Thermal comfort: resilient cooling strategies

In the pursuit of a comfortable indoor environment, managing heat is a key concern. Too much heat can impact the well-being of people present in indoor spaces, creating a sense of discomfort and compromising air quality. However, by targeting specific areas and effectively removing both sensible and latent heat, it is possible to significantly improve comfort and air quality. In this article, we will explore various strategies for reducing the amount of heat that enters indoor spaces and enhancing the well-being of occupants.

Thermal inertia

Thermal inertia is a key concept for designing energy-efficient buildings. Indeed, a building with high thermal inertia will tend to maintain a more stable temperature inside by storing heat and dissipating it with a lower intensity and with a time delay, thus reducing the need for heating and cooling.

Time lag of temperature due to the thermal properties of the building envelope materials (5)

Thermal inertia depends on several factors, such as the thermal mass of the building, i.e. the amount of materials that can store heat or coolness. Materials with high thermal capacity, such as concrete, brick, and stone, are particularly effective in increasing the thermal inertia of a building. Other factors that affect thermal inertia include thermal insulation, ventilation, and the design of the building envelope. Well-insulated buildings can reduce heat and coolness losses, while adequate ventilation can help regulate indoor temperature. A well-designed building envelope can also reduce excessive heat gains in summer and heat losses in winter.

Phase change material

Materials with phase change (MCP) have the ability to absorb, store, and release thermal energy in a cyclic manner, usually on a daily basis, to regulate internal temperature and improve thermal comfort in buildings. They can store thermal energy in latent form when they go through a phase transition such as melting (from solid to liquid state, for example: melting of ice) or solidification (from liquid to solid state, for example: formation of ice).

Principle of operation of a PCM (6)

This energy can be used for passive cooling of buildings and electricity production. In summer, they can delay and even reduce the peak of the heat wave in the building structure by absorbing excess heat during the phase transition process, which maintains a comfortable ambient temperature. Finally, when the temperature drops at night, the MCP releases the stored heat to maintain a comfortable ambient temperature and complete the cycle through MCP solidification.

The use of geothermia

Ground energy structures are a technique that allows for the exploitation of natural resources in the ground to heat or cool buildings. This method involves using structures in contact with the ground, such as foundations, parking lots, roads, tunnels, etc., to capture the thermal energy present in the first few meters of depth since this thermal energy is constant over time from a few meters depth. By integrating heat exchangers into these structures, the heat can be redirected to a heat pump (HP) that can heat or cool the building. This technique is particularly effective as it reduces energy consumption by exploiting a renewable and inexhaustible resource. Furthermore, it has the advantage of being inexpensive and easy to implement, making it an interesting solution for both new and renovated buildings. By using ground energy structures, buildings can benefit from a heating and cooling system that is efficient and environmentally friendly.

Ventilated facades

The natural cooling technique for buildings involves using ventilated surfaces to dissipate accumulated heat and maintain a comfortable temperature inside. Ventilated facades and roofs consist of having a space between the exterior and interior surfaces of the building. This space creates a buffer zone that reduces the transfer of heat into the building by blocking solar heat and limiting heat transfer through conduction. To enhance the cooling effect, air circulating in this space can be mechanically ventilated using fans, vents, or natural openings. Additionally, the use of reflective materials or light colors for exterior surfaces helps reduce the amount of absorbed heat, thereby contributing to reducing the building's thermal loads. High thermal capacity materials can also be used for interior surfaces, allowing them to absorb heat during the day and slowly release it at night, thereby improving the cooling effect.

A ventilated facade exemple (1)

In summary, the strategies outlined earlier contribute to ensuring optimal thermal comfort in buildings without relying on energy-intensive systems. These passive approaches are also beneficial for limiting the urban heat island effect, making them a sustainable solution for urban planning and environmental preservation

Source:

1. Resilient cooling strategies – A critical review and qualitative assessment, Chen Zang (2021)

2. Energy saving potential of phase change materials in major Australian cities, Morshed Alan et al. (2014)

3. CFD modelling of naturally ventilated double-skin facades with Venetian blinds, Y. Ji (2008)

4. Intégration thermique et mécanique des géostructures thermiques : de l'échelle du bâtiment à l'échelle de la cité, Y. Delerablee (2019)

5. Thermal inertia in buildings: A review of impacts across climate and building use, S. Verbeke (2018)

6. https://www.researchgate.net/figure/1-Operating-principle-of-PCM-in-buildings_fig19_326092265