A compressor parameter recommended for verification by the acceptance standard for positive displacement compressors PN-ISO 1217, annex C, defined as the ratio of the total active electrical power consumed by the compressor in the full load operation phase of the compressor to its measured output. Given either in (kW)/(m3/min) or (kW)/(m3/h). This type of indicator is easy to determine in the compressor manufacturer’s laboratory. It is more difficult or impossible for a compressor operating in a real industrial installation, because the measurement results are also influenced by the air consumption characteristics of this installation.
Specific Power: A measurement of power per fixed volume and stated pressure of compressed air.
Variations:
- Rated Specific Power: Is the specific power tested in a laboratory with measured atmospheric conditions and then converted to the reference conditions of the testing authority. It gives a value that can be utilized to aide in the purchasing decision of a new compressor. Due to the impact of variations in the actual conditions as opposed to the reference conditions, this number is rarely, if ever, witnessed with instrumentation in the field.
- Measured Specific Power: Is the specific power calculated with a flow meter and a power meter. It can be “DIV/0” (uncalculatable) when the flow rate measured is zero. Unlike “Rated Specific Power” this value varies with system pressure. Further subclassifications are preferred.
- At Compressor Discharge:
- At wet header:
- At post filtration:
- At post compressor station:
- At process rated flow
- Specific Power Variant: Is the comparison of “Measured Specific Power” taken at multiple points in the same system. It is used to evaluate how changes in demand profile, pressure, temperature, air quality, and maintenance affect the efficiency of the compressed air system. It is also used to evaluate if the system is operating inside its designed parameters.
Specific Power Limitations/ Clarifications:
- If “Measured Package Power”* is used for the value, then variances in control, cooling, and separation will all effect this number.
- Test pressure is not controlled by any certifying authority.
- Duty cycle, unloaded power, backpressure, blowdown, and venting are not factors of “Rated Specific Power”.
*Measured Package Power: Measured where the leads come into the compressor’s electrical cabinet. Includes the power requirements of all components inside the compressor package from fans, to drains, to internal dryers, to drives, et cetera. Includes the power factor (NOT Apparent Power).
Specific Power measurement at Compressor Room Wet Air Discharge:
Air cooled type compressor:
Specific Power measurement at Compressor Discharge:
Specific Power measurement of Compressor Room:
(Air-cooled compressor)
(Water-cooled compressor)
