NK4HTWP – Stiebel-Eltron

High temperature heat pumps with new generation of Low-GWP refrigerants for space heating and domestic hot water heating in multi-family houses

Funding code: 03ET1488 A/B

Funding period: 05/2017 until 04/2020

Project partner: Fraunhofer ISE, Stiebel Eltron


  • Demonstration heat pump is designed/built, operating with a new generation of refrigerant having low ozone and global warming potential and providing heating and DHW in multi-family houses
  • DHW heating that must supply a minimum hot water temperature of 60° at the tap (keyword: large-scale plant according to DVGW W 551)
  • Low noise emissions of the appliance since very likely to be installed in a densely-built area
  • High efficiency heating/hot water
  • High robustness of the appliance



Measurement of the refrigerant compressor

For the installation of heat pumps in existing multi-family houses, the required high flow temperatures – especially in compliance with the health standards for domestic hot water –   and the limited availability of adapted surrounding heat sources pose significant challenges.

Part of the heat pump development consists in the measurement of the refrigerant compressor for the energy assessment. This is combined with structural dynamical measuring technology for assessing mechanical loads and structure-bone sound.

Velocity field on the surface

The information collected on the velocity field on the surface is an important factor to evaluate the mechanical load resulting from the excitation by the compressor and the inducted currents.

Work plan

  • Target market identification and system analysis for MFH
  • Cooling circuit development of a heat pump for MFH
  • Implementation and vibration damping of the cooling circuit
  • System development with focus on domestic hot water (experimental)
  • Field study

On the basis of comprehensive tests carried out on its own as well as by Fraunhofer ISE, the company Stiebel Eltron generates the technical specifications and builds demonstrators. This involves all aspects of a new installation. The Fraunhofer Institute measures components for compression, heat extraction as well as the complete device both energetically and acoustically. It provides component models for the system simulation and also partly carries them out for optimising the building elements and processes.

Contact persons

Thore Oltersdorf
Fraunhofer ISE
Heidenhofstrasse  2
79114 Freiburg
+49 761 4588 5239

Dr.-Ing. Judith Möller
Stiebel Eltron GmbH
Dr.-Stiebel-Straße  33
37603 Holzminden
+49 5531 70296281


Poster NK4HTWP