WO2008142458A1

WO2008142458A1 - Energy management system

Info

Publication number: WO2008142458A1
Application number: PCT/GR2007/000031
Authority: WO
Inventors: Gerasimos Paizis
Original assignee: Petcor H/M Erga-Efarmoges Klimatismou S.A.
Priority date: 2007-05-23
Filing date: 2007-05-23
Publication date: 2008-11-27

Abstract

The Energy management system is applied to shelters (1) housing telecommunications equipment. These shelters are not connected to the electric network and their electric supply is assured by one or more generating sets (generators) (2). The energy management system (8) takes over the management of the operation of the generating set in such a way as to optimize its efficiency, with concomitant reduction of fuel consumption and hours of operation, thus saving financial resources from the fuel, the spare parts and the man-hours needed for the corresponding maintenance labor. The energy management system (8) dictates the installation of the battery bank (11) in a separate space, a cabinet located outside of (6) or inside (7) the shelter, equipped with cooling devices comprising thermoelectric couples, for the purpose of storing them at the temperature dictated by their specifications. The Energy management system, for a further energy reduction, exploits the 'free cooling' system (4), which cools the interior of the shelter with fresh air when this is possible, and can cooperate with any type of commercial air-conditioning apparatus.

Description

DESCRIPTION

Energy management system.

The present invention relates to small isolated installations not connected to the electric network and housing electronic equipment used for receiving and emitting telecommunications signals of any kind, for the operation of radio aids and radio beacons used in aircraft navigation and military applications and for isolated scientific stations, such as meteorological stations and installations using photovoltaic arrays.

These installations are defined as shelters and their design principles differ depending on the type of the application.

The active components of a generic shelter comprise the telecommunications equipment, consisting mainly of advanced technology electronic devices performing all required management procedures for the telecommunications signals, whether wired or wireless. Its basic equipment comprises the power supply devices of the above electronic apparatus which are virtually always accompanied by an battery bank, supplying the shelter with electric energy for a certain period, in the event of power failure, and air-conditioning devices rejecting to the environment any heat generated during use of the telecommunications equipment from the interior of the shelter. Finally, it comprises one or a plurality of generating sets (generators combined with reciprocating internal combustion engines), which, for safety reasons, are located in a different enclosed space inside the shelter and which generate electric power for its uninterruptible functioning.

As already mentioned, the shelters are not connected to the electric network and they depend totally (with minor exceptions) on one or more generating sets, hereafter abbreviated as GSs, as their main and only power source.

The mandatory selection of one or more GSs provides a solution to the problem of the shelter's power source, but creates a number of technical problems. The use of GSs requires, for their normal operation, a plurality of operations relating to the frequent and periodic supply of the Gs with the appropriate fuel, the frequent and periodic maintenance of all the parts of the set, the replacement of a plurality of consumable materials and spare parts, the machining of parts of the internal combustion engine (honing of pistons and cylinders) and, finally, the partial or complete replacement of the generating set after a certain operating life has been reached. The schedule for the above operations is set by the manufacturer of the apparatus and depends on its size, type (two- of four-stroke) and thermodynamic cycle (Otto or Diesel cycle). Finally, to the cost for the above operations must be added the cost relating to the transport of the specialized personnel to the site of the shelter, which is mostly in a remote and not easily reachable location, such as for example a mountain peak.

The purpose of the existence of the one or more GSs in a shelter is mainly to cover the base electric load demands, that is those electric loads that operate continuously and uninterruptibly inside the shelter, and to cover the peak loads, arising intermittently and related solely to the operation of the compressor of the air-conditioning unit. The compressor is an energy consuming, high power machine and is an essential part for the operation of a refrigerating device with vapor compression. As is obvious, the daily amount of hours of operation of the compressor depends directly on the external weather conditions, varies according to the alternation of the seasons and is at a maximum during summer. Finally, it must be noted that the compressor, during its start-up, absorbs for a few seconds a large amount of power, which frequently is more than three times its nominal rating.

The need and the safety margins to cover the above mentioned peaks of load demand result in over-dimensioning the one or more GSs. Thus, during large time intervals, where the compressor of the air-conditioning unit is not in operation, the one or more GSs operate under a markedly low load, compared to its nominal load. For illustrative purposes, we mention that, based on actual observations, the base load of a shelter used for telecommunications applications does not exceed 25% of the nominal power of the GS. This has as a consequence the operation of the mechanical part of the GS outside its specifications, resulting in an overall malfunctioning of the reciprocating machine, in an over-consumption of fuel, in the appearance of the phenomenon of incomplete combustion inside the cylinders and in the evolution of excessive amounts of noxious pollutants into the environment. All the above impact significantly on the operating cost of the one or more GSs, as well as on their amortization, while at the same time increase the quantities of fuel consumed and the burden on the environment.

