Buildings consume a significant amount of energy. This article will explore the influence of the type of building materials used on heating and cooling costs.
The most commonly used building materials are clay brick and Autoclaved Aerated Concrete brick (AAC). Both of these materials release a lot of carbon dioxide during the manufacturing process.
U-Values
U-values are an important concept to understand when designing and specifying building elements. They are often discussed in relation to insulation materials, such as cladding and wall, roof and floor insulation. They are also essential for the energy efficiency of buildings and can help to reduce energy consumption and associated CO2 emissions.
A U-value is a measure of the rate at which heat can escape from a particular element, such as a wall or roof, and it takes into account the thermal resistance of the individual materials that make up that element. This includes the insulating material itself, as well as air gaps and any other materials that may be present within the element. The lower the U-value, the better insulated the element will be.
The u-value of a building element can be calculated using a series of formulas, including the R-values of the individual materials that make up the element (Rt and Rsi) plus the additional thermal resistances associated with the internal and external surfaces of the element. It is also necessary to take into account the environmental temperature differences, as these will impact on the overall u-value of the element.
The U-value of a building element can be affected by the quality of workmanship and installation standards, so it is important to ensure that insulation is correctly fitted and there are no gaps or cold bridges. Linear thermal bridging values should also be considered, particularly for junctions between different elements, such as walls to ceilings and floors to ceilings.
Thermal Mass
The ability of building materials to absorb, store and release heat is referred to as thermal mass. Buildings constructed from heavyweight construction materials like concrete, brick and stone tend to have high thermal mass, while lightweight materials like timber frames have low thermal mass. Appropriate use of thermal mass throughout a home can make it more comfortable and save energy.
A material’s thermal mass depends on its density, which indicates how much it weighs per volume and its specific heat, which is the amount of heat energy needed to raise the temperature of a unit of the material by one degree Celsius. Ideally, materials used in building have a high volumetric heat capacity and a moderate specific heat, which ensures that the rate at which heat flows in or out of them will be roughly in line with the building’s daily heating and cooling cycle.
Some materials, such as lava rock and concrete, have a very high heat storage capacity, while others, such as insulation foam, have very little. Using materials with high thermal mass in conjunction with passive cooling strategies can help to reduce the time it takes for heat to reach comfort levels, which can significantly cut electricity consumption in summer.
Thermal Lag
High thermal mass materials (heavier and denser construction such as rammed earth, mud brick and concrete) can take longer to absorb and release heat than lightweight wall systems (straw bale, timber frame, brick veneer). This is due to their higher volumetric heat capacity which is influenced by thickness, insulation levels, temperature differences either side of the walls and conductivity. Appropriately sized and located, however, the thermal lag of these materials can be useful in controlling building temperatures. For example, if an external brick wall is positioned facing north it can absorb the winter sun’s radiant energy in the evening and radiate it back into the home, effectively reducing heating demands.
This control of internal temperatures is particularly helpful in climates that have wide diurnal temperature variations. In such climates, a well-designed system using external brick walls with appropriate lag times can significantly reduce energy use, by making it possible for the low night-time temperatures to reach and cool the building interior before the higher day time temperatures come in contact with the walls.
It should be noted, however, that concrete and brick have a high embodied energy and therefore require careful consideration as to their utility in each climate to ensure the lifetime energy savings they deliver are greater than their embodied energy content. Alternatives with lower embodied energy such as water and recycled brick are often more appropriate.
Energy Efficiency
Energy Efficiency, or EE, is the ability to use less energy and get more work done through innovations in building materials. A re-thinking of the way buildings are designed and used can lead to dramatic energy savings for homeowners, businesses and communities.
Using energy-efficient products and implementing efficient building design can reduce heating and cooling costs. The use of rammed earth or straw bale walls in new buildings, the addition of insulation to existing homes and the choice of paint colors and roofing materials can all result in lower home and business energy costs.
Many buildings, products and appliances waste energy through inefficiencies or by using more energy than needed to provide a service or product. This energy wastage contributes to climate change, health problems and economic instability in developing countries.
The products of chemistry, including high-performance building insulation, vinyl windows and reflective roof coatings can help to achieve energy efficiency. Reflective light-colored roof coatings and pigments can slow heat absorption in warmer climates, helping to reduce air conditioning costs and the urban heat island effect.
The ENERGY STAR® program is an excellent way to find the most energy-efficient products available for your home or business. ENERGY STAR helps you to choose the most energy-efficient models of appliances, lighting fixtures and other products. In addition, ENERGY STAR provides information on the environmental impact of each appliance and home or commercial building.