Application of thermal inertia in construction – How important it is

Thermal inertia is a characteristic of a material, it tells us how much heat an object can contain and at what speed it generates or stores heat. Translated into a building, we can immediately conclude that it is as if the mass of a house gradually absorbs energy and releases it over time.

Thermal inertia is the ability of a certain element to store the received thermal energy (heat), store it and release it gradually. The energy storage capacity of a material depends on its quality, density and specific heat.

For decades we have not considered thermal inertia in buildings, and our buildings can basically be reduced to face bricks and insulation rooms. Buildings that absorb heat during the day and provide heat at night require less energy to heat and cool.

In Spain, according to Junk Bunk rubbish removal, since the technical building code came into force in 2006 and was revised in 2013, some types of buildings should benefit from this material feature.

The thermal inertia of the materials used in the building allows the maintenance of the most stable temperature throughout the day in a habitable interior space. In summer, materials with high thermal inertia absorb heat during the day and due to the temperature change between indoor and outdoor environments, they are gradually stored and dispersed overnight (heat delays several hours). The next morning, the material lowers its temperature and begins to circulate again: it absorbs heat during the day and emits heat at night.

Importance of thermal inertia in construction

When currently using approved procedures to calculate energy ratings, we must consider the building envelope. Here we can see something like “the skin of a building”. The skin of the building will be the roof, facade, window sill, etc.

This “skin” of the building should be defined as accurately as possible in the program, because the technician enters the program according to the characteristics of the material, reads its extensive database, interprets the various thermal inertias of the material and translates it into heat transfer data.

For them, when a technician makes an energy certificate, they will present the closure in three different ways:

1. Default: When the technician enters the shell data, due to lack of experience or ignorance, he selects the “default” option, the program will recognize a certain shape according to the construction date and heat transfer will take place. The problem with entering data this way is that we “minimize” and the result may be lower than the result we get when we use one of the other methods.

2. Dear: By entering the data as “rating”, the program will guide us and explain the contents of the heat transfer. Based on some questions, such as the date of construction of the house, we think it is insulating, etc. Will provide data on heat transfer.

3. Known: This will always be the best way to enter closure data into programs. We can form the closure by gradually inserting the layers (from outside to inside).

Isolation mechanisms

It is often said that the properties of good insulation materials in the home will be mentioned, those things that protect us from the cold in winter, but how to effectively prevent heat stroke and cold? The hot summer of mid-August makes us feel the importance of protection from overheating at home, making us feel comfortable without losing cooling energy.

Especially in the space below the deck, the selection of thermal insulation materials with suitable characteristics and known effects on the structure, such as adjustment and size of windows, ventilated facades and roofs, as well as ventilation, are of particular importance.

It is a passive mechanism, which takes advantage of the temperature difference between the building element and its surroundings, softens the thermal differences by making them more stable and delays heat transmissions (time delay) to achieve greater thermal comfort inside.

This concept of thermal inertia is key in climates with significant daily thermal fluctuations to achieve one of the most important objectives in a home: thermal stability; that the temperature changes very little and does not expend excess energy for its maintenance.

Wood to improve thermal inertia

Wood is the construction material with the highest specific thermal capacity, 2100J / kg, and at the same time has high density and low thermal conductivity. Its natural characteristics make natural wood fibre insulators a material with a high capacity to maintain thermal mass: they have high thermal inertia, which provides very low fluctuations in internal temperature, which is an area where the outside temperature represents a large difference between day and night and night

For example, if a 180 mm fiberboard is used to store heat, the delay time (delay) for heat absorption and distribution reaches 10 hours. As shown in the figure below, the outside air temperature fluctuates at 21ºC and the indoor air fluctuates at 3ºC (damping coefficient = 7).

In addition to high thermal inertia, wood fibre insulators are open to vapour diffusion (value μ = 3) and regulate air humidity by inhaling or exhaling air, depending on the ambient conditions of the room. up to 20% of its weight in a humid environment without losing its insulating capacity. The combination of these two characteristics has a positive impact on the ambient conditions of the room.

I hope that with this information you will learn more about thermal energy, its characteristics and its obligation in the field of construction.