To make this clearer, in the diagram of figure 5 is shown the variation of the specific fuel consumption referred to the consumption under 100% of the

GS load, versus its loading. In the diagram two curves have been traced, the first of which represents the theoretic variation of the consumption and the second the variation of the consumption based on actual measurements on a GS of the company PERKINS. In these diagrams is noted an increase by about 50%, compared to the consumption under full (100%) load.

A major parameter to maximize the working life of the active equipment is the air-conditioning apparatus, having to maintain the temperature of the shelter inside a certain strict range, defined by the telecommunications equipment manufacturer. Thus, from the equipment specifications, the limits of variation of the temperature are between 22°C and 35⁰C. The increase of the internal temperature is due to the thermal loads dissipated by the electronic machinery (telecommunications equipment and power supplies) during their operation. The situation is considerably aggravated during summer, especially in cases where the installation is located in an open space without any shading, in which there is direct exposure of the shelter to the sun rays for several hours.

Maintaining the temperature of the interior of the shelters inside defined limits is also a requirement of the specifications for the batteries and the power supplies. In particular, according to the batteries' manufacturers, in order to maintain their capacity within the specified levels and simultaneously not to decrease their operational life, the safe temperature limits for storage vary between 22°C and 24°C.

Usually, until now, there is one common interior space in the shelters for both the telecommunications equipment and the batteries and it is clear that the batteries' requirement for constant, low levels of temperature (about 22°C

- 24°C) must hold for the entire shelter and entrains the need to maintain a low constant temperature for a larger volume than necessary, affecting unfavorably the amount of consumed energy and resources and in addition straining the air-conditioners with all the resulting consequences.

The battery bank, even though representing a considerable part of the invested cost of construction of the shelter, is seldom used, since, as we already mentioned, the batteries supply with energy the shelter only in case of failure of the generating set or during its necessary maintenance. Thus, conforming to the specifications of the manufacturers for the regular lubrication of the generating set(s) dictating the lubricant replacement and a general inspection after about 250 hours of operation, i.e. about every 10 days, we conclude that, in the course of a month, the GC(s) will be down due to maintenance about 2 to 3 times. From the data we possess (from the maintenance and failure report sheets filled by the specialized personnel) and from practice we know that a GS is down at most 3 times per month, with very few exceptions related to other parameters, such as part failure and aging, bad fuel quality, etc.

The present invention, designated an "Energy management system", proposes a complex application aiming to decrease the fuel consumption of the GS(s), as well as to decrease the annual operating time. These decreases of fuel and operating time decrease correspondingly the maintenance cost for spare parts and the man-hours for the maintenance and the transport to the shelter.

In order to achieve the above objects, the "Energy management system" takes advantage of the excess power of the GS(s) due to their obligatory over-dimensioning, the capability of the batteries to store energy due to their high capacity, and finally, of the low operating power of the air-conditioning system when it can function in energy saving mode (free-cooling) without needing to activate the compressor.

The core of the "Energy management system" consists of the central control unit, which is responsible for the energy management and comprises a set of controls, high precision measuring instruments and sensors, controlling in real time the environmental parameters inside and outside of the shelter, the operation of the generating set and the operational characteristics of the batteries (charging-discharging current, terminal voltage and capacity). This central unit is responsible for optimally exploiting the ability of the batteries to continually charge-discharge by means of automatic systems and at the same time to determine the activation of the generating set. This central unit contains a telematics and telemanagement system incorporating a wireless modem compatible with all the cell phone networks, which helps in the immediate control of all the system's functions from any remote position (provided that there exists a cell phone network coverage), in the immediate report and tracking of errors and damages, in the modification of settings, in the recording, in a log, of the relevant operational parameters, and in the transmission of this information, and finally in informing the system about the next regular service of itself or of the GSs and about the filling-up of its fuel tank. Alternatively, in the event that this is desirable, depending on the needs of the totality of the installation, or for places not covered by the cell phone network, it is possible to connect the system with any other communication channel or protocol (serial connection of RS232 type, through an Ethernet network and TCP/IP, ModBus, etc.) In the front of the central unit of the system there is a liquid crystal touch screen, through which it is very easy to operate the system, to be informed about the relevant parameters and to enter new settings.

For the air-conditioning and the correct refrigeration of the telecommunications equipment chamber inside the shelter, we can select any of the conventional air-conditioning systems. What is sought from the refrigeration system is its reliable operation under the especially high requirements of the entire installation, its long life, the energy savings, the reduction of regular services for the entire installation and the environmental friendliness.

