Common Causes of High Bills

To gain control over your energy consumption, it’s helpful to understand the most common causes of high bills. They are:

1.Weather – Weather is the No. 1 cause of high bills.
◦Hot weather – Even if you never change your thermostat, cooling can account for half or more of your electric bill during hotter weather. When you lower your thermostat to stay comfortable in humid weather, it causes your A/C to run longer, which increases energy use. To save energy, cool your home at 78 degrees or warmer with the thermostat fan switch on "auto." For additional savings, raise your thermostat to 82 degrees or warmer when you're away from home. Also, clean or replace your air conditioner's filter every month to trim your cooling costs and help your unit run more efficiently.
◦Cold weather – During periods of cold weather, strip heating and portable heaters are among the highest sources of electric demand. In fact, strip or electric resistance-based heating requires two to three times more energy than air conditioning. That is why for every two degrees you lower your thermostat, i.e. setting your thermostat from 68 degrees to 66 degrees, we estimate you will save approximately 20 percent on the heating portion of your bill. Also, people tend to take longer showers in colder weather, which increases water heating costs. View more cold weather tips.

2.Electronics and appliances* – Many electronic devices continue to draw power even when they are not in use. So, consider either plugging these devices into a power strip with an on/off button or unplugging items when not in use. This includes:
◦TVs (Larger and plasma TVs use more electricity and produce more heat, which makes your A/C operate more.)
◦Stereos
◦DVDs and DVRs
◦Cell phone or battery chargers
*Caution: Shutting some items off may require reprogramming.

3.Household – House guests, including kids home from college, can use a lot more electricity — more showers, laundry, cooking and dishes, all of which use hot water. In addition, the size, age and type of house you live in can impact the amount of energy you consume.

4.Length of billing cycle – A billing cycle is the number of days in each bill. Normally, your meter is read on the same day every month, but some months are longer than others and weekends and holidays can sometimes get in the way. Occasionally, an FPL employee can't get to your meter because a gate is locked or a dog is in the backyard, and it’s not safe to enter. As a result, some monthly bills cover as few as 25 days and some as many as 35 days.

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Energy Conservation Measures for Commercial

Office Equipment Tips

• Turn off all office equipment and lights every night and weekend. If you can't turn off the whole computer, turn off the monitor and the printer.

• When purchasing PCs, monitors, printers, fax machines and copiers, consider ENERGY STAR® models that "power down" after a user-specified period of inactivity.

• Install free software from the Environmental Protection Agency that puts monitors in sleep mode when not in use. This can save $0.085/kWh of power used by networks.

• If appropriate, use laptop computers and inkjet printers — they consume 90 percent less energy than standard desktop computers.

• Use e-mail instead of sending memos and faxing documents.

• If you need to print, consider double-sided printing and reusing paper.

Lighting Tips
• Retrofit T12 lights with magnetic ballasts to T8 lights with electronic ballasts.
• Replace incandescent light lamps with compact fluorescent lamps (CFLs), wherever appropriate. CFLs use at least 66% less energy and last an average of 10 times longer.
• Consider removing excess fluorescent lights and installing reflectors. Lighter colored walls need less light.
• Install motion detectors to control lighting in frequently unoccupied areas, such as restrooms.
• Retrofit incandescent or fluorescent exit signs with long-lasting, low-energy LED exit signs.
• Clean dusty diffusers and lamps every 6-12 months for improved lumen output.
• Turn off the lights when not needed. It is a myth that leaving them on uses less energy than turning them off. Turn off signage and other lights not necessary for security and safety.
• Open blinds and shades. Turn off lights in unoccupied areas or in spaces with sufficient natural lighting.
• Use teamwork to reduce lighting loads. Cleaning staff can work in teams (instead of different areas simultaneously) to reduce lighting usage. This can save up to 20% in lighting energy.

