to Presentation - AABC Commissioning Group

Report
Fundamentals of Test & Balance
for Engineers
Objectives
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Help the CxA understand and identify challenges of the
TAB Agency
Explain what can be accurately measured in the field in
an HVAC system
Obtain an understanding of the proper use & limitations
of TAB instrumentation
Promote a team approach between the CxA and TAB
Agency
Assist in delivering a project to the owner meeting
system design intent
Specification Challenges
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One of the most beneficial and productive parts
of the Cx process is a specification and drawing
review.
Utilize common sense; what is the goal or intent?
If the CxA is utilizing the project specifications to
establish PFC’s and FPT’s make sure they are
applicable. (Who performs their own PFC’s?)
Specification Challenges:
TAB Data
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Understand what is meaningful data. Just because the specification
calls for a “measurement”, that does not mean it is relevant or
useful.
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For example; Wet-bulb temperatures – a single point measurement is not
extremely accurate and a steady state load needs to be introduced. Is this data
really needed? Will this data provide a benefit to the owner? The coil should be
ARI certified.
Try to think of how data will be obtained and what data will be
required before requesting the data:
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Will the requested data be accurate, repeatable and meaningful?
Specification Challenges:
Measurement Tolerances
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Avoid ±5% tolerances
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Adds cost, but not necessarily value.
May not be feasible, depending on the system and its components.
Reserve tight tolerances for special applications, not comfort
cooling/heating. Keep in mind, that in Labs and ORs, the main criteria
for airflow is ACH and room pressurization. Typically the room envelope
dictates the amount of airflow required to maintain proper
pressurization.
The TAB equipment manufacturer’s tolerances sometimes are greater
than the specification tolerances.
Specification Challenges:
Marking Damper/Valve Positions
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Verify that all balancing damper handles are exposed
and visible on externally insulated ductwork. Do these
need to be marked? If so, make sure that quadrant style
damper handles with standoffs and locking devices are
specified and installed so they can be clearly marked.
Marking the external duct insulation is not
accurate/helpful.
If valve handles required to be marked, make sure the
specified and installed valve has provisions for marking.
Recording the valve position in the TAB report should
suffice in most situations.
Specification Challenges:
Marking Damper/Valve Positions
Specification Challenges:
Controls
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Make sure that access to the control system is made available to the
TAB agency and CxA. This includes any required hardware and
software.
This seems to be a regional issue, not a manufacturer’s issue.
Specification Challenges:
Seasonal Testing
Make sure that the “Seasonal Testing”
required is affected by the season.
 Utilize the DDC system for trending data.
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 Typically
airflows and water flows are tested
at maximum flow conditions and the season
does not affect the test data.
Specification Challenges:
Sheaves
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Sheave changes are NOT automatically
the responsibility of the mechanical
contractor or TAB agency.
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It is difficult to define who is responsible -- Manufacturer,
contractor, engineer? How many are required? At bid time,
sheaves are an unknown cost and unknown quantity.
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Sheave changes for fans should be included as an allowance in
the project or handled as a cost plus change order.
Specification Challenges:
Domestic Water Systems
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Is domestic water balancing required?
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Most TAB equipment manufacturers prohibit the use of
their equipment on potable water systems due to potential
contamination and liability.
 Consider having temperature sensors installed on the
domestic hot water recirculation loop that can report the
temperatures to the DDC system.
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Plumbing pumps, fire pumps, steam condensate
pumps: Typically cannot be accurately tested
without a constant, established water flow.
Specification Challenges:
Domestic Water Systems
Specification Challenges:
Duct Air Leakage Testing
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Duct leakage testing needs to be coordinated in
the specification
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Who does the testing? Define responsibilities; providing
sheet metal blank offs, providing of test equipment, who
signs off, etc.
 How many tests are required? Define systems to be tested,
etc.
 Define the standard and test requirements. Test pressure,
etc.
 Realize there is a schedule impact
Specification Challenges
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Calibration of instruments per manufacturer’s
recommendations. (As a note, most require
calibration every 2 years.)
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Help promote identifying each piece of
equipment (fans, AHUs, HPs, VAVs, etc.) with a
unique tag.
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Never rely on face dampers for air balancing.
Specification Challenges:
Vibration & Sound Testing
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If required, make sure the specification is
specific about what sound and/or vibration
data is required.
Define where readings should be taken and
under what test conditions the readings should
be obtained.
Airflow Measurement & The Flow Hood
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The flow hood is a
proportioning device.
The airflow measurement
of the flow hood may have
to be corrected with a “K”
factor.
Airflow Measurement & Fan Curves
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Fan curves
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AMCA Tested
Produced under laboratory conditions
Free inlet
Straight discharge
Ideal traverse plane
Multiple speeds-extrapolated data
Standard temperature & pressure (STP)
Normal manufacturing tolerances
Know the limitations of fan curves
Airflow Measurement & Fan Curves
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ASHRAE Journal Article, November 2005
Airflow Measurement:
Traverse Locations & Alternatives
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Ideal traverse plane:
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For round duct, AABC, AMCA & ASHRAE all identify the
ideal traverse plane as 2 ½ diameters from condition
(discharge, elbow, etc.) for up to 2500 fpm. Add 1
diameter for each additional 100 fpm.
 For rectangular duct, EL= (4a*b/π)0.5 , where “a” & “b” are
the duct dimensions.
Airflow Measurement:
Traverse Locations & Alternatives
Example:
Alternatives to Traverse:
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10,000 cfm, 30” x 20”
duct, 2400 fpm
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Face velocity reading of
filters, coils, etc.
