Energy Audit Analysis of Homes in Austin, TX
Joshua D. Rhodes – Presenter
Brent Stephens
Dr. Michael E. Webber
The University of Texas at Austin
ASHRAE Winter Conference, Chicago, IL
January 22, 2012
Paper # CH-12-C018
Learning Objectives for this Session
•  How energy audits can be helpful in aggregate
•  Energy audit procedures and problems
•  The state of the residential building stock of Austin,
TX
•  Energy retrofits as compared to new peaking power
acquisitions
Slide 2/19
January 22, 2011
AIA Disclaimer
ASHRAE is a Registered Provider with The American Ins9tute of Architects Con9nuing Educa9on Systems. Credit earned on comple9on of this program will be reported to ASHRAE Records for AIA members. Cer9ficates of Comple9on for non-­‐AIA members are available on request. This program is registered with the AIA/ASHRAE for con:nuing professional educa:on. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construc:on or any method or manner of handling, using, distribu:ng, or dealing in any material or product. Ques:ons related to specific materials, methods, and services will be addressed at the conclusion of this presenta:on. Slide 3/19
January 22, 2011
This Presentation Will Discuss:
•  Results of our energy audit analysis of homes in
Austin, TX
–  State of homes in database
–  Results of “fixing” homes using Home
Performance with Energy Star© (HPwES)
–  Comparison to peaking power acquisitions
•  Some future ideas and research
Slide 4/19
January 22, 2011
Austin’s Energy Conservation Audit and
Disclosure Ordinance (ECAD)
•  Most homes > 10 years old must get energy audit before
they are sold
–  Use market forces to increase the energy efficiency
of buildings
–  Address the Austin Climate Protection Plan
–  Reduce peak demand by 700 MW by 2020
•  This ordinance is semi-unique to Austin
–  We analyzed ~5000 single family detached home
(SFD) audits
Slide 5/19
January 22, 2011
The ECAD Procedures are Good but Not
Perfect…
•  200+ companies perform audits
–  Standard form, now electronic PDF
•  Many characteristics were visually noted, some measured
–  A/C efficiency
–  Window type, etc.
–  Attic insulation
–  Delta T, duct leakage
•  Some audit problems
– 
– 
– 
– 
Auditors assumed A/C air flow rates
Outside temp not noted for Delta T
Walls assumed to be code when built
No blower door or ACH measurements
Slide 6/19
January 22, 2011
The ECAD Database Includes a Representative
Sample of Austin Homes
Number of Homes 200
Number = 4893
150
100
50
0
1925
1935
1945
1955
1965
1975
Year Built 1985
1995
2005
Slide 7/19
January 22, 2011
Attic Insulation Levels in ECAD Homes are
Lower than Recommended
Number of Homes 500
Mean: R-­‐21 Median: R-­‐21 Std. Dev.: R-­‐9.5 Number: 4555 400
300
200
100
0
<2
6
10
14
18
22
26
30
34
38
42
46
50
AEc Insula:on R-­‐value (hr·∙I²·∙°F/Btu) Slide 8/19
January 22, 2011
Air-Conditioning System Characteristics
Parameter
Nominal Capacity,
tons [kW]
Airflow Rate,
CFM [m3/s]
Rated Efficiency,
Btu/hr/W [COP]
Mean
Median
Standard
Deviation
Number of
Units
3.1 [11]
3.0 [10.6]
0.8 [2.8]
4763
1296 [0.61]
1200 [0.56]
651 [0.31]
4714
10.0 [2.9]
10.0 [2.9]
1.7 [0.5]
3818
502 [13.2]
91.4 [2.4]
4693
11
5.7
3480
Floor Area/Capacity
505.6 [13.3]
ft2/ton [m2/kW]
Unit Age
years
10.8
Slide 9/19
January 22, 2011
Ducts are Notoriously Leaky
Percentage of Systems
10%
Blasnik et al. 1995
Cummings et al. 1990
Proctor et al. 1997
Modera and Jump, 1995
Siegel et al. 1996
8%
6%
26%
24%
20%
19%
16%
4%
2%
0%
0%
10%
20%
30%
40%
Total Duct Leakage
50%
60%
Slide 10/19
January 22, 2011
The Temperature Difference Across the Coil
Reveals A/C Capacity Issues
600
Number of Homes 500
Mean: 17.1 °F Median: 17 °F Std. Dev.: 5.9 °F Number: 3687 400
300
200
100
0
2
4
6
8
10 12 14 16 18 20 22 24
Temperature Difference Across the Coil (°F) 26
28
30
Slide 11/19
January 22, 2011
Many Installed Air-conditioners are Inefficient
600
Mean: EER 9.9 Median: EER 10 Std. Dev.: EER 1.7 Number: 3839 Number of Homes 500
400
300
200
100
0
Up To 6
7
8
9
10
11
12
Installed EER (BTU/hr per W) 13
14
Slide 12/19
January 22, 2011
Our Analysis Methods are Two-Fold
•  First characterized homes by their current state of
efficiency
–  Calculated power draw based on A/C capacity
and efficiency
•  Increased the efficiency of homes in the database
–  Used the Home Performance with Energy Star©
(HPwES) guidelines
–  Calculated new power draws
–  Extrapolated to 156,000 SFD homes in Austin
Slide 13/19
January 22, 2011
We Used the HPwES Program to Upgrade the
ECAD Homes
•  “Fixed” homes to the following specs
–  ACH to 0.35 (ASHRAE)
–  Attic insulation to R-38 (Energy Star)
–  Sealed ducts to 10% leakage
–  Windows to generic double pane, U value of
0.56
•  Used Manual J to re-size A/C
–  Increased A/C efficiency to EER 12
Slide 14/19
January 22, 2011
Our Analytical Results of ECAD Data Reveal
Opportunities to Reduce Peak Demand
•  Average A/C sized decreased from 3.1 tons to 2.2
tons
–  Average power draw reduced by 1.8 kW
•  Aggregate demand reduction of ~200 MW
–  Assuming constant 70% runtimes
–  Increasing A/C runtimes to 100%
•  Peak reduction of ~86 MW
Slide 15/19
January 22, 2011
Home Efficiency Upgrades can be Comparable
to Power Plant Acquisitions
•  Generic 160 MW natural gas peaking plant
–  $110 million (overnight costs)
–  $2 million/year O&M
–  $20 million for 20 years fuel (200 hr/yr)
–  20 years ~ $230 million
~ $1440/kW of power generation
•  Austin Energy’s max efficiency upgrade rebate is
$1575
–  Only ~ $865/kW of power draw reduction
•  Up to $2600 rebate reaches parity with
generation
Slide 16/19
January 22, 2011
Our Analysis Concludes that
•  97% of homes in Austin would benefit from the
HPwES© program
•  Single family detached homes in Austin account for
about 18% peak power demand
•  Significant reductions in peak demand available
•  Cost can be comparable or better than new
generation acquisitions
Slide 17/19
January 22, 2011
Thanks to the following
•  Mr. Brent Stephens
•  Dr. Michael Webber – Advisor
•  Pecan Street Inc.
•  The Doris Duke Foundation
Slide 18/19
January 22, 2011
Thank you - Questions?
[email protected]
Slide 19/19
January 22, 2011