HVAC Tips
• Set thermostats at 78 degrees F for cooling in the summer when the workplace is occupied, and 85 F or off after business hours. During the winter, set the thermostat to 68°F when the work place is occupied and 63°F after business hours. The energy savings can be as much as 2% of your air conditioning costs for each one degree that you raise the thermostat.
• Install electronic time clocks or setback-programmable thermostats to maximize efficiency.
• Install locking covers on your thermostats to prevent employee tampering with temperature settings.
• Regularly clean condenser coils, replace air filters, and check ducts and pipe insulation for damage.
• Consider installing an air conditioning economizer to bring in outside air when cool outside.
• Consider replacing old HVAC systems with new energy-efficient systems.
• Install ceiling fans.
• Install blinds or solar screen shades. Use reflective window film or awnings on all south-facing windows. Consider solar control window films applied to existing glass in windows and doors to reduce peak demand during hot months and conserve energy anytime air conditioning might be required. These films can also reduce exposure to ultraviolet radiation and reduce glare. Save 5 to 10%.
• Perform regular maintenance to keep heating, ventilation and air conditioning (HVAC) systems running more efficiently. Maintenance activities can save up to 30% of fan energy and up to 10% of space conditioning energy use.
• Install ceiling and wall insulation.
• Insulate water heaters and supply pipes.

Refrigeration Tips
• Perform scheduled maintenance on units, especially keeping evaporator coils clean and free of ice build-up.
• Adjust door latches, replace worn door gaskets, install autoclosers, and add strip curtains to walkin doors.
• Use night covers on both vertical and horizontal display cases.
• Disconnect anti-condensate heaters.
• Keep refrigerators full (water jugs make good fillers).
• Turn off and recycle your second refrigerator. Many of these secondary units (usually older and less energy efficient) use as much as 40% more energy than a new model.

Food Service Equipment Tips
• Consider replacing some or all electric cooking equipment with comparably sized gas-fired equipment.
• Purchase insulated cooking equipment whenever possible (e.g., fryers, ovens, coffee machines).
• Preheat cooking equipment no longer and at no higher setting than the manufacturer's recommendation.
• Use cooking equipment to capacity. Fully loaded equipment utilizes energy more efficiently. Turn off unused and backup equipment during low production periods.
• Filter fryer oil at least once a day to extend the oil life.
• Don't overload fryer baskets beyond the recommended capacity. Overloading increases cook time.
• Where applicable, replace broilers with grooved or smooth griddles to significantly reduce the associated energy consumption.
• Make sure oven doors fit tightly and gaskets are in good condition.
Other Energy Savings Tips for Commercial Sector:
• Implement a dress code for warm weather. Allow employees to wear comfortable clothing during warm or hot weather. It makes little sense to keep a room cold enough that workers must wear suits and coats.
• Adjust workplace schedules to reduce energy use during the "peak" hours when there is most demand for electricity, typically noon to 7 p.m.

Sources:

http://www.pge.com/biz/energy_tools_resources/small_biz/
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Electrical Systems: Power Factor Correction (2)

Power Factor Charges
Many utilities charge for low power. To measure power factor, the most common type of utility meter measures the total kVAr-hours and kVA-hours over the billing period and calculates the average power factor as:

PF = Cos [ ArcSin (kVArh / kVAh) ]

The most common methods of charging for low power factor are:

1. Adding a demand penalty when the power factor dips below a set amount (usually 90%)

2. Basing the demand charge on the supplied power Ps (kVA), rather than the actual power used Pa (kW).

3. Basing part of the overall charge on the reactive power kVAr, which increases as power factor decreases.

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Electrical Systems: Power Factor Correction (1)

Resistive devices, like electric resistance heaters and incandescent lights transform all the power supplied to the device into heat or useful energy. Inductive devices, like motors, use some of the power supplied to the device to energize the inductive windings and create a magnetic field. This power, called reactive power, is alternately stored and given up by the windings, but is not used to do actual work. When this happens, the line supplying power to the device now carries the actual power used by the device and the reactive power created by the device.

Actual power used by the device is measured in kW, reactive power created by induction devices is measured in kVAr, and the apparent power in the supply lines is measured in kVA. The mathematical relationships between these types of power are described by the “power triangle” shown below. For example,

The ratio of the actual power consumed by equipment (Pa) to the power supplied to equipment (Ps) is called the power factor.

PF = Pa / Ps = kW / kVA = cos Phi

Devices which generate/require large amounts of reactive power in relation to actual power consumed have low power factors. Such devices include:

• Motors
• HID and fluorescent lights with low PF ballasts
• Devices which convert AC power to DC power such as:
• DC drives
• Welding machines
• VFDs
• Induction furnaces

Fully loaded motors generally have a power factor of about 80%. However, if the motor is under loaded, the fraction of reactive power (for the coil) to actual power (for mechanical work) increases and the power factor decreases.

Two potential problems are associated with low power factor. First many utilities have explicit or implicit charges for low power factor. Second, low power factor increases the current, and hence losses, in transformers and the electrical distribution system. These losses cost money and generate excess heat in the electrical distribution system, which may shorten equipment lifetime or cause production shut downs. These potential problems are discussed in the sections that follow.

