LIFE CYCLE ANALYSIS OF A RESIDENTIAL HOME IN MICHIGAN



3.0 RESULTS

3.1 Life Cycle Mass

The total life cycle mass of all construction and maintenance/improvement materials of SH, consumed during its assumed 50-year life-time, was determined to be 305.9 metric tons. Figure 3-1 shows the 10 SH materials with the largest life cycle mass contributions (the materials shown represent 89.4% of SH mass over 50 years).


FIGURE 3-1 Mass Distribution SH, top-ten materials, total life cycle (incl. all building materials and appliances, new and replacements)



FIGURE 3-2 Mass Distribution EEH, top-ten materials, total life cycle (incl. all building materials and appliances, new and replacements)

The total life cycle mass of all construction and maintenance/improvement materials of EEH, consumed during its assumed 50-year life-time, was determined to be 325.6 metric tons.. Figure 3-2 shows the 10 EEH materials with the largest life cycle mass contributions (the materials shown represent 92.4% of EEH mass over 50 years). EEH is more massive because the additional weight of gravel and lumber exceed the weight of deleted concrete. Figure 3-3 shows the weight of the top-10 materials for SH that are used in the initial construction of the home. The total weight of SH after construction is 277.4 metric tons, while the weight of all maintenance and improvement materials in SH is 28.3 metric tons.


FIGURE 3-3 Mass Distribution SH, top-ten materials, year 0 (incl. all building materials & appl.)

FIGURE 3-4 SH/EEH Mass Comparison by System, total life cycle (incl. all building and appliances, new and replacements)

Figure 3-4 shows the SH and EEH life cycle materials by home system as defined in 2.6. Figures 3-5 and 3-6 provide a percentage breakdown of all materials in both SH and EEH. Four basic material types were identified: minerals (e.g., gravel, gypsum, limestone), metals, petroleum based (e.g., plastics, solvents), and timber. Minerals include all materials extracted from the earth that are used without excessive processing including gravel, gypsum and concrete. Petrochemicals include all plastics, solvents and adhesives.


FIGURE 3-5 SH Mass Breakdown by Material Groups, total life cycle (incl. all building materials and appliances, new and replacements)


FIGURE 3-6 EEH Mass Breakdown by Material Groups, total life cycle (incl. all building materials and appliances)





3.2 Life Cycle Energy Consumption

The total life cycle energy consumption of SH is 15,455 GJ (equal to 2,525 barrels of crude oil). This takes into account the embodied energy of all construction and maintenance/improvement materials, all use phase energy, as well as demolition and transportation energy. SH raw material extraction/production and construction (pre-use phase) energy is 942 GJ or 6.1% of total life cycle energy use, while its use phase energy is 14,482 GJ (93.7%), and its end-of-life phase energy amounts to 31 MJ (0.2%).

The total life cycle energy of EEH in contrast is 5,653 GJ (equal to 927 barrels of oil). Raw material extraction/production and construction (pre-use) phase energy is 905 GJ (16.0%), use phase energy is 4,714 GJ (83.4%) and end-of-life phase energy is 34 GJ (0.6%). EEH life cycle energy consumption is 9,802 GJ less than the SH, which is a reduction of 63% (or 1,598 barrels of oil). Figure 3-7 graphically illustrates the percentage of pre-use, use, and end-of-life phase energy in both SH and EEH.


FIGURE 3-7 SH and EEH Primary Energy, total life cycle (incl. all building materials, appliances, and utility energy consumption)

SH energy consumption due to heating, cooling, and electricity consumption contributed 95.8% (13,877 GJ) to the use-phase number. The remaining 4.2% (605 GJ) came from replacement and home improvement materials. The same break-down for EEH on the other hand shows that 89% (4,195 GJ) of the use-phase primary energy is also consumed as natural gas and electricity, while 11% (519 GJ) went into replacement and home improvement materials.

Figures 3-8 and 3-9 show the total life cycle primary energy of the 15 most energy intensive materials in SH and EEH, respectively. In both houses, PA (polyamid) as a main constituent of carpet, consumes the most energy. This is a result of the high embodied energy of PA, the large amount of carpet used, and the fact that the carpet has a high replacement rate (every eight years). Alternative flooring materials with lower embodied energy were explored.

