Energy smart meters integration in favor of the end user

Norma Anglani, Ezio Bassi, Francesco Benzi, Lucia Frosini, Tommaso Traino Department of Electrical Engineering

University of Pavia Pavia, Italy

fbenzi@unipv.it

Abstract— - Digital meters (electricity, gas, water, heating and cooling energy) play a crucial role within the Smart Grid environment. The paper will address the issue of their employment in two ways: i) the different type of counters, each at different stages in their digital implementation, should be able to exploit their computing and communication capabilities to achieve a complete integration of measurements and information, in order to provide a comprehensive energy assessment and added value compared to individual devices, ii) their use and their deployment should be evaluated not only in relation to the possible advantages for distributors and utilities, but also with special attention to the end user and the community, given the key role of the final consumer in achieving energy efficiency. To this aim, the paper will present the latest technological developments of the meter types and will propose a design methodology (architecture and protocols) that makes their integration possible and profitable.

Keywords - smart metering; smart grid; energy efficiency; communication standard.

I. INTRODUCTION The smart meter can be defined as a metering device, based

on different operation principles (electrical, electronic, mechanic) but more and more enriched with electronics and digital features, that make it a flexible and interactive tool , and always communicating with the environment through a digital interface. The concept of Smart Meter, at first addressed to the electricity area and later extended to other energy carriers (gas, water, heat) can be seen as a transposition of the Smart Grid principles in the local context, to perform a more comprehensive, efficient, official measurement reading of energy consumption.

Smart meters are revolutionizing the traditional role of the device, originally intended to record in incremental way the consumption related to a specific commodity (water, gas, heat or electricity); in their new role they allow for interaction and mutual sharing of information between different types of devices and computer systems, within the utility environment and beyond.

Therefore smart meters cannot be considered as elements in their own right, but as integral parts of a communication infrastructure, also including: i) a local data acquisition system (gateway / concentrator), that supervises the different metering

devices of a user or group of users; ii) a two-way communications infrastructure, required to exchange information between the various nodes of the network and the management unit; iii) a specific operating system, fitted at remotely coordinating the activities over the network and concentrating the data from / to all nodes; iv) a computer unit interfacing with the core operating system, responsible of all data processing on behalf of stakeholders (utilities, network operators, service providers, billing offices, other).

Limited to the electricity consumption reading, the smart meters are an established accomplishment in many countries, operating as the last element of the network control chain. The utility is thus enabled at communicating remotely with the final distribution point, by detecting the consumption data from the meters and sending to them information and enabling signals, in automated and controlled way. In the electricity area the smart meter allows for the detailed analysis of certified energy consumption, is able to raise awareness among consumers and to improve the user's network planning. Besides, in the face of the growing needs for energy efficiency, they can contribute at implementing Demand Response (DR) services [1]. In fact custom surveys report that the sensibility of end users on such data is still far from being a stimulus for taking full advantage from the new devices [10].

The mentioned features can take further advantage from the integration of other types of energy counters, such as gas, water and heat; the involved data are increased in quantity and type, and this can allow for a more comprehensive exchange of information between the management bodies and delivery points, by favoring the optimum management of energy.

An integrated meters system allows all parties, including the end users, to hold and use the meter data, complemented with relevant information available from the utilities. The integration of water, heat, gas and electricity meters in a single structure is still a difficult goal, due to technical problems, but more because of the obstacles among the different actors at sharing sensible data.

This paper aims at defining the additional benefits arising from the smart meters integration and proposes architecture and communication schemes compatible with the state of the art technology, targeting a solution useful not only for the utilities, but also to benefit the end user and the community.

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The paper thus starts by considering international standards and goal (Par. II), then it reviews the state of the art technology for smart meters (Par. III), and the specific opportunities arising from their integration (Par. IV), finally it defines a methodology for designing an integrated system (Par. V) based on realistic assumptions, starting from the requirements of the local network and including the more relevant type of smart meters.

II. INTERNATIONAL LEGISLATION AND MAIN TARGETS. There are many legal provisions at international level, that

have stimulated the use of smart meters, usually within the policies for energy efficiency.

