Materials engineering

An economic curtain

Plastic film developed within the Unicamp incubator blocks solar rays and reduces energy consumption

A curtain capable of blocking up to 94% of solar radiation upon a building totally encased in glass, demonstrates that it is possible to reduce expenses with the electrical energy used in air conditioners by up to 60% during the summer. This evaluation is the result of simulation tests carried out by the Technological Research Institute (IPT) with the new product developed by VacuoFlex, a company installed in the Technologically Based Company Incubator of the State University of Campinas (Unicamp). The company’s innovation was to apply a metallic plastic film upon a curtain, manufactured from plastic sheeting or cloth. “The cost of the industrial application of our product on curtains is paid for through the economy obtained over three summer months”, says the civil engineer Antônio Sérgio Assunção Tavares, a company partner and director.

In order to produce the metallic film, the technology known as Radiant Energy Control Films (RCF) was made use of, which is a technology developed in the decade of the 1960’s by NASA, the North American Space Agency, for the thermal control of satellites and of the clothes worn by astronauts. Based on the use of plastic films with a deposit of aluminum to reflect the incident heat and to impede its emission into the environment, the technology, after having been locked way for two decades, became public domain at the start of the decade of the 1990’s.

The simple deposition of aluminum does not confer durability to the products destined for terrestrial use, which are exposed to humidity and abrasion. In order to guarantee that they are durable, it is necessary to carry out vacuum deposition making use of the process of cathodic spraying (sputtering) – a physical method of metal coating that makes use of ionized argon gas -, used in Europe and the United States in some rigid products, such as car rear mirrors and the lenses of sunglasses with anti-reflex and anti-misting properties. Here in Brazil its use is still restricted to research laboratories. And it was the Fine Films Laboratory of the Gleb Wataghin Physics Institute, of Unicamp, which suggested the technological solution for the manufacture of flexible plastic films with the properties of reflection and emission of radiation, which, in accordance with the application, can either be metalized and therefore opaque or transparent.

Since 1979, when the physicist and partner at VacuoFlex, Carlos Salles Lambert entered Unicamp to begin his scientific career, has been studying the technology of the deposition under high vacuum via cathodic spraying, which is the technique for the production of a metalized plastic film This study was essential in order to transfer the initial idea of professor Tavares into producing a curtain that would block solar radiation into a product with various applications.

Thermal insulator
The RCF developed by VacuoFlex has incorporated the advances in the deposition of fine films to the original concept of thermo reflective insulation. And this has already resulted in a licensing contract, signed in April with the Rentank Group, with their headquarters in Taboão da Serra, Greater Sao Paulo, the leader in the segment of cloth tents, which also works in the area of transport and storage of chemical products and in the agronomy business sector. The company is making an initial investment to the order of R$ 500,000 for the application of a thermal insulator on the polyvinyl cloth used for large scale tents used in aviaries and by companies in the food, steel making, logistics operations and events sectors, both for short and long periods of time.

The efficiency of the RCF film was tested by the IPT in cloth covered storage sheds, verifying a reduction of internal temperature of up to 7.5°C. In this manner, there would be a significant lowering in energy consumption used for the acclimatization of the environment and in the losses of products in the food sector, for example. The plastic clothing with the insulating film is also being tested to cover open trucks that transport beverages and horticultural, fruit and grain products. “With the application of the insulator on the cloth, the part of the heat radiated into the cargo is practically eliminated, significantly reducing the loses that occur during the transport of products”, says Tavares. As well as the curtains and cloth for large sheds, the plastic film that controls the solar or thermal radiations can be used in roofing, refrigerated trucks, agricultural greenhouses and helmets.

Obtaining the different properties depends on the quantity and on the materials used. Nanoparticles of metals, oxides and other materials are deposited under vacuum on a plastic film, in layers with a thickness that varies between 5 and 70 nanometers – the unit that corresponds to 1 millimeter divided by 1 million. In order to manage to produce films in rolls, one of the company’s machines installed in Campinas was adapted to work on the process of cathodic spraying under high vacuum. “In this process the atoms or molecules penetrate into the substrate of the plastic film due to the synergic energy of the particles, by a physical and not chemical process”, says Lambert. In this manner it is possible to form a union of materials that via traditional processes would not join together.

The thermal reflector curtain, destined to bar solar radiation, was the first product developed by VacuoFlex within the Small Business Innovation Research (PIPE) program, funded by FAPESP. In order to evaluate the curtain’s efficiency with the RCF film, an entire floor of a recently constructed building was chosen, all glass encased, located in the southern zone of the city of Sao Paulo. “The test carried out by the IPT showed that the curtains managed to bar incident solar radiation much more than any other known alternative”, says Tavares. “Initially we worked on the determination of the emissive level of the film, a property that measures the quantity of heat that is irradiated by a product”, advised Fúlvio Vittorino, from the Environmental Comfort Laboratory of IPT. In the case of the curtain, the lower this index, the lesser the heat being transferred into the building.

