Achieving Very High Efficiency 

and Net Zero Energy in an 

Existing Home in a Hot-Humid 

Climate: Long-Term Utility and 

Preliminary Monitoring Data

D. Parker and J. Sherwin

BA-PIRC

February 2012
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iii

Achieving Very High Efficiency and Net Zero Energy in an Existing 

Home in a Hot-Humid Climate: Long-Term Utility and Preliminary 

Monitoring Data

Prepared for: 

Building America

Building Technologies Program

Office of Energy Efficiency and Renewable Energy 

U.S. Department of Energy 

Prepared by: 

D. Parker and J. Sherwin

BA-PIRC / Florida Solar Energy Center

1679 Clearlake Rd

Cocoa, Florida 32922

NREL Technical Monitor: Stacey Rothgeb

Prepared under subcontract #: KNDJ-0-40339-00

February 2012
iv

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v

Contents

List of Figures ........................................................................................................................................... vii

List of Tables ............................................................................................................................................... x

Definitions................................................................................................................................................... xi

Executive Summary.................................................................................................................................. xii

1 Introduction........................................................................................................................................... 1

2 Importance of Improving Existing Florida Housing.......................................................................... 2

3 Building Description ............................................................................................................................ 4

4 Initial Measures: Exposure of Tile Floor, Ceiling Insulation, and Reduction of Pool Pumping ... 5

5 Audit Evaluation and Infiltration Characteristics .............................................................................. 8

6 Space Conditioning Equipment .......................................................................................................... 9

7 Instrumentation................................................................................................................................... 10

8 Analysis of Savings From Duct Repair ............................................................................................ 12

9 Refrigerator Retrofits ......................................................................................................................... 14

10 Impact of Cleaning Refrigerator Coils.............................................................................................. 17

10.1 New Kitchen Refrigerator......................................................................................18

10.2 Detailed Monitoring of Refrigerators in 2011 .......................................................20

10.3 Garage Refrigerator Performance ..........................................................................22

10.3.1 Possible Explanations for Degraded Refrigerator Performance ............................23

11 Attic and Garage Temperatures........................................................................................................ 24

12 Floor Slab Cooling Potential ............................................................................................................. 28

12.1 Detailed Monitoring in Spring 2011......................................................................30

13 Effect of Building Mass on Natural Ventilation Cooling Potential................................................. 32

13.1 Installation of Whole-House Fan ...........................................................................34

13.1.1 Monitoring in Spring 2011.....................................................................................38

13.2 Reflective Roof Coating ........................................................................................40

14 Second Phase of Retrofit Progress .................................................................................................. 43

14.1 Efficient Lighting...................................................................................................44

14.2 Conversion of Electric Resistance Loads to Natural Gas......................................45

14.3 Solar Water Heating System..................................................................................46

14.4 Tankless Gas Auxiliary Water Heater for Solar System .......................................47

15 Remodel and Progress Toward Reducing Energy Use .................................................................. 51

15.1 Occupancy Changes and Remodel.........................................................................51

15.2 Television and Home Entertainment .....................................................................52

15.3 Home Computers...................................................................................................53

15.4 Real-Time Energy Feedback..................................................................................54

15.5 ENERGY STAR Clothes Washer..........................................................................55

15.6 Energy-Efficient Dishwasher.................................................................................57

15.7 Window Replacement............................................................................................58

15.8 Wall Insulation Retrofit .........................................................................................60

15.9 Photovoltaic-Powered Pool Pump .........................................................................61

15.10 Very High-Efficiency Mini-Split...........................................................................63

15.10.1 Variation in Room-to-Room Temperatures......................................................65

15.11 Photovoltaic System...............................................................................................67

16 Combined Retrofits ............................................................................................................................ 71

16.1 Long-Term Utility Records: Electricity Consumption ..........................................71

16.2 Changes to Natural Gas Consumption...................................................................73

16.3 Reduction in Source Energy Use ...........................................................................74

16.4 Net Energy Use Since Installation of Photovoltaic System...................................75
vi

16.4.1 Data Sharing Website ............................................................................................76

17 Challenges to Efficiency and Future Retrofits ................................................................................ 78

17.1 Initial Comments About Retrofit Process, Cost Effectiveness, and Repeatability78

17.2 Opportunity for Addressing Refrigeration in Florida Homes................................78

18 Conclusions ........................................................................................................................................ 80

References................................................................................................................................................. 81
vii

List of Figures

Figure ES-1. 4.9-kW rooftop PV system is connected in February 2009. The white metal roof was 

part of house improvements in the 1998 remodel. ........................................................................ xiii

Figure ES-2. Changes in source energy use over the 22-year period of home occupancy. Green 

triangles are the 12-month moving averages. Source energy use has dropped by about 90% 

over the period................................................................................................................................... xiv

Figure 1. The home as it appeared when purchased in 1989................................................................. 1

Figure 2. Lot and floor plan schematic for house in 1989 ...................................................................... 4

Figure 3. Thermographic image of the thermal influence of the floor on space cooling needs. Color 

is proportional to temperature with the furniture at approximately 79°F. The tile floor is about 

5° cooler with the throw rug surface between................................................................................... 5

Figure 4. Pool pump timer. Immediately after taking over the house, this was set from 8 h/day to 

only 3–4 h/day, saving an estimated 2000 kWh annually................................................................. 6

Figure 5. Outdoor unit for SEER 10, 2-ton A/C installed in 1995 and still in use ................................. 9

Figure 6. Multiple pulse initiation gas meters to measure gas end use.............................................. 11

Figure 7. A/C evaporator and plenum showing segments sealed with mastic .................................. 12

Figure 8. Hourly A/C demand before and after duct leakage repair, plotted against interior to 

garage temperature difference in 1992 ............................................................................................ 13

Figure 9. Original kitchen refrigerator in 1990 ....................................................................................... 14

Figure 10. Replacement refrigerator in August 1991 ............................................................................ 15

Figure 11. Month of June 1990, showing the measured 15 minute W of the original refrigerator. The 

lower plot month of August 1991 shows the power of the replacement more efficient 

refrigerator. ......................................................................................................................................... 16

Figure 12. Infrared image of 25-ft3 refrigerator showing heat rejection at the base of the unit, but 

also warm temperatures near through the wall ice and water access. The unit was using 4.4 

kWh/day prior to replacement in January 2011............................................................................... 17

Figure 13. Kitchen refrigerator power before and after coil cleaning on September 22, 2010. 

Orange line is average power in days before cleaning (182 Watts); green line is average power 

after (165 W). Energy reduction is about 10%, but daily power use (3.96 kWh) is far above rated 

performance for the refrigerator (2.12 kWh/day) later replaced in January 2011. ....................... 18

Figure 14. Kitchen refrigerator installed in January 2011..................................................................... 19

Figure 15. Energy Guide Label for new bottom freezer ENERGY STAR GE refrigerator .................. 19

Figure 16. Calendar plot of measured garage refrigerator power (red) and new kitchen refrigerator 

(green) in April 2011 showing power and periodic defrost cycles. Y-axis is Watts (0–1000)..... 21

Figure 17. Average measured garage refrigerator power (red) and new kitchen refrigerator (green) 

draw profile by time of day (January 15–May 15 2011). Y-axis is Watts (0–200). Average daily 

power seen was 3.25 kWh/day for the garage refrigerator and 1.59 kWh/day for the new 

ENERGY STAR kitchen model. ......................................................................................................... 21

Figure 18. Measured power of new kitchen refrigerator (green) and garage refrigerator (red)........ 22

Figure 19. Garage against ambient air temperature over a four-day period in the summer 1990.... 24

Figure 20. Attic against ambient air temperature over a four-day period in the summer 1990 ........ 25

Figure 21. Average garage, ambient, and attic air temperatures when air conditioning over the 

month of July 1990 ............................................................................................................................. 26

Figure 22. Measured garage and ambient air temperatures from December to May 2011. Note 

similarity in temperatures, but increasing differences in April and May as the garage remains 

warmer. ................................................................................................................................................ 27

Figure 23. Average measured garage and ambient air temperature profile from December to May 

2011. Note that the garage is both several degrees warmer than the outdoor temperature and 

out of phase with its amplitude by about +2 hours. ....................................................................... 27

Figure 24. Moderating influence of ground temperature against ambient air temperature, summer 

1990...................................................................................................................................................... 28

Figure 25. Interior floor slab and main zone temperatures during an uncomfortable period when 

natural ventilation was used: June 1990.......................................................................................... 29
viii

Figure 26. Summer living room and slab temperatures during periods of natural ventilation and 

A/C........................................................................................................................................................ 29

Figure 27. Measured living room tile surface temperature (red) and west house exterior ground 

temperature at a 1-ft depth (green) from November 2010 to May 2011......................................... 30

Figure 28. Tile and ground temperature during the spring season 2011 without mechanical cooling31

Figure 29. Average daily temperatures of tile floor and ground during the period without A/C. Note 

the warming of the ground in the afternoon by the sun incident on the ground surface on the 

west side of the house. Tile temperature inside is also out of phase with the ground 

temperature......................................................................................................................................... 31

Figure 30. Ambient (red) and living room (green) zone temperatures over a four-day period during 

attempted natural ventilation in June 1990...................................................................................... 32

Figure 31. Average zone temperatures and ambient air temperature during natural ventilation in 

summer 1990....................................................................................................................................... 33

Figure 32. The average indoor temperature, tile, and outdoor temperature profiles shown over the 

24-hour cycle are plotted in a conventional fashion from December 2010 to May 2011 ............ 34

Figure 33. First WH fan installed showing operable louvers that open during operation ................ 35

Figure 34. Two plots showing six-day periods in summer 1991 before and after a WH fan was 

installed to augment natural ventilation .......................................................................................... 37

Figure 35. Image plot of tile surface temperature (top), house indoor temperature (middle) and 

outdoor ambient temperature (bottom) from December to May 2011. Color is proportional to 

temperature and X-axis is the Julian date. Note that the tile temperatures are slowly warming, 

with the house indoor temperatures generally warmer than the outdoor temperatures, 

particularly at night from internal heat gains. ................................................................................. 38

Figure 36. Average ambient temperature (Y-axis = °F) as well as attic and garage temperatures and 

interior temperatures (pink) when WH fan cooling was used April 1–May 15, 2011 ................... 39

Figure 37. Average living room temperature (green), average tile surface temperature (blue), and 

living room relative humidity (red) during the time when the WH fan was used for cooling in 

spring 2011.......................................................................................................................................... 39

Figure 38. WH fan power from April 1 to May 15, 2011 when the system was used for cooling. Note 

nighttime use. Average daily power was 0.95 kWh/day or 43 kWh over the six-week period.... 40

Figure 39. Thermographs taken on northeast interior ceiling on a summer afternoon before and 

after the roof coating. Note large change in heat conduction to the interior. Curtains over a 

north-facing window can be seen in the lower right....................................................................... 40

Figure 40. A highly reflective elastomeric coating was applied over shingles in an experiment in 

July 1992 (a practice that is no longer recommended because of moisture-related problems) 41

Figure 41. Measured change to attic air temperatures and measured A/C power from reflective roof 

coating done in July 1992.................................................................................................................. 41

Figure 42. White metal roof after 12 years of weathering on the south exposure. The 5-vee metal 

panels have maintained their reflectance. PV modules are seen in the image with the solar 

water heater at the far end................................................................................................................. 42

Figure 43. During the home remodel in 1998, high-efficiency ceiling fans were installed throughout 

the house to help shorten the A/C season (number of weeks A/C was necessary for comfort).43

Figure 44. Infrared thermographs of a floor standing lamp with 60-W lamps (left) versus 20-W 

CFLs (right). With color proportional to temperature, the impact of CFLs on reducing cooling 

loads in Florida homes can be seen................................................................................................. 44

Figure 45. Measured electricity use (0.36 kWh) of natural gas clothes dryer over a single drying 

cycle..................................................................................................................................................... 45

Figure 46. Average range/oven natural gas use (cubic feet), November 2010–May 2011................. 46

Figure 47. 4 ft × 8 ft solar collector. System is PV pumped by two 5-W PV modules mounted in 

parallel. ................................................................................................................................................ 46

Figure 48. Tankless water heater elevated above 80-gal storage tank (lower right).......................... 47

Figure 49. Auxiliary gas consumption of tankless gas water heater when the solar system could 

not meet the load November 2010–May 2011; average daily use is 10.4 ft3

/day or the equivalent 

of 38 therms/year). This is the average for the entire period......................................................... 48

Figure 50. Measured daily hot water gallons used each 15-minute interval on calendar plot from 

April 12 through May 15, 2011. Provides an indication of the large day-to-day variability. ....... 48
ix

Figure 51. Measured average daily hot water gallons used on a typical day from April 12 through 

May 15. Average consumption for the four-person household was 60 gal/day over the six-week 

period. The use pattern shows typically two to three showers at night and hot water use 

associated with morning meal preparation and one additional shower....................................... 49

Figure 52. Thermal performance parameters of the solar water heating system during draws on 

May 14, 2011. Inlet water temperature (red) is about 78°F. Output from solar storage tank is as 

high as 170°F. Output after tankless gas water heater (blue) shows considerably lower 

temperatures. Note gas use in last hot water draw of the evening as the tankless auxiliary 

must make up for an insufficient delivery temperature (see Figure 53)....................................... 49

Figure 53. Auxiliary tankless water heater natural gas use on May 14, 2011 corresponding to the 

solar system performance shown in plot above............................................................................. 50

Figure 54. Three-foot overhang on the south face of the home and resulting shading pattern 

shown at noon on June 10, 2011. Note that the windows, walls, and foundation are fully 

shaded. ................................................................................................................................................ 52

Figure 55. Measured other electricity use from lighting, kitchen small appliances, computers, 

ceiling fans, and plug loads from November 2010 to May 2011. Y-axis is W every 15 minutes. 53

Figure 56. Average measured other electricity use from lighting, small kitchen appliances, 

computers, television, ceiling fans and plug loads from November 2010 to May 2011 (red). 

