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A/V ratio

The ratio of the exterior building envelope (total area of all walls, windows, etc.) and the total volume of heated premises in it. A low A/V ratio is an important indicator of an optimized low-energy design of a building. The tighter the building, the lower the A/V ratio and the lower the need for heating.

Additional heat accumulator (register)

The minute volume of heat needed for heating of a low energy or passive house is supplied through a device that warms up the incoming air. This is done through an additional heat accumulator installed in the ventilation system.
See also: Passive House


The air-tightness of the building envelope is an important feature of the building quality to avoid unpleasant air currents, unnecessary energy losses and the deterioration of the building structure. In Germany, boundary permissible standards of building air-tightness are applied.


A process, under which initial costs of a property, building or additional energy efficient building components are covered by the generated profits or savings in, for example, energy consumption. The duration of this process is called amortization period. The term "amortization" is used both in the economic and the energy context. In energy, amortization period means the time needed for a certain energy-generating component or system to produce the same amount of energy as needed for its construction and operation.

Annual demand for primary energy resources

It is the volume of energy per year which is necessary for heating and hot water supply of a building including the cost of generation, preparation and supply of energy to the building.
See also: Primary energy

Annual heat consumption

The volume of energy per year which is supplied to a certain building for the purpose of heating, ventilation and hot water supply.


All organic substances generated by plants or animals, or products of their life activities. When using biomass for energy purposes, e.g. for the generation of electricity, heat or fuel, one should distinguish between renewable raw materials and agricultural crops grown mainly for the energy generation purposes, on one hand, and organic waste, on the other.

Renewable raw materials include:

  • fast-growing trees and special annual agricultural crops grown mainly for energy-generation purposes and having a high content of dry substance to be used as fuel,
  • field crops containing sugar or starch that can be used to produce ethanol and oil crops for production of biological oils and diesel biological fuel (methyl ether from rape oil) and their use as lubricants or fuels.

Organic waste is generated in agriculture, forestry, industry and households. It includes:

  • wood waste and residue,
  • hay, grass, fallen leaves and manure,
  • wastewater sludge, and
  • organic household waste.

Blower Door Test – pressure difference test

A diagnostic test designed to measure the air tightness of a building or individual interior space of a building to help locate air leakage sites. During this test, air is blown into the building, which creates a small pressure difference between inside and outside. This pressure difference forces air through all holes and penetrations in the building enclosure. As a result, the so called n50 indicator is identified: the number of air exchange with a 50 Pa pressure. Typical air change rates are: leaking existing (old) buildings 4 to 12 h-1; new buildings without special low energy design 3 to 7 h-1; low energy houses 1 to 2 h-1 and passive houses 0,1 to 0,6 h-1.

Climate change

Climate change is any long-term significant change in the expected average weather patterns of a specific region, or, more relevant to contemporary socio-political concerns, of the Earth as a whole over an appropriately significant period of time. Climate change reflects abnormal variations to the expected climate within the Earth's atmosphere and subsequent effects on other parts of the Earth, such as in the ice caps, over durations ranging from decades to millions of years.
See also:

CO2 equivalent

Is a measure for describing how much global warming a given amount of CO2 may cause, using the functionally equivalent amount or concentration of carbon dioxide (CO2) as the reference. It is the quantity of the total gross consumption of the end-use energy from non-renewable sources of primary energy.

Dew-point temperature

The dew point is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapour to condense into water. The condensed water is called dew. The dew point is a saturation point. The dew point is associated with relative humidity of the air. The higher the relative humidity, the closer the dew-point temperature to the actual temperature of the air. The lower the relative humidity, the lower the dew-point temperature compared to the actual air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and the air is maximally saturated with water.

Drainage canal

Drainage is a system of perforated pipelines laid below and/ or around the building foundation to protect a building against the penetration of ground water. Drainage pipes or drainage canals should be laid within the gravel bedding with pebbles of different sizes in order to avoid packing with sand. Drainage canals should be laid with an inclination in order to allow discharge of accumulated water with a suction pump, for example.

