Ludwig Irrgang and Christopher Schifflechner are currently preparing the large heat pump to simulate real operation. In the test, the system is expected to generate 100 kilowatts of cooling and 150 to 200 kilowatts of heat. When scaled to real conditions, the output will be about 10 to 20 times higher, i.e., one to two megawatts. In his doctoral thesis, Irrgang analyzes the refrigeration machine optimized for the conditions of deep geothermal energy. Additionally, he demonstrates its operation as an absorption heat pump and as a heat transformer.
"A system that combines these three applications in this size is unique: Sustainable cooling in summer and additional heat supply in winter is particularly interesting in connection with geothermal energy, as it combines the seasonally fluctuating demand for heat and cold with the constant heat supply of geothermal energy. Cooling and heating networks connect producers and consumers. This makes geothermal heat more efficiently utilized and reduces the consumption of other, especially fossil, energy sources," explains Irrgang.
The basic idea behind absorption heat pumps and chillers is to reduce the electrical energy consumption for heating and cooling by using heat at a high temperature level instead of electricity for driving. The third operating mode, the heat transformer, works differently: It upgrades heat from a medium temperature level to a higher one. This raises previously unused residual geothermal heat to a usable level. The test stand simulates the system operation with all temperature levels that occur in deep geothermal energy in the Munich metropolitan area. This allows researchers to make statements about the locations that are suitable for use.
The innovative project design also analyzes the conditions for the economic operation of such a system. "The efficiency of an absorption heat pump, unlike classic compression heat pumps, is not defined by electrical energy consumption but by the amount of heat or cooling provided in relation to the driving heat consumed. Since geothermal heat is already available, the question of efficiency is secondary for us. The primary question is when the acquisition of such a system becomes economical and the electricity saved covers the increased acquisition costs. This strongly depends on the conditions of the geothermal drilling and the demand scenarios. A reversible system that can be operated year-round will improve economic viability. Such a system can also be flexibly used for various developments in the energy market. Our simulations already show great potential here," says Schifflechner.
Geothermal will power up sustainability
Heat and cold generation from geothermal energy is an environmentally and climate-friendly alternative to fossil energy, avoiding greenhouse gas emissions. In the South German Molasse Basin, geothermal energy is extracted from deep geothermal energy through drilling at depths of 2 to 5.5 kilometers. Therefore, geothermal cooling and heating with absorption technologies is a sustainable alternative to compression heat pumps and chillers, as long as our electrical energy is largely generated from fossil sources. The working fluids used, water and lithium bromide, are neither toxic nor do they negatively impact the greenhouse effect or the ozone layer, unlike today's refrigerants in compression machines, and they do not release forever chemicals (Per- and Polyfluoroalkyl Substances, abbreviated PFAS).
Irrgang is convinced of the investment: “The electrification of the German energy system in the coming years poses a major challenge for the German electricity market. Any technological relief is therefore good news. Absorption heat pumps should therefore be used alongside compression machines wherever excess heat is available.”
Deep geothermal energy combined with district heating and cooling networks enables reliable heat and cold supply with predictable costs and very low electrical energy consumption. The independence from the electricity and gas market generates high demand and leads to increased expansion in the Munich metropolitan area. "The biggest challenge for central cooling and heating provision is the expansion of hydraulic networks needed for distribution. Large consumers at the site of provision, such as industrial companies, do not need these networks and may therefore be early adopters. Although a system pays off quite quickly in operation, the high material usage and high investment costs of acquisition could deter potential investors. We want to investigate the potential for use and find out how heat pumps can contribute to decarbonization and what costs will be incurred by the public," says Schifflechner.
Ludwig Irrgang M.Sc.Bachelor of Engineering Sciences and Master of Energy and Process Engineering at TUM
Doctoral Candidate since 2022
Christopher Schifflechner M.Sc.
Bachelor of Industrial Engineering at the University of Bayreuth and Master of Mechanical Engineering/Sustainable Process and Energy Technology at TU Delft
Research Group Leader Geothermal Alliance Bavaria, Head of Thermodynamic Cycles and Heat Transfer at the Chair of Energy Systems