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Electrical Energy Equipment: Fans and Blowers

FANS AND BLOWERS
1. INTRODUCTION ................................................................................ 1 2. TYPE OF FANS AND BLOWERS..................................................... 6 3. ASSESSMENT OF FANS AND BLOWERS ................................... 10 4. ENERGY EFFICIENCY OPPORTUNITIES ................................. 13 5.OPTION CHECKLIST ..................................................................... 18 6. WORKSHEETS ................................................................................. 19 7. REFERENCES ................................................................................... 21

1. INTRODUCTION
This section describes the main features of fans and blowers. 1.1 What are fans and blowers?Most manufacturing plants use fans and blowers for ventilation and for industrial processes that need an air flow. Fan systems are essential to keep manufacturing processes working, and consist of a fan, an electric motor, a drive system, ducts or piping, flow control devices, and air conditioning equipment (filters, cooling coils, heat exchangers, etc.). An example system is illustrated inFigure 1. The US Department of Energy estimates that 15 percent of electricity in the US manufacturing industry is used by motors. Similarly, in the commercial sector, electricity needed to operate fan motors composes a large portion of the energy costs for space conditioning (US DOE, 1989). Fans, blowers and compressors are differentiated by the method used to move the air, and by the system pressurethey must operate against. The American Society of Mechanical Engineers (ASME) uses the specific ratio, which is the ratio of the discharge pressure over the suction pressure, to define fans, blowers and compressors (see Table 1). Table 1: Difference between Fans, Blowers and Compressors (Ganasean) Equipment Specific Ratio Pressure rise (mmWg) Fans up to 1.11 1136 Blowers 1.11 to 1.20 1136 –2066Compressors more than 1.20 -

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Electrical Energy Equipment: Fans and Blowers

Figure 1: Typical Fan System Components (US DOE, 1989)

1.2 Important terms and definitions
Before types of fans and blowers are described it is important to first understand terms and definitions.1 1.2.1 Systemcharacteristics The term “system resistance” is used when referring to the static pressure. The system resistance is the sum of static pressure losses in the system. The system resistance is a function of the configuration of ducts, pickups, elbows and the pressure drops across equipment, for example bag filter or cyclone. The system resistance varies with the square of the volume of air flowingthrough the system. For a given volume of air, the fan in a system with narrow ducts and multiple short radius elbows is going to have to work harder to overcome a greater system resistance than it would in a system with larger ducts and a minimum number of long radius turns. Long narrow ducts with many bends and twists will require more energy to pull the air through them. Consequently, for a given fanspeed, the fan will be able to pull less air through this system than through a short system with no elbows. Thus, the system resistance increases substantially as the volume of air flowing through the system increases; square of air flow. Conversely, resistance decreases as flow decreases. To determine what volume the fan will produce, it is therefore necessary to know the system resistancecharacteristics. In existing systems, the system resistance can be measured. In systems that have been designed, but not built, the system resistance must be calculated. Typically a system resistance curve (see
1 Except for Figure 2, Section 1.2 is taken (with edits) from Energy Efficiency Guide Book (2004), Chapter 5, p 93-112, with permission from the Bureau of Energy Efficiency, Government of...