Cork tiling and parquet wood flooring do have lower embodied energy, and also have other aesthetic properties. The higher cost of these alternatives led to their being disqualified however. The initial installation cost of a cork floor covering , replacing all carpet and tiles on the first and second floors would be 2.4 higher than that for carpet. However, over the full life cycle of the house, cork would be approximately 10% less expensive, using established cost estimation data [73]. This is because with proper care (sanding and application of two layers of lacquer every 10 years), it does not need to be replaced over the 50 year life of the home [74]. Another alternative to carpet is tongue-and-groove wood flooring. This option was not investigated.


FIGURE 3-8 SH Primary Energy Consumption of top 15 materials, total life cycle (incl. all building materials and appliances)

Redesign of the EEH foundation has reduced concrete life cycle energy consumption by nearly half, and has more than doubled gravel life cycle energy. As a result of the EEH roof redesign, asphalt has been eliminated altogether, and its replacement (plastic/wood composite) is not even in the list of the 15 most energy intensive materials.


FIGURE 3-9 EEH Primary Energy Consumption of top 15 materials, total life cycle (incl. all building materials, and appliances)

Figure 3-10 shows annual natural gas use for both SH and EEH. The dramatic decrease in natural gas consumption is due to the greatly improved thermal envelope, a much more efficient HVAC system, causing a decrease in heating natural gas consumption of 91.8%, and a hot water heat recovery unit (providing a decrease of 40%). While EEH uses natural gas for the stove and dryer (which is not the case for SH), EEH total annual natural gas use is only 21% that of SH.


FIGURE 3-10 SH/EEH Annual Natural Gas Energy Use

Annual electricity use for both, SH and EEH is shown in Figure 3-11. EEH electricity use for cooling is approximately half of that for SH, again due to an improved thermal envelope, and a much more efficient HVAC system. SH uses electricity for the stove and dryer. EEH electricity use for other appliances is also almost half due to more efficient lights and appliances. EEH annual electricity use is reduced to only 58% that of SH.


FIGURE 3-11 SH/EEH Annual Electrical Energy Use

Energy-10 determined that the annual heating energy requirement of SH was 120 MJ based on a value of 46.4 kBtu/ft2. This value was compared to the average 1993 heating energy for Midwest homes (average size 1,880ft2) of 97 MJ [75]. Normalized for SH floor area, this is equal to 127 MJ which is within 6% of the calculated SH annual heating energy.

Figure 3-12 provides life cycle energy of all systems (including embodied energy of construction and maintenance/improvement materials) for both SH and EEH. For both houses, floors and foundation/basement are the two highest energy consumers with walls being the third highest. The SH roof is the fourth largest energy user.


FIGURE 3-12 SH/EEH Life Cycle Energy Comparison by System (incl. only building materials and appliances, not utility energy consumption)



3.3 Life Cycle Global Warming Potential

The total global warming potential for SH (see Figure 3-13) was determined to be 1,013 metric tons of CO2 equivalent. This includes all GWP gases emitted to the atmosphere during:

-extraction and processing of raw materials
-manufacturing and assembly of construction components and finished goods
-transportation of all materials in the pre-use phase (rail and truck)
-construction of the home
-use phase (home heating and power plant emissions generating electricity for the home)
-end-of-life demolition
-disposal transportation to landfill/recycling centers


The total global warming potential for EEH on the other hand was determined to be only 374 metric tons of CO2 equivalent. The design changes therefore brought about a reduction of 639 metric tons of GWP gases over the 50 years period. This is a 63% reduction.

FIGURE 3-13 SH/EEH Life Cycle GWP (incl. all building materials, appliances, and utility energy consumption)

Figures 3-14 and 3-15 show life cycle GWP emissions of the fifteen materials contributing the largest quantities of GWP gases in SH and EEH.


FIGURE 3-14 SH Global Warming Potential of the top-15 materials, Total Life Cycle (incl. all building materials, and appliances)


FIGURE 3-15 EEH Global Warming Potential of the top-15 materials, Total Life Cycle (incl. all building materials, and appliances)

Figure 3-16 compares life cycle GWP for construction and maintenance/improvement materials for the eight systems in SH and EEH (use-phase-utility related GWP not included). EEH walls produce more life-cycle GWP because of the additional wood in the thicker wall. Pre-use phase GWP for EEH is 2,014 kg less than SH.


