1. Net Zero Energy Case
Study
Amber Wood
Manager, Energy Programs
EEBA Conference 2011
September 16, 2011
Driving Innovation in Housing Technology

2. NAHB Research Center
Upper Marlboro, MD
 Housing R&D and laboratory testing
 Promote innovation
 Enhancing quality & affordability
 Promoting high standards for the
building industry
2

3. Building America
 Private/public R&D
partnership sponsored by
DOE
 Energy-efficient solutions
for new and existing
housing
 Technologies/Systems
 Whole-House Test Homes
 Quality Processes

4. Maryland ZEH Project
Why ZEH?
4

5. What is ZEH?
Efficient Efficient Renewable
Envelope Equipment energy
systems
Annually producing as much
energy as consumed

6. ZEH Disclaimer
A Zero Energy Home is NOT:
 Zero energy consumption
 Utility independent
 Energy rationed
 Energy unlimited
6

7. The Basics
Hathaway home,
Purcellville, VA.
NREL photo
archive
1. Decrease total energy use
2. Produce energy from renewable sources
7

8. An Energy Efficient Home
House Shell:
More wall and roof insulation, Water Heating:
low-e windows, insulated Solar preheat,
foundation, overhangs, efficient delivery,
passive solar orientation low-flow fixtures
Air-sealing: Lighting:
Seal vents, holes and Fluorescent,
gaps through walls and daylighting
roof
Appliances:
Heating & Cooling ENERGY STAR®
Equipment: Label
High Efficiency,
programmable
thermostat, sealed
ducts, ventilation Plug & Small Appliances:
Individual homeowner’s 8
choice to decrease use

9. Effect of Efficiency
Upgrades
12,000 120%
110%
10,000 100%
90%
Annual Consumption (kWh)
Percent Reduction in Use
8,000 80%
70%
6,000 60%
50%
4,000 40%
30%
2,000 20%
10%
0 0%
Heating Cooling Water Heating Ventilation Air All Other Loads
Primary Energy Category
Base House Net-Zero Design Reduction in Use
9

10. Example ZEH Energy Use
Baltimore, MD
Base House
Percent Net-Zero Annual
Annual Percent of
Energy End Use of Consumption
Consumption Total (%)
Total (%) (kWh)
(kWh)
Heating 12,749 47 2,110 26
Cooling 5,100 19 850 11
Water Heating 3,627 13 167 2
Ventilation Air 0 0 175 2
All Other Loads 5,730 21 4,833 59
Annual Consumption 27,206 100 8,135 100
 PV System
 5,700 W
 500 sqft area
 Produce 8,266 kWh 10

11. ZEH Approaches
ZEH
Details Involving
Builder, Trades,
Government, etc.
11

12. Current ZEH Experience
 Over 50% minimum reduction in
total energy
 Typically 50 – 70%
 Net-zero electric bill
 Gas offset unavailable
12

13. Solar Water Heating System
13

14. Solar Electric (PV) Systems
 Convert sun energy
to electricity
 Operate daily
 Output varies
 PV Systems are ZEH remodel in NJ, courtesy of Bill Asdal
 Available,
 Reliable, &
 Low maintenance
 Quiet
14

15. Utility Connection
15

16. ZEH Utility Requirements
 Utility must “net-meter”:
credit for electricity fed
back to the utility
 Utility must “settle”
credit not less than once
a year
 Utility must be ON to
have PV power
16

17. Armory Park del Sol
A Historic Solar Community
John Wesley Miller Companies
And
NAHB Research Center

18. Armory Park del
Sol
 Urban in-fill
 Former site of Southern Pacific RR executive
homes
 Utilization of existing infrastructure
 Downtown Tucson
 Rio Nuevo Project
 Walking distance – downtown & University
of Arizona
 Cultural activities, arts & music
 Tucson Convention Center
 Theatre, Symphony, concerts
 Artist galleries
 Museums

19. Armory Park del
Sol
 14 acre subdivision
 Urban in-fill in downtown
Tucson
 Single family homes
 Awards for energy efficiency
construction
 Utility collaboration

