energy ABC
From twin fuel burners to thermal energy. The MIWE energy ABC explains all important terms involved in optimised energy use.


Twin-fuel burner
Can use oil or gas for heating.


Annual utilisation
Ratio of energy which can be used for heating (and poss. water heating) and the final energy quantity used to do so. By contrast to the efficiency, the annual utilisation takes various operating states throughout the entire year, affected by various losses. While the utilisation of the boiler only takes the boiler losses into account the utilisation of the entire heating system also takes heat distribution losses into account.

Alternative energy/Renewable energy
Renewable energy sources are energy sources which are available infinitely in a human time scale. The three original sources are solar radiation, geothermal heat and tidal energy. A distinction is made between renewable and non-renewable fossil energy carriers (e.g. coal, petroleum, natural gas) which are finite (see Fossil energy). The advantages of using renewable energy are the sustainable availability of resources, the reduced dependency on energy exporters (also on a political level) and better environmental compatibility.


Created from organic material (e.g. organic sludge, manure) via methane fermentation and can be used as a heating gas (see Biomass).

Biomass occurs in solid, liquid or gaseous form and is used to obtain energy and fuel. Solid biomass, in addition to wooden biomass (e.g. forest residues in the form of split logs or chopped wood, saw chippings, wooden pellets etc.) also includes straw-like fuels such as straw, grain-type plants, miscanthus and energy plants (see Wood chips). Liquid biomass includes oils (e.g. rapeseed oil, sunflower oil,...), which are processed to form fuels, for example. Gaseous biomass is called biogas and is a fermentation product of solid and liquid biomass (corn, liquid manure, ...). Biogas is converted to useful energy (heat, electricity) by burning in motors.

Boiler feed water/Feed water
Water stored in a feed water reservoir fed continuously to a steam generator is referred to as feed water. Steam power plants require large quantities of feed water. The steam boiler generates steam which is used for heating, processing technology workflows, or to drive a steam turbine or steam engine.


When biomass is burned, only the quantity of CO2 previously withdrawn by the plant from the atmosphere is released into atmosphere.

Calorific value
The calorific value of a fuel specifies the heat quantity released on burning and subsequent cooling of the combustion gases to 25 °C, and their condensation. The calorific value incorporates both the necessary energy for heating the combustion air and exhaust gases, as well as the evaporation or condensation heat from liquids, in particular water.

Combined heat and power plant
(abb. CHP) A combined heat and power plant is a plant for generating thermal energy and electricity simultaneously. The cogeneration principle results in a higher overall efficiency, which means that CHP pants can save up to 40% of primary energy. The same applies to a combined heat and power plant as to a thermal power plant, however it is usually used to refer to smaller systems such as those powered by a gas turbine or a diesel motor.

Combustion efficiency
The combustion efficiency specifies the use of the heat generated when a fuel is burned at the nominal power. It only incorporates the loss of heat by cooling the waste gases to the ambient air.

Combined power and heat generation
In an energy converter system using a combined power and heat generation plant (CHP), the thermal energy (heat) generated both on chemical or physical use (burning,...) of energy carriers, as well as the electrical energy generated by energy conversion are used.


The dew-point or dew-point temperature is defined as the temperature at which a balanced state of condensing and evaporated water on an item occurs (when moisture is present), i.e. condensate formation just starts. The fundamental direct measurement is implemented using a dew-point mirror hygrometer, indirect measurements can also be measured with impedance or capacitive sensors.


Energy efficiency
In very general terms, energy efficiency refers to the ratio of energy implemented to actually used - the higher the yield (or efficiency), the more efficient the use of the energy. Domestic devices are classified in energy efficiency classes; that is just a rating scale for the energy consumption of the devices.

Emission Term
for air pollution, noise, radiation etc., released by technical systems.

Exhaust gas
Pollutant components created when heating oil, coal, natural gas are burned (e.g. carbon dioxide, carbon monoxide, nitrogen oxides, sulphur dioxide, hydrocarbons).


A furnace is a technical device for heat generation by burning solid, liquid or gaseous fuels.

Fossil energy
Fossil energy is the collective term for energy raw materials stored in the earth and formed millions of years ago from animal and plant residues (e.g. turf, coal, petroleum and natural gas). It occurs in limited quantities and is not renewable. On combustion with oxygen, energy in the form of heat and carbon dioxide is released, contributing to global warming.

