TUNNEL LIGHTING – DESIGN & CONTROL

Research and Development Sector - Technical University, Sofia

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ABSTRACT

I. DESIGN OF TUNNEL LIGHTING

I.1. INTRODUCTION

I.2. PROGNOSES ABOUT THE hourly charts of luminance L20 AND TRAFFIC INTENSITY ICAR

I.3. COMPUTING THE ANNUAL HOURLY CHART OF THE NECESSARY LUMINOUS FLUX

I.4. OPTIMIZATION OF ARTIFICIAL LIGHTING OF ROAD TUNNELS

II. COMMUNICATION SYSTEM OPERATING PRINCIPLES

II.1. HIERARCHY LEVELS AND OPERATING PRINCIPLES

II.2. SUPERVISORY CONTROL AND DATA ACQUISITION

III. HARDWARE OF CONTROL SYSTEM

III.1. CONTROLLER FOR SUPERVISORY CONTROL

III.2. EMBEDDED CONTROLLERS FOR TUNNEL LIGHTING

III.3. LUMINANCE-METERS FOR CURRENT MEASUREMENT OF L20 AND LTH

III.4. DIMMING DEVICES FOR HIGH PRESSURE DISCHARGE LAMPS

IV. SOFTWARE OF CONTROL SYSTEM

IV.1. PC-SUPERVISORY CONTROL

IV.2. DATABASE

V. REFERENCES

 

I. DESIGN OF TUNNEL LIGHTING

 

I.1. INTRODUCTION

 

The necessary luminance Lth [cd/m2] of the road surface in the threshold zone, immediately after entering the tunnel, is determined by the condition:

(1)        Lth  ³ R.L20.

The level of adaptation luminance L20 [cd/m2] of a driver approaching the tunnel is determined for 20-degree zone of observation measured from a distance equal to the breaking distance to the tunnel entrance. The parameter R [1,2] depends on the conditions of movement in the tunnel (one-way vs. two-way traffic), the kind of lighting installation, and the traffic intensity ICAR [car/h].

The annual maintenance costs for tunnels without ventilation (up to 800 m long) mostly depends on the annul expenses for artificial lighting. Their extent depends on the annual hourly charts of the access zone luminance L20 and traffic intensity Icar. The necessary working power for illuminating a unit area of the road is proportional to the luminance determined from equation (1), and the parameter k:

(2)        p(t)=k.Lth(t)=k.R(ICAR(t)).L20(t), [W/m2].

The parameter k [(W/m2)/(cd/m2)] is a basic quality factor of the lighting system – specific power for achieving a unit luminance on the road. It depends on the type of the lamps used, on the luminous intensity distribution of the luminaires [14], on their placement in relation to the road (centrally or laterally), and on the indicatris of road pavement reflection [25]. The calculated necessary specific power is provided by the simultaneous work of luminaires from a number of circuits. The optimal number of circuits for day lighting is determined by solving an optimization task with the objective of minimizing annual maintenance costs [21].

When step control of the day lighting is used, the optimal number of circuits can be quite large. This is one way of decreasing the over-expenditure of electricity caused by inaccurate adherence to condition (1). Further improvement in the control of the lighting in the threshold and transition zones can be achieved by providing a possibility for smooth adjustment of the intensity of lighting of the lamps in some circuits [19]. The control of the luminous flux is not done individually for each luminary, but rather, it is centralized, with a special dimming device for the whole circuit [22].

Fig.1.1 shows an example of such control devices [20]. Non-dimmable luminaries 1 and dimmable luminaries 2 in the threshold and transition zones are connected to lighting control panel 3, respectively with n circuits with circuit closers 4, and (m-n) circuits with special dimming devices 5. The total number of circuits is m. Lighting control panel 3 is connected to a controller of the lighting 6. The latter is in turn connected to a luminance-meter 7 for measuring the adaptation luminance L20, and a luminance-meter 8 for measuring the luminance Lth of the road surface in the threshold zone and the traffic intensity ICAR (when a vehicle passes through the field of the luminance-meter, the sudden change in the road surface luminance is recorded).

 

 

Fig.1.1. Control of the tunnel lighting with two kinds of circuits – with dimming and without dimming of the luminous flux of the luminaries

 

 

I.2. PROGNOSes ABOUT THE annual hourly charts of THE access zone luminance L20 AND TRAFFIC INTENSITY ICAR

 

The annual hourly charts of the access zone luminance L20[365,24] and traffic intensity ICAR[365,24] are used to calculate the annual chart of the luminous flux FNEED[365,24] necessary to meet the lighting requirements for the threshold and transition zones [1,2]. The annual chart is part of the input data for the optimization task.

