Last update: 04/15/2008
Energy Use Simulation and Economic Analysis
This
chapter provides the information needed to perform the energy use simulation
and economic analysis required for the "detailed analysis" method of
compliance. The energy use simulation and economic analysis constitute the
bulk of work for ELCCA submittal.
Here, the energy systems selected in the work plan are analyzed and compared. With careful analysis, the ELCCA analyst can identify and recommend energy systems having the lowest life cycle costs for design into the building. The ELCCA analyst is responsible for running energy use simulations and economic analyses for the energy systems identified in the work plan and for documenting the results. For the maximum benefit to the project, the simulation and analysis are run early in the design development phase of overall building design. When the basic systems are identified, the ELCCA analyst should select feasible system enhancements. Table 4.1 provides a few possible options. Select two additional options. At least one option should deal with HVAC enhancements or HVAC controls. For assistance in this selection, contact the ELCCA reviewer.
T4.1 Suggested System Controls/Enhancements
| Lighting Controls | HVAC Controls |
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HVAC Enhancements |
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| DHW System | Electrical Distribution System |
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Energy Use Simulation
Energy use simulation means computer modeling the energy behavior of a building. The computer models simulate the time-based phenomena that affect a building's energy use, e.g., occupancy schedules, thermal mass response, and HVAC control sequences. This section provides the analysis requirements and tools needed to perform the energy use simulation.
Developing the Baseline
The Washington State Energy Code (WSEC) and other applicable codes must be met when developing life cycle cost analyses. However, the State wants to do more than meet minimum code requirements. The following information specifies the required prescriptive levels for thermal performance and lighting power densities for publicly owned or leased facilities. Alternatives will need to be analyzed if any component does not meet the prescriptive requirements.
Building Envelope Performance
Each envelope component must meet either the prescriptive requirements (Table 3.1) or the governing energy code whichever is stricter. Proposed envelope designs meeting these levels will not require further analysis.
Lighting Systems
Typical layouts and lighting density calculations are required for each functional area. The lighting design must meet either the prescriptive lighting power densities (Table 3.2) or the governing energy code, whichever is stricter. Proposed lighting designs meeting these levels will not require further analysis. Project design teams are encouraged to improve the efficiencies of their designs beyond the prescriptive standards by evaluating new technologies.
Building Mechanical Systems
The ELCCA guidelines require that three distinctly different HVAC systems be analyzed. The baseline mechanical and HVAC control systems should be a prescriptive system from Table 3.3
Domestic Hot Water
The baseline domestic hot water system should be the lowest first cost system that is acceptable to the building owner.
Approved Simulation Models
If the prescriptive path is not used, a computer energy simulation is required for the ELCCA report. It is the best available tool to properly assess the energy impacts of design alternatives. Approved computer software programs are shown in Table 4.2. These programs have been extensively tested and widely used. Other programs or other versions of the listed program may be used with prior approval from the ELCCA reviewer; however, only commercially available software specifically created for building simulations will be considered.
T4.2 Approved Energy Simulation Software |
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It is the responsibility of the ELCCA analyst to select the best computer program for the facility being modeled. A model that does not properly address features or characteristics of a particular facility should not be used if a more appropriate program is available. The program selected must be one in which the analyst has sufficient experience to produce accurate results. The "hourly model" is the preferred tool for larger or more complex facilities. If modeling assumptions are accurate, a skilled analyst can make good comparative estimates of the various design alternatives.
Certain complex and innovative measures cannot be accurately modeled with any existing software. In these cases, the ELCCA analyst needs to describe in detail the technique that will be used to estimate the results of installing a complex or innovative measure. Before completing the analysis, the analyst and the ELCCA reviewer should agree on the method that is likely to work best.
First Cost Interactions
Certain alternatives produce benefits beyond simply saving energy costs and improving occupant comfort. For example, alternatives that reduce transmission heat gains or internal heat gains may reduce the first cost of mechanical cooling systems as well as save energy dollars. The added cost of increased roof insulation or high-efficiency electronic ballasts may be at least partially offset by downsized chillers, cooling coils, chilled water piping, pumps, ductwork, and fans. First cost interactions must be considered in the analysis.
Computing Interactive Alternatives
Changes in one energy-using system (envelope, lighting, HVAC) often interact and affect the energy usage of other systems. For all interactive alternatives, a computer energy simulation must be used to calculate energy usage.
The iterative or rolling baseline, method is the preferred way to account for interactions among various energy-efficiency measures. The steps involved in this method are:
- Incorporate into the reference baseline model any envelope measures that have a lower life cycle cost than the reference baseline.
- Next, add any lighting measures that have lower than the reference baseline.
- Finally, with the proposed envelope and lighting measure incorporated, analyze HVAC alternatives.
Input Assumptions
Envelope U-values. Care must be exercised in calculating effective U-values for all envelope components to ensure that they comply with the ASHRAE Handbook of Fundamentals. The effects of window frames, stud walls, insulation voids, thermal bridging, sloped roofs, and other losses should be accounted for in the calculations.