Total house electric power use (green) shows that “other” is the largest component of total 

consumption use (7.9 kWh/day compared with total of 14.5 kWh/day). The load shape of total 

looks so much like that of other since other is the largest component of the home’s total 

electrical loads.................................................................................................................................... 54

Figure 57. The Energy Detective real-time energy feedback device ................................................... 54

Figure 58. Kenmore 2706 ENERGY STAR washer................................................................................. 55

Figure 59. Measured clothes dryer gas use in the month of April 2011 showing day-to-day 

variability. Y-axis is measured cubic feet of gas used per 15 minute interval. Note that often 

two loads are done in a single day. .................................................................................................. 56

Figure 60. Average cubic feet of gas used each 15 minutes for clothes drying (November 2010–

May 2011). Shows greatest laundry activity around noon time. Average = 8.7 ft3

/day or 32 

therms/year). ....................................................................................................................................... 57

Figure 61. Installation of new ENERGY STAR dishwasher................................................................... 58

Figure 62. Poorly fitting single-glazed awning windows with aluminum frames before retrofit ...... 58

Figure 63. New high-efficiency solar control low-e windows on the south side of the home 

installed in August 2010. These casements open fully for ventilation. ........................................ 59

Figure 64. Measured household total electric power before and after retrofit to energy-efficient 

windows. Thermostat was set to a constant level; non-A/C loads averaged about 16 kWh/day. 

Savings appear to be approximately 8 kWh/day. ............................................................................ 60

Figure 65. Exterior EIFS wall insulation retrofit in progress. Insulation consists of 1 in. of 

expanded polystyrene on the exterior covered by fiberglass mesh and vinyl texture stucco. . 61

Figure 66. 450 W of solar modules powers pool pump directly. Solatube on white metal roof can 

be seen in the background. Array shown before installation of larger 4.9-kW PV system. ....... 62

Figure 67. PV-powered pool pump in operation with the automatic pool cleaner operating during 

daytime. This retrofit saved at least 2000 kWh/year. ...................................................................... 62

Figure 68. Attic ducts, while sealed, are only insulated to R-6 and a major source of heating 

system heat loss in winter and cooling season heat gain in summer. Using the mini-split 

allows the duct system to be largely abandoned in place without these losses for space 

conditioning. ....................................................................................................................................... 63

Figure 69. Outdoor unit of Fujitsu 9RLS mini-split heat pump as it appeared during the installation 

of the wall insulation retrofit. The outdoor unit is located outside the west garage................... 63

Figure 70. Specifications for the Fujitsu 9RLS mini-split heat pump.................................................. 64

Figure 71. Mini-split heat pump (red) and central air handler power (green) (for distribution) from 

November to March 2011. Y-axis is average Watts.-The mini-split and air handler were used 

only for heating over this period, consuming only 196 kWh for heating and the air handler for 

periodic distribution only used 4 kWh more. .................................................................................. 65

Figure 72. Measured room-by-room temperatures in home during space heating with mini-split 

heat pump in November and December 2010 showing the degree of variability ........................ 66
x

Figure 73. Installation of 4.1-kW PV system in February 2009............................................................. 67

Figure 74. SMA 5000-W inverter is located on the east side of the home with the utility 

bidirectional meter. A ventilated enclosure was built to protect the inverter from sun and rain.68

Figure 75. South roof of the home showing 4.92-kW PV system, 450-W PV pumping array, and 

solar water heating system (far left)................................................................................................. 68

Figure 76. Calendar plot of daily PV power generated in the month of April 2011. Average daily 

output was 24.7 kWh/day. Y-axis is Watt power generation. ......................................................... 69

Figure 77. Image plots of the PV module temperature (top), W/m2 irradiance (middle) and Wh/15 

minutes for the PV system from December 2010 to May 2011 (bottom). ..................................... 69

Figure 78. PV output summarized over a daily cycle. Note the array irradiance and the inverter 

output every 15 minutes is virtually identical for the 4.92-kW array. This means that power 

output for 15 minutes is well predicted by array irradiance (W/m2

) * 4 kW. Note that inverter 

efficiencies appear somewhat better at maximum output and clearly are lower on morning 

startup.................................................................................................................................................. 70

Figure 79. Changes to electricity consumption over the 22-year occupancy of the home............... 72

Figure 80. Changes to natural gas consumption over the 22-year occupancy of the home. Natural 

gas was installed in February 1993. The red triangles are the 12-month moving average. ....... 73

Figure 81. Changes in source energy use over the 22-year period of home occupancy. Green 

triangles are the 12-month moving averages. Source energy use has dropped by about 90% 

over the period.................................................................................................................................... 75

Figure 82. Total house power (W in red) against total PV output from inverter (November 2010–

May 2011). House power averages 14.5 kWh/day; PV output averages 19.8 kWh/day. .............. 76

Figure 83. Six-month data summary ....................................................................................................... 77

Figure 84. Home as it appears today from the northern exposure...................................................... 80

Unless otherwise noted, all figures were created by BA-PIRC.

List of Tables

Table 1. Infiltration Tests of the Monitored House .................................................................................. 8

Table 2. Monitoring Dataset ..................................................................................................................... 10

Table 3. Daily A/C Electricity Consumption Before and After Duct System Repair in 1992 ............. 13

Table 4. Garage and Attic Temperatures ................................................................................................ 26

Table 5. Main Zone and Floor Slab Temperatures During Summer 1990............................................ 30

Table 6. Retrofit History for Parker Household...................................................................................... 43

Table 7. Entertainment-Related Miscellaneous Electric Loads............................................................ 52

Unless otherwise noted, all tables were created by BA-PIRC.
xi

Definitions

A/C Air conditioning

ACH Air changes per hour

AFUE Annual fuel utilization efficiency

Btu British thermal unit

CD Compact disc

DC Direct current

DOE U.S. Department of Energy

DVD Digital video disc

DVR Digital video recorder

EER Energy efficiency ratio

EF Energy factor

EIFS Exterior Insulation Finishing System

FSEC Florida Solar Energy Center

GE General Electric

hp Horse power

kWh Kilowatt per hour

LCD Liquid crystal display

MW Megawatts

MWh Megawatt hours

Pa Pascal

PV Photovoltaic

SEER Seasonal energy efficiency ratio

SHGC Solar heat gain coefficient

WH Whole house
xii

Executive Summary

This study summarizes the first six months of detailed data collected about a single-family home 

that experienced a series of retrofits targeting reductions in energy use. The project was designed 

to develop data about how envelope modifications in heating, ventilation, and air conditioning 

and domestic hot water and renewable measures can result in considerable energy reductions and 

potentially net zero energy for an existing home. Using utility billing records and recent detailed 

monitoring data, this study was also able to chronicle the progress of energy reduction over a 22-

year period

The home featured in this report was built in 1958. The original structure was 1300 ft2 and 

comprised two bedrooms and two baths. At some point, a 15,000-gal pool was installed by the 

original owners. When the current homeowner initially occupied the house, several changes were 

immediately implemented that substantially cut energy consumption. This resulted in a first year 

energy use of about 10,000 kWh. These immediate changes had a very large impact on 

consumption—about half the electricity use of a typical home with similar characteristics.

• Removal of carpet to expose tile floor for earth contact cooling

• Insulation of attic to approximately R-19

• Natural ventilation for cooling during spring and fall

• Limiting air conditioning from June to September

• Use of ceiling fans and a cooling thermostat setting of 79°F

• Nighttime setback in winter months

• Lower hot water set temperature, tank wrap, and low-flow showerheads

• Reduction of pool pump operation from 8 h/day to 4 h/days in summer and 3 h/day in 

other months.

The current homeowner purchased the house in 1989. Initial occupancy was two adults.

1 In 

1998, the house was expanded to 2,000 ft2, and occupancy grew to four as the family expanded. 

Since the purchase in 1989, many improvements and retrofits were installed (detailed in Table 6 

in the report). Recently, these included the installation of a 4.9-kW photovoltaic (PV) system

(Figure ES-1), high-efficiency windows, exterior wall insulation, and a supplemental ultra-high 

efficiency mini-split heat pump.

 1 Unfortunately, utility records for the home were not available from the former occupants.
xiii

Figure ES-1. 4.9-kW rooftop PV system is connected in February 2009. The white metal roof was 

part of house improvements in the 1998 remodel.

When the new owners took possession of the house, the envelope was grossly inefficient, even

lacking ceiling insulation. Statistics show that with a family of four in a home built before 1960 

with a pool, the average electricity use in Florida is about 20,000 kWh/year (Parker, 2002). The 

net use of electricity (consumption less PV power production) has been less than zero for the last 

12 months.

In 2010, the output of the 4.92-kW PV system totaled 7,415 kWh (20.3 kWh/day), which was 

190 kWh more than the house used (7,225 kWh). Given the large drop seen in natural gas 

consumption in winter 2011 with the improved windows and wall insulation and the use of the 

mini-split for heating, gas consumption in the preceding 12 months has been cut to only 107 

therms versus 221 therms in previous years.

Figure ES-2 shows that the 12-month moving average of source energy consumption in the home 

had been reduced by 90% to only 1 million Btu/month. Comparing to average homes of the same 

type and vintage, the reduction is more than 95%. Based on early data from summer 2011 with 

the mini-split heat pump and thermal improvements, the home appears to be on track to achieve 

zero net source energy in the calendar year.
xiv

Figure ES-2. Changes in source energy use over the 22-year period of home occupancy. Green 

triangles are the 12-month moving averages. Source energy use has dropped by about 90% over 

the period.
1

1 Introduction

This report summarizes the first six months of detailed data collection about a single-family 

home in Cocoa Beach, Florida (Figure 1). The study is intended to demonstrate the potential of 

deep retrofits for achieving zero net annual energy with an existing house. We also analyze the 

22-year utility bill history over the long period when retrofits were made to the home. This 

project was designed to develop data to evaluate how efficiency and renewable measures can 

result in deep energy reductions and potentially zero energy for an existing home. Results

demonstrate that useful verification of deep energy reductions can be obtained from the detailed 

monitoring as well as from utility records.

Figure 1. The home as it appeared when purchased in 1989
2

2 Importance of Improving Existing Florida Housing

Currently, the residential sector in the Florida uses approximately 1.025 quadrillion Btu of site 

energy per year; this amounts to fully 5% of all residential energy use in the United States. 

Florida’s residential electricity demand per capita is among the highest in the country, largely 

because of high air-conditioning (A/C) use during the hot summer months and the widespread 

use of electricity for winter heating. 

Based on 2008 data, total summer electrical generation capacity exceeds 59,000 MW and annual 

consumption exceeds 218 million MWh. Both are the third highest of any state in the nation, 

surpassed only by California and Texas (U.S. Energy Information Administration, 2009a).

Florida households consumed fully 52% of all state electricity production and strongly depend 

on increasing cooling electricity use (U.S. Energy Information Administration, 2009b). Further, 

supplying energy to the residential sector in Florida is responsible for most of its annual 

greenhouse gas emissions (115 million metric tons from electric generation alone). Despite 

technological improvements in refrigerators, A/C efficiency, and energy codes improving 

insulation, Florida lifestyle changes have placed higher demands on appliance and cooling 

resources. The reasons are numerous.

Homes built in Florida have increased significantly in size, from an average 1500 ft2 in 1970 to 

approximately 1900 ft2 in 1993 and 2300 ft2 in 2006 (Shimberg Center for Housing Studies, 

2009). The two-person household in a large home has become more common, as has central A/C. 

In 1960 only 18% of Florida households had A/C, although this increased to 60% by the 1970 

census. Moreover, more of the home is being conditioned: just 3% of Florida households had 

central A/C in 1960 against 38% of Florida households in 1973 at the beginning of the first 

energy crisis (Schrock et. al., 1975). However, by 1993, that figure rose to more than 98%

(Shimberg Center for Housing Studies, 1994). Against that trend, recent analysis of the U.S. 

Department of Energy’s (DOE) Residential Energy Consumption Survey data has shown that 

central cooling and heat pump systems (as opposed to zoned window or wall systems) are 

correlated with considerably higher space conditioning energy use in spite of higher machine 

efficiencies (Steemers & Yun, 2009). Almost 95% of the supply cooling ducts are located in the 

attic space, leading to large cooling leakage and conduction losses for central systems.

Moreover, the state’s housing is very dependent on electricity for nearly all residential energy 

needs. Fully 87% of the state’s homes are electrically heated and about 90% of water heating is 

electric as well (U.S. Census Bureau, 2011a). The saturation of electric cooking and clothes 

drying is even greater.

Also, miscellaneous electric end uses in Florida households since 2000 have been rapidly 

expanding, largely offsetting efficiency gains in the conventional end uses of heating, cooling,

and water heating (U.S. Energy Information Administration, 2011). Although not existing before 

1978, home computers are now ubiquitous in American households. For instance, the first highdefinition digital video recorder (DVR) shipped in 1999; by 2009, 43% of U.S. households had 

them—an appliance that draws approximately 20–32 W even when off and uses half as much 

electricity as a modern refrigerator (Natural Resources Defense Council, 2011 June). Similarly, 
3

in 1978, the average household had one television. By 2009, the average home had three and 

often with much larger screen sizes and power levels (Parker & Fairey, 2009).

There are approximately 8 million residential dwellings in Florida—6 million of them detached 

single-family homes—with many of the structures of varying vintages (U.S. Census Bureau, 

2011b).

