Class 3

Building Re-Tuning
(BRT)
Lesson 3: SOI Air-Handling Unit Part I
Lesson 3: Sections
•
•
•
•
•
Review of last class (0:20)
Section 1: AHU (Minimum Outdoor Air Operation (0:45)
Break (0:10)
Section 2: AHU (Air-side Economizer Operation) (0:60)
Section 3: AHU (Static Pressure Control) (0:45)
2
Review of last class
• An SOI is a system and its components that could offer energy
savings and which you will investigate for improvements using
the 6-step BRT Process.
• Delta T: the difference between supply and return
temperatures.
• ECAM: Energy Charting And Metrics
– “Converts” data to graphics/charts for easy interpretation.
– Uses multi-point data.
– Several types of ECAM charts.
3
For Each SOI…
For each SOI, we will focus on:
Step #2: Building Walk Down: Identify common operational
issues.
Step #3: Data Collection: Establish baseline through trend-log
data (“before BRT”).
Step #4: Data Visualization & Interpretation: Create graphs &
interpret data.
4
Check Your Understanding
Based on the chart of HW
supply and return at right, what
can we say about system
operations?
1. Distribution system
(secondary loop, zones)
(a) Is operating well
(b) Has starved zones
(c) Needs higher
temperature supply
(d) Has excess flow
5
Check Your Understanding
How do we read the two
charts at the right?
Why are there Y-axis labels
on both the left and the
right?
Which chart shows better
operation? Why?
6
Homework: What have you found
during the week?
• Questions on reading?
– Air-side Economizer Operation
– AHU Minimum Outside Air Operation
– AHU Static Pressure Control
• Watch ECAM Webinar: Part I Introduction
• Issues with completing your Project Report?
– Complete the BAS Section
• Trial trend log set-up – were you able to?
• Engage intern support – do you need?
7
Section 1
Time Spent on this Section (45 Minutes)
AHU – MINIMUM OUTDOOR
AIR OPERATION
8
There are Several Operations to
Investigate Under the AHU SOI
Let’s Talk about Your Building!
What issues might your building have for the AHU SOI?
• Minimum Outdoor Air Operation
• Air-side Economizer Operation
• Static Pressure Control
• Discharge Air Temperature Control
• AHU Heating + Cooling Control
We’ll discuss these operations over this class and next.
9
Minimum Outdoor Air Operation
• Minimum
– For ventilation
– Even less when unoccupied
• Maximum
– Economizer cooling when OAT < RAT
• OA Dampers
– Closure not reliable
– Not “linear”
– Full closure during unoccupied and pre-occupancy start-up
• Outside Air Fraction
– OAF = (MAT – RAT) / (OAT – RAT)
– OA fraction at light load – needs to be much higher fraction
10
of total air supply
Minimum Outdoor Air Operation
Step #2. Building Walk Down:
• Identify issues as you walk around, such as:
– Are dampers fully operational?
– Are linkages all attached and lubricated?
– Is there a fixed minimum air louver or can
dampers be fully closed?
– Do dampers seem appropriately
positioned for conditions at time of walkdown observation?
11
Minimum Outdoor Air Operation
Step #3. Data Collection:
• Outdoor-air damper position signal (OAD)
• Occupancy mode
• Outdoor-air fraction
• Supply fan speed
• Outdoor-air temperature
• Return-air temperature
• Mixed-air temperature
12
Minimum Outdoor Air Operation
Step #4: Data Visualization & Interpretation:
• Trends to look for in the data:
– Is outdoor air sufficient for ventilation or is overventilation occurring?
– Does the outdoor-air damper close during unoccupied
times?
– Is OAF > minimum OAF for ventilation when the
system is not economizing?
13
Minimum Outdoor Air Operation
Step #4: Data V&I:
Is outdoor air sufficient for ventilation
or is over-ventilation occurring?
14
Now you try: Interpret the Data
Step #4: Data V&I:
CLASS ACTIVITY
Does the outdoor-air damper close
during unoccupied times?
15
Air Fraction Formula
OAF (%) = ((Return-Mixed)/(Return-Outside))*100
• Use to find % of outside air:
– Works if air is mixed relatively evenly.
– Add into code for all air handlers and track history.
– Can also indicate damper leakage.
– 20% damper position is never 20% outdoor air.