20. Armory Park del
Sol

21. Armory Park del
Sol
 14 acre subdivision
 Purchased land in 1999
 99 lots
 Construction started 2000
 Historic Armory Park/
Armory Park del Sol
 Designs blend with area
tradition
 Neighborhood has embraced
project
 Local property values much
higher

22. Armory Park del
Sol
 Single family
homes
 New technology/
construction methods
 Traditional Southwestern
exterior design
 Metal framing
 Termite-proof
 Concrete construction
 Thermal mass
 Significant energy savings

23. Armory Park del
Sol
 Energy efficiency construction
 Thermal mass wall – exterior insulation
 Insulation through slab edge
 Raised heel truss, R-38 ceiling
 Dual-pane, Low E & Low Solar Heat Gain
windows
 Ducts in conditioned space
 14 SEER heat pump
 HVAC system design using Manual J
 Optimized (reduced) duct runs
 Return air pathway from each room
 Passive ventilation system

24. Armory Park del
Sol
 Solar Electric Technology
 1.5 kW Photovoltaic (PV) system minimum
 Garage roof mount (parapet wall)
 Utility approved components & systems; annual
utility inspection

25. Armory Park del
Sol
 Solar System Attributes
 One Subcontractor (The Solar Store) installed all systems
 Subsystems & components from major U.S. or multi-national firms
 BP PV Modules
 Trace Inverters
 System meets TEP SunShare requirements (ACC approved)
 Compliance
 IEEE
 National Electric Code
 TEP Service Requirements Book

26. Armory Park del
Sol
 Single family homes
 Information age design
 Minimum 3 telecom ports
 Digital Satellite Service
 CAT5e wiring
 Pre-wired for fiber optics
 Security system
 Central vacuum

27. Armory Park del
Sol
 Utility collaboration
 Tucson Electric Power 5 year A/C guarantee
 TEP inspects each home during construction
 Guarantee qualifies Armory Park del Sol for
reduced residential utility rates
 Guarantees heating & cooling portion of annual bill

28. Armory Park del
Sol
 Utility Collaboration / Solar
Electric System
 State & federal tax credits
 Homeowner qualifies for TEP cash rebates
 Output offsets highest Time-of-Use rate
 TEP inspects solar electric system annually
 City permit fee credit up to $1,000

30. Armory Park del
Sol

31. Armory Park del
Sol

32. Armory Park del
Sol
Solar Energy Homes in Downtown Tucson
An Award Winning Community!
 SAHBA Builder of the Year, 2003
 City of Tucson Most Energy Efficient Builder, 2003
 Sonoran Institute Livable Community Award, 2005
 NAHB Builder of the Year Award Winner, 2005
 Metropolitan Pima Alliance Common Ground Award, 2006

33. Armory Park del
Sol
 APdS Standard Homes
 Predicted to use less than half the energy of a typical regional home

34. Net Zero Energy Home
Project

35. Tucson Zero Energy Home
Construction
35

36. Zero Energy Home at APdS
 Natural extension of
work at APdS
 Engineering work
funded by DOE through
NREL
 Goal of net-zero annual
energy use
 Started with clean sheet
of paper
3

37. Zero Energy Home Design
Team
NAHB Research Center, Inc. Armory Park Del Sol
Project Management Build
Design Support Define Constraints
Monitoring Consumer Education
Project Summary
Information Dissemination
Consumer
Information
Feedback
Solar Store
Manufacturers
Design
Design Support
Manufacturer Contact
Product Specification
Solar Components
Installation Requirements

38. Zero Energy Home
Construction Features
 Concrete walls with 2” polyiso
 R-41 attic
 U-0.32, SHGC-0.35 windows
 SEER 18 AC
 Combined solar (128 sf) space and water
heating system with tankless backup
 4.2 kW PV array
 PEX piping (with some copper)
 Fluorescent lighting throughout
 Outdoor living spaces
 Ceiling fans without light kits
 Energy Star appliances
38

