Multi-WP

Multi WP - Efficient heat transition through multivalent heat pump systems

In Austria, around 40% of final energy consumption is accounted for by heating and cooling, including process heat in industry (data from 2023, energie.gv.at). This sector therefore accounts for the largest share of total energy consumption - ahead of the transport sector and other applications. Heat utilisation is particularly dominant.

Currently, 39% of the energy used for heating and cooling comes from renewable sources. This means that over 60 % is still covered by fossil fuels. This dependency emphasises the central role of the heating transition in the success of the overall energy transition.

In urban areas in particular, there are a large number of locally available, non-fossil resources for heat supply, such as groundwater, solar energy, waste heat from cooling or industrial processes, waste water, outside air and soil. However, many of these heat sources are not available everywhere or only to a limited extent. Outdoor air and solar energy, on the other hand, are available almost everywhere to a significant extent. Geothermal probes can be installed at most locations, while groundwater can only be utilised at selected locations. What all heat sources have in common, however, is that they have hardly been utilised to date.

The "Multi-WP" project

The aim of the Multi-WP project was to optimise multivalent heat pump systems - consisting of air and brine heat pumps, photovoltaics and geothermal probes as seasonal heat storage - in terms of efficiency, flexibility and load shifting. Through the intelligent combination of these technologies, locally available, non-fossil energy sources are to be better utilised and the annual performance figures of heat pumps significantly improved. The project thus contributes to the reduction of greenhouse gas emissions, the strengthening of domestic technology development and independence from energy imports.

Methodology and tools

A central element of the system design was the rapid assessment of the geothermal potential at each location. GeoSphere Austria's Geothermal Atlas was used for this purpose - a free online tool that calculates the energy potential of a geothermal probe field for heating and cooling purposes over 20 years based on site data, operating mode and optional nominal output. It provides automated energy flow diagrams, temperature forecasts and reports and was used in the project to evaluate various scenarios and to estimate the area required for the geothermal storage facility in relation to the available area.

The detailed simulations were carried out with the advanced tool PYGsim, which uses the Python library "pygfunction" (Cimmino, M., & Cook, J.C., 2022) for the geothermal probe simulation.

In addition, modules were programmed for the technical storage tanks, air heat exchangers and heat pumps, which allow coupling on an hourly basis. The input of the characteristic curves of real heat pumps enables the dynamic coupling of the heat pumps with the temperature level of the heat sources and sinks, taking into account regeneration effects. Real weather data (2016 to 2022) from GeoSphere Austria was used to calculate the hourly heating and cooling profiles. The profiles are based on the annual energy demand and temperature-dependent functions, adapted to the building inertia. The simulations over 20 years allow a solid temperature forecast of geothermal energy utilisation and its effects on the performance factor of the heat pumps.

Case studies

Six case studies were carried out as part of the Multi-WP project to investigate the technical, ecological and economic feasibility of multivalent heat pump systems.

An overview of the investigated locations, building types and characteristics of the case studies are summarised in the following table.

Location	Building type/use	characteristics NHM Vienna	Museum	district heating, district cooling in realisation, deep storage available, high simultaneous demand for heating and cooling Amstetten	Landesklinikum	cogeneration plants (CHP) for heat demand and absorption chillers, high flow temperatures, gas boiler and district heating as a redundant system, high simultaneous demand for heating and cooling Vienna, Abelegasse	residential building (refurbishment and new build)	space for probes under new build and in the courtyard, insufficient district heating, heating and cooling demand (temperature control) Vienna, Aslangasse	multi-family houses	no district heating, decentralised hot water preparation, low thermal building standard, central heat generation to cover heating requirements via gas boiler system Vienna, Hohe Warte	office/institute building with computer centre	waste heat from computer centre is currently released to outside air, refurbishment concept in place, high simultaneous demand for heating and cooling Perchtoldsdorf	public buildings and residential buildings	drinking water protection area, waste heat from ice rink is currently released to outside air, anergy network planned

Client	FFG, BMIMI
Project management	Franziska Zimmer
Project team	Franz Zach Deyan Dimov
Project partner	Ochsner Process Energy Systems GmbH (OPES) GeoSphere Austria
Project duration	November 2021 to April 2025