Comfort to the Ninth Degree
Advancing Retrofits in Georgia
As part of a road map to foster the implementation of deeper energy retrofits, DOE’s Building America program has set research goals to develop and demonstrate market-ready retrofit solutions to reduce home source energy use by 30–50%. To this end, DOE is funding research to explore what it takes to generate deep energy savings. Topics being researched are 1) the measures needed to achieve large energy savings; 2) the total cost of these measures; 3) the difference between predicted energy savings and actual energy savings; and 4) the beyond-energy benefits of home energy retrofits. The results of this research will help home performance contractors to advance residential retrofits in the United States.
Pre- and Postretrofit HERS Indices
Table 1. Primary Energy Upgrades Performed in Nine Homes*
Table 2. Heating Season Utility Bill Summary
Table 3. HVAC Consumption and Run Time
Heating Season Energy Savings
Nine homes were retrofitted in the Atlanta, Georgia, area. The retrofits were performed by a variety of contractors, most of whom were participating in both the Southface Home Performance with Energy Star program and the Georgia Power EarthCents Home Energy Improvement Program. This article presents an overview of the retrofits for each home, and the impact of these retrofits on important home performance metrics, such as air infiltration and duct leakage. In addition, a case study on one of the homes presents the expected and realized energy savings of completed retrofit measures.
Summaries of Retrofit Measures
All nine homes in the study are single-family detached structures. Table 1 provides an overview of the primary retrofit measures, predicted source energy savings, and total retrofit costs for each home. Measures in these homes were projected to generate average site and source energy savings of approximately 45% and 33%, respectively. The "North Carolina" home is discussed in further detail, with an analysis of comfort and space-conditioning energy use. Figure 1 shows the pre- and postretrofit estimated HERS indices for all nine homes. The average initial and final HERS indices are 161 and 95, respectively.
Please note that we gave each of the homes a nickname to ensure anonymity of the homeowners.
“There have been no more squirrels in the attic and fewer bugs around the house. The dust doesn’t settle as often”.
Home 1: “Yellow Jackets”
Estimated source energy savings = 18%; total retrofit cost = $27,720.
Built in the 1970s, Yellow Jackets is a two-story home with 3,170 square feet of living area; it is occupied by three adults. Key retrofit measures included HVAC upgrades and conversion of the attic to an unvented space by insulating the roof deck with R-21 open-cell spray foam. The crews also applied open-cell spray foam to the garage ceiling and the exposed knee walls to both insulate and air seal them. Open-cell foam was applied to the wall separating the garage and the living area to replace the R-11 batts. In addition, the foundation band joist was sealed and insulated with about 3 inches of open-cell foam. Through these measures, the building air infiltration was reduced from 14.7 to 5.4 ACH50.
Crews replaced the existing HVAC system in the attic (10 SEER air conditioner) with a 14 SEER air conditioner and a 95 AFUE gas furnace. Because the attic was converted to an unvented, insulated space, the new HVAC system was now located within the conditioned space of the home. The gas water heater, with an efficiency rating of 0.57 energy factor (EF), was also replaced with a high-efficiency gas water heater with a 90% thermal efficiency. Energy savings of 20% were achieved during the heating season based on weather-corrected energy bill analysis.
“The smell of bacon lingers longer when we cook now. That’s not a bad thing.”
Home 2: “Michigan”
Estimated source energy savings = 27%; total retrofit cost = $27,950.
Built in the 1920s, Michigan is a one-story home with 3,380 square feet of living area, a vented attic, and a vented crawl space. It is occupied by two adults and one child. Open-cell foam was used to seal the gap at the intersection between the attic floor and the top of the balloon-framed wall. Approximately 4 inches of open-cell foam was also sprayed in the knee walls to replace R-13 fiberglass batts. The R-value of the attic floor insulation was increased from R-18 to R-38 with blown-in fiberglass. In addition, about 3 inches of open-cell spray foam was applied on the crawl space band. The subfloor was already insulated with R-19 fiberglass batts. Through these measures, the building air infiltration was reduced from 14.8 to 11.5 ACH50. HVAC improvements included replacing the 9 SEER and 10 SEER air conditioners for the main and master suite zones, respectively, with two 14.5 SEER systems. A 95 AFUE gas furnace replaced the 80 AFUE unit that initially heated the main zone. Energy savings of 27% were achieved during the heating season based on energy bill analysis.
