Commissioning of Existing Buildings
Why Retro-CxWhat is Retro-Cx ?How do you do it / what to look forCase StudiesTake-Away
AGENDA
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Why Retro-Cx
• Older bldgs. (Pre 1990) on average consume more energy
• Antiquated control systems that don’t 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
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Why Retro-Cx
• Energy cost are only expected to rise
• Economic outlook may prevent new construction
• Employee / Community goodwill – “It’s 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
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Why Retro-Cx
Leased Buildings
• LEED EB / ENERGY STAR buildings may become a differentiator
• High energy costs translate into increased rent cost
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Why Retro-CxSource: 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
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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
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Why Retro-Cx
Lawrence Berkeley National Laboratory (LBNL) – 2004
Value of Energy Savings $0.11 - $0.72/ft2
Value of Non Energy Savings $0.10 - $0.45/ft2
Non Energy: Equip Life, thermal comfort, IAQ, productivity, liability, etc.
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• 1996 PECI/EPA/DOE Study of 60 Commercial Buildings:
40% 33%15%
HVAC Problems
Sensors not operating properly
Missing Equipment
Why Retro-Cx
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Why Retro-CxRetro-Commissioning X-nth Examples
Energy Savings $/sf
Building Sq.Ft. Annual Savings
Savings $/sf % Energy Savings
Hospital 185,000 $100,000 $0.54 18%
Healthcare 100,000 $135,000 $1.35 30%
Hospital 190,000 $75,000 $0.39 13%
Hospital 150,000 $80,000 $0.53 18%
Office Bldg 54,000 $38,500 $0.71 40%ROI
Building Annual Savings
5 year ROI
Hospital in Orlando $200,000 2,000 %
University Research Bldg $114,000 2,000 %
Aquarium $200,000 350 %
Casino $75,000 400 %
Hospital in Central Florida $200,000 450 %
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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 !
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What isRetro-Commissioning?
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DISCOM
What is Retro-Cx
DesignInstallationSet-up / TABControls /
OptimizationOperationMaintenance
RETRO-Commissioning is evaluating and performance testing an Existing building’s HVAC….
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• 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
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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
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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-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.
Retro-Commissioning Defined: It’s a Tune-up, not just an ECM list
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Retro-CommissioningHow do you do it?Uncovering the waste in DISCO&M
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Show Me the Easy MoneyHVAC 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
$3.00 Office/School
$4.00 Institutional
$5.00 24/7 Hospital
$6.00 Laboratory
“Average” building = 46% HVAC
“Wasteful” building = 2X
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Where is the HVAC Energy Savings?Gas Pedal / Brake Pedal SyndromeImproper DISCO&M = energy savings
opportunities
HVAC systems have many combinations of gas pedal / brake pedals that could be affected by improper DISCO&M.
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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
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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
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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
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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
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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
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“DIS” ProblemsImproper 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” ProblemsOverridden 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 forHidden DISCO&M Problems = High Energy Costs
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Things to look forChiller 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
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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?– 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
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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 AHU 7% of cooling capacity
(10,000 cfm = 35 tons)
CEP generation capacity = ‘Load’, Attack the Load first
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Retro-Commissioning ExerciseExpose 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
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System Component PerformancePerformance
Cost (6 summer months) = $12,000 (62 kW, $.07)$25,000 (129 kW)
Fan 7,500 cfm = 5 kW 10 kWOA 2,500 cfm (95F/78F) = 33 tons (52 LAT) 45 tons (50F LAT, +OA)Preheat coil = 0 kW 23 kWReheat coils 20% = 9.5 kW 23 kW (50%)Chilled water 45F = 47 kW (45F) 72 kW (42F)
Both set-ups have comfortable 72F space temps !!
Retro-Commissioning ExerciseEvil Performance = 2 x Groovy
T T
VFD
DP
VAV
T
The Good!
The Bad!
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Retro-Commissioning4 Case Studies
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Retro-CommissioningDISCO&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.
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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 ??
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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
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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 SideGas: pre-heat coilBrakes: cooling coilGas: re-heat coil
Air SideGas: Supply fanBrakes: VAV damper
University Biological Science Building Hidden Discoveries
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PROBLEM SAVINGSDISCO&M
AHU 1-1 Low Leaving Air Temp – Re-heating by VAV: $15,000 C,O
AHU 1-1 Low Leaving Air Temp – Over-cooling: $30,000 M
AHU 1-1 Pre-heat Coil Operation – Pre-heating: $27,000 M
AHU 1-1 Pre-heat Coil Operation – Re-cooling: $25,000 M
AHU Excess Fan Speed: $17,000 C,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
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Retro-CommissioningDISCO&M Case Study #2CA Research
Laboratory“DSCO&M”
Corporate Mandate: 10% energy savings.
HVAC operators did not understand where the ‘optimized’ operating points were.
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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.
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BAS Interrogation - VAV w/ ReheatOptimization Opportunities from Base Design
Min airflow, max heating,
still over-cooling the
space?
Room is 2 deg lower
than setpoint.
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BAS Interrogation - Cooling TowersBad 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)
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BAS Interrogation - CHWInstallation Defects, Bad Data
How did the CHWS go from 44ºF to 50ºF ?
“Short Decoupler Effect”
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BAS Interrogation - HW BoilersImproper Base Sequence of Operations
Design coil delta-T is 40ºF
The boilers are dying from short cycling at 20% loading.
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Retro-CommissioningCase 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 SP’s 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
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PROBLEM SAVINGS 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
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Retro-CommissioningDISCO&M Case Study #3Not-For-Profit Hospital
“O&M”
Looking for HIDDEN CAPACITY resulting from possible improper operation.
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Hospital 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
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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.
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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-CommissioningCase Study #3: Summary Not-for-profit Hospital
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Retro-CommissioningDISCO&M Case Study #4For-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.
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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)
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For-Profit Hospital: Improper Constant Volume Pump Set-up
Circuit Setter – 80% Closed. Should have trimmed impeller
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For-Profit Hospital: AHU Investigation – Improper Design
Original Design / Construction Problems: Low first cost solutions = high long term operating costs
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PROBLEM SAVINGSDISCO&MAHU Supply Air Temp Reset Logic $72,000
D Condenser Water Reset Temp Reset Logic $33,000
DChiller ON/OFF Logic $10,000DPump Valve Adjustment $26,000
SAHU Device Tune-up $58,000O&MModify AHU Re-heat coil retro-fit $186,000
DISTotal: $385,000
Implementation Cost: $150,000
Baseline Savings: $385,000 /yr ($1.50 / sf)Retro-Cx Investment: 5 month
Retro-CommissioningCase Study #4: Summary For-Profit Hospital
Prevention: Design review ,Performance TestingTraining
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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 isn’t working• ‘HVAC loads’. CEP’s can only meet loads. • BAS Computer Screens = anything at 100%
capacity
Take-Away Retro-Commissioning Existing Buildings
DISCO&M
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Questions?