average lighting power densities

REPORT

on

DETERMINATION of AVERAGE LIGHTING POWER DENSITIES

for

COMMERCIAL BUILDINGS

prepared for

Australian Building Codes Board Office

By

Brian Reilly Booth and Reilly

Consulting Engineers Brisbane

6 May, 2002

ABCB Office Lighting Power Densities - Commercial Buildings

SYNOPSIS

This report considers the average lighting power densities inherent in basic lighting design for commercial buildings. It is predicated on the lowest practicable cost solution, within the constraints of AS1680. The lighting power densities do not take into account any power savings which would result from a life cycle cost analysis.

It is based on lighting design where minimum installed cost is the sole determinant.

The report also considers probable future developments in energy efficiency in commercial lighting within the next few years. External lighting (facade floodlighting) is also considered in general terms.

ASSUMPTIONS

Luminaires Considered The following luminaires have been selected on the basis of being the most probable selections for a spec builder and being available throughout the country. This was determined by surveying wholesalers as to their perception of the most cost effective fittings in the various categories.

2/36W budget troffer, K12 2/36W budget troffer, K19st 2/36W budget Low Brightness

Thorn BTN236HHS Thorn BTN236HHS Thorn BTN236HHS/LOU

Pierlite ET236QS Pierlite ET236QS Pierlite ET236QS/S

Harcroft TB236Q/K12 Harcroft TB236Q/K19st Harcroft CR236Q

For commercial building applications in the mid range lighting levels, where uniformity requirements dictate a higher installed flux than is necessary to meet the base lighting requirements of AS1680, single lamp fixtures would obviously offer energy saving benefits. However, the capital cost of recessed single lamp luminaires far exceeds that of the ubiquitous twin lamp fittings, and they therefore not relevant in an installed cost only analysis.

For lower lighting levels (160 lux and below) it was considered that surface mounted fittings with wrap around diffusers, and recessed compact fluorescent downlights, may offer cost advantages over the standard recessed twin lamp fluorescent troffers. It was found that the costs of standard commonly used luminaires of these types varied little. It was therefore decided, for this analysis, to select typical middle of the road luminaires as follows.

2/36W diffused batten 1/36W diffused batten

Thorn CBDN236 Thorn CBDN136

2/18W recessed downlight 1/18W recessed downlight

RLM 13910 RLM 126103

Booth & Reilly April 2002 2 / 12



General

Room reflectances 70/50/20

lamp lumens 36W fluorescent 3350 initial 18W compact fluorescent 1200 initial

Ballast Magnetic low loss (LLEC) with ballast factor of 0.945

Starter Standard FSU type

Other For comparison of installation costs, it has been assumed that the luminaire has a fused terminal block, and flexible cable with 10A plug top.

Maintenance Factor Assumptions

Enclosed luminaire (e.g. K12/K19 troffer)

Open bottom luminaire (e.g. louvred fitting)

Lamp lumens, tri-phosphor lamps 0.9 0.9

Lamp lumens, halo-phosphor lamps 0.76 0.76

Luminaire 0.9 0.95

Room surfaces 0.95 0.95

Based on the above, maintenance factors were selected as follows :-

Luminaire type with tri-phosphor lamps with halo-phosphor lamps

Enclosed luminaire 0. 78 0.65

Open bottom luminaire 0.81 0.68

In developing the maintenance factors, it has been necessary to consider the intent of AS1680 and to recognise that a speculative builder is not constrained by maintenance issues. In essence, such a builder could decide on any maintenance regime to suit their purposes. The factors therefore lean more to a commercial reality, the sort of factors a luminaire manufacturer would employ when providing a lighting layout, under tender conditions, for such a development.



Room Aspect Ratios Most commercial spaces have aspect factors close to 1:1, with 1:2 maximum. However, in a constrained site, and looking at an open plan situation prior to breaking the space up into workstations and/or individual offices, very high aspect ratios could result.