• Apply OAF to total supply air (CFM) / Occupancy to estimate meeting
code requirement.
• Use CO2 sensors whenever possible for areas with changing occupancy
and larger spaces (conference rooms, auditoriums, etc.)
16
Minimum Outdoor-Air Operations
Step #4: Data Visualization & Interpretation:
Outdoor-air fraction, outdoor-air temperature and damper position vs.
time: Building occupied 24 hours.
Outdoor-Air Fraction/Damper Position Signal/
Outdoor Air Temperature vs. Time
Damper Signal
Outdoor Air Fraction
120
120.0
100
100.0
80
80.0
60
60.0
40
40.0
20
20.0
0
4/9/07
12:45 PM
Outdoor-Air Temperature
o
( F)
Damper Position Signal and
Outdoor Air Fraction (%)
Outdoor-Air Temperature
0.0
4/10/07
12:45 AM
4/10/07
12:45 PM
4/11/07
12:45 AM
4/11/07
12:45 PM
4/12/07
12:45 AM
4/12/07
12:45 PM
Time
17
Minimum Outdoor-Air Operations
Step #4: Data Visualization & Interpretation:
Outdoor-air fraction, outdoor-air temperature and damper position vs.
time: Building occupied 12 hours.
Damper Signal
Outdoor Air Fraction
Occupancy
Outdoor-Air Temperature
120
120.0
100
100.0
80
80.0
60
60.0
40
40.0
20
20.0
0
4/9/07 12:45
PM
Outdoor-Air Temperature
o
( F)
Damper Position Signal, Occupancy, and
Outdoor-Air Fraction (%)
Outdoor-Air Fraction/Damper Position Signal/
Outdoor Air Temperature vs. Time
0.0
4/10/07
12:45 AM
4/10/07
12:45 PM
4/11/07
12:45 AM
4/11/07
12:45 PM
Time
4/12/07
12:45 AM
4/12/07
12:45 PM
18
Break
(10 Minutes)
Break Time!
19
Section 2
Time Spent on this Section (60 Minutes)
AHU: AIRSIDE
ECONOMIZER OPERATION
20
Air Side Economizer Operation
Step #2. Building Walk Down:
• Identify issues as you walk around, such as:
– Failed actuator
– Disconnected wires or compressed air lines
– Disconnected or damaged linkages
– Stuck dampers
– Blocked open damper (2 X 4 in damper)
– Also… see next slides…
21
Air Side Economizer Operation
During a walk down you see…
22
Air Side Economizer Operation
During a walk down you see…
23
Air Side Economizer Operation
During a walk down you see…
24
Air Side Economizer Operation
Step #3. Data Collection:
• Outdoor-air temperature (OAT)
• Mixed-air temperature (MAT)
• Discharge-air temperature and set point (DAT and DATSP)
• Return-air temperature (RAT)
• Outdoor-air damper position signal (OAD)
• Cooling-coil-valve signal (CCV) (or compressor status)
• Outdoor-air fraction (OAF)
25
Air Side Economizer Operation
Step #4. Data Visualization & Interpretation:
• Trends to look for in the data:
– With AHU in cooling mode, is the OA damper fully open when
conditions are favorable (OAT < RAT)? At minimum when
unfavorable (OAT > RAT)?
– How close is the outdoor-air fraction compared to the outdoorair damper position signal?
– Is the minimum outdoor-air damper position reasonable
(between 10% and 20%)?
– With conditions favorable for economizing, is the cooling coil
open or compressor running?
– When conditions are favorable for economizing, is the mixed-air
temperature closer to return-air or outdoor-air? When
conditions are unfavorable?
26
Air Side Economizer Operation
Step #4. Data Visualization & Interpretation:
Is the outdoor-air damper closed or at minimum position when
outdoor conditions are favorable for economizing and the AHU is in
cooling mode?
27
Air Side Economizer Operation
Step #4. Data Visualization & Interpretation:
Is the outdoor-air damper closed or at minimum position when
outdoor conditions are favorable for economizing and the AHU is in
cooling mode?
28
Activity
Now you try: Interpret the Data
GROUP ACTIVITY
HANDOUT!
Goal
#4: Data Visualization & Interpretation: Analyze the ECAM
Graphs on the handout and decide if it is a good or bad
operation.