Emission trading

Emission trading is an administrative approach used to control pollution by providing economic incentives to reduce the emission of pollutants. It is sometimes called “cap and trade”. See also:

End-use energy

End-use energy is the part of the primary energy, which is supplied to the consumer after the processes of conversion and transportation. This is the form of energy, which is directly used in the consumers' production, transportation or household processes.

Energy audit

An energy audit is an inspection, survey and analysis of energy flows in a building or technical system with the objective of understanding the system’s energy dynamics. Typically, an energy audit is conducted to seek opportunities to reduce the amount of energy input into a system without negatively affecting the output(s) such as particular user requirements. When the object of study is an occupied building, the reduction of energy consumption while maintaining or improving human comfort, health and safety is of primary concern. Beyond simple identification of energy use sources, an energy audit seeks to prioritize energy uses from the greatest to the least cost effective opportunities for energy savings.

Energy balance

The correlation of all energy flows in the building: incoming (for example heat gains via heating, solar radiation, etc.) and outgoing (for example heat losses via ventilation, heat transfer, etc.). Under simplified conditions the sum of the heat losses equals the sum of the heat gains.

Energy policy of the European Union

The European Union introduced and the European Council approved the concept of a mandatory and comprehensive European energy policy on 27 October 2005 in London.
See also:

Energy Service Company (ESCO)

An energy service company (ESCO or ESCo) is a professional business that provides a broad range of comprehensive energy solutions including the design and implementation of energy savings projects, energy conservation, energy infrastructure outsourcing, power generation and energy supply and risk management. The ESCO performs an in-depth analysis of the property, designs an energy efficient solution, installs the required elements and maintains the system to ensure energy savings during the payback period. Energy costs savings are often used to pay back project capital investment over a five- to twenty-year period, or are reinvested into the building to allow for capital upgrades that otherwise may be unfeasible. If the project does not provide a return on investment, the ESCO is often responsible for the difference.

Energy-supplying company

Usually, an energy-supplying company is an enterprise that either generates and supplies and distributes electricity, gas and/ or heat through a public supply system. Often an energy-supplying company also operates and owns energy distribution networks (electric power network, gas or heating network).

EU directive on the energy performance of buildings

The objective of the Directive 2002/91/EC on the Energy Performance of Buildings is to promote the energy performance of buildings within the European Community taking into account outdoor climatic and local conditions, indoor climate requirements and cost-effectiveness. The Directive was brought into force on 16 December 2002. Each member state was required to incorporate Directive provisions into national law by 4 January 2006. See also:

Extraction ventilation system

All air drawn out of the building interior by the ventilation system is called outgoing air. While the used air is extracted by a ventilator, fresh air is directed to the inside through regulated blowholes in the outer walls. The advantage of an extraction ventilation system is that the smells and humidity are extracted from the premises. The air volume may be regulated and ensures permanent inflow of fresh air not only at daytime but also throughout the night. The energy-saving effect is achieved in any case due to decrease of the air exchange, which may be further reduced.


An indicator showing transmission of energy into the building from outside as percentage. The more solar energy penetrates into the building through glazing in the form of radiant heat, the higher the energy transmission ratio (g-ratio) is. Therefore, a high g-ratio means a high heat accumulation. For an ideal radiation window, the g-ratio is 1.00 or 100 %. For conventional windows, this ratio varies between 0.7 and 0.9.

German International Climate Protection Initiative

On 5 December 2007, the German government adopted the Integrated Energy and Climate Programme (IEKP) to make an important contribution to attaining European and international climate protection goals. One component of this programme is the Climate Protection Initiative that uses income from the sale of CO² certificates through the emissions trading system to fund climate protection projects. This makes Germany the first country to invest the proceeds of certificate auctions directly into national and international climate protection measures.