The requirement for DR policies and smart meters deployment has been stimulated in US from the $4.5 billion federal economic package, allocated for research related to smart grids. Accordingly, in a quite likely “partial deployment” scenario, about 80 million meters will be installed by 2019. [2]

The European Union has favored the use of smart meters in two Directives. In the arrangement 2006/32/EC (end-use energy efficiency) (Article 13): "…final customers for electricity, natural gas, district heating and/or cooling and domestic hot water are provided with competitively priced individual meters that accurately reflect the final customer's actual energy consumption and that provide information on actual time of use. ". In Directive 2005/89/EC (measures to safeguard security of electricity supply and infrastructure investment) (Article 5): “...Member States may also take additional measures, including: ... encouragement of the adoption of real-time demand management technologies such as advanced metering systems”. The EU Council has also highlighted that the lack of standards is the first obstacle to the process of innovation in the field of intelligent reading and, to cope with this problem, the European mandate M/441 EN, requires that chosen official organization work at defining a standard for interoperability of intelligent measurement (electricity, gas, water and heat), with the aim of developing an architecture of communication open to all users. In the first technical report about this activity the Smart Metering Co-ordination Group (SM-CG, www.extranetnormapme.com) also defined better the main targets of this mandate: i) A European standard comprising a software and hardware open architecture for utility meters that supports secure bidirectional communication upstream and downstream through standardized interfaces and data exchange formats and allows advanced information and management and control systems for consumers and service suppliers; ii) the architecture must be scalable to support from the simplest to the most complex applications.; iii) the architecture must consider current relevant communications media and be adaptable for future communication media; iv) the communication standard of the open architecture must allow the secure interfacing for data exchanges with the protected metrological block.

From the metrological point of view, the mandate M/441 EN refers to Directive 2004/32/EC, better known as the "MID" ("Measuring Instruments Directive). The latter, in its recently updated version, provides new features, strongly linked to the use of smart meters: remote reading of metrological records for

billing purposes and supervision; two-way communication between group size and remote management centers (utilities, service managers, etc..); support for advanced charging and payment systems; ability to disable the power and limitation of power; one-way communication, where permitted, with the home devices of users; providing information via website / gateway to a display home and other devices its user.

III. ELECTRICITY, GAS, WATER AND HEAT METERS The technical features of smart electricity meters have

received considerable attention in recent years as documented by the literature [3-4] and are already in use in selected countries (e.g. Italy); under fast development in most countries, where there immediate advantage even in economic terms are understood from utilities. For them it is inherently provided the processing and transmission of measured data in digital form; there are still problems with the choice of a communication protocol. Different and not as well-established is the state of the art for gas, water and heat meters, still largely operating on analog basis; for them the signal conversion and processing to a digital form is still a relevant issue.

Gas Smart Meters. In a short review these can be based on mechanics (membrane type, turbine type or rotor type) or electronics (based on ultrasound “time of flight” or “ Doppler effect; based on micro-thermal flow rate; based on pressure sensors or orifice meters).

In most cases residential gas meters are still using mechanical diaphragm technology. The common solution to generate pulses from the analog signal is through a magnetically operated electrical switch (Reed Switch), with a magnet installed inside the counter, while the Switch is contained in a sealed box, to be applied to the mechanical dial in "plug and play" through a sensor interface, with no interference with the measuring unit. As such it is easy to install, does not require the presence of skilled operators and can be purchased at a later time. In order to detect attempts to tamper with the measurement group, a “tamper switch” can be added, activating an alarm in this case. A pulse adapter can further be included, together with a data logger to interface with a digital network and specific standards (M-Bus is among the traditional for these devices). As an alternative some manufacturers have equipped the group of measure with an absolute encoder providing an opto-electronic scanning of the mechanical dial.

The more relevant data processing associated with gas meters is the correction required (PTZ, Pressure, Temperature, Compressibility factor) in order to normalize the raw volume measurement according to such parameters as pressure and temperature, since they affect the actual energy quantity transferred; this requirement is more and more crucial as long as the pressure is varying during the service [5].

Water Smart Meters. Even water meters are classified according to the material (either for hot water or cold water or mixed) and according to the measurement principle in mechanical meter or solid state.

