Parabolic Solar Reflectors
Since the Monastery is 13 miles from the nearest power lines and operates primarily on solar-generated power, conservation of electricity is a very high priority. The use of as much natural daylight as possible to light interiors or rooms was a clear way to reduce the draw on solar batteries. Besides using strategically-placed windows, the project team experimented with the use of skylights, solar conduits and parabolic solar reflectors to bring in light when and where needed.
Since we turned to solar photovoltaics for the main energy source at MCD, we needed to reduce power consumption and maximize the result of money spent. One aspect of energy consumption studied was lighting. Our goal was to reduce or eliminate the need for generated energy to light interior space during the day. To achieve this goal, sunlight needed to be brought into each room. Each of the monks' cells had a window of approximately 2'x 4' in the exterior wall which lit the room generally, but required a monk to be sitting in front of the window directly for enough light to read or write. We decided that the answer to extra lighting was in bringing in the light through the roof.
We considered two options to accomplish our goal: standard skylights and solar conduits which have been introduced to the market in the last few years. The solar conduits are circular, domed, double glazed skylight devices that have a reflective tube attached to the underside that allows light to enter the building through the space between the roof and ceiling. Typically they can span a space from 1'-8' (with extensions).
In the 24 monk cells at MCD, the space between the roof and the ceiling is an average of 2'8". We decided to test one 2'x 2' skylight with clear double acrylic glazing, and three solar conduits of varying size: 16", 10" and 13".
We built a mock-up of the roof line and a ceiling in one assembly and mounted all four units on the "roof" of the assembly. The space between the "roof" and "ceiling" on the skylight was spanned with a "skylight well" made of sheetrock splayed out at an approximate angle of 20° on two sides and painted white. We ran five separate tests at different times of the day, measuring the light transmitted by all four devices at a location 1' and 2' below the diffuser on the "ceiling" of the mock-up structure. The standard skylight out-produced all the other devices, gathering substantially more light in all tests. Plus, the skylight's retail cost was less than one half of the cost of each of the other devices.
These tests resulted in our choosing skylights with white, splayed "wells" made of sheetrock for each of the 24 monk cells. We added a clear acrylic glazing panel at the ceiling level to isolate the "dead" air in the "skylight well" and reduce heat loss through the skylight.
In the next construction phase
In the next construction phase, including computer room, library, kitchen, corridor and other various rooms, we used larger skylights and similar "skylight wells" painted white. We added parabolic solar reflectors to significantly increase the amount of light directed through the skylights.
We will continue our testing to compare gathered light and the costs of skylights with and without reflectors. We are also testing the third glazing panel at the ceiling level for effectiveness in minimizing heat loss in winter and heat gain in summer.