Energy efficiency is one of the most important topics of this era. Dr. Holger Pletsch from Evonik Oil Additives, a leading German company which is an expert in the field of efficiency, indicates that it is possible to achieve great energy efficiency by using the right hydraulic fluid in industrial equipment, and to decrease costs while minimizing the environmental impact thanks to the productivity and performance benefits such products offer.
Energy-efficient hydraulic fluids are becoming more and more important and also more and more available on a global scale. It is not only the trend towards sustainability, but also very fundamental cost considerations that make those kinds of hydraulic fluids attractive to the end user.
Hydraulic oils in industrial equipment are supposed to transfer pressure, but there are other important factors that are decisive in the selection of a hydraulic oil. The oil needs to protect the equipment, to reduce friction and wear, to dissipate the heat, especially under high load conditions. Some applications under extreme environmental conditions require more specialized properties such as stability against water or biodegradability.
Efficiency and Productivity, however, are typically not associated with the hydraulic fluid. And in fact, the majority of hydraulic fluids on the market do not provide any efficiency or productivity benefits. Only dedicated fluids will bring you a benefit.
But how much benefit can you really expect? Depending on the application, a two-digit efficiency increase is plausible and proven in the field. Compared with conventional hydraulic fluids, energy-efficient hydraulic fluids will save up to 20% of fuel in construction or mining equipment and up to around 10% of energy in stationary manufacturing equipment.
Different applications have substantially different requirements.
Stationary equipment in manufacturing typically runs at much lower operating oil temperatures than construction or mining equipment but nevertheless the oil has to handle peak loads and it typically has to operate under 24/7 conditions. Any equipment failure, any interruption is a critical concern for the equipment owner. Long oil drain intervals are therefore in favor of the maximum possible output. Because of the 24/7 operation, energy typically is one of the biggest cost positions of the users.
Looking into mobile equipment on the other hand, we can conclude that the environmental conditions are much more demanding. Typically, excavators will need to handle cold start conditions in the mornings and high load, high temperature conditions during operation. Overheating is a serious problem and will lead to productivity deficiencies. In general, a high productivity and high fuel efficiency are some of the main concerns of construction and mining end users.
How can hydraulic fluids improve the energy-efficiency of a hydraulic system? The simple answer to the question is – we need to exert control over the viscosity of the hydraulic fluid.
Viscosity is the fluid’s resistance to flow, we can also call it thickness of the fluid. A fluid with low viscosity is water, a fluid with high viscosity is honey. By instinct, I bet we would all agree that it requires more energy stirring a glass of honey than stirring a glass of water. So we already know that the higher viscosity of the honey has a consequence on the energy that we need to invest to stir the honey.
Cross-reading to our application, does that mean that the viscosity of the hydraulic fluid must be as low as possible in order to maximize the energy saving? It may come as a surprise, but the answer is no. In fact, a viscosity compromise is required to maximize the energy saving ability.
Again, a well-balanced viscosity is the key for energy efficiency because only then we can minimize both the hydromechanical losses and the volumetric losses that we observe in every hydraulic system.
Having said that, we can also conclude that any fluctuations in viscosity need to be avoided as much as possible during operation.
There are two sources of viscosity fluctuations. The first is the variation in operating temperature. The higher the oil temperature, the lower the viscosity and vice versa. The second root cause for viscosity fluctuations is oil aging. The longer you are using your oil in operation, the more it will change its performance. Viscosity losses can be observed because the shear stress in the hydraulic system is physically destroying components in the hydraulic fluid. Shear stress is just another word for pressure gradient and in hydraulic systems the oil typically operates at the interface of very high and low pressures.
We can benefit from a guideline how you can identify those hydraulic oils that avoid viscosity fluctuations as much as possible. The first indicator is the viscosity index, or short VI. The VI is a measure to describe the relationship between temperature and viscosity.
So the higher the VI level, the lower is the viscosity fluctuation. At the same time, a high VI fluid will also have lower start up viscosities, that means improved resistance against cold temperature conditions. And last but not least, the higher the VI, the lower the risk of overheating.