The German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) promotes climate protection measures for increased energy efficiency and greater use of renewable energies. The International Climate Initiative supports measures for adapting to climate change in developing and newly industrialising countries. It aims to bring new momentum to negotiations on an international climate protection agreement for the post-2012 period. Thus, the initiative makes an important contribution to reaching ambitious climate protection targets in Germany, Europe and worldwide.

Since the beginning of 2008, the BMU has made available up to 400 million euro from the sale of emissions allowances for the Climate Protection Initiative. The Initiative is subdivided into two areas:

  • Promotion of sustainable energy supply
  • Adaptation to climate change impacts and conservation of biodiversity

This new form of environmental cooperation in these two priority areas will complement existing cooperative developmental activities and support their cost-effective implementation as well as promote innovative pilot projects.
See also:

Global (total) radiation

The total of direct solar radiation and diffuse sky radiation received by a unit horizontal surface. The Earth atmosphere reduces the space radiation (solar [radiation] constant) through interception, reflection and diffusion in a way that the intensity of radiation on the Earth surface on the middle European latitude (in the summer midday time under the clear sky) decreases approximately to 1.000 W/m2. The volume of solar energy varies depending on the geographical location, meteorological condition and astronomic regularities which also determine the sequence of the four seasons of the year. The total average annual radiation on a horizontal surface, for example, near Hannover, is about 1.000 kW-hour/(m2/year). This is approximately equal to the calorific value of 100 l of liquid fuel or 100 m3 of natural gas.

Heat demand

The unit which defines how much thermal energy is needed for heating. In the building sector it is called heating energy demand Qh which is indicated in Joule (J).

Heat load

The quantity of heat per unit time to be provided to maintain the temperature in a building at a given level, usually according to the normative requirements. The heat load is indicated in Watt (W).

Heat recuperation/recovery

(lat. recuperatіo – “return”) Heat recuperation is the partial return of energy within the same technological process, for example in buildings, when fresh incoming air is warmed up by warm outgoing air. Thus, the energy of hot air is not wasted through an open window.

Heat/thermal conductivity

Heat or thermal conductivity, k, is the property of a material that indicates its ability to conduct heat. Thermal conductivity is measured in watts per kelvin per metre (W K-1 m-1). Multiplied by a temperature difference (in kelvins, K) and an area (in square metres, m2), and divided by a thickness (in metres, m) the thermal conductivity predicts the power loss (in watts, W) through a piece of material.

Municipal energy management

Municipal energy management (in German Kommunales Energiemanagement – KEM) summarizes the various activities and initiatives to permanently reduce the energy consumption of municipal buildings within the municipality. There are two approaches: strategic and operational energy management. Through strategic energy management, a municipality develops long-term energy concepts for the entire municipality that provide a general orientation, not only for the building sector, but also for municipal services and administrative organization. With a practical orientation, operative energy management focuses on the analysis of the energy performance of individual buildings and services and the introduction of measures to reduce and optimize their energy consumption.

Passive house

The term Passive House (in German Passivhaus) refers to a rigorous, voluntary, passive house standard for energy efficiency in buildings. It results in ultra-low energy buildings that require little energy for space heating or cooling. The standard is not confined only to residential properties: several office buildings, schools, kindergartens and a supermarket have also been constructed to the standard. Passive design is not the attachment or supplementation of architectural design, but an integrated architectural design process. Although it is mostly applied to new buildings, it has also been used for refurbishments. Previous experience from other low-energy building standards include the German Niedrigenergiehaus (low-energy house) standard and that of buildings constructed to the demanding energy codes of Sweden and Denmark.

The Passive House standard for central Europe requires that a building fulfils the following requirements:

  • The building must not use more than 15 kWh/m² per year (4746 btu/ft² per year) in heating and cooling energy
  • Total energy consumption (energy for heating, hot water and electricity) must not be more than 42 kWh/m² per year
  • Total primary energy (source energy for electricity and etc.) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year (3.79 × 104 btu/ft² per year)

See also:


PHPP is an abbreviation for the German «Passivhaus Projektierungsрaket» (Passive House Planning (Design) Package) – a comprehensive software for the design of passive houses. This software may be used by architects to design passive houses, to determine energy balances and heat loads for specific buildings. The software was developed and implemented by the Passive House Institute Darmstadt in 1998.
See also:


PHVP is a simplified version of the PHPP software for the design of passive houses. It serves for the calculation of the expected heat consumption in the building during various phases of the design.

