calculation of energy efficiency in space for telecommunications

BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI Publicat de

Universitatea Tehnică „Gheorghe Asachi” din Iaşi Tomul LX (LXIV), Fasc. 2, 2014

Secţia AUTOMATICĂ şi CALCULATOARE

CALCULATION OF ENERGY EFFICIENCY IN SPACE FOR TELECOMMUNICATIONS EQUIPMENT

BY

GHEORGHE DORU DICU

University of Craiova,

Faculty of Automation, Computers and Electronics Received: September 8, 2014 Accepted for publication: October 15, 2014

Abstract. This paper will consist of a study on energy needs for heating, cooling and ventilation of the spaces for telecommunications equipment (shelters). The study is performed two options when heating equipment, cooling or ventilation or not monitored and controlled by a controller.

Key words: ambient parameters, temperature, monitoring, ventilation, equipment, telecommunications.

2010 Mathematics Subject Classification: 68M99, 68W35.

1. Introduction

There are currently a multitude of companies producing telecommunications shelters which are unsuitable for this activity, where condensation is common or there is poor ventilation, protective systems against voltage are missing and, not least, the insulation is undersized if not absent.

The idea of this approach is the safe operation of telecommunications equipment, lowering the maintenance costs, maintenance of environmental parameters within shelters, extending the life of both the telecommunications equipment and air conditioning equipment and lowering energy consumption. Corresponding author; e-mail: [email protected]

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Fig. 1 − The layout of telecommunications equipment and air conditioning in a shelter. These shelters are equipping mobile networks and the equipment of the Ministry of National Defense, Ministry of Interior, the National Meteorological Administration, etc.

1.1. Requirements Imposed for Operating a Shelter The environmental conditions in which you can install telecommunications containers must comply with ETSI EN 300 019 class 4.1 ETSI EN 300 019-1-4 V2.1.2 (2003-04), including:-ambient temperature between −33°C and +40ºC; Maximum relative humidity 100%; the maximum air-speed of 50 m/s; the maximum intensity of rain-6 mm/min. Recommendations made by manufacturers of telecommunications equipment, indicate that the temperature must be guaranteed within a shelter conform to the ETSI EN 300 019 class 3.6 ETSI EN 300 019-1-3 V2.3.2 (2009-07), i.e. an internal temperature between 15ºC and 30ºC.

1.2. Climate Parameters Energy consumption of one shelter depends on external and internal factors. External factors are climatic characteristics of the site: air temperature, wind speed, sunshine and humidity. Designing shelter and related facilities should be made based on statistical averages of climatic parameters corresponding to a certain period of the year (day, month heating season). These conventional values are standardized in SR 4839 and SR 1907-1for the air temperature and wind speed, in STAS 6648/2, for sunlight, moisture, etc. − The air temperature: For the calculation of the heat demand of a shelter (the heat demand that scales the heating zone) is used the conventional external temperature for calculating ( eT ). According to SR 1907-1 Romania is

Bul. Inst. Polit. Iaşi, t. LX (LXIV), f. 2, 2014

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divided into four climate areas with corresponding outside conventional temperatures for calculating. To calculate the annual heat requirement of a building and the need for the heating fuel use average monthly outdoor temperatures.

Fig. 2 − Zoning Romania after conventional external temperature for calculation. When designing ventilation and air conditioning installations for the summer situation, and setting the cooling heat load, the daily average outside temperature for July is used, in accordance with standard STAS 6648/2. − Wind. Outside air penetration in the rooms (air infiltration) occurs due to wind action. Usually the lowest outdoor temperatures do not correspond with the highest wind speeds. On statistical basis, on concomitance wind – temperature, values were adopted for calculating the wind speed, which determines the four wind zones in the country. Framing the localities in wind areas is indicated in SR 1907-1. Conventional wind speeds for calculating are given in the Table 1:

Table 1 Conventional Wind Speeds

− Sunshine. Climatic data on sunshine (sunshine duration and intensity of solar radiation) is of interest both for the warm season and for the cold

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season. They are used for sizing the air conditioning in summer, establishing the solar contributions to be taken over. Also on sunshine climate information is used to correct the heat requirement for heating, to the extent that the building is properly conformed to capture the solar energy in cold season. The Table 2 give average amounts of sunshine duration in hours per month for some cities in Romania.

