WorldWide Drilling Resource

55 WorldWide Drilling Resource ® FEBRUARY 2014 &% ! "" * "(%$ ))) (" $( ' & $ %# # " (" $( $ ( " !" !! ! &% ! % ! (" $( & $ $ $ " ! $ $ ! ! $ ! $ # $ $ $ Are We Efficient? by Britt Storkson Owner, P2FlowLLC Efficiency, by definition, is the amount of work performed versus the amount of energy expended to perform the work. It is usually expressed as a percentage. For example, a tank-type water heater is near 100% efficient in converting elec- trical energy to heat energy. However, some of this heat (energy) “leaks out” over time through the water heater insu- lation, reducing the efficiency so more energy must be added to maintain the desired water temperature. Electric motors work in a similar way. Motor horsepower is torque (U.S. units: foot-pounds) over time. 1 horsepower = 540 foot-pounds per second. 1 horse- power is 746 watts at 100% efficiency. But nothing is 100% efficient. You will always need more than 746 watts of electricity to get 1 horsepower from an electric motor. How much more wattage you need depends on how efficient the motor is. If an electric motor is 67% efficient, the motor will consume 1113 watts of power to generate 1 horsepower (746 divided by 0.67). Electric motors are fairly efficient compared to other motors. The internal combustion engine is only 20-30% efficient, but the liquid fuel is easy to store and transfer, and it con- tains far more energy than an equivalent size battery bank. With water pumping, we need to know the pumping efficiency to know what size pump motor to use. With all water pumps, different flow rates (gallons per minute) have different efficiencies. Water pumps can have near zero effi- ciency up to about 94% efficiency for high-flow/ low-head (pressure) applica- tions. Water pump efficiency determines how much energy you “need to buy” to pump water at a given flow rate at a given pressure. With a pump running at full speed (typically 3450 revolutions per minute), reducing the flow through the pump will also reduce the power required to pump the fluid. That’s the good news. The bad news is the efficiency is also reduced so you end up spending more in power per unit of fluid pumped at a given pres- sure. Like most things it’s not so much what you pay; it’s what you get for what you pay. One of the advantages of variable speed water pumping is the best effi- ciency point is maintained at lower flow rates by reducing the speed of the motor. (See illustration/pump curve). With vari- able speed water pumping, top efficiency can be maintained over a wide range of flow rates instead of at one flow rate. Not only is there energy efficiency, there is material efficiency. We have been using alternators in our cars and trucks instead of generators since the early 1960s. Why the switch to alterna- tors? Was it because the generators didn’t do a good job? No, generators worked adequately to provide electric power for automotive applications. So if generators did an adequate job generating electricity, why switch to alternators? It’s not because alternators were so much more energy efficient, they were material efficient...meaning it takes less metal to produce a given unit of electricity (watt). Simply put, alternators are cheaper to make. They are also physically smaller and lighter than an equivalent-output generator. They also have fewer parts so they tend to last longer. This also applies to power trans- mission. Why do we have both 220- and 110-volt power? Ohm’s law says if you double the voltage, the amperage goes down by half for a given unit of energy (watt). The amperage is what limits the flow of electricity through the wire, so with higher voltage one can get more energy through smaller wire (metal). It’s material efficient, not energy efficient. This is also why we have three- phase power as well as single phase. Three-phase power allows 1.73 times more energy through a given wire than single-phase power. The switching is more expensive...one has to switch three “legs” of the power instead of one “leg” with 110 volt or two “legs” with 220-volt power. The cost of the wire and cable is much less expensive, more than off- setting the extra cost of the switches and relays so the overall cost is much less. When evaluating efficiency, one must look at all of the factors affecting cost... not just one or two. Britt Britt Storkson may be contacted via e-mail at admin@ worldwidedrillingresource.com