Trane TRG-TRC013-EN - Manuals

TRG-TRC013-EN iii Contents Introduction ........................................................... 1 period one Fan Performance .................................................. 2 Fan Performance Curves ....................................... 11 System Resistance Curve ...............................

TRG-TRC013-EN 1 notes Introduction Efficient distribution of conditioned air needed to heat, cool, and ventilate a building requires the service of a properly selected and applied fan. The types of fans commonly used in HVAC applications include centrifugal and axial designs. In a centrifugal fan th...

2 TRG-TRC013-EN notes period one Fan Performance Compared to compressors, the pressures generated by these air-moving devices within the ductwork of HVAC systems are relatively small. The measurement of these pressures is, however, essential to the determination of fan performance. One instrument th...

TRG-TRC013-EN 3 period one Fan Performance notes When the pressure within the ductwork is positive, that is, greater than atmospheric, the water column is forced downward in the closed leg and forced upward in the open leg. Conversely, a negative pressure within the ductwork causes the water column ...

4 TRG-TRC013-EN notes period one Fan Performance Since some of the pressures observed in air conditioning systems are very small, the U-tube has been modified to improve the ability to read such small differences in water levels. The modification replaces one leg of the tube with a liquid reservoir ...

TRG-TRC013-EN 5 period one Fan Performance notes The total amount of pressure generated by a fan has two components: velocity pressure and static pressure. The velocity pressure is due to the momentum of the air as it moves axially through the duct, while the static pressure is due to the perpendicu...

8 TRG-TRC013-EN notes period one Fan Performance Another probe can be placed in the duct with its open end facing into the air stream. This probe senses total pressure — the combination of velocity pressure plus static pressure. Therefore, static pressure can be read directly, while velocity pressur...

TRG-TRC013-EN 9 period one Fan Performance notes The characteristics of a fan’s performance under various duct pressure conditions is tested by an apparatus similar to the one shown here. The fan is connected to a long piece of straight duct with a throttling device at the end. The throttling device...

10 TRG-TRC013-EN notes period one Fan Performance Next, the measured velocity pressure is used to calculate the airflow delivered by the fan. The manometer measures the velocity pressure (P v ) by subtracting static pressure (P s ) from total pressure (P t ). Next, the air velocity (V) can be calcul...

TRG-TRC013-EN 11 period one Fan Performance notes Fan Performance Curves This point can then be plotted on a chart that has static pressure on the vertical axis and airflow on the horizontal axis. Additional data from the fan tests establish other static pressure and corresponding airflow performanc...

12 TRG-TRC013-EN notes period one Fan Performance When a series of points is plotted, a curve can be drawn. The resulting curve graphically illustrates the performance of this fan when it is operated at a constant speed. Notice that the curve extends from blocked-tight static pressure, with a corres...

TRG-TRC013-EN 13 period one Fan Performance notes Next, the fan laws are used to calculate the performance characteristics of this same fan at other rotational speeds. The subscript 1 refers to the tested performance conditions; the subscript 2 refers to the calculated performance conditions. The re...

14 TRG-TRC013-EN notes period one Fan Performance Finally, using the measurements from the dynamometer and the fan laws, curves can be calculated and plotted to represent the fan’s power consumption at each operating condition. When most fans approach the blocked-tight static-pressure condition, ins...

TRG-TRC013-EN 15 period one Fan Performance notes A surge line is established during the fan test procedure to indicate the area on a fan performance curve where surge occurs. As long as the fan’s operating point falls to the right of this line, the fan will operate in a stable manner. If the fan is...

16 TRG-TRC013-EN notes period one Fan Performance Fan manufacturers may present their performance data in graphical and/or tabular form. Similar to using the fan curve, by knowing the desired airflow and pressure-producing capability of the fan, the table can be used to determine the fan’s speed and...

TRG-TRC013-EN 17 period one Fan Performance notes System Resistance Curve Now that a typical fan performance curve has been developed, let’s see how the fan will perform within a system. With each airflow, an air distribution system imposes a certain resistance to the passage of air. The resistance ...

TRG-TRC013-EN 19 period one Fan Performance notes By plotting several such points, a curve can be established. This system resistance curve represents the static pressure that the fan must generate, at various airflows, to overcome the resistance — or static-pressure loss — within this particular sy...

20 TRG-TRC013-EN notes period one Fan Performance Consider a case where the air resistance through the system is greater than predicted. Instead of the design operating point A , the actual system resistance curve intersects the fan performance curve at B , delivering a lower airflow than intended. ...

