HEAVEN – Viessmann

Modulating brine heat pump with multi-source system and decentralised ventilation units

Funding code: 03ET1540 A/B

Funding period: 01/2018 until 12/2020

Project partners: Fraunhofer ISE, Viessmann Wärmepumpen GmbH



  • Development of a functional model of a modulation brine heat pump for the addressed performance range as well as dimensioning and operating strategies for a multi-source system integrating ground and outside air
  • Optimisation of the apartment and room regulations of decentralised ventilation units as well as the development of an evaluation method and of a test stand for the combined examination of energetic performance and ventilation efficiency
  • Development of a functional model for an energy-efficient and low-noise decentralised ventilation unit with coaxial heat exchangers



Because of the small usable surrounding surface in urban areas the trend is towards outside air as a heat source, which is comparatively inefficient and subject to the requirements of TA Lärm. In work package 1 the advantages of both sources outside air and ground should be exploited and a modulation brine heat pump should be developed in the addressed performance range.

The decentralised domestic ventilation can play a key role in the energetic renovation of multi-family houses (a.o. no pipe network) and a demand-driven control offers considerable energy-saving potential. In work package 2 the control of decentralised ventilation units is therefore optimised and an adapted method for assessing these units is developed. Moreover, the requirements on ventilation units, such as compactness, heat recovery and noise generation, are continuously increasing and should be met by means of a coaxial heat exchanger in work package 3.


Top left: Schematic structure of the heat pump heating unit (work package 1); top right: draft test chamber design for the combined evaluation of decentralised ventilation units (work package 2); below: cross-section illustrating the planed geometry of the coaxial heat exchanger and picture of a 3D-printing (work package 3)

Work plan

  • Modulating brine heat pump and combined heat sources
  • Optimisation and assessment of domestic ventilation
  • Decentralised ventilation unit with coaxial heat exchanger and energy-efficient axial fans

The tasks of the project range from the conception work to the experimental assessment and simulation of components and systems to the development of assessing methods and the demonstration (work package 1 and 2) of the new development in the field.

Contact persons

Danny Günther
Fraunhofer Institute for Solar Energy Systems ISE
Department Energy-efficient buildings
+49 (0)761/ 4588-5371

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