Time:
20 minutes
Instructions
• Divide into teams (2-4 people).
• For each graph, decide if it is good or bad operation
(write your answer on the handout).
• Be prepared to share your answers with the class.
29
Section 3
Time Spent on this Section (45 Minutes)
AHU: STATIC PRESSURE
CONTROL
30
Static Pressure Control
Step #2. Building Walk Down:
• Identify issues as you walk around:
– SME to add
31
Static Pressure Control
Step #3. Data Collection:
• Duct static pressure
• Duct static pressure set point
• Zone damper (VAV) position signals
• Time of day (time-series plot)
• Occupancy
• Fan speed
32
Static Pressure Control
Step #4. Data Visualization & Interpretation:
• Trends to look for in the data:
– Is there a reset-schedule for the duct static pressure?
– Is the static pressure set point too high or too low?
• Dampers position >75% open – static pressure too low
(starved boxes)
• Dampers position <45% open – static pressure too high
• Dampers that aren’t modulating with changing conditions
• VAV boxes that are not being controlled or not
responding to control signals
33
Static Pressure Control
Step #4. Data Visualization & Interpretation:
Is there a reset-schedule for the duct static pressure?
Avg AHU1_DuctStcPres
Avg AHU1_DuctStcPresSp
0.50
0.45
0.40
0.30
0.25
0.20
0.15
0.10
0.05
Sat, 8/21/2010
Fri, 8/20/2010
Thu, 8/19/2010
Wed, 8/18/2010
Tue, 8/17/2010
Mon, 8/16/2010
0.00
Sun, 8/15/2010
Avg AHU1_DuctStcPres
0.35
Time
34
Now you try: Interpret the Data
CLASS ACTIVITY
Step #4. Data Visualization & Interpretation:
Is this good or bad operation? Why?
35
Now you try: Interpret the Data
CLASS ACTIVITY
Step #4. Data Visualization & Interpretation:
Is this good or bad operation? Why?
36
Now you try: Interpret the Data
CLASS ACTIVITY
Step #4. Data Visualization & Interpretation:
Is the static pressure set point too high or too low?
37
Discharge Static Control
Does the discharge static vary with some input signals?
• Ideally VAV dampers should run in the 50% to 75% range.
• Like discharge-air temperature, discharge static should follow the real
load conditions:
– Too high and VAV boxes have trouble controlling
– High noise levels in ceiling or at diffusers coming from VAV box
– Extra load on air handler not required
• Higher CFMs
• More chiller load
• More fan wear and belt wear
• Higher fan energy cost. Horsepower varies with the CUBE of
the RPM
38
Timed Reset vs Dynamic Reset Control
• Michael to add
This section on SP MUST introduce the concept of timed reset vs
Dynamic Re-set control. The latter is a response to a changing
system variable, like the position of VAV box dampers.
39
Static Pressure Reset
• WHY? Remember the Power Laws:
• As fan speed varies, change in:
– FLOW is linear
– PRESSURE is by a squared function (power of 2)
– POWER is by a cubed function (power of 3)
NxN
NxNxN
40
Let’s Talk about Your Building!
• Remember the activity from the beginning of the
lesson…
• Consider the AHU SOI:
– Minimum Outdoor Air Operation
– Air-side Economizer Operation
– Static Pressure Control
• Answer the following questions:
– What issues might you investigate (Step #2)?
– What data points would you to measure (Step #3)?
41
42
Lesson Summary
• Minimum Outdoor Air Operation
– For ventilation.
– Even less when unoccupied.
– Damper fully closed during unoccupied and pre-occupancy
start-up
• OAF (%) = ((Return-Mixed)/(Return-Outside))*100
– Use to find % of outside air
• Air-side Economizer Operation
– Packaged rooftop units with economizers are often neglected,
hard to access, or installed poorly.
• Static Pressure Control
– Like discharge-air temperature, discharge static should follow
the real load conditions.
– Static Pressure Re-set - Power Laws.
43
Homework
• READ in Guide
– AHU Discharge Air Control
– AHU Heating and Cooling Control
• Watch ECAM Webinars:
– Part II ECAM Basics
– Part III Creating & Analyzing Retuning Charts
• On your Project Report:
– Complete the SOI Section
• Continue trend log set-up and logging
44

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