Thermally driven heat pump

Thermally driven heat pumps (TDHP) are an innovative and promising segment of the heat pump market. They prove useful for several fields of application and contribute to the claim that heat pump technology can meet nearly all requirements in the marketplace for heating, cooling and domestic hot water. This heat pump technology can be used in a lot of possible applications: new and existing buildings, industrial processes, district heating and cooling.

Technology overview

Cooll refers to a thermally driven heat pump as defined in the draft Ecodesign and Energy Labelling Regulation (EU) 813/2013 and 814/2013: “Thermally driven heat pump means a heat pump using heat or an engine to drive the sorption or compression cycle”. There are three main type of thermally driven heat pumps:


Gas sorption heat pump (EN 12309)


Thermal compression heat pump (EN 12309)


Gas engine heat pump (EN 16905)

A heat pump uses energy to “pump” renewable heat (e.g. ambient heat) from a low temperature level to a temperature level where it can be used to heat a house or produce domestic hot water. While a vapour compression heat pump uses electricity to drive the heat pump, a thermally driven heat pump uses heat to drive a “thermal” compressor. This heat can come from a gas burner that drives the thermodynamic cycle, for example.

Key performance factors of TDHP

The key performance indicators of thermally driven heat pumps are:

  • Contribution to EU energy and climate targets: CO2-emissions reduction of 25 to 40% compared with traditional heating technologies), primary energy savings and efficient use of energy, diversification of energy sources. When using renewable gases in TDHP, CO2 emissions can be further reduced.
  • Reduction in primary energy required compared to traditional heating technologies of up to 40%.
  • Good performance at low outdoor air temperatures (not only on ground source applications) and higher heating supply temperatures (also with radiators).
  • Application in areas with insufficient available load from the electric grid (extra load on the grid from TDHPs is negligible) and in areas with harsh climates (and available gas supply, also LPG).
  • Lower cost for drilling (ground source heat pump) due to the need for a smaller heat source and reduced need for back-up/bivalent systems due to stable output power.
  • Feed-in temperature up to 70°C: compatible with “retrofit applications” and DHW requirements.
  • Reversible heating & cooling possible.
  • Heat pump technologies offer more efficient use of energy than the traditional heating technologies and this no matter the energy use (renewable electricity, gaseous fuel, natural gas). Use of gaseous fuel, widely distributed in many European countries, which can be converted into green gas (bio-methane, hydrogen) in the next few years, further reducing CO2 emissions. In fact, the introduction of fuels such as syngas, biogas, biomethane and hydrogen (so-called “green hydrogen” available through the electrolysis of water using renewable electricity) will make the gaseous fuel renewable. Syngas and biogas could be used in TDHP units through an upgrading process of Biogas to bio-methane.

The ability to provide high output temperatures allows TDHPs to be directly used with existing heating systems. “High temperature levels” means heating and DHW supply temperatures 55°C and higher. Sorption heat pumps currently market available and under development are specifically addressing the retrofit market in existing buildings with existing heating systems, which often still means supply temperatures at these levels. In the respective standards there are two heating maximum supply temperatures defined:

  • Low temperature supply 35°C
  • Intermediate temperature supply 45°C
  • Medium temperature supply 55°C
  • High temperature supply 65°C

These are the nominal (maximum) heating supply temperatures at the respective heating design outside temperature of the considered climatic zone (e.g. -12°C for average climate). Due to their design for use with hydronic systems (very often based on radiators), TDHPs easily integrate with other heating technologies (solar energy systems, condensing boilers, or electrical heat pumps). TDHPs are receiving increased interest in the marketplace due to the previously mentioned advantages leading to high sales growth in all market segments and geographic areas that are currently addressed.