39. Masonry Walls

40. 2” Polystyrene

41. Radiant Roof Decking

42. Window & Porch Overhangs

43. Air Admittance Valves

44. Systems in Conditioned
Space

45. 4 kW PV System

46. 46

47. Armory Park del
Sol
 Zero Energy Home 1
 Now averaging about $10/mo (including $5.28 monthly base fee)
 Average 23 kWh/day Total Average Energy Use
Tucson ZEH at Armory Park del Sol
Monthly Total Energy Use and Cost
1,800 $90
Modifications to solar thermal system
1,600
(+ values = House Use; - Values = Utility Feedback) complete $80
Electric Energy, kWh; Solar Insolation, kWh/m 2
1,400 $70
1,200 $60
Monthly Energy Cost
1,000 $50
800 $40
600 $30
400 $20
200 $10
0 $0
-200 -$10
Values less than zero indicate sell-back to the utility
-400 -$20
Apr-04
Apr-05
Apr-06
Aug-04
Aug-05
Aug-06
Oct-03
Dec-03
Sep-04
Dec-04
Sep-05
Jan-04
Feb-04
Jun-04
Jul-04
Oct-04
Jan-05
Feb-05
Jun-05
Jul-05
Oct-05
Dec-05
Jan-06
Feb-06
Jun-06
Jul-06
May-04
May-05
May-06
Nov-03
Nov-04
Nov-05
Mar-04
Mar-05
Mar-06
Energy Cost Utility Supply PV Supply PV Insolation

48. Tucson ZEH
Data from 9/1/05 to 8/31/06
A/C Compressor, kWh,
1,847
Other, kWh, 3,536
Utility
Supply,
kWh,
1158,
Blower, kWh, 663 14%
PV
Supply,
kWh,
7209,
86%
Demand Water Heater,
kWh, 1,040
Refrigerator, kWh, 631
Lights, kWh, 651

49. ZEH 1st Year Monitoring

50. ZEH Occupied
Period Monitoring

51. ZEH Monitoring Results

52. Year 1 ZEH Monitoring
Results

53. ZEH Monitoring Results
Electric Demand

54. ZEH Monitoring Results
Electric Demand
(w/o Dmd. Heat)
54

55. ZEH Monitoring Results
Cooling Stage Operation
5° Decrease in T’stat setpoint
10° Rise in average ambient T
1.86 kWh/day to 17.3 kWh/day

56. ZEH Monitoring Results
Solar Thermal - Losses

57. Solar Thermal System
• 210 gallon non-pressurized storage tank
• 18 kW demand heater
• 128 sf collector area
57

58. Solar Thermal Heating
Summary
Table 1. Summary of Daily Solar Thermal System Performance
Average Min Max
Insolation on Solar Thermal Array,
6.15 0.63 8.38
kWh/day
Storage Tank Temperature, deg F 129.5 94.1 159.9
Hot Water Usage, gallons per day 62.4 33.8 122.8
Domestic Hot Water Energy Use,
23,750 10,858 46,572
Btu/day
Solar Thermal Collector Production
56,400 0.0 104,000
(Btu/day)
Solar Thermal Collector Efficiency
22.8% 6.0% 35.2%
(days > 5,000 Btu production)
The solar thermal system did not perform as expected. The average thermal energy
collected during the heating season was much lower than the anticipated 80,000 to 90,000
Btu/day. If the system had performed as anticipated, the average daily heating and water
heating load of 70,800 Btu/day could easily have been met by solar energy. Further
investigation is needed to determine why the collector system is not performing as
designed.
3rd Quarterly Report
58

59. Solar Thermal Heating
Summary
Table 1. Summary of ZEH Heating Season Performance
Measured Results Simulated Results
Heating Period (November 1 – March 31) 151 days*
HDD (November – March) 1,084 1,412
Ambient Temperature (average) 58.1 °F 55.3 °F
Average Daily Minimum Temperature, °F 44 °F 42 °F
Average Indoor Air Temperature** 73.6 °F 73.3
Indoor Thermostat Set Point, °F 72 72
Heating Energy Used, million Btu 7.105 4.637
Domestic Hot Water Energy Use, million Btu 3.586
Solar Energy Collected, million Btu 8.512
Demand Water Heater Supply, million Btu 6.257
System Losses, million Btu 4.079
Proportion of Heating Energy Supplied by Solar 60%
Daily Average Heating Energy Use, Btu/day 47,050 30,700
Daily Average Thermal Load (heat and DHW), Btu/day 70,800
Average Daily Solar Energy Collected, Btu/day 56,370 (80,000-90,000 per
design specs)
*excluding 1 day of cooling (12/6); **Average at Thermostat
3rd Quarterly Report
59

