Twin research in building physics

Research in focus April 2014

Monozygotic twins have an almost identical genetic makeup and look physically the same. Research on the topic normally focuses on the fields of human genetics and psychology. Since 1980, however, twin research has also been a part of the work of the Fraunhofer Institute of Building Physics IBP – though the results obtained are admittedly of considerably more interest to the building industry than to biologists. The outdoor testing site in Holzkirchen features two typically-sized single-family homes that have been built to an identical design – the “twin houses”. This set-up gives researchers at Fraunhofer IBP the opportunity to perform comparative measurements of different building, insulation and heating systems in situ under identical climatic conditions. Both houses are detached and face in the same direction. This test facility is particularly useful for researchers from the Energy Efficiency and Indoor Climate department.

“Since they were first mounted the buildings have been periodically updated to meet the latest energy efficiency standards,” explains Dr Ingo Heusler, a researcher from the Evaluation and Demonstration working group. “The way the houses are built means we can completely replace the external components relatively easily. As a result the houses can be tailored to the requirements of each particular experiment.” Fraunhofer IBP generally collaborates with industry partners to define test scenarios for the experimental house and the comparison house (reference house). These test scenarios are then used to further develop or optimize novel components or systems or to compare them with reference technologies. The building services of the twin houses currently comprise a gas condensing boiler, radiator and underfloor heating, and a ventilation and cooling system. The ground floor consists of a kitchen, bathroom/WC, a living room and corridor as well as two bedrooms. The floor area is 10 x 10 meters in both cases.
In summer 2013, for example, Heusler and his colleagues carried out in situ measurements for a project run by the International Energy Agency (IEA). The IEA was founded in the 1970s to facilitate energy cooperation among member countries. Its goal is to promote research and development and the roll-out and application of energy technologies.
A reliable description and prediction of a building’s energy performance characteristics is a fundamental prerequisite for finding ways to reduce its energy consumption. Efforts to quantify real building behavior investigate existing computer models and integrate new, innovative solutions for near zero-energy buildings that can make effective progress only with the help of in situ experiments and dynamic methods of data analysis. As part of a sub-project entitled IEA EBC Annex 58, which was scheduled to run from 2012 through 2015, scientists had worked on a number of goals including validating and had optimized the simulation software used to calculate energy consumption in buildings. As part of the project, Fraunhofer researchers measured the energy performance of both buildings under real conditions over a period of some two months, recording the energy consumption and temperature values with the south-facing blinds open in one of the houses and closed in the other. “Previously, the standard way of obtaining the thermal energy performance of a reference building for software validations was to use simulation calculations of individual rooms. For the first time, our twin houses enabled the building to be viewed as a single construct,” says Heusler. Fraunhofer IBP has now made its guarantee of suitable test environments and analysis methods into one of its core competencies, comprising the provision of real buildings, the required sensor precision and the correct installation of the sensor technology as well as its very own data collection and evaluation software program IMEDASTM (only German). In parallel to the in situ measurements, suppliers and users of simulation software (about 20 participating teams from various countries) had carried out their own calculations using the same parameters. The results obtained in workshops and seminars from the comparison of the calculated data with the real-life site measurements and the resulting optimized simulation models are summarized in the final report published by the IEA.
And that’s not all the twin houses have to offer. “Since we inaugurated the twin houses we’ve worked on numerous industrial contracts as well as a wide range of national and international research projects,” says Heusler. The test facility can be used to study many areas, including demand-driven ventilation systems both with and without heat recovery components, wall, window and roof systems, and different types of heating systems, components and control concepts, as well as radiator and underfloor hot water heating systems. The facility is equally suitable for the study of energy-saving house designs, particularly the passive use of solar energy, different orientations of glassed-in porches and transparent thermal insulation systems. Fraunhofer IBP also uses its twin house site in research projects to conduct comparative studies of roof constructions and the thermal and energy performance of sloped roof designs equipped with IR reflective insulation materials or mineral wool insulation. Customers include manufacturers that wish to test their products before launching them on the market. The test houses offer the perfect opportunity to try out the new products under real-life conditions and to compare them with other products that are already commercially available.

More Information

Home Research in Focus

All contributions at a glance