A Method for Driving the Solar Control Mechanism Selection

Abstract

Highly glazed spaces are continuously increasing in popularity due to architectural attractiveness. However, increased use of glass often jeopardizes thermal comfort in several ways and problem of overheating is one of them. A way to face this problem is to appropriately use solar control mechanisms. However, a proper selection of solar control mechanisms from an early design stage is a complex task that often can puzzle experienced building physicists, façade designers and architects.

In this project a method was developed, which drives the selection of appropriate solar control mechanisms based on analysis of overheating due to solar heat gains. The aim of the method is to maintain adequate thermal comfort levels in highly glazed spaces. Two thermal comfort models, Predicted Mean Vote and Adaptive Model, were chosen to set the thermal comfort boundaries included in the method. Moreover, in order to make the output of this method more realistic, the effect of direct solar component was considered as an adjustment to the mean radiant temperature. Three different types of solar control mechanisms have been investigated and assessed, those are solar control glass, interior and exterior fabric blinds.

The results present the overheating in annual overheating charts colored after the scaled range of temperatures for every hour of the year. As a result of the analysis, the appropriate solar control mechanisms are defined according to their performance in solving particular overheating problem. By that the method suggests solutions and helps the designer to understand the potential improvements that can be realized by implementing solar control mechanisms. The method aims to assist specialists with the selection process of solar control mechanism that respects the architectural vision without compromising the quality of thermal comfort.

Due to limitations, only three types of solar control mechanisms were included in this study and a future investigation of angular dependent shading devices would be a valuable addition to the method.

Popular Abstract

An increased use of glazing is architecturally attractive and beneficial in terms of daylight and view out. On the other hand, the problem of overheating due to excessive solar heat gains makes it challenging to provide thermal comfort for the occupants. Temperature control by air conditioning and cooling alone cannot always solve the problem of overheating, as the direct solar radiation falling on the occupant plays an important role in the perception of thermal conditions. Therefore, the use of solar control mechanisms is preferable as a more effective and energy-efficient measure. However, the choice of appropriate combination of solar control mechanisms is a complex task. An efficient control of solar heat gains needs to be provided without compromising the benefits of a highly glazed façade, such as daylight and view out.

To solve this problem, a method for the solar control mechanism selection was developed and formed as an Excel-based tool for an early design stage. Based on the user’s input parameters, the method defines the problem of overheating in an examined space and suggests an effective solution to provide thermal comfort. To make the results more visual, an overheating chart was developed and implemented in the tool. This chart shows all hours of the year, colored after the degree of overheating that occurs. The scale was also developed within the method and serves for ranging the perception of thermal comfort. Solar control mechanisms, used in the method, are represented by two types of solar control glass in combination with interior and exterior fabric blinds. When advising on the solar control mechanism, the method ensures that the selected solar control blinds are not used too often.

For the development of the method a single office room was simulated using a dynamic thermal modeling (DTM) tool. A parametric study was performed in order to examine the effect of the reduced cooling set-point, glazing area and façade orientation on how effective the solar control mechanisms are in solving the problem of overheating. The results of the parametric study stood as a base for the decision-making part of the method. Based on the analysis of the results, a lower cooling set-point and a smaller glazing area were chosen as the options which are recommended if the problem of overheating cannot be solved by means of solar control mechanisms. The validation of the method has shown, that the difference between the mean radiant temperature (MRT) and the indoor air temperature (Tair) is an important control parameter for the solar control mechanism selection. This parameter indicates to which extent the problem of overheating is caused by solar heat gains and, therefore, can be solved by means of solar control mechanisms.

Overall, the results of the study showed that an effective combination of solar control glazing and fabric blind can be chosen to provide the required thermal comfort based on the thermal comfort assessment at an early design stage. To achieve that, it is important to account for the effect of the direct solar component and to control the difference between the mean radiant and the indoor air temperatures. At the same time, the frequency of the blind use can be controlled, potentially providing better conditions for daylight and view out. Providing that the developed method accounts for these parameters, it can be used in an early design stage to advice on the effective combination of the solar control mechanisms. However, a future development of the method is recommended in order to implement other types of solar control mechanisms and thermal comfort models and to validate the method for varied locations, geometry of the room and the position of the occupant.

• author: Mokhava, Vitaliya and Nilsson, Christopher
• supervisor: 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: Solar control mechanisms, Thermal comfort, Overheating, Solar control glass, Solar control blind
• language: English
• id: 8919528
• date added to LUP: 2017-08-23 16:32:37
• date last changed: 2017-08-23 16:32:37