HEAVEN – Viessmann

Modulating brine heat pump with multi-source system and decentralized ventilation systems

Funding code: 03ET1540 A/B

Duration: 01/2018 until 10/2022

Project partners: Fraunhofer ISE, Viessmann Wärmepumpen GmbH


  • Development of a functional model of a performance modulating brine heat pump for the addressed performance range as well as of dimensioning and operating strategies for a multi-source system for the integration of the ground and outdoor air
  • Optimization of the apartment- and room-by-room control of decentralized ventilation units as well as the development of an evaluation method and a test rig for the combined consideration of energy performance and ventilation effectiveness
  • Development of a functional model for an energy-efficient and low-noise decentralized ventilation unit with coaxial heat exchanger


Due to the small usable ambient area in inner-city areas, the trend is towards the heat source outside air, which is comparatively inefficient and subject to TA Lärm regulations. In WP1 the advantages of the two heat sources outside air and ground shall be utilized and furthermore a performance modulating brine heat pump in the addressed performance range shall be developed.

Decentralized ventilation of living spaces can play a key role in the refurbishment of residential buildings (e.g. no ductwork) and a demand-driven control promises considerable energy saving potentials. In WP2, therefore, the control of decentralized ventilation devices will be optimized and a suitable method for evaluating these devices will be developed. In addition, the requirements for decentralized ventilation units, such as compactness, heat recovery and noise emission, are constantly increasing. In AP3, these requirements will be addressed by using a coaxial heat exchanger.

Top left: Schematic design of the heat pump heating system with combined heat source (WP1); top right: Design of a test chamber setup for the combined evaluation of decentralized ventilation devices (WP2); bottom: Cross-sections explaining the planned geometry of the coaxial heat exchanger and photo of a 3-pressure (AP3).

Work plan

  • Modulating brine heat pump and combined heat sources
  • Optimization and evaluation of residential ventilation
  • Decentralized ventilation unit with coaxial heat exchanger and energy efficient axial fans.

The tasks in the project range from conceptual work, experimental evaluation and simulation of components and systems to the development of evaluation methods and the demonstration (WP1 and WP2) of the new development in the field.


Danny Günther
Fraunhofer-Institute for Solar Energy Systems ISE
Abteilung Energieeffiziente Gebäude
+49 (0)761/ 4588-5371

Steffen Obermann
Viessmann Werke Allendorf GmbH
Advance Engineering  and Control Strategy Development
+49 (0)15174656783