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Glossary of Energy Efficiency terms

Types of buildings

New building

New buildings are completely new erected. They are constructed by respecting the newest laws and standards, including meeting minimum energy performance requirements laid down in national legislation. A building will be called new, until newer legislation, newer energy performance standards or refurbishments had taken place. 

Existing building

Existing buildings are representing older energy standards. For these buildings data necessary to assess their energy use are known or can be measured. A new building will become an existing building, as soon as newer standards and energy requirements are published by the national legislations. 

Public building

The building is occupied by public authorities or provides public services to a large number of persons. It is frequently visited by members of the general public e.g., administration buildings, schools, hospitals and buildings for sports. Public funding is used for its maintenance.

Residential house

Occupied or unoccupied, owned or rented, single-family or multifamily house, excluding institutional housing such as hostels or school dormitories, hospitals, night shelters, and military barracks. Types of residential houses:
· detached house (free standing house e.g., for a single family)
· semi-detached or twin house (a pair of houses built side by side as units sharing a party-wall and usually in such a way that each house's layout is a mirror image of its twin)
· row house (a row of identical or mirror-image houses share side walls;
the first and last of these houses are often larger than those houses in the middle)
· a multi-storey residential building contains more than one apartment, drawn together in one building structure. Mostly with similar storey-plans, it has centralized staircases and supply units. 

Social housing

 Social housing is a paraphrased term referring to rental housing, which may be owned and managed by the state, municipal house building associations or by mutual benefit organizations. A key function of social housing is to provide housing that is affordable to people on low incomes. Rents in the social housing sector are kept low through state or municipal subsidy.

Pre-fabricated building

 Buildings which are partially or completely built in factories. Most of the prefabricated buildings are made of wooden or of concrete elements which will be completed on site.

Types of energy efficient buildings

Passive house

A passive house is a building in which a comfortable room temperature of about 20oC can be achieved without conventional heating and cooling systems. Such buildings are called „passive“, because the predominant part of
their heat requirement is supplied from „passive“ sources, e.g., sun exposure and waste heat of persons and technical devices. The heat still required can be delivered to rooms by the controlled ventilation system with heat recovery. The annual heat demand for passive house is very low - in the middle of Europe about 15 kWh/m²/year). The need for total primary energy use should not exceed 120 kWh/m²/year), including heating and cooling, domestic hot water, and household electricity. The basic features that distinguish passive house construction: compact form and good insulation; southern orientation and shade considerations; good air tightness of building envelope; passive preheating of fresh air; highly efficient heat recovery from exhaust air; using an air-to-air heat exchanger; hot water supply using renewable energy sources; using energy saving household appliances. The design of passive houses is a holistic process of planning and realization. It can be used for designing new buildings or for energy renovation of existing buildings.

Low energy house

Generically said, a low-energy house is any type of house that uses less energy than a regular house but more than a passive house. Energy performance of a low-energy house is about half lower than the minimum requirement. There is no global definition for low energy house because national standards vary considerably among countries. For example, in Germany a “low energy house” has an energy consumption limit of 50 kWh/m²/year for space heating.

Energy - selfsufficient building

An energy-self-sufficient building is completely independent of external power supply. Electricity and heat are produced and stored completely with e.g. micro power plants or active solar systems in or at the building.

Engineering networks (heating, cooling, ventilation)

Passive heating

At passive heating a large part of the heat for heating is covered over internal profits, i.e. the heat emission by persons and devices as well as over solar profits (heat entry over the windows).

Passive cooling

Passive cooling is minimising heat gain from the external environment (e.g.,by shading a building from the sun and insulating the walls) and removing unwanted heat from a building e.g., by using natural ventilation.

Natural ventilation

Process of supplying and removing air of an interior room with air from the outside by openings and leakages in the building shell/envelope. There are two principles of natural ventilation: wind driven ventilation and stack ventilation. Stack ventilation is generated by a difference in the density of warm interior air and the cold air from outside. Both ventilation systems are depending on the weather and so they are uncontrollable, mostly too low or much too strong. Modern, energy efficient buildings are working with controlled mechanical ventilation“ (by fans) - the antonym for „natural ventilation“.

