Trane SYS-APM001-EN Energy and economic analysis of alternatives, Application Considerations

Prominent software for energy analysis includes TRACE™, System Analyzer™, eQuest, and EnergyPlus.

Blended electricity rates computed from a full year’s energy cost divided by the full year’s kWh are not acceptable. Not every alternative will use energy the same way, and not every unit of energy will have the same effective cost. See Table 2, “Analysis of high-efficiency chiller options with combined vs actual rates,” on page 17.

ASHRAE Standard 1407 was developed to create a basis for defining and testing capabilities of energy analysis software packages. Test results are submitted to ASHRAE and publicly available before software is considered compliant with the Standard.

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Application Considerations

Energy and economic analysis of alternatives

The process of making decisions between multiple, competing alternatives is simplified with the assistance of simulation software. Many packages are available for this purpose (see sidebar). While not every analysis will require the same level of detail for decision-making purposes, computer-assisted analysis computations are now easy and fast, and it is no longer necessary to make many simplifying assumptions. When performing a simulation of alternatives, use software that allows for:

1Full year analysis

a Schedules, including holidays, affect the loads and the equipment.

b Weather, including coincident temperature, solar, and wind effects will have an effect, not just on the loads but on the energy performance of equipment.

2Actual energy rate definition

a Time-of-day and time-of-year rate capabilities are important. Some utilities stipulate that some hours and/or months are “on peak,” while others are “mid peak” or “off peak,” and charge differently.

b Demand or other fixed costs are almost always present in some fashion, so that utilities are compensated for the amount of instantaneous capacity they provided. Some rates will include "ratchet" clauses, which charge a minimum percentage of the previous 12 months’ peak demand.

c Stepped-rates, also known as floating cut-offs, are used to reward energy consumers with flatter load profiles. The amount of energy used almost all the time will have the least expensive rate.

d Blended or combined electricity rates are not acceptable (see sidebar).

3Life-cycle analysis

a First costs are rarely overlooked in an economic analysis.

b Maintenance costs also are likely to be different in each alternative.

c Replacement costs will be important when evaluating alternatives with equipment not expected to have the same useful life, or if one alternative is to delay some amount of action by one or more years.

d Escalation factors on recurring costs such as maintenance and energy.

e More advanced economic parameters may be desirable as well to include financing and tax implications.

For the purposes of achieving ASHRAE Standard 90.1 compliance using the Energy Cost Budget method, or for certifications under the United States Green Building Council’s LEED® program, software tools must be tested in accordance with ASHRAE Standard 140. This test is also required for tax incentives offered by the United States federal government.

Chiller System Design and Control SYS-APM001-EN