2 For instance, about half of these homes were built before 1990 when building codes 

began to be significantly improved. Since the construction slowdown in 2007, the emphasis on 

improving existing homes to realize energy savings has been emphasized. One question that 

emerges, however, is how energy use in existing Florida homes, particularly older ones, can be 

realistically reduced through energy efficiency. As newer homes have been thermally improved 

with better machines and appliances—in most cases due to the energy codes (with the notable 

exception of windows)—older existing buildings in Florida represent an attractive resource for 

potential statewide energy reductions.

Over the last 22 years the Florida Solar Energy Center (FSEC) has emphasized finding ways to 

dramatically improve the energy efficiency of homes in the United States, particularly those in 

Florida’s challenging hot-humid climate. Given FSEC’s emphasis on practical empirical 

research, much has been learned about how to reduce residential energy consumption using a 

variety of technologies and techniques (e.g., reducing duct losses, high performance fenestration 

products, reflective roof/wall surfaces, and advanced HVAC equipment). However, a detailed 

investigation into the cumulative effects of these measures has not been performed.

In 1991, FSEC began simulation work to see if it might be possible to design extremely efficient 

homes and match them with residential PV to realize an imagined apex of efficiency with 

renewable resources—houses that produced as much energy as they used (Parker & Dunlop,

1994). In 1998, an attempt to realize that goal resulted in the construction of a “zero energy 

home” (before the moniker existed) in Lakeland, Florida. The house received much attention,

which led to questions about whether this level of performance could be achieved in existing 

homes. Accordingly, a primary research goal for this project was to develop expertise in the

evaluation of such potential in an existing home. Other goals included:

• Gain experience with the processes involved in residential monitoring of an occupied 

existing home in a cooling-dominated climate to demonstrate the ability to dramatically 

drop loads. 

• Demonstrate the ability to use either utility bills or detailed monitoring data to show 

progress from improvements.

• Acquire cooling, heating, and appliance load shape data and examine how these are 

modified by retrofits.

• Investigate other aspects affecting residential energy use in an occupied home and what 

they might reveal about efficiency improvements for existing Florida housing.

• Document deep energy reductions for the Affordable Comfort Inc. Thousand Home 

Challenge.3

 2 The six million total includes manufactured homes. 3 This project’s energy use for the period April 2010–March 2011 meets its Thousand Home Challenge threshold 

allowance (OPTION B). It will officially meet the Thousand Home Challenge when the application is completed. 

For additional information www.ThousandHomeChallenge.org, 

www.affordablecomfort.org/initiatives.php?PageID=16 .
4

3 Building Description

The monitored building is a single-family detached structure with a rectangular footprint totaling 

approximately 1800 ft2

; of that total area, 1300 was conditioned living area, The house has an 

attached single car garage (200 ft2) and an enclosed south porch or Florida room (300 ft2).

In 1998, the house underwent a remodel that added 660 ft2 living space and converted the Florida 

room to conditioned area. This brought the total conditioned area to 2000 ft2. Figure 2 illustrates 

the residence’s general configuration and orientation. The house faces north-south and is located 

two blocks from the Atlantic Ocean in Cocoa Beach, Florida. The floor consists of slab on grade 

without carpeting (terrazzo). Built in 1958, the building was highly representative of construction 

techniques and practices of that era (wall and ceilings are devoid of insulation and windows were 

single glazed, awning style). 

Figure 2. Lot and floor plan schematic for house in 1989

Approximately 7 in. of fiberglass insulation was blown into the attic immediately after 

occupancy. The attic space was ventilated by soffit vents and two rooftop rotary ventilators. The

garage does not have a ceiling and is directly exposed to the roof decking. It is also directly 

connected to the attic space over the living area. The house was fairly well shaded by a tree on 

the east face; a 15,000-gal outdoor swimming pool is situated on the south side of the building.
5

4 Initial Measures: Exposure of Tile Floor, Ceiling Insulation, 

and Reduction of Pool Pumping

When the house was purchased, all carpet was removed to expose terrazzo flooring underneath

in an attempt to take advantage of the slab’s thermal mass cooling effect (Figure 3). Benefits to 

terrazzo or tile flooring include:

• Tile flooring typically is 4°–5°F cooler than the space in the spring months, providing 

free cooling (Figure 3). Given standard heat transfer rates, this results in a free cooling 

rate of approximately 0.5 tons (5000–8000 Btu/h) under spring conditions.

4

• Reduced exposure to indoor allergens, dust mites, and fleas (Chandra & Beal, 2002).

• Given the subtropical location, bulk moisture is more readily removed. This greatly 

reduces the incidence of mold and mildew issues. 

Figure 3. Thermographic image of the thermal influence of the floor on space cooling needs. Color 

is proportional to temperature with the furniture at approximately 79°F. The tile floor is about 5°

cooler with the throw rug surface between.

Within two weeks of taking occupancy of the home, insulation was added to the attic of the 

home. The existing attic floor was completely uninsulated. Seven inches of blown fiberglass was 

blown into the attic in February 1989 at a cost of $254. This achieved an R-value of 

approximately R-19/h/ft2

/Btu.

Pool pumping hours (Figure 4) were reduced by more than 50% (3–4 h/day seasonally versus 8 

h/day), based on research showing this is an adequate time for pool circulation (Messenger &

Hays, 1982).

 

4 However, later summer warmer soil temperature conditions argue for more detailed full year data.
6

Figure 4. Pool pump timer. Immediately after taking over the house, this was set from 8 h/day to 

only 3–4 h/day, saving an estimated 2000 kWh annually.

One apparent question from examining the early utility data for the home was the low level of 

electric energy consumption—only about 10,000 kWh in the first year of occupancy. How can a 

consumption level, half of that typical, be understood? A partial explanation comes from 

evaluating how the home was operated differently from a standard home and the collection of 

measures that were instituted immediately upon taking occupancy.

To illustrate, a building energy simulation model was created for the home using EnergyGauge 

USA. The predicted consumption of the home with its initial characteristics prior to occupancy 

was 20,598 kWh. The model was then altered to reflect the actual energy reduction strategies 

incorporated by the new homeowners. Those strategies and their cumulative effects are as 

follows:

• Reduce pool pump hours by two thirds: 18,598 kWh.

• Reduce hot water consumption to 45 gal to reflect a two-person household with low-flow 

shower heads, external tank wrap: 17,826 kWh.

• Use natural ventilation and limit cooling season to June–August, inclusive: 14,506 kWh.

• Set back thermostat at night in winter: 14,111 kWh.

• Remove all carpet to expose tile floor: 13,824 kWh.

• Add R-19 ceiling insulation: 13,110 kWh.

• Alter cooling setting to average 79°F from 78°F: 12,843 kWh.

Although still somewhat higher than the first year utility billed consumption, the evaluation 

clearly shows that the change in pool pump operation and the comfort-related compromise to 

limit the cooling season had very large impacts on the consumption in the first year. Some of the 

overprediction is likely associated with less dryer, dishwasher, range, and miscellaneous electric 

use with a two-person household as well a conservative behavior relative to lighting and other 

such loads.
7

This evaluation also suggests that homeowner adoption of an energy-conserving lifestyle (or 

conversely unwillingness to adapt) can have major impacts on real home electricity use. Such 

adaptation can often compromise the reputation of efficiency, because comfort can be adversely 

affected. Also, some effort and vigilance is required to achieve the best results.
8

5 Audit Evaluation and Infiltration Characteristics

Because a single building is monitored, a before-and-after experimental design was used to 

evaluate the impact of retrofits. The prime advantage of the before-and-after design is that there 

is little introduced variation due to occupancy behavior, assuming that lifestyle remains constant 

during the monitoring period. However, it must be admitted that the addition of two additional 

occupants (children) provided strong upward pressure on consumption levels. Thus, stable 

energy use during this period can be looked on as a favorable result. Detailed monitoring began 

in November 2010. Monthly utility bill data collection has been ongoing since the house was 

occupied in 1989.

The house was audited according to an established protocol for existing residential buildings 

(Ternes, 1987). The audit examines all the characteristics of the building that may be related to 

energy use along with the contained equipment that uses electricity or other fuels.

In 1990 and 1991, detailed submetered data were obtained about interior temperatures and 

weather conditions to evaluate replacement of the old, pre-existing refrigerator, to examine the 

potential of duct sealing and to examine how a whole-house (WH) fan might help reduce 

household cooling needs.

A series of tests was also completed to establish the airtightness of the structure, before and after 

duct leakage repair. This consisted of blower door fan-pressurization tests and sulfur 

hexafluoride (SF6) tracer gas tests to determine the house air infiltration characteristics. The 

latter test was completed, both with the house exposed to local weather only as well as with the 

air handler powered. The infiltration test results are described in Table 1.

Table 1. Infiltration Tests of the Monitored House

Test Test Results

Blower Door Air Change Rate @ 50 Pa 9.3 ACH*

% of Leakage in Duct 18.2%

Tracer Gas Tests

Natural Air Infiltration 0.58 ACH

Air Handler Operating 0.86 ACH

Return Leak Fraction 9.7%

* Air changes per hour

In 2010, the blower door tests were repeated for the home, which had become much leakier in 

the meantime—growing to 24 ACH @ 50 Pa pressure. The large increase in house envelope 

leakages were subjectively observed to be associated with:

• Awning windows that no longer closed properly

• Added recessed can lights in the kitchen area that leak

• Bathroom fans that are undampered.

As will be seen, the retrofit of the windows done in the summer of 2010, made very large 

changes to the building overall leakage.
9

6 Space Conditioning Equipment

The original space conditioning system in 1989 consisted of an aging seasonal energy efficiency 

ratio (SEER) 10.0 2.0 ton Sears Climate Master water-to-air heat pump using aquifer well water. 

The A/C and air handler was located in the west-facing single-car garage. The air distribution 

system consisted of approximately 60 ft of R-5 rigid-fiberglass ducts passing through the 

unconditioned attic. A total of seven supply registers provided conditioned air to the house 

interior.

The relative performance of this cooling system was poor compared to newer, more efficient 

units. Maximum compressor current power draws approximately 4,370 W. The measured 

cooling capacity under minimum capacity conditions (67.4°F dry bulb) was 20,884 Btu/h,

corresponding to an energy efficiency ratio (EER) of 5.2 Btu/W. The measured before and after 

coil enthalpy showed a 18°F temperature drop across the evaporator when in cooling mode under 

normal summer conditions. Capacity at 88°F outside temperature was measured at 28,478 Btu/h 

or an EER of 6.5 Btu/W.

A four-day test of the A/C thermostat performance was performed in 1991 beginning on July 16 

with a separate data logger to characterize its operation. The tests revealed an average summer

A/C runtime of 27% and an average interior relative humidity of 60%.

In June 1995, a new SEER 10, two-ton air conditioner was installed (Figure 5). Air handler and 

outdoor unit power were approximately 2,800 W at 92°F and constant run. For two years prior, 

the household had used a WH fan for summer cooling and suffered through the cooling season in 

a failed effort to see if comfort could be achieved without A/C. An AFUE 78% natural gas 

furnace was installed in January 1993.

Figure 5. Outdoor unit for SEER 10, 2-ton A/C installed in 1995 and still in use

In October and November 2010 a 0.75-ton SEER 26.0 mini-split heat pump was centrally

installed for experimental evaluation.
10

7 Instrumentation

There have been two periods when the house was instrumented: in 1991–1993 and then in much 

greater detail in November 2010. Below, we describe the more recent instrumentation effort.

The installed instrumentation in September–October 2010 consisted of a total of 29

measurements considered important to document research results (Table 2). Site weather data are

gathered on temperatures, relative humidity, and insolation. Temperature, humidity, and power 

consumption measurements are taken on the interior of the building.

Table 2. Monitoring Dataset

Monitoring Data Parameter Units

Outside air temperature °F

Garage air temperature °F

Return air temperature °F

Supply register temperature °F

Slab floor temperature °F

Attic air temperature °F

PV array temperature °F

Indoor temperature by thermostat °F

Indoor temperature in kitchen °F

Ground temperature (1 ft depth) °F

Tile surface temperature °F

Water inlet temperature °F

Solar hot water outlet temperature °F

Outlet water temperature from instantaneous gas water heater °F

Single-Ended Voltage Measurements

Pyranometer (horizontal rooftop) W/m2

Pyranometer (plane of PV array) W/m2

Ambient relative humidity %

Interior relative humidity (thermostat) %

Interior relative humidity (by kitchen) %

Electric Power Measurements

Household total power Wh

Central A/C Watt-hours Wh

Mini-split Watt hours Wh

Refrigerator Watt-hours (kitchen refrigerator) Wh

Refrigerator Watt hours (2nd refrigerator in garage) Wh

Whole house fan power Wh

Gas Measurements

Furnace (ft3) ft3

Clothes dryer (ft3) ft3

Oven/range (ft3) ft3

Instantaneous tankless water heater (ft3); auxiliary for solar ft3

Type-T copper-constantan thermocouples were used to record air and surface temperatures. 

Vaisala resistance temperature detector probes were used to measure interior temperatures and 

relative humidities. Measurements of tile and earth temperatures were made using double-ended 

thermocouples. Single-ended thermocouples were used for most other measurements. Insolation 

was measured using a silicon-cell pyranometer with a current output. Electrical consumption was
11

recorded using pulse-initiating power meters. Gas consumption was measured using four positive 

displacement pulse-initiating gas meters (Figure 6).

Figure 6. Multiple pulse initiation gas meters to measure gas end use
12

8 Analysis of Savings From Duct Repair

An objective of the early monitoring in 1990–1992 was to ascertain the effect of duct repair on 

the house A/C demand. The experiment began in July 1992. Two weeks of 15-minute data were 

collected with the A/C and duct system in an as-is configuration.

After another three weeks, the duct system was sealed with mastic on August 27, 1992 (Figure 

7). The initial 18.2% duct leakage was reduced to 5.3% measured leakage. Blower door testing 

before and after the duct repair showed that 71% of the measured duct leakage area was sealed. 

