Thermal Efficiency Saves Money

Thermal Efficiency of CarbonCast®
The U.S. Department of Energy estimates that 42 percent of energy consumed in a building is ultimately lost through the building envelope, or the barrier between the building interior and outdoor environment. A significant portion of any commercial envelope is the exterior wall.

The building envelope is critical in regulating internal building temperatures and determining how much energy is required to heat or cool a structure for occupant comfort. Heat transfer through envelope components such as walls wastes energy. Thermally efficient exterior wall systems aim to mitigate heat transfer and energy loss. They are engineered to minimize the opportunities for heat to flow from the interior surface through the wall to the building’s exterior.

The role of wythe connectors
In insulated precast concrete wall panels, wythe connectors act as a mechanical connection between the inner and outer layers of concrete. Because they form a connection through the insulation, there is an opportunity for thermal bridging to occur as well. Traditional wythe connection options such as solid zones of concrete or metal connectors – while providing a reliable mechanical connection – permit heat transfer between the wall because of the materials’ inherent conductivity.

What is important is designing a performance specification on the overall wall system rather than just the connector alone. A specification based on the overall wall system is one of the best ways of ensuring that the enclosure will meet the owner’s standards.

The role of insulation
Insulation helps to prevent the flow of heat across the exterior envelope. The use of continuous insulation further stems the flow by eliminating the presence of building materials that could facilitate thermal transfer.

Continuous insulation is defined in ASHRAE 90.1 as “insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior or exterior or is integral to any opaque surface of the building envelope.”

The thermal performance of edge-to-edge insulated precast sandwich wall panels with no or minimal thermal bridges and no solid zones maintains the R-values for continuous insulation as defined in ASHRAE 90.1, thereby lowering energy costs for the owner and occupant.

~ Courtesy of AltusGroup

Design Assist Impacts Project Delivery

In recent years, a trend toward early integration of the design/build process has developed into what is now called design assist.

In this process, the precast concrete producer is selected based on qualifications for executing the demands of the specific project, PCI Certification, and the capability for technical expertise to assist the design and construction team in the development of the project. A contract is then awarded and should, at a minimum, include compensation for the design assistance. Significant benefits can be achieved if the contract also includes the supply and installation of the final products.

Benefits of design assist include development of concrete mixtures and finishes during the development process rather than going through a sample approval process after bid and award. Requests for information are eliminated with the precast supplier as a participating member of the design team. Precast erection drawings are prepared as design development nears completion, leading to a much smoother shop drawing review process. The structural design of the precast panel connections are completed in collaboration with the Engineer of Record to assure coordination with the design of the supporting and bracing structural system. The construction schedule is coordinated with the precast production schedule to assure timely delivery and installation. Any activity that normally occurs after award in a typical bid/build arrangement would be coordinated much earlier when the total precast contract is executed shortly after the design and construction team is assembled.

Precasters can offer detailed expertise that allows for expedited development of the design with engineering innovations and scheduling improvements while enhancing aesthetics and controlling budgets from conceptual design to project completion. Each element can be made as cost-effective as possible, taking advantage of the inherent performance characteristics of precast concrete. The precaster will be able to contribute design and detailing suggestions to ensure that maximum efficiency is achieved at the lowest erected cost. The result should be a functionally efficient and aesthetically pleasing enclosure that meets or exceeds the expectations for the project. Finally, the precaster should be considered as a partner on the design team. This will impose a responsibility on the precaster to understand related construction materials that must interface with the precast concrete so details appropriate to all the materials can be developed.

- Information courtesy of PCI