Fundamentals, Designs and Applications
Huiming Yin Department of Civil Engineering and Engineering Mechanics, Columbia University, NY, United States
Mehdi Zadshir Department of Civil Engineering and Engineering Mechanics, Columbia University, NY, United States
Frank Pao Sustainable Product Development Lab, NY, United States
Building Integrated Photovoltaic Thermal Systems: Fundamentals, Designs, and Applications presents various applications, system designs, manufacturing, and installation techniques surrounding how to build integrated photovoltaics. This book provides a comprehensive understanding of all system components, long-term performance and testing, and the commercialization of building integrated photovoltaic thermal (BIPVT) systems. By addressing potential obstacles with current photovoltaic (PV) systems, such as efficiency bottlenecks and product heat harvesting, the authors not only cover the fundamentals and design philosophy of the BIPVT technology, but also introduce a hybrid system for building integrated thermal electric roofing. Topics covered in Building Integrated Photovoltaic Thermal Systems are useful for scientists and engineers in the fields of photovoltaics, electrical and civil engineering, materials science, sustainable energy harvesting, solar energy, and renewable energy production.
Novel Concrete Wall Panels Lower a Building’s Energy Footprint
About 20% of total energy con- sumption in the U.S. comes from the heating and cooling of buildings using conventional sources like fossil fuels. While standard thermal insula- tion, with its low thermal conductiv- ity, can help mitigate heating/cooling loss, researchers have sought to incorporate thermal storage capacity within the building envelope to better control the temperature variations across building walls.
Previous attempts to do so have relied on mixing a phase-change material (PCM) like petroleum wax into the cement paste. The wax would absorb heat during a hot period and release stored heat during a cold period, thereby significantly reducing the temperature variation inside the building. Unfortunately, this approach has not succeeded in becoming a com- mercial reality due to technical and commercial challenges.
A new method developed by scientists at the Center for Energy Harvesting Materials and Systems (CEHMS) at Columbia Univ., part of the National Science Foundation’s Industry-University Cooperative Research Centers program, promises to overcome these challenges.
The CEHMS team used a multi- scale modeling method to guide the design and manufacture of PCM wall panels. The end result was a light- weight wall panel that has a relatively uniform microporous structure — with up to 75% porosity — that retains adequate structural strength to meet the required building codes for non- structural use.
The team developed an optimal mixing process that involves the application of pressure and foaming surfactants, which generates micro- sized air bubbles in the cement paste. By modulating the process conditions, they can control the microstructure and porosity of the concrete. Typi- cally, it is very difficult to control the generation of uniform microstructure and porosity in concrete; a standard concrete has only 7% porosity. Using their novel process, the researchers have created materials that have as high as 83% porosity.
Next, they embedded polymer fibers and metal mesh into the cement for reinforcement. After a curing process within a mold, the micropores are filled with PCM by a vacuum infusion process. The PCM-filled capillary pores provide thermal energy
p (a) A novel wall panel consists of foamed concrete with a (b) micropore structure filled with a phase change material (PCM). The PCM can absorb heat during warm periods and release heat during cold periods, helping to regulate a building’s temperature. (c) A higher porosity corresponds to less temperature fluctuation.
storage while the polymer fibers in the composite provide adequate strength (3.3 MPa) to support the workload in service and installation.
The phase-change wall panel can suppress room temperature fluctua- tions to a minimum, and significantly reduce energy needed to heat and
cool a room. Lab tests and numeri-
cal simulations demonstrate that a 1-in.-thick wall panel with 70% PCM embedment could shrink the electricity demand of a 1,000 ft2 home by ~50% in the summer months of the U.S. Northeast. Larger-scale applications could improve energy efficiency of buildings even more and reduce their heating/cooling-related carbon foot- print. The novel foam concrete exhib- its better thermal and acoustic proper- ties than standard thermal insulation, as well as good mechanical properties. Such wall panels could represent a sustainable and energy-efficient way to combat climate change. In additionto its use as an energy-efficient wall panel, the novel concrete could also
be used in building-integrated photo- voltaic thermal roof panels.
The organization is now looking
to create customized wall panels for specific climates that would contain several PCMs with tuned melt-
ing temperatures. “This technology could be a game-changer, bringing deep energy savings with affordable price to the energy-efficient buildingenvelope market,” says Orin Herskow- itz, Columbia Technology Ventures Director. Columbia Univ. is working with a startup to license and further drive commercial development of this technology. CEP
This technology was funded through the NSF Industry-University Cooperative Research Centers Program.
This article was prepared by the National Science Foundation in partnership with CEP.