Investment in VSD compressor units

There are many versions of Variable Speed Drive (VSD) compressors on the market. Some seem similar, yet vary significantly in price.

A customer asked me recently, "Can you point out the differences between the price levels and explain how the extra investment brings extra value?"

The differences are hidden deeper in the concept of VSD compressor units. Over the years, the VSD compressor unit has proven itself to be a good investment in saving energy. On the other hand the same VSD compressor unit can be more expensive due to oil-carry over and more wear in E-motor bearings, or more wear in shaft seals in oil pumps and the compressor itself.

One of the reasons for price variability can be found in design differences. With the use of VSD compressor units, a variable load develops in the entry of the compressor. In other words, the speed drive is variable; thus the generated heat, the load on the oil separator and the heat to the oil cooler are variable as well.

The effects of these extra loads can also be seen on the components. For example, most standard compressor shaft seals are designed for one drive speed based on pressure range, temperature and heat generation at that particular drive speed.

Additional effects of load variation can be seen in the oil separator. Variations in load on the oil separator can lead to oil carryover if the standard design calculations are used. The oil separator design needs to be altered in order to account for the effect of these variations and to know its limitations.

Fine-tuning between all components of the compressor unit is the key to flexibility, saving energy and reducing operational costs to optimize cooling energy vs. input energy.

The choice of components and the modifications of these components increases the flexibility of the compressor unit. In  most cases correcting systems (CS) and control systems are necessary in order to achieve compressor reliability. These additional systems cost more money initially, but can save you money over time.

The best results are achieved by attention to details. For example, with the E-motors used in flex drive units, each frequency drive has an energy loss of approximately two percent (due to heat generation). A way to compensate for this loss is to use a permanent magnetic E-motor, which saves four percent.

The price differences in VSD compressors can also be explained in another way.  Purchase of capital equipment like a compressor unit is necessary once every 35 years. In most cases, the compressor will be designed for the demands of that time. If additional needs surface at a later date, an extra compressor unit must be added with additional space and power supply.

Why not invest in the future with more flexibility now? Imagine a VSD controlled compressor unit capable of handling a wide range, with a controller unit that provides the operator with the information to operate in all cases with the lowest energy input vs cooling capacity. This is no longer just a VSD compressor unit. Now we must call this a Flex Drive compressor system.

So, after hearing my explanation about the differences in VSD compressors, this same customer said it was a nice idea, but if we decide to go with the best option, who will provide the warranty to insure that the investment is earned back?

I answered: We can provide you with this warranty. RM Support’s proposal is that if the extra investment is not earned back within 5 years, you will receive the difference back between the two options based on similar equipment and working circumstances.

How can we provide this warranty? Because as a result of our service inspection reports, our field experience, our research and investigations, and modification to components, we know the effects of the variables in VSD compressor units and have made improvements to them.

The Flex Drive compressor system concept is not limited to one particular brand or model of compressor. In fact, it is not even limited to screw or reciprocating compressors. The concept can be used on all compressors. The design is based on the capacity of the compressor block rather than on the load requirements at that time.

A question for investors: what is most important for your total investment? Purchasing a solution at a lower initial price, or having the most reliable compressor over the whole operation period, which results in a lower operation cost and more flexibility, therefore lowering costs to produce your products?