Expert Meeting Report:
Achieving the Best Installed
Performance from High-
Efficiency Residential Gas
Furnaces
Larry Brand
Partnership for Advanced Residential Retrofit
(PARR)
March 2012
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iii
Expert Meeting Report: Achieving the Best Installed Performance
from High-Efficiency Residential Gas Furnaces
Prepared for:
Building America
Building Technologies Program
Office of Energy Efficiency and Renewable Energy
U.S. Department of Energy
Prepared by:
Larry Brand
Partnership for Advanced Residential Retrofit
Gas Technology Institute
1700 South Mount Prospect Road
Des Plaines IL 60018
Technical Monitor: Stacey Rothgeb
Task Order KNDJ-0-40346-02
March 2012
iv
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v
Contents
Meeting Overview ........................................................................................................................................ 1
Title ............................................................................................................................................1
Who ............................................................................................................................................1
What ...........................................................................................................................................1
When ..........................................................................................................................................1
Where .........................................................................................................................................1
Why ............................................................................................................................................1
How ............................................................................................................................................2
Attendees ..................................................................................................................................................... 4
Agenda ......................................................................................................................................................... 5
Welcome ....................................................................................................................................5
Presentation 1 - U.S. DOE Building America Overview...........................................................6
Presentation Title .................................................................................................................6
Key Points ............................................................................................................................6
Presentation 2 – Introduction to PARR .....................................................................................6
Presentation Title .................................................................................................................6
Key Points ............................................................................................................................6
Presentation 3 – GTI Lab Testing ..............................................................................................6
Presentation Title .................................................................................................................6
Key Points ............................................................................................................................6
Presentation 4 – National Laboratory Perspective .....................................................................7
Presentation Title .................................................................................................................7
Key Points ............................................................................................................................7
Presentation 5 – Expert Manufacturer Advice - Carrier ............................................................8
Presentation Title .................................................................................................................8
Key Points ............................................................................................................................8
Presentation 6 – Expert Manufacturer Advice - Trane ..............................................................9
Presentation Title .................................................................................................................9
Key Points ............................................................................................................................9
Presentation 7 – Expert Installer Advice from Bartholomew Heating and Cooling................10
Presentation Title ...............................................................................................................10
Key Points ..........................................................................................................................10
Presentation 8 – Measuring Air Handler Flow in the Field .....................................................11
Presentation Title ...............................................................................................................11
Key Points ..........................................................................................................................11
Summary .................................................................................................................................................... 12
Meeting Aftermath and Next Steps ......................................................................................................... 13
Acknowledgments .................................................................................................................................... 14
Appendix I: Meeting Slides ...................................................................................................................... 15
Welcome ..................................................................................................................................15
Presentation 1 - U.S. DOE Building America Overview.........................................................16
Presentation 2 – Introduction to PARR ...................................................................................16
Presentation 3 – GTI Lab Testing ............................................................................................17
Presentation 4 – National Laboratory Perspective ...................................................................17
Presentation 5 – Expert Manufacturer Advice - Carrier ..........................................................18
Presentation 6 – Expert Manufacturer Advice - Trane ............................................................18
vi
Presentation 7 – Expert Installer Advice from Bartholomew Heating and Cooling................19
Presentation 8 – Measuring Air Handler Flow in the Field .....................................................19
Appendix II: Meeting Flyer ....................................................................................................................... 20
References ................................................................................................................................................. 22
vii
Definitions
ACCA
Air Conditioning Contractors of America
AFUE
Annual Fuel Utilization Efficiency
AHRI
Air Conditioning, Heating, and Refrigeration Institute
ASHRAE
American Society of Heating, Refrigeration and Air
Conditioning Engineers
HVAC
Heating, Ventilation, and Air Conditioning
NFPA
National Fire Protection Association
1
Meeting Overview
Title
Achieving the Best Installed Performance from High-Efficiency Residential Gas Furnaces
Who
The Partnership for Advanced Residential Retrofit (PARR) invited industry experts from
Building America (BA), Building America research teams, manufacturers, HVAC installers,
national laboratories, DOE, and PARR partners. A total of 33 individuals from 18 organizations
participated in the meeting (see list).
