Waste heat recovery: introductory guide
Information about waste heat recovery and its potential as a low carbon heat source, as well as the process of capturing and utilising heat from industrial and commercial processes. The recovered heat can be used in a range of applications including heat networks.
Glossary
Ambient heat recovery
The process of collecting heat from the surrounding environment – typically held in the air, water bodies and the ground, and reusing it in other applications.
Borehole
A deep hole drilled into the ground (typically tens of metres, or kilometres for specialist uses), used to extract heat from underground (directly from the ground or ground water) and used typically by ground source heat pumps to provide heating, cooling, and hot water.
Carbon intensity
Refers to how many grams of carbon dioxide (CO2) are released to produce a kilowatt hour (kWh) of electricity.
Combined heat and power (CHP)
The process of capturing and using heat that is a by-product of generating electricity, often in specialist combined heat and power engines that are typically powered via natural gas.
CO2
Carbon dioxide is an important heat-trapping gas, also known as a greenhouse gas. It is produced during the extraction and burning of fossil fuels (such as coal, oil, and natural gas).
Consumer
The party which purchases the heat for their own use.
Curing
A process used for hardening polymers. The curing process can involve the use of heat, ultraviolet radiation, and chemical additives.
Distillation
A process of separating, concentrating, or purifying a liquid by condensing the boiling vapour.
District heat network (DHN) operator
The organisation that manages the operation of a DHN (see also ‘Heat Network’).
Economiser
A type of heat exchanger used to recover heat from the exhaust gases of boilers or other heat sources. The recovered heat can be used to pre-heat streams of air or water.
Edge computing
An approach that brings computers closer to the servers storing the data the computers are using. The intention is to make computational processes faster.
Efficiency
A measure of a technology’s ability to convert one type of energy into another. For example, a gas boiler’s ability to convert energy stored in natural gas to useful heat.
Effluent
Liquid waste discharged typically from a sewage system or an industrial process.
Electrolysis
The process of using electricity to split water into hydrogen and oxygen.
Energy centre
Typically, a building that houses heat generation and sometimes power generation equipment, with the heat and power fed into a heat network or the local power grid respectively.
Energy from waste
The process of generating electricity or heat from the treatment or processing of waste.
Feedstock
Raw material that is fed into an industrial process.
Flue
A duct that leads from a furnace, oven, or fireplace through which exhaust gases flow.
Fuel cell
A device that converts a fuel and oxidant, such as hydrogen and oxygen, into electricity directly (i.e. without combustion).
Geothermal energy
Energy stored in the ground in the form of heat. Temperature, quantity and accessibility of heat vary as a function of factors such as depth and geology.
Green hydrogen
Hydrogen produced by splitting water into hydrogen and oxygen using an electrolyser and renewable electricity.
Heat exchanger
A device which transfers heat between two fluids (liquids or gases) at different temperatures as part of heating and cooling processes.
Heat network
In this document ‘heat network’ is used to refer to a: District heat network – a network by which thermal energy is distributed from one or more sources of production to more than one building Communal heating system – a system by which thermal energy is distributed from one or more sources of production to one building comprising more than one building unit.
Heat pump
A device that extracts heat from an ambient heat source, raises its temperature using mechanical energy, and transfers the heat typically into a heating system. Ground source heat pumps (GSHP) extract heat from the ground, air source (ASHP) generally from ambient air, and water source (WSHP) from water bodies such as rivers, estuaries, and the sea. Heat pumps range in scale from small domestic units providing heating for individual homes to much larger units serving heat networks. Heat pumps can also be used to provide cooling, not just heating.
LHEES
Local Heat and Energy Efficiency Strategy (LHEES) set out the long-term plan for decarbonising heat in buildings and improving their energy efficiency across an entire local authority area in Scotland.
Linear heat density
A means of relating annual heat demand to a distance and is expressed as annual heat demand per meter of pipe
Medium
A substance that carries or through which heat (and other types of energy, such as sound) can pass. For example, water is often the medium used to convey heat through a heat network.
Offtaker
The party which purchases the heat from the waste heat producer. This can be the consumer of the heat or an intermediary party who may purchase heat for resale, typically within a heat network.
Refrigerant
A liquid used in heat pumps and heat exchangers that facilitates heat transfer.
Refrigeration
The process of cooling or freezing substances such as foods or process liquids and maintaining them at a temperature below ambient temperature.
Retrofit
Typically used in this context to describe the addition of new technology or features to existing systems and buildings – for example, this may mean upgrading insulation, lighting, windows, and heating systems to improve energy efficiency and reduce carbon emissions.
Sewage
Waste liquids and solids which are carried away for treatment via drains and sewers.
Wastewater
Any water which has been used, either domestically or industrially, and now requires water treatment before reuse or discharge.
Waste heat producer
Used in this document to refer to an organisation with processes producing heat that would otherwise be wasted without the implementation of waste heat recovery methods.
Waste heat recovery
The process of collecting heat, typically from industrial processes and from sources such as exhaust gases, effluent and hot air, and reusing it in other applications.
Units
kW
Kilowatt – unit of power, equivalent to 1000 Watts.
kWh
Kilowatt hour(s) - a standard measure of electrical energy equal to the power consumption of 1 kW for one hour.
MW
Megawatt - unit of power, equivalent to 106 Watts.
MWh
Megawatt hour(s) - a measure of electrical energy equal to the power consumption of 1 MW (1,000 kW) for one hour.
GW
Gigawatt – unit of power, equivalent to 109 Watts.
GWh
Gigawatt hour(s) - a measure of electrical energy equal to the power consumption of 1 GW (1,000,000 kW) for one hour.
TW
Terawatt – unit of power, equivalent to 1012 Watts.
TWh
Terawatt hour(s) - a measure of electrical energy equal to the power consumption of 1 TW (1,000,000,000 kW) for one hour.
Contact
Email: heatnetworks@gov.scot
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