WISE - Extension of the safety concept for heat pumps with flammable refrigerants for gas boiler replacement

Starting point/Motivation

Despite the uncertain supply situation and short-term price shocks, natural gas remains the largest primary energy source for heating in Europe. In large cities such as Vienna, around half of all households continue to use gas boilers for heating or domestic hot water. This mainly applies to existing large-volume residential buildings.

Heat pumps represent a sustainable alternative in renovation projects. As a result of the tightening of the F-Gas Regulation, the use of refrigerants with a high global warming potential will be further restricted in future. As a result, the focus is shifting to natural refrigerants as an alternative. However, these refrigerants, most of which are classified as flammable, place high demands on safety.

Content and goals

Safety concepts are being developed for the event of a leak in which flammable refrigerant escapes from the refrigeration circuit. One concept is the integration of several modules into a complete heat pump, which increases safety through smaller individual filling quantities.

However, modularity is partly at the expense of energy and resource efficiency. The large-scale replacement of gas boilers therefore requires a compromise between modularity and resource efficiency. Not only the power density (heat output per refrigerant volume), but also the cost and resource efficiency are considered as decisive parameters of the system.

The concepts to be developed guarantee a higher level of safety for installation in the home than is required by the current safety standard. The aim is to keep the concentration of the refrigerant in the environment of the heat pump below the explosion limit. The basis for this is the energy-, cost- and resource-efficient concepts for heat pumps with flammable refrigerants in residential installations to replace gas boilers.

Methods

In the first step, safety concepts for typical refrigeration circuits using various natural, flammable refrigerants are developed to minimize the released mass in case of leakage while maintaining high efficiency. This involves creation of abstract models and research into safety concepts, as well as the setup of modeling and dynamic 1D simulation using Modelica/Dymola.

In the next step, test enclosures and measurement concepts for leak detection are developed and optimized in the laboratory. For this, transient 3D simulations with Navier-Stokes solvers - CFD tools (Ansys Fluent) - are used as support. In the final step, a guideline for the individual sizing of components is created, derived from the simulation studies and laboratory experiments.

The development of new, physical leakage simulators including optimized control enables more realistic and simpler leakage tests compared to the current safety standard - for an even higher level of safety in the residential sector.

Expected Results

The knowledge gained will be incorporated into the international IEA HPT TCP Annex 64 "Safety measures for flammable refrigerants", which will help to expand research knowledge. To disseminate and reuse the know-how gained, best practices are available with regard to the innovative coupling of 1D and 3D simulations at the location of the leakage to realistically determine the mutually influencing processes inside and outside the refrigeration circuit.

Project management

OCHSNER Wärmepumpen GmbH

Project or cooperation partners

AIT - Austrian Institute of Technology GmbH

Stephan Preisinger
Ochsner-Straße 1
Stadt Haag
Tel.: +43 (5) 04245 - 548
E-mail: stephan.preisinger@ochsner.com
Web: www.ochsner.com