What
The objective of this Expert Meeting is to identify installation practices that provide the best
installed efficiency for residential gas furnaces, explain how AFUE and field efficiency can
differ, and investigate the impact of installation practices on the efficiency and long-term
durability of the furnace.
When
Thursday July 28, 2011; 1:00 p.m. to 4:00 p.m. Central
Where
This meeting was conducted via webinar. Many participants were not able to travel to make their
presentations.
Why
In Building America research, there is an often-identified gap between predicted energy savings
according to the Energy Plus or BEopt models and the actual energy savings of the home. In cold
climates with gas warm-air furnaces as the
primary heating system type, the largest
energy savings measure is often upgrading
the furnace from mid to high-efficiency.
PARR is developing a measure guideline to
provide information and guidance to the
research community and installing
contractors so that the installed performance
of high-efficiency furnaces is as close as
possible to the modeled or rated
performance. As a corollary, PARR’s
laboratory-based research into furnace
performance will identify gaps related to
part-load performance and installation variability that may result in changes in the rating
standard or the algorithm used in the models.
Currently, PARR is testing three types of high-efficiency furnaces in the laboratory under several
installation scenarios. These tests are expected to show how variations in furnace type and
installation practices can impact AFUE when measured according to ASHRAE standard 103.
PARR and several BA teams are also conducting field-efficiency tests under less-controlled
2
conditions. In this Expert Meeting, speakers from the Gas Technology Institute, furnace
manufacturers, an installing contractor, Oak Ridge National Laboratory, and the University of
Illinois Building Research Council provided their perspectives on methods to achieve the best
installed performance.
Research questions addressed:
1. How do installed efficiency and AFUE differ?
2. What are common installation issues affecting efficiency and how are they
addressed?
3. How do researchers evaluate field performance?
4.
What type of furnace gives the best performance in difficult installations?
How
Expert Meetings are designed to be an interactive experience, where all participants contribute in
substantive ways. Representatives from manufacturers, identified with the assistance of the Air
Conditioning, Heating and Refrigeration Institute (AHRI), and other panel members were chosen
to discuss several unique perspectives on the issue of installed performance. Panel members,
listed below, included NREL, manufacturers, researchers, and an installing contractor.
This report contains the first page of each presenter’s slides in Appendix I. Full presentations
and webinar recording are provided at: http://www.baparr.net and accompany this report on the
NREL website: http://www1.eere.energy.gov/buildings/building_america/meetings.html.
Panel Member
Company
Title
Brad Bartholomew Bartholomew Heating and
Cooling
Owner
Bio: Brad Bartholomew is the Owner of Bartholomew Heating and Cooling, an installing
contractor in Kalamazoo Michigan. He is also a BPI and RESNET certified energy auditor.
Larry Brand
Gas Technology Institute
R&D Manager
Bio: Larry Brand is an R&D Manager at Gas Technology Institute and Principal
Investigator for the Partnership for Advanced Residential Retrofit Building America team.
He has an MSME from U of Illinois and has been working in R&D management for the
residential sector for 25 years, including development of a new furnace, boiler, and wall
furnace.
Paul Francisco University of Illinois Building
Research Council
Research Specialist
Bio: Paul Francisco is a Research Specialist at the Building Research Council at the
University of Illinois - Urbana-Champaign. Paul's research focuses on field evaluations of
energy efficiency and indoor air quality. Paul has done numerous field research projects in
the last 15 years on airflow in forced-air distribution systems.
3
Panel Member
Company
Title
Paul Haydock United Technologies Carrier Manager of Heating
Products
Bio: Paul Haydock is Manager of Heating Products at United Technologies Carrier. He
has an MS in Mechanical Engineering from Purdue and has 22 years’ experience in gas
furnace development; the last 16 years with Carrier where he is currently a manager of
condensing furnace development. A 22-year member of ASHRAE, he was a voting
member on the ASHRAE Standard Project Committee, SPC103-1993R, which is basis for
the DOE AFUE testing standard.
Steven Kowalski
Trane
Engineering Manager
Bio: Steven Kowalski is the Manager of Furnace, Electrical, and Power Electronics
Component Engineering at Trane where he has 16 years gas furnace development
experience. He has an MS in Mechanical Engineering from Princeton University and is
working on his MBA from Indiana University. Steve has been involved with ASHRAE for
15 years and was also a voting member of SPC 103.