Controlled ventilation with heat recovery

Ventilation is a necessary procedure of replacing the used up interior air by air from outside. Through a duct – system, the air from outside is being drawn in by electrically propelled fans (direct current motors). It is filtered, and led to a heat transducer, optionally warmed up and then led into the individual areas (e.g. living room, sleep area, classroom, work spaces). Used up air is drawn off in the kitchen, bath-room, toilets and led by the way of a
second duct system to the heat transducer and blown outside. The amount of air needed per person amounts to approx. 20-30 m³/h. A controlled ventilation system with heat recovery is necessary for all energy-efficient buildings. The efficiency for high-efficient heat recovery systems is over 90%.

Thermal comfort

Human thermal comfort is defined as the state of mind that expresses satisfaction with the surrounding environment. Maintaining thermal comfort for buildings’ inhabitants is one of the most important goals for engineers when designing plans for heating, ventilation, air conditioning and the building envelope. Factors, which determine thermal comfort are: indoor and outdoor air temperature, air movement, relative humidity, clothing people are wearing and the activity level they are engaged in.

Air humidity

Humidity is the amount of water vapour in the air. Water sources in buildings are:
· the exhalation of people staying inside (dependent on the level of the
physical work);
· the utilization of the room (drying, cooking, working, doing sports);
· “free water” which is coming into new buildings by manufacturing the materials and by the manufacturing process of the building itself.
To describe the amount of water vapour in the air the “relative humidity” is used. Comfortable feeling for a human being is at relative air humidity around 50% (air temperature of 20°C).

Energy performance of buildings

Minimum energy performance requirements Member States should set minimum requirements for the energy performance of buildings and may differentiate between new and existing buildings as well as different categories of buildings. The requirements should be set with a view to achieving the cost-optimal balance between the investments involved and the energy costs saved throughout the life-cycle of the building.

Energy audit 

Inspection, survey and analysis of energy flows in a building with the objective of understanding the energy dynamics of the system. Typically an energy audit is conducted to seek opportunities to reduce the amount of energy input into the system without negatively affecting the output. It seeks to prioritize the energy usage according to the greatest to least cost effective opportunities for energy savings. Member States shall ensure the
availability of efficient, high-quality energy audit schemes which are carried out in an independent manner, to all final consumers.

Energy performance certificate

It shows energy performance of a building. Member States shall ensure that, when buildings are constructed, sold or rented out, an energy performance certificate is made available to the owner or by the owner to the prospective buyer or tenant, as the case might be. The validity of the certificate shall not exceed 10 years. The energy certificate for buildings shall include reference values such as current legal standards and benchmarks in order to make it possible for consumers to compare and assess the energy performance of the building. The certificate shall be accompanied by recommendations for the cost-effective improvement of the energy performance.

Major renovation

Renovation is changing or substitution of parts of a building. A major renovation is the case, where the total cost of the renovation related to the existing building is more than 25% of the value of the building (exclusive the land where the building is situated) or the case where more than 25% of the building shell undergoes renovation.

Blower door test

A diagnostic tool developed to measure the air tightness of a building and to help locate air leakage sites. The test procedure consists of the measurement of the volumetric air flow, which is produced by the differential pressure by a calibrated fan. With a differential pressure of 50 Pa the air flow volumes is determined [m³/h]. The change of air rate is determined by division with the internal air volume of the building. SI-Unit: [h-1].Typical values for the air-change-rates (n50) are:
· untight building: n50 > 3 h-1
· low-energy house: n50 < 1,5 h-1
· passive house: n50 < 0,6 h-1

Building shell /building envelope

A building shell is the separation between the interior and the exterior environments of a building. The building shell includes the roof, the walls, the doors and the windows, as well as the bottom slab and encloses thereby the heated or air-conditioned space volume.

Floor area Floor area gross

Total floor area of all floors of a building calculated with the external dimensions of the building including structures, partitions, corridors and stairs.

