sign in sign up
<<
Home , Horsepower

SRAC Publication No. 375

Southern Regional Aquaculture Center

VI May 1995 PR

Powering Aquaculture Equipment

J. David Bankston, Jr.1, and Fred Eugene Baker2

The choice of a source for 8. Current and future costs. pare favorably when total costs aquacultural production is a 9. Safety. for the entire life of the unit are choice between electric motors considered. Availability of natural and internal combustion engines. While many of these factors are gas service also impacts natural In some instances a combination site specific, this publication is gas fueled internal combustion of electric motors and generators intended to help you analyze engines. Diesel, gasoline, and LPG powered by internal combustion your situation. engines can be supplied with fuel engines may be used. Internal Typical efficiencies and lifetimes from storage tanks which allows combustion engines include of power plants and accessories considerable freedom in siting the diesel, gasoline, natural gas and are listed in Table 1. power plant. liquefied petroleum gas (LPG) The speed of internal combustion engines, with diesel being the Internal combustion engines may be varied if needed most common. Each power source engines (efficiency may suffer), giving has its advantages and disadvan- them more flexibility in this tages, many of which are site and Internal combustion engines sup- respect than electric motors. On application dependent. ply a significant percentage of the other hand, internal combus- Which type of power plant you power for aquacultural opera- tion engines are sensitive to their use will depend upon your partic- tions. This is largely due to the duty cycle. Cycles of short dura- ular situation and preferences; scattered nature of power needs tion with lengthy off cycles are however, you should consider the which may make a low-cost elec- particularly detrimental to their following factors before making tric power source (electric service) performance and longevity be- your decision: unattainable. Even under these cause ofsubstantial running time conditions, electricity may com- 1. Ability to do the job. under cold-engine conditions. In 2. Reliability of power source and fuel supply. Table 1. Typical efficiencies and lifetimes of power plants. 3. Initial cost of equipment and Attainable Useful installation. Type of Pumping Equipment Efficiency Life* 4. Expected useful life. Percent 5. Convenience of operation. Right-angle drive (gear head) 95 15 6. Cost and ease of maintenance. Automotive engines (gasoline) 28 9 7. Cost to run the power plant. Natural gas or lpg 28 14 Light industrial engine (diesel) 25-37 14 1Louisiana Cooperative Extension Service and Sea Grant Program and Electric motors 85-92 25 2Louisiana Cooperative Extension Service, Louisiana State University Agricultural *Based on 2,000 hours per year of use. With proper maintenance and Center. fewer hours of annual use, the useful life could be increased.