60. ZEH Monitoring Results
Hot Water Storage - Summer

61. ZEH Monitoring Results
Hot Water Storage - Winter

62. ZEH Monitoring Results
Inverter-Demand Heater
Compatibility

63. ZEH Monitoring Results
Thermal Energy Supply/Use

64. ZEH Monitoring Results
Thermal Energy Supply/Use

65. ZEH Monitoring Results
PV System Comparison

66. ZEH Monitoring Results
PV System Output

67. ZEH Monitoring Results
1st Year PV System Output
PV system output = 7323 kWh (32°, 0° azimuth)
Solar Input = 2370 kWh/m2 (6.49 sun-hours/day)
Average AC Array Size = 3100 W
TEP PTC rating for BP4200 dc = 3112 W
TEP Average Annual Supply = 6300 kWh (17.3 kWh/day)
Running Annual Average = 19.5 kWh/day

68. ZEH Monitoring Results
Thermal System Output

69. Plug Loads
The big
challenge…
69

70. Energy Simulation
Summary
Annual Electrical Consumption
Description Cooling Heating Fan DHW Lighting Appl/Othr Total
(kWh/yr) (kWh/yr) (kWh/yr) (kWh/yr) (kWh/yr) (kWh/yr) (kWh/yr)
JWM Standard * 3,568 621 772 1,855 1,873 3,687 12,376
ZEH As-Built ** 2,207 200 430 158 779 3,072 6,846
Tucson
Standard*** 6,770 669 1,229 4,064 1,873 3,687 18,292
*(includes passive SDHW)
**(Option A+B+C+D+E w/ R41 ceiling instead of R43)
***Light Frame, R19 ceiling, 10 SEER, double pane wood frame windows
Occupied Use To Date :
Demand Heater = 1,918 kWh, Lighting = 640 kWh, Other = 3,116 kWh
Total Use to Date = 6,406 kWh (26.3 kWh/day)
Estimated Daily = 18.8 kWh 70

71. Lighting Energy
 Heating season lighting  Annual DOE
energy estimated residential
 2.4 kWh/day average lighting use
 1.4 - 5.6 kWh/day range  1444 kWh average
 Simulation lighting  164 watts average
estimates  Tucson ZEH design
 Interior 0.13 w/ft2  100 watts average
 Exterior 0.04 w/ft2
 Average winter lighting
energy use
 0.06 w/ft2 for both
71

72. Tucson Lessons Learned
 Project Success, Builder interest
 PV system
 Utility interest prime
 Knowledgeable installer
 Inverter compatibility problems (new)
 Solar Aesthetics
 Even with flat roofs
 Solar thermal system performance
 Temperature limitations
 Controller
 Losses 72

73. Tucson Lessons Learned
 Integration of HVAC & thermal system
 Simple design/connections
 Space and access for thermal storage
 Thermal mass
 Winter penalties?
 Air admittance valves
 Manufacturer design required
 Plumber reticence
 Work
73

74. Tucson Lessons Learned
 PEX plumbing
 Plastic material questioned
 Negative history
 Different installation method
 Lighting
 Whole-house permanent fluorescent
lighting options NOT mainstream
 Cost is very high
 Plug loads
74

75. Recommendations
 Continued monitoring
 Solar thermal system design
 Thermal mass analysis
 Resolve inverter/heater compatibility
 Design for additional ZEH at Armory Park
 Integration of mechanical systems in
conditioned space
75

76. Recommendations
 Develop homeowner information
 Identify values of ZEH
 Utility flat-rate billing (TOU better)
 Identify Repeatability
 Would this house be built again???
 Continue On With ZEH
76

77. Armory Park del
Sol
 Zero Energy Home 2 - Utility Savings
 PV system cost benefit offsets utility-supplied energy

78. Questions?
78

79. Thank You!
Amber Wood
NAHB Research Center
Manager, Energy Programs
400 Prince George’s Blvd  Upper Marlboro, MD 20774
(direct) 301.430.6309  (fax) 301.430.6180
www.nahbrc.com
Driving Innovation in Housing Technology