Home 3: “Two Cities”
Estimated source energy savings = 30%; total retrofit cost = $10,620.
Two Cities is a 1940s single-story home with 1,110 square feet of living area, a vented attic, and a vented crawl space foundation. It is occupied by one adult. The initially uninsulated crawl space ceiling was insulated with 3 inches of medium-density, open-cell spray foam. Other air-sealing measures included installing a damper in the chimney, identifying and sealing major air infiltration bypasses, and applying one-part spray foam along the top and bottom wall plates. A drill-and-fill technique was used to dense pack R-13 cellulose insulation into the previously uninsulated wall cavities. Two single-pane windows with a total area of 55 square feet were replaced with double-pane Energy Star windows, while a third single-pane 7 ft2 window was removed and replaced with wall framing. Through these measures, the building air infiltration was reduced from 24.9 to 10.4 ACH50.
A programmable thermostat was installed; and the clothes washer and dryer, ceiling fans, dishwasher, refrigerator, and lighting were all replaced with Energy Star units.
Home 4: “Lakeview”
Estimated source energy savings = 31%; total retrofit cost = $17,520.
Built in 1985, Lakeview is a two-story home with 1,710 square feet of living area, a vented attic, and a slab foundation; it is occupied by two adults and one child. The main envelope measure taken in this home was to convert the attic to an unvented space, with the roof deck insulated with R-21 open-cell spray foam. This measure reduced the building air infiltration from 11.7 to 10.1 ACH50.
A variable-capacity inverter-driven heat pump with an efficiency rating of 18 SEER and 8.9 heating seasonal performance factor (HSPF) replaced the original 12 SEER air conditioner and 80 AFUE gas furnace. A pressurized glycol solar-thermal hot-water system consisting of two 8-foot x 4-foot flat panels was also installed on the garage roof.
Home 5: “Eagle”
Estimated source energy savings = 32%; total retrofit cost = $20,885.
Built in 1955, Eagle is a one-story home with 1,318 square feet of living area; it is occupied by two adults. The energy retrofits were completed in conjunction with a planned renovation that increased the conditioned floor area of the home; this new space was insulated in the walls and ceiling with spray foam. The energy-related retrofits applied to the original living space included increasing the attic floor insulation from R-11 to R-38 with blown-in cellulose. Penetrations through the crawl space ceiling were air sealed, and 3 inches of closed-cell foam was applied to the foundation band. A drill-and-fill technique was used to dense pack R-13 cellulose insulation into the previously uninsulated wall cavities.
The original HVAC system, consisting of a 2.5-ton air conditioner, and a 9 SEER air conditioner/ 76 AFUE gas furnace was located in the attic. Duct leakage in the attic was 266 CFM25. This HVAC system was replaced with a 2-ton 18 SEER, 9.5 HSPF heat pump and relocated to the sealed crawl space. Energy savings of 43% were achieved during the heating season based on energy bill analysis.
Home 6: “Virginia”
Estimated source energy savings = 34%; total retrofit cost = $37,700.
Built in the 1920s, Virginia is a two-story home with 2,940 square feet of living area, a vented attic, and a vented crawl space. It is occupied by two adults and two children. Additional fiberglass insulation was blown over the existing R-11 insulation in the attic floor to increase it to R-38. Approximately 4 inches of open-cell foam was applied in the knee walls to replace the existing R-13 fiberglass batts. Penetrations through the crawl space ceiling were air sealed, and 3 inches of open-cell spray foam was applied on the crawl space band. The subfloor was already insulated with R-19 fiberglass batts. Through these measures, the building air infiltration was reduced from 14 to 8 ACH50.