1 general, internal combustion Table 2. Derated engine. engines are best suited to higher applications with Deduct Maximum Brake high annual hours of use. Fuel Type of Service Horsepower efficiency is usually better for Percent higher horsepower engines (prop- erly matched to load), and the Continuous load 20 higher fixed cost can be spread Each 1,000 feet elevation above sea level 0.3 over more operating hours. Each 10-degree rise of ambient air Selecting an internal temperature above 60 degrees F 1 combustion engine Accessories (generator, air cleaner, water pump-heat exchanger, etc.) 5 Base your selection of an engine as a power source for pumping or Fan and radiator are used 5 similar applications requiring Right-angle drive (if not used in calculating long run times on the continuous water horsepower) 3 service rating rather than on the maximum brake horsepower Allowance for wear over time 10 (bhp) rating. Be aware that many engines are tested without com- ponents such as alternators, radi- a higher percentage of fuel con- O2/hp-hour), the increased effi- ator fans or water . If an sumption. ciency of the engine more than engine does not have a continu- This may be seen in the data of doubled the oxygen transfer per ous rating or its maximum rated Professor Claude Boyd, Auburn of fuel (22.6 compared to brake horsepower is given, use University. This data is presented 9.5 pounds O2/gallon). Table 2 to derate the engine for in Table 3. The Specific Oxygen The engine should be maintained continuous service. Transfer Rate (SOTR) is the in good operating condition. An engine may show substan- amount of oxygen put into the Ignition, timing and carburetion dard performance if it is not water per hour. It is a measure of should be adjusted on spark-ignit- loaded properly. An internal com- the amount of aeration that can be ed engines. Diesel engines require bustion engine operates most effi- accomplished. The horsepower timing. Have a qual- ciently at 75 to 90 percent of its requirements for the 4- drum ified specialist make adjustments continuous horsepower rating at with 4-inch paddle depth are to ensure the greatest efficiency its design speed. Overloading the nearly the same for both the 540 under the operating conditions. engine can seriously shorten its rpm PTO and 1,000 rpm PTO. The An additional consideration for life as well as increase fuel costs. 1,000 rpm PTO allows the diesel, gasoline and LPG engines Underloading causes inefficient engine to run at a slower speed is fuel storage. Storage tanks operation. and still turn the paddlewheel at should be designed to prevent the same speed. The tractor Diesel, gasoline and propane pollution and, if a leak or spill engine is more fully loaded at the engines should be sized to the occurs, to permit cleaning up the slower speed and its efficiency is load, whether the load is a gener- fuel. For this reason, underground higher, resulting in the consump- ator or an aerator. Properly sizing tanks are usually avoided. tion of only 0.7 gallon/hour for the power source can improve the 1,000 rpm PTO compared to Above-ground tanks may need fuel efficiency. For example, in a 1.6 gallon/hour for the 540 rpm provisions to contain leaks or situation where a high horsepow- PTO. When the 4-inch drum is spills. Check with your appropri- er (85 hp) tractor powers a small lowered to a paddle depth of 14 ate regulatory agency. Fuel loss or drum (6-inch) paddlewheel, near- , the power requirement at adulteration can occur in storage. ly 90 percent of the fuel consump- 540 rpm changes from 4.9 to 16.9 Fuel loss could occur through tion is required to run the tractor horsepower - a factor of 3.4. evaporation, which is particularly engine and gear train at 1,800 Because the engine was more fully a problem for gasoline and may rpm, while only about 10 percent loaded, the efficiency of the lead to higher gum content of the of the fuel is used to turn the pad- engine increased. The SOTR in- fuel. Adulteration can occur by dlewheel and aerate the pond. creased from 15.2 to 45.1 pounds condensation of water vapor from When the aerator load is O /hour, a factor of 3.0; the fuel the air or, in the case of diesel, by increased by deeper paddle depth 2 consumption increased from 1.6 bacteria which feed on the fuel in or the tractor engine rpm is /hour to only 2.0 gallons/ the presence of water. Proper pre- reduced by the proper gearing, hour-a factor of 1.3. Thus, even cautions such as filters, water sep- the tractor engine is more fully though the efficiency of the aera- arators, and periodic draining of loaded, and aeration accounts for tor decreased (3.1 to 2.7 pounds water from the tank should be

2 Table 3. Test results of two sizes of paddlewheels. (Power source was an 87 hp tractor.) PTO Tractor Shaft Paddle Fuel Speed Depth Speed Reqmt. SOTR Consumption lb O2/gal lb O2/ Aerator (rpm) (inches) (rpm) (hp) (lb O2/hr) hp-hr PTO paddle-wheel 540 4 1,800 4.9 15.2 1.6 9.5 3.1 4-inch drum 1,000 4 950 4.8 15.2 0.7 21.7 3.2 540 14 1,800 16.9 45.1 2.0 22.6 2.7 1,000 14 950 16.7 45.1 1.2 37.6 2.7 PTO paddle-wheel 540 4 1,800 12.4 26.0 1.8 14.4 2.1 20-inch drum 1,000 4 950 12.0 26.0 1.0 26.0 2.1 540 14 1,800 40.2 90.0 3.0 30.0 2.2 1,000 14 950 39.0 90.0 2.3 39.1 2.3 taken to assure that the fuel deliv- volt current. Your power supplier load the motor. If motor require- ered to the engine is clean and can also advise you on the type of ments fall between motor sizes, fresh. Remember, fuel cannot be starting equipment which must be select the larger motor. For exam- stored indefinitely; it deteriorates used and equipment needed to ple, if power required is 34 hp, with age. If the fuel is not suitable protect against overloads, under- choose the 40 hp motor rather for use, even after filtration or voltage, and short circuits, and on than the 30 hp one. treatment, it must be disposed of correct wiring procedures and Electric motors vary in efficiency properly to prevent environmen- materials for safe installations. of converting electric energy to tal damage. Your power representative can mechanical energy. Motors in the also tell you of applicable rate 15 to 40 hp range average about Electric motors schedules. You might be particu- 86 percent efficiency; in the 50 to larly interested in the availability There are obvious advantages of 150 hp range, they average about of off-peak rates, but also inquire 90 percent efficiency. electric motors if the energy and about demand charges (charge on standby charges are not prohibi- peak use of electricity), service Fuel costs tive. The provides charges and other charges which ease of operation (flip a switch to may apply. You might think of One of the biggest costs of a start), and long life, requires mini- demand and service charges as a power plant that operates many mal maintenance and maintains cost of fuel storage; knowing hours is the cost of the fuel. In its performance level year after these charges and your anticipat- order to estimate this cost, the year. In addition, initial costs are ed operating schedule will enable performance of the power plant usually less than the cost of inter- you to estimate your cost per kilo- must be known. Manufacturers nal combustion engines. Reliabili- hour. This is illustrated with have performance data for their ty of electric motors is higher than an example later. products. This data was obtained that of internal combustion As a rule, electric motors need not under specified conditions, and engines; however, they can be for internal combustion engines shut down by the loss of electrical be derated from the horsepower indicated on the nameplate. Most from the same tests used to deter- power. This may be a deciding mine the power output (not all factor if you live in an area that manufacturers base the horsepow- er rating on 70o F air temperature engines are tested). Data for fully has frequent power losses or you loaded engines is most often cannot tolerate a loss of power. and a 10 to 15 percent overload factor. This is a built-in service available, part-load performance If electric motors are being consid- factor to compensate for varying being harder to obtain. ered, you should contact your temperature and voltage condi- The fuel economy can be express- power supplier to assist in plan- tions. An electric motor should be ed in several ways. Electric ning and assessing costs. The selected to operate at nearly full motors and some internal com- amount of power needed is one of load since the motor efficiency is bustion engines use efficiency. the first points to consider. lower when underloaded (particu- For other internal combustion Motors of five horsepower or less larly at 50 percent or smaller engines, fuel economy is express- can be powered from the usual load). Standby and energy costs ed in terms of power and amount 220 volt single-phase current sup- are also higher than necessary of fuel used. For example, gallons ply. Larger motors usually when the motor is underloaded. per hp hour and pounds of fuel require three-phase, 220 or 440 However, you should not over- per hp hour may be used to

