Overdoing it

It is now generally accepted that the only way the UK is going to achieve its carbon emissions targets is by tackling the energy wastage in existing buildings. This is because, while legislation such as Part L of the Building Regulations does a lot to control the energy consumption of new buildings and major refurbishments the fact is that the turnover of building stock is too low for this to make a major difference. In addition, the latest Part L consultation document makes no reference to the consequential improvements that will drive upgrades to the energy performance of existing buildings

However, other items of legislation, such as the Energy Performance of Buildings Directive and the Carbon Reduction Commitment for larger energy users, do have a direct impact on energy consumption.

It is to be hoped, therefore, that building operators will be incentivised to look more closely at their energy consumption, and the widespread problem of over-lighting in many spaces is an obvious area that needs attention. It’s also a problem that many end-users are unaware of, so specifiers can help to identify and resolve this issue.

In many commercial buildings, before easily dimmable fluorescent lamps with high maintained illuminance were readily available, it was common practice to design for higher illuminance levels than were needed. Then, as the light output of the lamps reduced over time, the design conditions would be met for a longer period before re-lamping was required. An eminently sensible solution at that time and one that helped to reduce end-clients’ maintenance costs.

For example, if the space only required 3 x 18W to achieve the required illuminance levels it may have had 4 x 18W T8 fluorescent fittings instead. The legacy of this is that there are still many buildings that are overlit immediately after re-lamping – and the lamps continue to consume the same amount of electrical energy even when the light output reduces.

Now that there are alternatives using more efficient T5 lamps it makes sense to deploy them and help end users reduce their energy bills and carbon footprint – usually with a sensible payback.

In our experience, a very cost-effective solution to this problem is to replace existing 4 x 18W T8 fittings with 2 x 14W T5 luminaires on a point for point basis. This will provide comparable light output while reducing the installed electrical load by well over 60% when ballast losses are taken into account – as well as delivering energy savings of as much as 70%. And, of course, the improved controllability of T5 light sources means that additional savings can be achieved by ensuring the lighting is only used when it is needed.

Similar principles can be applied to many low bay and high bay lighting installations, such as warehouses, factories and large retail ‘sheds’. Here, the tradition has been to light these areas with high intensity discharge (HID) light sources such as high pressure sodium and metal halide because of the high light outputs required. Indeed, until T5 light sources came along there was really no viable alternative.

Now, however, the high lumen packages that can be achieved with T5 lamps, combined with well-designed fittings that ensure a high light output ratio (LOR) offer an effective, controllable alternative. And very often replacement can be on a point-for-point basis so no extra cabling is required. Straight away, such a replacement strategy will reduce the installed electrical load considerably.

Just as importantly in relation to the over-lighting referred to above, installing T5 fittings introduces a high level of controllability that is not possible with HID lamps. The latter need to cool down before they can re-strike – and can take up to 15 minutes to reach full light output, imposing severe limitations on the practicality of turning HID lamps on and off in relation to occupancy or daylight levels entering the space.

In contrast, it is very straightforward to link T5 lighting to occupancy detectors and photocells, switching them on and off or dimming as and when appropriate.

In fact, given the fast paybacks that can be achieved on such projects, plus the interest free loans that may be available from The Carbon Trust, eliminating over-lighting and energy wastage should really be a no-brainer for any organisation that wants to reduce its overheads and its carbon footprint.

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