The use of synthetic oil in air compressor applications has become quite commonplace over the course of the past 20 years. Cost saving benefits of extended life, reduced oil consumption, maintenance reduction, energy conservation, decreased oil for disposal, and increased parts of life have been thoroughly documented to the point that their validity cannot possibly be denied. Synthetic compressor oils continue, however, to make up a small albeit increasing segment of the oil being used for air compressors. The continued use of petroleum oil in the majority of these applications can only be attributed to a lack of understanding of the cost effectiveness of the synthetics. The ability to look beyond the initial cost of the synthetics and to compare the resulting advantages will be rewarded with economical, operational, and environmental benefits.
It can be a difficult, if not possible, proposition to predict the precise economic advantage of switching to a synthetic lubricant in a specific application. We can however, make use of the tremendous amount of testing which has been done to establish an average value for extended drain intervals, reduced lubricant consumption, and energy savings. Once this has been accomplished and the synthetic lubricant has been justified merely on the basis of the savings in these areas, additional benefits can be considered. While it is much more difficult to place a dollar savings value on areas such as longer parts of life, reduced deposit formation, decreased downtime, and lower maintenance costs, documented test cases and field experience insure these savings will materialize.
Extended Drain Intervals (Table 1, Part A)
The most obvious, concrete savings in choosing a compressor oil are those resulting from the extended drain intervals achieved. The exceptional oxidative and thermal stability of these compressor oil will allow an average extension from 1,000 hours with a petroleum oil to between 8,000 and 10,000 hours when using a synthetic. The use of a synthetic compressor oil for 8,000 hours will fall in the accepted recommendation of every major O.E.M. of rotary screw air compressors, while the use of a petroleum oil for greater than 1,000 hours would be absolutely discouraged and probably cited as a source of equipment problems.
Savings resulting from extended drain intervals can be easily computed by multiplying the initial cost of the petroleum oil times a factor of eight to represent the eight times greater life of the synthetic compressor oil. Subtracting the cost of the one fill of synthetic compressor oil from the cost of the eight fills of petroleum compressor oil will illustrate the net savings.
Example:
Net Lubricant Cost Savings ($4 x 8)/gal - $20/gal
$32/gal - $20/gal
$12 per Gallon
1. A compressor oil with a 20 gallon sump requirement would save $240 (20 x $12) on the lubricant cost in an 8,000 hour operation period.
2. The resulting maintenance costs of the additional seven oil changes should also be considered. Based on an average labor charge of $40 per oil change, these savings would total $280 (7 x $40).
3. A further resultant of the extended drain intervals is the economic and environmental benefit of less used oil for disposal. Based on an average disposal cost for used oil of $0.50 per gallon, the savings in the disposal cost from the above example would amount to $70.
It would be hard to place a value on the moral obligation we each have to reduce waste for disposal. The disposal of lubricants and their effects on our environment continue to be sensitive environmental issues which can be addressed by using synthetics.
Reduced Lubricant Consumption (Table 1, Part B)
In fairness, the additional cost of the synthetic oil used for make-up purposes during operation versus the less expensive petroleum oil must also be considered. This additional cost is, however, offset to a certain degree by the reduction of the amount of make-up oil required. Field testing has demonstrated a 30 to 40 percent reduction in make-up oil required when using a synthetic oil. This is accomplished with the extremely low volatility of the synthetic oil reducing the tendency of the lubricant to migrate downstream in vapor form.
Energy Saving (Table 1, Part C)
An often overlooked are of savings when choosing a synthetic compressor oil is in energy efficiency. It seems to be no more than an afterthought until considering that a 7.5 percent energy savings on a 30 HP compressor can save over $650 at a conservative rate of $0.05 per kWh. When one considers the potential energy savings in a power house full of air compressors, it can quickly become one of the foremost areas of operational savings yet to be addressed.
A field test using over 30 different rotary screw and reciprocating compressors of different manufactures established an average energy savings of over eight percent when switching from a petroleum to a synthetic oil of like ISO grade. Using a much more conservative figure of five percent (5%) and energy cost of $.08 per kWh (national average), one can generate a savings factor of $23.86 per hp per 8,000 hours (.7457 kW per hp x $.08 per kWh x .95 x 8,000 hours)
Example: A reduction of 5.0 percent in energy consumption in a 150 hp compressor converted to synthetic compressor oil would result in a savings of $3,579 per year (8,000 hours).
Additional Benefits (Table 1, Part D)
While it is irrefutable that there are additional advantages obtained from using synthetic compressor oil and monetary savings associated with these advantages, there is not a reliable method of accurately prediction the savings for an individual application. For this reason, it is probably more beneficial to be aware of the added benefits and potential savings of the synthetic compressor oil beyond what are considered to be the absolute savings mentioned previously.
Some of these are:
Conclusion
The substantial body of data generated by compressor testing has produced a number of absolute as well as potential savings associated with using synthetic lubricants. Beyond the economic advantages are benefits in the areas of safety, energy conservation, and environmental projection. These savings as well as qualify their use as the most cost effective of operation an air compressor.
