Daylighting 101

Daylighting 101

Since the inception of LEED, daylighting has become a more integral part of building design. The option of providing daylight into the space to earn a point has left many engineers and designers looking for more ways to get light and views into the space. I plan to give a quick overview of daylighting, talk about ways to introduce daylight into a space, and finally some benefits to daylighting. In a following post, I will explore more into how the daylight system can work, energy code, and what makes a daylighting system really successful.

Let’s start with getting light into the space, as, coincidentally; the concept of daylighting revolves around having day light. The common daylighting techniques involve vertical and horizontal options.

The most common type of daylighting scenario we see (particularly in Washington DC) is vertical windows. All buildings (except the occasional top secret ones) have windows. Typically called side lighting, providing vertical glazing on a building introduces both daylight to a space, as well as an exterior view to the space. Vertical solutions are supplemented with additional systems to introduce light deeper into the space. Light shelves, open office space, and glass walls are architectural solutions that help bring daylight deeper into the space.

Less common solutions to introducing daylighting into a space, are the horizontal options. Horizontal glazing will typically provide larger amounts of light into the space, particularly the interior spaces, but it limits the opportunity for exterior views. Horizontal lighting introduces daylight with less manipulation of the common architectural elements, but with more extensive design of the ceiling and roof top spaces. Skylights and Light pipes are two common solutions for horizontal lighting.

Great, so we’re bringing light into the space from either the vertical windows or a roof top solution. But what do you have to worry about? Well the number one thing you have to worry about is the sky. Depending on your location, the common sky condition will be a clear sky, a partly cloudy sky, and an overcast sky. You cannot depend on sunlight. It will vary based on your location and based on the time of day. Sunnier cities receive a higher ROI on their systems. The last thing to remember about the sky is how the clouds will affect the dimming system. Fade time is the length of time between the photosensor sensing the lack of sunlight and adjusting the lighting levels. Areas with quickly passing clouds need to have a slow fade time, while areas with slowly passing clouds can have quicker fade times.

One of the harder daylighting considerations for the engineer to control is the building orientation. Coordination with the Architectural team prior to building design can help orient the building in the most beneficial location. The buildings length should be located on the east/west axis while the area with the primary daylight harvesting systems being exposed to the North. Of course, you also want to make sure that your daylighting system isn’t going up at a window that has a giant tree on the other side of it.

The final concern for daylighting is the effects of the sun. While the sun is providing the light that we want to harvest, we want to avoid harvesting the harsh direct light from the sun. Adding daylight into the space while not accounting for solar heating gain can severly tax the HVAC system, and cause a temperature discomfort along with the daylight gain. Coordinate specification of windows with a low solar heat gain coefficient, or install a system that eliminates the harsh direct sun light.

So why daylight? What can you possibly get out of a system?

The first argument the owner wants to hear is payback, or more simply, how much energy are you saving me? Keep in mind, the results I’m about to give you are based on a building designed for daylighting. The space has glass walls, low partitions, and a system set up with two daylighting zones (first zone is 10’, the second zone is 10’ to 30’). In the study, performed by Lawrence Berkeley National labs, the energy saving was between 30% and 60% with the second zone saving 10% to 40%. Done right, daylighting can be a powerful tool.

But daylighting can bring more to the table than monetary savings. For one, having a building with a daylighting system sends the correct corporate message of sustainability and a commitment to new technology. Day lit spaces also create an incredible psychological benefit for the people using the space. People tend to be happier and work more efficiently in spaces with large amount of daylight. For a company, the salary of its employees is typically the largest cost associate with the company, and a happy more efficient work force can go a long way in justifying a daylit space.

Stay tuned for part two, and feel free to leave any questions below.

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