AS1680 considers that room indices are valid up to 1:4 aspect ratio.

Consequently, 1:1, 1:2, 1:3 and 1:4 aspect ratios have been considered.

Lumen Method As this report considers only basic lighting installation, Coefficient of Utilisation tables, as published by the manufacturers, have been used, with specific room indices.

Glare Exact calculations for glare are not practicable for this basic lighting design analysis.

The following general limitations were adopted based on luminaire types:-

Glare index Luminaire types acceptable

>19 Diffused battens, recessed troffers, downlights

16 - 19 K12, K19 silvertint, low brightness louvre



LIGHTING POWER DENSITIES

General

The lighting power densities in the following Summary sheets are the average values for the cheapest complying lighting installation. The averages are :-

for room indices 0.75. 1.0, 1.25 and 1.5

for room indices 2, 2.5, 3, 4 and 5

Due to the requirement to comply with a 1200x600 ceiling grid, averages are considered the most appropriate representation, to eliminate extremely high figures purely as a result of room dimensions.

A room index of 1.5 was chosen as the demarcation point between large and small rooms. RI1.5 represents a 6m x 6m room at 2.7m ceiling height.


SUMMARY OF LIGHTING POWER DENSITIES 2700mm CEILING HEIGHT Function (AS1680.1-1990, Table 3.1) Re-

commended Illuminance Level, Lux

Work Plane, m

Glare Index Typical Luminaires Room Index 1.5

Watts/m2

Comment

Waiting rooms 160 0.7 22 K12 recessed troffers, diffused battens, compact fluorescent downlights

8.74 5.2

staff canteens 160 0.7 22 K12 recessed troffers, diffused battens 8.74 5.2

food preparation 240 0.9 22 K12 recessed troffers 16.33 13.15 K12 cheapest

training rooms 240 0.7 19 K12 recessed troffers, K19st recessed troffers, low brightness recessed troffers

16.33 13.15 K12 cheapest

Routine office work, e.g. reading, writing, typing, inquiry desks.

320 0.7 19 K12 recessed troffers, K19st recessed troffers, low brightness recessed troffers

16.47 13.15

Routine office work, e.g. reading, writing, typing, inquiry desks - Screen Based Tasks

320 0.7 16 K19st recessed troffers, low brightness recessed troffers

17.15 13.51

Inspection of medium work 400 0.7 19 K12 recessed troffers, K19st recessed troffers, low brightness recessed troffers

18.76 13.5 K12 cheapest

Drawing boards 600 0.9 16 K19st recessed troffers, low brightness recessed troffers

26.53 21.61

proof reading, CAD 600 0.7 16 K19st recessed troffers, low brightness recessed troffers

25.9 20.83

colour matching. 600 0.9 19 K12 recessed troffers, K19st recessed troffers, low brightness recessed troffers

26.58 18.32 K12 cheapest

Fine inspection 800 0.9 19 K12 recessed troffers, K19st recessed troffers, low brightness recessed troffers

33.76 23.96 K12 cheapest

Graphic arts inspection; 1200 0.9 19 K12 recessed troffers, K19st recessed troffers, low brightness recessed troffers

48.18 35.36 K12 cheapest





Work Plane, m


Watts/m2

Comment

Waiting rooms 160 0.7 22 K12 recessed troffers, diffused battens, compact fluorescent downlights

8.77 4.5




13.36 10.35 K12 cheapest



15.39 10.7



14.91 12.05


17.82 12.24 K12 cheapest


25.9 20.83


25.64 21.6


26.3 18.25 K12 cheapest


33.51 23.93 K12 cheapest


47.34 35.09 K12 cheapest





Work Plane, m


Watts/m2

Comment

Waiting rooms 160 0.7 22 K12 recessed troffers, diffused battens, CFL downlights

7.63 5.39




11.23 7.51 K12 cheapest



14.1 9.87



13.93 11.58


17.34 12.14 K12 cheapest


25.56 21.67


27.16 21.92


25.47 17.92 K12 cheapest


32.52 23.61 K12 cheapest


47.58 35.01 K12 cheapest



ENERGY SAVING MEASURES

The power consumption of the various lighting systems considered for the basic lighting power densities can readily be reduced as follows :-

Ballasts The current cheapest conventional control gear has a power consumption of 10W per 36W fluorescent lamp. This type of ballast is will be phased out under the MEPS scheme by 1 February, 2003.

