ASHRAE 4673-2004 A Switched Reluctance Motor in a Variable-Speed Pumping Application《在变速泵应用中的开关磁阻电机》.pdf
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1、4673 A Switched Reluctance Motor in a Variable-Speed Pumping Application Horacio G. Vasquez, Ph.D. Student Member ASHRAE Joey K. Parker, Ph.D. Timothy A. Haskew ABSTRACT : A variable-speed pumping system based on a switched reluctance motor (SM) and a centrifugal pump was devel- oped, and it is inte
2、nded to be used in heat pump or similar applications. A ground-source heat pump (GSHP) uses a centrifugal pump to circulate water in an underground loop using water as a means to transfer heatfi-om theground to room air inside a building or vice versa. SRM. are appearing as alternative actuators in
3、many engineering applications because of their simple construction, reliability, and low manufacturing and maintenance costs. In general, an SM, its power convertel; and control strategy have to be adequately designed or selected and integrated in order for the entire system to operate efficiently a
4、nd satisfactorily. The special application ofan SMin thisproject was to drive a centrifugal pump required to operate efficiently at all speeds-in partic- ulal; at low and medium speeds. The SRM-based variable- speedpumping system was experimentally tested and demon- strated potential to save energy
5、in central system GSHP or similar applications. INTRODUCTION A central system GSHP consists of a pump, underground heat exchanger, supply and return pipes, and several air- handling units (AHUs), as shown in Figure 1. The under- ground piping system is used as a means to transfer heat from the room
6、air to the ground or vice-versa (Rafferty 1997). In some installations, additional loops and heat exchangers are installed to heat utility water. AHUs are turned on or off inde- pendently of each other, and a variable-speed drive (VSD) is required to maintain a setpoint differential pressure across
7、the AHUs and also to save energy and avoid unnecessarily high pressure and losses in the piping system. Otherwise, valves, which always waste energy, are used to regulate the water flow rate. In addition, to justify the use of a variable-speed drive for the pump, the friction losses in the rest of t
8、he piping system must be similar to or greater than the setpoint differential pres- sure across the AHUs when the pump is running at full speed. The justification of a variable-speed drive for the pump must also be based on the energy savings that can be achieved due to operation of the pump at spee
9、ds lower than full speed when the pumping system demand changes. This situation commonly occurs in central system GSHP systems; hence, a variable-speed pump is almost always required in such appli- cations. In general, a VSD motor pump system is designed to liRetum Figure 1 Central system ground-sou
10、rce heat pump. Horacio G. Vasquez is a lecturer at the University of Texas-Pan American, Edinburg, Tex. Joey K. Parker is an associate professor in the Department of Mechanical Engineering and Timothy A. Haskew is an associate professor in the Department of Electrical and Computer Engi- neering, Uni
11、versity of Alabama, Tuscaloosa, Ala. 02004 ASHRAE. 67 satis maximum heating and cooling loads in a GSHP appli- cation, but most of the time the system operates at low or medium loads due to reduced building occupancy andor favorable atmospheric conditions. It is ideal that the variable- speed drive,
12、 motor, and pump operate with high efficiency at low and medium speeds to maximize energy savings. The most common variable-speed drives (VSDs) used in heat pump and similar applications are the type called variable- frequency drives (VFD), used with conventional alternating- current induction motor
13、s (AC IMs). VFDs and AC IMs are characterized by having high efficiency when operating near their rated speed and load; however, their combined efficiency starts decreasing substantially at speeds below 50% of the motor rated speed (Bernier and Bourret 1999; Casada et al. 2000). When oversized IMs a
14、re selected, this efficiency draw- back becomes more significant (Henderson et al. 2000). Kavanaugh and McInerny (2001) determined that drive- motor-pump efficiency data are not widely available at low speeds and that additional research must be performed to establish variable-speed pump demand at l
15、ow loads and speeds. Kavanaugh and McInerny (2001) also concluded that more than 50% of annual energy consumption by the central system GSHP in a school facility occurs when the building is unoccupied and when the pump is operating at low speeds. Therefore, a more efficient, economical, and practica
16、l VSD- motor system alternative will provide important contributions toward the development of more efficient heat pumps and pumping systems that operate similarly. The main goal of this research was to determine the opportunities and benefits that switched reluctance motors (SRMs) could contribute
17、to solve this problem. Therefore, an SRM was modeled, simulated, implemented, controlled for variable speed, and experimen- tally tested, driving a centrifugal pump in a closed-loop piping system like that in a central system GSHP application. BACKGROUND Several studies have demonstrated that variab
18、le-speed drives save considerable energy when used in central system GSHPs. A few studies have demonstrated the use of SRMs to drive pumps at constant speed and at particular loads, as in a hydraulic system or in a fuel delivery system. Nevertheless, it was determined that there are not reported stu
19、dies of SRMs used in central system GSHP applications, where vanable- speed drives operating at high efficiency at low and medium speed for a long number of hours are required for the centrif- ugal pumps. Kavanaugh and McInerny (2001) addressed a study of pumping options for the air-conditioning sys
20、tem of a 72,000 fi2 (6689 m2) school facility using four ground-source heat pump (GSHP) arrangements. The heat pump options consisted of the following arrangements: (a) a decentralized system with multiple individual heat pumps throughout the building, (b) a central system with a variable-speed pump
21、, (c) a system with a constant-speed pump, and (d) a system with primary and secondary pumps. It was indicated that a well- designed ground loop does not require a high water flow rate to effectively transfer or absorb heat from the ground, which also implies operation with lower head losses. To det
22、ermine the number of hours that the pumps were required to operate for each of the heat pump arrangements, the piping loop was designed, the pumps were specified, and the pump demand based on building load was computed. Bin weather data were used with pump power demand to compute the annual energy c
23、onsumption. The decentralized system used circulator pumps running at constant speed and controlled using an odoff method; therefore, the energy consumption was computed based on the circulator rated power and the number of hours at work. For the central system, the energy consumption was more diffi
24、cult to determine, and a correlation between pump power consumption and water flow rate, power consumption at full load, and water flow rate at full load was determined. Such correlation was convenient because the relationship between building load and water flow rate was established. Consequently,
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