For this fundamentally new heating concept, a minimally invasive refurbishment system is combined with the low-exergy heating principle. Here, a surface heating system is applied to the outside of the facade during the refurbishment of the building. It is then clad with a thermal insulating layer so that even small temperature differences are enough to enable the building to be cooled or heated via the exterior wall.
In the research project, the practical applicability of the research findings from the previous LEXU I project is being investigated using a demonstration building.
The exterior wall tempering offers new solutions for low-exergy heating and cooling systems. The installation of such a system should always be seen in the context of optimising the energy of the "overall building system". Exterior wall tempering is therefore particularly suitable for the refurbishment of the existing building stock that is still required on a large scale. The demonstration building is an office building from the 1960s and '70s. During the course of necessary concrete repair measures, one of the building's facades was clad with the exterior wall tempering.
The waste heat flow can already be compensated through the exterior wall when the supply temperatures are just above the stagnation temperature of the wall at the heating level – and more than compensated when the supply temperatures are higher than the indoor temperature. The rooms are then heated.
For this purpose it is possible to use renewable heating or cooling energy from the ground, solar heat or waste heat. The exterior wall tempering between the existing exterior wall and the thermal insulation enables the building to be refurbished almost completely from the outside in heating terms. Impairments to the residents remain comparatively low.
Added to this are the comfort advantages of a surface heating system combined with the energy benefits of using renewable heat sources at a low temperature level and with a low exergy content. Optionally, the exterior wall tempering can be extended to provide external air heating, whereby the air gap between the surface heating system and the thermal insulation provides a supplementary, quickly controllable air heating system.
The aim of the demonstration project is to demonstrate the feasibility of the concept in a real building. In addition, the wall heating shall also be extensively investigated in terms of its functioning, application limits and time constants, etc. Furthermore, during the research project the potential exergy benefits of the exterior wall heating and cooling shall be enhanced by combining it with innovative system concepts. In the case of the demonstration object at Saarland University, the exterior wall heating is coupled with a heat pump, an ice storage system and PVT collectors.
In collaboration with Dürr Thermea GmbH, a prototype of a CO2 heat pump with a thermal output of 20 kW was initially developed and built. The prototype was intensively tested on a test rig in the experimental laboratory at IZES gGmbH in terms of its functionality and performance scope and limits. The prototype was then tested and measured using a realistic load profile for a simulated apartment building. The load profile was based on the use of the exterior wall tempering and external air heating. The results of the laboratory tests were deemed to be positive.
In a second work package, the exterior air heating concept was investigated by constructing a model wall as part of a laboratory experiment. In addition to practical measurements on the model wall in the laboratory, the exterior wall heating was also theoretically modelled and depicted in several simulation programs. The measured results compared very well with theoretically calculated results. In the demonstration building, a small area was also realised as an exterior air heating system in addition to the exterior wall tempering.
New products are not the main focus of the project. Instead, new application areas are being found for products on the market, for example surface heating. The CO2 heat pump developed by the project partner Dürr Thermea GmbH can be classed as a potentially new product that is unique in this performance class (20 kW).