Energy efficient motors for HVAC applications: An experimental approach
The empirically derived data presented in this paper are the result of a program established by the State of Arizona to replace all the existing HVAC motors in the majority of State-owned buildings. All motors from 5 HP up were selected as candidates for retrofit. The largest motor was 125 HP. After obtaining questionable data from the initial existing motor field measurements, it was decided that some further study and testing was needed. By dynamometer testing aging motors from the field and new energy efficient motors, some startling conclusions were realized. One of the most common methods for determining motor loads in the field, the slip method, is highly inaccurate and cannot be used to reliably determine the load on the motor. Field measurements reconciled with dynamometer testing reveals that the slip method can be over 40% in error. Replacing an existing motor with an energy efficient motor may actually use more energy due to the effects of full load speed differences. Energy efficient motors generally run faster than standard motors because of the inherent lower internal losses. However, because the power required by a centrifugal load induction motor varies as the cube of the speed, the savings due to the higher efficiency may be completely offset by the increased power requirement due to the faster speed. Some of the conventional practices for protecting and determining energy savings from HVAC system energy efficient motor retrofits are misleading. Using the slip method for calculating motor load and not accounting for the speed difference between the existing motor and new motor are two examples presented here.
- OSTI ID:
- 54722
- Report Number(s):
- CONF-941218--
- Country of Publication:
- United States
- Language:
- English
Similar Records
Higher Efficiency HVAC Motors
Evaluation of methods for estimating motor efficiency without removing motor from service