**Energy Measurement Techniques for Energy Efficiency Programs**

Luís F. C. Duarte, Elnatan C. Ferreira and José A. Siqueira Dias

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/47791

## **1. Introduction**

The reduction of energy consumption and elimination of energy waste are among the main goals of all countries that recognize that the world climate is changing due to these problems. Reducing greenhouse gas (GHG) emissions is mandatory for preserving a healthy biosphere and all earth's ecological systems.

The main source of greenhouse gases originated by human activities is the burning of fossil fuels [21]. Studies show how it is possible to generate electricity from renewable energy sources other than burning fossil fuel. Unfortunately, those technologies are not yet widely spread or haven't reached a development stage where the production costs are adequate for the economic scenarios [18, 20, 23].

BP Statistical Review of World Energy 2009 [3] showed that in 2008, the total worldwide energy consumption was 474 exajoules (474 <sup>×</sup> 1018 J), with 80 to 90 % derived from the combustion of fossil fuels. If this scenario does not change, it can lead us to an unpleasant future with several environmental issues, from global warming caused by fossil fuel combustion and deforestation due to acid rain and destruction of the ozone layer.

In order to change this scenario, utilities and governmental agencies all over the world are implementing energy efficiency programs. These programs are designed to implement solutions which help customers to manage the energy use and save money on energy bills. However, the first step in achieving an energy-efficient houses is the understanding of where the energy is going. Is has been shown that the effectiveness of an energy efficiency program depends strongly on the feedback that the consumers receive about their energy use.

A good knowledge of where the energy is going is fundamental for the customers to decide how it is possible to reduce energy waste and maximize energy bill savings. There are different approaches for implementing energy efficiency programs, and basically two types of actions that can be taken: by changing the behavior and habits of the customers in what concerns the use of home appliances or by making investments in energy-efficient technologies. Many

©2012 Duarte et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0),which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### 2 Will-be-set-by-IN-TECH 194 Energy Effi ciency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities Energy Measurement Techniques for Energy Efficiency Programs <sup>3</sup>

times, in order to achieve a significant improvement in energy savings, these two actions must be implemented simultaneously.

of each home appliance, contributing to the knowledge of the relative demand of different

This chapter will present and discuss several energy measurement methods and technologies of advanced metering initiatives (AMI) for in-house use (devices which are installed after the electric panel) which can be used to distinguish the power consumption of each electrical

Power is, by definition, a work done per unit time. Measured in Watts (W), electrical power is commonly acquired indirectly, by measuring the voltage and the current of the circuit. In alternating current (AC) circuits, instantaneous electrical power is calculated by multiplying

Electrical energy is obtained by accumulating instantaneous electrical power measurements

In energy meters integrated circuits, the signals of voltage and current are discretized in time

*i*=*T* ∑ *i*=0

In the energy meters integrated circuits (ICs) the voltage is is usually obtained using a resistive voltage divider connected directly to the ac line, and the current can be acquired by measuring the voltage drop across a shunt resistor or across a burden resistor connected to a current

Figure 2 shows the basic schematic diagram of an electrical energy meter IC. A current transformer with a burden resistor is used to provide the current-to-voltage conversion needed by the current channel ADC, and a simple resistive divider network attenuates the

In order to achieve high accuracy, modern electrical energy metering ICs perform the signal processing, such as multiplication and filtering, in the digital domain. This approach provides superior stability and accuracy over time even in extreme environmental conditions. Their operation is based on high precision Sigma-Delta Analog to Digital Converters with resolution

To achieve high resolution and reduce noise, the Sigma-Delta Analog to Digital Converters in the IC convert the signals from the current and voltage channels using oversampling. The signals are sampled at a frequency that is many times higher than the bandwidth of interest and this spreads the quantization noise over a wider bandwidth. With the noise spread over

a wider bandwidth, the quantization noise within the band of interest is lowered [2].

by an analog to digital converter (ADC), and the electrical energy is then written as:

*E* =

line voltage which will be fed into the voltage input channel ADC.

between 16 - 24 bits, and signal data processing integrated in hardware level.