Mechanical meters can be based on Positive displacement (Oscillating Piston, Nutating Disc) or Velocity (Multi jet,

Single jet); also Woltmann counter is an alternative for industrial applications, while Single jet or Multi jet are quite common for residential use. As a summary mechanical counters have benefit from a proven, long lasting technology, widely accepted and trusted in the industry; nonetheless they also show a number of disadvantages: such as inherent low flow performance limitations; accuracy subject to wear; problems due to particulates and calcium in water; significant pressure losses; maintenance required; relevant dependence on correct sizing [6]. Even for them a conversion to pulse and thus digital signals is required and can be implemented with similar devices as those mentioned for gas meters, like Reed switch and Absolute encoder.

A total different principle is employed in Solid state water counter, that share some common features: no moving parts to wear out; no particles sensibility; reduced pressure lost; low or no maintenance; better low-flow accuracy; better high-flow durability; easier interface to digital signal networks.

They rely on different principles like: i) Fluidic oscillator (a device that generates an oscillating jet when supplied with fluid at pressure) [7]; ii) Ultrasonic Meter Theory (these flow meters measure the difference of the transit time of ultrasonic pulses propagating with and against flow direction) [8]; iii) Magnetic based metering (by using Faraday’s Law a magnetic field is applied to the flow tube detecting a voltage signal proportional to the flow rate) [6].

Even for water meters output, different communication standard are in use to be hopefully integrated (M-bus, ZigBee, Wireless M-Bus).

Heat Smart Meters. More precisely they are thermal energy meters, and are more and more in use for residential and building application. Their main destination is for: i) distributing the heat in apartment buildings with central boiler, with a precise accounting for each apartment; ii) private heating: users installing solar panels for the production of hot water or to supplement the traditional boiler employ the heat meter to have a measure of the amount of energy produced by the plant, or to send the data in (almost) real-time automatic control system to supplement a traditional gas boiler, which reduces its operation based on the energy produced by solar panel; iii) in cities where district heating plants are in use for urban distribution of heat for space heating and domestic hot water production; the heat meter is used to issue invoices to the client on the quantitative basis of thermal energy provided.

The measurement of the heat transmitted to the environment or water for domestic use is based on the calculation of the difference between thermal energy between flow and return pipe. To this aim the value of water flow and temperature in the flow and return pipe need to be available.

Water flow can be measured as in water meters, with the sensor inserted in the return pipe (where the water is colder) for detecting a displacement volume of water

The temperature measurement is entrusted to a pair of temperature sensors PT100, PT500 and PT1000, which will be located respectively in the flow and return water pipe. A microprocessor will thus calculate the dissipated thermal energy value. The calculated values can also be stored in

memory for further use. The electronic interface unit with other devices is via pulse output, RS-232 or radio communication module, or M-Bus.

IV. OPPORTUNITIES FROM METERS INTEGRATION Once integrated measurement data are available to the user

a number of opportunities are given to him and indirectly to the community.

Feedback. The knowledge of the raw or processed data of energy consumption makes the individual an active participant in energy savings behavior, mostly with an intelligent reading of the counters. An interface system must be first established through: i) display purposely installed in the houses; ii) devices already owned by the user (eg TV, PC, thermostat display, phone); iii) web portal (primarily used for receiving information from the utility). The purpose of these systems is to provide clients with a range of tools to make him conscious of the domestic consumption and thus to minimize the impact of energy and environment for the house. Therefore the interface must be located or have a termination display within the home living area, for immediate accessibility and consultation of the data.

User controlled services. Energy management services based on the energy measurement offered by the meters can be implemented directly by control units according to the strategies chosen by the user, operating automatically on particular devices in the home (e.g. boiler , air conditioning, temperature control, etc..). To make these services actually convenient for the user it is crucial that the employed metering systems be those officially installed by the utilities in order to take advantage of the Demand Side programs established; also the tariff data, required in optimization program, must be transmitted to the user in official, real-time and reliable way by the utilities themselves, either through the meters or through web connected pages. Using different metering devices can result in inconsistent, ineffective energy control strategies

Utility controlled services. Automatic implementation of selected services can be implemented directly from the utility, under permission given by the user to interact with the home domestic appliances. This allows the companies to implement more effectively Demand Side programs. On the other hand sensible privacy issues can be raised with this formula, which is the reason because in many countries this is not admitted.

In the following are shortly reported a number of significant services available with different kind of energy, by using the related meters.