Jeffrey Munk Oak Ridge National
Laboratory
Research Staff
Bio: Jeffrey Munk is a member of the Building Equipment research group at ORNL. He
has been working with ground source heat pumps for space conditioning and water heating
at experimental research houses for the past year and a half. He has 5 years of industry
experience working for Carrier Corporation on residential packaged products and gas
furnaces in the areas of product development and problem resolution. He has a B.S. and
M.S. degree in Mechanical Engineering from Purdue University.
Stacey Rothgeb National Renewable Energy
Laboratory
Chief Engineer
Bio: Stacey Rothgeb is the PARR Building America Research Coordinator at the National
Renewable Energy Laboratory.
Jim VerShaw
Trane
Chief Engineer
Bio: Jim VerShaw is Chief Engineer, Residential Solutions at Trane.
4
Attendees
Organization
Rheem
Bartholomew Heating and Cooling
Gas Technology Institute
ECR International
National Renewable Energy Laboratory
National Renewable Energy Laboratory
Rheem
University of Illinois Building Research Council
Davis Energy Group
National Renewable Energy Laboratory
United Technologies Carrier
Ferris State University
Rheem
Sacramento Municipal Utility District
Trane
NAHB Research Center
Ferris State University
Ferris State University
Michigan State University
Oak Ridge National Laboratory
Nordyne
Rheem
Steven Winter Associates
National Renewable Energy Laboratory
National Renewable Energy Laboratory
Carrier
Gas Technology Institute
Rheem
Air Conditioning, Heating, and Refrigeration Institute
Trane
Midwest Energy Efficiency Alliance
National Renewable Energy Laboratory
5
Agenda
Topic
Presenter
Time (central time)
Welcome
Larry Brand, GTI
1:00 p.m.
Introduction to Building America
Stacey Rothgeb, NREL
1:00 – 1:05
Introduction to the Partnership for
Advanced Residential Retrofit
Larry Brand, GTI
1:05 – 1:10
PARR High Efficiency Furnace
Testing – Test Plan, Results to
Date, Future Plans
Larry Brand, GTI
1:10 – 1:30
Expert National Lab Advice –
How to Get the Best Installed
Performance - Lessons from the
Lab
Jeff Munk, Oak Ridge
National Laboratory
1:30 – 1:50
Q&A
1:50 – 2:00
Expert Manufacturer Advice –
How to Get the Best Installed
Performance
Paul Haydock, Carrier;
2:00 – 2:20
Expert Manufacturer Advice –
How to Get the Best Installed
Performance
Steve Kowalski/Jim
VerShaw, Trane
2:20 – 2:40
Manufacturer Q&A
2:40 – 3:00
Expert Installer Advice – How to
Get the Best Installed Performance
- Lessons from the Field
Brad Bartholomew,
Bartholomew Heating and
Cooling
3:00 – 3:20
Expert Field Measurement Advice
– Measurement of Air Handler
Flow in the Field
Paul Francisco, University
of Illinois Building
Research Council
3:20 – 3:40
Q&A and Discussion
3:40 – 3:55
Conclusion
3:55 – 4:00
Welcome
Larry Brand from the Gas Technology Institute welcomed the panel and participants and
introduced the topic of the Expert Meeting: “Achieving the Best Installed Performance from
High-Efficiency Residential Gas Furnaces.” He indicated that the webinar was presented by the
Partnership for Advanced Residential Retrofit team on behalf of the U.S. Department of
Energy’s Building America program. He mentioned that the speakers will focus on how to
identify installation practices that provide the best efficiency for residential gas furnaces, explain
how AFUE and field efficiency can differ, and investigate the impact of installation practices on
the long-term performance of the furnace.
Larry introduced each speaker in turn. Questions and responses are included in the key points for
each presentation.
6
Presentation 1 - U.S. DOE Building America Overview
Stacey Rothgeb, Research Coordinator at the National Renewable Energy Laboratory, presented
an overview of the Building America program.