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Variable Frequency Drives (4) - FINISH

4. Basic Operation of a PWM Inverter (VFD)

In this section we will discuss how the five basic drive system components work together. After this discussion we shall include a detailed, component level, discussion of operation.

The rectifier circuit of a pulse width modulated drive normally consists of a three phase diode bridge rectifier and capacitor filter. The rectifier converts the three phase AC voltage into DC voltage with a slight ripple. This ripple is removed by using a capacitor filter. (Note: The average
DC voltage is higher than the RMS value of incoming voltage by: AC (RMS) x 1.35 = VDC)
The control section of the AFD accepts external inputs which are used to determine the inverter output. The inputs are used in conjunction with the installed software package and a microprocessor. The control board sends signals to the driver circuit which is used to fire the inverter.
The driver circuit sends low-level signals to the base of the transistors to tell them when to turn on. The output signal is a series of pulses, in both the positive and negative direction, that vary in duration. However, the amplitude of the pulses are the same. The sign wave is created as the average voltage of each pulse, the duration of each set of pulses dictates the frequency.
By adjusting the frequency and voltage of the power entering the motor, the speed and torque may be controlled. The actual speed of the motor, as previously indicated, is determined as:

Ns = ((120 x f) / P) x (1 - S)

where: N = Motor speed; f = Frequency (Hz); P = Number of Poles; and S = Slip.

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Variable Frequency Drives (3)

3. Basic Drive System

The AFD consists of several basic components:

• Line Voltage - In this case 3-phase AC voltage.
• Input Section - Consists of a rectifier and filter. Transforms the AC voltage into DC voltage.
• Control Section - The control board accepts real world inputs and performs the required operations. The tasks are performed by a microprocessor.
• Output Section - This section includes the base drive circuits and the inverter. The base drive signals are low level signals that tell the inverter to turn on.
• Motor - Already described.
  
  
  

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Variable Frequency Drives (2)

2. Constant Torque Loads

Direct Current electric motors, eddy-current clutches, transmissions, etc. used to be the best way of controlling process speed. With present AC drive technology, greater speed control and fewer losses can be realized. Additionally, there are fewer moving parts that would have to be maintained.

Vector drives can deliver full rated torque from full speed to zero RPM. Torque can be controlled, with precision, allowing even large motors to position loads much like servo motors. This allows for greater flexibility of control over the other methods of speed control.

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Variable Frequency Drives (1)

1. Variable Torque Loads

Variable loads offer a tremendous opportunity for energy savings with AFD's. The areas of greatest opportunity are fans and pumps with variable loads.

Fan and pump applications are the best opportunities for direct energy savings with AFD's. Few applications require 100% of pump and fan flow continuously. For the most part, these systems are designed for worst case loads. Therefore, by using AFD's, fluid affinity laws can be used to reduce the energy requirements of the system (Fig. 1).

Fig.1 Pump and Fan Affinity Laws

Eq. 1: N1 / N2 = Flow1 / Flow2
Eq. 2: (N1 / N2)^2 = Head1 / Head2
Eq. 3: (N1 / N2)^2 = T1 / T2
Eq. 4: (N1 / N2)^3 = HP1 / HP2

By using the affinity laws, you can determine the approximate energy savings:

Ex. 1: 250hp Fan Operating 160 hrs / Week

hp1 / hp2 : (N1 / N2)^3
100% spd = 40 hrs = 100% ld = 250hp
75% spd = 80 hrs = 42% ld = 105hp
50% spd = 40 hrs = 13% ld = 31hp
kWh / wk = (hp) x (0.746) x (hrs / eff)
250 x 0.746 x (160 / 0.95) = 31,411kWh/wk

Assuming no loss of efficiency at reduced speeds:
(250 x 0.746 x (40/0.95)) + (105 x 0.746 x (80/0.95)) + (31 x 0.746 x (40/0.95)) = 15,422 kWh

By using an AFD the approximate kWh savings per year would look like:
(31,411 - 15,422) x 50 = 800,000 kWh/yr

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Motors & Energy Saving (6) - Finish

8. Electric Motors Checklist

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Motors & Energy Saving (5)

7. Diagnostic Tools

• Thermography – An infrared thermometer or camera allows for an accurate, non-contact assessment of temperature. Applications for motors include bearing and electrical contact assessments on motor systems and motor control centers.