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EL= (4a*b/π)0.5 =27.6”
2 ½ * 27.6” = 69.1”
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Summation of airflows at
individual outlets
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69.1” (~ 6’) straight duct
required
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Summation of calibrated
VAV boxes as read at the
DDC computer
Airflow Measurement:
Equipment Considerations
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Can outdoor air be measured to AHU?
 Is there enough ductwork for a proper
traverse?
 Does unit configuration allow for proper
measurement (damper configuration)?
Roof Top Units
 Outdoor air measurements are not possible.
 Static pressure profile of RTU is not practical
unless factory “ports” are installed.
Airflow Measurement:
Airflow Monitoring Stations
 The
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AFMS –
Requires calibration and maintenance
Requires filtered air
Will the AFMS work properly in the installed location?
Is the velocity profile acceptable?
Will the AFMS work at minimum airflow, but function
improperly at maximum airflow or vice-versa?
Will the control damper create turbulence and measurement
issues?
VAV Systems and Return Air Balancing
Water Flow Measurement:
Pump Curves
Design Requirements:
 800 gpm @ 68’
9” Impeller, 20 hp motor,
5BC,1750 rpm (Point 1)
Field Measurements:
 Shutoff ΔP = 73’ (Point 2)
 Operating ΔP = 70.0’
Results:
 Actual: 700 gpm w/9” imp
 12.5% below design
 Flat Pump Curve – Hard to
interpolate.
 Utilize measured flows at
terminals or branches to
determine pump total.
Water Flow Measurement:
Pump Curves
Design Requirements:
 800 gpm@ 68’
10-3/8” Impeller, 20 hp motor,
4E, 1750 rpm
Field Measurements:
 Shutoff ΔP = 104’
 Operating ΔP = 72’
Results:
 Actual: 775 gpm w/10-3/8” imp
 3.1% below design
 Steep Pump Curve –
Immediate Resolution.
Pump Flow Measurement
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Provide test
ports/pump taps at
the pumps (Extend
outside of
insulation).
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Provide a flow
measuring device at
the pump
Fixed orifice type device
preferred, use MultiPurpose Valves with
caution.
Water Flow Measuring Stations:
Sizing
Flow
measuring stations need to be sized to allow for a
measurable and useful pressure drop.
Too often the flow measuring station is too large and
the pressure drop is too low to be useful or accurate.
Several balancing valve manufacturers will have different
orifices available so the valve is sized for flow quantity.
The use of Multi-Purpose Valves for total pump flow
measurement is typically not accurate
Typically
sized line size and not for flow (oversized)
Location is not ideal, need 5 pipe diameters before and after
the valve.
Water Flow Measuring Stations:
Strainer Effect
¾” Balancing Valve
50% Open
¾” Balancing Valve
25% Open
Water Flow Measuring Stations:
Strainer Effect
Water Flow Measurement:
Automatic Flow Limiting Devices
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These devices do not eliminate water balancing.
Ideal for fan coil units, unit ventilators, heat
pumps, VAV reheat coils and areas where
access to valves is limited (actual pressure
readings might not be obtained for each autoflow).
Factory-installed piping kits frequently do not
provide access to the ports!!!
Water Flow Measurement:
Factory-Piped Balancing Valves
Water Flow Measurement:
AFLD Installation
Testing a Water System with
Diversity
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Repeating water flow measurements in a system
with diversity is very difficult. Several
considerations are required:
 How
was the system set up for testing?
 What data is required to be reported?
 How is the system currently operating?
Testing a Water System with
Diversity
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Understand the goals of the TAB Process & FPT’s in
a system with diversity
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Verify pump performance
Make sure that all coils/elements can provide
heating/cooling
Establish the differential pressure operating setpoint
Set up system to operate as efficiently as possible –
Obtain water flow to the coil/element with the most
resistance without creating excessive resistance in the
system (let the control valve do the work)
Access Challenges
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Proper clearance and access must be provided
to all dampers, valves, equipment, etc.
 Sheetrock
ceilings, architectural features, etc.
 Locate devices in the corridors outside of OR’s,
classrooms, etc.
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Access to outlets, dampers, etc. in theatre type
seating areas. How will this be accomplished?
AHU is typically not in operation when
scaffolding is installed.
Scheduling Challenges
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There needs to be enough time allowed in the
schedule for the TAB & Cx work to be
completed.
All work must be complete for TAB work to
commence.
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Clean air filters installed.
All strainers cleaned and start-up strainers removed.
All balancing dampers installed and 100% open.
All manual balancing valves and flow measuring stations
installed and 100% open.
Temperature Controls complete and functional.
Scheduling Challenges
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Phased projects:
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Remember that TAB work is completed by system, not by area.
Very seldom does the HVAC system match the “Phasing Areas.”
Make sure that the Owner & Architect understand the possibility
that the TAB work might be performed after occupancy.
Variable volume systems (air and water) can have provisions to
balance partial HVAC systems. Constant volume systems can
pose major complications if they overlap several phases.
Hydronic systems need to be carefully considered for scheduling
issues.
TAB Reports
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Typically a final TAB report is not available at time of
commencement of the Cx FPT’s.
Have an experienced, responsible engineer review the
report. It is not just about matching numbers. It is
reviewing system performance and employing
engineering judgment.
Don’t hesitate to call the TAB agency to review the report
together or ask questions.
Keep in mind that there is no benefit to the TAB Agency
(owner’s benefit) to report problems or deficiencies, it is
our responsibility. Be cautious of the “pristine” TAB
report.
Questions?
Thank you for your time!
Additional Presentation Topics:
Duct Leakage Testing
Testing Hydronic Systems with Diversity
Water Flow Measurement:
Flow Measuring Stations
Two main types of flow measuring stations:
Fixed orifice or venturi type.
 Variable orifice.
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Water Flow Measuring Stations:
Fixed Orifice
<>
Water Flow Measuring Stations:
Variable Orifice

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