Obtaining an annual hourly chart of the luminance L20 is not a problem if there is a tunnel with similar entrance exposure and working monitoring system in exploitation. In this case the easiest way is to use the annual hourly chart of L20 for the previous year directly from the database of the system. Before using the chart it has to be re-scaled using the highest for the new tunnel value of L20, calculated by (1).

When data from a similar tunnel are not available, the annual hourly chart of L20 can be calculated from the regional monthly charts of daylight for sunny, mixed and cloudy days [7]. A statistically reliable data for the ratio between the different type of days for every month [3,21], the maximum value of L20 for the new tunnel, the hourly measurements of L20 for one sunny day, information about the day of the measurements, and the geographic exposure of the tunnel entrance is needed. A satisfying prognostic result for L20 can be received with a method that takes into account the trace of the sun for the specific parallel.

The annual hourly chart of traffic intensity ICAR can be obtained from the road authorities. They have weekly, monthly and seasonal charts of traffic intensity.

Similar approach was used for solving the optimization task for a tunnel on highway “Hemus” in Bulgaria [20]. The annual chart of ICAR was calculated from 12 monthly 168 hourly charts of ICAR, obtained from the road authority. Special software was developed to make the calculations and the arrangement of charts easier 

 

I.3. COMPUTING THE ANNUAL HOURLY CHART OF THE NECESSARY LUMINOUS FLUX FOR THE THRESHOLD AND TRANSITION ZONES

 

Given the parameters of the tunnel, the annual hourly charts of the adaptation luminance L20 [cd/m2], and the traffic intensity ICAR [car/h], the computation of the annual hourly chart of the necessary luminous flux for the threshold and transition zones is done in the following sequence [19]:

Ø      For every hour of the year (1-8760), for the given parameters of the traffic (Table 1), the given hourly charts of the adaptation luminance L20 [cd/m2], and the traffic intensity ICAR [car/h] (Fig.1.2), the class of the tunnel (Table 1) and its coefficient R[I] (Table 2) are determined. Here I denotes the index of the hour;

Ø      From the calculated values R[I], the annual hourly chart of the road surface luminance at the beginning of the threshold zone in the tunnel, LTH[I]=R[I].L20[I], is determined;

Ø      The maximum value LTH_MAX [cd/m2] of all values LTH[I] during the year is found;

Ø      Given the general requirements for decreasing the luminance from the middle of the threshold zone to the end of the transition zone [1], the graph of the luminance in the threshold zone, LTR_l=LTH_MAX*(1.9+l/v)-1.4, is plotted. Here l [m] is the distance from the beginning of the threshold zone to the point, at which LTR is determined, and v [m/s] is the speed limit in the tunnel;

Ø      The line LTH_MAX (up until the middle of the threshold zone) and the curve LTR_l=LTH_MAX*(1.9+l/v)-1.4 (from the middle of the threshold zone to the end of the transition zone) are integrated numerically. From the value obtained for the conditional area, S [(cd/m2)*m], the conditional length of the threshold and transition zones, l_CONDITIONAL =S/LTH_MAX  [m], is computed;

Ø      The necessary luminous flux for achieving the luminance, LTH_MAX, is calculated using the width of the road WK [m] and the specific coefficient of the lighting installation LE [(lm/m2)/(cd/m2)]. The latter corresponds to the efficiency of the particular kind of tunnel luminary and its mounting. FNEED_MAX=LTH_MAX*l_CONDITIONAL*WK*LE [lm];

Ø      The annual hourly chart of the necessary luminous flux FNEED[I] for creating luminance LTH[I] is computed from the formula FNEED[I]=FNEED_MAX*LTH[I]/LTH_MAX;

Ø      The so-computed luminous flux for each hour of the year can be achieved by different combinations of circuits of luminaries, with different levels of dimming of the lamps. If a circuit is non-dimmable, the lamps work at their nominal flux yield (luminous efficiency), while if a circuit is dimmable, the lamps work at a level of the flux yield that depends on the level of dimming.

 

Table 1. Class of the tunnel according to the requirements for artificial lighting (see [2]).