• Ultrasonic analyzer – Electric motor systems emit very distinct sound patterns around bearings. In most cases, these sounds are not audible to the unaided ear or are drown-out by other equipment noises. Using an ultrasonic detector, the analyst is able to isolate the frequency of sound being emitted by the bearing. Changes in these ultrasonic wave emissions are indicative of changes in equipment condition-some of these changes can be a precursor to component degradation and failure.

• Vibration analyzer – The rotational motion within electric motors generates distinct patterns and levels of vibration. Using a vibration analyzer and signature analysis software, the analyst can discern the vibration amplitude of the point on the motor being monitored. This amplitude is then compared with trended readings. Changes in these readings are indicative of changes in equipment condition.

• Other motor analysis – Motor faults or conditions including winding short-circuits, open coils, improper torque settings, as well as many mechanical problems can be diagnosed using a variety of motor analysis techniques. These techniques are usually very specialized to specific motor types and expected faults.

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Motors & Energy Saving (4)

6. Maintenance of Motors

Preventative and predictive maintenance programs for motors are effective practices in manufacturing plants. These maintenance procedures involve a sequence of steps plant personnel use to prolong motor life or foresee a motor failure. The technicians use a series of diagnostics such as motor temperature and motor vibration as key pieces of information in learning about the motors. One way a technician can use these diagnostics is to compare the vibration signature found in the motor with the failure mode to determine the cause of the failure. Often failures occur well before the expected design life span of the motor and studies have shown that mechanical failures are the prime cause of premature electrical failures. Preventative maintenance takes steps to improve motor performance and to extend its life. Common preventative tasks include routine lubrication, allowing adequate ventilation, and ensuring the motor is not undergoing any type of unbalanced voltage situation.

The goal of predictive maintenance programs is to reduce maintenance costs by detecting problems early, which allows for better maintenance planning and less unexpected failures. Predictive maintenance programs for motors observe the temperatures, vibrations, and other data to determine a time for an overhaul or replacement of the motor. Consult each motor’s instructions for maintenance guidelines. Motors are not all the same. Be careful not to think that what is good for one is good for all. For example, some motors require a periodic greasing of the bearings and some do not.

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Motors & Energy Saving (3)

4. Safety Issues

Electric motors are a major driving force in many industries. Their compact size and versatile application potentials make them a necessity. Motors are chosen many times because of the low vibration characteristics in driving equipment because of the potential extended life of the driven equipment. The higher rpm and small size of a motor will also make it a perfect fit for many applications.

Motors can be purchased for varying application areas such as for operating in a potentially gaseous or explosive area. When purchasing a motor, be sure to check the classification of the area, you may have a motor that does not meet the classification it is presently in! For example, a relatively new line of motors is being manufactured with special external coatings that resist the elements. These were developed because of the chemical plant setting in which highly corrosive atmospheres were deteriorating steel housings. They are, for the most part, the same motors but have an epoxy or equivalent coating.

5. Cost and Energy Efficiency

An electric motor performs efficiently only when it is maintained and used properly. Electric motor efficiencies vary with motor load; the efficiency of a constant speed motor decreases as motor load decreases. Below are some general guidelines for efficient operations of electric motors.
• Turn off unneeded motors – Locate motors that operate needlessly, even for a portion of the time they are on and turn them off. For example, there may be multiple HVAC circulation pumps operating when demand falls, cooling tower fans operating when target temperatures are met, ceiling fans on in unoccupied spaces, exhaust fans operating after ventilation needs are met, and escalators operating after closing.
• Reduce motor system usage – The efficiency of mechanical systems affects the run-time of motors. For example, reducing solar load on a building will reduce the amount of time the air handler motors would need to operate.
• Sizing motors is important – Do not assume an existing motor is properly sized for its load, especially when replacing motors. Many motors operate most efficiently at 75% to 85% of full load rating. Under-sizing or over-sizing reduces efficiency. For large motors, facility managers may want to seek professional help in determining the proper sizes and actual loadings
of existing motors. There are several ways to estimate actual motor loading: the kilowatt technique, the amperage ratio technique, and the less reliable slip technique. All three are supported in the Motor Master Plus software.
• Replacement of motors versus rewinding – Instead of rewinding small motors, consider replacement with an energy-efficient version. For larger motors, if motor rewinding offers the lowest life-cycle cost, select a rewind facility with high quality standards to ensure that motor efficiency is not adversely affected. For sizes of 10 hp or less, new motors are generally cheaper than rewinding. Most standard efficiency motors under 100 hp will be cost-effective to scrap when they fail, provided they have sufficient runtime and are replaced with energyefficient models.