Usually, for the specific applications, we select the use of industrial type, vapor compression-based cooling, air-conditioning units. These air- conditioning devices are equipped, in the scope of the general trend toward reduced energy consumption, with a "free cooling" energy saving system, commonly controlled by a microprocessor-based control system. The "free cooling" control microprocessor commands the operation of a damper which, when the outside temperature and humidity conditions are within a defined range of operation of the electronic equipment, allows the introduction of fresh air, in order to achieve the desired cooling. That is, it conditions the space with fresh air, when the outside conditions are convenient, without activating the compressor. Also, this happens in the event of a failure of the refrigerant circuit, when the microprocessor assures the opening of the "free cooling" damper in order to keep the electronic equipment within the safer possible temperature limits, since it is cooled with fresh air entering by means of a fan. The conditioning of the space, when heating is needed, e.g. during winter, is effected using electric resistance heaters, usually located inside the air-conditioning apparatus. Their operation is coupled with the operation of the fan of the air-conditioning apparatus.

The main directions of development and design of the system are based on: a) the periodic operation of the generating set under full load, divided into the load absorbed by the operation of the electronic equipment and of the air-conditioning of the shelter, b) the storage of the generated electric energy to the batteries up to their full charging, always in relation to their available charge, which is defined by the dimensioning of the needed electric energy store, and c) the possibility of operation of the air-conditioner using

' the "free cooling" system, where the compressor is inactivated and the GS(s) is (are) commanded to turn off.

During the period of inactivity of the GS(s), the telecommunications loads are uninterruptibly supplied with direct current through the batteries of the power supply, and the loads requiring alternating current are supplied through an inverter of the appropriate size. The GS(s) is (are) restarted whenever the temperature conditions require it (e.g. when "free cooling" is insufficient to maintain the desired levels of temperature of the interior space), or whenever the total electric energy supplied by the batteries has reached some predefined allowable limits signaling the safe end of discharging.

When the conditions permit, and more specifically when the batteries are fully charged and the air-conditioner is able to operate using the free-cooling system, it is commanded to re-stop the operation of the GS(s) and initiate a new cycle of operation.

In order to clarify the methodology of the system, we will examine the mode of operation from the beginning. The GS(s) is (are) commanded from the respective control to initiate its operation and to generate electric energy. The generated electric energy supplies electrically the shelter to cover its needs, and a portion of it is directed for storage to the battery bank. After the batteries are fully charged, the control that monitors their characteristics commands the GS(s) to turn off and thereafter the shelter is supplied solely by the batteries. Where an AC voltage is needed, this is produced by means of inverters, which transform the direct current of the batteries to alternating current. After some time, and as the batteries are discharged with concomitant decrease of the voltage and the remaining capacity, the control that monitors them commands the GS(s) to restart, to prevent the capacity of the batteries to drop to critical levels resulting in complete discharge. The reason why complete discharge is avoided is that it is desired for the batteries to retain some small charge, which will, in the event of a failure of the generating set, assume the electrical supply of the station until a repair squad is transported to the site to repair the GS. With this process the GS(s) initiate and repeat the charging of the batteries. The operating cycle is repeated continually, with sequential charging-discharging.

The cooperation of the "Energy management system" in conjunction with the operation of the air-conditioning units exploiting the energy savings due to the cooling of the shelter with fresh air, originating from the environment when the outside conditions permit, entrains the optimization of the energy

^•savings. In the case where the installation is not equipped with a free-cooling system, the Energy management system can be integrated without problems to the installation with, as is obvious, the expected reduction of the energy - fuel savings. More specifically, due to the fact that the GS(s) is (are) working fewer hours under almost full load, compared with the previous state where it was (they were) working continuously for 24 hours a day under partial load, we have an improvement of the efficiency, a decrease of the emitted pollutants through the improvement of combustion conditions, a decrease in the fuel consumption, an increase of the expected life of all parts, since they are stressed for a smaller time interval, compared with the hours of operation of the set, an increase of the interval between consecutive services, a decrease in the number of visits by specialized squads for the maintenance of the generator, down to 1 visit for the regular service per 30 days, and finally the considerable decrease of the required man-hours for the above jobs as well as of the cost of transport to and from the shelter.