Infiltration. Infiltration losses can be significant depending on how the facility is used. E&AS recommends that 0.038 cfm/sf (source: Guidelines for Energy Simulation of Commercial Buildings, page 41) be used as a beginning assumption. The ELCCA analyst may use a different value if the reason for an adjustment is stated and justified by the characteristics of the facility.
Glazing and shading coefficients. The manufacturer's tested window unit U-value and shading coefficients should be used if available. If the ELCCA analyst does not know the specific window to be installed, he or she should use the Washington State Non-Residential Energy Code (WSEC) default U-value for the type of window being considered.
Internal gains. Internal gains due to latent and sensible heat given off by occupants should be adjusted to reflect activity and actual occupancy levels for each zone (e.g., elementary school occupants are children and internal gains will be less than ASHRAE figures for adults).
Lighting. Table 3.2 provides typical power densities for various building types. Input the correct lighting power density for each HVAC zone of the model. Some zones, such as corridors, may have less density, while others, such as drafting rooms, may have more. Do not select a global building code default value for lighting power densities. Include off-hour activities and custodial work in the hours of operation.
System and occupancy schedules. The analyst should use the actual building schedules or the default occupancy schedules found in the Washington State Energy Code, Appendix, Reference Standard 29 (RS-29)(see the online WSEC for more details).
Miscellaneous equipment loads. The ELCCA analyst should only use rated equipment capacities if the simulation offers a load diversity factor or calculates the equipment load using an operating schedule profile that permits fractional amounts.
Do not use default values for the entire building. Instead, input reasonable values for each zone. The usage for unoccupied hours should be set at no less than 30 percent of the peak equipment load. See Table 4.3 below for typical receptacle power densities for various building types.
T4.3 Typical
Occupancy Densities, Receptacle Power Densities, and Hot Water Usage
The following values should only be used if specific design information is
not available.
|
Building Type |
Occupancy |
Receptacle |
DHW |
|---|---|---|---|
|
Assembly |
50 |
0.2-0.4 |
215 |
|
Health/Institutional |
200 |
1.0-1.5 |
135 |
|
Office |
275 |
1.0-1.5 |
175 |
|
School |
75 |
0.5-1.0 |
215 |
|
Warehouse |
15,000 |
0.1-0.3 |
225 |
Values are adapted from ASHRAE Standard 90.1-1989.
Critical HVAC parameters. Every input should be as realistic as possible using manufacturer's data if available. Equipment capacities, diversities, percentage of outside air, economizer cooling setpoint, and efficiencies for motors, fans, pumps, and heating and cooling equipment are all important parameters that should be carefully checked. Part-load efficiencies should be used when available. Equipment capacity should match design intent to the extent known unless output indicates the equipment does not meet loads.
Zoning. Model zoning should be based on the expected HVAC design zoning; however, there may be fewer zones in the model. Use the following basic criteria: Usage-similar internal loads Controls type-same setpoint and operation schedule Solar gains-rooms with greatly differing gains should not be in the same zone Perimeter or interior locations-12 to 15 feet from exterior in one zone Fan or HVAC system type
Temperature setpoints. Thermostat settings should reflect the way the building will actually be operated.
Economic Analysis
Economic analysis employs life cycle cost analysis to compare the costs of
owning and operating a building's energy systems throughout the building's
economic life. In addition to initial construction and installation costs,
life cycle cost analysis accounts for annual maintenance and energy costs,
escalation and inflation of fuel prices, time value of money, and
equipment replacement costs and salvage values. This section provides the
analysis requirements and tools needed to perform the life cycle cost and
economic analysis.
ELCCA Spreadsheet
For the economic analysis portion of the
report, analysts must use the ELCCA spreadsheet-available in Excel
format-provided by E&AS. To obtain a copy of the spreadsheet on an
IBM-formatted 3-1/2" floppy disk, see the contacts listed inside the
front cover.
After obtaining an electronic copy of the spreadsheet and retrieving the file, input the following: Title (project name, description, and project number) Construction Costs and Periodic Equipment Replacement Costs First-Year Maintenance Costs First-Year Energy Costs (each fuel type) Fuel Price Escalation (over and above general inflation) Real Discount Rate
The spreadsheet calculates the following for each year of the facility's economic life: Total Annual Costs Present Worth Factor, 1/(1+i)^n, where n = year, i = discount rate
The present worth of cumulative cost is the summation of the present worth of annual costs over the study period, also known as "net present value" or "30-year life cycle cost". It predicts life cycle costs of the alternatives.
Fuel Price Escalation Rates
ELCCA analysts should use the escalation rates presented in Table
4.4. There may be reasons to deviate from these regional average
escalation projections in certain utility service areas, where
unusual economic or demographic conditions exist. In such special
cases, the ELCCA analyst may elect to perform an "escalation
sensitivity analysis." To do this, calculate life cycle costs
first using the escalation rates given in Table 4.4 and again
using assumed local escalation rates. Document the local rates and
their source, and explain why they were chosen.
