2-bed Adsorption Heat Pump


Engelpracht, Mirko © Copyright: Lehrstuhl fuer Technische Thermodynamik der RWTH Aachen


Mirko Engelpracht

Group Leader Sorption Systems Engineering


+49 241 80 98176



The Chair of Technical Thermodynamics of the RWTH Aachen has developed, in cooperation with the Vaillant company, a gas-powered adsorption heat pump with an average annual utilisational efficiency of 135%. The average annual supply of energy for heating and hot water generation is only 75% by combustion, the other 25% comes from the environment. The annual utilisation efficiency of Zeolite heat pumps is approximately 30% higher than condensation boiler equipment. The Zeolite adsorption heat pump can switch from heat pump mode to condensation boiler mode continuously. This technology represents the future trend in gas condensation boiler equipment.


Environmental Protection

Nearly one third of the energy in Germany is used for heating and hot water generation in private households. A substantial part of this thermal energy is produced in both gas condensation boiler equipment and by conventional combustion. This modern gas-driven adsorption heat pump offers reduced energy consumption and therefore reduced CO2 output, by up to 20-30%.

The working mediums are water as the refrigerant and Zeolite as the sorbent. Unlike conventional refrigerants, (Ammonia, Propane), these substances are ecologically safe. Zeolite has been used since the early 1980's as a substitute for Polyphosphate in cleaning agents.


  • Ceramic base material of AlO2 and SiO2
  • Non-toxic, Non-flammable
  • Environmentally friendly in every respect
  • Thermal stability up to 600 °C
  • Forms: Granulate, Pellets, Sticks
  • Applications in
    • Cleaning agents (approx. 2m t/a)
    • Catalytic converters (approx. 100 000 t/a)
    • Adsorbers (approx. 80 000 t/a)

Technology of Heat Pumps

Heat cannot flow naturally from a cold to a warm body (R. Clausius, 2nd. Fundamental Theorem of Thermodynamics). If ''cold'' energy from the environment is to be used for heating purposes, then the temperature level of this energy must be raised. According to the laws of thermodynamics, a third, higher temperature or energy level is necessary. G. Fluegel conceived the term ''heat pump'' for this type of machine in 1920. The most common heat pumps have electrically-driven compressors. The refrigerant frequently used is HFKW, a rare Propanoder Ammonia. These type of plants are found operating mostly in Switzerland, Austria and Scandinavia. The absorption machines have a much smaller distribution. With this type, only the medium of Ammonia/Water has been established and are normally used in air conditioning for large buildings. Adsorption machines mostly use the medium, Silica gel/water. In some fields they are used for air conditioning. In this research project, ''Zeolite-Water Heat Pump'', a heating system is developed for the heating of living rooms and industrial water. The sorbent is Zeolite, the refrigerant is water.


The Operating Principle of the Zeolite Module

The sorption process in the module operates in two steps: In the first, indexing step, the Zeolite is heated by a gas burner to 200 °C. The water desorbs and flows as steam to the lower part of the module. Here, the steam condenses and delivers its heat by condensation. This step terminates, if the Zeolite is dry and all the water is in the lower part of the module.

Now the burner is switched off and the module cools down to ambient temperature. The water now evaporates in the lower part of the module by ambient heat. Steam flows to the top of the module and is adsorbed by the Zeolite. This released adsorption energy can also be used. If the water is evaporated completely, the process begins again.


Function of the Heat Pump

In Figure 5, the heating system (HZ) and the hot water tank (WW) are shown. They are heated by three heat exchangers, WÜ1, WÜ2 and WÜ3, which are represented as black in the diagram. In the right module, the refrigerant is evaporated by environmental heat and afterwards adsorbed into the Zeolite. The heat of adsorption is transferred to the primary circuit. In the left module, the refrigerant is desorbed from the Zeolite and condenses afterwards. The energy for desorption comes from the primary circuit. The condensation heat is transferred in WÜ1 to the heating system. Adsorber and desorber are hydraulically connected via the primary circuit. Between the desorber and the adsorber, energy is transferred from the primary circuit to the heating network by WÜ2. After the adsorber, the heat transfer medium is heated in this circuit by a gas burner up to the desorption temperature. The remaining heat from the exhaust gas is transferred to the heating system by WÜ3. Therefore, optimal utilisation of energy is guaranteed.

  • Applied to single family households
  • Inlet temperature: 20 bis 75 °C
  • Heating power: 10 kW, später 5 bis 25 kW
  • Dimensions : 1610 X 615 X 590
  • Maintenance: every 2 years (+ annual inspection)
  • Efficiency of 135%
  • Environmentally safe
  • Ecological working combination
  • Durable and silent module technology
  • Low running costs

Project Details

Project Partner