Tall buildings cluster form rationalization in a Nordic climate by factoring in indoor-outdoor comfort and energy

Highlights

• The research investigates urban clusters of tall commercial buildings in Tallinn.

• A workflow integrating thermal models of indoor and outdoor domains is developed.

• Indoor comfort and energy consumption of tall commercial buildings are analyzed.

• First-time assessment of outdoor thermal comfort in commercial areas in Tallinn.

• The research suggests building layouts for improving indoor and outdoor comfort.

Abstract

Considering climate change, controlling outdoor microclimates is an increasingly pressing concern. Microclimates have a significant effect on both outdoor and indoor comfort, and on the energy efficiency of buildings. This concern is particularly important as current climate conditions reveal that warmer summers are threatening the comfort of pedestrians and causing overheating in office environments, which is consequently increasing cooling energy consumption. A further concern is that this trend now extends to Nordic latitudes.

Existing literature demonstrates how a local microclimate depends on many factors such as urban density, shape and orientation of buildings, the types of materials present, the number of green areas and anthropogenic activities. However, there is little research focusing on how reciprocal distances among tall buildings, and their relative position, affect outdoor and indoor comfort, and the associated energy consumption of buildings. This paper presents a unique and comprehensive insight into the interconnected nature of indoor and outdoor comfort via coupled simulations.

It presents a study of clusters of tall commercial buildings located in the Nordic climate of Tallinn (Estonia) with different microclimates, and shows that the differences are due to variable shadowing and reflections and different wind patterns. The results, which focus on summer conditions, show that small variations of cluster layout strongly affect the local indoor and outdoor comfort, thus highlighting the need to conduct both studies simultaneously in research aiming to increase pedestrian and indoor comfort and resource efficiency.

Introduction

The practice of climatic design is currently shaped by two mono-focused scales: the larger city (macroscale) fostered by the zoning approach, and the single building approach (microscale), which is shaped according to energy codes [1]. This latter approach seems to be inefficient when new business districts hosting tall buildings are planned. It leaves the medium scale district (i.e., building groups) unregulated in a sort of “design limbo”, which can have negative consequences for the livability and resource efficiency of our cities, and for the climate at large.

The medium scale is where the decisions affect the microclimates and where bioclimatic design for buildings have always taken place [2], [3], [4]. The iconic urban plan of Barcelona, Spain of 1859 by Ildefons Cerdà has been shaped through quadrangular blocks to improve natural ventilation and solar accessibility to improve the comfort of pedestrian areas and the health of building occupants [5]. Located on a peninsula, the historic center of the city of Korčula, Croatia presents wide streets positioned east to west to favor the flow of summer breezes to cool the urban environment, and short narrow alleys positioned north to south to block cold winter winds [6]. The New York Zoning Resolution of 1916 provided a set of geometrical rules to allow sufficient daylight to reach the sidewalk and lower floors of the nascent tall building typology, which strongly influenced the image of Manhattan before the second world war [7]. More recently, the solar neighborhood of Vauban in Freiburg, Germany was designed so that building distances, layouts, sizes, and orientations allow for direct solar radiation to interplay with outdoor and indoor spaces, thereby providing outdoor comfort of pedestrians and livability of private gardens, reduction of energy consumption and energy generation [8].

In recent times, many new districts of tall commercial buildings have also been built in the European Nordic cities. This trend warrants greater attention to the middle-scale thinking and the related issues of outdoor and indoor thermal comfort and energy consumption during the warm season. In that regard, tall commercial buildings strongly contribute to and are affected by the Urban Heat Islands (UHI) [9]. The glazed surfaces reflect solar radiation at ground levels, which contributes to local warming [10]. In most cases, these buildings are sealed and cooled, and exhaust heat into public spaces. The effects of climate change, such as warmer summers and heatwaves, further increase the magnitude of UHI, leading to two intertwined adverse effects: 1) warmer days and nights, along with higher air pollution, which contributes to local discomfort, respiratory difficulties and illness, and 2) buildings overheating, further affecting indoor comfort, energy consumption and emissions [11], [12].

However, the modernist idea of amorphous and decontextualized tall commercial building came with a new concept for the use of mechanical systems: any building design, even a fully glazed tower building, can be made comfortable using air-conditioning and heavy energy use. When unregulated, tall buildings cast extensive shadows, cause a wide range of multidirectional reflections and block or accelerate wind flows. These factors strongly impact on the local microclimate and the magnitude of meteorological parameters such as air temperature, relative humidity, wind direction and velocity, mean radiant temperature, surface temperature and long and shortwave radiation [13].

With these above points in mind, an obvious research question arises: how can the design of tall buildings be rationalized in relation to the climatic and urban context in which they are built? In other words, is it possible to configure geometrically correct tall building clusters so that outdoor and indoor comfort are achieved and the use of energy is minimized?

The study presented here addresses this question through the use of a novel digital design process based on Ladybug Tools that couples indoor and outdoor thermal models [14]. After defining the framework and scope of the research, the paper outlines an approach that investigates the mutual relations between local microclimate, overheating of tall commercial buildings and energy performance of buildings. Analyses are performed on nine cluster layouts composed of tall commercial buildings located in three different areas of the city of Tallinn (Estonia). The scope is to provide insight into the relation between indoor and outdoor comfort and highlight the need for designers to analyze and control this aspect during the early design phases when the most influential design choices are made. In addition, this study provides recommendations for optimal solutions for tall building arrays to achieve a more livable environment and accelerate the required neutral-carbon transition.