FIGURE 3-16 SH/EEH Life Cycle GWP by System (only for construction/maintenance materials, and appliances; no utilities)



3.4 Life Cycle Cost Analysis

3.4.1 Description of Scenarios

As explained in Section 2.8, four energy cost escalation scenarios were established to determine how both, discounted present value cost and un-discounted cumulative life cycle cost vary with changes in future energy prices. Following are more complete descriptions of the various scenarios:

Scenario 1 Constant Energy Costs

To provide a baseline for the other energy cost comparisons, scenario 1 was run with rates for the natural gas, and grid-supplied electricity remaining at 1998 levels for 50 years.

Scenario 2 DOE Projection [76] (falling energy costs)

The DOE projection foresees falling energy costs of utility-supplied natural gas and electricity due to the increased efficiency of new power plants built to replace aging lower efficiency power plants, and due to utility deregulation. Natural gas prices fall 1.1% annually between 1998 and 2010, and thereafter rise 0.03% annually between 2010 and 2020. It was assumed that prices stabilize between 2021 and 2048. Electricity prices fall 1% annually between 1998 and 2010, and thereafter decline only 0.48% annually between 2011 and 2020. It was assumed that prices stabilize between 2021 and 2048.

Scenario 3 Wefa Projections for Global Warming [77] (Rising Energy Costs)

Wefa Inc., a Pennsylvania-based consulting firm, performed a study to determine the impact of global warming legislation on US utility rates. The study assumes rapidly escalating energy prices as a result of US energy policies to meet the CO2 reduction targets outlined in the Kyoto Agreement. The projection assumes both natural gas and electricity costs rise 4.2% annually between 1998 and 2010. It is assumed that energy costs escalate 1% annually thereafter until 2048.

Scenario 4 Current German Energy Costs

To provide a broader perspective on the impact of higher utility costs, a fourth scenario was run using 1998 energy rates in Germany. Utility-supplied energy in the City of Dresden costs $0.127/kWh and $0.721/therm for electricity and natural gas respectively [78]. Both of these values are approximately 59% higher than US energy prices. The scenario assumes energy prices rise 1% annually between 1998 and 2048.

3.4.2 Summary of Present Cost Analysis

The time value of money makes investments made in the future worth less today at a given discount rate. The additional cost of EEH was determined to be $22,801 (see appendix E page 153, for a complete breakdown of differential costs between EEH and SH). To determine if this additional $22,801 spent on EEH energy efficient enhancements would be economically justifiable, the present value of both SH and EEH was calculated for comparison. Using a discount rate of 4%, the present value of each future annual total cost was determined. This determines an amount, that if set aside in 1998, at 4% compounded interest, would be sufficient to meet all future costs. This provides a means of comparing the two options as if they were investments. Table 3-1a below summarizes the present value of SH and EEH for the four utility escalation scenarios. For comparison, the same calculation was performed using a 10% discount rate (see Table 3-1b).

TABLE 3-1a Present Value LC Cost for Various Utility Escalation Scenarios (4% discount rate)

Scenario
SH present value
EEH present value
Present Value Difference between SH and EEH
1
$426,697
$434,122
($7,425)
2
$423,544
$433,063
($9,519)
3
$445,842
$440,408
$5,434
4
$454,343
$443,200
$11,143





TABLE 3-1b Present Value LC Cost for Various Utility Escalation Scenarios (10% discount rate)

Scenario
SH present value
EEH present value
Present Value Difference between SH and EEH
1
$231,561
$237,458
($5,898)
2
$230,506
$237,114
($6,608)
3
$237,272
$239,309
($2,037)
4
$242,316
$240,943
$1,373

Tables 3-1a and 3-1b indicate that the higher initial cost of $22,801 for EEH energy efficient enhancements do not pay for themselves (from a present value perspective) at falling or constant energy prices during the next 50 years. At escalating energy prices (Wefa-scenario) EEH is marginally better at a 4% discount rate and, worse at 10% discount rate. If the US adopted German energy prices that continued to escalate, EEH would be a marginally better investment.


3.4.3 Accumulated (un-discounted) Life Cycle Costs

Life cycle costs in this study consists of accumulated mortgage, natural gas, electricity and maintenance/improvement costs over the assumed 50 year life of the home. The accumulated, un-discounted summation of these costs are presented in Figures 3-17 through 3-20 based on the energy-price escalation scenarios. Tables 3-2 through 3-5 summarize the major components of life cycle cost for each scenario. The linear portion of each curve (year 1 through 30) indicates constant annual costs. The slope change after year 30 represents completion of mortgage payments. Abrupt slope changes throughout the curves represent home maintenance and improvement payments with large expenditures at years 25 and 40.