The A/C consumption was then monitored for another two weeks. Data showed that the garage 

temperature where the duct plenum was located had the most pronounced influence on hourly 

A/C demand.

Figure 7. A/C evaporator and plenum showing segments sealed with mastic

The duct repair did show major savings in A/C energy use. The strongest correlation of cooling 

compared the interior temperature to that in the garage where the air handler was located. As 

shown in Figure 8, the duct repairs reduced A/C use by about 19% for a group of days with 

similar interior-exterior temperature differences (interior temperature was measured by the 

thermostat).
13

Figure 8. Hourly A/C demand before and after duct leakage repair, plotted against interior to 

garage temperature difference in 1992

This result compares favorably with the 17% savings realized in 46 homes with duct systems that

were repaired in a similar climate (Cummings, Tooley, & Moyer, 1991). The data collected for 

the single house are summarized in Table 3.

Table 3. Daily A/C Electricity Consumption Before and After Duct System Repair in 1992

Case Number of Days kWh/Day dT (°F)

Before Repair 6 45.5 5.15

After Repair 4 36.7 5.83

Difference 8.8 (19% reduction)
14

9 Refrigerator Retrofits

A total of four refrigerators have been utilized in the home over the 22-year period of 

monitoring. Part of the high turnover rate comes from the beach environment, which promotes 

rust. However, a larger explanation was the growing household size in the 1990s.

The original kitchen refrigerator (Figure 9) was in service for approximately 15 years before the 

house was purchased. The unit was a 19.2-ft3 frost-free Sears Coldspot refrigerator-freezer with 

an automatic ice maker and a water dispenser. Monitoring showed its summertime utility peak 

hour (5:00 p.m. to 6:00 p.m.) electricity demand to average approximately 303 W with annual 

consumption of about 2,510 kWh—a very substantial end-use of electricity in the home. Based 

on monthly utility bills from the monitored house when occupied, the initial refrigerator 

represented more than 25% of the total annual electrical use in the home.

Figure 9. Original kitchen refrigerator in 1990

This estimate is in line with another monitoring study in Florida in the 1980s, which found the 

average annual use for each monitored refrigerator-freezer was 2,361 kWh (Messenger et al.,

1982). Refrigeration in that study accounted for 15% of overall residential electrical 

consumption.

Refrigeration electricity consumption was measured in detail prior to replacement. Consumption 

was metered for an entire year from June 1990 to June 1991 at a 15-minute resolution. Both 

kitchen refrigerator and freezer temperatures were collected as well as recorded door openings. 

The existing refrigerator was replaced in July 1991 with the most energy-efficient model of its 

size possessing the consumer desirable amenities (automatic ice maker, automatic defrost), a 

1991 Frigidaire FPES19TIP (Figure 10). This model had a DOE estimated annual energy use of 

760 kWh.
15

Figure 10. Replacement refrigerator in August 1991

The upper plot in Figure 11 depicts the electricity demand of the original refrigerator over the 

month of June 1990. Even with the scatter, a time-of-day use pattern for the refrigerator is 

apparent; electricity demand is highest at 6:00 p.m. after dinner preparation. The lower plot in 

Figure 11 plots the load shape for the first month of data collected on the more efficient 

refrigerator. The average electricity demand is reduced by more than half (287 versus 122 W), 

although the newer refrigerator appears to use more electricity (300 kWh/year) than the DOE test 

predicts. Parker and Stedman (1992) provide a full description of the original replacement study.
16

Figure 11. Month of June 1990, showing the measured 15 minute W of the original refrigerator. The 

lower plot month of August 1991 shows the power of the replacement more efficient refrigerator.
17

10 Impact of Cleaning Refrigerator Coils 

In 1998 during the house remodel, a side-by-side 25-ft3 unit, with an Energy Guide label of 777 

kWh (2.12 kWh/day) was installed. Coils are in the bottom of the refrigerator and discharge out 

the front. Figure 12 shows an infrared image of the front discharge. In the initial data stream, we 

had about five days pre and post the coils being vacuumed on September 22 at 5:00 p.m. It took 

about half an hour to clean the coils, which were completely faced over with dust and dirt.

Figure 12. Infrared image of 25-ft3 refrigerator showing heat rejection at the base of the unit, but 

also warm temperatures near through the wall ice and water access. The unit was using 4.4 

kWh/day prior to replacement in January 2011.

Prior to cleaning, consumption was 4.37 kWh/day, which was quite high. After cleaning, 

consumption was better, but still high: 3.90 kWh/day—a reduction of 0.44/ kWh/day or 11%, but 

far from the rated performance for this unit (2.12 kWh/day). This is virtually identical to the 12% 

saving (0.36 kWh/day) we measured from coil cleaning in eight Habitat homes in 1997 (Parker 

et al., 1997). Still the kitchen refrigerator needed replacing as there are several units available 

today with similar features that use less than 1.5 kWh/day.

In the plot below (Figure 13), we can see that the unit has shorter compressor run times after 

cleaning, as one would expect. The vertical red line at Julian Date 265.75 is the point where the 

coils were cleaned. The values around 200 W show the compressor power; the occasional 500 W 

values are the activation of the resistance heaters for the periodic freezer section defrost cycle.
18

Figure 13. Kitchen refrigerator power before and after coil cleaning on September 22, 2010. 

Orange line is average power in days before cleaning (182 Watts); green line is average power 

after (165 W). Energy reduction is about 10%, but daily power use (3.96 kWh) is far above rated 

performance for the refrigerator (2.12 kWh/day) later replaced in January 2011.

10.1 New Kitchen Refrigerator

The side-by-side kitchen refrigerator was replaced with a GE Profile 22.2 ft3 French Door 

Bottom Freezer Refrigerator (PFSS2MJY) on January 8, 2011 (Figure 14). The unit has an 

estimated annual energy use of 463 kWh/year (1.3 kWh/day). Figures 14 and 15 show the unit 

and Energy Guide label, respectively. 
19

Figure 14. Kitchen refrigerator installed in January 2011

Figure 15. Energy Guide Label for new bottom freezer ENERGY STAR GE refrigerator
20

10.2 Detailed Monitoring of Refrigerators in 2011

In early shakedown monitoring from September 17–23, 2010, we saw that the new kitchen and 

garage refrigerators were using substantial electricity. For example, it looked like spending 

$3000 on two new refrigerators could save more than the anticipated insulation and window 

retrofits. Estimated savings from this would be about 1500 kWh/year or ~$180.

The garage and kitchen refrigerators in autumn 2010 were measured to use almost exactly the 

same electric power at 4.3 kWh/day each (>1,500 kWh/year). These were judged ripe for 

replacement as there are now models of 26-ft3 models now using less than 500 kWh/year.

The kitchen refrigerator that was replaced in 1991 used considerable electricity: 2510 kWh/year. 

There are certain to be many of those in Florida in need of replacement. Many of them have 

compressors that run constantly at 200 W (which is about 2600 kWh), and a simple test with a 

Kill A Watt meter over a two-day period may be the single most important retrofit test to be 

conducted in homes by auditors. The potential for savings by replacing such units is illustrated 

by what we found at a comprehensive retrofit site in 1995—an existing indoor refrigerator that 

was measured to use 3,040 kWh/year (Parker et al., 1997). We replaced it with an efficient unit 

using 849 kWh—the single largest saving measure in the project.

In our climate the consumption is certain to be 20%–30% more than the DOE label value (higher 

kitchen temperatures in Florida directly increase consumption). Note too that these refrigerators 

are not the worst possible models. The unit in the garage of this report’s study home was the 

interior refrigerator (1991) vintage. Located inside in that year, it was measured to use about 2.1 

kWh/day or 760 kWh in 1991–1992. Now almost 20 years later and located in the garage, the 

same refrigerator is using 4.4 kWh/day in summer or 1600 kWh over the year if that continued

(Parker & Stedman, 1992).

The newer indoor refrigerator—installed in 1998 (Kenmore 5756079)—has a DOE label 

estimated energy use of 777 kWh/year. Over the week of September16–23, it used 4.3 kWh/day. 

Although consumption is certain to be less in winter, before replacement, both of the 

refrigerators would likely use about 1300–1400 kWh/year each, which is largely 

disadvantageous for an effort to reach a zero energy home design. As a first step, the kitchen 

refrigerator was replaced in January 2011.

Figure 16 shows detailed monitoring of the new refrigerator compared with the older unit in the 

garage in April of 2011. Figure 17 shows the average power demand profile of the two 

refrigerators over the 24-hour cycle from January through May 2011. Note that the new kitchen 

replacement unit uses only half the electric power of the garage refrigerator despite being 10% 

larger in interior volume.
21

Figure 16. Calendar plot of measured garage refrigerator power (red) and new kitchen refrigerator 

(green) in April 2011 showing power and periodic defrost cycles. Y-axis is Watts (0–1000).

Figure 17. Average measured garage refrigerator power (red) and new kitchen refrigerator (green) 

draw profile by time of day (January 15–May 15 2011). Y-axis is Watts (0–200). Average daily 

power seen was 3.25 kWh/day for the garage refrigerator and 1.59 kWh/day for the new ENERGY 

STAR kitchen model.
22

Because refrigeration is so important in Florida homes (and arguably extremely important for 

energy reducing retrofits), how they interact with thermostat set point, refrigerator location, and 

their internal gains is important to understand and account for. Also, their electricity use will 

vary with the season whether cooling or heating (something we eventually need to model).

A common idea would be to get rid of the outdoor refrigerator. However, this is not really 

feasible in our household. Lots of Florida houses have second refrigerators (in fact the saturation 

is 1.2 per household): We have two, and with two teenagers, these get a lot of use. Two units 

allow lots of snacks, drinks, flour, eggs, bread, and milk to be stored. In colder climates, you 

could have a pantry for much of that, but in Florida you would likely have a biological mess.

10.3 Garage Refrigerator Performance

Although the kitchen refrigerator in the home was replaced with a new ENERGY STAR model, 

the old refrigerator (1991 vintage), which was efficient 20 years ago, now uses much more 

electricity than it did previously.

As seen in Figure 18, the indoor 24-ft3 refrigerator (green) used 2.4 kWh on April 23, whereas 

the garage model (red) used 6.4 kWh, and the compressor never turned off (~250 W). Red spikes 

are defrost cycles. A single defrost spike for the indoor unit can be seen at 19:00 hours.

Figure 18. Measured power of new kitchen refrigerator (green) and garage refrigerator (red)

One key thing that emerges is to understand how refrigerator performance can be degraded over 

time. In 1992, the refrigerator used only about 2 kWh/day in the kitchen, whereas now it uses 

more than twice as much electricity in the garage. If it is not coil fouling, then what could lead to 

degraded performance over time? Certainly it is not the higher garage temperature, as lower

garage temperatures were seen during the autumn monitoring period.
23

10.3.1 Possible Explanations for Degraded Refrigerator Performance

Out-gassing, shrinkage, or diminishment of refrigerator shell insulation

Failing performance of door gaskets

Refrigerant leakage (unless this is very slow, then this would seem less likely; most units will 

present complete failure with a refrigerant leak)

Compressor efficiency degradation (this seems less likely)

Although this seems poor, there are certain to be millions of refrigerators like these in Florida as 

seen in earlier monitoring efforts that found refrigerators using even more electricity (Parker et 

al., 1997). This suggests that the garage refrigerator (in lieu of data) should be assumed to be 

worse than the indoor unit in simulation analysis and audit. In any case the garage refrigerator is 

now the major load for the home. The household used 20 kWh total on April 23, so the garage 

refrigerator is now fully one third of daily load.

With more than 6 million refrigerators in Florida, substitution with more efficient units 

represents a major opportunity for statewide utility demand reduction particularly. The average 

demand of these units is at least 1000 MW. The least efficient refrigerators are older existing 

models, of which approximately 5% of the stock is replaced each year. The average life 

expectancy of a residential refrigerator is 20 years, such that at least 25% of Florida’s existing 

stock is old inefficient units. Moreover, the ownership of second refrigerators in the state is 

generally higher than elsewhere in the United States. Fully 20% of Florida households have 

second refrigerators, which often are much older and less efficient units, often located in a 

garage.
24

11 Attic and Garage Temperatures

Data analysis of the A/C load in 1990 revealed that with the A/C evaporator located in the 

garage, its electricity demand was more closely linked to garage temperatures than to ambient 

conditions. We also found with a gray shingle roof that the attic reached very high temperatures

with large potential heat gain to the attic duct system. The data illustrate the importance of the 

thermal conditions in buffer spaces in determining A/C electricity demand when there is 

substantial return side leakage that may be linked to these spaces. We also used developed data 

to target retrofits to reduce cooling use.

Figures 19 and 20 show that the summertime temperatures in the garage and attic spaces in the 

monitored home are quite high. The summer garage temperatures were almost always higher 

than the ambient daily temperature—commonly exceeding 90°F. The difference between the 

garage and ambient temperatures were most pronounced during the afternoon peak load hours. 

The rapid drop in garage temperature on the final day shown was due to a sudden afternoon 

rainstorm. 

Figure 19. Garage against ambient air temperature over a four-day period in the summer 1990
25

Figure 20. Attic against ambient air temperature over a four-day period in the summer 1990

Peak attic temperatures may reach nearly 120°F, although the attic cools off rapidly during the 

evening hours, often to a level lower than the ambient temperature because of the radiative 

cooling of the roof surface to the night sky. Figure 21 summarizes the average daily 15-minute 

garage, attic, and ambient air temperatures for the month of July while the house was almost 

continuously air conditioned.
26

Figure 21. Average garage, ambient, and attic air temperatures when air conditioning over the 

month of July 1990

Table 4 summarizes the four summer months of data in 1992 on the garage and attic 

temperatures in the home and provides a summary of these temperatures during the utility peak 

demand hour. These data, as shown in Figure 21, show that the average attic and garage 

temperatures from 12:00 p.m. to 6:00 p.m. exceed 90°F.