Type of traffic through the tunnel

One-way

Two-way

Traffic intensity [vehic./h]

>1500

500÷1500

<500

>400

100÷400

<100

Traffic type

Ñ

̀

Ñ

̀

Ñ

̀

Ñ

̀

Ñ

̀

Ñ

̀

Tunnel class

4

3

3

2

2

1

4

3

3

2

2

1

Ñ – mixed traffic including bicycles; ̀ – motorized traffic only

 

Table 2. Recommended values for R (see [2])

Stopping distance

60 m

(60 km/h)

100 m

(80 km/h)

120 m

(100 km/h)

Tunnel class

4

0.05

0.06

0.10

3

0.04

0.05

0.07

2

0.03

0.04

0,05

1

Only day and night duty lighting  (<6 cd/m2)

 

 


Fig.1.2. Annual hourly charts of the adaptation luminance L20 [cd/m2], the traffic intensity ICAR [car/h], and the necessary luminous flux FNEED [klm] for the threshold and the transition zones of the tunnel

 


I.4. OPTIMIZATION OF ARTIFICIAL LIGHTING OF ROAD TUNNELS

 

The annual operating costs consist of the cost of the consumed electricity, the price of lamp replacement during the year, the labor costs associated with cleaning the lighting fittings, and amortization deductions.

The lighting fittings in the threshold and transition zones are arranged in circuits, and are powered from a central panel. Usually, the circuits are controlled with circuit closers that provide a simple on/off mode (100% or 0%) of the lighting fittings, depending on the access zone (adaptation) luminance L20 at the tunnel entrance. Modern lighting installations allow for smooth group control of the luminous flux of the light sources by dimming the nominal luminous flux of each of them. The problem of finding the optimal number of circuits, as well as of how many of these circuits should be dimmable, can be formulated as an optimization problem. The data consist of hourly values of the luminous flux needed to produce the required luminance of the road surface at the threshold and transition zones during the year. These values are calculated based on the characteristics of the particular tunnel, on annual hourly charts of the access zone luminance L20, and on the traffic intensity ICAR. From the hourly values of the luminous flux, the hourly values of the necessary electrical power can be computed. The latter enter into the calculation of the cost of electricity. Since the ratio of the flux to the necessary power (the so-called yield) decreases as a larger percentage of the nominal flux of the lighting fitting is dimmed (see Fig.1.3), the most cost-efficient combination of dimmable and non-dimmable circuits in the lighting installation is not immediately obvious. Every combination of dimmable and non-dimmable circuits contributes to the overall operating costs both in terms of different setup prices, and in terms of consumed electricity that depends on the particular dimming schedule for each hour during the year.


Fig.1.3. Characteristics of a high-pressure sodium lamp

 

FL = 1 corresponds to luminous flux of the lamp equal to 48000 lm; PL = 1 - to lamp power of 400 W;  FL/PL = 1 – to flux-yield of 120 lm/W;  UL = 1 – to lamp voltage of 105 V; I = 1 – to current through the lamp equal to 4,3 A

 

The objective of the optimization problem is to determine the optimal total number of circuits m, and of those, the number of dimmable circuits (m-n), so that the operating annual expenses for the lighting installation are minimal. The hourly values of the luminous flux necessary for ensuring safe transition through the tunnel are known (see Fig.1.2). The problem data include also the costs of raw materials, equipment, and labor during the construction and maintenance of the lighting installation, as well as the prices of electricity for the three zones of a 24-hour period (night, day, and peak).

The exact expression for the objective function is:

(3)                                Z = CEN + CMAINT + CA = min,

where:

CEN is the annual cost of electricity for lighting, determined from the calculated chart of necessary electric power given a particular combination of working dimmed and non-dimmed circuits for every hour of the year;

CMAINT is the cost of maintenance of the lighting installation (lamp replacement, labor costs, etc.);

CA is the annual payments, including interest, on a loan taken out in order to build the lighting installation. If a loan has not been taken out, the interest is assumed to be equal to the interest paid on money deposited in a bank. This accounts for the fact that the money should not lose its value by investing it in the construction of the lighting installation as opposed to holding it in a bank.

 

I.4.1. Calculation of the annual cost of electricity for lighting

The cost of electricity CEN is determined from the values PNEED[i] [kWh], the power needed to sustain the necessary luminous flux FNEED[i] [klm] for every hour i during the year (FNEED[i] was illustrated in Fig. 2). The necessary power is computed as:

(4)        .