*Pi* = *Vi* × *Ii* (1)

Energy Measurement Techniques for Energy Effi ciency Programs 195

*V*(*t*) × *I*(*t*) *dt* (2)

*Vi* × *Ii* (3)

appliance in a building and provide a detailed breakdown of the energy bill.

*E* = *t* 0

appliances and also showing bad habits of the inhabitants.

**2. Electrical energy measurement basics**

the instantaneous values of the voltage and current:

over a period of time, and is written as:

transformer.

Some programs provide direct payments or subsidies (rebates, discounts and loans) to customers who decide to purchase or install a specific energy efficiency home appliance. Other programs address non-financial incentives such as information and technical services. Non-financial incentives/services may be bundled with direct or indirect incentives, or may be offered on a stand-alone basis. Depending on the customer type and market characteristics that a given program targets, an effective energy efficiency program design may include any one of these incentive types, or may bundle them together in various ways [17].

It has been shown that the reduction of energy consumption by customers or the adequacy of their consumption behavior is strongly related with the quality of feedback on where (an what for) the energy spent was used. This understanding leads to changes in behavior that can both reduce energy consumption and shift the energy use from peak periods to off-peak periods. The more detailed is the feedback information that the customer receives, the more efficient and substantial are the energy savings.

The results from surveys conducted by the American Council for an Energy-Efficient Economy in [8] are shown in Figure 1, where it can be noticed that Real-Time Plus Feedback (real-time information down to the appliance level) offered to households can provide energy savings of up to 12%.

It has been observed that technical and physical improvements in housing are not enough to guarantee reduced energy consumption since consumption in identical homes can easily differ by a factor of two or more depending on the behavior of the inhabitants. Thus, smart metering (or advanced metering) was proposed as a promising way of developing the energy market and contributing to social, environmental and security-of-supply objectives [4] because this technology allows households to have a feedback on the energy consumption of each home appliance, contributing to the knowledge of the relative demand of different appliances and also showing bad habits of the inhabitants.

This chapter will present and discuss several energy measurement methods and technologies of advanced metering initiatives (AMI) for in-house use (devices which are installed after the electric panel) which can be used to distinguish the power consumption of each electrical appliance in a building and provide a detailed breakdown of the energy bill.

#### **2. Electrical energy measurement basics**

2 Will-be-set-by-IN-TECH

times, in order to achieve a significant improvement in energy savings, these two actions must

Some programs provide direct payments or subsidies (rebates, discounts and loans) to customers who decide to purchase or install a specific energy efficiency home appliance. Other programs address non-financial incentives such as information and technical services. Non-financial incentives/services may be bundled with direct or indirect incentives, or may be offered on a stand-alone basis. Depending on the customer type and market characteristics that a given program targets, an effective energy efficiency program design may include any

It has been shown that the reduction of energy consumption by customers or the adequacy of their consumption behavior is strongly related with the quality of feedback on where (an what for) the energy spent was used. This understanding leads to changes in behavior that can both reduce energy consumption and shift the energy use from peak periods to off-peak periods. The more detailed is the feedback information that the customer receives, the more

The results from surveys conducted by the American Council for an Energy-Efficient Economy in [8] are shown in Figure 1, where it can be noticed that Real-Time Plus Feedback (real-time information down to the appliance level) offered to households can provide energy savings of

12%

9.2%

8.4%

6.8%

Anual savings [%] <sup>0</sup> <sup>4</sup> <sup>8</sup> <sup>12</sup>

It has been observed that technical and physical improvements in housing are not enough to guarantee reduced energy consumption since consumption in identical homes can easily differ by a factor of two or more depending on the behavior of the inhabitants. Thus, smart metering (or advanced metering) was proposed as a promising way of developing the energy market and contributing to social, environmental and security-of-supply objectives [4] because this technology allows households to have a feedback on the energy consumption

**Figure 1.** Average household electricity savings, based on 36 studies carried out between 1995-2010

one of these incentive types, or may bundle them together in various ways [17].

be implemented simultaneously.

efficient and substantial are the energy savings.

