2723 Cost Benefit Analysis

The target for work for the USAF has been 5% of the savings.184 The cost of the M&V can exceed 5%

if the risk of losing savings exceeds predefined limits. The Variable Speed Drive ECM illustrates these opportunities and risks. VSD equipment exhibits high reliability. Equipment type of failures normally happen when connection breaks occur with the control input, the remote sensor. Operator induced failures occur then the operator sets the unit to 100% speed and does not re-enable the control. Setting the unit to 100% can occur for legitimate reasons. These reasons include running a test, overriding a control program that does not provide adequate speed under specific, and typically unusual, circumstances, or requiring 100% operation for a limited time. The savings disappear if the VSD remains at 100% operating speed.

For example, consider a VSD ECM with ten (10) motors with each motor on a different air handling unit. Each motor has fifty (50) horsepower (HP). The base case measured these motors running 8760 hours per year at full speed. Assume that the loads on the motors matched the nameplate 50 HP at peak loads.

Table 27.18: Overview of Risks and Costs for ECMs.
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