The Role of Pumps for Energy Consumption and Energy Saving

The yearly generation of electric energy in various types of power plants and the “energy mix” determine the yearly CO2 emission. Distributions of the consumption of electric energy illustrate the significant contribution of electric motors in general and in particular that of electric motor driven pumps. The consumption of electric energy by the use of rotodynamic pumps (that form the objects of the book) depends not only on the efficiency of the pumps and their drives but also on characteristics of the hydraulic installation, which is supplied with fluid energy, and on the mode of operation. There exist a considerable energy-saving potential for pumping systems and technical measures to realize this potential. Legislative measures promote the practical realization and lead to benefits for the environment and consequences for the pump market.

Keywords

Electric energy generation; electric energy consumption; electric motors; rotodynamic pumps; efficiency; hydraulic installation; energy-saving potential; technical measures; legislative measures; benefits

1.1 Generation and Consumption of Electric Energy

The utilization of electric energy for many various purposes is a characteristic aspect of modern technics and human life.

1.1.1 Generation of Electric Energy

Electric energy is generated by converting primary energy sources. A significant part of these primary sources consists of the fossil combustibles black coal, brown coal, mineral oil, and natural gas. These combustibles are converted into electric energy in conventional power plants. A second part of primary sources consists of radioactive materials, which are used in nuclear power plants to generate electric energy by nuclear fission. A third and increasing part of primary sources is renewable (water power, wind, solar radiation, biomass) and is converted in different technical facilities (e.g., water power plants, wind turbines, solar energy plants, biomass power plants) into electric energy.

In the European Union (EU), the total generation of electric energy was 3295 TWh in 2012 [1].

According to Ref. [2], the following mix of electric energy generation in the EU existed in 2007 and is expected for 2020, respectively (Table 1.1):

One aspect of both the fossil-fueled and the nuclear power plants is their contribution to the irreversible consumption of limited reserves of primary energy sources. This is a first motivation, to reduce electric energy generation by saving electric energy.

In the case of nuclear power plants, the risk of nuclear accidents and the issue of nuclear waste having possible effects on the environment and on humans are motivations to reduce their number worldwide.

Concerning the fossil-fueled power plants, a severe aspect is their emission of CO2, which is classified as a “greenhouse gas” and is responsible for medium- and long-term climate change. Therefore, international commitments, especially in the EU and in its member countries, aim for the general reduction of CO2 emissions by certain amounts and by certain dates. The major EU policy package, called the climate and energy package, which was adopted and became a binding legislation in 2009, includes as one of the targets for 2020 the reduction in EU greenhouse gas emissions of at least 20% below 1990 levels.

This leads—besides other goals, such as to reduce the CO2 emission of traffic and heating of buildings—to the requirement of reducing CO2 emissions that result from the generation of electric energy. Depending on the fossil fuels used as primary sources in the different types of fossil-fueled power plants, on their plant efficiency, and on the mix of the electric energy generated by them, the emission of CO2 caused by generating electric energy in fossil-fueled power plants ranges from 630 to 980 g/kWh, according to Ref. [3]. This means that the mass of CO2 emitted from fossil-fueled power plants is approximately proportional to the electric energy generated by them. In combination with the numbers given above, this results in an emission of approximately (2–3)·109 t of CO2 by generation of electric energy in fossil-fueled power plants within the EU in 2012.

The electric energy generated in power plants and other generation facilities of different types and located at various sites is fed into common electric supply networks and transmitted to each end user. It is supplied to the end users as three-phase alternating current (AC) of constant voltage and frequency. In the EU, the latter is generally 50 Hz for residential, public, and industrial applications.

1.1.2 Consumption of Electric Energy

The total consumption of electric energy can be divided into several categories, such as driving (electric motors), lighting, heating, communication, information, and others.

Concerning the worldwide situation, it is estimated in Ref. [5] that electric motor driven systems (EMDSs) account for between 43% and 46% of the global electricity consumption. This amount is more than twice that of the second largest, which is lighting, contributing by 19% to the total consumption.

The share of electric energy consumption by motor-driven systems to the various sectors of application is given in Ref. [5] as:

with a total consumption of about 7100 TWh/year. This value is expected in Ref. [5] to rise to more than 13,000 TWh/year by 2030 if no comprehensive and effective measures to improve the energy efficiency of motor-driven systems are taken soon.

The global consumption of electric energy by electric motors is dominated by four major motor applications. According to Refs [5,8], in 2006 the corresponding share was as follows: compressors 32%, mechanical movement 30%, pumps 19%, and fans 19%. It follows from these values that pumps are responsible for about 8–9% of the global consumption of electric energy.

According to Ref. [21], in the EU electric motors converted 1300 TWh of electricity into mechanical energy in 2012, corresponding to 520 Mt of CO2 emissions. This value is expected to increase to around 1500 TWh in 2020 and 1800 TWh in 2030.

In the industrial sector in the EU, EMDSs are by far the most important electric energy consumers and use about 70% of the totally consumed electric energy, while in the tertiary sector, EMDSs use about one-third of the consumed electric energy [8]. In both sectors, EMDSs comprise compressors, refrigerator systems, pumps, ventilations, conveyors, and other equipment.

In the EU, the share of pumps in the annual consumption of electric energy by motor-driven systems was 21% in the industrial sector and 16% in the tertiary sector for the year 2000 [8].

The share of consumption of electric energy by motors in respect to their nominal power is described in Ref. [5] as follows:

Small-size electric motors with a nominal output power of less than 0.75 kW are the great majority and are applied primarily in the residential and commercial sectors. But these motors account for only about 9% of all electric energy consumed by motors.

About 68% of the electric energy consumed by electric motors is used by medium-size motors with a nominal output power of 0.75 to 375 kW. These are mostly AC induction motors with two to eight poles, but some are special motors (e.g., direct current, permanent magnet, switched reluctance, stepper, and servo motors). They are manufactured in large series according to standard specifications and can be ordered from catalogs. These motors account for about 10% of all motors.

Large electric motors with more than 375 kW nominal output power are usually high-voltage AC motors that are custom designed. They comprise just 0.03% of the electric motor stock but account for about 23% of all electric energy consumption by motors.

In the EU, the market shares of AC induction motors are 50–70% four-pole motors, 15–35% two-pole motors, and the remainder six- and eight-pole motors [8].

Electric motors used as pump drives are dominated by AC induction motors in the power class ≥0.75 kW. In the EU-251 market in the low-power range (<5 kW), the share of other motor types that have better efficiencies than AC induction motors shows a trend to increase on a low level. For example, in the EU-25, the share of permanent magnet motors was only 1.4% in 2002 [8].

Some typical functions of the motor-driven pumps are as follows [5]:

In the residential sector, the pumps serve for central heating systems, circulation of hot and cold water, and pressure boosting of water supply. In the commercial building sector, pumps are used for heating, ventilating, air conditioning, and water supply, including pressure boosting. In...