Heat capacity is a material property used to assess a wall’s thermal mass, and it is often used as a criteria in energy codes and standards. Thermal mass is defined as: the absorption and storage of significant amounts of heat in a building or in walls of a building. Wall thermal mass, such as that present in concrete masonry construction, tends to decrease both heating and cooling loads in a given building, thus saving energy. The amount of savings realized by incorporating thermal mass into a building’s design is a function of several variables. These include local climate, wall heat capacity, fenestration (window) area, fenestration orientation, fenestration solar gain, building occupancy load and other internal gains such as lights and office equipment. The most manageable approach to account for energy savings due to thermal mass is to relate the savings to the wall heat capacity and local climate.
Heat capacity (HC) is defined as the amount of heat necessary to raise the temperature of a given mass one degree (refs. 2, 3), and is calculated as the product of a wall’s mass per unit area by its specific heat. In other words, double insulated masonry have the greatest capacity to story heat inside in the winter and conserve cooling in the summer.
A building with massive walls, such as concrete masonry, uses less energy for heating and cooling than lightweight frame walls, wood or steel studs for example. Because of this, the International Energy Conservation Code and ASHRAE Standard 90.1, prescribes lower R-value requirements for concrete masonry walls than those for frame walls and metal buildings, in many cases. (This lower required R-value corresponds to a higher required U-factor.)
Put in simple terms, the enemy to energy savings is found in the windows. During the summer, heat enters through the windows. As the air conditioning runs, it is cooling the mass density of the walls. This then maintains a constant ambient temperature in the home. Since heat chases cold, as the sun enters the windows and begins to transfer heat to the living area, the heat chases after the walls, and with the walls maintaining the cool temperatures and with a very slow direct heat transfer from the outside wall to the inside wall, the entire living space remains comfortable throughout the home. The same follow for the winter, the interior density of the masonry walls stores the heat and this saves in energy costs. Building with wood frame construction acts more like an insulator than a storage of energy. With Omni Block, you have the benefits of both.