Porous bricks (cellular bricks)

Modern energy-saving requirements and improvements let to the production of bricks out of clay with many pores. Within a special technological process, a thin structure of pores and capillaries is created to provide clay with pores. Hence the name Poroton (= "pores" and Ton – "clay" in German). The porous structure works as an air layer and improve the thermal insulation characteristics significantly. In addition, such bricks "breathe" naturally by absorbing and releasing air humidity.

Primary energy

Primary energy is energy that has not been subjected to any conversion or transformation process. Primary energy is energy contained in raw fuels and other forms of energy system inputs. Primary energy includes non-renewable and renewable energy. Primary energies are transformed in energy conversion processes to more convenient forms of energy such as electrical energy and cleaner fuels. In energy statistics, these forms are called secondary energy.


(Lat. recuperator – “the one which returns”) A recuperator is a special purpose counter-flow energy recovery heat exchanger used to recover waste heat from exhaust gases. In many types of processes, combustion is used to generate heat, and the recuperator serves to recuperate, or reclaim this heat, in order to reuse or recycle it. As opposed to a regenerator, the heat carrier channels in the recuperator do not change. Recuperators are classified: by the schemes of heat carriers' relative movement - into reverse-flow, direct-flow and others; by construction - into tubular, plate, ribbed and others; by use - into those for heating of air, gas or liquids, evaporators, condenser, etc.

Renewable energy

Renewable energy is energy generated from natural resources such as sunlight, wind, rain, tides and geothermal heat that are renewable or naturally replenished.
See also:

Secondary energy

Primary energies are transformed in energy conversion processes to more convenient forms of energy, such as electrical energy, refined fuels, or synthetic fuels such as hydrogen fuel. These forms are called secondary energy.
See also: Primary energy

Thermal conductivity coefficient

The thermal conductivity coefficient (U-value) is the intensiveness of heat losses, the volume of heat penetrating 1 m² of a certain structure (for instance, wall or roof) per unit time. The lower the U-value, the higher the structure's heat insulation qualities.

Thermal expansion coefficient

The coefficient of thermal expansion describes how the size of an object changes with a change in temperature. Specifically, it measures the fractional change in volume per degree change in temperature at a constant pressure. The R-value, thus, is the inverse of the thermal conductivity coefficient, the U-value, which reflects the structure's resistance to heat losses. The higher the R-value, the higher the thermal comfort of the structure.

Ventilation system with heat recovery

For sanitary and hygienic reasons, buildings must be ventilated. Heat recovery ventilation is an energy recovery ventilation system, using equipment known as a heat recovery ventilator, heat exchanger, air exchanger or air-to-air exchanger that employs a counter-flow heat exchanger between the inbound and outbound air flow. It provides fresh air and improved climate control, while also saving energy by reducing the heating (or cooling) requirements.

Thermal bridge

A thermal bridge is created when materials that are poor insulators come in contact (windows, doors, angles of premises, structure junctions, etc.), allowing heat to flow through the path created. Insulation around a bridge is of little help in preventing heat loss or gain due to thermal bridging; the bridging has to be eliminated, rebuilt with a reduced cross-section or with materials that have better insulating properties, or with an additional insulating component.

WLG – Thermal conductivity group

The WLG indicator reflects the maximum heat conductivity (U-value) of insulation materials. The lower the indicator, the higher the material's insulation qualities. Depending on the heat conductivity group, various materials of the same thickness have different thermal insulating qualities. Typical insulation materials, such as polystyrene or mineral fibre have a U-value of 0,04 W/mK and, thus , belong to the WLG 040 heat conductivity group. With the same thickness of the insulation layer of the WLG 035 materials, the insulation qualities are improved by 12%.