VSD compressors remain a popular choice where compressed air demand fluctuates. This may be due to changes in shift patterns, production or workloads. Here, a VSD compressor is able to vary the speed of the airend to directly match the free air delivery - or flow - required of the application. By maintaining a steady discharge pressure in widely varying loads, VSD compressors are more efficient than those which idle a lot or use modulation control. The end result is energy savings. From this simplistic perspective you can therefore see why someone would automatically think they need a VSD compressor if their compressed air demand fluctuates greatly. However, VSD compressors will only be the most energy efficient option under specific circumstances and unfortunately it is certainly not a one-size-fits-all option.* Let’s look at a real case study to explain more…
We had one end user approach us recently requesting a quote for multiple VSD compressors, firmly believing that this was the most energy efficient option to meet their compressed air requirements.
In order to understand an end user’s compressed air requirements so we can present the most energy efficient and cost effective solution, we would normally recommend undergoing an Air Demand Analysis 4.0 (ADA 4.0). Here, accurate performance data is gathered by attaching a data logger to the compressed air system for a set period of time (usually a minimum of 7 days). This collects data which can then be uploaded and analysed using the Kaeser Energy Saving System 4.0 (KESS 4.0) software.
Based on the resulting air consumption profiles, a range of compressed air supply system solutions can be simulated and compared within the KESS 4.0, crucially demonstrating the different energy consumption profiles of each option.
In this case, the compressed air system was being specced up for a completely new greenfield site. So there was no existing system to measure. However, by undergoing a requirement analysis and gathering key estimated data from the end user we were still able to enter this information into KESS 4.0 and simulate a range of compressed air supply system solutions.
For this end user, the simulation and comparisons revealed that on the surface, when you compared the free air delivery and energy costs of a selection of VSD compressors with a single fixed speed compressor, then opting for the VSD compressors could be more energy efficient. However when you consider the selection of equipment and how they are controlled, the outcome can be very different, especially when taking into account all lifecycle costs.
In the simulation made up of fixed speed compressors controlled by a SAM 4.0 controller, the losses often associated with fixed speed compressors were dramatically reduced. The SAM 4.0 controller achieves this by managing the compressors as a collective group via an advanced dynamic algorithm which turns compressors off to eliminate unnecessary idling and switching. Compared to standard ‘local’ control, in this scenario this option worked out to be 20% more efficient than standard local control. Turning off compressors means less running hours and less energy consumed than conventional controlled fixed speed systems. And in this comparison, the fixed speed system with SAM 4.0 is actually more energy efficient than the VSD option!
With energy the largest cost of running a compressed air system, this is already a huge benefit. However, the most significant savings really revealed themselves when the overall lifetime operational costs were considered.
When all lifetime operational costs were considered, the fixed speed compressors controlled by a SAM 4.0 had an estimated 60% longer life than the scenario with VSD compressors. Why? Because the SAM 4.0 turns fixed speed compressors off rather than VSD which needs to run all the time for it to provide its energy savings. Lower running hours also results in lower lifetime maintenance costs. The fixed speed system also offered the best partial redundancy, which means the plant would not be at risk if one compressor was out of service. All up these factors significantly increased the expected lifetime of the equipment and contributed to a low risk profile for the site.
The big takeaway from this case is twofold - it shows how important it is to assess your specific requirements and situation and compare the real data behind various compressor technologies and solutions. Secondly, it shows how important it is to estimate what all of the associated lifetime operating costs will be so you can see the full lifetime cost and efficiency picture. In assessing system solution options it is therefore important to consider the; finance/capital costs, installation costs, maintenance costs, electricity costs, downtime costs and depreciation costs.
In the end if you want to operate an energy efficient and cost effective compressed air system, then you should be seeking a ‘solution’ over any given ‘technology’. As we have said before, one-size-does-not-fit-all and the same technology may not present the same benefits for different end users. Utilising advanced analysis and comparison tools such as the ADA 4.0 and KESS 4.0 from Kaeser can however assist in achieving the most optimum solution that has been designed to meet your specific situation and needs.
*For a more detailed overview, check out our blog post ‘The pros and cons of variable speed drive compressors’
Find out how our ADA 4.0 and KESS 4.0 can assist you in operating an energy optimised compressed air station. Just phone 1800 640 611 or fill in the form below and we will get back to you.