Fresh water/Drinking water
Drinking water is water for human consumption. Drinking water is the most important foodstuff, it cannot be replaced by other substances (first and key statement of DIN 2000).

Fuel value
The fuel value is the maximum quantity of heat which can be used on combustion, where the steam in the exhaust gas does not condense, relative to the quantity of fuel used. See also calorific value?


Heating gas circulation
The combustion gases flow around the ovens on all sides. This creates a static baking atmosphere.

Heat exchanger
Heat exchangers are recuperative systems for transferring heat and used in building air conditioning and in almost all convection baking ovens and MIWE heating panels. It is installed downstream of a heat recovery system to raise the supply temperature above the exhaust air temperature. Recuperative means that the exhaust and intake air currents are transported past one another without exchanging air or moisture, i.e. are separated from one another by solid separators.


Natural gas
Collective term for combustible natural gases, largely consisting of methane, whose further components e.g. ethane, propane, nitrogen, carbon dioxide, and in some cases, also nitrogen dioxide. In some cases, natural gas formed together with petroleum, and in some cases it formed from coal as part of coalification. It is largely used as fuel (see Fossil energy).

Nitrogen oxides
Nitrogen oxides are collective terms for gaseous oxides containing nitrogen. They are abbreviated to NOx, as there are multiple compounds of nitrogen and oxygen due to the many oxidation levels. The abbreviation NOx is also used for nitrous gases (see below?).


Pellets are produced in a special manufacturing process from natural chippings in the timber processing industry, where they are compacted to form hard wood pellets under high pressure. The characteristics of wood pellets are standardised per ÖNORM M7135 or DIN plus.

Primary energy consumption
The primary energy consumption is the consumption of primary energy carriers which occur in nature, such as anthracite or lignite, petroleum, natural gas, uranium and renewable energy sources. Primary energy is generally converted to consumer-friendly forms in power stations (e.g. electricity, remote heat, heating oil, coke...).

Process water/Industrial water/Service water
Water used for commercial, industrial, agricultural or similar purposes which do not require drinking water quality standards (except for foodstuffs plants, for example, which must comply with drinking water requirements, see Fresh water). Depending on the purpose, process water must have certain qualities.

Plant efficiency
The efficiency of a plant incorporates the efficiency of all individual components, so that their losses are totaled and the actual efficiency of the overall system is calculated, corresponding to the energy consumption and the useful energy provided. It describes the performance of the system over a longer period, e.g. one year.

Power supply system
We define a power supply system as a closed circuit of heat generators, heat exchangers, and heat (or refrigeration) consumers, in which energy (generally in the form of temperature-controlled water) is stored and distributed in a controlled state.


Sulphur dioxide
Sulphur dioxide is a colourless, strong-smelling gas, which is produced in particular when burning sulphurous coal and heating oil and when manufacturing cement. In combination with dust, it is an irritant, and can cause breathing problems in higher concentrations. When it reacts with oxygen in the air and in steam, sulphurous acid results, which damages the environment as acid rain.

Secondary raw material
Raw material recovered by recycling. Most products can be returned to the production process via recycling. However, upstream sorting and treatment steps are required. Glass and plastics are treated to become secondary raw materials, paper is sorted by quality, tin plate by selection and compacting, aluminium by pyrolysis. The following applies for all processes: When recovering secondary raw materials, a small proportion of unusable residues remains, which must be disposed of in accordance with the regulations.


Thermal energy
In everyday language, thermal energy is referred to imprecisely as heat or heat energy or confused with the temperature. As the specific heat capacity is a function of the temperature, the thermal energy of a body is not proportional to its temperature. Thermal energy is the energy stored in the disorderly movement of atoms or molecules of a material. It is a condition factor and part of the inner energy.


Useful energy
Useful energy is the energy which is available after the final implementation in the devices of the consumer: for example room heating, forward motion of the car or the work performed by a vacuum cleaner. On average, the high conversion and distribution losses mean that only roughly one third of the primary energy implemented is actually used. See Energy efficiency and Efficiency.


Waste heat
The energy in the primary energy carrier is not used fully in most energy conversion processes. Waste heat in the form of hot air or hot water is produced. This reduces the primary energy requirement if used via heat recovery.

Wood chips
Mechanically cut wood with and without bark with a maximum length or approx. 100 mm. Chips are largely used as a biogenic and renewable fuel. Depending on the type of wood, they have a fuel value of approx. 4.0 kWh per kg.