The first term contains a summation of the power consumed by all non-dimmable circuits, while the second term contains a summation over all dimmable circuits. YIELD, the yield of the non-dimmed circuit, is the nominal lighting yield FLnom/PLnom from Fig.1.3. YIELDDIM[j], the yield of the jth dimmable circuit, depends on the degree of dimming of j. It equals FL/PL, with FL varying between 10% and 100%.

The price of electricity, e[i], EUR/kWh, is different depending on the hour zone within a 24-hour period (night, day or peak), in which the particular hour falls. Choosing a time interval Δt equal to 1 hour, the annual cost of electricity can be written as

(5)        .

 

I.4.2. Calculation of the annual cost of maintenance of the lighting installation

The cost of maintenance consists of expenses for lamp replacement, as well as expenses for cleaning the optical systems of the lighting fittings. It can be computed from the expression:

(6)        ,

where the notation is as follows: eL  price of a single lamp, eL_CH  cost of lamp replacement and cleaning the optical system of a lighting fitting, NLtotal number of the lamps in a circuit, TDIM (respectively, TNODIM) annual use of a dimmable (respectively, non-dimmable) circuit in hours,  TL_LIFE nominal life of the lamps used in hours.

 

I.4.3. Calculation of the annual payments on a loan

Today’s cost of a loan of size K, paid over T equally long periods, and charging interest rate of r per period, can be computed to be (see the concept of “present value” in [24]):

(7)                                .

In our case, K is the amount of capital investment necessary for the construction of the lighting installation. We assume that each time period is a year. r is therefore the annual interest rate. K is calculated from:

(8)        ,

where:

KLUMIN is the cost of purchase of luminaries;

KLINE is the cost of building the circuits;

KDIM_APAR is the cost of purchase and installation of dimmable circuit apparatus;

KNODIM_APAR is the cost of purchase and installation of non-dimmable circuit apparatus.

The components of the cost of capital investment themselves are computed from the following formulas:

(9)         ,

where FNEED_MAX  [klm] is the maximum value of necessary luminous flux in the annual hourly chart, eLUMIN [EUR] is the price of a single luminary, FLUMINARY  [klm] is the luminous flux of the luminary;

(10)      ,

where m is the number of circuits,  eLINE_COST [EUR/m] is the price per meter of a circuit line (the price depends on the number of circuits m, because the cross-section of the line has to be different for different m), length_line is the length of the circuit lines in meters (it equals the length of the threshold and transition zones);

(11)      ,

where eDIM_APAR_COST [EUR] is the cost of a single dimmable circuit apparatus (it is different for different total number of circuits m because of the different power it controls);

(12)      ,

where eDIM_APAR_COST [EUR] is the cost of a single apparatus for control of non-dimmable circuits (automatic fuse and circuit closer). Again, this cost depends on the number of circuits m, because the apparatus has to control different power.

It is assumed that in terms of present value, the first two components of the annual operating costs (CEN  and CMAINT) remain the same over the years. This assumption can be made, because the annual inflation is approximately equal to the base interest rate on bank deposits. The present value calculation is therefore applied only to the costs associated with repayment of the loan, but not to the costs associated with increase in the prices of lamps, labor, and electricity.

The optimization problem is solved for an example of an annual hourly chart of the adaptation luminance L20, taken from real annual measurements of the natural luminance for the region of the city of Sofia [7] and from measurement data of the hourly variation of the luminance L20, obtained with a specialized luminance-meter on a sunny day at the entrance of a tunnel on the “Hemus” highway that faces southwest. Based on data for the average monthly traffic intensity on the “Hemus” highway, and on actually recorded hourly traffic over a week, an example annual hourly chart of the traffic intensity ICAR is put together. The traffic through the tunnel in consideration is one-way, with a speed limit of 80 km/h, and only motor vehicles are allowed.

Using the algorithm described in [21], a C++ program was written to compute the annual costs by enumeration. The goal was to observe how the three types of costs change for each configuration. We consider discrete levels of dimming for the lamps (multiples of 10%), up to 9 circuits, and up to 4 dimmable circuits. We compute all possible outcomes for the present costs of equipment, labor, and electricity in Bulgaria (see the results in [20]). The interest rate is set to 5%, i.e., it is assumed that the tunnel lighting installation is re-configured using private capital as opposed to a loan from a bank.

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