**Real-Time Plus Feedback**

**Real-Time Feedback** Real-time premise level info

**Daily/Weekly Feedback**

daily or weekly basis **Estimated Feedback** Web-based energy audits with info on ongoing basis

**Enhanced Billing** Household-specific info, advice

Household-specific info, advise on

3.8%

Real-Time info down to the appliance level

up to 12%.

Power is, by definition, a work done per unit time. Measured in Watts (W), electrical power is commonly acquired indirectly, by measuring the voltage and the current of the circuit. In alternating current (AC) circuits, instantaneous electrical power is calculated by multiplying the instantaneous values of the voltage and current:

$$P\_{\bar{i}} = V\_{\bar{i}} \times I\_{\bar{i}} \tag{1}$$

Electrical energy is obtained by accumulating instantaneous electrical power measurements over a period of time, and is written as:

$$E = \int\_0^t V(t) \times I(t) \, dt \tag{2}$$

In energy meters integrated circuits, the signals of voltage and current are discretized in time by an analog to digital converter (ADC), and the electrical energy is then written as:

$$E = \sum\_{i=0}^{i=T} V\_i \times I\_i \tag{3}$$

In the energy meters integrated circuits (ICs) the voltage is is usually obtained using a resistive voltage divider connected directly to the ac line, and the current can be acquired by measuring the voltage drop across a shunt resistor or across a burden resistor connected to a current transformer.

Figure 2 shows the basic schematic diagram of an electrical energy meter IC. A current transformer with a burden resistor is used to provide the current-to-voltage conversion needed by the current channel ADC, and a simple resistive divider network attenuates the line voltage which will be fed into the voltage input channel ADC.

In order to achieve high accuracy, modern electrical energy metering ICs perform the signal processing, such as multiplication and filtering, in the digital domain. This approach provides superior stability and accuracy over time even in extreme environmental conditions. Their operation is based on high precision Sigma-Delta Analog to Digital Converters with resolution between 16 - 24 bits, and signal data processing integrated in hardware level.

To achieve high resolution and reduce noise, the Sigma-Delta Analog to Digital Converters in the IC convert the signals from the current and voltage channels using oversampling. The signals are sampled at a frequency that is many times higher than the bandwidth of interest and this spreads the quantization noise over a wider bandwidth. With the noise spread over a wider bandwidth, the quantization noise within the band of interest is lowered [2].

Practically every current waveform in real appliances have some harmonic content. Using the Fourier transform, the instantaneous voltage can be expressed in terms of their harmonic

*Vh* × sin(*hωt* + *αh*) (4)

Energy Measurement Techniques for Energy Effi ciency Programs 197

*Ih* × sin(*hωt* + *βh*) (5)

*P* = *P*<sup>1</sup> + *Ph* (6)

(7)

(8)

2 × ∞ ∑ *h*� 0

2 × ∞ ∑ *h*� 0

Thus, using Equations 1, 4 and 5, the real power *P* can be expressed in terms of its fundamental

*P*<sup>1</sup> = *V*<sup>1</sup> × *I*<sup>1</sup> cos(*φ*1)

Some energy meter ICs stores in registers the information processed in the digital domain. According to the energy meter IC, all that information (or part of it) can be retrieved via serial communication (like SPI, I2C or RS-232). Access to that information is a key element to the development of centralized systems that can identify different appliances on a household

Another technique to implement precision low-cost electrical energy meters is to perform all the signal processing at software level. This can be done by using microcontrollers ICs with integrated ADCs. If a hardware multiplier is integrated in the microcontroller IC,

*Vh* × *Ih* cos(*φh*)

*φ*<sup>1</sup> = *α*<sup>1</sup> − *β*<sup>1</sup>

∞ ∑ *h*� 1

*φ<sup>h</sup>* = *α<sup>h</sup>* − *β<sup>h</sup>*

*Ph* =

*<sup>v</sup>*(*t*) = *<sup>V</sup>*<sup>0</sup> <sup>+</sup> <sup>√</sup>

*<sup>i</sup>*(*t*) = *<sup>I</sup>*<sup>0</sup> <sup>+</sup> <sup>√</sup>

content as:

where:

where:

*v*(*t*) is the instantaneous voltage.