Scenarios 1 and 2 are relatively close, indicating that constant and falling energy rates affect life cycle cost comparisons between EEH and SH little. Scenarios 3 and 4 are also relatively similar, indicating that the Wefa energy cost projection would bring US energy costs more in line with those in Germany or Europe in general.


FIGURE 3-17 Life Cycle Costs Using Utility Escalation Scenario 1

The accumulated life cycle costs of scenario 1 are higher in EEH up until year 48, and are $1,054 (or 0.1%) less at year 50.

TABLE 3-2 Life Cycle Cost Elements for Utility Escalation Scenario 1

LIFE CYCLE COST ELEMENT
SH
EEH
Amount
Percent
Amount
Percent
MORTGAGE COSTS
$546,314
68.3%
$598,216
74.8%
NATURAL GAS COSTS
$32,699
4.1%
$7,029
0.9%
ELECTRICITY COSTS
$40,521
5.1%
$17,014
2.1%
MAINTENANCE COSTS
$180,828
22.6%
$177,049
22.2%
TOTALS
$800,361
100.0%
$799,307
100.0%








FIGURE 3-18 Life Cycle Costs Using Utility Escalation Scenario 2

The accumulated life cycle costs of scenario 2 are slightly higher in EEH throughout the assumed 50 year home life, being $4,783 higher (0.6%) than SH at year 50.

TABLE 3-3 Life Cycle Cost Elements for Utility Escalation Scenario 2

LIFE CYCLE COST ELEMENT
SH
EEH
Amount
Percent
Amount
Percent
MORTGAGE COSTS
$546,314
69.0%
$598,216
75.1%
NATURAL GAS COSTS
$29,208
3.7%
$6,279
0.8%
ELECTRICITY COSTS
$35,183
4.4%
$14,772
1.9%
MAINTENANCE COSTS
$180,828
22.8%
$177,049
22.2%
TOTALS
$791,533
100.0%
$796,316
100.0%







FIGURE 3-19 Life Cycle Costs Using Utility Escalation Scenario 3

The accumulated life cycle costs are slightly higher in EEH up until year 35, and are significantly lower thereafter, being $40,874 (or 4.8%) less than SH at year 50.

TABLE 3-4 Life Cycle Cost Elements for Utility Escalation Scenario 3

LIFE CYCLE COST ELEMENT
SH
EEH
Amount
Percent
Amount
Percent
MORTGAGE COSTS
$546,314
63.6%
$598,216
73.1%
NATURAL GAS COSTS
$59,177
6.9%
$12,721
1.6%
ELECTRICITY COSTS
$73,332
8.5%
$30,790
3.8%
MAINTENANCE COSTS
$180,828
21.0%
$177,049
21.6%
TOTALS
$859,650
100.0%
$818,776
100.0%








FIGURE 3-20 Life Cycle Costs Using Utility Escalation Scenario 4

The accumulated life cycle costs are almost equal between years 1 to 30, and diverge thereafter, with EEH being $51,761 (or 5.9%) less than SH at year 50.

TABLE 3-5 Life Cycle Cost Elements for Utility Escalation Scenario 4

LIFE CYCLE COST ELEMENT
SH
EEH
Amount
Percent
Amount
Percent
MORTGAGE COSTS
$546,314
62.4%
$598,216
72.6%
NATURAL GAS COSTS
$66,416
7.6%
$14,277
1.7%
ELECTRICITY COSTS
$82,302
9.4%
$34,557
4.2%
MAINTENANCE COSTS
$180,828
20.6%
$177,049
21.5%
TOTALS
$875,859
100.0%
$824,098
100.0%



3.4.4 Energy Efficient Mortgages

Energy efficient mortgages (EEM) are financial strategies that allow home owners to increase their housing debt-to-income ratio and total debt-to-income ratio, by two percentage points. These ratios are typically 28% and 36% respectively, and can be raised to 30% and 38% for EEM's [79]. The logic behind this is that with energy efficient measures, the home owner's combined housing related debt consisting of principle, interest, property tax and insurance (PITI) and utility costs will be equal to or less than that for a less energy efficiency home. EEM's qualify home owner's for bigger mortgages.