Presentation Title
Building America Program Introduction
Key Points
The BA program was created to reduce energy use through a building science and system
engineering approach. The primary goal of the research is to create cost-effective, least-cost, and
highest-value solutions. The secondary goal of the research is to develop whole systems
knowledge to clearly understand cost/performance tradeoffs, identify and resolve knowledge
gaps, and clearly define stakeholders’ needs. A third goal of the research is to produce
continuous evaluation and performance feedback on measure guidelines, measures database,
audit and analysis tools, and test houses and community-scale performance data. In 2011, there
are 15 Industry Research Teams addressing both new construction and retrofit.
Presentation 2 – Introduction to PARR
Larry Brand, R&D Manager at the Gas Technology Institute, presented an overview of the
PARR team.
Presentation Title
Introduction to PARR
Key Points
The Partnership for Advanced Residential Retrofit (PARR) is a Midwest Building America team
with a Chicago hub with a concentration on residential retrofit. PARR and its five research team
members focus on systems and whole home solutions in cold climates targeting high potential
building stock with opportunities for energy savings and scalability. PARR is led by the Gas
Technology Institute (GTI). GTI is a not-for-profit with a 65-year history in energy R&D
including residential and commercial buildings. The other four PARR team members are CNT
Energy, the Midwest Energy Efficiency Alliance, the University of Illinois Building Research
Council, and Future Energy Enterprises. PARR partners include 40 industry members from
manufacturers, developers, utilities, EE program implementers, government agencies and
neighborhood organizations. PARR is active in five research areas in Building America for 2011.
Presentation 3 – GTI Lab Testing
Larry Brand from the Gas Technology Institute presented recent laboratory research on
condensing furnaces.
Presentation Title
Installed Performance of High Efficiency Gas Furnaces - GTI Lab Testing
Key Points
The installed performance of residential gas furnaces and the AFUE rating number can be quite
different. These differences come from the AFUE test requirements and the environment and the
home. AFUE is tested in a very controlled laboratory setting without ductwork and with very
accurate instruments. AFUE is also tested with standard oversizing of 70%. The conditions in a
7
home are generally uncontrolled. Residential duct work can be significantly undersized and it
can be very difficult to get accurate measurements in the field. In addition, residential furnaces
can be significantly oversized for the application.
ASHRAE standard 103-2007 is the current consensus standard used for testing AFUE. DOE uses
a version of that standard in the labeling process (Title 10). GTI (through PARR) is using the
ASHRAE test method as the basis for identifying performance degradation associated with
oversizing, high static pressure, and high pressure drop filters. PARR is testing three types of
furnaces and will make recommendations on the best type for particular installation issues found
in the field – over-sized furnace, undersized ducts, and using high efficiency filters. PARR will
report on efficiency degradation and blower power requirements under these scenarios.
Key takeaways from this presentation were:
1. GTI believes AFUE will vary a few percent with over-sizing up to twice the load and
distribution system deficiencies will not impact AFUE.
2. Undersized ducts and high efficiency filters will have a significant impact on fan power
requirements. The extent of the impact will be determined in the research project.
3. Among the three furnace types being tested, single stage furnaces are the most cost-
effective option for broad application, two stage furnaces provide improved efficiency
and air mixing with properly sized distribution systems, and modulating furnaces are the
best solution for undersized distribution systems.
Presentation 4 – National Laboratory Perspective
Jeffrey Munk from Oak Ridge National Laboratory (ORNL) presented a compilation of research
from the national labs.
Presentation Title
Lessons from the Lab
Key Points
Reducing losses to the unconditioned space is the top installation best practice. Losses can be
minimized by moving equipment inside the envelope or extending the envelope around the
equipment if installed outside the conditioned space, and then sealing and insulating everything
including the ductwork and blower compartment. Preheating combustion air from 30
o
F to 150
o
F
can provide a 1% improvement in AFUE at some cost. Using indoor air creates an infiltration
penalty of 0% to 3% and is often overlooked in the efficiency analysis.
Furnace part-load efficiency was studied extensively in the 80’s and 90’s by DOE and NIST. The
analysis was largely done on furnaces with standing pilots. That information shows a very flat
profile down to 10% of full load and then a significant drop to zero. BEopt uses a linear
relationship dropping to 80% of steady state performance at a part load factor of 0 from 100% of
steady state performance at a part load factor of 1. Two-stage and multistage AFUE is controlled
by the amount of time the furnace operates on lower stages (better performance at low stages).
