By compressor sizing, we don't just mean the physical size of the compressor, but also the entire air pressure air system, which takes into account the physical size and focuses more on meeting production needs while delivering the air needed for production at maximum efficiency.
Today, many new compressor technologies allow small compressors to provide the desired flow and pressure. In addition to this, correctly sizing a compressor can not only help to increase productivity and utilisation of an existing compressor room, but can also be an effective way to save energy. Determining the ‘size’ of an air compressor can be a difficult task, and it requires you to have a good understanding of your business's production and processes, including the production line's air pressure, flow, frequency of operations and the amount of air used at one time, etc., and the need to meet the production volume of any changes or business expansion plans.
1. Characteristics of small air compressor sizes
If your compressor is too small, it may need to run all the time to ensure your production needs. If this is the case, a screw compressor is the ideal choice, while a piston compressor is not suitable for round-the-clock operation. In addition, please further judge whether the pressure drop to meet the production requirements (some processes require high pressure, if the flow is insufficient, it will lead to a pressure drop, which in turn affects the equipment can not work), this is often the case that your air compressor selection is too small.
2. Air compressor selection of large features
Does the air compressor often idle, stop and start many times? If this situation occurs frequently, it is likely to be due to the selection of too large, which means that after the start of your air compressor, after a short period of time for the supply of air, resulting in the rise of the network pressure to reach a critical point, the machine enters the idle or shutdown state; and then, with the end equipment of the air, the network pressure will continue to fall, the air compressor will once again be recognised as the need to operate, and will start again. This frequent occurrence will result in high energy costs. In addition to this, too frequent start/stop cycles can lead to potential failures such as burnt out motors and mechanical damage.
So, how can you choose a suitable air compressor? There are several key steps you need to take:
1. Understand the flow rate of the air compressor (m³/min)
The flow rate of an air compressor depends on the production requirements, and a good understanding of your plant's needs is essential to selecting an air compressor and avoiding wasted energy. If you are trying to determine your plant's flow requirements, it is important to ensure that the flow rate of the unit is accurate and to estimate the duty cycle of the unit. We recommend that you contact your local air pressure specialist to assist with this calculation. Your Pneumatic Air Specialist will also be able to guide you in planning future expansion and ensure that your airflow and quality is suitable for your application.
2. Understanding Air Compressor Pressure (bar)
Air compressor pressure is generally measured in bar, which refers to the pressure required by various types of tools/equipment in the production process. Most general purpose equipment will have a pressure between 6-7 bar, with different industries having different requirements. You may tend to enlarge the pressure margin (e.g. the actual requirement is 7bar, enlarge it to 8bar to choose the air compressor) to ensure that the production air pressure is sufficient, but this method is not desirable, because more pressure often means more cost waste.
3.Check the voltage/capacitance/phase of the compressor
Your air compressor needs the right input power to ensure operation, so it's vital to know the voltage and phase of where your air compressor is located (whether inside or outside the building). If you are unsure, consult an electrician. They can tell you if the power source is single-phase or three-phase, as well as the voltage and capacitance.
One of the best starting points for proper selection of an air compressor is to perform a parametric evaluation of the air compressed air application. Understanding the true needs of production air and achieving a balance between production needs and life cycle costs will help you make the right selection.
On the basis of correct selection, how can air compressors be energy efficient? I believe that many enterprise equipment managers will think of inverter air compressor. It can be said that frequency conversion (or permanent magnet frequency conversion) technology has become synonymous with energy saving in today's industrial field, and has been widely used in various types of transport, production equipment and auxiliary equipment.
Variable frequency air compressor, also known as variable speed air compressor, is to change the motor speed through the intervention of the frequency converter, and then control the rotor speed, to achieve different air flow output, to meet the air demand of different customer scenarios. So why can variable frequency (variable speed) air compressor achieve such a huge energy saving compared to fixed frequency (fixed speed) air compressor?
We need to be clear that the biggest premise of inverter air compressors to achieve great energy savings is that the vast majority of enterprises are compressed air demand is fluctuating. According to the big data research (as shown in the figure below), 88% or more of the customers' compressed air demand is fluctuating violently, which is the basis for the great achievements of variable frequency air compressor.
Inverter air compressor compared to fixed frequency air compressor, specifically in which aspects of energy saving? Mainly through four aspects to explain:
1, unloading power consumption
As we know, a fixed-frequency air compressor can only be frequently added / unloaded to meet the customer's changing demand for air, so fixed-frequency air compressors often have a huge waste of unloading power. Under the same working condition, if we use frequency conversion air compressor, we can adjust the speed (air volume) according to the customer's actual air demand, and always keep matching with the customer's actual air volume, no longer unloading state, naturally also avoid the unloading power consumption.
2、Discharge loss
Industrial air compressor in the process of adding / unloading constantly switching, venting is also an essential part of the unloading stage. The so-called venting is a part of the compressed air to the environment, reduce the oil drum pressure, to ensure that the frequency compressor in the next start can be smooth (no load or light load start). If the industrial frequency air compressor does not carry out the action of venting, when the air compressor start the moment, the strong back pressure of the oil drum at the back end will bring a great load to the motor, which will easily lead to jumping or even damage. So for fixed-frequency air compressor, knowing that emptying is a waste of energy, but must be done to ensure that the air compressor lasting stable operation. The inverter air compressor does not have this problem, because in the inverter technology clamped, the motor speed is slowly increasing, even if the back pressure is very high, will not be overloaded to start.
3、Energy loss due to pressure
Fixed-frequency air compressors need to set the loading/unloading pressure in order to carry out the orderly loading/unloading cycle. Generally, the difference in loading/unloading pressure is guaranteed to be at least 0.6bar, and most of them are set at 1bar pressure difference in practical applications. For example, if the customer's demand pressure is 6 bar, then the set pressure of the compressor will be 6.5 bar loading and 7.5 bar unloading. So a fixed-frequency air compressor will continue to run between 6.5 and 7.5 bar, with an average pressure of 7 bar, exceeding 1 bar (compared to the customer's actual demand pressure of 6 bar), which naturally brings about more waste of energy consumption. But if you use frequency conversion air compressor, do not need to set the loading and unloading pressure, and can stabilise the pressure in the range of ± 0.1bar, that is, basically stable at 6.5bar pressure or even lower, greatly reducing the system operating pressure, to achieve lower energy consumption.
4、Multiple start-up loss
As we know, the starting current is 6-7 times higher than the working current, although the starting time is relatively short, but frequent starting and stopping will definitely bring the waste of energy consumption. Fixed-frequency air compressor in the customer's drastic fluctuations in air demand will be accompanied by frequent start and stop action. Then for the frequency conversion compressor, because there is no starting current peak, also eliminates the waste of energy consumption.
Of course, in addition to the above four points, many companies will also consider the operating efficiency at full load (specific power), this idea is correct. But we also need to clearly understand that the efficiency of the current air compressor field is very limited, 5% efficiency improvement is already a very big thing. And such as the above four aspects (unloading / emptying / pressure band / multiple start-up) of the improvement and enhancement is a huge energy-saving space, to achieve a greater degree of cost reduction.
