Retro-Commissioning:

A Tool for Improving HVAC

Systems and Energy Cost

Reduction

Speaker: William McGuire, P.E.

Retro-Commissioning of Existing Buildings

Why Retro-CxWhat is Retro-Cx ?How do you do it / what to look forCase StudiesTake-Away

AGENDA

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

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

Why Retro-Cx

Leased Buildings

• LEED EB / ENERGY STAR buildings may become a differentiator

• High energy costs translate into increased rent cost

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

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/ft2

Value of Non Energy Savings $0.10 - $0.45/ft2

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-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 %

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 isRetro-Commissioning?

DISCOM

What is Retro-Cx

DesignInstallationSet-up / TABControls /

OptimizationOperationMaintenance

RETRO-Commissioning is evaluating and performance testing an Existing building’s 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

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-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

Retro-CommissioningHow do you do it?Uncovering the waste in DISCO&M

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

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.

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” 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

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

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

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

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

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!

Retro-Commissioning4 Case Studies

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.

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 SideGas: pre-heat coilBrakes: cooling coilGas: re-heat coil

Air SideGas: Supply fanBrakes: VAV damper

University Biological Science Building Hidden Discoveries

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

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.

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/ ReheatOptimization Opportunities from Base Design

Min airflow, max heating,

still over-cooling the

space?

Room is 2 deg lower

than setpoint.

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)

BAS Interrogation - CHWInstallation Defects, Bad Data

How did the CHWS go from 44ºF to 50ºF ?

“Short Decoupler Effect”

BAS Interrogation - HW BoilersImproper Base Sequence of Operations

Design coil delta-T is 40ºF

The boilers are dying from short cycling at 20% loading.

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

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

Retro-CommissioningDISCO&M Case Study #3Not-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 point2. Supply Fan VFD – is at 100%, no spare capacity for filter loading3. 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-CommissioningCase Study #3: Summary Not-for-profit Hospital

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.

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

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

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

Questions?