The Audit Procedure

8/8/2019 The Audit Procedure

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Consultancy is not about knowing all the answers; rather it is about

asking the right questions.

DETERMINING THE NEED

Before any step is taken to work towards conservation of lighting energy, it

should first be ascertained whether such an activity should at all be

undertaken.

The following questionnaire should help in determining the need for

lighting audit.

a) Has the function of buildings remained the same since they were

constructed?

b) Have you developed a lighting schedule for indoor and outdoor lighting?

c) Have you converted from incandescent lighting to fluorescent?

d) Have you converted from standard fluorescent to more energy efficient

compact fluorescent lamps?e) Have you converted from conventional magnetic to energy eff icient

electronic ballasts?

f) Do you use metal halide, high pressure sodium, or low pressure sodium

lamps for outdoor lighting?

g) Do you have controls in your lighting system to provide increased flexibility

and energy savings?

h) Has the lighting system been modified to accommodate rearrangement of

desks and workstations?

i) Have employees been exposed to awareness programmes regarding energy

conservation in lighting?

j) Was the building lighting system designed with energy efficiency in mind?

k) Have you investigated rebate programs, if any offered by your local utility or

the government?

IF ANSWER TO ANY OF THE ABOVE QUESTIONS IS A "NO",

THEN YOUR ESTABLISHMENT NEEDS A LIGHTING AUDIT .


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Pro

dure for Assessmentof Li

htin

Systems

To Determine the MinimumNumber and Positionsof Measurement Points:

Calclate the

e

:

=

Where L = length of interior; W = width of interior; Hm = the mounting height, which is the

height of the lighting fittings above the horizontal working plane. The working plane is usuallyassumed to be 0.75m above the floor in offices and at 0.85m above floor level in manufacturingareas.

It does not matter whether these dimensions are in metres, yards or feet as long as the same unit is

used throughout. Ascertain the minimum number of measurement points from Table10.1.

Table 10.1 Determinationof Measurement Points

To obtain an approximately square array, i.e. the spacing between the points on each axis to

be approximately the same, it may be necessary to increase the number of points.

For example, the dimensions of an interior are:Length = 9m, Width = 5m, Height of luminaires above working plane (Hm) = 2m

Calculate RI=

From Table 10.1 the minimum number of measurement points is 16

As it is not possible to approximate a square array of 16 points within such a rectangle it is

necessary to increase the number of points to say18, i.e. 6 x 3. These should be spaced as shown

below:


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Therefore i thi example the spaci bet een points along rows along the length ofthe interior= 9 6 = 1.5m and the distance ofthe 'end' points from the wall = 1.5 2 = 0.75m.Similarl the distance between points across the width ofthe interior = 5 3 = 1.67m with halfthis val e, 0.83m, between the 'end' points and the walls.

If the grid of the measurement points coincides with that of the lighting fittings, large errors are

possible and the number of measurement points should be increased to avoid such an occurrence.

Calculation of the Installed Load Efficacy and Installed Load Efficacy Ratio of a GeneralLighting Installation in an Interior

STEP 1 Measure the floor area ofthe

interior:

Area = -------------------- m

STEP 2 Calculate the Room Index RI = --------------------

STEP 3 Determine the total circuit

watts ofthe installation by apower meterif a separate

feeder forlighting isavailable. Ifthe actual value isnot known a reasonable

approximation can be

obtained by totaling up the

lamp wattages including theballasts:

Total circuit watts = -----------

--

STEP 4 Calculate Watts per square

metre, Value of step 3 valueof step 1

W/m = ------------

STEP 5 Ascertain the average

maintained illuminance byusing lux meter, Eav.Maintained

Eav.maint. = ------------

STEP 6 Divide 5by 4 to calculate lux

per watt per squareMetre

Lux/W/m = ------------

STEP 7 Obtain target Lux/W/m lux

fortype ofthe type of

interior/application and RI(2):

Target Lux/W/m =

STEP 8 Calculate Installed LoadEfficacy Ratio ( 6 7 ).

ILER=


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Table 10.2 Targetlux/W/m (W/m/100lux)values for maintaine illuminance onhorizontal

plane forallroom indicesandapplications:

Ra : Colour rendering index

The principaldifferencebetweenthetargets forCommercialandIndustrial Ra: 40-85 (Cols.2 &

3) of Table 10.2 isthe provision foraslightlylower maintenance factor forthelatter. Thetargets

forverycleanindustrialapplications

with Ra: of 40 -85, areascolumn 2.

ILE A m

Comparethecalculated ILERwiththeinformationin Table 10.3.

Table 10.3 Indi atorsof Performan e

ILER Ratios of 0.75 or more may be considered to be satisfactory. Existing installationswith

ratios of 0.51 - 0.74 certainly meritinvestigationto seeifimprovementsare possible. Ofcourse

therecanbegood reasons fora lowratio, suchashavingto use lowerefficacy lamps or less

efficient luminaires in orderto achievethere uired lightingresultbut it isessentialto chec

whetherthereisascope fora moreefficientalternative. Existinginstallationswithan ILER of 0.5

orlesscertainlyjustifycloseinspectionto identify options forconvertingtheinstallationto use

moreefficientlightinge uipment.


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Having derived the ILER for an existing lighting installation, then the difference between the

actual ILER and the best possible (1.0) can be used to estimate the energy wastage. For a given

installation

Annual energy wastage (in kWh)

= (1.0- ILER) x Total load (kW) x annual operating hours (h)

This process of comparing the installed load efficacy (ILE) with the target value for the Room

Index and type of application can also be used to assess the efficiency of designs for new or

replacement general lighting installations. If, when doing so, the calculated ILE (lux/W/m) is less

than the target value then it is advisable to ascertain the reasons. It may be that the

requirements dictate a type of luminaire that is not as efficient as the best, or the surface

reflectance are less than the normal maxima, or the environment is dirty, etc., whatever the

reasons, they should be checked to see if a more efficient solution is possible

Exa ple of ILER CalculationSTEP 1 Measure the floor area of

the interior:Area = 45 m

STEP 2 Calculate the Room Index RI = 1.93

STEP 3 Determine the total circuitwatts ofthe installation bya power meterif a separatefeeder forlighting isavailable. Ifthe actualvalue is not known areasonable approximation

can be obtained by totalingup the lamp wattagesincluding the ballasts:

Total circuit watts = 990 W

STEP 4 Calculate Watts per square

metre, 3 1 :

W/m = 22

STEP 5 Ascertain the averagemaintained illuminance,Eav. Maintained (averagelux levels measured at 18

points)

Eav.maint. = 700

STEP 6 Divide 5by 4 to calculatethe actuallux per watt persquare Metre

Lux/W/m = 31.8

STEP 7 Obtain target Lux/W/mlux fortype ofthe type ofinterior/application and RI

(2):(Refer Table 10.2)

Target Lux/W/m = 46

STEP 8 Calculate Installed LoadEfficacy Ratio ( 6 7 ).

ILER= 0.7

Referring to table 3, ILERof 0.7 means thatthere is scope for review ofthe lighting system.Annual energy wastage= (1 ILER) x watts x no. of operating hours

= (1 0.7) x 990 x 8 hrs/day x 300 days=712 kWh/annum

The Audit Procedure

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