Fans and Blowers
Different types of fans used in air conditioning systems and are classified as a propeller tube-axial, vane-axial and centrifugal. Propeller and tube axial fans consist of a screw or a disc-type wheel mounted inside the ring or a plate and belt-driven or direct-drive motor.
Avane-axial fan consists of a disk-type wheels are mounted inside the cylinder. Dial-guide vanes is before or after the wheel and belt-driven or direct-drive. Centrifugal fan fan rotor, or wheel for scrolling type of housing. This fan type is better known as the cage units. Whenever possible, the fan wheel should be directly connected to the motor shaft. Where the fan speeds are critical, belt drive works, and the different size of the pulleys are used.
The various devices used to power air circulation in air conditioning applications are known as fans, blowers, mufflers, or screws. Different fan types can be classified with regard to their construction as follows:
Propeller fan, essentially consists of a screw or disc wheels in the mounting ring or plate and includes a driving mechanism supports either a belt or direct drive.
Tube axial fan consists of a screw or a disc-type wheel inside the cylinder and includes a driving mechanism supports or belt-driven or direct connection. Turntables-axial fan consists of a disk-type wheel inside a cylinder and a great number of air vanes, located before or after the wheel. It includes a driving mechanism supports or belt-driven or direct connection. Centrifugal fan consists of a rotor fan or a scroll wheel, type of building and includes a driving mechanism supports or belt-driven or direct connection. Fig. 3-28 shows the wiring diagrams.
The output of the fan can be defined in various ways, from the air per unit of time, full of pressure, static pressure, speed and power of the input signal is the most important. In the conditions of the National Association of Fan Manufacturers, are as follows:
The volume of processed fan number of cubic feet of air per minute
expressed as a fan output conditions.
Fan total pressure rise from the pressure of the fan inlet opening of the fan.
Speed fan pressure pressure corresponding to the determination of the average speed of the volume of air flow at the outlet of the fan area.
Static pressure fan total pressure decreases fanvelocity pressure.
Fan capacity, expressed in horsepower and is based on fan volume and fan total pressure.
Fan capacity, expressed in horsepower and is measured in horsepower delivered to the fan shaft.
Mechanical efficiency of the fan ratio of output power to the power consumption.
Static fan efficiency of mechanical efficiency, multiplied by the coefficient of static pressure total pressure.
Fan output plot is situated within the area of the fan outlet.
Fan inlet area is inside the entrance collar.
Resistance Losses in HVAC Duct Systems
In General, we can say that the duct size and depth of the channel, in particular, touched upon the available space in the building. For this reason, although circular ducts is the most economical form in terms of friction per unit area and from the point of view of the metal required for the construction of the unit of area is rarely, except for industrial buildings, use round air ducts to a large extent. Rectangular duct is the preferred form among those rectangular section. Supply restrictions usually require to be flat duct.
To illustrate the use of the graph design of the pipeline system, look at the Example below.
3-2 Assume systems that require delivery 5000 ft3/min Distribution requirement movement of the entire volume of approximately 80 feet, with the longest branch beyond that point transportation of 1,000 ft3/min for additional 70 feet. We further assume that the operating specifications of the fan and coil resistance, filters and so on, share the feed channel resistance 0.10. water-gage pressure resistance. Supply duct no more than 12 century deeply.
solution the total length of the longest run is 80 + 70 = 150 metres:
100/150 =0.10=0.067 in.water gage
Starting with this resistance in the lower part of Fig. 3-27, follow up from the horizontal line representing 5000 ft3/min In this time of reading the equivalent size of a round duct is required, about 28. in diameter. Move diagonally, up, right, on 28-century-line diameter, and then horizontally on this line in Fig. 3-27 to a vertical line representing 12. side of a rectangular duct. At this moment reading 60. the width of the rectangular duct required at the intersection of the curve.
Thus, for the main duct, the size of the pipeline will amount to 60 G 12 century For the branch of transportation of 1,000 ft3/min, to the point in which 0.067. a resistance line crosses the 1000-ft3/min line, read the 16th century equivalent of the round duct is required. Below in Fig. 3-27 for large duct, read 12 G the 18th century as the size of the branch duct.
Duct passes consider the number of bends and offsets. Obstacles of this kind are usually presented in the equivalent length of straight duct is required for the production of the same values of the resistance. Where conditions require a sharp corner or bends, vane elbows, consisting of a series of curved air vents across the air flow must be used.
Fig. 3-27 A graphical representation of the duct areas.
For the sake of convenience, this section provides a simplified duct size of the order, which excludes ordinary complicated engineering calculations, necessary for the design of the pipeline system. Cm. Fig. 3-23 to 3-25, which show the plans of the typical family residence, having a total cubic content of about 19 000 ft3. It is desirable to provide hydration, ventilation, filtration and air movement in all of the rooms on the first and second floors.
Air-conditioning, as shown in Fig. 3-23 was just vent. capacity of 1,000 ft3/min If the rooms have individual air network, table 3-3 shows the methods for calculating the volume of air fed into each room.
The second column in the table is the ability of a separate premise, as a percentage of the total. For example, 3000 ft3 30 percent of the total area (from 10 000 ft3), to which the air network will. The third column indicates cubic feet of air per minute, be provided with separate rooms. These indicators are achieved in the following way. Air conditioning processing 1,000 ft3 per minute of air; 30 percent of the 300 ft3/min Similarly, 10% is 100 ft3/min, which would indicate the amount of air supplied to the living room and the house в„– 3, respectively. Having, thus, the amount of air to be delivered to each of the rooms, design ducts can now be considered.
For duct size, consider the branch duct in both the living room and the house в„– 1 (see Table 3-3). Please note, that the branch leading to the house в„– 1 processes 150 ft3/min Channel living processes 300 ft3/min Obvious connection air line will process 300 + 150 or 450, ft3/min, in accordance with the foregoing recommendations to the speed of 600 m/min for branches and 700 m/min supply air the main thing. Therefore, it is necessary duct areas can be calculated using the following formula:
The rest of the ducts can be calculated similarly. Recommended main supply air outlet of the unit to be the same size as the outlet of the unit up to the first branch of take-off. Return of the main unit, you should run the same size as the input unit (at a distance of about 24 C. It must be supplied with a large door at the bottom of the length of the full size of the duct. Fig. 3-26 useful as a further simplification in the definition of air ducts.
Example It is desirable that the size of the main duct for 250 ft3/min, in 500 m/min speed. That the cross-sectional area required?
solution Find 250 ft3/min on the left side (Fig. 3-26. With a ruler or straightedge, transfer line horizontally 500 line speed and read on the base line 72 in.2, or 1/2 m2, the area required. All branches, struts, or grilles can be picked up the same way.