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Energy recovery includes any technique or method of minimizing the input of energy to an overall system by the exchange of energy from one sub-system of the overall system with another. The energy can be in any form in either subsystem, but most energy recovery systems exchange thermal energy in either sensible or latent form.

A common utilization of this principle is in systems which have a exhaust stream or waste stream which is transferred from the system to its surroundings. Some the energy in that flow of material (often gasesous or liquid) may be transferred to the make-up or input material flow. This input mass flow is often comes from the system's surroundings, which often being at ambient conditions, are at a lower temperature than the waste stream. This temperature differential allows heat transfer and thus energy transfer, or in this case, recovery.

Thermal energy is often recovered from liquid or gaseous waste streams to fresh make-up air and water intakes in buildings, such as for the HVAC systems, or process systems.


System approach

Energy consumption is a key part of most human activities. The consumption means converting one energy system to another like one will do if electric power is powering computers, light, motors etc. The input power propels the work and is mostly converted to heat or follows the product in the process as output energy. Energy recovery is about harvesting the output power and provide this as input power to the same or another process.

An energy recovery system will close this energy cycle to prevent the input power from beeing released back to nature and rather be used in other forms of desired work.

Examples of energy recovery

  • Heat recovery is implemented in heat sources like e.g. a steel mill. Heated cooling water from the process is sold for heating of homes, shops and offices in the surrounding area.
  • Regenerative brake is used in electric cars, trains, heavy cranes etc where the energy consumed when elevating the potential is returned to the electric supplier when released.
  • Active pressure reduction systems where the differentioal pressure in a preassurized fluid flow is recovered rather than converted to heat in a pressure reduction valve and released.

Envirnomental impact

It is today very difficult to quantify the realistic envirnomental impact of a global energy recovery implementation in industries and households. The main impediments are

  • Lack of efficient technologies. Heat recovery systems in private homes can have an efficiency as low as 30% or less. It may be more realistic to use energy conservation like insulation or improved buildings. Many areas are more dependant on forced cooling and a system for extracting heat from dwellings to be used for other uses are not widely available.
  • Ineffective infrastructure. Heat recovery in particular need a short distance from producer to consumer to be viable. A solution may be to move a large consumer to the vicinity of the producer. This may have other complications.
  • Transport sector not ready. With the transport sector using about 20% of the energy supply, most of the energy is spent on overcoming gravity and friction. Electric cars seems with regenerative breaking seems to be the best candidate for energy recovery. Wind systems on ships is under development. Very little work on the airline industry is known in this field.

It is however a large potential for energy recovery in compact systems like large industries and utilities. Together with Energy conservation it should be possible to dramatically reduce the world energy consumption. The effect of this will then be:

  • Reduced number of coal fired power plants
  • Reduced airborne particles, NOx and CO2 - improved air quality
  • Slowing or reducing climate change
  • Lower fuel bills on transport
  • Longer availability of crude oil
  • Change of industries and economies not fully researched

External references

  • 26 Projects Funded: Energy Recovery Methods Studied with ASHRAE Undergraduate Grants [1]
  • Heat Recovery in Industry [2]

External links

Industry examples

  • [4] Zeropex, technology and products for active pressure reduction


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