Table 4. Garage and Attic Temperatures

Value Mean Min Max

Garage Temperature (°F) 88.1 76.2 99.8

Attic Temperature (°F) 87.6 72.1 119.1

Ambient Temperature (°F) 84.5 72.1 98.6

Figures 22 and 23 show recent data about the temperature of the garage and how it corresponds 

to ambient air temperature.
27 

Figure 22. Measured garage and ambient air temperatures from December to May 2011. Note 

similarity in temperatures, but increasing differences in April and May as the garage remains 

warmer.

Figure 23. Average measured garage and ambient air temperature profile from December to May 

2011. Note that the garage is both several degrees warmer than the outdoor temperature and out 

of phase with its amplitude by about +2 hours.
28

12 Floor Slab Cooling Potential

Like most Florida homes, the studied house has a slab-on-grade foundation. However, the 

monitored home is somewhat unusual in that the floor is not carpeted and has a terrazzo surface. 

Previous research has indicated that exposed floor slabs may offer some cooling season benefit 

for Florida homes (Fairey, Kerestecioglu, Vieira, Swami, & Chandra, 1986). Interestingly, 

Florida homes built after World War II—before the advent of A/C—most often had terrazzo or 

tile floors, likely for this reason.

Figure 24 gives an indication of the moderating influence of the ground as a heat sink during 

periods of natural ventilation. The ground temperature at a 2.5-ft depth varies only slightly over 

the daily cycle over the entire summer in contrast to the large amplitude of the swing in daily air 

temperatures. Figure 25 shows the distribution of living room and floor slab temperatures over a 

hot week-long period in June 1992 when natural ventilation was utilized. The daily cycle of heat 

storage within the floor slab is obvious in the plot. This indicates that the slab mass is providing 

a significant moderating influence on the house internal temperatures when ventilating. Figure 

26 shows the slab temperature against the main zone temperature for the entire summer period. It 

is noteworthy that the slab temperature is lower, even during periods of A/C.

Figure 24. Moderating influence of ground temperature against ambient air temperature, summer 

1990
29

Figure 25. Interior floor slab and main zone temperatures during an uncomfortable period when 

natural ventilation was used: June 1990

Figure 26. Summer living room and slab temperatures during periods of natural ventilation and 

A/C
30

Table 5 summarizes the data about the floor slab and main zone (living room) temperatures, both 

while naturally ventilating and when using A/C. The data show that the floor slab surface is 

cooler under both conditions. Assuming 2000 ft2 of exposed terrazzo and use of the American 

Society of Heating, Refrigerating and Air-Conditioning Engineers surface heat transfer 

coefficient (1.08 Btu/h⋅ft2⋅°F) the data indicate an average level of cooling from the slab of 

approximately 3000 Btu/h when ventilating and half this figure when using A/C at an average 

81°F interior temperature. It appears likely that a floor slab is adiabatic for cooling set points of

77°–80°F. This would seem to suggest that the floor slab can offer cooling potential down to 

77°F with A/C, but below that point the floor becomes a sensible cooling load.

Table 5. Main Zone and Floor Slab Temperatures During Summer 1990

Value Mean Min Max

Air Conditioning

Main Zone Temp. (°F) 81.6 76.2 86.8

Slab Temp. (°F) 80.9 77.6 84.4

Ventilating

Main Zone Temp (°F) 85.3 78.4 92.4

Slab Temp. (°F) 83.9 78.8 88.6

12.1 Detailed Monitoring in Spring 2011

During spring 2011, we used natural ventilation and a whole house fan to maintain comfort 

conditions. The plots below (Figures 27–29) summarize the detailed data now being collected.

Figure 27. Measured living room tile surface temperature (red) and west house exterior ground 

temperature at a 1-ft depth (green) from November 2010 to May 2011
31 

Figure 28. Tile and ground temperature during the spring season 2011 without mechanical cooling

Figure 29. Average daily temperatures of tile floor and ground during the period without A/C. Note 

the warming of the ground in the afternoon by the sun incident on the ground surface on the west 

side of the house. Tile temperature inside is also out of phase with the ground temperature.
32

13 Effect of Building Mass on Natural Ventilation Cooling 

Potential 

The monitored house has concrete wall construction with a slab-on-grade foundation. This is 

typical for many existing Florida homes. Such a massive construction should lead to a structure 

that moderates the swing in daily internal air temperatures, hopefully providing a comfortable 

living environment without A/C when combined with natural ventilation. However, house heat 

gains and interior humidity made this attempted strategy quite oppressive.

Figure 30 shows a plot of the ambient air and living room temperatures over a five-day period in 

June 1990 during which the house was naturally ventilated. The moderating influence of the 

building mass is clear; the ambient temperature rises higher during the day and, at night, falls 

lower than the internal temperature, which varies considerably less. However, the data also show 

that outside nighttime temperatures are always closer to comfort conditions than the interior 

conditions, even with windows open. Two important reasons for this nightly difference are: (1) 

the delayed solar heat flux through the walls of the building; and (2) the very low wind speeds 

that are typical on hot summer days and the inability to flush out interior heat.

Figure 30. Ambient (red) and living room (green) zone temperatures over a four-day period during 

attempted natural ventilation in June 1990

Figure 31 shows the average interior, slab, and ambient temperatures for the entire natural 

ventilation period in June 1991 when attempting to avoid A/C. The data show that on average the 

outside air temperature becomes lower than the main zone temperature at 3:00 p.m., and that 
33

substantial differences exist during the entirety of the evening hours. During this time ambient 

temperatures are much closer to comfortable levels. Figure 32 is a plot of monitored data from 

December 2010 to May 2011, also showing significant differences between the main zone and 

the ambient temperature during the evening and early morning hours.

Figure 31. Average zone temperatures and ambient air temperature during natural ventilation in 

summer 1990
34

Figure 32. The average indoor temperature, tile, and outdoor temperature profiles shown over the 

24-hour cycle are plotted in a conventional fashion from December 2010 to May 2011

These results indicated that a WH fan that assisted airflow to the interior at night should provide 

significant improvements in comfort in high-mass Florida homes during periods when natural 

ventilation is utilized. Such a strategy would help to rapidly remove the accumulated heat within 

the building walls while helping to maintain comfort conditions closer to an acceptable level. 

Presumably, such forced ventilation would also extend the morning comfort conditions by 

removing heat within the massive construction of the house during evening hours to achieve 

better sensible comfort conditions early in the day.

13.1 Installation of Whole-House Fan

An experimental study was carried out in summer 1991 to investigate the natural cooling 

potential of a WH fan in the home (Figure 33). The house was ventilated with all windows open 

during the three-month summer test period (June–August). Air temperatures and relative 

humidity inside the home along with exterior meteorological conditions (insolation, wind speed, 

air temperature, relative humidity) were scanned every five seconds with integrated averages 

recorded every 15 minutes. The house was naturally ventilated during the first half of summer. 

After a significant period of pre-retrofit summer data had been collected characterizing the 

building’s thermal response, a 24-in. WH fan was installed in July 1991. The house was then 

force ventilated during evening hours for the remainder of the summer to establish potential of 

WH fans to improve interior comfort conditions. The electrical consumption of the fan was 

measured at both available fan speeds.
35

Figure 33. First WH fan installed showing operable louvers that open during operation

Figure 34 shows the results: the operating whole house fan dramatically increased our perceived

comfort during nighttime hours even during the hottest part of summer. The measured electrical 

consumption of the whole house fan (3.2 kWh/day) was less than one tenth of that used on 

average and during the previous summer with A/C (36 kWh/day). However, it is readily admitted 

that the achieved comfort conditions were quite arbitrary, with regard to both temperature and 

relative humidity. In particular, increased interior relative humidity was found to likely reduce 

the effectiveness of this strategy, because moisture and temperature levels would not suit agreedupon standards.
37

Figure 34. Two plots showing six-day periods in summer 1991 before and after a WH fan was installed to augment natural ventilation
38

Measurements revealed that the building interior was 3o– 6oF cooler during the evening hours 

after the WH fan was operated. However, data also showed that nighttime humidity levels rose: 

relative humidity increased from 74% to 83% during the nighttime period when fan-powered 

ventilation was used. This was more fully analyzed in a more detailed report, which concluded 

that WH fans have limited potential in humid Florida—primarily confined to the nonsummer 

seasons when we generally use them now (Parker, 1992).

13.1.1 Monitoring in Spring 2011

Figure 35 shows an image plot of the tile and indoor air temperatures and how they relate to 

outdoor temperatures from December 2010 through May 2011. This shows that the tile surface 

exerts a moderating influence on the temperature indoors during natural ventilation.

Figure 35. Image plot of tile surface temperature (top), house indoor temperature (middle) and 

outdoor ambient temperature (bottom) from December to May 2011. Color is proportional to 

temperature and X-axis is the Julian date. Note that the tile temperatures are slowly warming, with 

the house indoor temperatures generally warmer than the outdoor temperatures, particularly at 

night from internal heat gains.

Figures 36 and 37 show the temperatures and relative humidity when a new Tamarack WH fan 

was used in spring 2011. The new WH fan draws only about 120 W, but also provides only about 

1000 cfm of airflow (Figure 38).
39

Figure 36. Average ambient temperature (Y-axis = °F) as well as attic and garage temperatures and 

interior temperatures (pink) when WH fan cooling was used April 1–May 15, 2011

Figure 37. Average living room temperature (green), average tile surface temperature (blue), and 

living room relative humidity (red) during the time when the WH fan was used for cooling in spring 

2011.
40

Figure 38. WH fan power from April 1 to May 15, 2011 when the system was used for cooling. Note 

nighttime use. Average daily power was 0.95 kWh/day or 43 kWh over the six-week period.

13.2 Reflective Roof Coating

In July 1992, another experiment was conducted on the home to examine how a reflective roof 

coating might reduce space cooling needs (Figure 39). The aging gray shingle roof was nearing 

the end of its useful life and had a measured solar reflectance of 21%. The attic of the home was 

insulated to approximately R-19 (although uneven distribution may have degraded the actual 

performance to only about R-11) but the A/C was more than 15 years old and inefficient. The 

roof was coated with a white elastomeric coating on July 6, 1992 (Figure 40). The measured 

solar reflectance after coating was 73%.

Figure 39. Thermographs taken on northeast interior ceiling on a summer afternoon before and 

after the roof coating. Note large change in heat conduction to the interior. Curtains over a northfacing window can be seen in the lower right.
41

Figure 40. A highly reflective elastomeric coating was applied over shingles in an experiment in 

July 1992 (a practice that is no longer recommended because of moisture-related problems)

The measured impact on A/C energy and attic temperatures, shown in Figure 41 during the week 

of the treatment was dramatic (Parker, Barkaszi, Chandra, & Beal, 1995). Although air 

temperatures and solar radiation were comparable, A/C power was reduced by an average 25% 

from 1690 W to 1264 W. The average electricity demand of the A/C system during the utility 

coincident peak period (between 5:00 p.m. and 6:00 p.m. was 2,373 W before the coating and 

1,712 W after the application. This 661 W reduction represented a 28% reduction in peak power 

demand attributable to the coating.

Figure 41. Measured change to attic air temperatures and measured A/C power from reflective roof 

coating done in July 1992
42

It must be noted that although the roof coating had a beneficial impact on cooling loads, it also 

had a deleterious effect on the roof, because coating a shingle roof can cause water vapor to 

condense under the plywood decking during evening hours because of night sky radiation. 

Coatings are fine for use on metal, tile, or torchdown roofing without seams, but we specifically 

warn that coatings should not be used on shingle roofs to prevent moisture damage. 

When the home was remodeled and expanded in 1998, the coated roof was replaced by a white 

metal 5-vee roof (solar reflectance of 67%), which does not have this problem and has 

maintained its reflectance well ever since (Figure 42).

Figure 42. White metal roof after 12 years of weathering on the south exposure. The 5-vee metal 

panels have maintained their reflectance. PV modules are seen in the image with the solar water 

heater at the far end.
43

14 Second Phase of Retrofit Progress

In 1993, the first monitoring equipment was removed, although the retrofit process in the house 

went on. However, it was still possible, in a coarser way, to evaluate the impact of the various 

retrofits performed by continuing to collect utility records.

Within the home the second phase of improvements continued in order to decrease energy use.

Improvements have spanned a 22-year period that has included two additions to the family, 

adding 660 ft2 to the home, and a host of other changes (Figure 43), both helpful and unhelpful, 

to reducing energy consumption.

Figure 43. During the home remodel in 1998, high-efficiency ceiling fans were installed throughout 

the house to help shorten the A/C season (number of weeks A/C was necessary for comfort).

The installed retrofits are summarized in Table 6 and later described in detail.