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Motors & Energy Saving (2)

3. Key Components

3.1 DC Motor

• Field pole – The purpose of this component is to create a steady magnetic field in the motor. or the case of a small DC motor, a permanent magnet, field magnet, composes the field structure. However, for larger or more complex motors, one or more electromagnets, which receive electricity from an outside power source, is/are the field structure.

• Armature – When current goes through the armature, it becomes an electromagnet. The armature, cylindrical in shape, is linked to a drive shaft in order to drive the load. For the case of a small DC motor, the armature rotates in the magnetic field established by the poles, until the north and south poles of the magnets change location with respect to the armature. Once this happens, the current is reversed to switch the south and north poles of the armature.
• Commutator – This component is found mainly in DC motors. Its purpose is to overturn the direction of the electric current in the armature. The commutator also aids in the transmission of current between the armature and the power source.

3.2 AC Motor

• Rotor
- Induction motor – Two types of rotors are used in induction motors: squirrelcage rotor and wound rotor. A squirrel-cage rotor consists of thick conducting bars embedded in parallel slots. These bars are short-circuited at both ends by means of short-circuiting rings. A wound rotor has three-phase, double-layer, distributed winding. It is wound for as many poles as the stator. The three phases are wyed internally and the other ends are connected to slip-rings mounted on a shaft with brushes resting on them.
- Synchronous motor – The main difference between the synchronous motor and the induction motor is that the rotor of the synchronous motor travels at the same speed as the rotating magnetic field. This is possible because the magnetic field of the rotor is no longer induced. The rotor either has permanent magnets or DC-excited currents, which are forced to lock into a certain position when confronted with another magnetic field.

• Stator
- Induction motor – The stator is made up of a number of stampings with slots to carry threephase windings. It is wound for a definite number of poles. The windings are geometrically spaced 120 degrees apart.
- Synchronous motor – The stator produces a rotating magnetic field that is proportional to the frequency supplied.

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Motors & Energy Saving (1)

1. Introduction

Motor systems consume about 70% of all the electric energy used in the manufacturing sector of the United States. To date, most public and private programs to improve motor system energy efficiency have focused on the motor component. This is primarily due to the complexity associated with motor-driven equipment and the system as a whole. The electric motor itself, however, is only the core component of a much broader system of electrical and mechanical equipment that provides a service (e.g., refrigeration, compression, or fluid movement).

Numerous studies have shown that opportunities for efficiency improvement and performance optimization are actually much greater in the other components of the system-the controller, the mechanical system coupling, the driven equipment, and the interaction with the process operation. Despite these significant system-level opportunities, most efficiency improvement activities or programs have focused on the motor component or other individual components (Nadel et al. 2001).

2. Types of Motors

2.1 DC Motors

Direct-current (DC) motors are often used in variable speed applications. The DC motor can be designed to run at any speed within the limits imposed by centrifugal forces and commutation considerations. Many machine tools also use DC motors because of the ease with which speed can be adjusted. All DC motors, other than the relatively small brushless types, use a commutator assembly on the rotor. This requires periodic maintenance and is partly responsible for the added cost of a DC motor when compared to an alternate-current (AC) squirrel-cage induction motor of the same power. The speed adjustment flexibility often justifies the extra cost.

2.2 AC Motors

As in the DC motor case, an AC motor has a current passed through the coil, generating a torque on the coil. The design of an AC motor is considerably more involved than the design of a DC motor. The magnetic field is produced by an electromagnet powered by the same AC voltage as the motor coil. The coils that produce the magnetic field are traditionally called the “field coils” while the coils and the solid core that rotates is called the “armature.”
• Induction motor – The induction motor is a three-phase AC motor and is the most widely used machine. Its characteristic features are:
- Simple and rugged construction.
- Low cost and minimum maintenance.
- High reliability and sufficiently high efficiency.
- Needs no extra starting motor and need not be synchronized.
An induction motor operates on the principle of induction. The rotor receives power due to induction from stator rather than direct conduction of electrical power. When a three-phase voltage is applied to the stator winding, a rotating magnetic field of constant magnitude is produced. This rotating field is produced by the contributions of space-displaced phase windings carrying appropriate time displaced currents. The rotating field induces an electromotive force (emf).
• Synchronous motor – The most obvious characteristic of a synchronous motor is its strict synchronism with the power line frequency. The reason the industrial user is likely to prefer a synchronous motor is its higher efficiency and the opportunity for the user to adjust the motor’s power factor. A specially designed motor controller performs these operations in the proper sequence and at the proper times during the starting process.