Bi-fuel thermoregulation. Stems from the large spread in the residential sector of conditioning devices using electric heat pump, that can be used in winter as a heat pump. The availability of one or more heat pump equipment and a gas boiler makes it possible to use two different energy sources, electricity and gas, to achieve the same service for rooms heating at different times of the day. A home automation system, interfaced with a gas and electricity meter, according to the weather conditions, the user-set levels of comfort, the performances of the devices, the current tariff levels of gas and electricity, will determine at any time which of the two sources

is the most efficient from the standpoint of economic or environmental impact.

Temperature control system combined with a solar panel. Heat from solar thermal is becoming increasingly popular in residential construction. One may consider adopting a system of automatic adjustment of the gas boiler according to the thermal energy for heating made available from the solar panel, so as to maximize savings at times when the demand energy can be partially satisfied by this secondary source. In this case a heat meter must be installed in the water pipe flow and return and transmit data to the regulator of the gas boiler, according to the temperature value set by the user and as a function of the energy supplied by the panel.

Dynamic load control. The dynamic control of electric loads allows the user to directly manage the most energy consuming appliances (washing machine, air conditioning, water heater, dishwasher, pool pump), depending on the power rate plan agreed with the supplier. The goal is to limit the peak power absorbed by the loads and to differentiate the use of appliances according to the tariff, in order to save on energy costs and flatten the load curve at critical times of the day. A requirement in such controlled network is the availability of smart appliances, or more simply of relay controlled plugs. Here again it is relevant that the measurement reading be made by official metering systems [9].

Monitoring and detection of water leaks. This service is obviously based on a water smart meter, interfacing a control device. The water leak detection system is based on the setting of a standard consumption level, beyond which an abnormal situation is detected. This results in a simple feedback function (the home screen reports water leakage, due to accidental withdrawals due to forgotten faucets open or intentional vandalism). The tool can also interact with the system by locking the water supply via a mechanical-hydraulic device.

V. METHODOLOGY FOR A SMART METER INTEGRATION ARCHITECTURE

Requirements. For an effective integration of different meters, a local communication network must be first established. Here are some relevant requirements to be considered.

• The communication between the meters and the home devices (display, appliances) must ensure the least possible time interval between two consecutive updates in relation to the dynamics of the measurement variable (shorter intervals for electricity; larger intervals for gas, water, heat).

• The architecture must be interoperable, in order to integrate networked devices that belong to different manufacturers, according to an accepted communication standard.

• A reduced consumption is required for networked electronic devices, specially for wireless battery-powered meters.

• It must be able to provide alternative channel of communication between meters and the operator of the field devices, in case of network default, both locally (e.g.

optical port), and for walk-by drive-by (e.g. radio channel). Also it has to provide measures (e.g. encryption keys) for the safety of the transitions and data .

• To provide synchronization information from the meters, in order to coordinate real time operations under the same clock.

• To allow the user to operate as simply as possible in activities which required action (e.g. new device configuration) and to minimize user intervention in the daily routine.

Since the typical support of such network is a fieldbus, that is a serial digital mean, the network required speed depends on the number of meters included, and on the updating rate required.

Two kind of network can be considered.

For the purpose of counting and billing, the measurement information required are transmitted across an Wide Area Network (WAN) to the utility by PLC or GPRS; the frequency in this case is variable and depends on the class of the meter, the contract with the distributor and the type service, according to the minimum requirements of relevant legislation; in any case the automatic transmission of the data registers can be done on a daily, weekly or monthly basis.

For user related services the information has to be conveyed in a local network including the meters and the devices employed for display or energy management purpose. In this case a much higher rate of recovery is due, sometimes almost instantly. Even though the available communication technologies may provide information in near real-time, with refresh rates up to a fraction of seconds, the main limitation is set from meters power consumption, specially when the adopted physical mean is not self-powered, as for wireless devices.

All considered, the updating interval requirements depend on the nature and dynamics of the measured units and can be resumed in some typical values:

Device location. The physical location of devices within the

house and environment plays an important role in the choice of a data transmission interface and therefore in the data reading and processing, starting from the choice of the physical medium (e.g. wired or wireless).

In order to define a specific architecture the following items have to be defined: i) the dwelling typology; ii) the measuring devices to be connected in the network; iii) other user oriented devices (displays, actuators and home controllers) and their specific location within the house.

For the case study here reported the following has been established.