TRG-TRC013-EN 21 period one Fan Performance notes Reducing the fan speed causes the system resistance and fan performance curves to intersect at E . The fan delivers the design airflow at a lower static pressure, with less power required. In these examples, it was possible to compensate for the inac...

TRG-TRC013-EN 23 period one Fan Performance notes In a constant-volume system, where the fan is always delivering the same airflow, the fan is generally selected to balance the airflow and static-pressure requirements at a point on the fan curve that permits a certain margin of safety before surge o...

24 TRG-TRC013-EN notes period one Fan Performance The fan performance curves discussed so far are typical of both the centrifugal and fixed-pitch vaneaxial fans. To complete the discussion, the fan performance curves of the variable-pitch vaneaxial (VPVA) fan will be reviewed. While this type of fan...

TRG-TRC013-EN 27 notes The most common types of fans used in air conditioning applications are the centrifugal and axial designs. In a centrifugal fan the airflow enters the center of the fan from the side and follows a radial path through the fan wheel. There are three principal types of centrifuga...

28 TRG-TRC013-EN notes period two Fan Types Forward Curved (FC) Fans The first of these centrifugal fan wheels to be considered has blades that are curved in the direction of wheel rotation. These are called forward curved , or FC, fans. FC fans are operated at relatively low speeds and are used to ...

30 TRG-TRC013-EN notes period two Fan Types Notice how the fan input-power lines cross the FC fan performance curves. If the system resistance were to drop, the actual system resistance curve would also drop, moving the operating point ( A ) to a higher airflow ( B ). At the same time, the fan’s inp...

TRG-TRC013-EN 33 period two Fan Types notes A variation of this type of fan, called the backward curved (BC) fan, uses a slight curve in the fan blades, away from the direction of rotation. The performance characteristics of the BC fan are similar to those of the BI fan. Airfoil (AF) Fans A refineme...

TRG-TRC013-EN 35 period two Fan Types notes Vaneaxial Fans In an axial fan, the airflow passes straight through the fan, parallel to the shaft. There are three common axial fan types: propeller, tubeaxial, and vaneaxial. Propeller fans are well suited for high volumes of air, but have little or no s...

38 TRG-TRC013-EN notes period two Fan Types The selection of the type of fan to be used in a particular application is based on the system size and space availability. The forward curved fan is best applied in small systems requiring 20,000 cfm [9.4 m 3 /s] or less and static pressures of 4 in. H 2 ...

TRG-TRC013-EN 39 notes period three Fan Capacity Control The previous discussions assumed that the fan would perform at a single operating point, located by the intersection of the system resistance and fan performance curves, in a constant-volume system. This type of system provides a constant volu...

40 TRG-TRC013-EN notes period three Fan Capacity Control This modulation causes the actual system resistance curve to shift. In a VAV system, therefore, the fan no longer operates at a single point on its performance curve but must operate over a range of such points. “Riding the Fan Curve” The simp...

TRG-TRC013-EN 41 period three Fan Capacity Control notes This method of fan modulation can be used with any type of fan. It is most effective, however, when applied to FC fans. The configuration of the input power curves of the FC fan are such that its power requirement drops as the fan operating po...

42 TRG-TRC013-EN notes period three Fan Capacity Control Because of this issue, and since many VAV systems are large with high static pressures, some form of system static-pressure control is generally used. A VAV system’s static-pressure requirement consists of a fixed component and a variable comp...

TRG-TRC013-EN 43 period three Fan Capacity Control notes An exaggerated example is used to illustrate this system operation. Assume that the load on the system decreases, causing all or some of the VAV terminal units to modulate closed. This causes the system resistance curve to shift upwards. In re...

44 TRG-TRC013-EN notes period three Fan Capacity Control There are four methods used to actively control the capacity of a fan. They are discharge dampers, inlet vanes, fan-speed control, and variable-pitch blade control. Discharge Dampers The first method to be discussed is the use of discharge dam...

46 TRG-TRC013-EN notes period three Fan Capacity Control Inlet Vanes The next method of capacity control, inlet vanes , modulates a fan’s capacity by “preswirling” the air in the direction of fan rotation before it enters the fan wheel. By changing the air’s angle of entry into the fan, the modulati...

TRG-TRC013-EN 49 period three Fan Capacity Control notes along the VAV system modulation curve and the fan satisfies the systemstatic-pressure controller. The low end of the fan’s modulation range is limited by the surge region. The principal advantages of fan-speed control are its energy saving pot...

