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Motor Efficiency in Ground Source Heat Pump System
High Efficiency Motor Question
According to the working efficiency of the motor, there are two kinds of motors used in ground source heat pump system: standard efficiency motor and high efficiency motor. Compared with standard efficiency motors, the efficiency of high efficiency motors can be increased by 2 to 10 percentage points according to the different power. High efficiency motors are realized by better design and use of special materials that can reduce losses, but the price is about 10%~30% higher than standard efficiency motors, so only one fifth of the Motors sold worldwide are high efficiency motors. Motor efficiency is the ratio of mechanical power output to power input, usually expressed as a percentage. Figure 1 shows the difference between standard motor and high efficiency motor. High efficiency motor produced by improved design materials and technology can generate more power per unit power consumption.
Usually, high efficiency motors have high load coefficient, better insulation and voltage withstand, low calorific value and less vibration, thus increasing reliability. High efficiency motors must have a full load efficiency equal to or greater than that of ordinary motors specified by the American Association of International Electrical Manufacturers (NEMA). In other words, a motor efficiency must be equal to or exceed the NEMA high efficiency motor full load engineering efficiency value before it can be called a high efficiency motor. The cost of a high-efficiency motor depends on the price, efficiency, use time, installation and maintenance costs and labor costs of the motor. The extra purchase cost of high-efficiency motors can be quickly recovered by saving operating costs. Usually, the extra cost of high-efficiency motors can be offset by the energy consumption saved by two years of operation. For example, assuming that 50 hp, 75% of the load factor motor runs for more than 4,000 hours per year and the electricity cost is $0.04/kWh, an improvement point can save 4079 kwh or $163 per year. Therefore, a high efficiency motor, through 4% efficiency improvement, can save $1304 in two years compared with the standard motor, basically meet the two-year return standard.
The Relation between Motor Speed and Load
The load of centrifugal pumps and fans is extremely sensitive to the change of speed. Increasing the speed by only 5 r/min can lead to a significant increase in flow speed and energy consumption and a decrease in efficiency. Therefore, when replacing a pump or fan, the full load speed must be chosen to be equal to or lower than the speed of the replaced motor. The power of the centrifugal motor driving the fan is proportional to the cube of the rotational speed. For example, if the speed of the motor increases from 1740 r/min to 1760 r/min, the power consumption will increase by 3.5% even though it only increases by 20 r/min, and the air or water volume will change with the square of the speed. Slip and speed depend on load, which makes it possible for different motors to drive the same load. For example, when a 100 hp motor outputs 25% rated power, it can be replaced by a 50 HP or lower horsepower motor, but at this time the power is 50% of 50 hp, or 62.5% of 40 hp, 83% of 30 HP motor, and 25 HP full load output. When the load of the motor increases gradually, the speed will decrease, and the full-load speed will be the full-load speed. Hence, the Anhui Electric Power Motor indicates that only the motor with lower speed or larger load can operate in a way close to the synchronous speed, and that the motor with lower power and full-load efficiency can work at a speed close to the synchronous speed instead of the motor with higher power but lower speed, which can obviously save operation. Cost.