A look at claims for R-values
In the past Heatec has countered R-value claims made by competitors for their insulation by citing better R-values for thicker insulation on our products. Even though our R-values were taken from data sheets published by the insulation manufacturer, they were in reality intended for the building trade. They were not based on temperatures encountered in storing asphalt. However, those values made fair comparisons because the competitors also appeared to use R-values for the building industry.
We are now told that R-values used in the building trade vary according to test methods used by the manufacturer and other factors such as reflective facings, etc. So to get the true R-value for an insulation, ignore the ones published for the building industry and calculate it by taking the reciprocal of conductance C. And make sure to use the value of C based on the appropriate temperatures for asphalt tanks.
Be aware that R-values for insulation on asphalt storage tanks are significantly lower than R-values for the same insulation when used as building insulation. Again, this is due to the temperature differences. It doesn’t mean the insulation is inferior.
Incidentally, heat loss calculations are always based on conductance C. The heat loss calculations in all of our technical papers have always been based on C. Actually, you can’t use R-values to calculate heat loss because-as stated earlier-R-values are not units of thermal resistance. Again, R-values are useful only for comparing one insulation to another within the same context.
Strange claims
Claims for insulation made by another one of our competitors appear to be inexplicable. In March 1998 they simply said their tanks had 4 inches of firm fiberglass insulation. In January 2000 they claimed their insulation was high-efficiency R-15 rated firm fiberglass equivalent to 5” of standard fiberglass. In November 2002 they claimed their insulation was high-efficiency R-15 rated firm fiberglass insulation equivalent to 6” standard fiberglass. We don’t understand the magic of how the R-value for the same 4 inches of insulation is equal to 5 inches at one time and equal to 6 inches another time.
Moreover, it is interesting to note that their so-called high-efficiency fiberglass of R-15 is lower than the R-17 rating for 6 inches of Owens Corning 701M fiberglass that we use (see Figure 1). Furthermore, 6 inches of our 701M has a notably higher R-value than 4 inches of the same material. We think anyone considering purchase of their tanks should demand an explanation of their claims.
What about density?
Another area of concern has to do with density of the insulation. Don’t be misled by any claim concerning the effect of insulation density on heat loss. Density refers to the weight of a specified volume of insulation, such as pounds per cubic foot. And within a particular type of insulation material, density may indeed reduce conductivity, but only to a minor extent. Density has more to do with the mechanical properties (not thermal properties) of the insulation.
So, density is not the basis for selecting insulation to reduce heat loss. Again, conductivity is the key factor in choosing an insulating material. Conductivity takes density into account. So you can ignore density for heat loss comparisons.
Always separate fact from fiction
If you obtain quotations from various manufacturers for asphalt storage tanks you will likely find some questionable claims. We hope this document will alert you to that possibility and arm you with enough information to recognize suspicious claims. Compare claims with the information shown in Figure 1 to see if they match.
As already noted, you get 6 inches of insulation on Heatec asphalt storage tanks. We think the costs shown in Figure 6 will convince you that it pays to insist on a full 6 inches of insulation. If so, it would be appropriate to insist that all bidders provide quotes for tanks with no less than 6 inches of insulation.
Notes on calculations
1. Thermal conductance for insulation on the Heatec tank is for Owens Corning Type 701 M (ASTM C 553) from data sheets issued by the manufacturer.
2. Thermal conductance for insulation on the competitor tank is for Fibrex mineral wool tank wrap (ASTM C 1393) from data sheets issued by the manufacturer.
3. The asphalt storage tank used for calculations is a vertical tank with a capacity of 30,000 gallons. It is a steel cylinder with a painted metal skin that covers the insulation. It uses 1696 square feet of insulation total, including top and bottom.
4. Calculations of Btu heat loss were made using NAIMA 3E Plus 3.2 computer program. NAIMA is North American Insulation Manufacturers Association. Assumptions: 80°F ambient temperature. 10 mph wind velocity.
5. A low heating value (LHV) of 132,000 Btu per gallon (LHV) was used for No. 2 fuel.
6. Ccf stands for 100 cubic feet. The net heating value of one cubic foot of natural gas is 905 Btu. However, natural gas is normally billed at its gross heating value, which is approximately 1,000 Btu per cubic foot.
7. A cost of $0.69 per Ccf was used for natural gas. This is approximately equal to $1.00 per gallon for No. 2 fuel.
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