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Water Heating Systems
Astute readers (you know who you are) might think this is a Dave Barry column. Well, although both amazing and entertaining, it isn't one of his. It is my attempt to save the gazillions of BTUs Americans waste every year when they boil water. While you may now think this is a blonde joke, it is actually a very serious matter adversely affecting our national security. Assuming all 100 million U.S. households use the same water-boiling techniques as my spousal equivalent, Barbara, the exact amount of wasted energy is 1.05 x 1015 BTU, which equates to 178 million barrels of oil annually.
The research explored here was inspired by an article I found in the EPRI (Electric Power Research Institute) Journal online http://www.epri.com/highlights.asp?objid=292779. EPRI tested the efficiency of nine types of cooktop burners in heating water from room temperature to boiling. They did this to demonstrate the efficiency of a new type of electric kitchen range that uses magnetic induction to provide superior cooking performance at record energy efficiency on a surface that doesn't get hot. My report includes the efficiencies of the nine burner types they tested. In addition, however, I will calculate (OK, guess at) the further consequences of the way Barbara boils water.
The EPRI test consisted of heating 10 quarts of water from room temperature to the boiling point (212° F). Each burner was operated in its most efficient manner (these were scientists, not my Barbara). For simplicity, I have averaged the results for the two commercial gas burners, the two electric-coil elements and the two older type of induction ranges. Throughout this article, red indicates the most energy-wasteful, purple the most energy-efficient.
From the graph, several things are apparent:
1. Induction ranges are, by far, the most efficient.
2. The old-fashioned electric coil and the more modern-looking radiant coil under glass have essentially the same efficiencies.
3. Electric ranges are about twice as efficient as gas, but because (BTU-to-BTU) electricity is twice as expensive as gas, their operating costs are about the same.
4. Commercial gas ranges are extremely inefficient, putting only 30 percent of the heat into the pot, but 70 percent into the kitchen. Whoever coined the phrase, If you can't stand the heat, get out of the kitchen must have been thinking of commercial kitchens. With superior control, instant heating, and only 10 percent waste heat, induction ranges are likely to replace gas ranges in commercial kitchens.
Wasteful Cooking Habits
Here comes the part you've been waiting for how Barbara manages to heat and humidify the entire house by just making a pot of tea. There are five rules for using cooktop units efficiently. Ignoring some would be relatively harmless; others would be huge. The cumulative effect of violating all five renders the phrase energy efficiency meaningless!
Rule #1 Match the burner to the pot. Half of the heating element is in the outer 30 percent of the disk; i.e., in a 10-inch burner, 50 percent of the heat is within 1 1/2 inches of the outer edge. All of the heat of the uncovered portion of the burner goes into heating kitchen air, not the pot.
Rule #2 Use the least amount of heat that will accomplish the task. You may use maximum heat to reach the boiling point, but reduce the heat to minimum to hold the pot at a simmer. Once water reaches its boiling point (212° F), you cannot raise it above 212°, no matter how much heat you apply, until all of the water has boiled away!
Rule #3 Adjust gas flames to all blue. A yellow flame consists of incandescent, unburned carbon. The unburned carbon represents both a waste of fuel and soot, which will be deposited on your kitchen ceiling.
Rule #4 Keep burner reflectors clean. A polished chrome surface reflects about 90 percent of the heat that strikes it. Much of the heat from either an electric element or a gas flame is in the form of infrared energy, radiated both up and down. Reflecting the down component back to the pot may increase efficiency by 10 percent or more. So keep the reflector clean!
Rule #5 Always cook with a lid on the pot. Raising the temperature of a pound of water 1 Fahrenheit degree takes 1 BTU. Turning that same pound of water from water to steam soaks up the heat of vaporization, 970 BTU! In our 1-quart example, bringing the water up to a boil takes 280 BTU, but boiling all of the water away would take an additional 1,940 BTU. The pot lid causes the steam to return to water, thereby returning the heat of vaporization that would have escaped to the air with the steam.
Flaunting all five rules would result in incredible waste. Comparing the worst case (burner on high setting with no lid = 9,200 BTU) to the best case (best practice, or following all of The Rules = 600 BTU), a person (no names) might use more than 15 times as much energy as is necessary to boil a pot of tea.
In case you are wondering, the figure of 178 million equivalent wasted barrels of oil I mentioned at the beginning of this story is real. The assumptions are:
100 million households
1 quart of water simmered for 20 minutes, three times a day, 365 days a year in each household
Waste per heating = 9,200 BTU (worst case), 600 BTU (best case)
1 gallon of oil contains 140,000 BTU
1 barrel of oil contains 42 gallons n
Editor's note: Officially, Charlie Wing is unmarried. We thank his spousal equivalent, Barbara, for her good nature.