Table 6. Retrofit History for Parker Household

Date Retrofit Details Cost

February 1989 Remove carpet Expose terrazzo floor for cooling $0*

February 1989 R-19 ceiling insulation Add 7 in. of blown fiberglass $254

February 1989 Setback pool pump hours Set hours from 8 to 4 per day $0

July 1990 Seal duct leakage Air condition all summer $50*

July 1991 WH fan Natural ventilation all summer $500

November 1991 Compact fluorescent lamps Fluorescent lighting 80% of fixtures $400

July 1992 White coating to roof 70% reflectance >20% A/C R $500*

August 1992 PV pool pump Solar power for pool pumping $3000**

February 1993 Gas appliances Gas heat, dryer, range, hot water $2500***

April 1993 Separate freezer Add garage freezer $500

January 1994 Solar hot water5 4 × 8 ft; two tank system with gas $1814

March 1994 Efficient kitchen lighting Change to T8 lamps from T12s $100

July 1995 New SEER 10 A/C 2-ton size; straight cool $2000*

June 1998 Remodel house6 Add 660 ft2 under air, skylights NA

December 1999 25 ft3 side-by-side refrigerator7 Current refrigerator to garage8 $1360R

December 2000 Hi-efficiency ceiling fans Change six fans to Gossamer $1200

 5 Used 4 ft × 8 ft collector, new 40-gal tank; gas auxiliary elevated to provide 80 gal total storage 6 Included: white metal roof, sun tube skylights in interior bathrooms

7 SEARS 5756*79, 25-ft3 side-by-side unit, Energy Guide = 777 kWh/yr 8 Moved kitchen refrigerator to garage and removed separate freezer at the same time
44

Date Retrofit Details Cost

July 2005 TED Real time feedback display $330*

October 2005 New E-Star LCD TV Flat screen 120 W operating $NA9 R

March 2006 ENERGY STAR Washer Kenmore 2706; modified energy factor 

= 2.0 $870R

April 2006 Locate standby loads Use The Energy Detective and new 

protocol $0*

January 2007 Tankless Gas DHW Solar primary with tankless gas $2178

April 2008 E-Star dishwasher Bosch, EF = 1.14 $1500R

May 2008 Low-energy WH fan Tamarack, HV 2000 $900

January 2009 4.095 kW PV system 5-kW SMA inverter; ESA 205 modules $30,000

10

October 2009 Add 820 W to PV system PV system => 4.92 kW total $3,800

June 2010 80-gal solar storage tank Change from 40 to 80 gal storage $548

August 2010 Retrofit windows U = 0.29; SHGC = 0.24 windows $13,800

October 2010 Exterior wall insulation Add R-5 EIFS**** system to CMUs $11,330

November 2010 Mini-split A/C 0.75-ton, central, SEER 26, heating 

season performance factor = 12 $1700*

-------------------------- Detailed Monitoring Begins -------------------------

January 2011 Retrofit kitchen refrigerator 24 ft3 unit; Guide = 463 kWh/yr $1,900

* Owner labor

** Provided free of charge for experimental research (comparable price)

*** With applicable rebates

**** Exterior insulation finishing system

R = replacement due to wear-out of equipment

14.1 Efficient Lighting

In late 1991, we changed all the lights in the house to compact fluorescent lamps (CFLs), except 

for the lights in the closets, which use 25-W incandescent lamps. Typically, this involved a 15-W 

CFL substituted for 60-W incandescent lamps. This totaled 31 indoor lamps replaced and 13 

lamps in outdoor fixtures. This provided a noticeable reduction in household electricity 

consumption—approximately 100 kWh/month. There were also impacts to internally generated 

heat, as seen in Figure 44. We also installed sun tunnel and skylights to provide daylight to the 

interior kitchen and bathrooms during the 1998 remodel.

Figure 44. Infrared thermographs of a floor standing lamp with 60-W lamps (left) versus 20-W 

CFLs (right). With color proportional to temperature, the impact of CFLs on reducing cooling 

loads in Florida homes can be seen.

 9 Not an efficiency related investment 10 Less $10,000 after federal tax credit
45

14.2 Conversion of Electric Resistance Loads to Natural Gas

In early 1993, we changed all possible electric resistance end uses to natural gas to reduce source 

energy and the associated building carbon footprint. This included replacing the heating system 

from the old water to air heat pump to a 78% efficient natural gas furnace. We also replaced the 

electric water heater (energy factor [EF] = 0.86) with a conventional natural gas unit (EF = 0.54) 

in the garage. At the same time, the electric clothes dryer was also changed to a natural gas unit 

and the electric range was converted to a natural gas model. We did note that the natural gas 

dryer actually used an appreciable amount of electricity for operation of the hot surface ignitors 

as well as the drum wheel and blower. Figure 45 shows the measured electricity use for the 

clothes dryer in operation.

Figure 45. Measured electricity use (0.36 kWh) of natural gas clothes dryer over a single drying 

cycle

Figure 46 shows the natural gas range gas consumption measured from November 2010 through 

May 2011. This shows expected bimodal use intensity, morning and evening. With frequent 

cooking for a household of four, the average daily use is 11.15 ft3

/day or 40.7 therms/year.

Although the heat transfer characteristics of an electric stovetop are about 25%–30% better than 

natural gas, the offset resistance electricity use is about 900 kWh/yr.
46

Figure 46. Average range/oven natural gas use (cubic feet), November 2010–May 2011.

14.3 Solar Water Heating System

Within a month of having a natural gas water heater installed, we had a solar water heating 

system mounted on the roof as the primary water heating system. This consisted of a used AET 4 

ft × 8-ft collector, pumped by two 5-W PV modules mounted in parallel and a small El-Sid DC 

pump (Figure 47). Storage consisted of an 80-gal tank that was plumbed such that it convectively 

circulated to the elevated auxiliary 40-gal natural gas tank whenever the 40-gal storage exceeded 

the temperature of the water in the natural gas tank (FSEC, 2006). This effectively provided 80 

gal of storage for the solar water heating system. The system provided about 50% of annual 

water heating required, although this was reduced by the inefficient auxiliary tank.

Figure 47. 4 ft × 8 ft solar collector. System is PV pumped by two 5-W PV modules mounted in 

parallel.
47

14.4 Tankless Gas Auxiliary Water Heater for Solar System

In January 2007, the standard gas water heater was removed and replaced by a tankless gas 

Rinnai R-28 water heater. It has a claimed heating efficiency of 81% (although data from 

FSEC’s hot water systems laboratory suggest these numbers are optimistic by about 10%). Still 

this is considerably better than the EF = 0.54 gas storage tank that it replaced. The standby power 

of the unit with its electronic controls is about 4 W. Electric power during hot water draws is 

about 40 W.

Figure 48 shows the installed configuration. A key innovation is the tankless gas water heater,

which is located above the solar storage such that the hot water naturally migrates to the heat 

exchanger in the tankless unit based on thermal buoyancy (the tankless auxiliary is elevated 

relative to the solar primary tank). Because the tankless heater is fully modulating, it does not 

come on if the hot water inside the unit is in excess of the set temperature. We have this set to 

120°F on its electronic key pad.

Figure 48. Tankless water heater elevated above 80-gal storage tank (lower right)

As seen in the data in Figure 49, this system resulted in a noticeable drop in natural gas 

consumption, which was also apparent in the monthly data. We estimate that approximately 70% 

of annual water heating needs are met by the solar water heater in combination with the tankless 

auxiliary.
48

Figure 49. Auxiliary gas consumption of tankless gas water heater when the solar system could 

not meet the load November 2010–May 2011; average daily use is 10.4 ft3

/day or the equivalent of 

38 therms/year). This is the average for the entire period.

Figures 50–53 show various performance indices for the solar water heating system.

Figure 50. Measured daily hot water gallons used each 15-minute interval on calendar plot from 

April 12 through May 15, 2011. Provides an indication of the large day-to-day variability.
49

Figure 51. Measured average daily hot water gallons used on a typical day from April 12 through 

May 15. Average consumption for the four-person household was 60 gal/day over the six-week 

period. The use pattern shows typically two to three showers at night and hot water use 

associated with morning meal preparation and one additional shower.

Figure 52. Thermal performance parameters of the solar water heating system during draws on 

May 14, 2011. Inlet water temperature (red) is about 78°F. Output from solar storage tank is as 

high as 170°F. Output after tankless gas water heater (blue) shows considerably lower 
50

temperatures. Note gas use in last hot water draw of the evening as the tankless auxiliary must 

make up for an insufficient delivery temperature (see Figure 53).

Figure 53. Auxiliary tankless water heater natural gas use on May 14, 2011 corresponding to the 

solar system performance shown in plot above
51

15 Remodel and Progress Toward Reducing Energy Use 

15.1 Occupancy Changes and Remodel

In 1998, after the births of two children, one in January 1994 and another in November 1996, we 

undertook a large-scale remodel of the home. This entailed adding approximately 660 ft2 of 

conditioned floor area (a third bedroom and an office). These changes, both adding household 

members and 50% more conditioned floor area, could be expected to increase energy use. 

However, at the same time, we made some improvements to reduce consumption:

• In the home remodel in 1998, new roof trusses were added that featured a standard 19-in.

overhang on the east, west, and north faces of the home (see Figure 54). However, on the 

critical south orientation, a 3-ft overhang was specified. This prevents the large glazed 

dining room porch from receiving sunlight in all months but winter. This substantially 

reduces cooling loads and improves room comfort.

• We added two solar tube tubular skylights to the interior bathrooms and added a 

conventional solar control north-facing skylight (using solar control Azurlite glass) in the 

kitchen to reduce interior daytime lighting needs.

• We added low-sone Fantech FR150 fans to the kitchen range hood and both bathrooms to 

allow removal of warm moist air from these areas.

• The newly added sections of the house had R-4 insulation added to the interior of the 

concrete block walls. R-19 fiberglass batts were added to the attic floor above the new 

additions.

• Soon after the remodel, we installed high-efficiency ceiling fans (Gossamer Wind series) 

on manual off switches that allow fans to be easily deactivated. A total of six ceiling fans 

were changed out. This was done in December 2000.

Within the second phase of retrofits, we pursued many actions to reduce energy loads in the 

home, most of which are summarized in Figure 79 (Section 16).
52

Figure 54. Three-foot overhang on the south face of the home and resulting shading pattern 

shown at noon on June 10, 2011. Note that the windows, walls, and foundation are fully shaded.

15.2 Television and Home Entertainment

Like most homes, the household has a television as well as a home stereo and associated 

components. When we moved into the home, this consisted of a Sony 27-in. tube television with 

a measured power demand of approximately 5 W (depending on picture). In 2006, the tube 

television failed after having reliably operated since 1988. Given the picture quality of flat screen 

televisions, we desired to obtain such a model for its replacement. Even with test data not 

typically being published, we found that the Sony Bravia series of LCD TVs had low power use 

(approximately 125 W depending on picture), as well as low power in standby mode (<1 W). 

Table 7 lists components of the revised home entertainment center after upgrading. We also used 

a Valhalla 2100 power analyzer to carefully measure power of both the new television and 

various other components used with it.

Table 7. Entertainment-Related Miscellaneous Electric Loads

Component Active (W) Power/Standby (W)

Sony Bravia 37-in. LCD television 150 1

Scientific Atlanta, DVR 35 26

Sharp stereo receiver (100 watts output) 65 3

Sony CD player (5 CD changer) 10 3

DVD player 17 8

Self-powered sub-woofer 15 12

We were able to verify that the power use of the television met the published specifications, but 

did also learn that the DVR used with it to obtain digital cable images and to record programs for 

later viewing consumed nearly 35 W when on and 26 W when off! Unfortunately, we also 

learned that there was no reliable way to turn off the DVR without sacrificing its functionality. 

This problem continues today.
53

We were, on the other hand, able to use a power strip with the television, DVD player, and audio 

system and sub-woofer that turned these items off when not in use. This was manually operated 

(in an imperfect fashion), but reduced the standby power of these combined elements by 20 

Watts during times when the systems were unused—a saving of more than 100 kWh/yr.

15.3 Home Computers

Like many homes, the household has multiple computers. One of these consists of a desktop 

machine used for word processing with few other connected peripherals other than its monitor. 

The other machine, however, is used extensively in the home office and has a printer, cable 

modem, speakers, a monitor, and wireless router operating. Through detailed monitoring, we 

discovered the components other than the central processing unit, the cable modem and router, 

still consumed 25 W when the computer was not in use. Although the computer can be shut

down, it was found that the computer and components were frequently left on when not in use. 

To address this energy waste, in mid-2006, we installed a motion-controlled power strip 

(Wattstopper Isole) that can shut down the unneeded components when not in use. When 

someone leaves the room for more than 30 minutes, the peripherals are automatically turned off. 

The office occupancy sensor reduced home office loads by 25 W per nonuse hour on average 

(0.3 kWh/day reduction). Based on use patterns, we estimate that this measure saves about 100 

kWh/year. As the motion control device sells for about $90, the payback is approximately 7 

years. In the last year, two additional laptop computers have been added to the household (one 

for each teenager in high school), although these have not been measured.

Figure 55 and 56 show the power of other plug loads such as computers, lighting, and minor 

appliances in recent detailed monitoring:

Figure 55. Measured other electricity use from lighting, kitchen small appliances, computers, 

ceiling fans, and plug loads from November 2010 to May 2011. Y-axis is W every 15 minutes.
54

Figure 56. Average measured other electricity use from lighting, small kitchen appliances, 

computers, television, ceiling fans and plug loads from November 2010 to May 2011 (red). Total 

house electric power use (green) shows that “other” is the largest component of total 

consumption use (7.9 kWh/day compared with total of 14.5 kWh/day). The load shape of total 

looks so much like that of other since other is the largest component of the home’s total electrical 

loads.

15.4 Real-Time Energy Feedback

In mid-2005, we installed a real-time electricity use feedback (The Energy Detective) device

(Figure 57). This allowed us to monitor real-time household power and to track how well we 

were doing relative to power consumption.

Figure 57. The Energy Detective real-time energy feedback device
55

In April 2006, we used the feedback device with a protocol to locate approximately 90 W of 

phantom loads that were being wasted. This included power use in the entertainment center, the 

home office, rechargeable tools in the garage, an unused transformer, and a potter’s wheel 

inadvertently left on. The protocol allows isolation of household loads through a two-person 

audit procedure with circuit breakers and plugs used to isolate all house-specific electricity end

uses (Parker, Hoak, Meier, & Brown, 2006). The monthly electricity consumption (see in Figure 

79) shows a measurable saving from this intervention at about the same time that the ENERGY 

STAR clothes washer was installed. The relatively low level of reduction seen on the installation 

of the device compared with actions shown at April 2006 suggests that feedback will be most 

productive when linked to actions to reduce energy, such as replacement of aging appliances,

identified though using the devices as a diagnostic tool.