3 express an engine’s fuel economy. This method is often denoted as Table 4. Typical field efficiencies. Brake Specific Fuel Consumption Equipment Description Typical Unit of (BSFC). Of the two, gallons per hp Efficiency Fuel Energy Content hour is easier to use since we usu- Values ally purchase fuel by the gallon; however, it is not used as much Diesel engines (new or since there is more variation in the fairly well maintained and energy content of a gallon of fuel matched to load) 27-37% gal. Diesel: 135,000 than in a of fuel. Diesel engines Manufacturer’s data can give us a (use tested in field) 18-25% starting point for calculating fuel Diesel engines (oversized) 7-15% costs, but what we really want is the performance in the field. The Gasoline engines 7-28% gal. Gasoline: 124,000 best we can do is to estimate. We LPG engines 7-28% gal. LPG: 92,000 could use typical efficiencies such as those found in Table 4 which Natural gas engines 7-28% ccf Natural gas:100,000 are based upon the energy content Electric motors 85-92% kWh Electricity: 3,412 listed in the table. Generator conversion This table corresponds with mea- Efficiency 75-85% surements taken by L. Leon New, Area Irrigation Specialist, Texas Gear head (right angle) 90-95% Agricultural Extension Service, on Belt drive 85-90% existing irrigation pump installa- tions. This data was taken during a period of time lasting nearly For example, suppose a diesel conditions is to be used. The two decades from engines fairly engine with a 37 percent manufac- engine is to be derated for a gen- well maintained and matched to turer’s efficiency rating at a speed erator, water pump, radiator, and their load. The 39 diesel units and load corresponding to field fan and for wear: tested ranged in efficiency from 23 percent to 35 percent (average 30.7 percent). Horsepower of these Table 5. Typical derating factors for fuel efficiency. units ranged from 20 to 209 (aver- age 107). Five hundred and sixty- Type of Service Deduct Efficiency % seven natural gas engines were Generator 1.7 tested with efficiencies from 8 per- cent to 29 percent (average 20.9 Water pump 1.7 percent) with power output from Fan and radiator 5.0 15 to 202 hp (average 86). New also tested 185 electric motor Right angle drive (if not used in installations ranging from 2 to 200 calculating water horsepower) 5.0 hp (average 69) with efficiency of Allowance for wear over time 10.0 60 percent to 92 percent (average 87 percent). New noted that the actual efficiency of electric motors agreed closely with the manufac- Deduction Factor turer’s rating, but that there was Item From Table 5 (100% - Deduction) greater variability in the perfor- mance and ratings of diesel and Generator 1.7% deduction 98.3% = 0.983 natural gas engines. Water pump 1.7% deduction 98.3% = 0.983 A way of obtaining effi- Fan and radiator 5.0% deduction 95.0% = 0.95 ciencies, if the manufacturers state performance in terms of efficiency, Wear 10.0% deduction 90.0% = 0.90 is to derate the fuel efficiency in much the same manner as that for The fraction of the rated efficiency expected under field conditions is: power. The manufacturer’s effi- ciency should be for the same (generator) x (waterpump) x (fan & radiator) x (wear) operating conditions you will (0.983) x (0.983) x (0.95) x (0.90) = 0.83 experience. Table 5 lists some typ- ical derating factors.