The original HVAC system consisted of a 56 AFUE gas furnace, a 9 SEER air conditioner, and three window units. Whereas this HVAC system supplied conditioned air to both floors, retrofit measures included rezoning the home in such a way that the new HVAC system, consisting of a 14.5 SEER air conditioner and a 95 AFUE gas furnace, conditioned only the first floor of the home. The window A/C units in the second-floor bedrooms were replaced with a 3-ton 19.2 SEER, 10 HSPF mini-split heat pump. Energy savings of 33% were achieved during the heating season based on energy bill analysis.
Home 7: “New York”
Estimated source energy savings = 42%; total retrofit cost = $41,669.
Built in the 1920s, New York is a two-story home with 3,050 square feet of living area, a vented attic, and a vented crawl space; it is occupied by two adults and three children. The crawl space was insulated with 3 inches of open-cell foam on the band and 4 inches of closed-cell foam on the wall. The attic was enclosed with 6 inches of open-cell foam applied on the roof deck and gables. Blown fiberglass was dense packed into the exterior walls. Through these measures, the building air infiltration was reduced from 17 to 8.7 ACH50.
A 14.5 SEER air conditioner and a 95 AFUE gas furnace replaced the 10 SEER and 80 AFUE units in the attic. A 14.5 SEER air conditioner was installed in the crawl space to replace the 10 SEER unit that served the first floor. Because the attic and crawl space were encapsulated during the retrofit, both HVAC systems are now located within the thermal envelope. In addition to the ducted system upgrades, a 19.2 SEER, 10.1 HSPF mini-split heat pump was installed in the home office to replace a through-the-wall room air conditioner and a Thermador space heater. The 0.59 EF gas water heater was replaced with a 2.4 EF heat pump unit. Energy savings of 36% were achieved during the heating season based on energy bill analysis.
Home 8: “South Carolina”
Estimated source energy savings = 45%; total retrofit cost = $38,380.
South Carolina is a 1920s single-story home with 2,990 square feet of living area and a typical occupancy of four or five college students. The home has a traditional vented attic and crawl space. The vented attic was sealed by insulating the roof deck with open-cell foam. The subfloor was already insulated with R-19 fiberglass batts. The final building air infiltration was 16.8 ACH50. While this is a 28% reduction from the original 23.3 ACH50, the home remained relatively leaky after all the air-sealing measures were taken. Revisiting the home to identify more infiltration improvements was not possible due to competing constraints on the amount of time the building contractor could commit to returning to the home to conduct more investigation versus the amount of lifestyle disruption the homeowner could tolerate.
The existing 9 SEER air conditioner and 80 AFUE gas furnace (both located in the vented crawl space) were replaced with a 14.5 SEER air conditioner and a 95 AFUE furnace, which were then brought into the conditioned building envelope. In addition to the HVAC upgrade, the 0.59 EF gas water heater was replaced with a high-efficiency water heater with a 90% thermal efficiency. Energy savings of 47% were achieved during the heating season based on energy bill analysis.
“My utility bills went down drastically. The bills used to be a huge financial burden on the family. . . some of our utility bills have been as high as $700.”
Home 9: “North Carolina”
Estimated source energy savings = 37%; total retrofit cost = $35,750.
Built in the 1920s, North Carolina is a two-story home with 3,710 square feet of living area. The first floor is 2,410 square feet and the second floor is 1,300 square feet. See Figure 2. The house has a vented attic, and a vented crawl space. It is occupied by two adults and three children.
During the initial survey, the family told the contractor that their primary concern was their very high energy bills. From February 2010 to January 2011, these bills totaled $6,380, representing 296 MMBtu of site energy. The second floor was so cold in winter that the family had to use space heaters to keep warm. In summer, the temperature on the second floor rarely reached the targeted set point and often did not go below 80°F.
