An early design tool/method for assessing the performance of complex fenestration systems

Abstract

It is common knowledge that shading systems and solar control glasses are used to avoid glare and overheating at expenses of daylight. In Dynamic Thermal Modelling tools, there is no assessment method where the shading use is expressed when predicting the building performance. Furthermore, literature often refers to studies where complex fenestration systems are optimized for specific cases. However, there is a lack of a component-based, or room-independent tool to be used in the early-design phase in common practice which fills the gap and assesses the use of shading together with the building performance. In this perspective, an innovative tool was created to provide hints on how to predict the performance of fenestration systems in real life, and help designers when choosing the glazing and shading control. As input, location information as well as hourly radiation data, and the basic window geometry are asked. Three different shading control strategies are used, namely a solar gains threshold, incident solar radiation, and a prediction on the user’s behaviour. Following, the tool assesses the solar gains and view to the outside per control strategy, and gives as an output the hourly shading use distribution and the View Quantity Index. Some important limitations that can be defined are: the simplification in the calculation of the secondary solar transmittance that is used for the solar heat gains; and the complexity of predicting the user’s behaviour, which is combined with the direct sun beam as glare factor. The study showed how this tool assesses the performance of different glazing products combined with shading control systems and strategies, to help designing a functioning façade that fills the gap between shading systems and solar control.

Popular Abstract

A newly developed design tool for evaluating the performance of windows with different shading systems.

An Excel-based tool was developed to judge different glazing and shading systems in terms of daylight, temperature increases due to heat from the sun, and view to the outside. Three different control strategies for the shading were used: i) to minimize the temperature increases due to heat from the sun, and therefore the cooling energy needed; ii) a manual control prediction, with 2 different behavioural patterns; and iii) a strategy that is similar to the way shading is evaluated in energy simulation tools. The selection criteria for this evaluation and these strategies were based on previous studies, that showed the need for a design tool that gives quick hints on the performance of a chosen window in an early stage of the building design. Therefore, the tool has an input sheet which can be filled in quickly, and which does not need detailed specifications of the building or room that is going to be calculated.

The glazing and shading system that the designer wants to assess are selected from a database made in the Excel tool. The database consists of 10 glasses for windows and 12 shading systems. The glasses are divided in double glazed units and triple glazed units. For the shading systems, the division is between venetian blinds and fabric roller blinds.

To actually perform the evaluation, the 3 control strategies calculate at each hour of the year if the selected shading system is used. The solar control strategy (i), calculates if the solar radiation, entering through the window system, is above a limit. This limit is asked to be put in by the designer. If the solar radiation is above the limit, the shading will close until it is below the limit. In the manual control strategy (ii), two occupants are defined: one that responds actively to the position of the sun and the weather; and one that responds to the sun only at the first time of the day that it is in the direct field of view. These two occupants are considered to prefer the shading system to be open more, in order to optimize the connection to the outdoors. At the same time, they also want to minimize the risk of glare. Lastly, the incident solar radiation strategy (iii) calculates with a limit for the amount of solar radiation hitting the façade on the outside. If the limit is met, the shading is used and is adjusted depending on the position of the sun.

The output from the tool contains 3 main categories: a) the calculated number of hours in the year that certain shading is used in each of the three control strategies; b) how the view to the outside can be quantified; and c) the hourly amount of solar heat gains entering through the system. The view to the outside is expressed in a View Quantity Index. This index represents how much of the outside can be seen through the window with the shading system. It is, however, an index that needs experimental validation to make certain it works in the presented way.
Finally, because the Excel tool was made to give quick hints for the designer of a building, a list of hours that the shading is used can be exported. This exported list can be used later when a more thorough calculation or simulation is needed to get the energy performance of the designed building.

This study was performed not to give optimized results, or to give design solutions, but to indicate how a shading system behaves in different situations.

• author: Hendrix, Anton and Arampatzis, Dimosthenis
• supervisor: Niko Gentile; Henrik Davidsson; Harris Poirazis
• organization: Division of Energy and Building Design
• course: AEBM01 20171
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Design tool, Glazing, Shading, User predictability, Solar gains, View
• language: English
• id: 8916938
• date added to LUP: 2017-06-22 12:59:29
• date last changed: 2017-06-22 12:59:29