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RESEARCH STRATEGY FOR RESIDENTIAL
CLOTHES DRYERS - DRAFT
Version 2.0 – For Review and Comments Only
REGIONAL TECHNICAL FORUM
Release Date: April, 2015
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Provisional Research Plan Template
TABLE OF CONTENTS
1. INTRODUCTION ................................................................................................................1
2. SCOPE OF WORK..............................................................................................................1
2.1 Objectives ......................................................................................................................................................... 1
2.2 Analysis Approach ........................................................................................................................................ 2
2.2.1 Validate Performance Metric ................................................................................................................ 2
2.2.2 Verify Performance Tiers ....................................................................................................................... 3
2.2.3 Describe HVAC Interactions .................................................................................................................. 5
3. ESTIMATED COSTS...........................................................................................................6
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Regional Technical Forum
Research Strategy
1. INTRODUCTION
This Research Strategy complements the RTF Planning UES measure for Residential Clothes
Dryers. The purpose of this Research Strategy is to define the data needed to improve the
reliability of the measure’s energy savings estimate, with an ultimate goal of developing a
Proven UES for residential clothes dryers. In addition to defining the data needs, this Research
Strategy proposes a methodology for analysis.
2. SCOPE OF WORK
2.1 Objectives
The RTF has identified the following research objectives to improve the reliability of the
Residential Clothes Dryer UES measure:
1. Validate Proposed Performance Metric: Currently, the RTF planning measure uses UCEF
as the performance metric. Additional laboratory and field data are needed for the
analysis to verify that UCEF can be reliably used to estimate residential clothes dryer
energy use, without bias for technology type, drum size, or proposed efficiency tiers.1
2. Characterize Performance Tiers: Use test results and market data to determine the
average performance of machines in each tier – including the current practice baseline –
with sufficient certainty. These estimates, and the quantification of their uncertainty,
can be used to estimate the precision of the savings estimates.
3. Quantify Dryer HVAC Interaction: Some heat pump dryers do not require venting to the
outside. Vented and ventless dryers have substantial, yet uncertain impacts on
residential HVAC loads. Engineering analysis and judgment are required to define and
quantify HVAC interactions of vented and ventless dryers in conditioned spaces in the
spectrum of regional home energy characteristics and climates. This work may define
further laboratory testing required to better quantify these interactions.
Non-energy impacts of clothes dryers, including wear and tear on clothing and fire risks, have
been identified. Additional research may be required to demonstrate that these benefits can be
monetized. As these do not impact UES development, they are not included in this Research
Strategy.
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Dryer size (drum size) has been identified as a possible area for additional investigation, since it may have an impact on dryer
energy use.
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Research Strategy
2.2 Analysis Approach
The following sections propose a potential analysis path and identify data needed for meeting
the RTF objectives defined above. Where possible, the analysis approach aims to leverage
existing research and data sets.
2.2.1 Validate Performance Metric
To date, residential dryer energy performance has been characterized by DOE’s test protocols.
These test protocols are summarized below:
 “D”: Previous standard. Uses Energy Factor (EF) – Pounds of clothes dried per kWh at
highest temperature, 66% change in remaining moisture content (ΔRMC), assumed
impact of auto-termination, no cool down.
 “D1”: Current standard. Uses Combined Energy Factor (CEF) – Pounds of clothes dried
per kWh at highest temperature, 53.5% ΔRMC, assumed impact of auto-termination, no
cool down.
 “D2”(Optional): Current standard. Uses Combined Energy Factor (CEF) – Pounds of
clothes dried per kWh at highest temperature, 55.5% ΔRMC, tested with autotermination and cool-down. (Required for ENERGY STAR qualification).2
The Northwest Energy Efficiency Alliance (NEEA) and Pacific Gas & Electric (PG&E) have
developed a performance metric, the Utility Combined Energy Factor (UCEF), and a laboratory
test procedure to measure UCEF that uses real clothing in multiple load sizes and cycle (mode)
settings.3 NEEA and PG&E have measured the UCEF for 11 electric resistance dryer models, one
gas dryer model, and three heat pump dryer models. The results from the 11 electric resistance
models are the basis of the current practice baseline UCEF estimate in the RTF’s planning UES
measure.
The RTF recommends the following analysis steps and data to verify that UCEF can be used to
reliably predict real-world energy savings, with sufficient accuracy across all performance levels
and technologies in the RTF’s Residential Clothes Dryer UES:

