Elsevier

Solar Energy

Volume 85, Issue 5, May 2011, Pages 757-768
Solar Energy

Quantifying the potential of automated dynamic solar shading in office buildings through integrated simulations of energy and daylight

https://doi.org/10.1016/j.solener.2011.01.010Get rights and content

Abstract

The façade design is and should be considered a central issue in the design of energy-efficient buildings. That is why dynamic façade components are increasingly used to adapt to both internal and external impacts, and to cope with a reduction in energy consumption and an increase in occupant comfort. To gain a complete picture of any façade’s performance and subsequently carry out a reasonable benchmarking of various façade alternatives, the total energy consumption and indoor environment need to be considered simultaneously. We quantified the potential of dynamic solar shading façade components by using integrated simulations that took energy demand, the indoor air quality, the amount of daylight available, and visual comfort into consideration. Three types of façades were investigated (without solar shading, with fixed solar shading, and with dynamic solar shading), and we simulated them with various window heights and orientations. Their performance was evaluated on the basis of the building’s total energy demand, its energy demand for heating, cooling and lighting, and also its daylight factors. Simulation results comparing the three façade alternatives show potential for significant energy reduction, but greater differences and conflicting tendencies were revealed when the energy needed for heating, cooling and artificial lighting were considered separately. Moreover, the use of dynamic solar shading dramatically improved the amount of daylight available compared to fixed solar shading, which emphasises the need for dynamic and integrated simulations early in the design process to facilitate informed design decisions about the façade.

Introduction

The ever-increasing focus on the environment and climate transformation as a consequence of the emission of greenhouse gasses means that the building industry is facing a new reality (IPCC, 2008, Brundtland, 1987). Energy consumption doubled in the period 1971–2007, and the operation of buildings accounts for 40% of the overall energy consumption (International Energy Agency, 2009). The Energy Performance of Buildings Directive (EPBD, 2002) has become an important part of the new reality, and with the recent political acceptance of the new version that prescribes that all new buildings must be “nearly zero-energy buildings” by 2020 (EPBD, 2010), energy efficiency at every level within the built environment has simply become a prerequisite.

The overall reason for constructing buildings is to shield occupants from the outdoor environment and obtain a certain level of indoor comfort. Consequently, to a great extent, it is the level of occupant comfort that determines how much energy is used to operate the building. This puts the façade, as the actual separator between the indoor and outdoor climate, at the centre of the “energy reduction issue”. Choosing the optimal façade, however, is a complex discipline with many, often contradictory, parameters of considerable interdependence (Ochoa and Capeluto, 2009).

The introduction of dynamic fenestration creates the possibility of obtaining a more beneficial utilisation of the available resources, such as insolation and daylight, with respect to both energy demand requirements and occupant comfort (Lee et al., 1998). There has been previous research into dynamic fenestration technologies to determine their significance in relation to energy consumption and occupant comfort. Results show the potential of dynamic fenestration components, ranging from a decrease in cooling and lighting demand (Athienitis and Tzempelikos, 2002, Tzempelikos and Athienitis, 2007), reduced overall energy demand (Lollini et al., 2010), and improved daylight utilisation (Koo et al., 2010). All this provides insight into how a certain degree of responsiveness in the façade can have a beneficial effect.

This article demonstrates that the selection of a façade design can only be justified by benchmarking various design alternatives early in the design process when decisions about the façade are made (Löhnert et al., 2003). When making this comparison, it is important to simulate the performance of the façades as a result of the interaction with the building sub-systems (Lee et al., 2004, Franzetti et al., 2004). The potential energy reductions and increases in occupant comfort from the ability of dynamic façades to adapt to the considerable seasonal changes can only be achieved through an integrated process (Lee et al., 1998). For example, improving the interior daylight conditions can reduce the energy consumption for artificial lighting, but also increase the heat gain, and therefore affect the energy demand for heating, ventilation and/or cooling (Johnson et al., 1984, Tzempelikos and Athienitis, 2007, Tzempelikos et al., 2007).

The main objective of this article is to demonstrate the potential of dynamic solar shading with regard to both energy demand and the quality of the indoor environment through a series of integrated simulations. Our aim is to clarify how a number of interdependent parameters define and affect the performance of the façade. The focus is on investigating the performance of dynamic solar shading compared to fixed solar shading or no solar shading. We use integrated simulations to illustrate the importance of providing data that facilitates early design decisions with regard to the façade (Wilde and Voorden, 2004, Strachan, 2008, Petersen and Svendsen, 2010).

Section snippets

Striking a balance

Obtaining the desired equilibrium between energy demand and occupant comfort can only be achieved at room level. Only on this scale is it possible to evaluate both behaviour and requirements with regard to the thermal and the visual indoor environment defined by the occupant. The balance that results in the desired level of comfort is often highly sensitive and is represented by many environmental factors (Fig. 1).

Even minor alterations in either internal or external loads can have a relatively

Simulation process

Analyses were carried out using iDbuild (Petersen and Svendsen, 2010), a tool developed at the Technical University of Denmark, that performs hourly-based calculations of the total energy demand taking into account the energy needed for heating, ventilation, cooling, domestic hot water and artificial lighting. In principle, the program is made up of two parts: a thermal simulation handled by BuildingCalc (Nielsen, 2005), and a daylight simulation handled by LightCalc (Hviid et al., 2008). The

Results

Comparative data with respect to both energy demand and daylight factors are presented below for the three solar shading types: no solar shading, fixed solar shading, and dynamic solar shading.

Discussion

The results for the simulated parameter variations illustrate that even in the relatively cold north-European climate, where heating often dominates the total energy consumption, energy demand for cooling and artificial lighting are also important – especially in low-energy buildings. General for all orientations, of course, is that increased façade transparencies allow more insolation into the room. A general tendency that is observed is a reverse proportionality between cooling and artificial

Conclusion

To quantify the potential of dynamic solar shading, we have presented simulation-based results from an investigation of three different solar shading types. Integrated thermal and daylight simulations were carried out to demonstrate comparable results of the performances of the façades with respect to energy consumption and indoor environment. The performances of the façades were evaluated in terms of total energy demand, the individual energy demands for heating, cooling and artificial

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