MIDWEST A Chapter of Precast/Prestressed Concrete Institute PRECAST THERMAL MASS AND ENERGY SAVINGS Thermal mass is the ability of a material to absorb and store heat energy (thermal sponge). A lot of heat energy is required to change the temperature of high-density materials like concrete, which is therefore said to have high thermal mass. Lightweight materials such as timber have low thermal mass.
Due to its density, concrete has the appropriate areas of glazing facing A high mass building needs to gain or capacity to absorb and store large appropriate directions with appropriate lose a large amount of energy to change quantities of heat, contributing to a levels of shading, ventilation, insulation its internal temperature, whereas a high-performance building envelope. and thermal mass. lightweight building requires only a small Its thermal mass allows concrete to energy gain or loss to change the air react very slowly to changes in outside HOW THERMAL MASS WORKS temperature. This is an important factor temperature to reduce peak heating and Thermal mass acts as a thermal battery. to consider when choosing construction cooling loads and delay the time at which During summer it absorbs heat during systems and assessing climate change these loads occur. The resulting savings the day and releases it by night to cooling adaptation. can be significant—up to 25% of heating breezes or clear night skies, keeping and cooling costs. buildings comfortable. In winter the same ASHRAE Standard 90.1 acknowledges thermal mass can store the heat from the thermal mass benefits of concrete Thermal mass can store solar energy the sun or heaters to release it at night, walls in specifying lower minimum during the day and re-radiate it at night. helping buildings stay warm. insulation R-value and higher maximum Used correctly, it can moderate internal wall U-factors for mass (concrete) wall temperatures by averaging out diurnal Thermal mass is not a substitute for construction. (day−night) extremes. This increases insulation. Thermal mass stores and comfort and reduces energy costs. Poor re-releases heat; insulation stops heat Research conducted by Oak Ridge use of thermal mass can exacerbate the flowing into or out of the building. National Laboratory compared the worst extremes of the climate and can be dynamic thermal performance of a huge energy and comfort liability. Thermal mass is particularly beneficial insulated concrete walls with that of a where there is a big difference between traditional wood frame. Research shows To be effective, thermal mass must day and night outdoor temperatures. that insulated concrete sandwich walls be integrated with sound-passive Correct use of thermal mass can delay constructed with composite connector design techniques. This means having heat flow through the building envelope technology utilize the thermal mass effect by as much as of concrete to create an “equivalent wall 10−12 hours, performance R-value” several times producing warmer greater than a traditional material R-value buildings at night calculation. in winter and cooler buildings Energy-saving benefits of thermal mass during the day in are most pronounced when the outside summer. temperature fluctuates above and below Daytime Absorption Nightime Flushing the balance temperature of the building,
WHO WE ARE PCI Midwest is a not-for-profit trade association that promotes precast/prestressed concrete, provides precast/ PCI MIDWEST Mike Johnsrud, PhD, PE • Executive Director prestressed concrete education, and facilitates relationships between its members and the construction and design communities. 612-760-6101 • [email protected] • www.pcimidwest.org causing a reversal of heat flow within the wall. The balance point is generally CONTINUING EDUCATION PROGRAM between 50 and 70°F.
These ideal conditions for thermal mass exist on a daily basis at all locations in THERMAL MASS, ENERGY the United States and Canada.
Another factor affecting the behavior of thermal mass is internal heat gain. CODES, AND PRECAST This includes heat generated inside the building by lights, equipment, appliances and people; and heat from CONCRETE the sun entering through windows. Generally, during the heating season, Mass walls in combination with insulation can save energy in benefits of thermal mass increase with buildings. This presentation describes the benefits of thermal the availability of internal heat gains. mass (thermal inertia) and how these benefits are recognized During the cooling season, thermal in national energy codes. An overview of compliance paths mass exposed to the building’s occupied of these energy codes is presented. The degradation of the spaces will absorb internal gains, R-value of concrete panels with metal thermal bridges shifting peak cooling periods. Concrete that pass through the insulation is also described. exposed to the interior, not covered by insulation and gypsum wallboard, works Credits: 1 PDH or AIA LU best to absorb internal gains, saving Contact PCI Midwest for additional information cooling energy. about this presentation.
Thermal mass also works well when daily temperatures have large variations between the daytime high and nighttime low and when outdoor air can be used for nighttime ventilation. Designs employing LIVE/ON-DEMAND WEBINARS LUNCH BOX PRESENTATIONS thermal mass for energy conservation should be given a high priority.
The benefits of thermal mass are different for each climate, location and capacity in buildings having high cycle cost will be lower or less insulation building orientation. Building codes and thermal mass. can be used for equivalent performance. standards now provide for the benefits Studies have shown that concrete PCI Midwest Producer Member Contributor: of thermal mass. In increasing numbers, Jeff Holt (Wells Concrete) they are beginning to acknowledge buildings have lower heating and cooling the effect of the greater heat storage loads than lightweight buildings, thus life
WHO WE ARE PCI Midwest is a not-for-profit trade association that promotes precast/prestressed concrete, provides precast/ PCI MIDWEST Mike Johnsrud, PhD, PE • Executive Director prestressed concrete education, and facilitates relationships between its members and the construction and design communities. 612-760-6101 • [email protected] • www.pcimidwest.org