Bricks are known for their durability and structural integrity, and they also retain heat. This property stems from their physical composition, allowing them to absorb thermal energy, store it, and release it gradually. This makes bricks valuable where stable temperatures are desired, contributing to energy efficiency and comfort in built environments.
How Bricks Store Heat
Bricks store heat primarily due to their thermal mass, a material’s capacity to absorb, store, and release thermal energy. Brick, concrete, and stone have high thermal mass. Its effectiveness is determined by specific heat capacity and density. Specific heat capacity is the energy required to raise a material’s temperature by one degree Celsius. Bricks, being dense, possess a high specific heat capacity, enabling them to absorb significant heat before their temperature noticeably increases.
When exposed to a heat source, such as sunlight or warm air, bricks absorb thermal energy. Once the heat source is removed or the surrounding temperature drops, the stored energy is slowly released back into the environment. This process, often referred to as thermal lag, means bricks release heat at a slower rate than they absorb it, contributing to a more stable temperature over time.
Where Brick’s Thermal Properties Are Used
The heat-retaining properties of bricks find practical application in various fields, contributing to energy efficiency and comfort. In passive solar building design, bricks absorb solar heat during the day and release it at night, helping maintain consistent indoor temperatures. This approach can reduce the need for mechanical heating and cooling systems. Brick masonry walls exposed to sunlight act as thermal storage, absorbing and slowly radiating energy into the living space.
Bricks are also a traditional and effective material for fireplaces and wood-fired ovens. In these applications, firebricks, a type of refractory brick, are used because they can withstand high temperatures and retain heat efficiently. The thermal mass of these bricks allows ovens to maintain stable, high temperatures necessary for baking, even after the fire has diminished. This stored heat radiates evenly, which is beneficial for cooking. Beyond residential uses, bricks, especially firebricks, are increasingly employed in industrial heat storage systems. These systems use bricks to store heat generated from renewable electricity, which can then be released on demand for various industrial processes like cement or steel production, offering a cost-effective alternative to battery storage for thermal energy.
What Affects a Brick’s Heat Retention
Several factors influence how effectively a brick retains heat. The type of brick plays a significant role, as different compositions affect thermal performance. Dense bricks, such as common clay or concrete bricks, generally have higher thermal mass and can store more heat than lightweight or hollow bricks. The density of clay bricks can range from approximately 1600 to 1900 kg/m³, directly impacting their thermal conductivity and heat storage capacity. Incorporating materials like perlite or vermiculite into brick mixtures, or creating air pockets through porosity, can reduce thermal conductivity and enhance insulating properties, but might decrease heat storage capacity.
The thickness of a brick wall also directly impacts its heat retention capabilities. Thicker walls provide more material to absorb and store heat, leading to greater thermal mass and a longer thermal lag. For example, the first 50mm of a wall is most effective for thermal mass, with diminishing returns beyond 100mm. The presence and placement of insulation around bricks are also important; for external walls, insulation placed on the exterior surface helps prevent heat loss from the stored warmth, while internal insulation can reduce the brick’s ability to absorb and release heat. Finally, the color and texture of a brick’s surface influence how much heat it initially absorbs, with darker, matte, or textured surfaces absorbing and re-radiating more energy than lighter, smooth, or reflective ones.