The conventional control gear assumed in the determination of the lighting power densities has a power consumption of typically 6W for each 36W lamp (type B2).

Super low loss ballasts are available, with a watts loss of typically 4W per 36W lamp. This would represent a power saving of 5% compared to the low loss ballast.

Electronic control gear The use of electronic control gear can reduce wasted power to typically nil, on a lumens per watt basis, taking into account the reduced lamp power for an equivalent lumen output at the higher operating frequency.

Presumably due to economies of scale, the cost of a single 36W lamp electronic ballast ($22) is little less than that for a twin 36W fitting ($24). Consequently, for single lamp fittings to be economically viable, and provide resultant energy savings, the use of tandem (aka master, slave or mother, daughter) ballasts (one per 2 fittings) should be considered.

Lamps It is difficult to see, in the near future, any lamps which will rival linear fluorescent for general lighting in commercial office buildings. Their high efficiency, stable colour, and relatively low luminance make them the ideal package.

Tri-phosphor lamps In the majority of the scenarios considered, tri-phosphor fluorescent lamps offer the more economic installation. However, at lower lighting levels where the maximum spacing criterion dominates, halo-phosphor lamps would suffice. These (with a lumen output of 79 lumens per watt) are less efficient than the tri-phosphor lamps (93 lumens per watt).

T5 lamps These have a projected output of 104 lumens per watt at the optimal lamp temperature. Luminaire designs are now being developed and produced to cater for this temperature, and for the higher luminances from the smaller diameter lamp. Energy savings will result.

Materials & finishes Polyester powder-coat paints with a reflectivity of 94%, and good surface integrity over time, are now available and are used on high quality luminaires. These will eventually be the


ABCB Office

Booth &

Lighting Power Densities - Commercial Buildings

Reilly April 2002

norm in the budget ranges.

Luminaires For open plan general lighting at office lighting levels, there is a struggle between luminaire efficacy, luminaire spacing (for uniformity) and glare control. There is also conflict on the way glare is quantified and whether the current glare limitations are valid for real environments.

Luminaires which resolve these issues will allow greater spacings and resulting reductions in power usage.

The most efficient solution is the use of a combination of task lighting and circulation lighting.

Control Zones A flexible switching system, and a culture of energy conservation will easily provide the most cost-effective energy reductions in commercial buildings.

Total floor or building controls are convenient, but have to cater for the worst common denominator, first in and last out. They are advantageous for housekeeping, but do not offer significant energy savings. For that, control should be at a more local level.

Each enclosed space should be separately controlled, either manually or automatically (e.g. movement sensors). Manual controls should be within view of the controlled space to minimise indiscriminate switching.

Open plan spaces should be zoned/switched on a logical basis to allow out of hours operation in specific areas. ASRAE/IESNA 90.1 (1999) insists on a maximum area to be switched as 232m2 in an open plan area of 1929m2 and a maximum of 929m2 in larger areas. Such switching should not subvert any building or floor automatic controls for an unlimited time (say 4 hours maximum).

Areas with a significant daylight component should have complimentary switching systems to maximise the energy savings.

The variations in luminaire types, luminaire placement, aiming angles, angles of incidence and the like would result in an infinite number of solutions. Another level of complexity would be added by the need to comply with the requirements of AS4282 (Obtrusive Lighting).

