Value Proposition: Designing warehouse lighting

The Value Proposition is a series that takes a look at the continuing developments in lighting technology, for all those seeking to improve the efficiency and performance of their projects. In our latest proposition we consider how improvements in LED performance can bring substantial savings in the cost of lighting a warehouse, with no reduction in lighting quality. This is all achieved with the assistance of GlamoxLuxo. 

 

The project briefing

A new distribution centre is due for a re-fit. It is assumed that the new lighting installation will use conventional metal halide high-bay luminaires, providing an average of 200 lux on the warehouse floor. The overall area measures 22.5m x 60m and storage will generally be low level, although some provision is required for high-level racking. With this in mind, an optimal spacing of 3.75m between rows of luminaires is required along the building’s transverse axis.

The Proposition

Calculations suggest that an array of 250W metal halide luminaires can deliver the appropriate lighting coverage, with a spacing of 3.75m x 8.5m and a mounting height of 11.5m. The spacing criteria suggests that 42 luminaires are required, with an installed electrical load of 11.5kW. In the interest of energy reduction, an LED solution is offered alongside the conventional metal halide solution.

EXISTING  i50 250W metal halide                                       PROPOSITION GIR-1500 LED 

Return on Investment

With the purchase price of an LED luminaire set just below a conventional metal halide solution there is no reason not to adapt to the new technology. Even allowing for a replacement of an LED luminaire at the end of its life, the annual cost difference between metal halide and LED runs to £959.70.

This means that the project would see an impressive return on investment from the time when the fixtures are first switched-on.

Luminaire maintenance

Value propositions involving LED luminaires often ignore any maintenance costs. Airborne grime will always have an effect on light output so lumen maintenance is important. This value proposition assumes that the metal halide luminaire would be accessed every two years for cleaning and a lamp change.

Replacing LED arrays and drivers

One of the more complicated aspects of shifting to LED is the issue of what happens when a fixture’s life-span limit is reached. There is growing concern that luminaires built to survive industrial environments should not be sacrificed because the light source has reached a given point and is still working. Some companies have opted to shift to a modular arrangement for LED array and driver, allowing the components to be removed and replaced.

The unique problem that is being addressed is that no one knows what the LED array will look like in the coming years.

With this in mind, GlamoxLuxo uses industry standard modular-designed LED boards, making the replacement of the light engine an option at the end of the rated life. The robust steel housing is not sacrificed, and the new lighting arrangement will be determined by the technology pertaining at the time of exchange.

This is all well and good, but doesn’t provide any clue as to what situation the end-user will be faced with in practice. Therefore, the annualised cost of lamps in the LED table above assumes a complete replacement and shows no discounting that would be expected from a take-back programme.

RUNNING COSTS

250W MBI BAYASSUMED ANNUAL HOURS OF USE: 3000 HRS

INSTALLED ELECTRICAL LOAD: 11550W

@ £0.10 / KWH

ANNUAL RUNNING COST: £1155.00.

LAMP CHANGE EVERY TWO YEARS

ANNUALISED COST OF LAMPS: £15.00

@ 42 LAMPS = £630.00

ANNUAL COST OF INSTALLATION: £1785.00
84W LEDBAYASSUMED ANNUAL HOURS OF USE: 3000 HRS

INSTALLED ELECTRICAL LOAD: 3528W

@ £0.10 / KWH

ANNUAL RUNNING COST: £352.80.

LED CHANGE REQUIRED EVERY 16 YEARS

ANNUALISED COST OF LAMPS: £11.25.00

@ 42 ARRAYS = £472.50

ANNUAL COST OF INSTALLATION: £825.30

Lighting controls

We've made an assumption for the figures given above that there is no energy management control strategy. The warehouse will operate for approximately 12 hours a day, 6 days per week. The lighting works continuously at 100 per cent during those times, but it doesn't have to be like this.

Traditionally, metal halide lamps have not been dimmed. Attempts to do so were never really successful, but the introduction of LED lighting has changed the potential for energy savings via dimming control. 

Lighting controls can be used to manage the use of energy across either the entire warehouse floor or in specific zones of operation. This will reduce energy spend when there is less activity in some areas and when there are no operatives on the floor. Once the racking is in place, lines of luminaires can be provided with zonal controls so that the lighting in aisles not in use can be reduced.

The Verdict

There is no argument that the LED option offers a better solution over the conventional high-pressure discharge lamp. Not only does the shift to LED offer an almost immediate return on investment, but a further investment in lighting controls could take advantage of the LED’s dimming ability to save yet more energy.

Some may argue that the metal halide lamp has been short-changed in terms of its life term, but this Value Proposition levels that playing field by looking at the point when lamp light output falls to 80 percent, rather than the typical 50 percent that is often quoted for conventional sources, to the detriment of the LED option. In any event, its the 250W rating against the 84W of the LED that causes the real financial damage.