Site Characteristics. Site. St. Louis. Pittsburgh. Hartford. Peak, Off-Peak. Rate Differential. $0.1018/kWh. $0.0640/kWh. $0.0350/kWh. Cooling. Degree Days.
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COST AND PERFORMANCE GOALS FOR RESIDENTIAL COOL STORAGE SYSTEMS D.R. Brown and G.E. Spanner Pacific Northwest Laboratory Cool storage systems have the potential to reduce the overall cost of cooling to residential customers by shifting all or part of the electric load occurring during peak demand periods to off-peak periods, thus lowering the total electric bill. The objective of this study was to develop system initial capital cost and annual performance goals for cool storage technologies in residential applications. The goals were developed by considering the cost and performance of currently available residential cooling equipment and the current economic opportunity for employing storage. Initial capital cost and annual coefficient of performance goals were developed for one new construction and two retrofit scenarios for nine combinations of site and building type. A TES-augmented system in the new construction scenario with the same annual COP as a conventional air conditioning system would be worth an incremental $700-1100 above the cost of the conventional system in St. Louis, the most attractive of the three sites evaluated, depending on the building type. The prospects for residential cool storage in the retrofit/add-on system scenario were found to be similar to the new construction scenario, while prospects in the retrofit/replacement system scenario were found to be extremely limited. Details regarding the approach, results, and conclusions of the study will be covered in the presentation.
Cost and Performance Goals for Residential Cool Storage Systems
D.R. Brown G.E. Spanner
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Banene Pacific Northwest Laboratory
Objective
Establish system initial capital cost and annual performance goals for cool storage technologies in residential applications
Purpose
• Identify characteristics that would make cool storage economically attractive • Provide a benchmark for measuring the R&D progress of concepts being developed
• Focus attention on factors affecting the attractiveness of cool storage
Approach
Market-Based Goals • Identify the service to be provided by the n_ew technology • Identify the conventional means of providing the service • Characterize the cost, performance, and economic figure-of-merit for the conventional means of providing the service • Solve for combinations of cost and performance for the new technology that yield the same figure-of-merit
Approach
Conventional Cooling System
• Central A/ C system selected based on market . share • Indoor evaporator coil; remote air-cooled· condenser
• Most common for current stock and new construction
Approach
Site Selection . • Utilities offering TOD rates considered • TMY cities matched with utility districts • Sites ranked by number of cooling degree days and peak, off-peak rate differential
• 90th, 50th, and 10th percentile sites selected
Approach
Site Characteristics
Peak, Off-Peak Rate Differential
Cooling Degree Days
St. Louis
$0.1018/kWh
1474
Pittsburgh
$0.0640/kWh
646
Hartford
$0.0350/kWh
583
Site
Approach
Building Cooling Loads • DOE-2 building energy simulation model • Hourly load estimates required • Ranch, 2-story, and townhouse residences • ASH RAE standard 90 practices
:Approach
Storage System Sizing
• Option 1: Move entire electric load off-peak • Option 2: Operate chiller continuously on peak day • Optimum size depends on site-specific characteristics
Approach
Calculational Assumptions
• Storage adequately charged to displace entire peak cooling demand
. • Storage charging occurs during off-peak periods • Standby losses included in overall system performance goal
Approach
Applications Perspectives
• New construction or retrofit • Add-on or replacement equipment
Approach
Economic Assumptions System Life
15 Years
Property Taxes
2% of Initial Capital/Year
Discount Rate
4.2%/Year (After Taxes)
General Inflation Rate
3.1o/o/Year
Electricity Escalation Rate
2.5%/Year
Maintenance Escalation Rate
3.1%/Year
Capital Escalation Rate
3.1%/Year
Results
Conventional A/ C System Annual Cooling and Electric Loads (MBtu) . Electric Load City
_ Building
Cooling Load
N~w ~yst~~
Qld System
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·--
-----
~
St. Louis St. Louis St. Louis
Ranch 2-Story Townhouse
23.47 19.28 16.34
13.09 11.03 8.69
15.36 12.90 10.17
Hartford Hartford Hartford
Ranch 2-Story Townhouse
6.56 3.61 4.42
3.86 2.28 2.44
4.53 2.65 2.86
Pittsburgh Pittsburgh Pittsburgh
Ranch 2-Story Townhouse
4.99 2.46 3.55
2.83 1.50 1.94
3.33 1.77 2.27
·Results
ConVentional A/ C System Annual Electricity Bills (1986$) · New System City
Building
Old System
Flat
TOD
Flat
TOD
St. Louis St. Louis St. Louis
Ranch 2-Story Townhouse
330.12 278.36 219.30
374.51 317.75 230.89
387.37 325.54 256.63
438.70 372.30 270.45
Hartford Hartford Hartford
Ranch 2-Story Townhouse
100.64 59.45 63.55
113.38 66.17 69.79
118.11 69.07 74.48
132.85 77.57 81.76
Pittsburgh Pittsburgh Pittsburgh
Ranch 2-Story Townhouse
NA NA NA
71.49 36.06 44.89
NA NA 'NA
83.64 42.24 52.59
Results
Conventional A/C System Capital and Maintenance Costs (All Costs in 1987$)
City
Building
Annual Compressor Initial MainteReplaceCapacity Capital - nance ment
St. Louis St. Louis St. Louis
Ranch 2-Story Townhouse
3.5 Tons 4.0 Tons 2.0 Tons
$2685 $2990 $2040
$125 $130 $115
$875 $950 $700
Hartford Hartford Hartford
Ranch 2-Story Townhouse
3.0 Tons 3.0 Tons 2.0 Tons
$2380 $2380 $2040
$120 $120 $115
$800 $800 $700
Pittsburgh Ranch Pittsburgh 2-Story Pittsburgh Townhouse
3.0 Tons 3.0 Tons 2.0 Tons
$2380 $2380 $2040
$120 $120 $115
$800 $800 $700
Results
Conventional System Life-Cycle Costs (Annualized Cost, 1986 $/MBtu) Building
New Construction
Retrofit
St. Louis St. Louis St. Louis
Ranch 2-Story Townhouse
$28 $34 $30
$23 $26 $24
Hartford Hartford Hartford
Ranch 2-Story Townhouse
$64 $104 $79
$44 $67 $53
Pittsburgh Pittsburgh Pittsburgh
Ranch 2-Story Townhouse
$78 $144 $93
$51 $89 $61
City
Results
New Construction Scenario Cost and Performance Goal.s 4000
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Conclusions
Construction Scenario
• New construction prospects favorable • Retrofit/ add-on prospects favorable • Retrofit/ replacement prospects poor
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Conclusions .
Site-Specific
Factor~
• Climate and rate structures highly variable • Currently attractive situations limited
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Conclusions
Residential Building Type
• Ranch, 2-story, and townhouse evaluated
• Residential type differences not significant
Conclusions
Comparison to Previous Studies
• Consistent with EPRI study results • Value of TES less than expected cost • Limited financial incentives provided by current residential rate structures
Conclusions
R&D Goal Setting
• Singular cost and performance goal difficult to justify
• Target market share should be considered • Residential rate structure trends uncertain