8
Key takeaways from this presentation were:
1. There is an infiltration penalty of up to 3% associated with furnaces that use indoor air
for combustion - largely overlooked in the AFUE calculation and the models.
2. Part-load performance of newer-designed furnaces has not been tested. Algorithms to
update furnace performance based on those test results need to be developed for the
building modeling tools.
3. Fan power requirements at part load also need to be developed for the building modeling
tools to properly reflect electric energy consumption.
Presentation 5 – Expert Manufacturer Advice - Carrier
Paul Haydock, Engineering Manager from United Technologies - Carrier, presented a
manufacturers perspective on the issue.
Presentation Title
Expert Manufacturer Advice – How to Get the Best Installed Performance
Key Points
Paul presented some advice on three topics: oversizing, installation location and combustion air,
and vent and combustion air pipe sizing.
On oversizing, the Air Conditioning Contractors of America (ACCA) recommend 0% to 40%
over-sizing to meet the needs of the occupants and avoids higher costs, greater energy
consumption, and wear and tear on the equipment associated with frequent cycling. The DOE
and ASHRAE AFUE calculation uses 70% oversize to determine the cycling time – a mis-match
perhaps based on older equipment. Oversizing provides extra capacity to meet peak heating loads
and to recover from setback, which generally saves 15% of energy for an 8 hour 10
o
F setback.
Reducing the amount of oversizing provides better comfort (temperature swings), better air
mixing, and less wear and tear on the furnace.
Paul agreed with the ORNL presenter regarding locating the furnace inside the conditioned space
to reduce heat loss, but added some information on other options. Outdoor furnaces are
weatherized and the rating deducts for heat loss from the jacket to the outdoor environment.
These furnaces have no infiltration loss because they use outdoor air for combustion. Isolated
combustion systems are not weatherized and a deduction is made for jacket loss as well with the
assumption that they can be installed in crawl spaces or attics. The assumption for these products
is that outdoor air is used for combustion through a direct-vent configuration or installation in an
attic or crawl space that communicates with the outdoors. Thus, there is no infiltration load.
Vent and combustion air sizing guidelines are provided in the manufacturers installation
instructions. Using the minimum diameter for run of equivalent length moves less air (because of
the pressure switch controls) and uses less fan power. Locate vent pipes in the conditioned space
as much as possible to transfer some of the unused waste heat in the vent pipe.
9
Key takeaways from this presentation were:
1. Oversizing reduces comfort, performance, and furnace life at the expense of faster
recovery from setback and meeting the heating load under extreme conditions. Better
sizing techniques in alignment with the ACCA recommendations should be used to
reduce energy consumption. ASHRAE should consider revising the AFUE test method
to use 40% over-sizing.
2. Both outdoor furnaces and Isolated Combustion Furnaces are rated assuming outdoor air
for combustion is provided. Installation instructions for Isolated Combustion Furnaces
only recommend (but not require) outdoor air for combustion, so there is a discrepancy
in the ratings.
Presentation 6 – Expert Manufacturer Advice - Trane
Steve Kowalski, Engineering Manager from Trane, presented his perspective on the issue. Jim
VerShaw, Chief Engineer from Trane, contributed to the material but did not present.
Presentation Title
Expert Manufacturer Advice – How to Get the Best Installed Performance
Key Points
Steve Kowalski presented information on several aspects of the problem: latent heat gain,
temperature rise, external static pressure, fan power, and selecting the right product.
Latent heat gain is measured in the lab under carefully controlled steady-state and cyclic
conditions. This measurement is too difficult to do in the field, so field measurements will not
include contribution from this part of the test. Installers will get the best field efficiency by
setting the proper air flow and external static pressure as listed in the manufacturers’ installation
instructions.
Steady state efficiency decreases with increasing temperature rise at about 1% per 15
o
F increase
in rise. Install with the lowest rise allowed on the nameplate to get the best performance but
beware of homeowner complaints.
