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Industrial heat pumps and vapour recompression: Science and thermodynamics

Why a small temperature lift makes heat pumps shine

What this tab covers The thermodynamics: the grade (temperature or pressure) of the energy being recovered, energy versus exergy efficiency, and how harsh the waste stream is on equipment.

Industrial heat pumps use electricity to lift waste heat from a temperature nobody can use to one a process can. Mechanical vapour recompression (MVR) does the same by compressing the steam boiled off in an evaporator so it can heat the next batch; thermal vapour recompression (TVR) and multi-effect evaporation reuse vapour with steam instead of electricity.

Grade of energy

Favourable

Heat pumps are the main tool for heat that is too cool for direct reuse. Large industrial units now deliver about 140 to 160 C, and commercial products reach up to about 200 C. In DOE's 2008 review, MVR could deliver up to about 190 C with a lift of up to 90 K, TVR up to 150 C with a lift of 40 K, and closed-cycle electric heat pumps only 120 C, so the temperature range has widened considerably since. That matters because the IEA finds about 75% of heat demand in less energy-intensive industries is below 200 C.3416

Large industrial heat pump supply about 140 to 160 C3 Commercial ceiling up to about 200 C4 MVR maximum sink and lift (2008) about 190 C; 90 K1 Light-industry heat below 200 C about 75%6

Exergy versus energy efficiency

Favourable

The coefficient of performance (COP, units of heat out per unit of electricity in) falls as the temperature lift grows. Commercial high-temperature units range from about 5.8 at a 40 K lift to about 2.4 at a 95 K lift; prototypes delivering 120 C reach 5.7 to 6.5 at a 30 K lift and 2.2 to 2.8 at 70 K. MVR evaporators, with small lifts, use only about 30 to 50 kWh (vendor figures) of electricity per tonne of water evaporated, against 1 t of steam for a single-effect evaporator and 0.25 t for a four-effect one. Using a latent heat of about 0.63 MWh per tonne of steam, that equals an effective COP of roughly 13 to 21 (calculated). Exergy efficiency is high because electricity is spent only on the lift. For steam, a Fraunhofer ISI study for Agora Industry estimates a COP of about 1.9 to 2.2 when lifting 60 C waste heat to 180 C steam, as practical machines reach about 50 to 60% of the theoretical (Carnot) limit.2713

COP, commercial units about 5.8 at 40 K lift to 2.4 at 95 K2 COP, prototypes at 120 C sink 5.7 to 6.5 (30 K lift); 2.2 to 2.8 (70 K)2 MVR electricity about 30 to 50 kWh per t evaporated7 Effective MVR COP about 13 to 21 (calculated)7

Media compatibility and corrosiveness

Mixed

Closed heat pumps keep the process fluid away from the refrigerant. Commercial units mainly use R245fa, ammonia (R717, toxic), CO2 (R744, high pressure), R134a and R1234ze(E); research units use newer low-global-warming fluids such as R1336mzz(Z), which reaches 160 C. MVR compressors handle the process vapour itself, so droplets, foaming and corrosive vapours must be controlled, and fouling of evaporator surfaces affects both MVR and multi-effect plants.2

Main commercial refrigerants R245fa, R717, R744, R134a, R1234ze(E)2 R1336mzz(Z) sink temperature up to 160 C2

Variants compared1342710

VariantMaximum delivery temperatureEnergy useDriver
Closed-cycle electric heat pump120 C in 2008; about 140 to 160 C now; up to 200 C offeredCOP about 2.4 to 5.8 depending on liftElectricity
Mechanical vapour recompressionAbout 190 C, lift up to 90 KAbout 30 to 50 kWh per t evaporatedElectricity
Thermal vapour recompressionAbout 150 C, lift about 40 KAbout 0.5 t steam per t evaporatedHigh-pressure motive steam
Multi-effect evaporation (2, 3, 4 effects)Set by steam supply0.5, 0.33, 0.25 t steam per t evaporatedSteam
Steam-generating heat pump (e.g. Skyven Arcturus)Boiler-quality steamNo figure published in cited sourceElectricity

Sources

  1. Waste Heat Recovery: Technology and Opportunities in U.S. Industry (BCS Inc. for US DOE Industrial Technologies Program) US Department of Energy, 2008
  2. High temperature heat pumps: Market overview, state of the art, research status, refrigerants, and application potentials (Arpagaus, Bless, Uhlmann, Schiffmann, Bertsch), Energy 152, 985-1010 Elsevier (via RePEc IDEAS), 2018
  3. The Future of Heat Pumps: Executive summary IEA, 2022
  4. Heat pumps key to helping industry turn electric (WBCSD and DNV report release) WBCSD, 2022
  5. Can low-temperature heat in factories be electrified competitively? (commentary, undated; 2024 cost data) IEA
  6. Heating options for thermal separation plants: MVR and TVR, specific utility consumption table (vendor data) GEA Group, 2026
  7. North Texas' Skyven Inks $70M Agreement with France's Kyotherm to Advance Industrial Decarbonization (trade press report of company announcement) Dallas Innovates, 2025
  8. Direct electrification of industrial process heat: an assessment of technologies, potentials and future prospects for the EU (Fraunhofer ISI for Agora Industry) Agora Industry / Fraunhofer ISI, 2024