Cost and Performance Goals for

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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

---

·--

-----

~

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


6.56 3.61 4.42

3.86 2.28 2.44

4.53 2.65 2.86

Pittsburgh Pittsburgh Pittsburgh


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



330.12 278.36 219.30

374.51 317.75 230.89

387.37 325.54 256.63

438.70 372.30 270.45



100.64 59.45 63.55

113.38 66.17 69.79

118.11 69.07 74.48

132.85 77.57 81.76



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



3.5 Tons 4.0 Tons 2.0 Tons

$2685 $2990 $2040

$125 $130 $115

$875 $950 $700




$2380 $2380 $2040

$120 $120 $115

$800 $800 $700

Pittsburgh Ranch Pittsburgh 2-Story Pittsburgh Townhouse


$2380 $2380 $2040

$120 $120 $115

$800 $800 $700

Results

Conventional System Life-Cycle Costs (Annualized Cost, 1986 $/MBtu) Building

New Construction

Retrofit



$28 $34 $30

$23 $26 $24



$64 $104 $79

$44 $67 $53



$78 $144 $93

$51 $89 $61

City

Results

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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