ASHRAE 103 prescribes external static pressure at 0.2 inches water column, not very realistic in
the field. PSC motors may need to be re-wired on the control board to meet the temperature rise
requirements thereby increasing the amount of energy used for fan power. ECM furnaces
automatically adjust to maintain air flow and by corollary temperature rise unless there is an
unusual condition such as a blocked duct or filter. Under high static conditions (undersized
ducts), the tradeoff is between an ECM, which will maintain airflow at the expense of blower
watts, and the PSC, which will not maintain airflow, but at least won't have the increased blower
watts. Unfortunately, the reduction in air flow for PSC motors under high static pressure
contradicts the advice for maintaining the highest gas furnace efficiency (above). It has been
reported by others that in very undersized duct systems ECM motors may use more fan power.
Testing is needed to verify this assumption.
Comfort versus efficiency – As we’ve already discussed, there is a tradeoff between installed
efficiency and comfort. Within the allowable temperature rise limits, lower temperature rise will
10
give higher installed efficiency at the price of reduced comfort (cold blow). Within the allowable
temperature rise limits, higher temperature rise will give better comfort at the price of a small
decrease in installed efficiency. The overriding concern, however, is to make sure the installation
is within the allowable temperature rise as stated on the furnace nameplate.
Selecting the right furnace for the job also requires making tradeoffs. For high static conditions,
the main tradeoff is between gas use and electric power consumption. An ECM blower motor
will maintain airflow, which will result in maintaining furnace efficiency at the expense of
increased blower watts. A PSC motor will not maintain airflow, which will reduce furnace
efficiency but blower power with PSC motors also decreases at high static. The tradeoff may be
a comparison between the relative price of gas energy and electric energy at the site. Electric
energy consumed by the blower is only a fraction of the amount of energy that is used in the
form of gas energy, so improvements in gas efficiency are generally advantageous – favoring
ECM motors for high static conditions.
Key takeaways from this presentation were:
1. The lowest temperature rise across the furnace produces the best efficiency but also the
most complaints from occupants. Changing occupant behaviors and expectations can
improve installed efficiency by 1% or 2%. In a comment provided after the meeting,
relocating or selecting air diffusers that better spread the jet can have a beneficial effect
for systems that have low temperature rise such as heat pumps.
2. To get the best applied efficiency in terms of fan power, maintain external static pressure
as low as possible through larger sized ducts. Testing is needed to determine fan power
versus external static pressure for the three furnace types.
3. There is a tradeoff between the best thermal efficiency and the best blower power.
Thermal efficiency is best at minimum temperature rise across the furnace, usually
accomplished by increasing the air flow and static pressure. Minimum blower power is
achieved by maintaining the lowest air flow and static pressure for ECM motors and the
opposite for PSC motors. An analysis of tradeoffs between these two factors based on
local gas and electric prices is needed to identify an optimum operating condition.
Presentation 7 – Expert Installer Advice from Bartholomew Heating and Cooling
Brad Bartholomew, Owner of Bartholomew Heating and Cooling presented tips and guidelines
from the installer perspective.
Presentation Title
Keys to Achieving the Best Installed Performance from High Efficiency Furnaces
Key Points
Brad Bartholomew presented information on common field problems encountered and solutions
that have worked for his team.
A key problem area is poor installation practices caused by not following the manufacturer’s
installation instructions for gas pressure adjustments, vent sizing, filter sizing, temperature rise,
and static pressure testing. The solution is to improve training and awareness of the importance
11
of these areas to achieve the best installed performance. A commissioning report left with the
homeowner is recommended to show all steps have been taken for the setup and what remedial
measures are needed. ACCA Quality Installer (QI) techniques should be followed.
Improper equipment and duct sizing can be addressed by installer training and proper use of
ACCA manuals. Duct systems that are undersized create high static and temperature rise issues
which lead to comfort issues, noise, and temperature swings. A typical problem is undersized
return air systems requiring additional return lines from the trunk to the furnace. Leaky and
poorly insulated ducts do not impact the furnace efficiency, but they do lose heat to the
unconditioned space. Air sealing of ductwork is recommended.
Key takeaways from this presentation were:
1. Proper installer training on set-up of furnaces can significantly impact installed
performance: external static pressure as low as possible, reducing the rise to the minimum
allowed, and adding return duct drops are key elements.
2. Additional steps to seal and insulate ducts, while not impacting furnace efficiency, will
reduce losses to the unconditioned space and reduce energy consumption - which is
equally important to the homeowner.