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Fans (5) - Finish

9. Fans Checklist





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Fans (4)

8. Case Studies

Blower for an Industrial Application
The operation of a centrifugal fan by damper control is energy inefficient as part of the energy supplied to the fan is lost across damper. The damper control has to be minimized by suitably optimizing the capacity of the fan to suit the requirement. One of the best methods to optimize the capacity of the fan is by reducing the rpm of the fan and operate the blower with more damper opening.


Previous Status. An air blower was operated with 30% damper opening. The blower was belt driven. The pressure required for the process was 0.0853 psi. The pressure rise of the blower was 0.1423 psi and the pressure drop across the damper was 0.0569 psi. This indicates an excess capacity/static head available in the blower.

Energy Saving Project. The rpm of the blower was reduced by 20% by suitably changing the pulley. After the reduction in rpm, the damper was operated with 60% to 70% opening. The replacement of the pulley was taken up during a non-working day. No difficulties were encountered on implementation of the project.

Financial Analysis. The reduction in rpm of the blower and minimizing the damper control resulted in reduction of power consumption by 1.2 kW. The implementation of this project resulted in an annual savings of approximately $720. The investment made was approximately $210, which was paid back in under 4 months (Confederation of Indian Industry 2001).

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Fans (3)

6. Maintenance of Fans

Typically, fans provide years of trouble-free operation with relatively minimal maintenance. However, this high reliability can lead to a false sense of security resulting in maintenance neglect and eventual failure. Due to their prominence within HVAC and other process systems (without the fan operating, the system shuts down), fans need to remain high on the maintenance activity list.

Most fan maintenance activities center on cleaning housings and fan blades, lubricating and checking seals, adjusting belts, checking bearings and structural members, and tracking vibration.

7. Diagnostic Tools

• Ultrasonic analyzer – Air moving systems emit very distinct sound patterns around bearings and fan blades. In most cases, these sounds are not audible to the unaided ear or are drown-out by other equipment noises. Using an ultrasonic detector, the analyst is able to isolate the frequency of sound being emitted by the bearing or blades. Changes in these ultrasonic wave emissions are indicative of changes in equipment condition-some of these changes can be a precursor to component degradation and failure.
• Vibration analyzer – Within air moving systems, there are many moving parts, most in rotational motion. These parts generate a distinct pattern and level of vibration. Using a vibration analyzer and signature analysis software, the analyst can discern the vibration amplitude of the point on the equipment being monitored. This amplitude is then compared with trended readings. Changes in these readings are indicative of changes in equipment condition.

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Fans (2)

3. Key Components

• Impeller or rotor – A series of radial blades are attached to a hub. The assembly of the hub and blades is called impeller or rotor. As the impeller rotates, it creates a pressure difference and causes airflow.

• Motor – It drives the blades so they may turn. It may be direct drive with the wheel mounted on the motor shaft or belt driven with the wheel mounted on its own shaft and bearings. It is important to note that fans may also be driven by other sources of motive power such as an internal combustion engine, or steam or gas turbine.
• Housing – Encloses and protects the motor and impeller.

4. Safety Issues

Continuously moving fresh, uncontaminated air through a confined space is the most effective means of controlling an atmospheric hazard. Ventilation dilutes and displaces air contaminants, assures that an adequate oxygen supply is maintained during entry, and exhausts contaminants created by entry activities such as welding, oxygen-fuel cutting, or abrasive blasting (North Carolina State University 2001).

5. Cost and Energy Efficiency

In certain situations, fans can provide an effective alternative to costly air conditioning. Fans cool people by circulating or ventilating air. Circulating air speeds up the evaporation of perspiration from the skin so we feel cooler. Ventilating replaces hot, stuffy, indoor air with cooler, fresh, outdoor air. Research shows moving air with a fan has the same affect on personal comfort as lowering the temperature by over 5˚F. This happens because air movement created by the fan speeds up the rate at which our body loses heat, so we feel cooler. Opening and closing windows or doors helps the fan move indoor air outside and outdoor air inside, increasing the efficiency of the fan. When it is hot outside, close windows and doors to the outside. In the morning or evening, when outdoor air is cooler, place the fan in front of a window or door and open windows on the opposite side of the room. This draws cooler air through the living area (EPCOR 2001).
In many applications, fan control represents a significant opportunity for increased efficiency and
reduced cost. A simple and low-cost means of flow control relies on dampers, either before or after the fan. Dampers add resistance to accomplish reduced flow, while increasing pressure. This increased pressure results in increased energy use for the flow level required. Alternatives to damper flow control methods include physical reductions in fan speed though the use of belts and pulleys or variable speed controllers.

