Learn How to Avoid Energy Loss in Your Buildings

Thermal comfort becomes very evident when it is not attended to. When thermal conditions are adequate in one location, our body is in balance with the environment allowing us to perform activities normally. On the other hand, when a space is too hot or too cold, we soon see changes in our mood and body. Dissatisfaction with the thermal environment occurs when the heat balance is unstable, that is when there are differences between the heat produced by the body and the heat that the body loses to the environment.

An analysis of 24 studies on the relationship between temperature and performance indicated a 10% reduction in performance at both 30°C and 15°C, compared with a baseline between 21°C and 23°C – demonstrating the impact thermal comfort can have on office occupants. A more recent study, in a controlled setting, indicated a reduction in performance of 4% at cooler temperatures, and a reduction of 6% at warmer ones. [1]

Protecting ourselves from the weather is one of the primary functions of architecture. This can be done in an active way (using heating or air conditioning equipment, for example), or passively, using solar radiation, ventilation, and materials in favor of the architecture. Although the advent of cooling and heating technologies has improved indoor conditions, they have also contributed to the creation of buildings that are poorly adapted to the environments in which they were installed, making them costly to cool, heat and enable comfort in their interiors. Office buildings with glazed facades, which are not specified with respect to local climate, relegate complex air conditioning systems to the task of maintaining a constant internal temperature.

The envelope of the building is an important part as it acts as a filter between the exterior and interior climate, and should take local climatic conditions into account when designing. In warm places, it is generally sought to ventilate the building as much as possible, with generous openings and shaded spaces. In a cold region, on the contrary, the envelope tends to allow the sun to enter the space, maintaining the heat in the building. The direction of heat flow always goes from the hottest to the coldest surface and the transmission occurs when there is a difference between the temperature of the external and internal surface.

Several pieces of research address the main forms of energy loss in a building. In general, the numbers are close to 35% for the walls, 25% for windows and doors, 25% for the roof and 15% for the floor. These heat losses occur by convection, conduction, and radiation. They will inevitably occur, but it is the architect's duty to manage how quickly heat is lost - this can be controlled through the use of appropriate building materials and techniques to establish and maintain a watertight building enclosure incorporating high levels of insulation.

At this point, it is important to address the concepts of thermal insulation and thermal inertia. Thermal insulation reduces heat loss during cold seasons and heat gain during hot seasons. Insulation materials like mineral wool, ceramic fibers, Styrofoam and polyurethane generally consist of many voids. Air or other gases captured in these voids act as an insulator. They will help reduce heat losses and gains. We have already discussed how to calculate the thermal transmittance, also called the U-value, in this article. This value allows us to know the level of thermal insulation in relation to the percentage of energy that crosses the envelope; if the resulting number is low, we will have a well-insulated surface. A high number will alert us to a thermally deficient surface. Another important concept is thermal inertia, which is the characteristic of a material to retain the heat and return it to the environment little by little. Materials with high inertia will have a delayed reaction on changes in atmospheric temperature. The thermal inertia is relevant in regions with climates with large thermal amplitudes between day and night. In coastal regions and sites where there is little temperature difference in days, the adoption of materials with low thermal inertia is adequate to prevent high temperatures from entering the spaces.

Walls

To reduce heat exchanges between the interior and exterior, it is important to invest in insulation materials, such as mineral wool, and their integration into façade systems. Plaster also acts to improve thermal comfort. Intelligent membranes assist in tightness and moisture management, while coatings can contribute by insulating and protecting against bad weather.

Roofs

It is always recommended to combine some type of thermal insulation to the roof for greater comfort inside the structure. In regions where it is advisable to work with high thermal inertia, it is recommended to build a massive slab with the final application of an insulator. In regions where it is possible to work with low thermal inertia, light linings can be used, but always with the application of thermal insulation. A technique that is widely used, and has proven positive results and low cost, is to paint the tiles white or use tiles of light colors, as they reflect the sun rays.

Floors

Although often overlooked, the insulation of the floor is important to reduce heat exchange between the ground and the building. In addition, it is important to mention that the choice of wall or floor covering will influence the perception of temperature by the occupants.

Windows and Doors

Glass in the windows and facades can allow solar radiation to enter the environment, but can also conserve the heat produced by the occupants, the heating systems inside the building, or allow the heat to be evacuated, depending on the type of building. In short, the control of solar radiation can be summarized in [2]:

• Admit or block natural light;
• Admit or block solar heat;
• Allow or block heat losses from the interior;
• Allow visual contact between interior and exterior.

For the study of the behavior of transparent closures, it is important to consider short waves and long waves. Short waves are visible and infrared. Long waves are infrared radiation emitted by heated bodies. The key is to find a good balance between the window's ability to reduce heat loss (u-value) versus its ability to increase or reduce solar heat gain. At this moment, the G-value (Solar Factor) is important, which is nothing more than the percentage of solar radiation that hits the glass and is transmitted directly and indirectly to the environment. A G-value of 1.0 represents the total transmittance of all solar radiation, while 0.0 represents a window without solar energy transmission. That is, in cold climates, a higher "g-value" helps to provide more useful solar gains and limit heating needs. In hot climate countries, a lower "g-value" helps control unnecessary solar gain to limit heating needs. In the figure below we show the operation of some types of glass.

Successful decisions influence the living conditions of the occupants, and each material can play a role within a general design strategy. The final specification should not only optimize power consumption, but also provide comfort to the user, that is why it is so important that architects know a little about the theory behind the phenomena and how the characteristics of the specified materials will influence the performance of the building in all its complexity.

References

[1] Wargorcki P (ed), Seppänen O (ed), Andersson J, Boerstra A, Clements-Croome D, Fitzner K, Hanssen SO (2006) REHVA Guidebook: Indoor Climate and Productivity In Offices. Lan L. Wargocki P. Wyon DP. Lian Z. (2011) Effects of thermal discomfort in an office on perceived air quality, SBS symptoms, physiological responses, and human performance.

[2] Lamberts, Dutra, Pereira (2014). Eficiência Energética na Arquitetura. Available at this link.