True package performance
In Atlas Copco, performance measurements and reporting are done according to the latest norm (ISO, CAGI etc) considering a full-scope blower. Performance is measured and reported as such:
Delivered flow: unit outlet flow at the customer’s demanded pressure
Package power: fully demanded electrical power from the grid at this operating point
Delivered flow vs (element) inlet flow and package power vs shaft power are substantially different. Match the true blower performance with your actual need! Numerous test and reporting codes exist for blower performance. How to compare?
Legend
A. Inlet – package
B. Inlet – element
C. Outlet – element
D. Outlet – package
E. Shaft power
F. Package power
G. Mechanical drive
H. Motor
I. Electric drive
J. Oil pump
K. Oil cooler with cooling fan
Blue: Air
Light blue: Compressed Air
Yellow: Oil
Purple: Electricity
Core performance vs package performance
Some norms/codes discuss the performance of the ‘core’ of the blower, some of the ‘full package’. Both are relevant, not the same though.
The core – or element – is the ‘heart’ of the blower; it is where the electric power is used to move air and build up pressure.
When integrated in a package; typically an inlet filter is installed upfront, a check valve and discharge silencer behind the element. Those auxiliaries generate pressure drops; next to that the element inlet flow will be at a higher temperature than the unit inlet grating. These effects result by definition in a “reduced” performance of the blower package compared to the core/element performance (higher power consumption for a lower mass flow).
Inlet flow vs outlet flow
Inlet flow = intake flow = suction flow = aspired flow
Outlet flow = delivered flow
What goes in must come out? That is not true. All blowers have some leak over the air seals; besides that, some blower technologies – by design – do not deliver all aspired air.
Why can inlet flow reporting be misleading? Often the inlet flow reporting is done based on an element/core suction flow measurement; as discussed in the section “core performance vs package performance”, the (flow) performance measured at core-level by definition is better than the one at package-level. As customer it is important to compare the way how flow-performance is guaranteed vs the actual flow-rate demanded by the process (where is the flow ‘needed’?).
Shaft power vs package power
Shaft power = mechanical power taken by the core/element to move/compress air from inlet to outlet (typically reported for core/element performance, referring to moving/compressing air from element inlet- to outlet flange)
Package power = full electric power taken by the blower package to move/compress air from package inlet to package outlet.
The difference between package power and shaft power is the sum of: transmission losses between motor and element (high for belts, low for gears, zero for direct drive), motor losses (depends on motor type, largely dependent on full/partial load operation!), electric drive (FS starter or VSD inverter losses) and auxiliaries (cooling fan, pump).
Plug & play unit
What is the scope of supply? This DOES have an impact on the performance guarantee.
Suppose package performance, based on outlet flow and package power is reported; then it still is very important to compare the scope of supply of the unit! Is there an inlet filter integrated in the package? Is there a check valve integrated? Is the VSD inverter integrated in the box? if not, are VSD inverter losses included in the reported package power?