4 Expected Efficiency: Example: What is the cost of natural gas per lower heating value therm (.83) x (37%) = 30.7% (100,000 Btu) if the gas is sold for 50¢ per therm (based on higher heating value). The lhv is 932 Btu/ft3 and the hhv is 1,040 Btu/ft3. Note that the cumulative effect of Solution: The number of cubic feet needed to obtain 100,000 Btu (hhv) is the factors was the product obtained by multiplying all the 100,000 Btu 3 factors. In both the Texas study = 96.15 ft and Table 4, the engine efficiencies 1040 btu/ft3 were based on a nominal heating value of 1,000 Btu/ft3 for natural Thus at 50¢ therm (hhv) we get 96.15 cubic feet for 50¢ or a cost of gas, 124,000 Btu/gal of gasoline 50¢ 3 and 135,000 Btu/gal diesel fuel. = 0.52 ¢/ft The actual heating value will vary 96.15 with the fuel. There are two differ- ent heating values: the higher Evaluated at it lhv, we would need heating value (hhv), which 100,000 Btu 3 includes the heat released in con- = 107.3 ft of gas densing the water vapor in the 932 Btu/ft3 products of combustion; and the lower heating value (lhv), which does not include the heat released It is the same gas and costs the same per cubic ft., thus the cost per lhv in condensing the water vapor. therm is: Since exhaust temperatures are 3 3 too high for condensation to (107.3 ft ) x (0.52¢/ft ) = 55.8¢/therm occur, many manufacturers rate their engines in terms of lower Cost is 11.6 percent higher for a lhv therm than a hhv therm. heating values. This should not present a problem as long as con- sistency is employed in using Unlike petroleum fuels, the energy determination. As an example, a such heating values; otherwise, an content of a unit of electricity fully loaded 50 hp electric motor error may result. For example, if (kWh) is constant. The actual cost is expected to operate 2,000 hours fuel cost calculations were per- of the fuel might be more difficult per year at 85 percent efficiency. formed using the higher heating to obtain since various rates and There is a 50 kW demand associat- value of the fuel and an engine rate components might apply and ed with the motor. The electric efficiency derived from the lower the cost per kWh may depend bill includes a demand charge of heating value, an erroneously low upon usage. Your utility represen- $2.50/kW/month for each month, cost of power would result. This tative should be able to help you whether the motor runs or not. error can be significant as the fol- determine a suitable average cost. Energy costs are 6¢/kWh. What is lowing example illustrates. A good idea of the operating cycle the average cost per kilowatt hour Manufacturer’s data for fuel eco- is usually needed for accurate if demand charges are included? nomy in terms of Brake Specific Fuel Consumption should also be Electrical energy consumption in kwh of an elec- Annual energy used is: derated with the same factors as tric motor is: used for efficiency. In this case, (50) x (2,000) x (0.746) = 87,882.4 kWh however, since a lower BSFC is (horsepower produced) x (hours of use) x (0.746) 0.85 obtained at higher efficiencies, the motor efficiency adjustment is obtained by divid- ing the BSFC by the total reduc- Annual energy charge is: tion. Another factor that can com- cost plicate calculation is that fuel (kWh) = (87,882.4) x (0.06) - $5,272.94 varies. For example, the weight of kWh a gallon of diesel fuel can depend Annual demand charge is: on temperature and the particular dollars (12 months) blend. If you lack specific infor- (50) (kW demand) x (2.50) x = $1,500/yr mation, a value of 7.07 lbs/gallon kW-mth yr of diesel fuel and 6.1 lbs per gal- Total annual charge: $6,772/94 lon of gasoline may be used. Cost per kWh = = 0.077 or 7.7¢/kWh 5,272.94 + 1,500 = $6,772.94 87,882.4 KWh