Brazilian conditions
During the tests measurements of the air temperature and solar incident radiation were taken. “The data was passed to a software program that makes this type of analysis”, says Vittorino. He was referring to the latest version of the Energy Plus program, from the Department of Energy, in the United States, used to simulate the consumption of energy in buildings. The process of validation of the software, necessary in order to verify if it can be applied to Brazilian climatic conditions, was carried out by the IPT over a two-year period with financing from the Financier of Studies and Projects (Finep).

The evaluation performance tests have as their objective the determination of how much a product, applied under real conditions, is going to improve the thermal comfort of people and reduce the electrical energy consumed by air conditioners. The next step in the research will be to extend the measurements to other Brazilian regions, in order to verify how the metalized curtain behaves under other climatic conditions. “Principally in the Northeast where there is a lot of heat and there is an intensive use of air conditioners”, says Vittorino. The cotton curtain with the metalized film could be used in meeting rooms and in hotel rooms, placed between the windowpanes and any decorative curtains. Another version, which is under study for use in offices and homes, will have translucent bands that will at least allow for the passage of a minimum quantity of light, with a small loss in the energy saving.

As well as the thermal reflector curtain and the covering for portable sheds, other uses are under test. A segment that also could well be counted upon to use this new product is poultry raising. In the hottest regions of the country, in the chicken feeding sheds thermal roofing is used that is manufactured with two sheets of steel interspaced with expanded polystyrene foam. This roofing, which costs around R$ 60,00 a square meter, brings about a lowering of temperature, and an increase in productivity, and a reduction in the mortality rate of the birds to less than one quarter.

Field tests carried out at the Civil Engineering School of Unicamp in December of 2004 compared the performance of the metallic roofing with a RCF application on the inside of the roofing with other two types of roofing, namely the simple metallic, without thermal insulation, and the thermal, made with two steel sheets and filled with 50 millimeters of polyurethane foam, all of them placed in sheds of identical dimensions. “We saw that the roofing with the RCF had a performance even a little better than that of the polyurethane foam, without taking into account that the price fell by half”, says Tavares. The cost reduction in the application of the thermal insulator has awakened the interest of a thermal roofing manufacturer, the supplier of a project that forecasts the construction of more than 1 million square meters (m²) of sheds for poultry farming in Central Brazil. Field tests are being done to evaluate the feasibility of using the product in the aviaries of the common chicken.

Optical filter
It was the perception of the various possible technological applications, in distinct sectors, that served to stimulate Tavares and Lambert to set up the VacuoFlex company. And all of the alternatives studied up until now have shown themselves to be promising, such as that of producing a transparent plastic for agricultural greenhouses. In this case the product functions as an optical filter, which impedes the entrance of solar infrared radiation, lowering the internal temperature, and at the same time allowing for the passage of light. Preliminary tests carried out with a film indicate 30% more light and 30% less heat in relation to the dark shading plastic used for example in Holambra, the town that produces plants and flowers located close to the city of Campinas.

“The chemical industry has been researching for decades, by way of the use of an additive, for a cold plastic that would allow the necessary light for photosynthesis to pass through, but would block solar infrared radiation”, says Tavares. “But the results obtained up until now by way of chemical means have been modest.” In countries with hot climates, such as Brazil, the increase in temperature in agricultural greenhouses lowers the productivity of the plant being cultivated. So that this does not occur, evaporation cooling systems are made use of, which consume electrical energy, as well as plastic coverings as shading cloaks, in order to reduce the temperature. But this system also reduces illumination and retards the plant’s growth.

Since in Brazil equipment for carrying out the deposition under vacuum by way of cathodic spraying on plastic films does not exist,  Lambert is adapting a machine to work exclusively with this technology, since the imported model costs around US$ 2 million. For now, the partners’ idea is to supply the treated plastic films for the companies that have licensed the products developed by VacuoFlex. In the future they could well manufacture the machines, via orders, from the licensed companies.

The Project
Optimization of the thermal performance of a thermal reflector curtain, looking towards a reduction in energy consumption in thermal conditioning (nº 01/13310-0); Modality Small Business Innovation Research (PIPE) Program; Coordinator Antônio Sérgio Assunção Tavares – VacuoFlex; Investment R$ 74,900.00 (FAPESP)