During the summer of 2011, temperature and humidity data were collected on the first and second floors before any retrofit work was done. From May 20 through July 9, the temperature on the first floor varied from approximately 70°F to 76°F. We also noticed that on the first floor there were considerable periods when the relative humidity (RH) exceeded 60%. An RH over 60% will make the house uncomfortably warm. Furthermore, the RH often approached 75%, which, when considered in conjunction with temperature, approaches or exceeds the recommended humidity ratio for thermal comfort, per ASHRAE 2004.
The second-floor temperatures were consistent with the family’s observation. Temperatures were typically above 80°F from afternoon until at least midnight. In addition, there were periods when the RH exceeded 70% and the dew point was 68°F or higher. Temperatures at the supply registers were probably below the dew point, given that auditors found condensation and mildew at those locations.
In light of these findings, the high energy costs and discomfort were not surprising. In the graphic of the building envelope shown in Figure 2, the dark-blue sections represent the attic knee walls, which comprised approximately 60% of the exterior walls on the second floor. Significant heat exchange occurred between the second floor and the attic because the knee walls were mostly uninsulated. Heat was also exchanged between these two spaces through many bypasses, some of which are shown in Figure 3. The attic access door shown in Figure 3 was neither insulated nor weather-stripped, and there was no mechanism to keep it closed.
Space conditioning was provided in North Carolina by two forced-air HVAC systems. The first floor had a 3.5 ton 9 SEER air conditioner and a 125 kBtu/h 91 AFUE gas furnace in the crawl space. The second floor conditioning system consisted of a 2.5 ton 9 SEER air conditioner, and a 50 kBtu/h 91 AFUE gas furnace in the attic.
Leakage tests were conducted to evaluate the airtightness of the building envelope and the ductwork. The blower door tests indicated that the house leakage rate was 12,690 CFM50 (20.6 ACH50). The ducts for the first-floor HVAC system, which were located in the crawl space, were insulated to R-6. These ducts had several disconnected joints that kept them from being adequately pressurized. The second-floor ducts were located in the attic and had a leakage of 280 CFM25, about 22% leakage by serviced floor area.
Air sealing and attic insulation took priority for this home. Insulation subcontractors sealed electrical penetrations, can lights, and other penetrations to reduce airflow between the attic and the living space. Blown-in fiberglass insulation was subsequently added to the attic floor for a final approximate R-value of 38. A low-density, open-cell spray foam was applied to the knee walls to align the envelope’s thermal and air barriers. Cavities under the knee walls were blocked and air sealed. In addition, the crawl space was encapsulated. The crews expect that this will reduce infiltration, improve moisture management, and enhance HVAC performance, since the system will now be in a semiconditioned space. After the retrofit was complete, a blower door test indicated a 39% decrease in air leakage, from 12,690 CFM50 (20.6 ACH50) to 7,688 CFM50 (12.8 ACH50).
Load calculations were completed in accordance with ACCA Manual J, based on the expected improvements from envelope measures. Although the second-floor zone benefited from most of the load reduction, the tonnage of the new 16 SEER air conditioner remained at 2.5 because the original unit was undersized. The load calculation for the first floor suggested that a larger-capacity system would be needed to meet the resulting postretrofit load. Therefore, the old system was replaced with a 4-ton 16 SEER system. In addition, R-8 insulated flex duct was installed throughout the house, which led to duct leakages of 103 CFM50 for the first-floor system and 43 CFM50 for the second-floor system. Finally, the original 0.59 EF gas water heater was replaced with a 50-gallon 2.0 EF heat pump water heater. The total cost of all retrofit measures was approximately $35,750.
Overall, there is an estimated 37% reduction in source energy use from the retrofit work performed.
Significant air-sealing and thermal insulation measures were taken on the knee walls and attic accesses to result in predicted source energy savings of 18%. Furthermore, because of the significant amount of duct leakage in the preretrofit case, coupled with the poor efficiency of the A/C unit, source energy savings of 20% are projected based on improvements in the HVAC system.
