Look to the sky

But before looking at alternative luminaries and light sources it is worth considering the construction of a significant proportion of warehouses and distribution centres.

I am referring to the installation of sky-lights.

The key point is; can the natural light be utilised thereby reducing energy consumption through the introduction of a “switching policy”.

Another point to consider; should consultants and installers advise clients to clean or upgrade their sky-lights; it is possible that the lighting project could be lost.

I will leave you to form your own conclusions.

What are the alternatives to 400w HID low bays;

Lamp Type   Annual Kw Hours   Saving Kw hours

400w HID       38400                      –

320w Eco       25600                    12800  possible use of existing luminaries

320w CFL      25600                    12800  possible use of existing luminaries

4 x 80w T5     25600                    12800

200w LED      16000                    22400

The table below examines the ROI of each option based on estimated materials cost and life expectancy.

Lamp Type   Est. Cost     Life Hours     Project Cost     ROI Years

320w Eco      £100             30000            £2000               1.60

320w CFL     £150             15000            £3000               2.40

4 x 80w T5    £250             30000            £5000               3.90

200w LED     £650             50000            £13000             5.80

The calculations are based on an installation comprising of 400w low bays with 20% gear losses; operating 4000 hours per annum.

It is not possible to include installation costs in the analysis as there are too many variables; the main one being installation height.

Obviously there is the potential to reduce energy consumption through the introduction of alternative technologies. However while the “maths” enable comparison, in this case there are equally as important factors to be evaluated.

There are three key issues to consider when reviewing warehouse lighting.

• Lighting levels (lux)
• Lighting controls
• Zone definition

Lux levels are directly linked to energy consumption. The more watts utilised the greater the energy consumption; SCIENCE. The efficiency of the luminaries has to be considered; this will have a direct impact on the number of luminaries required.

Manufacturers promote the LOR% of products on the basis that those luminaries with a high LOR% will require a fewer number of luminaries within an installation; resulting in a lower installation cost.

While on the face of it a reduction in luminaries and therefore a reduction in energy consumption would appear to be a cost effective option; there is still the installation costs to consider.

Point for point replacement is often the only option when considering installation; preventing the cost of a complete re-wire.

An important factor to consider, as part of the installation, is the height luminaries are suspended. If the luminaries can be suspended a metre lower the potential to reduce the luminaries wattage is increased. 

 T5 luminaries have flexibility; they can be configured in a variety of wattages. Listed are a few examples;

• 4 x 80w    320w
• 3 x 80w    240w
• 6 x 49w    294w
• 4 x 49w    196w

The range of configurations enables a more balanced lighting design to be achieved.

Lighting controls will have a significant impact on energy consumption and potentially maintenance efficiency. However the introduction of lighting controls has to be planned.

For example; if the warehouse has no natural light and is occupied continually, during operating hours, the key issue is to ensure the luminaries are turned off when the last person leaves; whether this is a lighting control or “switching policy” will be determined in conjunction with the client.

In the vast majority of case natural light is present and warehouse space is not always occupied. Intelligent luminaries with the functionality of occupancy, daylight and dimming will have a significant impact on energy consumption.

For example; if a combination of natural light, occupancy and dimming levels results in a 50% reduction in energy consumption;

         Lamp Type  Annual Kw hr        Saving       50%       Total Saving        ROI

• 400w HID  38400Kw 
• 320w T5    25600Kw              12800Kw   12300Kw  26100Kw           1.90

The ROI has changed from 3.9 years to 1.9 years.

Zone definition is important as it will influence the lighting specification and design.

How many times have you seen a warehouse used for storage and product assembly or similar activity? Where practicable the assembly area would be illuminated close to the activity while the storage space would be illuminated at high level.

Storage isles are often divided into frequent picking, towards the front, with infrequently picked items to the rear. This lends itself to individual and separate areas of lighting control.

Verdict

T5 fluorescent would be the preferred option due to the level of control and configuration flexibility; T5 is also great value and is tested.

As it is Winter; T5 technology does not operate at the optimum in cold conditions.

LED technology is a serious option but comes at a price. It is worth noting that both the CFL Cluster light and LED options are more conducive to the replacement/upgrade of High Bays.