15.5 ENERGY STAR Clothes Washer

With a four-person household, considerable laundry is done each week. In March 2006, the 

existing clothes washer in the home, a Whirlpool LA5668, (modified energy factor = 0.817) 

failed. To replace it, we purchased a high-efficiency Kenmore 2706 clothes washer (modified 

energy factor = 2.00), see Figure 58. Using established methods that use manufacturer’s data and 

DOE label information, it is possible to determine energy and operating characteristics of the 

washer. The energy use of the washer itself is quite small, 0.25 kWh/clothes wash cycle for the 

original washer and 0.09 kWh/cycle for the new unit.

Figure 58. Kenmore 2706 ENERGY STAR washer

The larger impacts, at least theoretically, are from hot water use. The original clothes washer 

theoretically used 17.6 gal of water of hot water per wash. The new ENERGY STAR washer 

uses approximately 5.5 gal per wash. Potentially, this would substantially reduce hot water 

energy use. However, in our case this is less influential on energy use, because given the high 

inlet water temperatures in Florida, we generally do a cold water wash. 

With a four-person household with two teenagers, we do approximately six loads of laundry per 

week, as seen in the associated clothes dryer gas consumption calendar plot in Figure 59 for the 

month of April 2011. Thus, the electricity saved by the new machine is too small to be observed.
56

Figure 59. Measured clothes dryer gas use in the month of April 2011 showing day-to-day 

variability. Y-axis is measured cubic feet of gas used per 15 minute interval. Note that often two 

loads are done in a single day.

Although a vertical axis washer, the new Kenmore Oasis machine has a very high spin rate to 

removed excess moisture, which could reduce clothes dryer energy. Based on test data for the 

two machines, the original and ENERGY STAR washers would produce clothes for the dryer 

with a remaining moisture content of 0.5 and 0.37, respectively. Indeed the first thing noted 

using the new clothes washer was the faster time to dry a load of clothes coming out of the new 

machine. Figure 60 shows the typical gas use of the clothes dryer during a typical drying cycle.
57

Figure 60. Average cubic feet of gas used each 15 minutes for clothes drying (November 2010–

May 2011). Shows greatest laundry activity around noon time. Average = 8.7 ft3

/day or 32 

therms/year).

Consequently with the monthly gas consumption data shown in Figure 80 (Section 16), a small 

reduction in gas use is suggested by the new clothes washer. This may reflect reduced dryer 

runtime with the new washer. Impacts to gas consumption associated with reduced hot water use 

are likely minimal, because most is solar heated.

15.6 Energy-Efficient Dishwasher

In April 2008, we substituted a very high-efficiency dishwasher (Bosch SHX98M09; EF = 1.14), 

as shown in Figure 61, for the existing Kenmore 665-1658220 unit. Extensive experiments were 

done on the existing dishwasher and the new model (Hoak, Parker, & Hermelink, 2008). The 

existing dishwasher with an EF of 0.49 had a measured per-cycle machine electricity use of 

about 0.74 kWh, whereas the new ENERGY STAR model had a measured energy use of 0.35 

kWh. We found that savings were increased by about 0.1 kWh/cycle if the dishwasher was run at 

midday when the solar water heater was providing the hottest water. 
58

Figure 61. Installation of new ENERGY STAR dishwasher

As the household dishwasher is used approximately six times a week, expected energy savings 

should amount to approximately 122 kWh/year or about 10 kWh/month. A small discernible 

reduction in electricity use can be seen in Figure 79 (Section 16). There were also measured 

reductions to the amount of hot water used per cycle: 6.7 gal for the standard unit versus 2.3 gal 

per cycle for the high-efficiency unit. However, this impact could not be observed in the overall 

household gas consumption.

15.7 Window Replacement

The existing windows in the house were subject to air loss, thermally uninsulated, and admitted a 

large amount of heat to the interior from radiation. The original windows were single-glazed

awning units with aluminum frames (Figure 62) that had begun to mechanically fail so that they 

were difficult to close and did not seal well. The situation is similar to that encountered in many 

older Florida homes, but had been put off for years because of the high cost of replacing 

windows.

Figure 62. Poorly fitting single-glazed awning windows with aluminum frames before retrofit
59

In the third week of August 2010, the windows in the home were replaced with high-efficiency 

low-e solar control double glass with vinyl frames and argon fill (Custom Window Systems: U =

0.29 Btu/ft2

-°F, SHGC = 0.24), shown in Figure 63. The windows were installed starting August 

16 and completed on August 20. 

Figure 63. New high-efficiency solar control low-e windows on the south side of the home 

installed in August 2010. These casements open fully for ventilation.

Sixteen glazing units totaling 306 ft2 of glass were replaced. Three bids were solicited, with the 

lowest bid being selected. The overall cost was $13,800 ($45/ft2), although the net cost was 

$1500 less because of the applicable federal tax credit. Analysis of daily A/C data on days pre 

and post with similar weather revealed approximately a 20%–25% reduction in cooling from the 

retrofit (Figure 64). This is greater than the 15% seen in an earlier study in two Florida homes 

(Anello, Parker, Sherwin, & Richards, 2001). We believe this was due to the large change in the 

building leakage characteristics from replacing the old leaky windows (McIlvaine, 2010). 11

 11 An initial analysis of data from this cost-effective, high performance residential retrofits for affordable housing in 

the hot humid climate project shows that homes replacing windows were made 15% more airtight than those that did 

not replace windows. A key initial finding is that retrofitting windows reduces building air leakage by about 2 

ACH(50) or about 14% more than whatever else was done in a sample of 41 audited Florida homes.
60

Figure 64. Measured household total electric power before and after retrofit to energy-efficient 

windows. Thermostat was set to a constant level; non-A/C loads averaged about 16 kWh/day. 

Savings appear to be approximately 8 kWh/day.

This reduction in air infiltration was verified by a blower door test, which found measured 

leakage of the home had dropped since the window retrofit from 24.4 ACH (very leaky) to 11.4 

ACH at a @ 50 Pa pressure. Although this is still relatively leaky (average household leakage in 

Florida homes tends to average about 10 ACH), auditors were able to determine that the 

remaining leakage sites consisted of primarily of two bathroom fans, an undampered kitchen 

range hood, two lighting recessed cans in the kitchen, and leakage from the front door and 

another door to the garage.

15.8 Wall Insulation Retrofit

The concrete block walls were insulated to R-5 on the exterior with an EIFS system in 

September–October 2010. Figure 65 shows the wall insulation retrofit in progress. The final 

system consisted of a vinyl stucco coat over fiberglass mesh and the 1 in. of expanded 

polystyrene. The final coating R-value is likely around R-5.5 Btu/ft2-h-°F.
61

Figure 65. Exterior EIFS wall insulation retrofit in progress. Insulation consists of 1 in. of 

expanded polystyrene on the exterior covered by fiberglass mesh and vinyl texture stucco.

The total cost of the improvement was $11,300 to cover a gross wall area of approximately 1,830 

ft2. The net area less doors and windows was 1,398 ft2, so the net cost was approximately $8/ft2. 

Data analysis of the impact of the walls on heating and cooling loads will have to await data 

from winter and summer 2011. Simulation analysis indicates only a 5%–10% saving in space 

conditioning energy, which is similar to previous FSEC research done on such systems (Barkaszi

& Parker, 1995). 

As shown in the gas consumption data in Figure 80 (Section 16), the measured average natural 

gas consumption prior to 2007 was 225 therms/year. However, after the installation of the better 

windows and insulated walls, the consumption over the last 12 months has totaled 107 therms—a 

reduction of 52%. As shown later, measured electricity use for the mini-split was only about 200 

kWh. Although it is misleading to attribute this to the walls alone, it can be confidently 

concluded that the combination of the wall insulation with the better windows and the very 

efficient mini-split allowed a large reduction in household natural gas consumption.

15.9 Photovoltaic-Powered Pool Pump

About 20% of Florida homes have swimming pools. Pumping represents a significant proportion 

of the overall energy use and cost of operation. The average pool pump in central Florida uses 

about 4,200 kWh/year (Parker, 2002). Pumps are frequently oversized with narrow piping and 

small filters. They also may be operated more frequently than necessary. The average pool pump 

runs about 8 h/day. A detailed experimental study of 120 pools by Florida Atlantic University in 

1981 found that pool pump operation no more than 4 h/day resulted in no degradation in pool 

clarity or increase in algae formation (Messenger & Hays, 1982). 

When the home was first occupied, pool circulation was reduced to 4–6 h/day depending on the 

season. The 3⁄4 hp pump drew about 1 kW in operation such that 120–160 kWh of monthly 

electricity was used to circulate the pool.
62

In an effort to totally eliminate this electricity end use, it was substituted with a PV-powered 1⁄2 

hp DC pool pump (ETA Engineering 90 Volt DC pump). The pump runs as long as the sun is up 

each day from a dedicated 450 W of PV (six 75-W modules), shown in Figure 66. The system 

works very well compared to the 3⁄4 hp A/C pump that was removed. It fully operates the 

automated pool cleaning system (Figure 67). The addition of the system produced a noticeable 

drop in total household electric power, as seen in monthly electricity consumption in Figure 79

(Section 16).

Figure 66. 450 W of solar modules powers pool pump directly. Solatube on white metal roof can 

be seen in the background. Array shown before installation of larger 4.9-kW PV system.

Figure 67. PV-powered pool pump in operation with the automatic pool cleaner operating during 

daytime. This retrofit saved at least 2000 kWh/year.
63

15.10 Very High-Efficiency Mini-Split

Fairly large cooling costs were experienced in the summer of 2010. Cooling was provided by an 

aging 10 SEER, straight cool split system with attic ducts and associated losses (Figure 68). In 

October 2010 this was supplemented with a centrally located Fujitsu 9000 Btu/h SEER 

26/heating season performance factor 12 mini-split heat pump (Figure 69). The evaporator is 

located centrally in the living room of the home with the outdoor unit located on the exterior of 

the west side of the house. 

Figure 68. Attic ducts, while sealed, are only insulated to R-6 and a major source of heating 

system heat loss in winter and cooling season heat gain in summer. Using the mini-split allows 

the duct system to be largely abandoned in place without these losses for space conditioning.

Figure 69. Outdoor unit of Fujitsu 9RLS mini-split heat pump as it appeared during the installation 

of the wall insulation retrofit. The outdoor unit is located outside the west garage.

The system cost was only $1700, including line-set, and all equipment and was owner installed. 

Professional installation would have cost about twice this amount. Performance specifications 

are shown in Figure 70.
64

Figure 70. Specifications for the Fujitsu 9RLS mini-split heat pump

The system draws only about 600 W under full load (roughly twice that of the blower alone for 

the central A/C system and furnace). Rated capacity is 9000 Btu/h in cooling mode and 12,000 

Btu/h in heating mode. Its EER at the 95/80/67 condition is 17.3/Btu/W and at 47°F in heating 

mode is 15 Btu/W.12

The system became operational in November 2010. With the addition of the EIFS and high 

performance windows, it was possible to use the centrally located mini-split for heating and not 

utilize the natural gas furnace in winter 2010–2011. Figure 71 shows average heating power use 

of mini-split heat pump from November 2010 through March 2011. If room temperatures were 

too low, the air handler and blower could be used to provide distribution. Cooling performance 

will await data in the summer of 2011.

 12 www.fujitsugeneral.com/wallmounted9-12RLS_specs.htm
65

Figure 71. Mini-split heat pump (red) and central air handler power (green) (for distribution) from 

November to March 2011. Y-axis is average Watts.-The mini-split and air handler were used only 

for heating over this period, consuming only 196 kWh for heating and the air handler for periodic 

distribution only used 4 kWh more.

Based on recent changes, it is anticipated that gas consumption will be reduced by approximately 

100 therms/year and annual electricity consumption will be reduced by 1000 kWh. However, so 

large was the change in the interior thermal environment from the wall insulation and the 

installation of the better windows that the household planned to use the single living room highefficiency mini-split to accomplish all heating during winter 2010–2011. 

15.10.1 Variation in Room-to-Room Temperatures

In autumn 2010, portable temperature loggers were deployed in each room of the home prior to 

the use of the mini-split heat pump. One idea was to see with the better wall insulation and 

windows if it might be possible to avoid using the natural gas furnace for space heating. The 

attractiveness of this is apparent. Approximately 100 therms/year are used for space heating. We 

found that it was possible to use the mini-split heat pump in this fashion without unduly 

sacrificing comfort in the main living zone. However, one question that arises is what difference

will be seen in the temperatures of individual rooms when using this strategy.

Figure 72 shows the measured variation in room-by-room temperatures in November and 

December 2010. Note that in early November, the house was floating, with no space 

conditioning and the room temperatures were fairly consistent, typically with less than 6°F 

difference from one room to the next. The higher temperature seen in the dining area comes from 

its large glazing fraction facing south, which tends to run warmer in daytime in winter. 
66

Figure 72. Measured room-by-room temperatures in home during space heating with mini-split 

heat pump in November and December 2010 showing the degree of variability

When space heating begins in earnest at the end of the first week in December, the temperature 

spreads apart with the highest temperatures seen in the living room zone where the mini-split 

indoor unit is located. A large office area was closed off on the southeast corner of the house to 

see how a closed door would influence space temperatures. Note that even ignoring the closed 

off room and the living room space, temperatures vary by 7°F or more from one space to 

another. Although this seems high, experiments this summer and next winter using the central 

system and the mini-split for various periods will allow further evaluation of how room-to-room 

temperatures are influenced by central system operation and what portion is intrinsic to the 

natural thermal zoning that occurs when the system is not operating.
67

A useful question to be answered later is how the room-by-room temperatures will vary with a 

central system versus the mini-split. This will be examined through A/B switch tests in the 

cooling season in summer 2011. Some days will use the mini-split, other days will use the central 

cooling system with temperature distribution and power use compared.