Table 3-6 below calculates the annual income required to secure a mortgage for both SH and EEH. Even though the EEH purchase price is $22,801 more than that for SH, because of lower annual utility rates and the two point mark-up on the home debt/income ratio, the annual income required to qualify for an EEH mortgage is $1,874 less than that required for an SH mortgage.

TABLE 3-6 Calculation of Required Annual Incomes using Energy Efficient Mortgages

Compenent
SH
EEH
Home Price
240,000
$262,801
Down Payment
36,000
$39,420
Mortgage Amount
204,000
223,381
Interest Rate (annual)
0.075
0.075
Term (Years)
30
30
Monthly Mortgage Payment
$1,417.54
$1,552
Monthly Taxes = 0.167% of property value
$400.80
$438.88
Monthly Insurance = 0.017% of property value
$40.80
$44.68
PITI (mortgage + taxes + insurance)
$1,859.14
$2,035.77
Monthly Energy Bills
$122.03
$40.07
PITI + Energy bill
$1,981.17
$2,075.84
Home debt/income ratio
0.28
0.3
Monthly Income Required
$7,075.61
$6,919.45
Annual Income Required
$84,907.31
$83,033.44




3.5 Other EEH Design Scenarios

3.5.1 Glazing Area Sensitivity

Of particular interest in the design of EEH was the total glazing area. SH glazing area is 337 ft2. EEH design for glazing looked at two alternatives; a) 337 ft2 lowE argon and b) 490 ft2 lowE argon. The 490 ft2 value was based on window-to-wall ratios recommended by Energy-10. However, Energy-10 simulations of EEH with 490 ft2 lowE argon windows resulted in an increase of 352 MJ/yr (primary energy) more than the EEH with 337 ft2 lowE argon windows. The increase in glazing area of 153 ft2 lowered heating energy requirements by 501 MJ/yr because of increased solar gain. However, this was offset by increased heat gains requiring additional cooling energy inputs of 853 MJ.

The recommended Energy-10 glazing to floor area for optimal solar gain were:

Most likely, these recommendations are for standard 2x4 stud wall construction, and may also not be applicable for areas with low insolation (solar radiation), such as Michigan's. Standard walls have R-values of between 12 and 14. EEH walls have an R-value of 35. Double glazed windows used in this study have an R-value of 2. This means that a window in a standard wall is a reduction in R-value of about 10 to 12. A window in the EEH wall would be a reduction in R-value of 33. Thus, the higher the insulative value of the wall, the less glazing is desired to reduce winter heat losses and summer heat gains.

Another likely explanation is the fact that South-East Michigan has insufficient insolation during a period when it would be most beneficial for passive solar heating.

3.5.2 HVAC and Infiltration Sensitivity

The air changes per hour (ACH) was modified from 0.67 in SH to 0.4 in EEH. The ACH value used for the EEH Energy-10 simulation however, was set at 0.1. This value was used to reflect a four-fold decrease in ventilation heat loss, achievable with the heat recovery system which would have otherwise not been possible to model in Energy-10. Given the volume of the house (22,500 ft3), the actual air exchange rate translates into an airflow of 131 cfm. This is the value used by Energy-10 to calculate the electricity consumption of the ventilation fan.

The effective leakage area (ELA) of SH was determined by a blower-door test [80]. A blower-door test is a measure of the total air leakage area in a building. The standard procedure is to set up a variable speed fan in the doorway, close all windows, and induce a vacuum in the building . A manometer is set up to measure the pressure differential between the outside and inside of the building. The fan is calibrated so the flow rate can be determined. The air flow rate exiting the building is equal to the air flow rate entering the building through gaps, vents and various holes in the building envelope. Air flow is measured at differential pressures of 10, 20, 30, 40, 50 and 60 Pascal. Table 3-7 below provides flow rates from the Princeton-Home (SH) test.

TABLE 3-7 Princeton (SH) Blower-Door Test Data

House Pressure (Pa)
Fan Pressure (Pa)
Air Flow (cfm)
Fan Configuration
60
74
4,118
Open
50
47
3,290
Open
40
36
2,884
Open
30
27
2,501
Open
20
95
1,720
Ring A
10
39
1,107
Ring A

The data were extrapolated to determine the air flow into the building at a negative pressure differential of 4 Pascal, which is what Energy-10 assumes to be the ambient pressure differential in a residential home under average wind conditions. The ELA for SH was determined to be 153 in2. The estimated natural infiltration rate was determined to be 242 CFM (or 0.48 air changes per hour). EEH ELA on the other hand, was set at 20 in2. This appears to be the lowest level achievable with present construction methods [81].

