1. RESULTS FROM CLOTHES
DRYER TESTING TO DATE
SEDI MEETING:
NOVEMBER 14, 2013
CHRIS CALWELL, ECOVA
1

2. Acknowledgments
• California’s investor owned utilities supported most
of the testing and analysis discussed here
• NEEA, CLASP and NRDC also supported some of this
testing and analysis
• Ecova dryer team: Shawn Andreatta, Chris Calwell,
Paolo Clavijo, Dave Denkenberger, Apurva Pawashe,
and Brian Spak

3. Dryers Largely Unchanged While Other Appliances Have
Improved Efficiency Dramatically. Now 1 Electric Dryer
= 1 Refrigerator + 1 Clothes Washer + 1 Dishwasher
3

4. Research Studies Indicate Energy Use Is Dropping Slowly in
Dryers Over Time as Washers Spin More Water Out of Clothes.
Annual Energy Use Today ~ 900 kWh
4

5. What Types of Measurements Do We Have?
•
DOE data (DOE test cloths)
•
Product database – 2005 test procedure
•
NOPR measurements – 2013 D1 and D2 test procedures and some
measurements with IEC test cloths for a subset of unnamed models
•
ENERGY STAR data (DOE test cloths) – mostly compilations of
other organization’s measurements; no compiled data set from
manufacturers yet
•
Ecova data (DOE and AHAM 1992 test cloths)
•
Early approximate measurements for NRDC
•
Detailed lab measurements for CLASP
•
Detailed lab measurements for PG&E
•
Detailed lab measurements for NEEA
•
Analysis and interpretation of NEEA field data
5

6. Sample of Early Measurements for NRDC

7. How Much Energy and Time Can Better Automatic
Termination Save?
•
•
•
•
•
Moisture sensors for dryers were invented in 1959 and appeared in
models in the early 1960s from Maytag.
50 years later, their effectiveness at saving energy was first
measured in a US test procedure for clothes dryers, D2, on a
voluntary basis.
Prior to that, the US test procedure awarded a 14% fixed energy
savings credit to dryers capable of automatic termination, relative
to models that lack that feature. This credit is still available to
manufacturers certifying compliance to the 2014 standards under
test procedure D1.
DOE data from the NOPR show that 4-38% of total drying cycle
energy can be saved from better automatic termination. Average
savings were approximately 20%.
Design strategies: placing moisture sensing strips in multiple
locations on the cabinet, or including them on the rotating drum, or
monitoring incoming air temperature and humidity along with
outgoing air temperature. Others?

8. The Best Automatic Termination Designs Stop Close
to 2% RMC Instead of Going to Bone Dry
8

9. On Simplified Test Procedures, the Correlation Between
Efficiency and Drying Time Is Quite Strong
2005 DOE Test Results, 7lb Test Load (Final RMC Shown as %)
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HP1 3.6%
8
HP2 2.9%
HP3 4.1%
Energy Factor (lbs/kWh)
7
HP4 3.9%
6
5
4
Conv2Eco 4.0%
Conv2 3.4%
3
Conv3 3.4%
Conv1 4.0%
2
1
0
0:00
0:15
0:30
0:45
1:00
1:15
1:30
1:45
Time (Hours:Minutes)
9

10. Early Testing for CLASP Showed How Test Procedure Choice
Influenced Efficiency and Drying Time in Multiple Types of Dryers
10

11. How Do Efficiency and Drying Time Relate to Each
Other?
•
Clothes dryers offer a valued convenience to their users – they dry clothing
much faster than it would take to hang each article on a clothes line, let it
dry in the wind, and then take it back down from the clothes line.
•
But that convenience carries with it three costs to the consumers, not all of
which are well understood:
1. The cost to buy, deliver and install a clothes dryer (typically $300 to $1,600)
2. The energy cost of operating it (about $40 to $200/year, depending on fuel
choice, energy rates, washer extraction effectiveness, and usage patterns)
3. The cost of accelerated wear and tear on clothing (difficult to quantify, but likely
higher than the energy cost per year)
•
Dryers that operate at higher temperatures tend to draw more heater
power and increase energy costs. The high temperatures can also cause
shrinkage in some types of clothing, increasing wear and tear. But high
temperatures also tend to reduce the amount of time clothes spend
tumbling, which can reduce wear and tear.

12. Why Does Drying Cooler and Slower Increase Energy
Efficiency?
•
There is a latent heat of vaporization to evaporate water in a clothing load
(0.3 kWh/pound of water). If a dryer only consumed that amount of energy
to evaporate the water, it would be considered 100% efficient.
•
Conventional electric resistance or natural gas dryers are about 50 to 70%
efficient on a site energy basis at evaporating water. The rest of the energy
goes to heating the clothing, the dryer, the laundry room itself, and the
outdoors.
•
As drying temperatures go down, the dryer runs in no-heat mode a greater
percentage of the time, taking advantage of the natural desiccating
properties of room air
•
Heat pumps run at lower average temperatures and create their heat more
efficiently than electric resistance dryers, so save energy, but take
significantly longer to complete the drying process. Heat pumps are
generally more than 100% efficient, but vary widely in efficiency depending
on specific design choices.

13. Comparing a Broader Set of Technologies on the
DOE D2 Test Procedure
CEF vs. Drying Time for Different Dryer Technologies using DOE 2013 D2 Test Procedure

14. Efficiencies Drop and Drying Times Increase as the
Test Load Becomes More Realistic
CEF vs. Drying Time for Different Dryer Technologies using AHAM 1992 Test Cloths

15. Conclusions
• Better automatic termination is a viable way to save roughly
20-25% of dryer energy use in the near term
• Heat pumps consistently save energy relative to electric
resistance dryers, but are much slower
• Establishing efficiency specifications that do not specify a
maximum drying time or vary with drying time creates a
loophole.
• Dryers could be designed to dry very efficiently and slowly in
the default (tested) mode, but be readily switched to
another, less efficient mode by users that is not tested.
• Loads and settings employed in the dryer test procedure
should be more varied and realistic to capture performance
under the range of conditions seen in the field, as is
currently done with clothes washers.
• As the test procedure becomes more realistic, efficiency
levels go down, but absolute energy savings from more
efficient models increase