In my last 20 years experience, the most common complaints from the Facility Managers are “Overstated performance of Compressor by Manufacturers “!
Let me explain.
In Compressor industry, an air-compressor is rated by manufacturers at their nominal flow-power level in the published commercial leaflet. The nominal power only refers to the frame size of the electrical motor. The flow is measured according to the ISO1217 standard.
For the Power, the actual running power for the electrical motor can be much higher than the stated nominal power. At full load, the running power is higher due to the usage of service factor. At partial load or unload condition, power is consumed during the transient period (when there is no compressed air is produced).
For the Flow, the compressor performance is indicated at reference condition, which is the most favorable condition. In reality, almost no compressor can deliver the stated flow capacity in real life industrial environment.
One more thing, most compressor manufacturer do not provide the Power Consumption level when the compressor is running at different Flow Rate. All compressor will have poorer Energy Efficiency when the compressor is running at lower flow rate. Without this information, how will the facility manager compare the Energy Efficiency Curve for different compressors or for different factory demand pattern ?
In short, it is time for Facility Manager, Energy Manager or Factory Management to start requesting the full performance data from the compressor manufacturer in order to make a right choice of the investment .
I have two units of compressors running at the factory. One unit 100hp and another unit 75hp. I noticed both compressors always change from loading to unloading frequently. Is this normal ? How will this affect efficiency ?
First of all, if both of your compressors are running load & unload frequently at the same time, then there is something wrong with your compressor pressure setting. Most likely both compressors are having similar pressure setting, which is not advisable.
During unloading, compressor still consume about 30% motor power. Also, the transient period from loading to unloading, the compressor consume more than 30% power. These are wasted energy, not producing any air.
You should set the bigger compressor (the 100hp) to higher unloading point than the smaller compressor. This will let the bigger unit to run a full load, without any unloading. With this, the 100hp will be running at its better efficiency point (full load).
Try this. You will see the energy saving by doing this simple adjustment.