Table 2

Sunshine Duration for Some Cities in Romania

On clear sky, the direct radiation maximum while on diffuse sky is minimum, and on cloudy sky, vice versa. Global solar radiation is different depending on the time of day; direct solar radiation is different according to the receiving surface orientation. Solar radiation intensity values are given in STAS 6648/2, on the months of the year and hours of the day.

Fig. 3 − Solar radiation (Wh/m2) within a year. − Humidity. Outdoor humidity plays a significant role in the venting and cooling technique. This can be expressed as the relative humidity as a percentage, or as absolute humidity (or moisture content) in grams of vapors per 1 kg of dry air. The values of the moisture content of outdoor air for the main cities in Romania are given in STAS 6648/2.


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2. The Structure of the Shelter

2.1. The Structure of the Shelter and the Heat Flow

Fig. 4 shows the structure of the shelter and heat flows inside and outside the shelter.

Fig. 4 − The energetic balance elements of a shelter.

Shelter is equipped with the following items: − heat source used in periods when the temperature is less than 15ºC and the temperature inside the shelter tends to fall below 15ºC; − source of air conditioning (cooling) used in periods when the temperature is higher than 30ºC and the temperature inside the shelter tends to increase over 30ºC; − fan system for introducing outside air when the temperature is between 15ºC and 30ºC or under power when the temperature exceeds 35ºC, if the air conditioning does not work. Control scheme of such equipment managed by a microcontroller is shown in Fig. 5 (Ciobanu, 2006).

Heating equipment

A.C.

Ventilation temperature

sensor

Fan 1

Fan 2

SMC-01

D.C. Control Panel 230/400 ac

Outside temperature sensor

Temperature sensor equipment

Ventilation temperature

sensor

Fig. 5 − Temperature control elements for shelters.

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2.2. Heat Air, and Moisture Flows Through the Envelope of a Shelter − Building envelope: The envelope of the building is made up of all surfaces, peripheral construction elements that separate the interior volume (heated or cooled) by the external environment or unconditioned spaces outside the building. Building envelope separates the internal volume of the building by: − outdoor air; − ground (the plates in direct contact with the ground or above ground level systematically placed either under this quota, and the walls in contact with the ground) (Vînătoru et al., 2008). Building envelope area ( A ) - the sum of all areas of the building perimeter constructive elements through which the heat transfers, and it is calculated using:

2, mjA A

where: jA represent areas of construction elements that are part of the building envelope.

Fig. 6 − Heat flow in a telecommunications shelter.

Maintaining the desired indoor climate conditions is achieved by controlling the flow of heat, air and moisture between the interior and exterior of the building. The presence of these flows is shown in Fig. 6, where it can distinguish the heat flows cQ (loss through the walls), the flow of air, and moisture carried by ventilation vQ . − The envelope and heat flow: The mechanisms (or modes) of heat transfer are thermal conduction, heat convection and thermal radiation. The flow of heat from the envelope may be accomplished by one, two or all three modes. The conduction of heat arises in a stationary environment (either solid, liquid or gas) by transferring the energy from microscopic particles of component (molecule, atom) with high speed to those with low speed as a result of inherent collisions between the particles.


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Thermal convection occurs between a surface and a moving fluid, being achieved by the combined action of thermal conduction through the fluid and the macroscopic motion. Thermal radiation is the energy emitted in the form of electromagnetic waves as a result of changes in the electronic configuration of the transmitter body. The thermal radiation occurs at any level of the temperature and despite convection and conduction, it doesn’t require a carrier environment. Through walls, a transfer occurs from the heat of the external environment by convection and radiation from the air and sun, by conduction in the shelter walls and by convection from walls to the air inside. The direction of the heat flow depends on the temperature difference according to the second principle of thermodynamics.

