I wrote:
> Measuring industrial quantities of heat is dangerous; . . . and you > cannot be as accurate. > People may not realize this. When you see a factory installation, you might assume that the instruments measure precise performance. In some cases they do. In something like a semiconductor plant, precise control is critical. Or, when you work with expensive raw materials such a gold, precise measurements of inventory are essential. But in something like a carpet factory boiler, they do not typically measure performance with less precision. Measurements are accurate but not precise. They often use look up tables with only a few divisions. They estimate numbers. Here is an example of what I mean, from the CleaverBrooks "Boiler Efficiency Guide" p. 11: Fuel cost comparison of boilers with different efficiencies Procedure 1. Determine the Fuel-to-Steam efficiency of the boilers. CB efficiencies are shown in tables 8, 9, and 10. (If you do not know the efficciency of existing equipement or competitive equipment, it can be calculated per the prior procedure based on stack temperature). 2. Select the fuel burning rates based on the efficiency per tables 5, 6, and 7. [Table 5 has divisions of 2.5%: 60.0, 62.5, 65.0 . . . up to 88% steam efficiency] 3. Determine the annual fuel usage based on the annual operating hours. 4. Determine the cost of the fuel used. 5. Calculate the annual fuel consumption and resulting annual cost for each boiler. Compare the results to determine the savings. 6. To determine approximate payback in years, divide the equipment cost difference by the fuel cost savings. 7. For the most accurate estimate of fuel savings and payback, evaluate each boiler at part load performance as well. Estimate the hours per year that the boiler is expected to operate at each firing rate (25%, 50%, 75%, 100% high fire). Using the same procedure, calculate the fuel usage at each firing rate, using the estimated hours of operation for that firing rate and substituting the respective boiler efficiency. Add up the results for each boiler to determine the annual fuel usage and fuel cost. Notice that in step 7 there are only 4 divisions: 25%, 50%, 75% and 100%. I suppose you could use instruments to measure the firing rates to within a few percent for the entire time the boiler is in use, but in an actual cost/benefit evaluation a factory engineer may well use this kind of rough estimate instead. Factories in the future will probably have more automatic data collection, which should allow more fine-tuned operation and cost/benefit evaluations. Things like grocery warehousing, shipping and sales (scanners) are now automated with intense data collection and evaluation to an extent that would have seemed like science fiction back in the 1970s. - Jed