5 If the same motor was used only 500 hours a year the cost would be: (50) x (500) x (.746) Energy cost = (21,941) x (0.06) = $1,316.46 kWh used = = 21,941 kWh 0.85 2,818. 24 12.8¢ Unit Cost = $0.128/kWh = Demand charges unchanged, $1,500.00 Total cost = $2,816.46 21,941 kWh

Maintenance costs Equations and example calculations

Maintenance costs are consider- Table 6. Electric motor facts. ably higher for internal combus- tion engines than for electric Required Single-Phase Three-Phase motors. The exact costs are diffi- Amps when hp is known 746 x (hp) 846 x (hp) cult to pin down as they depend E x (eff) x (pf) 1.73 x (E) x (eff) x (pf) on duty cycle, cost of labor and Amps when kW are known 1,000 x (kw) 1,000 degree of maintenance. However, E x (pf) 1.73 x (E) x (pf) a rough rule of thumb is to assess internal combustion engines a Amps when kva is known 1,000 x (kva) 1,000 x (kva) one cent per horsepower-hour E 1.73 x (E) maintenance cost penalty in com- kW (E) x (I) x (pf) 1.73 x (I) x (E) x (pf) parison with electric motors. 1,000 1,000 kVa (I) x (E) 1.73 x (I) x (E) 1,000 1,000 hp output (I) x (E) x (pf) x (eff) 1.73 (I) x (pf) x (eff) 746 746 Where: I = amperes pf = power factor E = volts kW = kilowatts eff = efficiency kVa = kiloVolt amperes (as a decimal) hp = horsepower

Calculations to determine your energy cost

Electric: Step 1: Determine the power in terms of brake horsepower (bhp), required by the device (pump, aerator, etc.). Step 2: Determine cost of power Electric Cost to Operate in $/hr = .746 x (bhp) x (energy cost in $/kWh) (electric motor eff) x (drive eff) Note: These efficiencies should be expressed in decimal form for equations. Example: 35% = .35. If a component is not used, omit its efficiency from the equation. The energy cost per kwh should include all charges such as demand charges. Example: What is the cost per hour of electricity to operate a 90 percent efficient direct coupled electric motor producing 40 hp if the cost per kWh is 8¢? .746 x (40) x (.08) Solution: Cost/hr = = $2.65/hr .90 Internal combustion requires a choice of equations nance cost penalty in comparison engines depending upon how the engine’s to electric motors. This procedure performance is stated. The is illustrated below using the same The first step is the same as with engine’s performance should be horsepower (40) requirement as electric motors, determine the derated, as described previously, if for the electric motor. power required. The second step, required. The third step, which is determining the cost of power, optional, is to assess a mainte-

6 Performance given in terms of efficiency

Internal combustion 2,545 (HP) (fuel cost in $/unit of fuel) engines cost to operate = (energy content) (power source EFF) (drive EFF) (generator EFF) (electric motor EFF)

Note: These efficiencies should be expressed in decimal form for equations. Example: 35 percent = 0.35. If a component is not used (example: a generator), omit its efficiency from the equa- tion. If specific energy factors for your fuel are not available, use those in Table 4.

Examples: (1) New sized properly (30 percent eff), 1 right angle gear drive (90 percent), diesel cost $.60/gal. Diesel cost to operate (2,545) x (40) x (.60) Cost/hr = = $1.68/hr (135,000 x (0.30) x (0.90) Energy content of 135,000 from Table 4 Maintenance cost penalty: 40 hp = 42.09 hp required of engine 0.90 gear efficiency In 1 hour engine would produce 42.09 hp-hr which at 1¢/hp-hr results in a maintenance penalty of $.42/hr. Total of energy and maintenance penalty $2.10/hr. (2) Used diesel engine, oversized (10 percent eff), right angle gear drive (90 percent eff) diesel cost $.60/gal. Diesel cost to operate (2,545) x (40) x (0.60) Cost/hr = = $5.03/hr (135,000) x (0.10) x (0.90) Same maintenance penalty of $0.42/hr. Total energy cost and maintenance penalty $5.45/hr.

