Daylight prediction based on the VSC - DF relation

Abstract

In 2017, 255 of Sweden's 290 municipalities reported a shortage of residential housing (Boverket, 2017). The answer is to build more. Due to urbanization pressure, concerns for saving valuable agricultural land, growing national and EU demands on energy-efficiency, there is an increasing number of new and dense urban developments. Daylight issues seem to have been of little concern in development of many of these new detailed plans, and daylight in buildings is often studied much too late into the project.
The aim of this master thesis was to seek through computer simulations for a simple method to assess daylight availability in residential housing at an early design phase. It is based on a presumed relationship between the median Daylight Factor and the in Sweden rather unfamiliar Vertical Sky Component (VSC).
Both the VSC and median Daylight Factor where evaluated for a simple room geometry located on the ground floor of five courtyard building typologies. Our aim was to obtain general threshold values of VSC to ensure that the Swedish national requirements of good access to direct daylight can be met. Additionally, the impact of both Glazing-to-Floor Ratio and the room depth on the base-case O-shaped typology was assessed and a guideline was formed.
A target VSC was found to be 29% to assure DFmed 1% indoors with conventional window and room design. Following the guideline, in the façade areas where VSC is below 15% it would be difficult to reach the target DFmed.
The performance of the proposed method was evaluated against common threshold values and rules-of-thumb. It was found that predictions from the established principles were often too optimistic.

Popular Abstract

The current trends in the building industry are aiming towards maximizing the plot ratio resulting in denser cities and high-rise buildings, where space availability is diminishing constantly. Along with urbanization pressure, the growing national and EU energy-efficiency demands has implicated the daylight performance. Many researchers have been studying the importance of solar insolation and its social and health benefits but also the potential to reduce the energy demand. Thus, achieving a balance between energy and daylight interest becomes more essential, especially if more attention is given on early stages of design.
The focus regarding daylight in Sweden has been on the building level and there is no daylight regulation in early planning phase which often causes potential problems in the successive stages. Moreover, the current standards part of the Swedish building code or Miljöbyggnad certification system are often associated with a lot of application limitations and uncertainties, beside the large amount of time required for calculations or simulations.
All these factors suggest that a new method is needed to facilitate the process of daylight estimation during early design phase, while potentially save considerable time and resources. Therefore a simple conceptual metric such as Vertical Sky Component is introduced and its relation with Daylight Factor is investigated with the purpose to develop a set of guidelines for architects and urban planners.
Initially, it was necessary to get an overview of building block configuration in Malmo, as a basis to define some theoretical models to carry out this study. Afterwards the investigation was basically divided in three parts. The core study consisted of using Grasshopper and Honeybee tool to perform a parametric study under CIE overcast sky condition in five typology representations, specifically “O”, “C”, “U”, “L”-type and lamella shape. The courtyard size, proportion and building height were varied, while measuring the indoor median DF in two different room placements on the ground floor level and the VSC on the room façade. Additionally, two other complement studies were applied to O-shaped courtyard, where glazing area and room depth and were further inspected.
The core study demonstrated that there is clearly a linear relation between the indoor and the façade daylight level. Considering the trendline of 480 simulated cases, the VSC threshold value to achieve the indoor target DF of 1% resulted to be 29%.
In general 1:2 yard ratio represented slightly better daylight penetration indoors, due to lower obstruction angle. For closed courtyards and those having only side open, it was observed that 1:1 proportion gave better indoor daylight than 2:1 ratio, even though the latter are more spacious, and the obstruction angle is the same as 1:1 courtyards. The proximity of the lateral walls on 1:1 courtyard proportion can be an explanation of more interreflected light, thus better daylight performance.
It was noted that the same VSC value per different building typology did not provide identical daylight illuminance indoors, mainly because of the interreflection contribution and exact patches of visible sky from the room. The U-shape building allowed the most daylight penetration into the room, whereas II-shape at the same VSC generally showed the lowest DF med.
The results from the GFR study showed that the VSC threshold did not decrease constantly, even though the GFR increment was in equal steps and the additional glazing area was roughly the same. The lowest threshold for the most optimistic case happened at a VSC of 15%, considering a realistic upper limit of 0.2 GRF in residential buildings.
The last supplemental analysis on room depth revealed that extending the room by 1 m of increment will not yield the same effect on DF for each of the enlargement steps. As anticipated, the narrowest room had a better performance, where 16% of VSC can potentially reach for indoor daylight level. Moreover, a confirmation that a space which has a GFR lower than 0.1 cannot reach the target value of indoor illumination was obtained. When comparing the outcome of the last two analysis, lower VSC threshold is needed for a smaller room compared to a deeper room with bigger window, given that the glazing-to-floor ratio is equal for both of the cases.
Finally, all the results of this research work are presented in a form of three interrelated graphs and some instructions are given for the potential users.

• author: Olina, Ance and Zaimi, Nevila
• supervisor: Jouri Kanters
• organization: Division of Energy and Building Design; Department of Architecture and Built Environment
• alternative title: A guideline for daylight in urban planning
• course: AEBM01 20181
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: Vertical Sky Component, Daylight Factor, building typology, Radiance simulations
• publication/series: Master Thesis in Energy-efficient and Environmental; Buildings Faculty of Engineering Lund University
• language: English
• id: 8955344
• date added to LUP: 2018-08-13 08:50:35
• date last changed: 2018-08-13 08:50:35