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9. Fans Checklist

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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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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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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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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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5. Case Studies

IR Diagnostics of Pump
A facility was having continual problems with some to its motor and pump combinations. Pump bearings repeatedly failed. An IR inspection confirmed that the lower thrust bearing was warmer than the other bearing in the pump.

Further investigation revealed that the motor-pump combination was designed to operate in the horizontal position. In order to save floor space, the pump was mounted vertically below the motor. As a result, the lower thrust bearing was overloaded leading to premature failure. The failures resulted in a $15,000 repair cost, not including lost production time ($30,000 per minute production loss and in excess of $600 per minute labor).

IR Diagnostics of Steam Traps
Steam trap failure detection can be difficult by other forms of detection in many hard to reach and inconvenient places. Without a good trap maintenance program, it can be expected that 15% to 60% of a facility’s traps will be failed open. At $3/1,000 lb (very conservative), a 1/4-in. orifice trap failed open will cost approximately $7,800 per year. If the system had 100 traps and 20% were failed, the loss would be in excess of $156,000. An oil refinery identified 14% of its traps were malfunctioning and realized a savings of $600,000 a year after repair.

IR Diagnostics of Roof
A state agency in the northeast operated a facility with a 360,000 square foot roof area. The roof was over 22 years old and experiencing several leaks. Cost estimates to replace the roof ranged between $2.5 and $3 million. An initial IR inspection identified 1,208 square feet of roof requiring replacement at a total cost of $20,705. The following year another IR inspection was performed that found 1,399 square feet of roof requiring replacement at a cost of $18,217. A roof IR inspection program was started and the roof surveyed each year. The survey resulted in less than 200 square feet of roof identified needing replacement in any one of the following 4 years (one year results were as low as 30 square feet). The total cost for roof repair and upkeep for the 6 years was less than $60,000.
If the facility would have been privately owned, interest on the initial $3 million at 10% would have amounted to $300,000 for the first year alone. Discounting interest on $3 million over the 5-year period, simple savings resulting from survey and repair versus initial replacement cost ($3 million to $60,000) amount to $2,940,000. This figure does not take into account interest on the $3 million, which would result in savings in excess of another $500,000 to $800,000, depending on loan interest paid.

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4. Equipment Cost/Payback

As indicated earlier, the cost of thermography equipment varies widely depending on the capabilities of the equipment. A simple spot radiometer can cost from $500 to $2,500. An IR imager without radiometric capability can range from $7,000 to $20,000. A camera with full functionality can cost from $18,000 to $65,000.

Besides the camera hardware, other program costs are involved. Computer hardware, personnel training, manpower, etc., needs to be accounted for in the budget.
Below is a listing of equipment and program needs recommended by a company recognized as a leader in the world of IR program development:
• Level I thermographic training
• Level II thermographic training
• Ongoing professional development
• IR camera and accessories
• Report software
• Laptop computer
• Color printer
• Digital visual camera
• Personal Protective Equipment (PPE) for arc flash protection

Payback can vary widely depending on the type of facility and use of the equipment. A production facility whose downtime equates to several thousands of dollars per hour can realize savings much faster than a small facility with minimal roof area, electrical distribution network, etc. On the average, a facility can expect a payback in 12 months or less. A small facility may consider using the services of an IR survey contractor. Such services are widely available and costs range from $600 to $1,200 per day. Contracted services are generally the most cost-effective approach for smaller, less maintenance-intensive facilities.

to be continued….

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3.3 Roof Thermography

Out of sight, out of mind. This old adage is particularly true when it applies to flat roof maintenance. We generally forget about the roof until it leaks on our computers, switchgear, tables, etc. Roof replacement can be very expensive and at a standard industrial complex easily run into the hundreds of thousands of dollars.

Depending on construction, length of time the roof has leaked, etc., actual building structural components can be damaged from inleakage and years of neglect that drive up repair cost further. Utilization of thermography to detect loss of a flat roof’s membrane integrity is an application that can provide substantial return by minimizing area of repair/replacement. Roof reconditioning cost can be expected to run less than half of new roof cost per square foot. Add to this the savings to be gained from reconditioning a small percentage of the total roof surface, instead of replacement of the total roof, and the savings can easily pay for roof surveys and occasional repair for the life of the building with change left over.

to be continued……..

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3.2 Mechanical System Applications

Rotating equipment applications are only a small subset of the possible areas where thermography can be used in a mechanical predictive maintenance program. In addition to the ability to detect problems associated with bearing failure, alignment, balance, and looseness, thermography can be used to define many temperature profiles indicative of equipment operational faults or failure.

The following list provides a few application examples and is not all inclusive:
• Steam Systems
– Boilers
• Refractory
• Tubes
– Traps
– Valves
– Lines
• Heaters and furnaces
– Refractory inspections
– Tube restrictions
• Fluids
– Vessel levels
– Pipeline blockages
• Environmental
– Water discharge patterns
– Air discharge patterns
• Motors and rotating equipment
– Bearings
• Mechanical failure
• Improper lubrication
– Coupling and alignment problems
– Electrical connections on motors
– Air cooling of motors

to be continued……….

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3. System Applications

3.1 Electrical System Applications
The primary value of thermographic inspections of electrical systems is locating problems so that they can be diagnosed and repaired. “How hot is it?” is usually of far less importance. Once the problem is located, thermography and other test methods, as well as experience and common sense, are used to diagnose the nature of the problem.

The following list contains just a few of the possible electrical system-related survey applications:

• Transmission lines
– Splices
– Shoes/end bells

• Inductive heating problems
– Insulators

• Cracked or damaged/tracking

• Distribution lines/systems
– Splices
– Line clamps
– Disconnects
– Oil switches/breakers
– Capacitors
– Pole-mounted transformers
– Lightning arrestors
– Imbalances

• Substations
– Disconnects, cutouts, air switches
– Oil-filled switches/breakers (external and internal faults)
– Capacitors
– Transformers

• Internal problems

• Bushings

• Oil levels

• Cooling tubes

• Lightning arrestors
– Bus connections

• Generator Facilities
– Generator

• Bearings

• Brushes

• Windings

• Coolant/oil lines: blockage
– Motors

• Connections

• Bearings

• Winding/cooling patterns

• Motor Control Center

• Imbalances

• In-Plant Electrical Systems
– Switchgear
– Motor Control Center
– Bus
– Cable trays
– Batteries and charging circuits
– Power/Lighting distribution panels