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Kurztitel: LEXU II
Ausführende Stelle: IZES gGmbH
Förderinitiative: Energieoptimiertes Bauen (EnOB)
Laufzeit: 01/2012 bis 12/2019
Bewilligte Summe: 1.151.250 €
Förderkennzeichen: 0327370Y
Topics: Exergy optimisation, Heating, ventilation and cooling, Refurbishment of individual buildings
Innovation: Regulating the exterior wall temperature offers new solutions for low-exergy heating and cooling systems and minimally invasive building refurbishment.
Keywords:

Quintessence

  • For refurbishment purposes, a surface heating system is installed on the external face of the facade and then insulated
  • The system for minimally invasive refurbishment is combined with the low-exergy heating principle
  • Heat generation is provided renewably via hybrid solar collectors, a CO2 heat pump and an ice storage system
  • The concept is being tested on an office building constructed during the 1960s and 1970s

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.

Project context

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.

Research focus

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.

The capillary tube mats are applied as a surface heating system on the exterior of the facade. In the picture the adhesive mortar is being smoothed for the lightweight render. The exterior wall heating is particularly ideal for refurbishing buildings.

The capillary tube mats are applied as a surface heating system on the exterior of the facade. In the picture the adhesive mortar is being smoothed for the lightweight render. The exterior wall heating is particularly ideal for refurbishing buildings.

© IZES gGmbH
Facade of the demonstration building with exterior wall heating following its refurbishment in January 2016. During the course of necessary concrete repair measures, one of the building's facades was clad with the exterior wall tempering.

Facade of the demonstration building with exterior wall heating following its refurbishment in January 2016. During the course of necessary concrete repair measures, one of the building's facades was clad with the exterior wall tempering.

© IZES gGmbH
The demonstration building before refurbishment in the middle of 2015.

The demonstration building before refurbishment in the middle of 2015.

© IZES gGmbH
The capillary tube mats are applied as a surface heating system on the exterior of the facade.

The capillary tube mats are applied as a surface heating system on the exterior of the facade.

© IZES gGmbH
Plastering the capillary tube mats with adhesive mortar.

Plastering the capillary tube mats with adhesive mortar.

© IZES gGmbH
Installation of the 16 centimetre thick thermal insulation (WLG 032).

Installation of the 16 centimetre thick thermal insulation (WLG 032).

© IZES gGmbH

Successes

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.

Schematic structure of the exterior wall heating, consisting of the existing wall, capillary tube mats, adhesive mortar, thermal insulation and surface render.

Schematic structure of the exterior wall heating, consisting of the existing wall, capillary tube mats, adhesive mortar, thermal insulation and surface render.

© IZES gGmbH
Schematic of the low-exergy heating system that is intended to be installed in the demonstration building.

Schematic of the low-exergy heating system that is intended to be installed in the demonstration building.

© IZES gGmbH
Test stand for the CO² heat pump.

Test stand for the CO² heat pump.

© IZES gGmbH
The ice storage complets the low-exergy heating system.

The ice storage complets the low-exergy heating system.

© IZES gGmbH

Application

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).

Last Update: 18. April 2017

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