A conventional hydraulic fluid has a VI of around 100. An energy-efficient hydraulic fluid has a VI of at least 160, or better 170, or even better higher than 180. This should serve you as a guideline when you look for energy-efficient fluids.
The other factor that I described is shear stress. We can avoid viscosity fluctuations if we design the fluid in a way that it can resist shear stress. In other words, the higher the shear stability of the fluid, the better. This is a second indicator that you can look out for when purchasing energy efficient hydraulic fluids.
Of course, these statements are based on experiment. There is plenty of data both from the laboratory and from the field that prove the relationship between VI, shear stability and hydraulic efficiency.
What you see here is an efficiency test using a Denison vane pump at fixed conditions. 6 fluids were tested, 3 with the relatively low VI of 150 and three with a very high VI of 200. Each of the fluid either had a poor, a medium or an excellent shear stability. And you can see that both factors, the VI and the shear stability are contributing to the increase in efficiency.
Now before I will demonstrate you that we see the same effects in the real world, as well, let me emphasize that energy-efficient fluids will also be able to pass the demanding durability requirements of certain OEM specifications.
One of the most important OEM specifications certainly is issued by Denison. The key element of the specification is an extensive pump test with a hybrid pump rig. Only highly shear stable hydraulic oils can pass this pump test and same holds true for other OEM specifications such as issued by Bosch or by Eaton. The respective pump tests differ from each other, but they have one thing in common – Once approved, the fluid has guaranteed protection against wear and corrosion.
I will now guide you through our experiences with injection molding. First of all, I want to emphasize that the performance demonstrations are done according to a strict test protocol. The test protocol intends to minimize systematic errors during data acquisition and for example defines that a reference fluid needs to be tested both as a first and as a last test fluid. It defines the flushing and oil change procedures, it defines the types and intervals of oil quality checks, and it specifies the test conditions. The data acquisition is done using highly sensitive test devices and after the data has been collected, the data set is probed for statistical significance by a team of mathematicians. Because these guidelines are strictly obeyed, we can guarantee a representative and reproducible test result.
The energy efficiency improvements were in fact proven on many different machines and under many different conditions. Here you can see a selection of performance demonstrations, on Boy, Engel, Husky, Haitian and KraussMaffei equipment. The smallest machine is the Boy 35E and by far the biggest machine is the Haitian machine. You can also see that different operating temperature ranges are covered in our tests. The duration of the performance demonstrations mostly were in the range of some weeks – except the field trial on the KraussMaffei machine that was covering a test time of one entire year.
In each of the cases we probed an ISO VG 32 energy-efficient hydraulic fluid, that means a fluid with a high Viscosity Index of around 185, in comparison with a conventional ISO VG 46 monograde hydraulic oil.
In general, we found energy saving potentials of up to 10-11%, while the average savings potential lies somewhere around 5 %. In summary, you can expect that the energy savings are statistically significant - and also reproducible under many different conditions in injection molding.
Allow me to switch gears and take a look at field trials in excavators, used for construction and mining.
Excavators typically operate in highly dynamic environments. The energy-efficiency of an excavator is depending on its work cycles and on the type of material that is moved. For example, it makes a difference if the excavator handles loose gravel or big rocks. Certainly, heavy loads are more demanding for the equipment. And also, the weather conditions play a role. Remember that overheating of the hydraulic system leads to losses in efficiency and productivity.
To account for all these dynamic conditions, and to make the field trials as comparable, as reproducible and as relevant as possible, our engineers pay sincere attention to minimize some of the most important influencing factors. For example, the respective field trial is done with the same excavator machine, operating with the same test work cycles. We even take care to have the same operators over the time frame of the trial. And of course we accurately document key parameters such as oil temperature, working hour protocol and fuel consumption. Together with statistical data analysis, the test results can be regarded as highly accurate and reliable.
Here I want to share four examples out of the many field trials we have conducted in excavators. Note that we are always comparing an energy-efficient hydraulic fluid with a conventional monograde hydraulic fluid of the same viscosity grade!