Floor area net

Sum of all areas between the vertical building components (walls, partitions), i.e. gross floor area reduced by the area for structural components.

Floor area usable

The fraction of the net floor area for the intended use of the building, i.e. net floor area reduced by circulation areas (corridors, stairs etc.) and Floor area usable The fraction of the net floor area for the intended use of the building, i.e. net floor area reduced by circulation areas (corridors, stairs etc.) and functional areas (WCs, storage rooms etc.).

Thermal bridge

An area in the building envelope which has a higher heat flow than the surrounding is called a thermal bridge. A classic thermal bridge is the overhanging balcony plate, leading through an insulated outer wall. Typical effects of thermal bridges are: decreased interior surface temperatures; in the worst cases this can result in high humidity in parts of the construction; significantly increased heat losses.

Air tightness of buildings

Airtight building is a building in which no air can get in or out through any kind of leakage. The air tightness of a building is a useful knowledge when trying to increase energy efficiency. If the building envelope is not airtight enough, significant amounts of energy may be lost due to exfiltrating air, or damage to structural elements may occur due to condensation. To ensure the necessary air-change rates, it has to be ventilated manually (by opening the windows) or by an air ventilation system.

Energy balance of a building

Energy balance of a building refers to the sum of the heat losses (e.g., heat going out through the roofs, external walls and windows) being equal to the sum of the heat gains (e.g., passive solar gains, internal gains and active heating).


Heat transmission coefficient (thermal transmittance) of a structure, describes the heat flow through a building element in W per m2 and temperature difference of one kelvin (K). SI-Unit: [W/(m2K)]. The higher the value the lower its thermal resistance and therefore the more heat/energy pass through the element. Examples of U-values depending of material
thickness (λ=0,040 W/(mK)):
· 10cm: U = 0,4 W/(m²K)
· 20cm: U = 0,2 W/(m²K)
· 40cm: U = 0,1 W/(m²K)
U-value is equal to the inverse of the sum of the R-values (thermal resistance) of the construction. SI-Unit: [(m²K)/W].

Double/triple glazing

Windows made by glazing with two or three glass panes. The inter-space between the panes is filled with gas in order to reduce the transmissions of energy. To reduce the solar radiation, the surface of one or more panes is
coated. Typical values are:
· 2-panes-glazing: Ug = 2,8-3,0 W/(m²K)
· 2-panes-heat protection glazing: Ug = 1,1-1,3 W/(m²K)
· 3-panes-heat protection glazing: Ug = 0,6-0,8 W/(m²K)

Energy production

Primary energy

Energy that has not been subjected to any conversion or transformation process. Primary energy includes non-renewable energy and renewable energy. If both are taken into account it can be called total primary energy. Co-generation Simultaneous conversion of primary fuels into thermal energy and electrical energy, meeting certain quality criteria of energy efficiency. Also known as combined heat and power (CHP).

White certificate

A document certifying a certain reduction of energy consumption, which has been attained by companies (energy producers, suppliers or distributors) in the energy market. In most applications, the white certificates are tradable.
Corresponding to the closely related concept of “emission trading”, it should guarantee, that the overall energy saving target is achieved. The system of the “white certificates” has to be set up and controlled by government bodies.

Sustainable approach

Holistic planning

A process, which tries to integrate a lot of different factors into the planning of urban & environmental areas. The importance is drawn on all affecting factors, like: all involved parties and their needs, the expertise of the designers, cost effectiveness over the entire life-cycle of the building, security, accessibility, flexibility, aesthetic and sustainability, the location of the property and used building materials.

Green public procurement

Green public procurement means that contracting authorities and entities take environmental issues into account when tendering for goods or services with tax payers money in order to reduce the impact of the procurement on human health and the environment. Examples - energy efficient computers and buildings, environmentally friendly
public transport, recyclable paper, organic food in canteens, electric cars, office equipment made of environmentally sustainable timber, electricity stemming from renewable energy sources, air conditioning systems
complying with state-of-the-art environmental solutions.

Women's journal ReLady