Do's and Dont's of Daylight Harvesting

Daylight Harvesting is a wonderful energy saving concept - if done right. Cutting corners in Daylight Harvesting does not pay off. For your consideration here are a few experiences and thoughts based on hundreds of successful Daylight Harvesting projects over the last decade.

Do a complete project cost calculation before selecting a solution

Although a comparison between different systems can be quite complex, it is worth the effort. Make sure you compare apples with apples. When you compare, look at

• planning costs and required design skills
• product cost (ballasts, sensors, wiring, etc.)
• cost of installation & wiring
• cost of commissioning (calibration) on site
• Service requirements and costs (e.g. how complicated is a system to diagnose if it is not working properly?)
• Achievable energy savings
• Last but not least: Lighting comfort (determines if users will accept or override it).

Negative Example: Large sensor zones (1 sensor dims several fixtures)

It might for example seem tempting to control several fittings from one sensor in the middle of the room as this might reduce product cost. However, this cost is just one small part of the overall equation.

Such an approach does not adequately take into account that in most rooms the lighting conditions vary significantly across the room. The sensor position usually does not reflect the lighting conditions at the different workplaces in an office. In turn, you will not receive the correct lighting levels everywhere. Adjusting the sensor to a higher lightlevel might seem like the solution to this problem but in turn you sacrifice a large part of the possible energy savings for which you want the system in the first place.

Even worse, during installation, you need to wire all fittings to the one sensor, calibrate it and test it, requiring a significant amount of (expensive) labour by specially trained electricians. This, in combination with the lower energy savings easily eats up any "savings" you made on product cost in the first place.

Disclosure: We also make sensors that can control several fittings, so we have the direct comparison from many projects. They can work very well for small, separate offices, especially when you want to implement Occupancy Sensing, too. However, they do require more skill to plan, install and commission than DAYTRONIC.

Do take time for planning and involve all parties

From the early stages of the project, involve your consulting engineers, fixture manufacturers, electricians and also your office staff who will be using the office. They will all have questions about what to expect, what they have to do (and when) and resolving all questions early can be a major contribution to a smooth and quick project.

Don't dim to 1%

Dimming below a certain point does not save more energy. Dimming to 1% is suitable for theatre applications but not for energy saving applications. Light output of 10% results in an energy consumption of 26% (i.e. 74% power reduction). Below this point the energy consumption does not go down further. The lower dimming limit of DAYTRONIC is 10%.