Real rates over and above the general inflation rate.
|
Fuel Type |
1998-2006 |
2007-2016 |
2017-2030 |
|---|---|---|---|
|
#2 Fuel Oil |
1.0% |
1.5% |
1.8% |
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Natural Gas |
0.7% |
0.6% |
0.7% |
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Electricity | |||
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Investor Owned |
0.7% |
0.7% |
0.7% |
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Public Utility |
0.7% |
0.4% |
0.4% |
- Forecast figures for natural gas are for medium growth rates from the draft 1996 Northwest Power Plan.
- Forecast figures for #2 Oil are based upon medium low growth rates.
- Forecast figures for public utilities are for high growth rates for the 1998-2006 period and medium high for 2007-2030.
The rates presented in Table 4.5 are to be used for the economic analysis. E&AS plans to update Tables 4.4 and 4.5 every two years.
Inflation and Discount Rates
T4.5 Forecast of Inflation, Discount,
and Maintenance Escalation Rates
Figures in percent per year.
|
Nominal |
Real |
|
|---|---|---|
|
General Inflation |
3.5% |
0.0% |
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Discount |
5.5% |
1.9% |
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Maintenance escalation |
4.0% |
0.5% |
Source: Discount Rate - Office of the State Treasurer; Inflation Rate - Office of Financial Management.
The general inflation rate does not enter into a "real rate" analysis. General inflation is input when a "nominal rate" analysis is performed. Either method will produce the same conclusions.
There are two methods to calculate price escalation and discounting: real price escalation and nominal price escalation. Either method can be used. However, if one is selected, then all calculations for economic forecasts and escalation rates must be consistent with the selected evaluation approach (real or nominal). The linkage between real and nominal escalation is the general inflation rate.
Example
% Nominal = [Real + Inflation + (Real x Inflation) X 100, where real
escalation and inflation are given in decimal equivalents.
For example, if the long-range real price escalation of #2 distillate oil was 1.5 percent per year and general inflation was 3.5 percent per year, then the corresponding nominal price escalation would be 5.05 percent per year.
% Nominal = [0.015 + 0.035 + (0.015 x 0.035) = 5.05%
Economic Building
Life/Equipment Service Life
A default of 30 years has been set as the building economic life. A longer
or shorter building life may be used if it is justified and approved in
the work plan.
ELCCA analysts should use the information on equipment lives presented in Table 4.6 This table is based on 1995 ASHRAE HVAC Applications Handbook and Service Life of Energy Conservation Measures produced by the Bonneville Power Administration. ELCCA analysts may deviate from the given values with prior approval. For equipment not found in this table, use the best available published data.
Construction and
Equipment Replacement Costs
Provide itemized system cost estimate for each alternative analyzed by
component. Cost should include materials, labor, overhead and profit, and
taxes. Proposed or expected utility incentives or rebates are not to be
included in the analysis.
Replacement cost for equipment should be included based on the estimated cost of replacing the equipment at the end of its expected life. The life expectancy for various equipment can be found in Table 4.6 or as determined from another source if the equipment is not specified in the table.
Maintenance Cost Estimating
Procedure
The ELCCA guidelines require a breakdown of maintenance costs for each
mechanical system analyzed. The following procedure explains how to estimate
annual total HVAC maintenance costs for heating and cooling equipment and
distribution systems for a building. This procedure compares maintenance
costs for various systems to a common baseline, which allows the cost of one
system to be compared to the cost of another. The
procedure should not be used to prepare operation and maintenance budgets.
ELCCA analysts may use the procedure explained below, or they may calculate annual maintenance costs using their own standard practice. Estimates based on standard practice must include a line-item breakdown of all costs; the same assumptions, procedures, and summary forms must be used to prepare all of the cost estimates.
Maintenance costs include all costs of labor, materials, and consumable products for the following categories: replacement/servicing (filters, belts, etc.) lubrication general housekeeping balancing control calibration troubleshooting service contracting (if any) small equipment replacement (an allowance for periodic replacement within the service life of the measure)
T4.6 Equipment Service Life
Energy Conservation Measure/Equipment Median Service Life (years)
| Building Envelope | Domestic Hot Water |
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| Electric Transformers 30 | Air Washers 17 |
| HVAC | Air Terminals |
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| Condensers | Coils |
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| Controls | Boilers, Hot Water (Steam) |
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| Cooling Towers | Fans |
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| Furnaces | Heat Exchangers |
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shell and tube 24 |
| Heat Pumps | Valve Actuators |
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| Package Chillers | Pumps |
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| Radiant Heaters | Reciprocating |
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| Thermal Energy Storage Systems | Unit Heaters |
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| Heat Recovery | Motors and Drives |
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| Lighting | Refrigeration |
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| Steam Turbines 30 | |
References "Service Life of Energy Conservation Measures" Bonneville power Administration (July 14, 1987); prepared by Xenergy, Inc. and Ecotope, Inc. Table 5, "Equipment Service Life", Chapter 49, 1995 ASHRAE HVAC Applications Handbook. Obtained from a nationwide survey conducted in 1978 by ASHRAE TC 1.8 (RP 186). "Building Maintenance, Repair & Replacement Database (BMDB) for Life-Cycle Cost Analysis" American Society for Testing of Materials (ASTM) E917.
