Core Sunlighting System

Supervisor: Dr. Lorne Whitehead
Researcher: Sepideh Khosravi Simchi

Introduction

One of the challenges of the building industry is illuminating the building with high quality lighting while using less electrical energy. This is one of the issues that the Green Building Council has been addressing in the last few years, particularly in commercial buildings. Architects and building designers address this problem by allocating larger area to windows or creating atria that capture daylight. However, these traditional methods of daylighting have limitations and drawbacks as most of them fail to illuminate the building’s core. In addition, these methods may be expensive and can sometimes increase the energy usage of the building as the thermal insulation of the glass walls is not as good as normal walls.

A research group at the University of British Columbia found a unique solution to this problem, the core sunlighting system (CSLS). This system consists of mechanical and optical elements which capture light outside the building and transfer it to the core of the building. One particular system has been designed and is under development, but it has a few limitations and a potential to improve. The main focus in this research project is addressing the limitations of the former model and discussing the modifications that can be done to improve the performance of the Core Sunlighting system.

Major components in the system will be modified. Some of them have already been redesigned. Preliminary results of raytracing modeling showed substantial improvement in the performance of the system. The details of these modifications and the results of the raytracing modeling presented in a Poster in “CAP” conference 2012 (Canadian Association of Physicists) and also in a talk in “Women in Physics” conference 2012.

Method

The Core Sunlighting System has three main components as shown in Figure 1: the redirector, the concentrator and the light distributor. The redirector elements are mounted on the perimeter edge of the roof. They track the sun throughout the day and will redirect the sunlight down to the building façade, at a certain glancing angle.

To achieve uniform and relatively constant outcome, a dual stage redirector, called “Bi-valve Rotary Venetian” will be used, Figure 2. This assembly consists of parallel sets of slats confined inside a circular frame.  The individual slats can rotate similar to slats in a Venetian window blind to track one component of the sun’s movement, and the entire ring can be rotated to track the other component. In our new design, each slat consists of a bi-valve arrangement, in which two independently movable slats can be controlled to optimize the redirection depends on the time of day. They could be either at simple reflection or double reflection mode, depending on the solar altitude.

Once all facades are bathed equally with sunshine, light will be captured with the concentrator unit, mounted on each floor above the windows. The concentrator unit captures sunlight and concentrates it to desired collimation angle. Once light enter the light pipes, it would be distributed uniformly across the building. Since all façade are bathed with sunshine, the light pipes would be fitted from all directions which make the light distribution more uniform across the building and more area could be covered with natural day light.

Results

Raytracing modeling has been done to confirm that the suggested design will have a better performance compare to the former model. The modeling results showed that the roof mounted light collector has larger operation window, on average 2.5 hours per day, compare to the façade mounted one. It also showed that the combining two modes in the redirector unit, can substantially improve the efficiency of the redirector. In the following graph the efficiency versus solar altitude is shown for each mode.  As you can see parallel follower mode, in which rays undergoes one reflection, works more efficient at low solar altitude. On the other hands, double reflection mode works more efficient at higher solar altitude.

Conclusions

It is expected that applying these modifications in the design of the Core Sunlighting System will improve the efficiency of the system at least by 50%. Apart from the higher average efficiency, it is expected that the new model of the Core Sunlighting System will have larger operation window. Thus the new system can provide daylighting for the building on average 2.5 hours more than the former model each day. This means that the new modification will decrease the payback period of the Core Sunlighting system and make it more economically feasible.

Figure 1  The new Core Sunlighting System

 Figure 2 Rotary Venetian