The overall aim of the DAYLIGHT-EUROPE (DL-E) joint European research project is the generation of daylighting design guidelines for architects and engineers. There are two main support activities: the monitoring of approximately 50 buildings and and the simulation of a subset of approximately 10 of these. Within the DL-E project, a team has been formed to undertake these simulations and provide thermal and visual performance statistics in support of guideline production.
The intention, for each case study, is to:
The present case study is a school building situated at Modane in the south-east of France, latitude 45o3' N and altitude 1000 m (see figure 1 and figure 2).This 8000 m2 building complex is divided into three sections: restaurant and dormitories; teaching spaces; and staff housing.
Figure 1 South view of the classroom blocks with the tilted windows and light shelves.
Figure 2 North view of the classroom blocks with the ordinary window design.
Each classroom block (this study is concerned with block B) has a central atrium which is lit by a rooflight, so that every classroom is lit from both sides and receives some winter sun, either directly or through the atrium. The rooflight is glazed with triple transparent polycarbonate ribbed sheets (see figure 3).
Figure 3 View into the atrium through classroom back internal window.
Tilted glazing on the south facades reduce glare and heat gain in summer, while stainless steel external light-shelevs reflect sunlight onto the classroom ceiling in winter (see figure 4). Combined with light from the atrium (see figure 3), this provides good daylight distribution across the classroom to a depth of more than 7 m. The artificial lighting in the classrooms is controled with a timer to switch off lights automatically at each class break. This can also be controled by a teacher or students. Experience thus far indicates that the classrooms need no artificial lighting provided that outdoor horizontal illuminance exceeds 10,000 lux, and that more than 70 % of the annual lighting power consumption between 9 a.m. and 5 p.m. is met by daylight.
Figure 4 View into the.
The DL-E simulation team applied a performance assessment approach to deliver the desired supporting performance statistics. This includes problem representation, base case formulation, boundary condition selection, simulation processing and performance characterisation.
Two models are being employed: the as-is model; and the base case model. The as-is model represents the actual building (see figure 4). The base case model is a fictive version of the building, with special features removed to serve as a relative comparison case. In this study the base case building model has been created from the as-is model by removing tilted windows, light shelves and internal windows to the atrium from the classrooms.
Roof
level
Second
level
First
level
Figure 4 Wireframe image of as-is model geometry.
For the Modane region, average monthly temperatures are available as summarised in Table 1. Two potentially relevant Test Reference Years (TRY's) of the weather data are available for Bolzano (Italy) and Carpentras (France).
Table 1 Monthly average outdoor temperatures oC for Modane and the two relevant TRY's
|
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
|
|
Modane |
-1.3 |
-0.1 |
3.5 |
5.5 |
10.6 |
13.0 |
16.8 |
17.1 |
12.9 |
8.0 |
2.4 |
-0.5 |
|
Carpentras |
5.5 |
5.8 |
9.8 |
11.3 |
15.1 |
18.9 |
22.9 |
21.3 |
18.4 |
13.9 |
8.8 |
5.4 |
|
Bolzano |
-1.1 |
2.0 |
7.2 |
11.8 |
16.2 |
18.9 |
21.0 |
19.9 |
17.2 |
10.6 |
4.6 |
0.0 |
From table 1, it is clear that the Bolzano TRY (latitude 46.5 o N, longitude 11.3 o E) is preferable. The three simulation periods were selected for use, corresponding to the average winter, spring and summer week climate conditions:
For each of the model, as-is and base case, a standard performance assessment result set was produced (see figure 5 and figure 6) to help evaluate integrated building performance. These result sets show:
Figure 5 Standard performance assessment result set for as-is case.
Figure 6 Standard performance assessment result set for base case.
The simulation results in the standard performance assessment result sets (figure 5 and figure 6) has shown that:
Heating load:
The maximum diversified heating load was analysed for the typical winter week when the minimum ambient temperature reaches -10.1 oC. As can be seen from figure 5A and figure 6A, there is almost no difference between the "as-is" and base case. This finding indicates that the capital costs associated with boiler plant would be the same for both cases. It can be concluded therefore that the "as_is" case does not represent an improvement in the terms of this criterion.
Energy requirements:
As can be seen from figure 5B and figure 6B, during the typical winter period the heating energy is higher by 2.8 % in the "as_is" case when compared to the base case. On the other hand, the artificial lighting consumption is higher by 3.7 % in the base case when compared to the "as-is" case. During a typical spring period, the heating energy is higher by 13.7 % in the "as_is" case, while the artificial lighting energy consumption is higher by 36.8 % in the base case. Clearly, the larger windows in the "as_is" case, in conjunction with the lower casual gains from artificial lighting, result in a higher heating energy consumption. However, power savings attributed to the enhanced daylight utilisation outweighs the higher energy consumption. Based on the total energy consumption, the results indicate that the "as_is" case offers a significant improvement to the base case.
Thermal comfort:
As can be seen from figure 5C and figure 6C, there is an almost identical performance for both cases during the spring period. For the typical summer period, the base case shows 17 hours more than the "as_is" case when operative temperature rises above 26 oC. From these results, it can be concluded that the "as_is" case performs better than the base case in the terms of summer thermal comfort.
Daylight factor distribution:
As can be seen from figure 5D and figure 6D, the "as_is" case has significantly higher daylight factors, even at the rear of the classroom. The comparison of the average daylight factors of 1.0 % and 1.9 % (room_1.1 and room_1.4) for the "as_is" case, and 0.3 % and 0.4 % for the base case, indicates the significantly improved daylight performance of the "as_is" case.
Visual comfort:
As can be seen from figure 5E, in the "as_is"case, the upper external window provides a direct view to the sky vault, which is a possible source of glare. However, the predicted Guth visual comfort probability for this case is relatively high with a minimum of 77 % (see figure 5F). In the base case there is no direct view to the sky vault (see figure 6E) and the predicted Guth visual comfort probability is higher with a minimum of 91 % (see figure 6F). It can be concluded therefore that there is no serious visual comfort problem for the "as_is" case, and for the given principal view direction, although the base case does perform better. In the case of the higher window in the base case model, the visual comfort performance of both models would be identical.
Based on the above performance indicators, it can be concluded that the "as_is " case (relative to the base case) offers:
This integrated performance study indicates significantly improved performance of the "as_is" case relative to the base case.