Performance in terms of fuel consumption If manufacturers’ BSFC figures are used, the appropriate second step is to derate to cover actual conditions, and convert to unit of fuel (gallons) per horsepower hour. This is accomplished by: BSFC (lb/hp-hr) gal = Fuel density (lb/gal) x derating factor hp-hr If consumption is given in terms of gal/hp-hr, derate to actual conditions. Example: A manufacturer’s engine has a BSFC rating of 0.44 lbs/hp-hr at operating conditions corresponding to our load requirements. The rating was obtained without a radiator, fan, alternator or water pump (all of which will be used) for a new engine. Determine an appropriate gal/hp-hr figure for a derated engine. Solution: Condition Derating Factor Multiplier (1.0 - Derating Factor) Wear 10% 0.90 Alternator 1.7% 0.983 Water pump 1.7% 0.983 Fan and radiator 5% 0.95

Derating factors were obtained from Table 5. Total derating is obtained by multiplying (0.9)(0.983)(0.9830)(0.95) = 0.83. Using 7.07 lb/gal of fuel: 0.44 gal Fuel consumption = = 0.075 (7.07) x (0.83) hp-hr The hourly fuel cost is determined from: (SFC (gal/hp-hr)) x (hp) x (unit fuel cost ($/gal) Internal combustion engine cost to operate = (drive eff) x (generator eff) x (electric motor eff)

7 Example: (3) Compute the $/hr cost for the diesel engine in the previous example teamed with a 90% efficient right angle drive for a diesel cost of 60¢/gal. The SFC as derated in gal/hp-hr is 0.075. The bhp output of the right angle drive is 40. (0.075) x (40) x (0.60) Cost to operate = = $2.00/hr (0.90) 40 hp Maintenance cost penalty: = 42.09 hp required of engine .90 gear efficiency at 1¢/hp-hr, maintenance penalty would be 42¢/hr. Total energy cost and maintenance penalty $2.42/hr.

Summary occur in aquacultural operations. References Make certain all safety guards are These calculations will provide in place and in good condition, “Selecting a Pumping Plant for only part of the costs and factors especially on PTO shafts and stub Aquacultural Production,” to consider. Don’t forget the fac- gear. Perform any inspection or Louisiana Agricultural tors listed at the beginning of this service only after equipment is Experiment Station, Louisiana publication: shut down. Refuel only when Cooperative Extension Service, 1. Ability to do the job. engine is not operating and is July 1988, pp. 12-16. 2. Reliability of power source and cooled down. Make sure that trac- “Designing Efficient Irrigation fuel supply. tor operators are experienced, Pumping Plants,” William A. especially when equipment is Hadden, Specialist, Louisiana 3. Initial cost of equipment and used on levees and around Cooperative Extension Service. installation. ponds. When using to “Pumping Plant Efficiency and 4. Expected useful life. relocate or place aeration equip- Irrigation Costs,” L. Leon New, ment, set brakes securely and 5. Convenience of operation. Texas Agricultural Extension block wheels. 6. Cost and ease of maintenance. Service, The Texas A&M Handle fuel with caution. Do not University System, 1992. 7. Energy cost to run the power smoke around fuel. Use a vent on plant. “Cost Comparison: Engine vs. your fuel storage tank and make Electric,” Robert H. Auley and 8. Future energy cost. sure the tank is grounded. Gerald D. Knutson, Irrigation 9. Safety. For electrical safety, do not drive Journal, May - June 1993. over wires. This can damage the “Small Cogeneration System Cost Safety wire’s insulation. Make sure that and Performances,” Electric power is shut off and locked out Power Research Institute, Your first priority should be safe at the control box before any Project EM5954, Research Project working conditions and safe maintenance is done. Use 1226-27, August 1988. working practices. Although a qualified electricians to install detailed safety discussion is wiring and avoid a jury-rigged “Cogeneration in Louisiana, Is it beyond the scope of this presenta- job. Use only approved wiring Right for You?” Joel S. Gilbert, tion, because of its importance a and follow applicable electrical Dames and Moore, Bethesda, few things will be mentioned. codes. Your local electrical inspec- MD. Safety is important. Many poten- tor, supply house, electrician or “Guide to Oxygen Management and tially dangerous activities such as power supplier may be able to Aeration in Commercial Fish tractor use on narrow levees, advise you. To prevent rodents Ponds,” Louisiana Agricultural operating PTOs and moving from damaging any wiring, place Experiment Station and gears, and the use of electricity exposed wiring in conduits. Louisiana Cooperative Extension near areas of activity and water Service, Louisiana State University, September 1991.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 92-38500-7100 from the United States Department of Agriculture.

8