Holmes: Watson, have I ever told you about the time our monitoring system caught a couple of employees loafing while they were getting paid double time and a half on a Sunday?
Watson: No you haven’t. I didn’t realize that was a capability of the system. Sounds like Big Brother to me. It wasn’t in 1984 was it?
Holmes: I didn’t realize that was one of the capabilities either. And no, it wasn’t 1984.
Watson: You’ve aroused my curiosity now. Tell me how it happened.
Holmes: It started out like all of our other projects. Our salesman found a Rexnord Plant in Indianapolis that was interested in reducing their utility costs. It was an older plant near the downtown that had been in business as Link Belt for decades before the name was changed.
Watson: What was their main product?
Holmes: The produced heavy duty industrial-grade chains used in all kinds of large drive systems for construction, agriculture, manufacturing and more.
Their biggest energy user was an electric heat treat furnace.
Watson: What exactly did they use the heat treat furnace for?
Holmes: I’m not a materials expert but essentially they fed the metallic parts of the chain drives through a furnace and heated them to more than 1000 degrees F to change the physical properties of the metal. The parts moved through the furnace in baskets on a conveyor belt and were immersed in a water tank for quenching (cooling) after exiting the furnace.
Watson: How did the furnace work? How much energy did it use?
Holmes: It was an electric furnace that was set to maintain the required temperature, let’s use 1000 degrees F. When it was first turned on it took few hours to heat all of the parts of the furnace itself in order to come up to the operating temperature. Once it was up to temperature then it would require 10-15% or 40-60 KW of the heaters to overcome all of the heat loss to the surroundings and maintain the 1000 F.
Watson: How often did they turn the furnace off and on?
Holmes: That decision was based on the production schedule, how long it took the furnace to come up to temperature and how much energy was required. If they were running parts two or three shifts a day they might only turn it off on weekends. One shift a day and they might turn it off every night.
Watson: I see. Once it was at the required temperature it only cost 40-60 KW to keep it there. What happened to the energy required when they ran the parts through?
Holmes: When the conveyor was started it would bring in the parts, they would be heated from room temperature to 1000 F and maintained at that temperature for a fixed amount of time. Tests had determined how long each part needed to remain in the furnace and the conveyor speed was set accordingly. The amount of heat required followed the most basic heat transfer equation, Ht = mc∆T
Heat Required (KW) = (pounds/hour) x (specific heat of the metal) x (conversion factors) x (temperature difference between leaving and entering parts)
Watson: So if you knew how many pounds of metal were passing through the furnace each hour you could calculate the Heat Required.
Holmes: Correct. And our records showed that when they were running full production the electrical demand of the furnace stayed very close to 400 KW.
Watson: I think I am beginning to see how the data caught the employees loafing. Tell me what happened.
Holmes: They had some big orders to fill so they were running the furnace two shifts during the week and decided they needed to run it during the first shift on Sunday. Other than security, the two heat treat operators were the only ones working then.
On Monday I got a call from Bruce, the Plant Engineer. He said, “I think there may have been something wrong with our furnace over the weekend. Your reports show it was only using 300 KW yesterday. It’s okay today though and back to 400 KW”.
Watson: Was there something wrong with the furnace?
Holmes: Bruce had a standalone temperature recorder on the furnace and he said it had maintained the required temperature, that wasn’t the problem.
So I reminded him that Ht = mc∆T. The amount of heat or KW required depended only on three factors. His records confirmed the entering and leaving temperatures of the metal, he knew the specific heat of the parts and the speed of the conveyor. That only left one variable – the mass.
Watson: I see Holmes. Elementary. The employees who were getting double time and a half on Sunday were only running three fourths of the parts they were supposed to.
Holmes: Right again Watson. Bruce dug further into the production records and confirmed that was what had happened.
Watson: I love a good mystery. Particularly when Physics catches the bad guys!
Holmes: You are such a Geek, Watson!
Tell us about your experiences, both good and bad with energy professionals, what has worked and what hasn’t. Send us your comments, thoughts and suggestions on how to improve our profession so we can all continue to learn from each other. Thanks – Holmes & Watson.