Development of efficient heating systems
From the Tritherm house to the Energy Plus house
Today, resource conservation and emissions reduction are central to the development of modern heating technology. At Bosch, however, the search for energy-efficient solutions began decades ago. A research project in Wernau demonstrated back in the 1970s how to combine different energy sources.
A single-family home as a research facility
In 1976, an unusual single-family home appeared on the factory premises of Junkers, then a division of Bosch, in the city of Wernau, near Stuttgart. The Tritherm house served as a test bed for the heating technology of the future. Starting in 1977, it helped researchers investigate how to provide heating and hot water in ways that used energy as efficiently as possible and conserved resources.
This happened against the backdrop of the 1970s energy crisis; the first oil crisis in 1973 had dispelled any remaining doubts that fossil fuel supplies are finite. That put heating systems more firmly in researchers’ sights. It also stimulated interest in the use of solar energy. However, the use of solar heat alone has one major drawback: of course it’s in winter, when heat is needed the most, that sunlight is at its weakest. Storing large amounts of heat over long periods of time was also technically and commercially challenging.
Three sources of heat for one house
With this in mind, Junkers opted to combine various technologies. The Tritherm house’s south-facing roof, which had a slope of about 60 degrees, was fitted with 25 solar collectors with a total surface area of about 40 square meters. These converted solar energy into heat. A major feature of the concept was the additional heat pump, which made use of the heat in the ambient air. If, on particularly cold days, neither of these energy sources would suffice, a gas heating system took over.
The name “Tritherm” was derived from these three heat sources — the sun, the ambient air, and supplemental heating. The concept was based on the simple idea that the collectors and heat pump didn’t need to be sized large enough to meet the maximum heat demand on the coldest days, since the supplemental heating would kick in during those few peak-load periods. This meant the system could be designed to be smaller and more cost-effective.
Trying out technology
The Tritherm house was much more than a demonstration of existing technology. It allowed components to be combined with one another and tested under various operating conditions. A total of 14 operating modes could be selected automatically or manually. The house’s control system constantly determined which type of heat generation was the most economical for the demand at that moment. Its heat pump, heat storage tank, hot-water tank, and control and measurement equipment were located in the basement. In addition, the researchers investigated how to recover heat from household wastewater and how to then reuse that water — for instance, for toilet flushing.
In March 1977, the Tritherm house concept debuted at the ISH trade show; it was subsequently presented to the general public in May. One unique feature of the house was that it let tradespeople test various components and operating modes. A research report published in 1979 highlighted the concept’s results, concluding that, under the then prevailing climatic conditions, it could reduce fuel consumption to less than 10 percent of previous levels. However, the project’s limitations also became clear, since the necessary investments were still too high to allow widespread adoption at that time.
From a research project to the Energy Plus house
For Bosch, the question of how to use energy as efficiently as possible in buildings remains a priority. More than three decades after the Tritherm house was built, the focus was no longer solely on combining different heat sources. Now, the goal was to take a holistic view of a building’s energy needs — and, if possible, to generate more energy than the house itself requires. In 2010, Bosch’s then Thermotechnology division presented the Energy Plus house concept. Among other things, this showcased a solar thermal system, condensing boiler technology, a heat pump, combined heat and power, a controlled domestic ventilation system, energy-efficient home appliances, and photovoltaics.
In 2011, a single-family home was built in Wetzlar as part of a joint project between Bosch’s Buderus brand and a specialist in prefabricated homes. Unlike the Tritherm house, this house wasn’t purely a research project: people actually live in it. A comprehensive energy concept was implemented for some 160 square meters of living space. A Buderus electric heat pump provides the heating, while a controlled domestic ventilation system recovers up to 91 percent of the heat. The building is equipped with photovoltaic modules covering an area of 75 square meters. Bosch also provided the home appliances, which met the A++ energy efficiency standard of that time. The aim was for the house to generate more energy over the course of a year than its residents needed.
The idea that was put to the test under research conditions in the Tritherm house more than 50 years ago is now a key component of modern heating systems, which combine various energy sources and technologies to optimize energy use in heat supply. Bosch can draw on decades of experience and early research in the field of heat pumps. Today, the electricity required to operate a pump can, for example, be generated using solar panels on the roof of a house. Bosch’s approach combines the use of ambient heat, high-performance systems technology, and smart connectivity to optimize energy consumption and ensure cost-effectiveness.
Author: Carmen Senger
