Engineering Expert Witness Blog

     Is there any price a man dying of thirst in the desert would not pay for a tall glass of cold water?  What is the point at which Americans will decide they can do without heat, refrigerators, electric lights?  My neighbor refuses to run the air conditioner, even when it’s 90 degrees and 90 percent humidity.  They have obviously made the choice to sweat and be uncomfortable in their homes rather than pay high utility bills. 

     Most of us are concerned with the environment, but when times are hard like they are now many of us become more concerned with our pocketbooks.  Just as we need to make our financial ends meet, so do energy suppliers.  Without a certain level of profit, their service to us will decline, and regular, dependable delivery of their precious commodities to us will suffer.  If they were to go out of business, what then?  Reading by candlelight may be romantic for a night or two, but nights on end?  

     Let’s consider the energy provided by coal-fired power plants, for example.  They’re in the electric utility business, and they provide us with the lion’s share of our energy.  To keep a handle on operating costs, power plant engineers monitor how many British Thermal Units (BTUs) of heat energy are going into the power generation process versus how many kilowatt-hours of electricity are coming out.  

     What’s a BTU and what does it matter to us?  Well, it’s the amount of heat energy your kitchen stove uses to raise the temperature of one pint of water by one degree Fahrenheit.  As for a kilowatt-hour, that’s a thousand watts of power produced over the space of an hour– enough to light ten 100 watt light bulbs.  Now that we’ve explained the key term, we can explore the notion of heat rate, terminology very important to efficient power plant operation.  Heat rate is simply the ratio of BTUs to kilowatt-hours.

     So what’s the importance of monitoring heat rate?  For one thing, in order to get the most bang for your buck you want to keep the heat rate as low as possible.  When the heat rate is high, you’re burning more coal than you have to because you’re wasting heat energy.  This results in higher electricity costs to the consumer.  This is exactly the situation at play when low sulfur coals are used as compared to the better burning coals of yester-year.  

     So where does the wasted heat energy go if it isn’t being converted into electrical energy?  For one thing, it can be lost through steam and water leaks in the power plant piping system.  There are other losses too.  Another way to lose heat energy is when thermal insulation is missing from pipes, causing heat to escape into the atmosphere.  The opposite side of inefficiency is presented by the problem of too much heat energy building up, unable to be transferred to the steam.  This is the result if ash is allowed to accumulate inside the boiler, acting as a thermal insulator.  The heat has nowhere to go except up the smoke stack and into the atmosphere. 

     Needless to say it’s important to keep heat rate as low as possible by keeping power plant equipment insulated and in good repair.  But there are some things that affect heat rate that we just can’t do anything about, they’re known as “uncontrollable factors,” and we’ll learn about them next week.

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