The SkyLouver™ System employs four innovative and complementary strategies to optimize the use of sunlight for the building’s energy needs.
1. Modulated Daylighting Aperture
Because natural light generates less heat per unit of light delivered, skylight systems have the potential to reduce building cooling loads. However, in practice the lighting levels associated with skylights far exceed the desired light levels during periods of peak cooling loads, and so traditional skylights end up increasing, rather than decreasing, the cooling load in the space. Not only is the goal of reduced heat loads unrealized, but this excess heat load effectively limits the density of skylights (skylight to floor ratio, or SFR) that can be installed on a given building to about 4%, and therefore puts an upper limit on the daylighting fraction that can be achieved.
SkyLouver is different in that it modulates the amount of light passing through the monitor by actively controlling the louver position in reaction to changing sky conditions. During very sunny conditions the louvers allow only enough sunlight to pass through to meet the lighting needs of the space, while harvesting the excess energy in the form of thermal energy. During lower light conditions, the louvers adjust to allow a higher percentage of the energy to pass through as light. In overcast conditions, or in early morning or late afternoon, the louvers open completely. This direct control of lighting levels has many important benefits:
- It reduces the amount of undesired over lighting, which allows the sought-after cooling loads to be realized.
- It frees the designer from the upper constraint on SFR, allowing higher daylighting fractions to be achieved with even further cooling load savings.
- Automatic lighting controls can be made much simpler, since the modules are doing the work of active control. Usually, simple on/off controls can be used in place of partial dimming or zoned lighting control systems.
- Peak building electricity demand is reduced since both electric lighting and cooling equipment loads are consistently reduced compared to un-modulated flat skylighting systems.
- Direct heating can he achieved using intentional over lighting when building HVAC is in heating mode.
2. Concentrating Optics
The design of the SkyLouver concentrating optic is one of the keys to delivering low cost lighting and thermal energy. On average, the curved mirrors in the module concentrate the sun’s rays by a factor of seven, which reduces by a factor of seven, the amount of light-diffusing and thermal-collecting materials used in their construction (when compared to non-concentrating technologies such as prismatic skylights and flat plate thermal collectors). For lighting, the concentration of light requires much smaller areas of light diffusers and reflectors compared to traditional skylights. Also, since the monitor transitions from 100% lighting to 100% heating in only a few degrees of motion, it is possible to make rapid changes in lighting levels in response to user input or to react to quickly changing sky conditions. For thermal collection, the reduced collection area not only reduces the amount of expensive selective surface coatings needed, but it also improves the efficiency of the thermal heat collection function. Unlike heat leaks in a typical flat plate solar collector that are due to the hot collecting surface conducting or radiating heat to the surrounding air or roof surface, the hot thermal collecting surface in the SkyLouver module has only 1/5 the surface area of a standard collector, which reduces the amount of heat lost to the environment. This allows the SkyLouver module to have higher thermal efficiency than any flat plate or evacuated tube collector on the market.
3. Intelligent Allocation of Energy
Solar energy use is intelligently prioritized to serve the highest (user defined) value load at all times. A SkyLouver module is capable of delivering five separate end-use energy streams: lighting, radiant heating, air conditioning, process heat, and space heating. SkyLouver modules make optimal use of the available energy by choosing the most valuable and efficient use of the solar energy based on the quantity of the energy available and the needs of the building at that time.
At any given time, the building may be calling for up to four of these simultaneously. In order to make the most cost-effective use of the solar resource, it is critical that the system controls prioritize appropriately. The most efficient and beneficial use of solar energy is almost always as light itself, which provides full spectrum illumination for the occupants and at zero electric use. Therefore, in most situations, SkyLouver automatically prioritizes the use of its available energy to provide illumination first above other uses. The actual ranking of energy allocation may be dependent on local utility rates, building energy state, customer needs and even time of day metering. This thermodynamic effectiveness built in to the intelligence of the SkyLouver modules maximizes the energy generation and economic benefit of the system.
4. Fixed Orientation of Monitor
Traditional skylights are designed to be installed at arbitrary azimuthal orientations; that is, they are not designed to be installed at any particular angle: east/west or north/south. But since the sun follows predictable patterns as it passes through the sky, a further degree of lighting efficiency may be achieved by fixing the orientation of the module. Thus, allowing each of the four walls of the SkyLouver monitor element to deliver bright, diffuse light into the space below given the particular type of light that strikes it. For example, the north wall of the monitor is never exposed to high angle direct sunlight that could cause glare, so it needs no diffusing elements and can be made of clear panels that allow the occupants of the space a view to the sky outside. The east and west walls are designed to capture indirect low-angle morning and afternoon light, diffuse it, and direct it into the space to maximize the hours the system can provide the required interior lighting levels. Most importantly, the louvered Energy Conversion Module (ECM) faces south where it can capture large amounts of solar energy for either lighting or heating. The simple innovation of fixed orientation in the monitor design increases the amount of light admitted into the space, improves the evenness of distribution of the light, and affords view windows that are not found with typical installations.