Robert Haberl

Due to the necessary decarbonization of the heat supply, heat pumps are becoming increasingly important for domestic hot water preparation. However, the relatively high requirements for hot water preparation and distribution temperatures for hygiene reasons often cannot be met with current heat pump concepts without the additional use of electric immersion heaters, and the system efficiency of the heat pump and storage tank combination often falls well short of the technical possibilities in the field. This project compares different concepts for hot water preparation with heat pumps in multi-family houses. The focus is on hygiene requirements and efficiency. The aim is to develop and investigate new approaches to achieve significantly higher efficiency in apartment buildings with hot water circulation. Only natural refrigerants are to be used. The project is co-financed by the Swiss Federal Office of Energy (SFOE) and involves the Institute of Energy Systems (IES) at the OST, Lucerne University of Applied Sciences and Arts (HSLU) and various industrial partners.

According to the model regulations of the cantons in the energy sector (MuKEn; as of 2018), the hot water in newly built residential buildings may no longer be heated 100 % directly by electricity. During the heating period, the drinking water must be heated or preheated with the heat generator for space heating, otherwise at least 50 % of it must be heated using renewable energy or waste heat. This means that the residual heat coverage of the drinking water to the desired hot water temperature can be achieved directly electrically. On behalf of the EnFK, this project aims to compile an overview of the types of direct electrical heating of drinking water in residential buildings (focus on apartment blocks) and how these are to be assessed from the point of view of the energy transition and energy efficiency, especially with regard to a possible shortage of energy in winter.

The importance of hydraulic balancing of heat distribution systems for energy-efficient building operation and resident comfort has long been recognized. Nevertheless, it can be stated that there is a lack of expertise and still far too often insufficient implementations occur in practice. Companies have also noticed this gap and have developed new products or solutions. The aim of this research project is to investigate how well and reliably these solutions for automatic hydraulic balancing work, and what benefits they provide in terms of comfort and energy efficiency. For this purpose, the products will be installed in real systems and tested by means of a hardware-in-the-loop procedure. The effects on a virtual building modeled in detail can be tracked and evaluated in real time. The results are presented to the professional community in the form of factsheets that enable an independent comparison.

Thermal stratification is an important parameter in the energy evaluation of storage tanks. The electrical energy consumption in a heat pump system can be up to 40 % lower with a well stratified storage tank than with a poorly stratified thermal energy storage.

In the StorEx project, SPF introduced stratification efficiency as a key performance indicator and at the same time a method for measuring it, which has already become established in Switzerland.

An alternative to this is the measurement of the storage tank according to the EN 12977-3 standard with a subsequent simulation with a calibrated model.

In order for the «thermal stratification» to become a generally, or internationally, recognized characteristic value for thermal storage tanks with a clearly defined measurement procedure, it is important that these two procedures are investigated in a comparative measurement. This is the aim of this project.

In the project HpCosy the basics for a decentralized brine-water heat pump system for flats in

multi-family houses will be developed and investigated. This "Comfort System" includes the functions heating, cooling and domestic hot water preparation, whereby the latter can optionally be controlled with the consideration of availability of own photovoltaic electricity as an individual system or in a swarm (cooperation for self-consumption).

The project is being carried out on behalf of the Swiss Federal Office of Energy and in collaboration with other partners from industry and research.

Thermal stratification of heat storage has a high impact on the efficiency of thermal energy systems. This correlation was shown in the StorEx project for combined storage tanks, with a new test procedure for stratification efficiency that is based on the second law of thermodynamics. This procedure is now well established, but could so far not be applied to domestic hot water (DHW) storage tanks. Therefore, in the DHWstrat project, the existing procedure was extended and applied to four DHW storage tanks. The results show that a well stratified DHW storage tank concept not only achieves higher comfort and better hygienic conditions, but in combination with a heat pump saves up to 40 % electrical energy compared to another storage tank. These results underline the need to evaluate the stratification efficiency also of DHW storage tanks.

The CCT-Bat project is to develop a system test for home batteries, with which all relevant operating conditions can be tested within three days using the hardware in the loop principle, in order to determine the cycle efficiency and other key performance indicators. Different target functions of the systems (self-consumption, electricity tariffs, and grid benefits), as well as single and multi-family houses and different load profiles will be considered.

Within the EU project Hybrid-BioVGE an innovative system for heating and cooling is developed. The cooling device is based on a Variable Geometry Ejection (VGE) cooler. Driving energy is heat from solar collectors or from biomass. SPF is supporting the development of collectors that deliver heat at 75 – 90 °C, and is testing the heating and cooling system with the established Concise Cycle Test (CCT) method. This method is specifically adapted in order to be able to test also cooling systems.

The project is supported by the research programme H2020 of the European Union – grant agreement ID: 818012, acronym Hybrid-BioVGE

Limiting the electrical purchase and feed-in power of buildings to a low level is attractive for grid stability. Because of this limitation, the building's own solar power consumption would be optimised, the PV system output limited, peak demand reduced and, if necessary, an electric energy storage installed. Due to the different interests of the stakeholders, the advantages and disadvantages of the new technical concepts for the power limitation must be examined. The feasibility of such a concept will be investigated by means of simulations.

The competition between photovoltaics and solar thermal systems for available roof area and investment capital of house owners is putting pressure on solar thermal heating systems to reduce cost and to simplify the product. This project aims to assist manufactures in this task. The goal is to reduce the complexity of solar thermal systems, and reduce likelihood of failures during planning and installations. Criteria for defining compactness and fault resistance will be defined and subsequent applied to different heating systems in the test bench. For this purpose, the well-established CCT method will be simplified and combined with the criteria for evaluation of compactness and fault resistance.

This project is financed by the Swiss Federal Office of Energy (SFOE).