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Fans (1)

1. Introduction

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) defines a fan as an “air pump that creates a pressure difference and causes airflow. The impeller does the work on the air, imparting to it both static and kinetic energy, varying proportion depending on the fan type” (ASHRAE 1992).


2. Types of Fans (Bodman and Shelton 1995)

The two general types of fans are axial-flow and centrifugal. With axial-flow fans, the air passes through the fan parallel to the drive shaft. With centrifugal fans, the air makes a right angle turn from the fan inlet to outlet.

2.1 Axial Fan
Axial-flow fans can be subdivided based on construction and performance characteristics.
• Propeller fan – The basic design of propeller fans enhances maintenance to remove dust and dirt accumulations. The fan normally consists of a “flat” frame or housing for mounting, a propellershaped blade, and a drive motor. It may be direct drive with the wheel mounted on the motor shaft or belt driven with the wheel mounted on its own shaft and bearings.
• Tube-axial fans – A tube-axial fan consists of a tube-shaped housing, a propeller-shaped blade, and a drive motor. Vane-axial fans are a variation of tube-axial fans, and are similar in design and application. The major difference is that air straightening vanes are added either in front of or behind the blades. This results in a slightly more efficient fan, capable of somewhat greater static pressures and airflow rates.
2.2 Centrifugal Fans
Often called “squirrel cage” fans, centrifugal fans have an entirely different design (Figure 5). These fans operate on the principle of “throwing” air away from the blade tips. The blades can be forward curved, straight, or backward curved. Centrifugal fans with backward curved blades are generally more efficient than the other two blade configurations. This design is most often used for aeration applications where high airflow rates and high static pressures are required. Centrifugal fans with forward curved blades have somewhat lower static pressure capabilities but tend to be quieter than the other blade designs. Furnace fans typically use a forward curved blade. An advantage of the straight blade design is that with proper design it can be used to handle dirty air or convey materials.

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Cost and Energy Efficiency

1. Efficiency, Safety, and Life of the Equipment

It is impossible to change the efficiency without changing the safety of the operation and the resultant life of the equipment, which in turn affects maintenance cost. An example to illustrate this relation between efficiency, safety, and life of the equipment is shown in the figure below.

The temperature distribution in an efficient-operated boiler is shown as the solid line. If fouling develops on the waterside due to poor water quality control, it will result in a temperature increase of the hot gases on the fireside as shown by the dashed line. This fouling will result in an increase in stack temperature, thus decreasing the efficiency of the boiler. A metal failure will also change the life of the boiler, since fouling material will allow corrosion to occur, leading to increased maintenance cost and decreased equipment reliability and safety.

2. Results Best Practices

In a study conducted by the Boiler Efficiency Institute in Auburn, Alabama, researchers have developed eleven ways to improve boiler efficiency with important reasons behind each action.

• Reduce excess air – Excess air means there is more air for combustion than is required. The extra air is heated up and thrown away. The most important parameter affecting combustion efficiency is the air/fuel ratio.
- Symptom – The oxygen in the air that is not used for combustion is discharged in the flue gas, therefore, a simple measurement of oxygen level in the exhaust gas tells us how much air is being used. Note: It is worth mentioning the other side of the spectrum. The so called “deficient air” must be avoided as well because (1) it decreases efficiency, (2) allows deposit of soot on the fire side, and (3) the flue gases are potentially explosive.
- Action Required – Determine the combustion efficiency using dedicated or portable combustion analysis equipment. Adjustments for better burning
• Cleaning

• Swirl at burner inlet
• New tips/orifices

• Atomizing pressure
• Damper repair

• Fuel temperature
• Control repair

• Burner position
• Refractory repair

• Bed thickness
• Fuel pressure

• Ratio under/overfire air
• Furnace pressure

• Undergrate air distribution.