3. A written commissioning report shared with the homeowner documents adjustments
made installation and identifies areas that need remedial attention.
4. Handheld combustion analyzers have limitations in accuracy and are not useful for
measuring the efficiency of condensing furnaces, due to the significant latent component.
Another field method is needed.
Presentation 8 – Measuring Air Handler Flow in the Field
Paul W. Francisco, Researcher with the University of Illinois Building Research Council
presented the results of his research on measuring air flow in the field.
Presentation Title
Air Handler Flow Measurement: What Works and What Doesn’t
Key Points
Measuring air volume is important to assess the adequacy of flow across coils for heat pumps
and cooling and to assist in diagnosing problems such as cycling on a limit switch, undersized
ducts, and poor dehumidification in the cooling season. Five techniques were identified and the
pros and cons of each method were reviewed:
1. Pitot traverse – difficult to perform in the field; large user error
2. External static pressure measurement – pressures can vary widely within plenums. In
many field installations (such as those with bypass humidifiers or those with radial duct
systems) there is not even a place to measure the static pressure that would represent the
entire air flow.
12
3. Temperature rise/drop – supply temperatures can be poorly mixed. Accuracy is
approximately 30%.
4. Calibrated fan assist – most accurate but time consuming to set up; need to attach
calibrated fan to air handler cabinet. Accuracy is about 3%. For this method, an airtight
barrier is required between the return plenum and air handler cabinet.
5. Calibrated flow plate – next most accurate (7%); easy to set up and use; easy to adjust for
mismatched pressures. A filter slot or other suitable insertion location is required at the
air handler.
Key takeaways from this presentation were:
1. Direct air flow measurement in the field is a more accurate measure than temperature rise
or external static pressure measurement when adjusting furnace blowers.
2. The calibrated flow plate technique is the simplest method to use with acceptable
accuracy.
Summary
Larry Brand thanked all the panel members and participants on the phone for their valuable
contributions. Gaps and barriers identified and key research questions to be addressed are
included in the key takeaway section for each presenter. While not all research questions were
addressed, the following expert advice can be drawn from this meeting:
• How do installed efficiency and AFUE differ?
AFUE is measured under controlled laboratory conditions with precise instruments
that cannot be replicated in the field. Installed efficiency can vary at least a couple of
percentage points if temperature rise is too high (poor adjustment and undersized
ducts) and if there is significant oversizing (BEopt algorithm). Fan power is not a part
of AFUE, but can significantly increase with undersized ductwork, low external static
for PSC motors, and very high external static for ECM motors. Testing is needed to
verify these findings.
• What are common installation issues affecting efficiency and how are they
addressed?
Efficiency in the field is impacted by furnace oversizing, undersized ducts, and poor
fan speed adjustment at installation. To address these issues, minimize oversizing
through the use of a good sizing tool, modify ducts (typically adding an additional
return drop), and properly follow the manufacturer’s installation instructions.
Although not part of the AFUE, electric power for circulating air blowers and
inducers are impacted by undersized ducts and oversized vent pipes. Modifying the
duct system as above and installing the minimum vent diameter and length permitted
by the manufacturer’s installation instructions address these areas.
• How do researchers evaluate field performance?
Field performance is difficult to measure with handheld devices and particularly
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difficult for condensing furnaces where the latent component cannot be measured.
The best field performance is achieved by following manufacturers’ installation
instructions for rise, rate, and external static pressure adjustments. Air flow is best
measured using a flow plate to provide improved diagnostics.
• What type of furnace gives the best performance in difficult installations?
a. Single stage furnaces are the most cost-effective and provide good
performance for installations without very high external static pressure.
b. Two-stage (and step-modulating furnaces) offer advantages in improved part-
load efficiency, longer on-times at lower rate to improve comfort/reduce
temperature stratification in the space, and reduced fan power at low input.
These furnaces provide better efficiency for installations where oversizing for
recovery from deep setback is required or where better mixing is needed.
c. Step modulating furnaces offer an additional comfort advantage in that they
produce rated air flow at higher external static pressures for installations with
significantly undersized and un-repairable ductwork. In addition, ECM blower
motors use less power than the PSC motors in two-stage furnaces at the same
airflow. Newer step modulating furnaces offer a three-stage burner for better
part-load efficiency than two-stage furnaces. These furnaces offer the best
performance for all cases but at the highest price.
