Building Physics

Nowadays we spend most of our time in buildings. The building designers are therefore responsible for creating a pleasant, productive and healthy indoor environment. Adequate thermal comfort plays a very important role in achieving this goal. Thermal comfort is also close related to the energy use. In the European Union, buildings are responsible for more than one-third of final energy consumption. As consequence the requirements for the energy efficiency of buildings becoming increasingly stringent, in particular due to global climate change mitigation targets. The thermal properties of building envelope have a decisive role in ensuring these objectives. This chapter describe the mechanisms of heat transfer in building structures in steady and dynamic outdoor and indoor environment conditions and the methods for assessment of thermal properties of opaque and transparent building structures and building envelope. The experimental and numerical assessment methods are explained. It also explains the principles and guidelines of the design and the evaluation methods for the in-situ assessment of indoor thermal comfort.

There are many sources of air pollutants in buildings, such as people, appliance and built materials, which cause the air in buildings to be more pollutant than in the outdoor environment. The increased content of pollutants in the indoor air can affect the well-being, work performance and even the health of the occupants. Such conditions can be avoided by dilution of pollutants with adequate ventilation of buildings, the process of the air exchange between building interior and outdoor. Buildings can be ventilated naturally due to the difference in air pressure caused by the difference in the air temperature and exposure of the buildings to the wind or forced ventilated by mechanical systems. Because ventilation of the buildings increases the energy use, the uncontrolled air exchange due to the air infiltration must be avoided as much as possible with consistent airtightness of the building envelope. In the chapter the principles of planning and the evaluation methods for indoor air quality comfort are presented. The impact of the ventilation on energy needs is explained, including the ventilation related measures for increasing of the energy efficiency of buildings.

Building structures are in constant contact with water in at least one of its states of matter. Water or water vapour enter and exit building structures as a consequence of precipitation, hydrostatic pressure, capillary suction and the water-vapour pressure difference between the indoor and outdoor air. The analysis of water and water-vapour transport in building structures is based on mass-transfer balance. Any moisture uptake in building structures is undesirable for a number of reasons. Moisture in construction materials increases the thermal conductivity and, consequently, the heat conduction. Moisture also deteriorates the mechanical properties of building structures, causing damage to the material and higher maintenance costs. Dampness is also closely connected with microbial growth, posing a health risk to the building’s occupants and reducing the quality of life in affected buildings. We must, therefore, be acquainted with the moisture-transfer mechanisms, as well as the methods and criteria to verify that the building structures were designed in such a way that moisture accumulation would not impair the thermal and mechanical properties of building structures.

Vision is the sense that provides us with the majority of information about the natural and built environments. The information received depends on the characteristics of the light source, the optical properties of the objects reflecting the incoming light, and the way we perceive light with our ability to see. Besides that, light is involved in the chemical and biological processes taking place in our bodies, so proper lighting is indispensable to our well-being and health. In this chapter, light will be treated as electromagnetic radiation over a range of wavelengths that can be detected by our vision. The most important source of natural light is the Sun, from which the Earth receives light in form of direct radiation emitted from the Sun’s photosphere and as the diffuse radiation from the sky. Natural light in the outdoor and indoor environments is complemented by artificial light sources, predominantly electric lamps. The technological development of electric light sources over the past two decades has given us products that are capable of emitting light that is very similar to natural light, yet with a significantly reduced consumption of electrical energy.

Designing the visual comfort in buildings is a process of optimizing the illumination of the spaces as well as light perception in the way that building occupants are provided with a comfortable, highly productive and healthy living environment.

Emitting and perceiving sound are the most important ways that people use to exchange information. Sound is a phenomenon related to mechanical waves and oscillations that propagate through compressible/elastic matter, such as air or building materials, in the form of sound waves. However, human hearing also senses disturbing sounds, referred to as noise. Noise is constantly generated by the people and equipment in buildings and their surroundings, affecting well-being, productivity and health. As most of our time is spent in buildings, ensuring the proper level of acoustic comfort and protection from all types of noise is an important function of any building. There are two important tasks for the discipline of acoustics in the scope of building physics, associated with the acoustic-related comfort in buildings: room acoustics deals with the quality of sound perceived by the listeners in rooms containing sound sources, while building acoustics deals with the protection of listeners from the transmission of the noise in the surroundings, as well as between the rooms in a building, with adequate sound insulation. The first task focuses on the design of the architectural form of the rooms and the sound-absorbing properties of interior surfaces that define the reverberation time of the rooms, while the building acoustics focuses on the design and evaluation of sound insulation against airborne and impact sound.

Besides providing indoor living comfort, a building must also ensure the safety of its occupants. Natural disasters excluded, the safety of a building’s occupants is most often threatened by fire. More than one-third of all fires in the world are related to fires in buildings, and currently more than 10 people per million of the population die in building fires. Due to the constant updating of fire-safety regulations, the number of deaths due to fires in buildings has declined by 65% over last 30 years [1]. Building physics in the field of fire safety focuses on a description of the physical fundamentals of the fires in buildings and the way that building materials and structures respond to a fire. A fire in a building occurs in several stages. In the first stage, which usually takes for up to several tens of minutes and is known as the fire growth stage, it is important to protect people as they are evacuating the building. In the second stage, with a fully developed fire, it is necessary for the building structures to retain their load-bearing capacity and prevent the spread of the fire to other building zones or the surrounding buildings. Thus, extinguishing a fire is less dangerous for the firefighters and leads to less damage to property. The fire safety in buildings is achieved with both passive and active measures. The passive measures are related to building materials and the building construction’s response to the fire, while the active measures include the control of smoke and heat propagation in buildings by either the natural or forced ventilation of fire compartments. Other active measures include technical systems for detection, alarm and fire-extinguisher systems.

More than 80% of the population in developed countries live in urban areas. Urban-area developments in the past century have led to major changes in land use and, what is even more problematic, it also affects the physical, chemical and biological processes occurring in the nature. One of the most obvious consequences of urbanization is the appearance of microclimatic conditions, described by the intensity of an urban heat island, and the specific air flow patterns in urban neighbourhoods that influence the thermal response of the urban environment as well as the spread of air pollutants. These conditions are a consequence of construction technologies, built materials and modern lifestyle, including the increasing levels of energy use and anthropogenic pollution. Sustainable architectural and urban planning can contribute significantly to the mitigation of urban heat islands and increased urban biodiversity, while improving the indoor environment’s quality and the energy efficiency of buildings. In this chapter the phenomena of the urban climate are described and techniques for the mitigation of an urban heat island are presented. The empirical models and the dedicated computational fluid dynamics (CFD) tools for modelling the thermal response of the urban environment are shown. The mitigation of urban heat islands and street canyons with the use of vegetated building structures, greened building blocks and city parks is discussed.