15.11 Photovoltaic System

The attempt to reach a zero energy existing home required renewable energy generation. As one 

of the most expensive elements in the overall project, it was carefully planned. After evaluating 

multiple bids, at the end of January 2009, we installed a 4.1-kW PV system, although the net 

metering did not go in until the following month. Figure 73 shows the south face of the house 

during the retrofit with its PV system in January 2009. The original system consisted of 20

south-facing Evergreen ESA 205 modules grid connected to an SMA-5000 inverter located on 

the east side of the house (Figure 74). In October 2009, we added another 820 W (4 modules) to 

expand the capacity to 4.92 kW (Figure 75). Average power production since the system was 

finalized has averaged about 20.3 kWh/day. Figure 76 shows a calendar plot of power produced 

by the PV system in April 2011.

Figure 73. Installation of 4.1-kW PV system in February 2009
68

Figure 74. SMA 5000-W inverter is located on the east side of the home with the utility 

bidirectional meter. A ventilated enclosure was built to protect the inverter from sun and rain.

Figure 75. South roof of the home showing 4.92-kW PV system, 450-W PV pumping array, and 

solar water heating system (far left).
69

Figure 76. Calendar plot of daily PV power generated in the month of April 2011. Average daily 

output was 24.7 kWh/day. Y-axis is Watt power generation.

More interesting, the image plots for the widening PV output band clearly show the changing 

day length over the analysis period (Figure 77). 

Figure 77. Image plots of the PV module temperature (top), W/m2 irradiance (middle) and Wh/15 

minutes for the PV system from December 2010 to May 2011 (bottom).
70

Figure 78 shows how the plane or array irradiance (IRRDPV) closely corresponds to the inverter 

power output (INVOUT) every 15 minutes. In Figure 77, the PV module backside temperature is 

also shown with the obvious finding that module temperatures increase as summer nears.

Figure 78. PV output summarized over a daily cycle. Note the array irradiance and the inverter 

output every 15 minutes is virtually identical for the 4.92-kW array. This means that power output 

for 15 minutes is well predicted by array irradiance (W/m2

) * 4 kW. Note that inverter efficiencies 

appear somewhat better at maximum output and clearly are lower on morning startup.
71

16 Combined Retrofits

16.1 Long-Term Utility Records: Electricity Consumption

More than 20 years of utility data were collected for the home and then used for retrofit analysis. 

Figure 79 illustrates the monthly electricity consumption, which totaled 9,774 kWh from April 

1990 through March 1991. The data clearly show increased electrical consumption associated 

with A/C in the months of July–September. The electrical base load, including hot water use, 

initially appeared to be about 600 kWh/month.

The figure also shows the annotated 22-year history of electricity use at the Cocoa Beach home. 

Monthly recorded kilowatt-hours, as well as the 12-month moving average, are shown. The 

figure also shows the various retrofits and changes that we made to the building and to the 

family. Some of these changes reduced energy use, but some changes also increased 

consumption.
72

Utility & Retrofit History for Parker Family

Cocoa Beach, 1989 - 2011

Year: 1989 - 2011

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Monthly kWh

-400

-200

0

200

400

600

800

1000

1200

1400

1600

1800 Monthly Electricity Consumption 

12-month moving average

R19

Ceiling

& tile

floor

Seal

Ducts WHFan

& new Frig

White

Roof

PV Pool

Pump

New

AC

Energy

Feedback

4.1 kW

PV

Remodel

Solar

DHW

& Gas

CFLs

Flat Screen

& DVR

Sarah * Wade *

FPL Average Use: 17,207 kWh/yr or 1,434 kWh/month

+500 ft2

Zero Electricity Objective

Add

2nd 

Frig

ES Ceiling

Fans ES Dish-

 washer

& WHF

ES

Washer

Add

0.8 kW

PV

HiEff

Windows

Wall Ins.

& M inisplit

ES Kitchen

Fridg

Add

Freezer

Remove

Freezer

Figure 79. Changes to electricity consumption over the 22-year occupancy of the home

Each of the retrofits is superimposed on the plot of the month-by-month electricity consumption 

(red) over the entire history of house ownership. The green triangles show the moving 12-month 

average, which takes out much of the seasonality of the data.

With the addition of the PV system, the moving 12-month average has reached zero electricity 

and below. Since installation of the PV system, and subsequent improvements, the household has 

not had an electric bill other than the cost for connection and tax. This totals $6.98/month. 

Moreover, at the end of 2010, the household received a credit from Florida Power & Light 

Company for $7.50 to compensate for the 190 kWh leftover credit at the end of the year.

Figure 80 shows the same type of presentation for natural gas, but only with the retrofit items 

shown that are expected to have an impact on that fuel use.
73

Figure 80. Changes to natural gas consumption over the 22-year occupancy of the home. Natural 

gas was installed in February 1993. The red triangles are the 12-month moving average.

16.2 Changes to Natural Gas Consumption

Figure 80 shows a similar presentation on how natural gas consumption has varied since gas was 

added to the home in February 1993. This was done in hopes of dropping the household 

electricity consumption as well as total source energy.

The following end uses were changed from electricity to natural gas all in the same month:

• Water to air heat pump to natural gas furnace (AFUE = 78%)

• Electric water heater to solar water heater with EF 0.54 natural gas storage water heater

• Electric clothes dryer to natural gas clothes dryer

• Electric range to natural gas range/oven.

Heating degree days are also shown on the plot as space heating is a major end-use of natural 

gas—particularly as seen in the cold winter of 2010.
74

16.3 Reduction in Source Energy Use

As seen in the analysis, natural gas was substituted for the following end uses in 1993:

• Water heating (with solar)

• Clothes drying

• Space heating (gas furnace)

• Range and oven.

Because electricity typically takes more energy to produce a unit of energy, it is useful to 

examine how source energy changed with the retrofits. Here, source energy use per month is 

given in million Btu. The conversions are according to the Building America analysis methods 

(Hendron, Anderson, Christiensen, Eastment, & Reeves, 2004, August) to reflect the following 

multipliers:

• Electricity: kWh * 3413 * 3.365 = source energy electricity MBtu

• Natural gas: Therm * 100,000 * 1.02 = source energy natural gas MBtu

The sum of these two items is plotted in Figure 81. Note that no large reduction is seen from the 

substitution of natural gas. Part of this is explained by timing. Two additional family members 

were added very soon after this change with known increases to clothes washing (uses more hot 

water), clothes drying, as well as cooking. Thus, source energy consumption rose from 1993 to 

1999 after remodeling that added 50% more conditioned floor area as well as a second 

refrigerator. From 2000 to 2006, consumption remained relatively stable, but with a drop seen 

from the addition of energy feedback and an instantaneous gas water heater. Much larger 

reductions are seen recently as the PV system was added, as well as better windows and wall 

insulation that have allowed most space heating to be accomplished with a single central minisplit heat pump.
75

Figure 81. Changes in source energy use over the 22-year period of home occupancy. Green 

triangles are the 12-month moving averages. Source energy use has dropped by about 90% over 

the period.

16.4 Net Energy Use Since Installation of Photovoltaic System

In 2009, the 4.1-kW PV system produced 6,052 kWh in 11 months (approximately 18 kWh/day), 

which was 98% of household electricity consumption. Net electricity use in the year was 112 

kWh. Annual natural gas use in 2009 was 155 therms for heating, hot water, cooking, and clothes 

dryer, but true zero energy remained the primary target. Total source energy use in 2009 was 

17.1 MBtu. Figure 82 shows recent data about how the PV power production profile compares 

with the house electricity demand from November 2010 through May 2011.
76

Figure 82. Total house power (W in red) against total PV output from inverter (November 2010–

May 2011). House power averages 14.5 kWh/day; PV output averages 19.8 kWh/day.

In 2010, the output of the 4.92 kW system totaled 7,415 kWh (20.3 kWh/day), which was 190 

kWh more than the house used (7,225 kWh). Summer 2010 featured considerably greater A/C

than the previous year from an aging air conditioner. Also, natural gas use increased to 205 

therms during 2010—stemming from a much colder January and February with considerable 

space heating before installing the insulation. Total source energy use in 2010 was 20.7 MBtu. 

This compares to about 230 MBtu (20,000 kWh) for a house of the same vintage with a pool in 

Florida.

Given the large drop seen in natural gas consumption in winter 2011 with the improved windows 

and wall insulation and the use of the mini-split for heating, the natural gas consumption in the 

preceding 12 months has been cut to only 107 therms versus 205 therms in the year before. 

Reaching zero net source energy will require further reductions in summer A/C, which we hope 

to demonstrate this summer with the better wall insulation, windows, and a high-efficiency minisplit air conditioner. A net annual sell back to the utility of approximately 1000 kWh of PV 

energy will reach zero net source energy at the current annual gas consumption level of 

approximately 100 therms/year.

16.4.1 Data Sharing Website

Since the installation of the detailed monitoring system in November, the 15-minute data 

acquired are shared on the Infomonitors.com website: www.infomonitors.com/dpr.

A summary of the data on the Infomonitors site from November 15, 2010 to May 15, 2011 is 

shown in Figure 83. Note that during this period, the house produced 907 KWh more than it 

used.
77

Figure 83. Six-month data summary
78

17 Challenges to Efficiency and Future Retrofits

Existing homes present special challenges to achieving zero net energy relative to new structures, 

because certain features are difficult to alter. For instance, the case study home had a 10-SEER 

A/C with a standard blower that operates more like 8-SEER because of its age and difficulty 

achieving proper airflow. It also has a sealed duct system that is still located in the attic, leading 

to conductive losses in both heating and cooling modes. The installed mini-split allows existing 

homes to cut duct-related losses and engage in zoning of the house. The old central system will 

later be replaced with a higher efficiency unit that will then be run in a series of A/B flip-flop 

tests with the centrally located mini-split.

Other appliances that continue to waste energy:

• The home entertainment center has a DVR that draws 25 W and cannot be turned off 

without defeating the programmable recording capability. This remains a nonaddressable 

electrical load that is responsible for approximately 220 kWh/year in consumption as well 

as waste heat released to the interior.

• A clothes dryer that, while modern, has low efficiency. 

17.1 Initial Comments About Retrofit Process, Cost Effectiveness, and 

Repeatability

It must be pointed out that within the overall project, the retrofits were not done in an optimal 

order or even with optimal selection based on some economic criteria. Often the improvements 

were made as a way for the author to learn what kind of difference the installed measure might 

make, even at the risk of unknown performance. Measures were installed based on convenience, 

available funds, or the breakdown of conventional equipment. Thus, the retrofit process was 

inherently arbitrary and not necessarily cost effective.

It must be said, however, that the overall process has provided a number of lessons learned and 

has provided information to bracket energy savings and measure costs. Although up until now, 

there has not been an attempt to establish the specific savings of the various measures installed, 

we intend to explore this in the final report. This process will be one of considerable uncertainty, 

however, as the point at which improvements are most efficient can have a large impact on the 

achieved savings. 

Similarly, replacing components on burnout (replacement) can have considerably differing 

economics. Thus, we may depend on simulation analysis to help with this evaluation, which will 

also be necessarily approximate.

17.2 Opportunity for Addressing Refrigeration in Florida Homes

Based on FSEC’s monitoring experience, replacement of older, inefficient refrigerators may 

offer a significant savings potential in existing Florida homes. Approximately 20% of Florida 

homes have second refrigerators. The monitored garage unit in the studied house will use an 

estimated 1,500 kW annually (over 25% of the total annual consumption in the studied house). 

Moreover, given the monitored performance of the refrigerator in 1992 and then again in 2011,

degradation of performance of even efficient refrigerators can be expected.
79

Two experiments found that cleaning of refrigerator coils was associated with about a 10% 

reduction in refrigerator energy. Although this maintenance did not account for the observed 

degradation in performance, it did agree closely with previous field experiments showing similar 

improvements to performance. This suggests routine cleaning of refrigerator coils every two 

years could produce measureable improvements to performance. One practical adoption would 

see future refrigerator models include an indicator lamp indicating the need for coil cleaning 

after a compressor runtime of approximately 5000 hours.
80

18 Conclusions

When the author moved into a 1958-vintage home in 1989, the structure was grossly inefficient, 

lacking basic ceiling insulation. Statistics show that with a family of four in a home built before 

1960 with a pool, the average electricity use in Florida is about 20,000 kWh/year (Parker, 2002). 

Using a combination of operational strategies, appliance, and envelope improvements, it has 

been transformed from an average dwelling to a very near zero energy home (Figure 81). Figure 

84 shows the home as it appears today. Its net use of electricity has been less than zero for the 

last 12 months. Moreover, natural gas consumption has dropped sharply from thermally 

improved windows, added wall insulation, and the use of a mini-split heat pump for heating.

Figure 84. Home as it appears today from the northern exposure

This evaluation is an interim report, as the detailed monitoring has been continuous for only 

about six months. The house will be monitored for A/C loads this summer. Monitoring over the 

full cooling season will emphasize obtaining more data about performance after the wall 

insulation and addition of the mini-split. This will also allow examination of the persistence of 

the savings from the various improvements. Data collection through November 2011 will allow 

evaluation of one full year of performance with the various improvements.

The existing garage and new kitchen refrigerator will be monitored through January 2012, 

providing a full year of data about this existing model. At the end of the time period the unit in 

the garage will be changed out to the most efficient model within the same size class. The new 

refrigerator will then be monitored over the following year. If cooling loads and the second

refrigerator electricity use are sufficiently reduced in summer, we may eventually use excess 

solar electric power production to charge a plug-in hybrid automobile. 

In summary, based on the experiences in this single case study, zero energy existing homes 

appear feasible in Florida. Moreover, the fact this has been accomplished in one home indicates 

that many thousands of homes could achieve similar results with appropriate will and resources.
81

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DOE/GO-102012-3487 ▪ February 2012

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 10% post-consumer waste.