Dwelling. Independent single-family dwelling, thereby excluding the problems related to a multi-family house

Metering devices disposition within the house:

electricity meter: installed inside the perimeter wall, towards the street;

gas meter: installed inside the perimeter wall, on the street; water meter: installed in the basement; heat meter: installed inside the house, close to the flow pipe

of district heating or solar panel. Home service devices considered as operating within the

house:

- for heating: a standard gas boiler and a solar thermal plant for combined heating of house and sanitary water;

- in-house displays for electricity, gas, water and heat, connected to the meters and to the utilities for official updated tariff data;

- a regulating device defining the best sharing between heat from gas boiler and district or solar heating;

- a dynamic electric load controller based on smart plug management;

- bi-fuel thermoregulation system connected to the meters and to the utilities for official tariff data;

- water leaks detection device, including a supply interruption electrical device.

The above mentioned devices become nodes of a star type network supervised by a residential gateway, that provides the interface within the house and with remote systems, as described in Figure 1. The choice of a common protocol is a relevant issue, which is here resumed in a simplified critical discussion about the merits and disadvantages of wired and wireless solutions.

The use of a dedicated wired solution to connect gateway and devices would result in the drafting of a cable through the

house, which in many cases will imply additional installation costs, and problems with future extensions or modifications of the network. On the other hand a number of solutions based on cable net are well assessed, specially for metering devices (e.g. M-Bus protocol) and would be beneficial in term of consumption (since they also bring supply power), reliability and durability performance. The wireless solution, in this context, is a viable alternative to cable, due to the easier installation of transceivers and repeaters (if required by distance) close to the devices. Nonetheless a number of problems related must be underlined such as: the occurrence of possible interference with other networks; a poor accessibility of signals in presence of obstacles (e.g. thick walls in historical buildings); the possible access of unauthorized persons to the data; encumbrance of transceiver devices; suspected and possible adverse effects of radio waves on the house inhabitants; the need to power the meters through batteries. Powerline solutions are included in the open medium category, like wireless, sharing some of the mentioned drawbacks, except the last one, since power supply is inherently provided.

Wireless technology, however, arises as a preferable solution for applications at the Home Area Network, where the cost and ease of installation, together with the requirements of interoperability and the possibility of future integrations, are criteria actually held in high regard by the final user. Looking at the available protocol solutions M-Bus 868 MHz (the wireless version of M-Bus) and ZigBee 2.4 GHz have been selected here as candidates of the proposed architecture, since both are found to be mature, well-standardized and reliable.

In the following a few criteria useful as a guideline to compare the protocols are discussed with special reference to M-Bus and ZigBee.

Figure 1 – The proposed house devices architecture.

Interoperability – All Zigbee components are subject to a strict approval test, in order to be certified for the market. For M-Bus only the two communication lower layer are in common, while they have more solutions at the higher levels employing different transmission data format .

Longevity and upgrading. – The technical solutions proposed by M-Bus suffer from an older basic technology. This aspect doesn’t restrict its upgrading to new, more convenient solutions, but some difficulties arise with retrograding the new software at older components.

Battery consumption – M-Bus (868 MHz) takes advantage from the lower frequency and reduced signal attenuation; nonetheless ZigBee (2,4 GHz) implements energy reduction strategies. Both have reasonable cost/performance ratio.

Disturbance rejection – Zigbee takes advantage from the multi-hop strategy to avoid disturbance on a specific frequency by hopping on the other allowing for the coexistence of more networks in a single dwelling,

As a summary the ZigBee solution has been here preferred and the integrated smart meter network results as in Figure 2, where all the meter types, including their adapting devices are inserted in a common network based on a wireless Zigbee network. All components here included are off-the-shelf products.

VI. CONCLUSIONS The main purpose of this paper was to bring together all

relevant issues related with the problems arising when different smart meters, energy related, are connected in a data network, thus allowing a better exploitation of the combined information.

The integration serves manifold scopes: i) the utilities, in an open market, can use the integrated data to design custom contracts, e.g. electricity + natural gas or natural gas + water; ii) from the end users viewpoint, a building manager can be entitled at dealing with collective tariff for all residential users; iii) a data base can be created and instructed by expert systems

to give customized tips and advices to improve the users energy footprints.

In conclusion a methodology has been proposed to take into account the main issues affecting the design of a reliable network integrating different smart meters.

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Figure 2 – An integrated smart meters architecture.