The heat exchange will be globally approximated with the one submitted by convection directly between outside and inside air temperature approximately with a relationship as:

conv i i z extQ h A T T

where iA are the areas of the shelter walls and hi are the global convection coefficients (Iancu & Vînătoru, 2003).

3. Mathematical Model of Shelter

3.1. Dynamic Model The dynamic model of shelter results from the thermal balance equation for the volume V of air of the shelter in the shape:

- -

- -

zs a a c v v a z ex r r a r z

ac ac a ac z p pi ex zi

dTV C Q F C T T F C T Tdt

F C T T h A T T

occurring the following terms:

cQ − amount of internal heat sources (lighting, electrical equipment, people).

p pi ex zh A T T − equivalent convective heat transfer from the outside air temperature with exT temperature to the shelter interior volume with zT temperature through the iA surfaces of the shelter.

min f P zC T T − heat transfer due to infiltration of outdoor air (doors, windows).

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v v v a z exQ F C T T − heat transfer through air circulation fans fitted to shelter.

rad r r a r zQ F C T T − the transfer of the heat from the heat radiator of the shelter used in the cold periods.

ac ac a ac zQ F C T T − the transfer of heat from the air conditioner, which introduces air at ac zT T temperatures. In the mathematical model heat sources using coefficients were introduced v , r , ac that have values equal to 1 if the source is used and equal to zero if the source is not used in function of control program of temperature shelter system (Vînătoru, 1993).

The values of these coefficients in accordance to exT outdoor temperature are presented in Table 3. In function of this strategy we develops the controller program.

Table 3

The Values of a Coefficients

3.2. Stationary Model of a Shelter Heat to be supplied or removed to maintain a site as intended, is the thermal load of a heating or air conditioning equipment. Calculations are similar to those in accounting. It is believed that all the heat is produced within the building or to be transferred through the envelope; total energy, including thermal energy stored inside, is conserved according to the first law of thermodynamics. Outside air, occupants, and certain equipment contributes to the term representing the sensible heat (temperature dependent), as well as to the term representing the latent heat (depends on the state of aggregation). Heat load calculations are simple as long as the operating mode is static (or stationary energy exchanges that are constant). Shelter stationary state the results from the equation by equaling to zero the right hand. This balance allows us the calculation of total installed power of the shelter and its annual energy consumption. Energy balance of the building includes the following terms of sensible and latent energy:


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a) Conduction through the shelter envelope , [W]cond cond i eQ K T T Thermal conductivities are characteristic to each type of material, thermal insulation materials are characterized by conductivity below 0.1 W/mK.

b) Conduction through the walls and floor In traditional construction, heat transfer to the ground is usually small and therefore neglected but in super-insulated buildings, it may be relatively important.

( ) , [W]sol sol sol i sol eperimetru

Q U A T T

In our case telecommunication shelter having no walls or floors in contact with the ground resulting 0solQ .

c) Heat due to air exchange (infiltration, seepage and/or ventilation) , inf , [W]aer sens i eQ K T T

, 0aer sensQ because inf 0K . There is no air exchange with the outside world (ventilation) than in winter when the temperature is above 15°C and in the summer when the outside temperature is more than 31°C. In winter the temperature often rises above 15 degrees in sunny times of the day and automatically turns off the radiator heating. In the summer temperature is below 31°C at night and during the day when it is cloudy, therefore the air conditioning comes on hold.

d) Heat gains due to solar radiation, lighting, equipment (home appliances, computers, fans, etc.) and the occupants , , , , [W]spor sens solar ilum echip sens ocup sensQ Q Q Q Q To calculate ,spor sensQ , sense there are two options:

− on the site there is no person and it is not used any lighting automatically and calculations are made for a total of seven devices that emitt each about 200 W/equipment and solarQ 20 W/m, then: , 1730 Wspor senseQ ;

− a person working in the room (who emitts the equivalent of 150 W/h/person) who uses a personal computer and lighting that is used to full capacity, then: , 2090 Wspor senseQ ; The power radiated by the sun on a square meter can easily pass 1000 W in our country.

e) Latent heat gains are mainly due to the exchange of air, equipment and occupants. , , , , , Wspor lat aer lat echip lat ocup latQ Q Q Q

, 0aer latQ , cannot be considered because air exchange is made by fans when the outside temperature is lower than the indoor temperature and that only in the range of 15 to 31°C, for saving electricity.