3.5.3 Analysis of the Effectiveness of Energy Efficient Strategies

Figures 3-21 through 3-24 are Energy-10 outputs showing the relative effectiveness of various energy efficiency strategies in achieving reduced cost and energy consumption in EEH. Energy-10 starts with SH, and adopts one energy-efficient strategy, determining the energy and cost savings realized. All other strategies are then sequentially employed individually. Figure 3-21 presents the savings of each of those strategies. It must be noted that the sum of all bars in Figure 3-21 does not equal the total energy savings between SH and EEH. This is because the inclusion of one strategy in most cases decreases the effectiveness of others. Figure 3-21 shows that the most effective strategy for reducing overall annual energy costs is installation of a high efficiency HVAC system. Use of insulation was ranked second and is almost as effective in reducing annual cost.

FIGURE 3-21 Annual Energy Cost Savings Ranking EEH Energy Efficient Strategies

The annual cost savings attributable to the energy efficient strategies displayed in Figure 3-21, were compared with the cost differential of installing each strategy. For example, an annual cost savings of $119.90 results from high efficiency HVAC, which is comprised of a higher efficiency furnace and A/C unit and an air-to-air heat recovery unit.

To determine the pay-back period for each system, the differential installment cost was divided by the annual savings. Table 3-8 provides calculations for seven different (but not all) systems that lend themselves to such comparison. Walls, ceiling and foundation were lumped into one group to allow for comparison with the Energy-10 insulation-savings number.

Table 3-8 Pay-back Period for Energy Efficient Strategies

INSTALLATION COSTS
ANNUAL
PAY-BACK
NO.SYSTEM
SH
EEH
EEH-SH
SAVINGS
PERIOD/YR.
1FOUNDATION
$19,778
$17,818
-$1,960
2FLOOR
$58
$0
-$58
3WALLS
$2,976
$13,668
$10,692
4CEILING
$7,722
$8,741
$1,018
subtotal (1-4)
$9,692
$114.2
84.9
5WINDOW/DOOR
$4,259
$5,318
$1,059
$20.7
51.2
6HVAC
$1,800
$7,700
$5,900
$119.9
49.2
7APPLIANCES
$2,730
$4,830
$2,100
$223.4
9.4
TOTALS
$39,324
$58,075
$18,751


The additional cost of EEH improvement (before developer profit) is $22,801. As can be deduced from the life cycle cost determinations in Section 3.4, the pay-back period for all EEH improvements is less than 50 years, given than EEH life cycle costs are nearly equal or less than SH life cycle costs. Thus, the greater pay-back time for insulation improvements is combined with the shorter pay-back time for appliance improvements. The air leakage pay-back period was not calculated because the differential cost of improved air leakage prevention was assumed to be absorbed in the additional cost of the wall design.

In terms of reducing annual energy consumption, insulation was the most effective strategy followed by high efficiency HVAC and air leakage control (see Figure 3-22 below).

FIGURE 3-22 Annual Energy Savings Ranking EEH Energy Efficient Strategies

While insulation saves more energy, more efficient HVAC systems save more money. This is because per unit of energy delivered to the home, electricity is more expensive than natural gas. Figure 3-23 shows the effectiveness of various strategies in reducing annual heating costs. It reiterates the fact that insulation is much more effective in reducing natural gas space heating requirements. Increased glazing provides some additional savings, while the use of window shading devices (i.e., roof overhangs) actually increase heating requirements (by limiting potential fall/spring heat gains).

Figure 3-24 shows which strategies are most effective at reducing cooling loads. By far the most effective strategy is an efficient HVAC system, consisting of a higher efficiency air conditioning unit, and air-to-air heat exchanger. Window shading is the second best strategy while improved window glazing surfaces (low emissivity) are the next best. Air leakage control has a negative effect on house cooling. More infiltration actually assists in releasing unwanted internal heat gains during warmer periods of the year. Of the strategies tested, added thermal insulation was the most detrimental to home cooling. However, the overall contribution that insulation makes to home energy savings is better understood by observing the scale factors of Figures 3-22 (26 million Btu) and 3-24 (483 thousand Btu).