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3
Conduct laboratory and field testing of a variety of electric dryer models across
technology type (resistance, hybrid heat pump, heat pump), drum size, and expected
efficiency tier. The same models of dryers should be used in the laboratory and field
testing. For both conventional and Tier 1 units, approximately 10 machines should be
tested to have sufficient data to evaluate the correlation between UCEF and real-world
performance. For Tier 2, 3, and 4 units there insufficient products in the market to use a
sampling approach. Instead, for these tiers, all available products should be tested.
DOE’s 2011 testing showed that results using Appendix D1 cannot be normalized to results using Appendix D2.
DOE’s test procedures employ a test cloth of 50% polyester and 50% cotton.
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Research Strategy
o If the effect of drum size on real-world energy consumption is indeterminate
from this research, an additional study focused on this single variable would be
needed. This would require field testing of three or more dryer sizes and
approximately 10 users per dryer size.

The original NEEA/PG&E laboratory testing of UCEF was conducted at 6500 feet in
elevation. To determine if sea level normalization is needed (or even possible), conduct
an engineering analysis supplemented with laboratory testing at sea level of the four
units still available the original testing.
2.2.2 Characterize Performance Tiers
The proposed Performance Tiers are based on technology types.





Conventional: Electric resistance dryers meeting Federal Standard but not the ENERGY
STAR specifications.
Tier 1: Dryers meeting the 2014 ENERGY STAR qualification (electric resistance)
Tier 2: Hybrid dryers (electric resistance and heat pump) available in the U.S. today4
Tier 3: Heat pump dryers and hypothetical high-performance hybrid dryers
Tier 4: Heat pump dryers (comparable to typical European units).
The UES for Tiers 1 through 4 is the difference in estimated energy consumption between the
Current Practice baseline and the Tier. There is uncertainty in both of these estimates that
contribute to the uncertainty in the UES.
For each Tier, the RTF’s planning measure uses estimated UCEFs. The Current Practice baseline
UCEF is based on the NEEA/PG&E laboratory testing of 11 resistance machines, one of which is
ENERGY STAR qualified and one of which has D2 CEF value from the NEEA/PG&E testing
sufficient to meet the ENERGY STAR specification. The dryer models tested were chosen from
lists provided by manufacturers and retailers of their top-selling dryer units. Top sellers
received higher weightings, with lower weighting assigned to less commonly sold units, and for
units that were considerably higher cost than market average.
The table below summarizes the uncertainty in savings estimates for each tier. Uncertainty in
the Current Practice baseline is sampling error. Uncertainty in Tier 1 through 4 energy
consumption is from uncertainty as to where within each Tier’s UCEF range that average value
for the Tier will be. These estimates do not include HVAC interaction effects.
4
This is approximately the same performance level as dryers meeting EPA’s 2014 Emerging Technology Award specification.
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Table 1. Uncertainty in Savings Estimates
UCEF, min
UCEF, max
kWh/year, max
kWh/year, min
average (kWh/yr)
estimated precision (kWh) +/combined estimated precision (kWh) +/estimated savings (kWh)
precision of savings estimate (%)
Tier 1
3.00
3.39
781
691
736
22
38
104
36%
Tier 2
3.40
3.79
689
618
653
18
35
186
19%
Tier 3
3.80
4.29
616
546
581
18
35
259
14%
Tier 4
4.30
4.80
545
488
516
14
33
323
10%
Table 1 illustrates that the Current Practice baseline developed for the Planning measure and
derived from 11 data points may provide sufficient certainty of savings for Tier 2 through 4
measures. However, for Tier 1, the Current Practice baseline must be known more precisely to
estimate savings reliably because absolute uncertainty in the baseline has a relatively larger
effect on savings uncertainty as savings get smaller.
The RTF recommends the following analysis to confirm that the average performance of
machines in each tier was determined with sufficient reliability:

Develop a transparent and replicable method of weighting baseline model results to
estimate the Current Practice baseline. It may suffice to document the method used to
estimate weights for the NEEA/PG&E baseline estimate. A technical subcommittee will
be required to evaluate the validity of a chosen method, as it would not be feasible to
test all or most of the machines currently in the market.