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,echip latQ is calculated for seven telecommunication equipment that produce about 200 W/h/equipment.

then: , 1400 Wspor latQ . f) Heat stored in the thermal capacity of the building. A dynamic

analysis includes this term, while it neglects stationary analysis because the building temperature does not vary over time.

, [W]stoc p efmateriale

dTQ V c C Tdt

where efC is the effective thermal capacity of the building. 0stocQ , in our case is considered stationary. Is customary for the sensible heat loss by conduction and air exchange to express themselves synthetically by a single term, since both depend on the temperature difference between inside and outside: , inf , [W]tr sens cond i e tot i eQ K K T T K T T where 1.15 W/KtotK , is the total coefficient of thermal losses or isolation.

, 12.65 Wtr sensQ . Where eT (10°C) is the annual average temperature around the globe.

In our country, yearly eT average is about 11°C. It is customary expression of loss per unit volume, where the Romanian

literature notes: 3, [W/m K]tot cladG K V

325.875 W/m KG where building volume cladV is heated building volume (3x3x2, 5 m),

bounded by the envelope. Instant heat load of the building is the sum of sensible and latent

components at a time: , [W]clad i e sol spor stocQ G V T T Q Q Q

When heating (outdoor temperature is 18°C and the indoor temperature to be maintained is 22°C): 568.75 WQ ;

The value is calculated for one day in April/October with the following temperatures:

Table 4

Temperature for one Day – April to October Times 08.00 12.00 16.00 20.00 00.00

Temperature [°C] 12 22 25 19 22


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On cooling (outdoor temperature is 25°C and the indoor temperature to be maintained is 22°C): 346.56 WQ .

The value is calculated for one day in May/September with the following temperatures:

Table 5

Temperature for one Day – May to September Times 08.00 12.00 16.00 20.00 00.00

Temperature [°C] 18 25 32 25 20

The sign convention is Q to be positive when there is a heating load

and negative when there is a cooling load. A negative value for aerQ , lat leads to a heating full load higher than the sensible heating load - but this is only relevant if the interior provides a humidifier to keep the iW humidity constant (Vînătoru & Iancu, 1999).

3.3. The Annual Energy Consumption

Optimal design of the building, in the sense of minimizing costs over its lifetime, requires an assessment of the annual energy consumption anQ representing the full-time snapshot consumption during heating or cooling. The calculation methods are of two major types: static methods (based on degree-day or temperature ranges) and dynamic methods (based on transfer functions). Methods degree-days are appropriate if the use of the building and equipment efficiency can be considered constant. For situations where the efficiency and conditions of use varies significantly with the outside temperature, consumption can be calculated for certain values of the outdoor temperature and this is multiplied by the number of hours corresponding year intervals centered around these values; annual consumption is the sum of the combined consumption associated with each outdoor temperature range. This approach represents the temperature ranges method. The equilibrium temperature echT of the building is defined as the outdoor temperature eT for which, for a given value iT , total heat loss is equal to the increments of heat (sun, occupants, lighting and so on). For static analysis, the effects of storage (stocking) are zero and if, moreover, the heat transfer to the ground is neglected, then energy balance becomes: , [W]clad i ech sporG V T T Q

Hence, the equilibrium temperature results:

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/ , [ C]; 19 Cech i spor clad echT T Q G V T where heat flow must be average values for the periods in question, not the peak. All calculations will be made for a shelter size of 3x3 m base and a height of 2.5 m. The heating is therefore necessary if eT falls below balT . Then, the energy consumption of the heating system is given by:

inc incQ ( ) , [ ]; Q 5155 Wcladech e

inc

G V T T t W

where inc is the annual fuel utilization for the efficiency (or other primary sources), its value taking into account the variation of efficiency at partial loads. If

inc , echT and totK are considered constant and using average daily values of outdoor temperature eT , medium, annual heating consumption can be calculated as:

incQ ( ) , [W/zi/an] ,clad clad eech e echzileinc inc

G V G VT T t dt T T

3.4. Calculation of Total Installed Power in a Shelter

In the Table 6 we present the electrical energy consumption in an unassisted shelter for heating/cooling of an intelligent monitoring and control of ambient parameters.