TRG-TRC013-EN 51 period three Fan Capacity Control notes These curves describe the performance characteristics of various methods of fan capacity control, in terms of the input power required versus the percent of design airflow. Realize that these are generalized curves based on a given set of test...

52 TRG-TRC013-EN notes period four Application Considerations Several considerations must be addressed when applying fans in air conditioning systems, including: ■ System static-pressure control ■ System effect ■ Acoustics ■ Effect of actual (nonstandard) conditions on fan selection ■ Equipment cert...

TRG-TRC013-EN 53 period four Application Considerations notes System Static-Pressure Control Fan capacity control requires a signal from a controller, which monitors static pressure using a sensor located somewhere in the supply duct system. This controller compares the sensed pressure to a set poin...

54 TRG-TRC013-EN notes period four Application Considerations Another method of static-pressure control, the optimized static-pressure control method, positions a single static-pressure sensor near the fan outlet. The static-pressure controller dynamically adjusts the static-pressure set point based...

TRG-TRC013-EN 55 period four Application Considerations notes System Effect At the end of Period One, we discussed the effect of the air resistance through the system being greater than predicted. This is often caused by failing to allow for the effects of the fan connections to the duct system. Thi...

56 TRG-TRC013-EN notes period four Application Considerations the fan outlet, this system effect should be accounted for in the fan selection. If an elbow, turning vanes, air straightener, or other obstruction is located too close to the fan inlet, this system effect should also be accounted for in ...

TRG-TRC013-EN 57 period four Application Considerations notes An HVAC system can be made quieter by reducing the source (fan) sound level and/or increasing the attenuation of the path. In many cases, fan selection is very important to the final sound level. Smaller, higher-speed fans often create mo...

58 TRG-TRC013-EN notes period four Application Considerations Effect of Actual (Nonstandard) Conditions Most fan performance data is published at standard air conditions, which are basically sea level elevation and 70 °F [21 °C]. If the airflow requirement for a given application is stated at nonsta...

TRG-TRC013-EN 59 period four Application Considerations notes Equipment Certification Standards The Air Movement and Control Association (AMCA) establishes testing procedures and rating standards for air-moving devices. AMCA also certifies performance and labels equipment through programs that invol...

60 TRG-TRC013-EN notes Let’s review the main concepts that were covered in this clinic on air conditioning fans. Period One introduced the method of determining and plotting fan performance. It also discussed static pressure versus velocity pressure and the interaction of the fan and the system. Air...

TRG-TRC013-EN 61 period five Review notes Period Two introduced the various fan types, including forward curved (FC), backward inclined (BI), airfoil (AF), and vaneaxial. Period Three presented various methods for controlling fan capacity, including “riding the fan curve,” discharge dampers, inlet v...

62 TRG-TRC013-EN notes period five Review Period Four covered several considerations in the application of fans in air conditioning systems, including system static-pressure control, system effect, acoustics, the effect of actual (nonstandard) conditions on fan selection, and equipment certification...

64 TRG-TRC013-EN Questions for Period 1 1 The total pressure generated by the fan is made up of two components, __________ pressure and __________ pressure. 2 The total pressure (P t ) measured within a duct is 3.5 in. H 2 O [872 Pa] and the static pressure (P s ) is 3 in. H 2 O [747 Pa]. Assume the...

TRG-TRC013-EN 65 Quiz 6 Between the forward curved (FC) and backward inclined (BI) fans, which one can handle higher static-pressure applications? 7 Explain why the forward curved (FC) fan is called an overloading type of fan. Questions for Period 3 8 List three methods of fan capacity control. 9 Wh...

66 TRG-TRC013-EN 1 velocity pressure and static pressure 2 a P v = 0.5 in. H 2 O [125 Pa] b V = 2,832 fpm [14.4 m/s] c Airflow = 4,248 cfm [2 m 3 /s] 3 a airflow b static pressure c fan speed (rpm) d input power 4 surge 5 forward curved (FC), backward inclined (BI) or backward curved (BC), and airfo...

TRG-TRC013-EN 67 adjustable-frequency drive (AFD) See variable-speed drive. airfoil (AF) A type of centrifugal fan that is similar to the backward inclined fan, with the exception that the fan blades are in the shape of an airfoil, like an airplane wing. AMCA Air Movement and Control Association ARI...