Increase the number of models included in the Current Practice baseline to 20.

Laboratory test 20 Tier 1 machines to estimate the performance of ENERGY STAR
qualified, non-heat pump dryers with sufficient reliability. (Units tested above for
performance metric would count towards this research need).

Laboratory test all candidate Tier 2 through 4 models for RTF measure qualification.
RTF Staff expect these recommendations to result in the following levels of precision of savings
estimates:
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Table 2. Precision of Savings Estimates
UCEF, min
UCEF, max
kWh/year, max
kWh/year, min
average (kWh/yr)
estimated precision (kWh) +/combined estimated precision (kWh) +/estimated savings (kWh)
precision of savings estimate (%)
Tier 1
3.00
3.39
781
691
736
22
25
104
24%
Tier 2
3.40
3.79
689
618
653
18
29
186
15%
Tier 3
3.80
4.29
616
546
581
18
29
259
11%
Tier 4
4.30
4.80
545
488
516
14
27
323
8%
2.2.3 Quantify HVAC Interactions
Vented and ventless dryers have substantial, yet uncertain impacts on HVAC loads. While
conventional, standard size dryers are all vented, at least one heat pump dryer on the
market is ventless. These technologies have significantly different interactions with HVAC
systems when located in conditioned spaces: vented dryers increase infiltration, increasing
heating and cooling loads. Unvented dryers increase internal heat gains, decreasing heating
loads, but increasing cooling loads.5 Because of these interactions, the location and type of the
dryer in a home can have a significant impact. Additional research is needed to more fully
describe these interactions and estimate their impacts. The RTF recommends the approach
outlined below:

Use engineering analysis to estimate if uncertainties are significant (greater than 10%) in
measure savings. Engineering analysis requires consideration of typical locations of
dryers within the home, building simulation, or secondary data on interactive effects of
infiltration and heat gain on homes with a variety of structural and energy performance
characteristics and climates, and a weighting of results to reflect the regional
composition of homes. If the uncertainties in this analysis result in savings uncertainty
greater than 10%, then further laboratory and field testing would be required to reduce
these uncertainties (see below), or measure identifiers for location would be needed.

A space conditioning interaction study, possibly utilizing the “Lab Homes” located at the
Pacific Northwest National Laboratory in Richland, Washington would be suitable for an
experimental study of the possible range of dryer locations and HVAC system
interactions, similar to ones being considered for heat pump water heaters.6 7
5
Space conditioning energy may increase or decrease to compensate for the heat pump clothes dryers’ induced temperature
change, similar to heat pump water heaters’ “thermal coupling” with HVAC systems, which has been documented by a
number of studies.
6 The Lab Homes are a set of two identical manufactured homes, one baseline (control) home and one experimental home,
which can be used for the purpose of EE experiments.
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Research Strategy
3. ESTIMATED COSTS
(< $25k) ($25k-$100k) ($100k-$250k) ($250k-$500k) ($500k-$1million) ($1million-$2million)
The cost range was estimated using the table below:
Type of Study/Research Approach
Typical Cost Range
Needed for This Research Strategy?
Data Analysis
$5,000 - $10,000
Yes
Desk Research/Modeling
$10,000 - $25,000
Yes
Laboratory Study
$100,000 - $200,000
Yes
Limited Field Study
$200,000 - $500,000
Yes
Significant Field Study
>$500,000
No
Notes on Types of Study:
 Data Analysis: No primary data collection required
 Paper Study/Desk Research/Modeling: No primary data collection needed, analysis by CAT or contracted
expert.
 Laboratory Study: Some data already available, only a few specific cases required
 Limited Field study/Billing Analysis: Data may be needed about a specific use case to inform/refine the
savings estimate (certain HZ/type of home, interactive effect, etc.)
 Significant Field Study: No data available, significant field data collection required.
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If it is determined that the uncertainty range in the space conditioning interaction term results in a substantial range in the
overall UES, the RTF and region may choose to weigh the benefits and costs of further research.
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