Daylighting 102

March 14, 2011

Daylighting 102

For the introduction to Daylighting, ways to introduce light into the space, and some of the benefits, please see Daylighting 101 (should be about 2 posts ago).  Any comments or questions, please feel free to post below.  For now, we are going to pick up where we left off with and take a look at how the systems work, energy codes and the effect on daylighting, and what makes a particular system successful. 

So we look at Daylighting, bringing daylighting into the space, we have to start talking about Daylight Harvesting.  Harvesting is defined by the use of sustainable architecture that reduces the use of artificial lighting when natural daylight is available.  When using Harvesting techniques, the daylighting sensors are set to measure in one of two ways: an open loop or a closed loop. 

Let’s start with an open looped sensor.  An open looped system is designed to measure only daylight contribution to the space.  An open loop sensor is typically placed in a position where the sensor can see only direct sunlight: on the exterior wall (facing out), on the roof (measuring daylight), or inside a skylight (placed to measure the light in the skylight). 

Alright, so going back to the closed loop system, we have a second type of system.  A closed loop system measures daylight in a space as well as the artificial light.  Closed loop systems differ from open loop, as they are typically used to measure light within a room.  Placed in a location where they will not get over exposed to sunlight or indirect light, the photocell measures all the light received on a surface. 

So now we have the options for the types of photocell that can be used to determine the daylighting in the space.  Closed loops should be utilized in spaces like offices and conference rooms where lighting levels need to be carefully monitored for important tasks.  Open loops will be utilized for spaces such as lobbies and exterior spaces.  But now that we have the proper type of sensor for our space, we need to look at the type of daylighting control these sensors will utilize. 

When controlling lights in spaces with daylight, there are three options to control the space: Switching, Bi-level switching, and dimming. 

Switching is the simplest solution, turning the lights off when there is enough daylight contributed to the space.  It is the simplest design, carries the lowest design cost, and easiest to commission.  Draw backs to the design have the most effect on the occupant of the space.  The occupant is limited to two light levels (on and off), high amounts of cost savings are hard to come by, there is little flexibility in the design, and lights switching on/off can be quite irritating.  These systems are typically used in Corridors, Atriums, and Bathrooms, spaces with non-stationary tasks and typically void of workers. 

The next level past switching is bi-level switching.  Bi-level switching still turns the lights on/off, but also offers levels of control between on/off.  These systems have more than 3 levels of lighting, the systems are cheaper than a full dimming system, and they will achieve higher levels of cost savings than standard on/off.  Disadvantages to the system are similar to that of the switching system.  The lights can be as distracting, and the ballasts need additional wiring with more commissioning.  Bi-level systems are typically installed in factories, gyms, warehouses, and other spaces were non-detailed tasks take place and where switching is not distracted. 

The final option is a dimming system.  Dimming systems gives an unlimited range of control in the space.  The benefits are that the system can be programmed to have an exact FC level at all times, it is the most comfortable for clients, and has the highest energy savings of any system.  The disadvantage to the system is the cost of the ballasts and the wiring of the ballasts as well as the commissioning level required to perfect the operation.  These systems are best utilized in classrooms, laboratories, office spaces, and libraries, spaces that have highly detailed tasks. 

With daylighting becoming more prominent in buildings, Codes have begun to put standards and requirements in place for monitoring the installation of daylight systems.  With California leading the US in Green Standards and design, requirements for ASHRAE 90.1 have been developed in conjuncture with California Title 24.  Daylit areas must have 2 levels of ouput, 0%-35% and 50%-70% or continuous dimming.  Additional lighting power is allowed per code if daylighting is incorporated into various spaces when mandatory and advanced lighting controls are used in the space.   

So the last piece to discuss is what makes a good daylighting system.  When you strip away the parts and pieces, the open and closed loops, the switching and the dimming, the system is really only as good as the commissioning that was put in place to tell the system to operate.  All the dimming ballasts in the world, all the sensors, and all the dimming curves, none of it means anything unless the system is set up right.   

Commissioning an open loop system, a single adjustment setting on a proportional control can be set at any time that daylight is present.  The adjustment should be made when the daylight distribution is representative of what is typical.  You cannot commission this system during a period of time when direct sunlight is streaming in, if that is not a norm. 

Commissioning of a closed loop system becomes a two step process.  Maintained illuminance level is set by making an adjustment with only the electric lights on (no daylight).  Once the level is set, the ratio between the photo sensor optical signal and the desired light level is set by dimming or switching the electric lights until the desired light level is achieved.

Bottom line, make sure you have a licensed commissioning agent commission your system for proper operation. 

So, Daylighting points to think about.  ASHRAE 90.1 2010 will be the first year of mandatory Daylight control requirements.  Options for daylighting system include open/closed loop and switched/bi-level/dimmed solutions.  Benefits of daylight systems vary from energy saving to improved occupant productivity. 

Daylighting is a reality that is fast approaching, and the more you can learn now…the more enlighting you will be later…


Daylighting 101

February 25, 2011

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.