Let me start with explaining the first example – conducted in Germany. In a road construction environment, we compared the two fluid types using a crawler excavator. The fuel savings in this case were reported to be up to 15% during normal use and up to 25% during stone milling.
In the second example, we were testing in a sand mine in Lithuania. Mines typically operate in 24/7 shifts, here we are talking about a day shift application. The test equipment was a mobile sand sieving unit and again, we compared energy-efficient type hydraulic fluid with a conventional hydraulic fluid. A diesel fuel saving potential of 3 Liters per hour was determined. It was further reported by the mine operators that the cold start behavior had improved with the energy-efficient hydraulic fluid. This goes back to the high Viscosity Index of the fluid. A high VI will guarantee lower viscosities at low outside temperatures and higher viscosities at high temperatures. Or short, less temperature-induced fluctuation of the viscosity.
The third field trial was done in the recycling industry where excavators are used to transport different types of waste materials from one place to another. The operators had complained about overheating issues with the conventional hydraulic fluid. Overheating is not only detrimental to the fuel consumption, but it also decreases the productivity of the hydraulic equipment. Overheated equipment can’t be used, and the workers are forced to take a break. In the interest of productivity, overheating is better be avoided. With the energy-efficient hydraulic fluids, the overheating problems were solved. On top, a 2 L per hour diesel saving was reported!
Last but not least, another example of 10% fuel saving in a crawler excavator, used for digging and material handling in an Italian pipeline construction job.
So in total, you can expect that energy-efficient hydraulic fluids can deliver around 10% fuel saving potential at least. It is not uncommon that the fuel saving is even higher than 20%. The equipment is proven to be better capable of handling both cold start conditions and high temperature, high load conditions. In other words, the risk of overheating is reduced, and therefore productivity increases can be expected.
I would like to detail a business case for energy-efficient hydraulic fluids. To do that, let’s assume a construction equipment application such as a crawler excavator. I will now further assume some of the boundary conditions – the first being the cost of diesel fuel. In Turkey, the Diesel price is something around 6 Lira per Liter – that’s around 71 Eurocents.
Second assumption is the cost of the conventional hydraulic fluid. A typical price is 1.10 Euro per kg, that’s around 10 lira per kg.
Obviously, the price of the energy-efficient hydraulic fluid is higher than the price of a conventional hydraulic fluid. The technology behind is much more sophisticated and the formulation is well-balanced. Let’s assume a price of around 1.70 Euro per kg, that’s around 15 Lira per kg.
Let’s assume the end user operates 30 machines at a fluid drain interval of 2500 h with a fluid changeout volume of 700 Liters. So that is a mid-sized excavator.
For the business case calculation, we are assuming a very conservative 8% efficiency increase, as well as a 25% increased oil drain interval.
Within the time frame of one oil drain interval, the energy-efficient hydraulic fluid will generate fuel savings of around 88,000 Euro for the 30 machines, that’s around 770,000 Lira. Because the oil drain interval is extended, another 7000 Euro savings come on top, that’s 60,000 Lira. For sure, there is an investment – the fluid itself is more expensive and this accounts for an additional 12,600 Euro investment, that’s 110,000 Lira.
Bottom line, the total savings will be around 80,000 Euros, that’s around 730,000 Lira, within the time frame of one oil drain interval, in this case 2500 hours of operation and for 30 excavators.
On the right hand side you can see that the initial cost of investment of 12,600 Euros are overcompensated after 154 hours of operation and that the return of investment is around 8x times the investment itself in this scenario.
This is just one scenario and for sure, each case is different. But based on our experience in the field in many different applications, under many different conditions and with a wide variety of hydraulic equipment, we are sincerely convinced that the investment will pay off in any case.
Allow me to summarize: The key advantages of energy-efficient hydraulic fluids are lower energy or fuel consumption, longer drain intervals, reduced risk of overheating and better cold-start behavior. As a consequence, you can expect savings on your energy costs, reduced maintenance efforts, lower specific CO2 emissions and even higher productivity in case of mobile equipment.
Despite higher investment, the total cost of ownership will reduce due to the fuel savings and due to the extended drain interval.