Table 6

Electrical Energy Consumption

Electricity consumption decreases a lot during a year, if the shelter is heating/cooling assisted by an intelligent monitoring and control of ambient


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parameters. At the same time, the stem provides temperature conditions specified by the manufacturer for a minimum of 15°C in winter and maximum 30°C in the summer leading to substantially extend of the equipment life and increased safety for voice and data transmissions. In the Table 7 we have the electric energy consumption in a shelter assisted for heating/cooling by a monitoring and temperature control system.

Table 7 Electrical Energy Consumption

If the shelter is unassisted for heating/cooling by a monitoring and temperature control system, then other costs arise that were not listed in table:

− the roads effectuated cost to attach/detach the cooling/heating equipment;

− personnel costs for these trips; − very high time allocated for this procedure.

4. Conclusions

In accordance with the law no. 199/2000 on efficient use of energy, all energy consumers are required to meet standards and technical regulations and possess a system for monitoring energy consumption. Consumers using more than 1,000 tons of oil equivalent per year must conduct an annual energy balance and to draw up programs of measures to reduce energy consumption. Smart energy management provides the greatest opportunity now, in order to decrease power consumption in a telecommunications network. The most important thing is the operation of telecommunications equipment in environmental parameters recommended by the manufacturer,

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leading to their safe operation, leading to increased life and lowering maintenance costs. On shelter telecommunications market that is in use at this point it can be said that there is no a product to manage heating equipment, air conditioning and ventilation although these heating and air conditioning equipment are in use, they are connected manually by maintenance personnel. As can be seen from the above calculations, saving electricity is at least 700 KW per year at a single telecommunications shelter. Considering that a telephone network has at least 100 shelters in a county, nationally results in a saving of at least 2800 MW at the end of calendar year.

REFERENCES

Ciobanu L., Sensors and Transducers. Ed. MatrixRom, Bucureşti, 2006. Iancu E., Vînătoru M., Analitical Methods for Fault Detection and Isolation – Case

Studies. Ed. Universitaria Craiova, 2003. Vînătoru M., Iancu E., Fault Detection and Location in Dynamic Systems. Ed. SITECH,

Craiova, 1999. Vînătoru M., Iancu E., Maican C., Cănureci G., Automatic Conduction of Industrial

Processes. Ed. EUC Universitaria Craiova, 2008. Vînătoru M., Teoria sistemelor. Tipografia Universităţii din Craiova, 1993.

CALCULUL EFICIENŢEI ENERGETICE ÎN SPAŢIILE DESTINATE

ECHIPAMENTELOR DE TELECOMUNICAŢII

(Rezumat)

Lucrarea dezvoltă o soluţie integrată de încălzire, răcire şi ventilaţie pentru spaţiile destinate echipamentelor de telecomunicaţii, ce sunt monitorizate şi comandate de un controller. În acest mod se asigură o scădere semnificativă a consumului de energie electrică, o scădere a costurilor de administrare, o creştere a siguranţei şi prelungirea vieţii în funcţionarea echipamentelor de telecomunicaţii. Contribuţiile personale în implementarea acestui proiect sunt: realizarea unui model matematic (dinamic şi staţionar), realizarea unui studiu privind consumul anual de energie; realizarea unui studiu privind calculul puterii instalate şi nu în ultimul rând, ideea folosirii unei reţele de senzori distribuiţi (în număr de patru - unul exterior şi trei interiori) gestionaţi de un microcontroler, ce conduce la folosirea temperaturii exterioare a aerului (prin ventilaţie) pentru o mai bună gestionare a fluxurilor de căldură din shelter, în toate anotimpurile atât ziua cât şi noaptea.

calculation of energy efficiency in space for telecommunications

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