In addition, in the invention is specified the permanent installation of the battery bank inside a separate storage space-cabinet, inside or outside of the shelter, with a separate cooling device at a temperature ensuring the optimal behavior of the batteries, the full exploitation of the batteries with constant charging-discharging. This separation makes possible the increase of the limits of operating temperature of the shelter with the telecommunications equipment between 29°C and 35°C, with as a consequence an increase of the time of operation of the air-conditioning units under "free-cooling" and a decrease of the hours of operation of the compressor and consequently an increase of the efficiency of the "Energy management system". The thermal insulation of the batteries offers the ability to create a microclimate inside the cabinet in order to maintain a strictly constant preset temperature. A collateral benefit from this solution, and for the case where we select the installation in a separate cabinet, is freeing valuable internal space. Finally, an important advantage of the separation of the batteries is that the involuntary contact of the technical personnel with the batteries is avoided and the protection of the batteries, in cases such as the approach of qualified personnel or other technical work taking place in the general area of the shelter, is ensured.

The external cabinet containing the batteries is about 850 mm long, 850 mm wide and 2050 mm high and is made of double high mechanical strength steel plates, appropriately painted to prevent corrosion, lined internally with a heat insulating material of high thermal capacity. Access to the cabinet is through two doors located in the front and the rear side, respectively, made of steel plates and heat insulating material. The external cabinet comprises as its base equipment a metallic mount for the batteries, designed to support the increased weight of the batteries, a small electric panel with the necessary automatic controls, magnetic contacts at the doors for signaling in the event of infraction of the doors, an electric heater, stuffing boxes for the cables, while in addition we can mention 2 rectangular holes on the front access door where the herein below mentioned thermoelectric element-based cooling devices are mounted. Naturally, the dimensions, equipment, paint color and some of the constructional details can be altered in accordance with the needs of the installation, the location and the dimensioning of the capacity of the batteries.

The internal cabinet is made similarly and is typically about 850 mm long, 850 mm wide and 2100 mm high. It is made of double aluminum plates, lined internally with heat insulating expanded polystyrene material.

The thermoelectric element-based cooling device is mounted on the ceiling of the cabinet. The available equipment is similar to that of the external cabinet and can be altered according to the specifications of the entire installation.

To achieve the predefined temperature inside the battery storage space and in view of the fact that the required cooling capacity is small since the batteries don't generate appreciable amounts of heat, we select to use a thermocouple-based cooling device or as they are also designated, thermoelectric elements or Peltier elements. These elements consist of a special alloy which, when fed with a DC voltage, can absorb, transfer and reject heat from an insulated - closed system to the environment. These thermoelectric elements possess in addition 2 axial fans, one inside the cooled space and the other externally to the device, on appropriate metallic radiators, which aid in rejecting to the environment heat transferred from the interior of the shelter. The major advantages of these devices are extended working life, small dimensions, small number of moving parts and the absence of any need of preventive maintenance. Also, as is well known, during charging of the batteries there is hydrogen evolution there from, which, at high concentrations, is explosive. For this reason on the upper part of the cabinet are located small circular cross-section ducts, which reject the hydrogen generated to the environment.

In the case of low outdoor temperature, such as during winter, the battery compartment of the external cabinet is equipped with an electric resistance heater with fan, which is appropriately activated to heat the space.

As an example, it is mentioned that from the practice of the invention in a shelter for telecommunications use, during a time period of 10 months with the continuous use of the "Energy management system" and in cooperation with a generating set of intermediate nominal power, a reduction of fuel consumption of more than 35% compared to the initial consumption and a reduction of the total operating time of the GS of almost 55% was observed. It is expected that the application of the "Energy management system" to larger GSs will result in an even larger reduction of fuel consumption.

The energy savings and consequently an even larger fuel and financial resource reduction and the overall efficiency of the "Energy management system" is enhanced by setting separately the temperature of the air- conditioning apparatus inside the telecommunications equipment compartment at a higher level than that required by the batteries. Thus, the temperature inside the shelter is set at values exceeding 30⁰C, while previously the set point was usually at 24°C. The result of this selection is a further reduction of the operating time of the compressor of the air- conditioning units and as a consequence an increase of the life time of the air-conditioning units, with subsequent reduction of the number of failures, of the cost of maintenance and an increase of the reliability of the overall air- conditioning installation.

Fuel savings constitutes an especially attractive motivation, because of the escalating price of oil in the international markets. As a whole and from an environmental viewpoint, the proper use of the invention reduces sensibly the evolving pollutants to the environment due to the consumption of fuel to produce energy, such as CO₂, sulfur- and nitrogen-containing compounds.

The "Energy management system" can cooperate with air-conditioning devices of several types, used in corresponding shelters. The major types are: a split type air-conditioning unit with an indoor evaporator and an outdoor condenser, an air-conditioning unit for installation in a closed space with openings in the walls for heat exchange with the environment and an outdoor air-conditioning unit with openings in the walls for heat exchange with the interior of the shelter. Thus, in the following figures, all possible modifications of the system are shown, relating to the selected type of air- conditioning device, as well as the proposed solutions of the system for the installation of the battery bank in a cabinet, inside or outside of the shelter.