1. Short, G.D., "Development of Synthetic oils for Extended Life in Rotary Screw Compressors", Lubrication Engineering, 40, 8, pp. 463-470 (1985)
2. Fairbanks, Donald R., "Diester Compressor oil in Petroleum and Chemical Plant Service", Presented to American Society of Lubrication Engineers, 30th Annual Meetings, Atlanta, GA, May 5, 1975.
3. Douglas, Patrick John, "An Environmental Case for Synthetic oils", Lubrication Engineering, 48, 9, pp. 696-700 (1992).
Table 1
Computed Savings of Synthetic Compressor Oil Versus Petroleum
Compressor Oil in Compressed Air Applications
A. EXTENDED DRAIN INTERVALS
Oil Cost Savings
Petroleum Compressor Oil Cost per Gallon$4 (a)
Petroleum Compressor Oil Changes Required per 8,000 hours 8 (b)
Effective Petroleum Compressor Oil Cost per Gallon (a x b)$32 (c)
Synthetic Compressor Oil Cost per Gallon$20 (d)
Synthetic Compressor Oil Changes Required per 8,000 hours 1 (e)
Effective Synthetic Compressor Oil Cost per Gallon (d x e) $20 (f)
Net Lubricant Savings per Gallon Using Synthetic (c-f) $12 (g)
Compressor Fill Capacity, Gallons 20 (h)
Net Lubricant Savings per 8,000 hours (g x h)$240 (i)
Oil Change Maintenance Cost Savings
Additional Oil Changes Required Using Petroleum (b-e) 7 (j)
Labor Cost per Oil Change $40 (k)
Labor Cost Savings per 8,000 Hours (j x k) $280 (l)
Disposal Cost Savings
Additional Petroleum Compressor Oil for Disposal,
Gallon (h x j) 140 (m)
Cost per Gallon For Disposal $.50 (n)
Disposal Cost Savings per 8,000 hours (m x n)$70 (o)
B. REDUCED OIL CONSUMPTION
Petroleum Compressor Oil Required for Make-up
per 8,000 Hours, Gals. 10 (p)
Cost of Petroleum Compressor Oil for Make-up (a x p) $40 (q)
Synthetic Compressor Oil Required for Make-up per
8,000 Hours, Gallons (px.7)7 (r)
Cost of Synthetic Compressor Oil for Make-up (dxr) $140 (s)
Additional Cost of Synthetic
Make-up per 8,000 Hours (s-q) $100 (t)
C. ENERGY SAVINGS
Compressor Horsepower 150 (u)
Energy Savings Multiplier Based on 5%
Energy Consumption Reduction, $.08/kWh $23.86 (v)
Total Energy Saving per 8,000 Hours
(u x v) $3,579 (w)
Total Savings per 8,000 Hour Operation (i +l + o - t + w) $4,069
D. ADDITIONAL BENEFITS
Table 2
Computed Savings of Synthetic Compressor Oil Versus Petroleum Compressor Oil in Compressed Air Applications
Oil Cost Savings
Petroleum Compressor Oil Cost per Gallon __________(a)
Petroleum Compressor Oil Changes
Required per 8,000 Hours __________(b)
Effective Petroleum Compressor Oil Cost per Gallon
(a x b) __________(c)
Synthetic Compressor Oil Cost per Gallon __________(d)
Synthecic Compressor Oil Changes
Required per 8,000 Hours 1 (e)
Effective Synthetic Compressor Oil
Cost per Gallon (d x e) __________(f)
Net Lubricant Savings per Gallon
Using Synthetic (c – f) __________(g)
Compressor Fill Capacity, Gallons __________(h)
Net Oil Savings per 8,000 Hours (g x h) __________(i)
Oil Change Maintenance Cost Savings
Additional Oil Changes
Required Using Petroleum (b – e) __________(j)
Labor Cost per Oil Change __________(k)
Labor Cost Savings per 8,000 Hours (j x k) __________(l)
Disposal Cost Savings
Additional Petroleum Compressor Oil for Disposal,
Gallon (h x j) __________(m)
Cost per Gallon for Disposal __________(n)
Disposal Cost Savings per 8,000 Hours (m x n) __________(o)
Petroleum Compressor Oil Required for Make-up per
8,000 Hours, Gallons __________(p)
Cost of Petroleum Compressor Oil for Make-up (a x p) __________(q)
Synthetic Compressor Oil Required for Make-up per 8,000 Hours,
Gallons (p x .7) __________(r)
Cost of Synthetic Compressor Oil for Make-up (d x r) __________(s)
Additional Cost of Synthetic
Make-up per 8,000 Hours (s – q) __________(t)
Compressor Horsepower __________(u)
Energy Savings Multiplier Based on 5% Energy
Consumption Reduction, $.08/kwh 23.86 (v)
Total Energy Savings per
8,000 Hours (u x v) __________(w)
Total Savings per 8,000 Hours Operation (i + l + o – t + w) _________
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