Meeting Aftermath and Next Steps
The feedback from meeting participants was decidedly positive. The results of this meeting were
shared with attendees at the Building America Technical Meeting in Denver, Colorado, in
August 2011, and were the basis for several conversations with manufacturers regarding
improvements to the ASHRAE AFUE test procedure.
Thirty-three individuals from eighteen organizations attended the webinar, a good turnout for an
Expert Meeting. There were only a few questions and comments from the attendees, much less
than anticipated. PARR recommends that future Expert Meetings be conducted only in-person to
foster interaction and improve the exchange of ideas.
Research topics identified during the expert meeting and under consideration for 2012 and
beyond include:
• Comparing current field efficiency measurements from installing contractors and lab
AFUE measurements on the same furnace removed from the field.
• Updating the part load performance curves with modern furnace types (proposed to Oak
Ridge National Laboratory).
• Expanding blower power consumption measurements for external static pressures from
0.2 to 0.8 inches water column.
• Measuring inducer motor power with several lengths and diameters of vent pipe allowed
by the manufacturers installation instructions.
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Acknowledgments
PARR would like to thank all the attendees for their participation in the meeting, especially our
panel members. We also want to thank Gail Werren from NREL for assistance in preparing the
webinar script and hosting the meeting.
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Appendix I: Meeting Slides
The first page of each presenter’s slides is shown in this Appendix. The full presentations and
webinar recording are provided at: http://www.baparr.net and accompany this report on the
Building America website:
http://www1.eere.energy.gov/buildings/building_america/meetings.html.
Welcome
Larry Brand from the Gas Technology Institute welcomed the panel and participants and
introduced the topic of the Expert Meeting.
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Presentation 1 - U.S. DOE Building America Overview
Stacey Rothgeb from the National Renewable Energy Laboratory presented an overview of the
Building America program.
Presentation 2 – Introduction to PARR
Larry Brand from the Gas Technology Institute presented an overview of the PARR team.
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Presentation 3 – GTI Lab Testing
Larry Brand from the Gas Technology Institute presented recent laboratory research on
condensing furnaces.
Presentation 4 – National Laboratory Perspective
Jeffrey Munk from Oak Ridge National Laboratory (ORNL) presented a compilation of research
from the national labs.
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Presentation 5 – Expert Manufacturer Advice - Carrier
Paul Haydock from United Technologies - Carrier, presented a manufacturers perspective on the
issue.
Presentation 6 – Expert Manufacturer Advice - Trane
Steve Kowalski and Jim VerShaw from Trane presented an additional manufacturers perspective
on the issue.
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Presentation 7 – Expert Installer Advice from Bartholomew Heating and Cooling
Brad Bartholomew from Bartholomew Heating and Cooling presented tips and guidelines from
the installer perspective.
Presentation 8 – Measuring Air Handler Flow in the Field
Paul Francisco from the University of Illinois Building Research Council presented the results of
his research on measuring air flow in the field.
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Appendix II: Meeting Flyer
21
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References
ANSI z223.1/NFPA 54, International Fuel Gas Code, International Code Council, 2012. Also
available from the National Fire Protection Association.
ASHRAE Handbook 2008, HVAC Systems and Equipment, Chapter S32, Furnaces
ASHRAE Standard 103 Method of Testing for Annual Fuel Utilization Efficiency of Residential
Central Furnaces and Boilers (ANSI Approved), 2007
Manual D - Residential Duct Systems, Air Conditioning Contractors of America, 2009
Manual J Residential Load Calculation Air Conditioning Contractors of America, 2006
Standard for the Installation of Warm Air Heating and Air-Conditioning Systems, 2009 Edition,
NFPA 90B
Title 10, Code of Federal Regulations, Chapter II Part 430 Appendix N, Subpart B Uniform Test
Method for Measuring the Energy Consumption of Furnaces, January 1, 2001
DOE/GO-102012-3536 ▪ March 2012
Printed with a renewable-source ink on paper containing at
least 50% wastepaper, including 10% post-consumer waste.