Step 5 Savings Analysis

Once the baseline has been determined, the same basic methodology, facility model, system model, or equipment model can then be used to determine the projected energy (and other resource) usage, demand, and operating cost for the proposed application options developed in the preliminary feasibility phase. The difference is that the performance characteristics of the proposed system(s) are substituted for the existing equipment, and changes in efficiency and operating conditions are included as part of each measure (e.g., equipment changes, space condition temperature setbacks, changes in outside air volumes, equipment modulation controls, etc.). In order to substitute the proposed equipment for the existing equipment, performance characteristics of the proposed equipment must be identified for all of the potential conditions to be experienced in the proposed operating regime. Whereas existing equipment performance can be based on actual field measurement, proposed equipment performance can usually be obtained by matching the data provided by the equipment manufacturer to the site-specific conditions.

Manufacturer's data should be obtained for performance under the full range of anticipated operating conditions. These performance data plots are particularly important for equipment such as chillers and gas turbines that experience widely varying performance under different loads and ambient air conditions. With a new chiller, for example, performance data should be provided for chiller loading ranging from 10 to 100% in 10% increments with condenser water temperature held constant at temperature increments from 85°F to 60°F (29°C to 16°C) in 5 degree increments. Varying condenser water temperatures, or condenser water relief, can also be modeled with the proper manufacturer's performance curves. If chilled water supply temperature is to be varied, it will be necessary to obtain performance data for operation under each anticipated chilled water supply temperature. Once the data is obtained, it will be a relatively simple interpolation process to determine the projected efficiency for any combination of load and operating conditions. These performance characteristics should be warranted by the manufacturer as part of the purchase agreement and confirmed by well-defined standards-organization testing data. Careful evaluation of the certified testing data is recommended to determine testing tolerance or margin of error allowed. It is sometimes necessary to de-rate the performance data to compensate for allowable test tolerances to ensure more accurate, risk-mitigated results. Refer to the discussion on equipment rating standards in Chapter 33 for an example of expected performance variation.

Annual operating costs for the proposed changes are determined in the same manner as with the baseline. The proposed new operating costs may be calculated for the entire facility with the new system included or on an incremental basis for a specific measure application. Operation cost savings projections are then computed by subtracting the proposed cost from the baseline costs, again on either a facility-wide or measure-specific basis.

The true measure of achievable savings is the incremental change in usage and cost that results from the installation of a given measure. The value of heat recovery, for example, will be measured by the cost avoided in using recovered thermal energy (or heat) for a specific purpose, as opposed to using another source of energy for the same purpose. Most commonly, recovered heat replaces thermal energy output from some type of fuel burning equipment, usually a boiler or furnace. In these cases, the value of recovered thermal energy is equivalent to the cost of fuel energy that would have otherwise been consumed. The amount of energy displaced by recovered heat is a function of the efficiency of the displaced energy conversion equipment. Refer to Chapters 2 and 8 for detail on methods used for accounting for value of recovered heat.

To properly evaluate thermal load requirements and fuel displacement potential, the thermal requirements of each end use must be accurately quantified. For example, steam may be required at numerous pressures. These requirements must be matched to available levels (for example, those that exist with extraction or back-pressure turbines).

In summary, the baseline development effort provides a mechanism by which to determine the energy or resource consumption and costs with the existing systems, given a set of independent variable conditions. This is based on actual operating measurements and data, in conjunction with equipment performance models. The facility system or equipment model permits the projection of the energy or resource consumption and costs with the proposed systems. This is based on actual equipment performance data where available or on engineering calculation. By comparing the two, the net benefit of the project will be determined.

Guide to Alternative Fuels

Guide to Alternative Fuels

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