Buzzwords and articles abound regarding indoor air quality, thermal barriers and "air-tight" structures – and yet, designers all too often ignore the opportunities presented by the building envelope to provide the ultimate energy-efficient solution.
Although smart lighting and HVAC units can be key opportunities, selecting the building envelope and the construction method are critical factors for constructing an energy-efficient structure. One building method with a proven track-record in providing owners with energy efficient solutions is site cast tilt-up construction. The combination of the thermal mass properties of concrete, reduced air-infiltration and more energy-efficient insulation systems allow tilt-up construction to be a growing solution in meeting the needs of today's owners.
Understanding thermal performance
The selection of building materials, equipment and energy management systems – all early design considerations – make a difference in the long-term performance of a building, which is why tilt-up is a smart solution. "Performance" of the exterior concrete walls should be recognized as a key element of success for tilt-up as an efficient insulating option. Concrete that is located adjacent to controlled interior spaces dampens the temperature swing that is normally experienced as daily temperatures rise and fall. This dampening effect can result in substantial energy savings due to reduced HVAC capacity. Essentially, the mechanical systems do not have to work as hard to control the temperature. The same quantity of energy may need to be removed or added, but it is done over a longer period of time.
Thermal mass reduces temperature swings by storing the incoming heat energy from the warming climate during the build-up phase, rather than requiring the building's HVAC systems to fully handle it. The stored energy is then released over a longer duration during cooler periods or removed by lower equipment tonnage during off-peak hours. Although this "thermal mass effect" is more pronounced in climate regions with larger differences between daytime and nighttime temperature or where cooling is dominant to the building operation, the same effect can have a strong impact in colder climates that rely on heating as much as or more than cooling. In these regions, the mass is conditioned to a target temperature and remains as a buffer to slow the affects of chilling temperatures on the building interior as well as more rapidly controlling sudden temperature changes in combination with the HVAC systems. For a facility with overhead doors, this effect is beneficial since the air infiltration that occurs every time a door is opened is balanced by the stored energy in the concrete mass. In contrast, a lightweight metal building has no such heat capacity and therefore cannot dampen the thermal cycle.
Thermal mass is certainly not a new concept to building technology. Without looking at historical precedents, the concept has been incorporated into the Model Energy Code alone for more than a decade and a half. Proven through a combination of testing and computer modeling, the thermal mass effect is leading energy consultants today to recognize the advantages that can be gained from tilt-up panels. In cases where insulation is added to tilt-up properly, as much as two to three times greater performance or impact to the building envelope can be achieved over the stated material R-value.
Mitigating air infiltration