Bills for November 2011 through February 2012 can be compared with the previous year’s bills to gain insight into the actual energy savings during the heating season. As shown in Table 2, there was a 46% reduction in gas consumption after the retrofit. Since the heating season period after the retrofit was considerably milder than the same period during the previous year, postretrofit gas consumption has been weather corrected. Also, approximately 130 therms of the reduction in gas use was estimated to be the result of replacing the gas water heater with an electric heat pump water heater. After adjusting for both factors, we estimated a 38% reduction in gas consumption associated with space heating. A total (gas and electric) source energy savings of 21% was calculated for North Carolina for the heating season.
Utility bills for the cooling season (June–August) after the retrofit are not available for analysis as of this writing. However, because an energy monitor was installed in the home before the retrofit began, submetered energy data are available for pre- and postretrofit analysis. Table 3 summarizes the average daily HVAC consumption and run time before and after retrofit measures were in place; outdoor temperatures were similar during the two periods. Envelope improvements coupled with air conditioner upgrades achieved reductions in HVAC consumption for the first- and second-floor systems of 66% and 71%, respectively. Furthermore, the total HVAC run time (a reflection of the ratio of thermal load to HVAC capacity) was reduced by more than half with only a 0.5-ton increase in total HVAC capacity.
Temperature and RH measurements were collected after the retrofit. In contrast with the preretrofit conditions, there are no significant periods of time when the temperature on the first or second floor exceeds 75°F. The RH on the first and the second floors is considerably lower. Also, there were very few hours when the RH on both floors was higher than 60%. These data clearly indicate that energy retrofits can both decrease energy use and improve comfort.
While source energy savings are an important metric for evaluating home energy retrofits, the improvement in comfort may be of equal benefit to the homeowner. It is noteworthy that an investment of $35,750 is expected to generate an average of $2,400 in annual energy savings. However, the fact that this investment also gave the homeowners an entire 1,300 square feet of second-floor living area—an area that they had previously used only sparingly and reluctantly—is remarkable.
This article was adapted from Jackson, R.K., et al. Advancing Residential Retrofits in Atlanta, ORNL-TM488. Oak Ridge, Tennessee: Oak Ridge National Laboratory, 2012.
This report was sponsored by the American Council for an Energy-Efficient Economy.
ASHRAE Standard 55-2004, “Thermal Environmental Conditions for Human Occupancy.” Atlanta, Georgia: ASHRAE, 2004.
Rutkowski, H. Manual J: Residential Load Calculation, 8th ed. Arlington, Virginia: ACCA, 2006.
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Summary & Recommendations
Seven of the nine homes that were retrofitted in the metropolitan Atlanta region are predicted to achieve source energy savings of at least 30% based on simulated energy consumption. Actual heating season source energy savings are higher than 33% for four of the seven homes for which preretrofit energy bill data are available (see Figure 4).
While the predicted energy savings of these homes are significant, the beyond-energy benefits of the retrofits may be of equal or more importance to homeowners. On multiple occasions, the retrofit resulted in a substantial improvement in home comfort, health, and safety. In one home, a room was converted into a comfortable living space. Here the homeowner felt he got a “good value” even though the energy cost savings were small when compared to the retrofit costs. However, the added comfort of the home (particularly that room), more than compensated. While in another home a whole floor was made comfortable and healthier. Here the occupant used words like “cozy” and “comfortable” to describe the home after the retrofit.
Finally, in a third home the retrofit changed the occupant’s reality of what was possible in his home. He thought the combination of the house size and age meant that he would be stuck with an uncomfortable and energy-inefficient home. Before the retrofit, he and his family would sacrifice their comfort to decrease energy bills. Now they’re comfortable. “Living in Atlanta and not being muggy is brand new,” said the occupant after the retrofit.
Home performance professionals need to understand and articulate these non-energy benefits if the industry hopes to advance residential retrofits across the United States. All of these homes prove that in order to sell building science, livability can be as strong a selling point as energy savings.
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