*i*(*t*) is the instantaneous current.

*I*<sup>0</sup> is the dc component.

where *P*<sup>1</sup> is given by:

and *Ph* is:

*Vh* is the RMS value of Voltage Harmonic *h*. *α<sup>h</sup>* is the phase angle of the voltage harmonic.

and the instantaneous current is given by:

*Ih* is the RMS value of Current Harmonic *h*. *β<sup>h</sup>* is the phase angle of the current harmonic.

real power (*P*1) and the harmonic real power (*Ph*) as:

installation, as it will be shown in the further sections.

*V*<sup>0</sup> is the average value.

**Figure 2.** Energy meter IC connected to a resistive voltage divider and current transformer with burden resistor.

This analog input structure greatly simplifies sensor interfacing by providing a wide dynamic range for direct connection to the sensor and also simplifies the antialiasing filter design. A high-pass filter in the current channel removes any dc component from the current signal, eliminating inaccuracies in the real power calculation which may appear due to offsets in the voltage or current signals [1].

The real power calculation is derived from the instantaneous power signal, which is generated by a direct multiplication of the current and voltage signals. To extract the real power component (that is, the DC component), the instantaneous power signal is low-pass filtered. Figure 3 presents a graph of the instantaneous real power signal and shows how the real power information is extracted by low-pass filtering of the instantaneous power signal. This scheme calculates real power for sinusoidal current and voltage waveforms at all power factors.

**Figure 3.** Signal Processing Block Diagram

Practically every current waveform in real appliances have some harmonic content. Using the Fourier transform, the instantaneous voltage can be expressed in terms of their harmonic content as:

$$v(t) = V\_0 + \sqrt{2} \times \sum\_{h \neq 0}^{\infty} V\_h \times \sin(h\omega t + \alpha\_h) \tag{4}$$

where:

4 Will-be-set-by-IN-TECH

**Figure 2.** Energy meter IC connected to a resistive voltage divider and current transformer with burden

This analog input structure greatly simplifies sensor interfacing by providing a wide dynamic range for direct connection to the sensor and also simplifies the antialiasing filter design. A high-pass filter in the current channel removes any dc component from the current signal, eliminating inaccuracies in the real power calculation which may appear due to offsets in the

The real power calculation is derived from the instantaneous power signal, which is generated by a direct multiplication of the current and voltage signals. To extract the real power component (that is, the DC component), the instantaneous power signal is low-pass filtered. Figure 3 presents a graph of the instantaneous real power signal and shows how the real power information is extracted by low-pass filtering of the instantaneous power signal. This scheme calculates real power for sinusoidal current and voltage waveforms at all power

Rborder

ADC

HPF

Instantaneous Power Signal - p(t)

HPF

LPF

Ʃ

Instantaneous Real Power Signal

Energy

Time Time

ADC

CT

N

A C M A I N S

resistor.

factors.

L

voltage or current signals [1].

CH1

CH2

**Figure 3.** Signal Processing Block Diagram

L O A D

R2 R1

Energy Meter IC

V+ V-I+ I-

*v*(*t*) is the instantaneous voltage.

*V*<sup>0</sup> is the average value.

*Vh* is the RMS value of Voltage Harmonic *h*.

*α<sup>h</sup>* is the phase angle of the voltage harmonic.

and the instantaneous current is given by:

$$\dot{q}(t) = I\_0 + \sqrt{2} \times \sum\_{h \neq 0}^{\infty} I\_h \times \sin(h\omega t + \beta\_h) \tag{5}$$

where:

*i*(*t*) is the instantaneous current. *I*<sup>0</sup> is the dc component. *Ih* is the RMS value of Current Harmonic *h*.

*β<sup>h</sup>* is the phase angle of the current harmonic.