Incandescent sources are listed. These would not normally be used, however it is not uncommon to see a PAR lamp installation for small buildings sign illumination. Similarly, tungsten halogen would not normally be used on buildings other than say single level.

The typical lighting power densities for building facade floodlighting are shown in the following Summary. These cover the various lamp types and environments.

BUILDING FACADE FLOODLIGHTING

10 / 12

ABCB Office

Booth &

Lighting Power Densities - Commercial Buildings

Reilly April 2002

Consequently floodlighting of a small area, say 10m2 on each building face, could be allowed without having to adhere to lighting power density requirements. This would then allow a more realistic LPD limitation of say 3.5 watts per m2 of facade to be specified for all buildings.

For an energy responsible approach to facade lighting, it is considered that there should be a limit on the allowed lighting power density. However, such a limitation should not prohibit minor floodlighting of signs and/or business names.

Therefore, in arriving at a schedule of watts per square metre of facade, we have made some very broad assumptions; in essence we have used a rule of thumb solution. Consequently, the results would generally err on the conservative side.

11 / 12



SUMMARY OF LIGHTING POWER DENSITIES BUILDING FACADE FLOODLIGHTING

SCENARIO WATTS PER M2 (of faade area)

surrounds surface

reflectivity

Illumination

Lux

INCANDESCENT TUNGSTEN HALOGEN MERCURY FLUORESCENT METAL

HALIDE HIGH

PRESSURE SODIUM

DARK HIGH 20 5.29 3.53 1.06 0.71 0.71 0.58

DARK MEDIUM 35 9.26 6.17 1.85 1.23 1.23 1.01

DARK LOW 50 13.23 8.82 2.65 1.76 1.76 1.44

BRIGHT HIGH 50 13.23 8.82 2.65 1.76 1.76 1.44

BRIGHT MEDIUM 100 26.46 17.64 5.29 3.53 3.53 2.89

BRIGHT LOW 150 39.68 26.46 7.94 5.29 5.29 4.33

ASSUMPTIONS

LUMENS PER WATT 12 18 60 90 90 110

UTILISATION FACTOR 0.35 0.35 0.35 0.35 0.35 0.35

MAINTENANCE FACTOR 0.90 0.90 0.90 0.90 0.90 0.90

6 May, 2002SYNOPSISASSUMPTIONSLuminaires Considered The following luminaires General

Maintenance Factor AssumptionsRoom Aspect RatiosMost commercial spaces have aLumen MethodAs this report considers only basic lighting installation, Coefficient of Utilisation tables, as published by the manufacturers, have been used, with specific room indices.Spacing To Mounting HeightFor the lighting power densities listed, ceilings are assumed to be 1200mm x 600mm T-Bar suspended. To determine the minimum number of fittings in the X & Y direction, it is assumed that the spacing is 2400mm one way, and the oWork Planes

LIGHTING POWER DENSITIESGeneralThe lighting power densities in the following Summary sheets are the average values for the cheapest complying lighting installation. The averages are :-for room indices 0.75. 1.0, 1.25 and 1.5for room indices 2, 2.5, 3, 4 and 5Due to the requirement to comply with a 1200x600 ceiling grid, averages are considered the most appropriate representation, to eliminate extremely high figures purely as a result of room dimensions.

SUMMARY OF LIGHTING POWER DENSITIES 2700mm CEILSUMMARY OF LIGHTING POWER DENSITIES 2900mm CEILSUMMARY OF LIGHTING POWER DENSITIES 3500mm CEILENERGY SAVING MEASURESBUILDING FACADE FLOODLIGHTINGSUMMARY OF LIGHTING POWER DENSITIES BUILDING FASCENARIOWATTS PER M2 $of faade area$

INCANDESCENTHALOGENASSUMPTIONS

average lighting power densities

Documents

commercial lighting

w fluorescent

w budget troffer

w compact fluorescent

basic lighting design

lower lighting levels

w recessed downlight

mid range lighting levels