• Install waste heat recovery – The magnitude of the stack loss for boilers without recovery is about 18% on gas-fired and about 12% for oil- and coal-fired boilers. A major problem with heat recovery in flue gas is corrosion. If flue gas is cooled, drops of acid condense at the acid dew temperature. As the temperature of the flue gas is dropped further, the water dew point is reached at which water condenses. The water mixes with the acid and reduces the severity of the corrosion problem.
- Symptom – Flue gas temperature is the indicator that determines whether an economizer or air heater is needed. It must be remembered that many factors cause high flue gas temperature
(i.e., fouled waterside or fireside surfaces, excess air, etc.).
- Action Required - If flue gas temperature exceeds minimum allowable temperature by 50˚F or
more, a conventional economizer may be economically feasible. An unconventional recovery device should be considered if the low-temperature waste heat saved can be utilized in heating water or air. Cautionary Note: A high flue gas temperature may be a sign of poor heat transfer resulting from scale or soot deposits. Boilers should be cleaned and tuned before considering the
installation of a waste heat recovery system.

• Reduce scale and soot deposits – Scale or deposits serve as an insulator, resulting in more heat from the flame going up the stack rather than to the water due to these deposits. Any scale formation has a tremendous potential to decrease the heat transfer.
- Symptom – The best indirect indicator for scale or deposit build-up is the flue gas temperature. If at the same load and excess air the flue gas temperature rises with time, the effect is probably due to scale or deposits.
- Action Required – Soot is caused primarily by incomplete combustion. This is probably due to deficient air, a fouled burner, a defective burner, etc. Adjust excess air. Make repairs as necessary to eliminate smoke and carbon monoxide.
Scale formation is due to poor water quality. First, the water must be soft as it enters the boiler. Sufficient chemical must be fed in the boiler to control hardness.

• Reduce blowdown – Blowdown results in the energy in the hot water being lost to the sewer
unless energy recovery equipment is used. There are two types of blowdowns. Mud blow is designed to remove the heavy sludge that accumulates at the bottom of the boiler. Continuous or
skimming blow is designed to remove light solids that are dissolved in the water.
- Symptom – Observe the closeness of the various water quality parameters to the tolerances stipulated for the boiler per manufacturer specifications and check a sample of mud blowdown to ensure blowdown is only used for that purpose. Check the water quality in the boiler using standards chemical tests.
- Action Required – Conduct proper pre-treatment of the water by ensuring makeup is softened. Perform a “mud test” each time a mud blowdown is executed to reduce it to a minimum. A test should be conducted to see how high total dissolved solids (TDS) in the boiler can be carried without carryover.

• Recover waste heat from blowdown – Blowdown contains energy, which can be captured by a waste heat recovery system.
- Symptom and Action Required – Any boiler with a significant makeup (say 5%) is a candidate for blowdown waste heat recovery.

• Stop dynamic operation on applicable boilers
- Symptom – Any boiler which either stays off a significant amount of time or continuously varies in firing rate can be changed to improve efficiency.
- Action Required – For boilers which operate on and off, it may be possible to reduce the firing rate by changing burner tips. Another point to consider is whether more boilers are being used than necessary.

• Reduce line pressure – Line pressure sets the steam temperature for saturated steam.
- Symptom and Action Required – Any steam line that is being operated at a pressure higher than the process requirements offers a potential to save energy by reducing steam line pressure to a minimum required pressure determined by engineering studies of the systems for different seasons of the year.

• Cogenerate – This refers to correct utilization of steam pressure. A boiler provides steam to a
turbine, which in turn, is coupled to an electric generator. In this process, all steam exhaust from
the turbine must be fully utilized in a process requirement.

• Operate boilers at peak efficiency – Plants having two or more boilers can save energy by load management such that each boiler is operated to obtain combined peak efficiency.
- Symptom and Action Required – Improved efficiency can be obtained by proper load selection, if operators determine firing schedule by those boilers, which operate “smoothly.”

• Preheat combustion air – Since the boiler and stack release heat, which rises to the top of the boiler room, the air ducts can be arranged so the boiler is able to draw the hot air down back to the boiler.
- Symptom – Measure vertical temperature in the boiler room to indicate magnitude of stratification of the air.
- Action Required – Modify the air circulation so the boiler intake for outside air is able to draw
from the top of the boiler room.

• Switch from steam to air atomization – The energy to produce the air is a tiny fraction of the energy in the fuel, while the energy in the steam is usually 1% or more of the energy in the fuel.
- Symptom – Any steam-atomized burner is a candidate for retrofit.
- Action Required – Check economics to see if satisfactory return on investment is available.

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