Heat recovery for buildings

Heat recovery is the process of collecting and re-using heat that is generated from any process where the heat would otherwise be lost (ref. The Carbon Trust, 2011). This can help reduce the energy consumption of the process or the heat can be used elsewhere, reducing running costs and carbon emissions.

Heat recovery devices can be used in most buildings since the majority use energy for heating, cooling, ventilation or some may house industrial processes that generate heat.

Sources of waste heat that might provide opportunities heat recovery include:

• Ventilation systems.
• Refrigeration units and chiller units.
• Boilers.
• Power generation plant.
• Plant cooling systems.
• Hot liquid effluents and high-temperature exhaust gasses.

This 'waste' heat can be recovered and re-used for applications such as; heating water, pre-heating fresh air for building ventilation systems, drying processes, power generation, pre-heating combustion air for furnaces, boilers and so on.

Heat recovery refers to the process of capturing and reusing waste heat that is generated from industrial or commercial processes. There are several types of heat recovery which include;

• Air-to-air heat recovery is a type of heat recovery involves exchanging heat between two separate air streams, such as ventilation air and exhaust air as in MVHR systems.
• Air-to-air mixing direct ducting of waste hot air in to other areas to use the heat perhaps through filters.
• Liquid-to-liquid (water-to-water) heat recovery is a type of heat recovery involves exchanging heat between two separate waterstreams, such as hot water and cold water, commonly used in manufacturing plants.
• Refrigerant-to-air heat recovery is a type of heat recovery involves capturing waste heat from a refrigeration system and using it to preheat incoming air, commonly used in HVAC plant and can improve energy efficiency.
• Steam-to-steam heat recovery is a type of heat recovery involves exchanging heat between two separate steam streams, such as high-pressure steam and low-pressure steam often used in power plants and industrial processes.
• Exhaust gas heat recovery is a type of heat recovery involves capturing waste heat from exhaust gases and using it to generate steam or hot water, commonly used in boilers and furnaces.
• Waste heat recovery from engines is a type of heat recovery that captures waste heat from engines and uses it to generate electricity or to preheat incoming air or fuel, common in condensers, power plants and industrial processes.
• Solid to solid heat recovery may refer to chemical heat that is captured by phase change materials and released again on phase change. It may be a form of heat recovery if the heat used to change phases initially was waste heat
• Phase heat recovery may refer to chemical heat that is captured by phase change materials and released again on phase change. It may be a form of heat recovery if the heat used to change phases initially was waste heat.
• Solids in heat recovery might be referred to a regenerative, as this is where waste heat with in air or water heats a solid as it passes, the solid material retains that heat and acts in a similar way to a battery, releasing it as a fresh elements comes in contact with it, such as single room ventilators.

The government document The Future of Heating: Meeting the Challenge (March 2013) highlighted the potential of heat recovery for helping reduce UK carbon emissions. In June 2013, a more detailed study was commissioned which found a total of 48 terrawatt-hours (TWh) per year of industrial waste heat across eight energy intensive industries; oil refining, iron and steel, food and drink, pulp and paper, chemical, glass, cement and ceramics. It identified 11 TWh/yr with technical potential and 8 TWh/yr with economic potential. The study identified commercially viable heat recovery for all eight industries.

In February 2023 the Guardian reported on the report published by Danfoss noted in their heat excess whitepaper that excess heat is the world’s largest untapped source of energy indicating that in the EU alone, excess heat amounts to 2,860 TWh/y, almost corresponding to the EU’s total energy demand for heat and hot water in residential and service sector buildings. Much of this excess heat could instead be captured and reused.

NB Approved document F: Volume 1: Dwellings, 2021 edition, defines heat recovery as: ‘Applied to mechanical supply and extract systems or a single room ventilator, extract air is passed over a heat exchanger and the recovered heat is put into the supply air.’

[edit] Related articles on Designing Buildings

• Air conditioning.
• Air handling unit.
• Chiller unit.
• Coefficient of Performance CoP.
• District energy.
• Ecobuild 2016 - Making the business case for large scale retrofit investment.
• Exhaust air heat pump.
• Geothermal pile foundations.
• Gross calorific value.
• Heat exchanger.
• Heat pump.
• Heat recovery ventilation.
• Heat source.
• Heating.
• HVAC.
• Mechanical ventilation.
• Mechanical ventilation's role in improving indoor air quality.
• Refrigerants.
• Tempering heating.
• Types of heating system.
• Types of heat exchanger.
• Variable refrigerant flow.
• Waste heat.
• Zero Bills Home.

[edit] External references

• Heat recovery: A guide to key systems and applications.
• Carbon Trust, How to implement heat recovery in heating, air conditioning and ventilation systems.
• The Future of Heating: Meeting the Challenge.
• The potential for recovering and using surplus heat from industry.