Add-on energy savings
Retrofitting controls to existing services can deliver significant benefits without the capital cost of a new installation. John Mercer of CP Electronics explores this principle with reference to retrofit lighting control.
When considering options for reducing the energy consumption of lighting the main focus tends to be on the efficacy of the light sources, such as upgrading incandescent or fluorescent lighting to LED. In these cases the emphasis is very much on reducing the installed electrical load by using lower-wattage light sources.
Installed load, though, is only part of the equation. At the risk of stating the obvious, maximum savings will only be achieved if the lighting is controlled effectively — and this applies equally to existing lighting as it does to a new lighting installation.
In fact, it is possible to achieve significant energy savings by retrofitting controls to the existing lighting without making any changes to the light sources or luminaires. Clearly the ideal situation is to upgrade the light sources, luminaires and controls. However, there are many instances where the cost is beyond the budgets available. In such cases it makes sense to consider the use of retrofit lighting controls.
While the benefits of retrofit lighting controls can vary considerably from one project to another, as a rule of thumb we would expect up to a 40% energy saving compared to basic manual on/off switching, with even relatively a simple control strategy.
For example, in a cellular office the occupant will usually turn the lights on first thing in the morning and may then go off to a meeting for two hours, leaving the lighting on. They may then come back in time for lunch and go off to another 2-hour meeting in the afternoon. For all of the time that the office is unoccupied the lighting is on unnecessarily.
With a relatively simple lighting control strategy, the lighting can be turned off when the office has been unoccupied for 10 minutes and automatically come on as soon as presence is detected. In the scenario above this would result in nearly four hours of savings — nearly half of an 8-hour working day.
The same principles can also be applied to groups of luminaires in an open-plan office. The important thing is for the specifier to understand the topology of the wiring so that a sensor is connected in such a way as to control a group of luminaires. Potentially up to 20 luminaires can be controlled within one zone, but this should be tailored to suit the layout and use of the space.
In both cases, simply by knowing the cost per kWh and the hours of lighting use that have been saved it is very easy to calculate a return on investment (ROI) for this kind of retrofit solution.
In terms of the return in investment (ROI), the cost of the project will be determined by the price of the sensors and the cost of installation. It is therefore important that any retrofit controls can be fitted quickly and easily to minimise this latter cost and thereby maximise the ROI. This is another aspect of the project that specifiers will need to investigate.
For example, surface-mounted fluorescent fittings have a knock-out at the end of the luminaire; it is useful if the detector has been designed to fit through this knock-out for wiring to the ballast as this will speed up the whole process.
Where recessed fluorescent fittings are in use, a detector that can be clipped to one of the fluorescent tubes or louvres will also help to facilitate fast installation.
In field trials of such retrofit products the average time to fit each detector is seven to eight minutes. On a large-scale retrofit project where the electrician is fitting many detectors, this time can reduce to as little as five minutes with practice.
Controls can be retrofitted to virtually any type of lighting that has a ballast to control it, though there are some older types of magnetic ballast that are not compatible with today’s controllers. It is therefore important for the specifier to establish what type of ballasts are already in place and then check compatibility with the controls manufacturer.
In fact, this problem doesn’t just apply to old lighting. Even with LED lighting, there are so many different drivers on the market that the same principles of checking compatibility apply.
The important thing in terms of arriving at the best solution for the end client is to include the potential for retrofit lighting controls in the range of options that are considered during the feasibility stage of the project. Then it is simply a matter of predicting ROIs for the various options and choosing the one that best meets the client’s criteria.
John Mercer is product manager with CP Electronics.