Transcript Retro-Cx - Commissioning

Retro-Commissioning:
A Tool for Improving HVAC
Systems and Energy Cost
Reduction
Speaker:
William McGuire, P.E.
AGENDA
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
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-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
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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:
etc.
Equip Life, thermal comfort, IAQ, productivity,
liability,
Why Retro-Cx
•
1996 PECI/EPA/DOE Study of 60 Commercial Buildings:
15%
40%
HVAC
Problems
33%
Sensors not
operating properly
Missing
Equipment
Why Retro-Cx
Retro-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 %
$75,000
400 %
$200,000
450 %
Casino
Hospital in Central Florida
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?
What is Retro-Cx
RETRO-Commissioning is evaluating and performance testing an Existing building’s HVAC….
DISCOM
Design
Installation
Set-up / TAB
Controls / Optimization
Operation
Maintenance
What is Retro-Cx
•
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
Retro-Commissioning Defined: It’s a Tune-up, not just an ECM list
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 overcooling, 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
How do you do it?
Uncovering the waste in DISCO&M
Show Me the Easy Money
HVAC Energy Cost Can Vary Widely
“Average” building = 46% HVAC
“Wasteful” building = 2X
Energy Cost vs. HVAC Complexity
$2.00/sf
Light Commercial
$3.00
Office/School
$4.00
Institutional
$1-2 = Good
$5.00
24/7 Hospital
$6.00
Laboratory
$4-6 = Evil
HVAC Energy Cost Variation
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:
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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:
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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
Dehumidification
Setpoint
Search for Improper
•
Set points
•
Device Operation
•
Modes
•
Input values
OA damper
position
Coil LAT
Unit LAT
Setpoint
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.
SA SP
Setpoint
Things to look for
Hidden DISCO&M Problems = High Energy Costs
VFD
DP
OA
T
SA
T
VAV
RA
T
“DIS” Problems
“CO&M” Problems
Improper programming sequence
Overridden BAS temp space set points
Coils piped backwards
Increased VAV airflow set points
OA damper occ. / unocc. set points
High duct static DP set point
VAV damper actuator / calibration
Disabled duct static DP reset logic
Service access restricted
Decreased cooling coil setpoint
Space thermostat calibration
Preheat and Cooling coil fighting
Sensors in wrong location
Disable supply air temp reset logic
VFD / fan sheave sized for ‘max concurrent’
Actual OA damper position
Dirty filters
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?
– 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 =
1 Ton cooling
$500
(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 Exercise
Expose the ‘Evil’ in HVAC Systems
One foot on the gas,
one on the brake
VFD
DP
T
T
VAV
T
One foot on the
gas
VFD
DP
T
T
VAV
T
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.
Retro-Commissioning Exercise
Evil Performance = 2 x Groovy
Both set-ups have comfortable
72F space temps !!
VFD
DP
T
T
VAV
T
The Bad!
The Good!
System Component
Performance
Performance
Cost (6 summer months) =
$12,000 (62 kW, $.07)
$25,000 (129 kW)
Fan 7,500 cfm =
OA 2,500 cfm (95F/78F) =
Preheat coil =
Reheat coils 20% =
Chilled water 45F =
5 kW
10 kW
45 tons (50F LAT, +OA)
23 kW
23 kW (50%)
72 kW (42F)
0 kW
33 tons (52 LAT)
9.5 kW
47 kW (45F)
RetroCommissioning
4 Case Studies
RetroCommissioning
University Biological
DISCO&M
CaseScience
Study
Building
#1
“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
30,000 CFM variable speed
fans
4 Different stories of how the
‘system’ was supposed to operate ??
Fan motor frame that kept breaking requiring
re-welding
University Biological Science Bldg: – Fan Operation in Surge
Turbulent
‘surge’ zone
of fan curve
60 Hz
Design
Adjusted
operating
point, 49Hz.
Fan Curve #1: Occupied Conditions
45 Hz
30 Hz
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 Building Hidden Discoveries
Static pressure setpoint set
too high at 2.2” , instead
of 1.0”.
VFD
Fan always at 60Hz.
DP
OA
T
SA
Re-heat coil
required to heat
the overcooled air.
T
VAV
RA
Pre-heat Coil
improperly on.
Heating summer air
from 84F up to 104F.
T
Cooling Coil actuator
broken. Overcooling the air
to 49F instead of 55F.
Water Side
Gas: pre-heat coil
Brakes: cooling coil
Gas: re-heat coil
2-position VAV box
closing more than
necessary to ‘eat’
excess static pressure.
Air Side
Gas: Supply fan
Brakes: VAV damper
University Biological Science Bldg: Retro-Cx Results
PROBLEM
SAVINGS
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:
Baseline Savings:
DISCO&M
$114,000 per year.
$114,000 /yr
Prevention: Training Legacy
($0.90 / sf)
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
Improper Technician set-up of Drives.
Release 60hz ceiling for direct drive fans.
Should be <100% at
part load
1.5” ???
Overflowing = extra
pumping
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 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
Retro-Commissioning Results
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
Total:
Baseline Savings: $200,000 /yr
($0.50 / sf)
$200,000 per year.
S
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.
Retro-Commissioning
Case Study #3: Summary Not-for-profit Hospital
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
Baseline Savings:
Retro-Cx Investment: 1 day
Value:
(25% of one big boiler)
$200,000 /yr ($0.90 / sf)
( Incidental)
Defer new 1000 ton chiller ($1000/ton)
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
Building
Load 1000
tons.
Three 550
ton chillers
ON.
(1650 tons)
Improper Chiller OFF Logic – Operating more pumps & towers than necessary
(2 chillers
needed)
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
Retro-Commissioning
Case Study #4: Summary For-Profit Hospital
PROBLEM
AHU Supply Air Temp Reset Logic
Condenser Water Reset Temp Reset Logic
Chiller ON/OFF Logic
Pump Valve Adjustment
AHU Device Tune-up
Modify AHU Re-heat coil retro-fit
SAVINGS DISCO&M
$72,000
D
$33,000
D
$10,000
D
$26,000
S
$58,000
O&M
$186,000
DIS
Total:
$385,000
Implementation Cost: $150,000
Baseline Savings:
Retro-Cx Investment:
$385,000 /yr ($1.50 / sf)
5 month
Prevention:
Design review ,
Performance Testing
Training
Take-Away
Retro-Commissioning Existing Buildings
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
DISCO&M
Questions?