Figure 3-23 indicates that the most effective strategy employed in the modeling of EEH was added thermal insulation in the building envelope. Energy-10 effectively turned off all other energy efficiency strategies and compared an SH version with EEH thermal insulation with SH. The energy reduction was 26%. With the furnace efficiency increasing from 80 to 95%, it becomes the second most effective measure with about 20% heating energy reduction.

FIGURE 3-23 Annual Heating Energy Savings Ranking EEH Energy Efficient Strategies

FIGURE 3-24 Annual Cooling Energy Savings Ranking EEH Energy Efficient Strategies



3.5.4 Comparison to Other Research

Table 1-1 below compares the results of this study (Princeton SH and EEH) with the four homes analyzed by Cole [82].

TABLE 3-9 Other Studies Determining Percentage of Construction and Use Phase Energy

Building
Size ft2
% of Total Life Cycle Energy
Status
Name
Pre-Use Phase
Use Phase
Life Cycle Period of Study (years)
Princeton (SH)
2,450
6
94
50
OriginalCole (Conventional Vancouver)I
3,750
15.8
84.2 III
50II
Cole (Conventional Toronto) I
3,750
12.2
87.8 III
50II
Princeton (EEH)
2,450
15
85
50
ImprovedCole (Energy Eff. Vancouver) I
3,750
26.3
73.7 III
50II
Cole (Energy Eff. Toronto) I
3,750
20.7
79.3 III
50II

I Conventional homes: 2x4 stud walls with R-24 roof, energy efficient homes: 2x6 stud walls with R-42 roof, additional glazing on south elevation and added thermal mass.
Construction energy includes material manufacturing, transportation and home construction.
II Cole's study provided annual heating energy, not life cycle energy. A 50 year life cycle was therefore assumed to normalize percentage results for comparison.
III Cole did not provide electrical energy consumption. This would make use phase percentages higher.


The embodied energy in the original houses analyzed by Cole are higher than that of SH (12.2-15.8% vs. 6%). The embodied energy for Cole's energy-efficient houses are also higher than that of EEH (20.7-26.3% vs. 15%).

The reason(s) for these discrepancies are not clear. Most likely, Cole used different assumptions in calculating pre-use and use phase energy. Possible assumptions that Cole may have used include:

FOOTNOTES

[73] Kiley, M.D., Allyn, M., "1997 National Construction Estimator, Labor & Material Costs, Manhours and City Cost Adjustments For All Residential, Commercial and Industrial Construction", Craftsman Book Company, Carlsbad, CA, 1996
[74] Personal communication with representative from Natural Cork, Ltd. (1825 A Killingsworth Rd, Augusta, GA 30904), July 1998
[75] ìHousehold Energy Consumption and Expenditures 1993î, DOE/EIA-0321 (93), October 1995, US Department of Energy, pg. 82
[76] "Annual Energy Outlook 1998, With Projections To 2020, December 1997", Energy Information Administration, Office of Integrated Analysis and Forecasting, U.S. Department of Energy, Washington, D.C. 20585, DOE/EIA-0383(98)
[77] "Annual Energy Outlook 1998, With Projections To 2020, December 1997", Energy Information Administration, Office of Integrated Analysis and Forecasting, U.S. Department of Energy, Washington, D.C. 20585, DOE/EIA-0383(98)
[78] Energy bill July 1998, Reppe family residence in Langebrück, Germany
[79] "Financing Energy Efficiency, A Handbook for Lenders, Overview of Energy Efficient Financing" Residential Energy Services Network <http:www.natresnet.org/Lhandbook/Overview.htm>, 8/2/98
[80] D.R. Nelson and Associates, Inc.
[81] Personal communication with Kurt Brandle, AIA, Emeritus Professor for Architecture, University of Michigan (Ann Arbor, MI), LeRoy Harvey, Executive Director, Urban Options, East Lansing, MI, and Kristine Anstead, Technical Support Director, Energy-10 consultant, July 1998
[82] Cole, Raymond J., Kernan, Paul C., "Life-Cycle Energy Use in Office Buildings:" Building and Environment, Vol. 31, No. 4, pp. 307-317.


End of section 3.0 Results

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0.0 Abstract and Executive Summary
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Last updated October, 9th '98, National Pollution Prevention Center