The modifications to the shelter, and the possible choices for the installation of the battery compartment inside or outside of the shelter, ' following the application of the "Energy management system", are shown in the drawings.

The drawings contain the following: Figure Ia: Shows the initial form of a shelter, without the application of the "Energy management system", with 2 air-conditioning units of the split type.

Figure Ib: Shows the initial form of a shelter, without the application of the "Energy management system", with an indoor type air-conditioning unit.

Figure Ic: Shows the initial form of a shelter, without the application of the "Energy management system", with an outdoor type air-conditioning unit.

Figure 2a: Shows the application of the "Energy management system" to the shelter, with installation of the batteries in a special cabinet, externally of the shelter and use of 2 split type air-conditioning units.

Figure 2b: Shows the application of the "Energy management system" to the shelter, with installation of the batteries in a special cabinet, externally of the shelter and use of an indoor air-conditioning unit. Figure 2c: Shows the application of the "Energy management system" to the shelter, with installation of the batteries in a special cabinet, externally of the shelter and use of an outdoor air-conditioning unit.

Figure 3 a: Shows the application of the "Energy management system" to the shelter, with installation of the batteries in a special cabinet, in the interior of the shelter and use of 2 split type air-conditioning units.

Figure 3b: Shows the application of the "Energy management system" to the shelter, with installation of the batteries in a special cabinet, in the interior of the shelter and use of an indoor air-conditioning unit.

Figure 3c: Shows the application of the "Energy management system" to the shelter, with installation of the batteries in a special cabinet, in the interior of the shelter and use of an outdoor air-conditioning unit.

Figure 4: Shows the interaction of the Energy management system with the electro-mechanical equipment of the shelter, in a flow diagram form.

In the drawings, the following items are shown:

• Basic structure of the shelter (1), safely housing all the equipment necessary for its functioning.

• Generating set (2), able to supply electric energy to the shelter's equipment and to charge the battery bank. In the dotted box a second GS is shown, for the cases where the supply of electric energy to the shelter is effected by more than one GSs.

• Air-conditioning devices (3), representing air-conditioning devices of any available type.

• Free-cooling mechanism (4), cooperating with the air-conditioning devices.

• Simple battery cabinet (5), for the placement of the batteries inside the shelter. Separate storage compartment (6), with metallic cabinet, for the placement of the batteries outside of the shelter.

Separate storage compartment (7), with metallic cabinet, for the placement of the batteries inside the shelter.

Central unit of the "Energy management system" (8). With dotted lines is presented the mode of cooperation of the system with the one or more

GS(s), the air-conditioning units and the storage compartment of the batteries.

Power supply - rectifier (9), electrically supplying the shelter, monitoring the characteristics of the current and rectifying the supplied current.

Telecommunications equipment (10), responsible for the handling of the telecommunications signals.

Battery bank (11), for the supply of the shelter with electric energy.

Claims

The "Energy management system" is a complex application consisting of 1) a central control unit (8) comprising a set of controls, measurement instruments, sensors, a touch screen and a tele-management system for monitoring and recording the operational parameters of the shelter as well as for making decisions to activate the corresponding automatic controls relating to the energy management and the operation (on - off) of the one or more GS(s) (2) needed for the electric supply of the shelter (1), by monitoring indoor and outdoor temperature data and storing the excess power generated by the over-dimensioned GS(s) (2), 2) a separate cabinet (6) and (7) for the isolation of the batteries (11), made of metal plates and heat insulating walls, thus ensuring its thermal isolation, located outside of, or inside the shelter, for the maintenance of appropriate temperature conditions of which the installation of DC voltage Peltier thermoelectric elements is chosen to reduce the temperature, the "Energy management system" being characterized by: a) its ability to manage the operation of one or more GS(s) (2), to satisfy the telecommunications and cooling loads, with operating conditions such as to reduce the fuel consumption and the operation time of the one or more GS(s) (2) and at the same time to increase its (their) efficiency, by exploiting the battery bank (11) needed by every shelter (1) b) its ability to store electric energy in the batteries (11) due to the excess power of the over-dimensioned generating set to satisfy the peak load during operation of the air-conditioning units and c) the additional energy savings deriving from the modulation of the temperature in the telecommunications equipment compartment independently from that of the battery compartment, which is optimized for the cases where we select to use air-conditioning devices equipped with a "free cooling" system (4) with fresh air, since the telecommunications equipment compartment is conditioned to a higher temperature compared to the battery compartment.