Innovative solar air heating and cooling system to reduce carbon dioxide emissions for the air conditioning of residential buildings

Development of an innovative solar air heating and cooling system for the air conditioning of residential buildings, resulting in at least 50 % reduction of carbon dioxide emissions compared to the current technology


Brief description

In the SolSpaces-E cooperation project, an air-based building heating and cooling system shall be developed. This system shall allow a reduction of carbon dioxide emissions by 50 % related to currently available air heating systems as well as building cooling with low carbon dioxide emissions. The reduction of carbon dioxide emissions from the building energy sector is an essential element [1] to achieve the climate protection targets of the German Federal Government and to further develop the transition to alternative energies. The Climate Change Act, adopted by the German Federal Government in 2019, includes the explicit objective of a further 40 % drop in carbon dioxide emissions in the building sector by 2030. A development objective in the residential and non-residential building sector is to pursue a drastic decrease in heat demand via efficiency measures.

In the SolSpaces-E project, this objective shall be achieved by a coordinated package of measures with a focus on:

  • High solar thermal contribution to heat supply by highly efficient solar air collectors and – to be newly developed – solids storage with airflow for solar thermal air heating
  • Optimization of ventilation effectiveness with specific analyses of indoor air ratios, combined with a novel approach of humidity recovery, for an efficient and energy-optimized residential air conditioning
  • Further development of the Schwörer air heating system to integrate solar energy sources and adaptation of the air/air-heat pump regarding an optimal use of photovoltaic power via an adapative system control (use of own electricity)
  • Prevention from overheating of buildings in summer with a combination of active and passive measures, consisting of a new concept of solar-sorptive cooling of buildings [2] and additional innovative sun protection measures

In Figure 1, the air heating and cooling system for the air conditioning of residential buildings is shown, resulting from these four measures.

The field of residential air conditioning with humidity recovery addresses the supply air ductwork for rooms and a heat exchanger with a membrane permeable to water vapor for the recovery of heat and humidity. The field of solar thermal energy addresses the integration of highly efficient solar air collectors and a new innovative solids storage. The field of heat pumps addresses air/air-heat pump, photovoltaic modules and battery storage as well as their control in the overall system. For the field of sorptive cooling, the system is completed by a sorbent bed, a heat exchanger (HX) and a humidifier (nebulizer) as well as additional passive measures to avoid the overheating of rooms.

Figure 1: Setup
Figure 1: setup of the solar air heating and cooling system for the air conditioning of residential buildings with a focus on four key areas: residential air conditioning with humidity recovery, solar thermal energy, heat pump, and sorptive cooling

An essential advantage of the air heating technology is the simplicity of the entire system technology as well as the very low installation costs since the cost drivers of conventional, water-based heating systems are eliminated. Neither radiators with complex pipework nor gas supply nor a chimney are required. The heat is transferred to the room direct via warm air which is distributed in the room as efficiently as possible by the HVAC system. The described air heating system responds quickly to load changes and therefore offers optimal conditions for the integration in intelligent cross-system control algorithms.

The main shortcoming of the technology is the fact that an air-based heating system provides relatively low heating power to a building. In the literature, there are references of approx. 10 W per sqm heated living space [3]. In a passive house, this is sufficient in normal yearly operation; in buildings with higher heat demand, the heating load cannot be fully covered at very low ambient temperatures. For these periods of time, the heating load is covered by electric afterheating in most cases. From an energetic point of view, the current electric energy expenditure of an air heating system is too high and not compatible with the requirements mentioned above.

Therefore, the objective of the project is to increase the performance capability of the technology, to develop its usability for more types of buildings, and to considerably reduce the electric energy expenditure at the same time. These four measures are the basis for a targeted technology development in the overall context of the air-based climate control of buildings. They are connected to each other and optimally complementary and thus enable the pursued 50 % decrease in carbon dioxide emissions.


[1] Key points for the Climate Action Programme 2030, German Federal Government

[2] In the SolSpaces project (grant number 0325984A), the current SchwörerHaus air heating system was investigated by measurements. The findings serve as a reference for the quantitative evaluation of the carbon dioxide reduction.

[3] Greml, Andreas; et al. Komfortlüftungsinfo Nr. 28, Luftheizung im Passivhaus, 2014


Project duration

09/2021 - 08/2024


Project partners

University of Stuttgart
Institute for Building Energetics, Thermotechnology and Energy Storage (IGTE)
Pfaffenwaldring 6, 70569 Stuttgart, Germany

Project partner:
SchwörerHaus KG
Hans-Schwörer Str. 8, 72531 Hohenstein-Oberstetten, Germany

Project partner:
airwasol GmbH & Co. KG
In der Kühweid 17, 76661 Philippsburg, Germany

Associated project partner:
Fröschenweidstrasse 12, 8404 Winterthur, Switzerland



The SolSpaces-E project is funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK), based on a decision of the German Bundestag, via Project Management Jülich (PtJ) under grant number 03EN6008A. The authors would like to sincerely thank for their support and take responsibility for this publication.


This image shows Dr.-Ing. Henner Kerskes

Dr.-Ing. Henner Kerskes


Team Lead

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