Thus, using Equations 1, 4 and 5, the real power *P* can be expressed in terms of its fundamental real power (*P*1) and the harmonic real power (*Ph*) as:

$$P = P\_1 + P\_{\text{lt}} \tag{6}$$

where *P*<sup>1</sup> is given by:

$$\begin{aligned} P\_1 &= V\_1 \times I\_1 \cos(\phi\_1) \\ \phi\_1 &= \alpha\_1 - \beta\_1 \end{aligned} \tag{7}$$

and *Ph* is:

$$\begin{aligned} P\_{\text{li}} &= \sum\_{h \neq 1}^{\infty} V\_{\text{li}} \times I\_{\text{li}} \cos(\phi\_{\text{li}}) \\ \phi\_{\text{li}} &= \alpha\_{\text{li}} - \beta\_{\text{li}} \end{aligned} \tag{8}$$

Some energy meter ICs stores in registers the information processed in the digital domain. According to the energy meter IC, all that information (or part of it) can be retrieved via serial communication (like SPI, I2C or RS-232). Access to that information is a key element to the development of centralized systems that can identify different appliances on a household installation, as it will be shown in the further sections.

Another technique to implement precision low-cost electrical energy meters is to perform all the signal processing at software level. This can be done by using microcontrollers ICs with integrated ADCs. If a hardware multiplier is integrated in the microcontroller IC,

#### 6 Will-be-set-by-IN-TECH 198 Energy Effi ciency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities Energy Measurement Techniques for Energy Efficiency Programs <sup>7</sup>

the multiplications that are constantly executed during the energy metering process can be executed very quickly, and measuring energy with these general purpose microcontroller ICs can be very competitive when compared to the energy meter ICs.

**4. Experimental results of a pilot project**

lead to changes in habits and substantial savings in electrical energy.

where the mesh wireless network is difficult to be implemented.

Recently a pilot project, supported by ANEEL (the Brazilian Electrical Energy Regulating Agency) and AES Eletropaulo (the major power electric utility in the State of São Paulo) was developed by the Department of Electronics and Microelectronics of the School of Electrical and Computer Engineering, at the University of Campinas [7]. The objective was to develop and test a prototype of a hybrid (wireless and PLC) intelligent sensor network system which should be able to perform the breakdown of the electricity bill of the customers. The premise was that with detailed information in hands, consumers could understand better how much they spend the electrical energy in every single electrical device in a house and, this would

Energy Measurement Techniques for Energy Effi ciency Programs 199

The developed system was planned to be offered as a service by the ESCOs, so that both customers who want to know better how they use the electrical energy and energy-efficiency programs were potential candidates for using the service. In order to be practical, the developed system had to be simple to install and easy to be deployed in a residence or small business, without requiring any changes in the original electrical wiring. Although the electrical appliances which are connected to the mains outlet could be read using a small module containing an energy meter IC, it was mandatory that the energy spent on lighting

The core of the system was designed around a ZigBee wireless sensor network, and is composed by five types of modules: a coordinator, a displaying-processing unit (DPU) and three types of smart energy meters. A PLC module was also implemented, for special cases

(a) Coordinator (b) DPU (c) Power outlet adaptor smart

(d) Clamp smart meter (e) Light smart meter

The coordinator is the main element, and only one module is required per each mesh network. The coordinator is responsible for storing the information sent by the smart energy

meter

should be monitored, and special sensors had to be designed for this application.

**4.1. Project overview**

**Figure 5.** System modules

This technique is similar to the one implemented in hardware level, using the same acquisition methods and digital processing principles. However, using this approach, the system can be customized to operate in ultra-low power, as in the technique developed in [15] to design a battery powered energy meter using the microcontroler MSP430AFE2xx [16]. The system was configured to operate in a 60 Hz AC line and during every period of one second, make the measurements only during 3 cycles and stay sleeping for the others 57 cycles. The system calculates the RMS value of the product *V* × *I* and adds this value a register. Assuming that there is no significant change in the current and voltage during each period of less then one second, the accumulated value in the register is equal to the energy.

**Figure 4.** Awake and sleeping periods
