NK4HTWP – Stiebel-Eltron

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

Funding code03ET1488 A/B

Funding period: 05/2017 bis 04/2021

Project partners: Fraunhofer ISE, Stiebel Eltron


  • Demonstration heat pump is designed/constructed/erected, which is operated with a new generation of refrigerant with low ozone and greenhouse potential and is to provide heating and hot water in a multi-family house.
  • Water heating system that must be able to provide a minimum hot water temperature of 60°C at the tap in MFH (keyword: large-scale system according to DVGW W 551)
  • Low noise emissions from the unit, as installation in dense development is likely.
  • High heating/hot water efficiency
  • High robustness of the device


Measurement of the refrigerant compressor

For the use of heat pumps in existing multi-family dwellings (MFH), the required high flow temperatures – especially for compliance with hygiene regulations for domestic hot water preparation – as well as the limited availability of suitable ambient heat sources pose considerable challenges.

As part of the heat pump development, a measurement of the refrigerant compressor takes place for energetic evaluation. This is combined with structural dynamic measurement technology for the evaluation of mechanical loads as well as structure-borne noise.

Velocity field on the surface

The information obtained from the velocity field on the surface is an important parameter for assessing this mechanical stress, which occurs due to excitation by the compressor and induced by flows.

Work plan

  • Target market identification and system analysis for multi-family houses
  • Refrigeration circuit development of a heat pump for MFH
  • Commissioning and vibration damping of the refrigeration circuit
  • System development with focus on water heating (experimental)
  • Field investigation

The Stiebel Eltron company generates a specification and builds demonstrators through extensive own investigations as well as through investigations by Fraunhofer ISE. This covers all aspects of a new plant. Fraunhofer ISE measures components for compression, heat extraction as well as the entire unit both energetically and acoustically. It provides partial models for the system simulation and also partially carries these out itself to optimize components 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