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Important definitions when talking about Energy Efficiency

When talking about energy efficiency, the terms can sometimes be confusing.  Below is a short list of terms related to energy efficiency in domestic and non-domestic buildings.

Air-conditioning system: a combination of all components required to provide a form of air treatment in which temperature is controlled or can be lowered, possibly in combination with the control of ventilation, humidity and air cleanliness [EPBD, 2002/91/EC]

Air Infiltration: Air infiltration is the uncontrolled entry of fresh air into a building through air leakage paths, e.g. gaps at junctions between external building elements and around openings, unsealed penetrations of the building envelope accommodating services.

Boiler: the combined boiler body and burner-unit designed to transmit to water the heat released from combustion [EPBD, 2002/91/EC]

Building Envelope: The building envelope is the line of separation between the inside and outside environments of a building.

Building Physics: Building Physics refers to Applied Science dealing with the hygrothermal (the movement of heat and moisture through buildings), acoustical and light related properties of building components (roofs, facades, windows, partition walls etc.), rooms, buildings and building assemblies. Basic considerations include requirements for thermal, acoustic and visual comfort, healthy environment within limitations imposed by architectural, material related, economic and ecological considerations [Building Physics – Heat, Air and Moisture, Hugo Hens, 2007, Ernst and Sohn]

Combined heat and power (CHP): Onsite or decentralised electricity generation plus the recovery and use of the heat by-product of the generation process for secondary use such as steam production, process and space heating.

Commercial building: A commercial building is a building that is used for commercial use. Types can include office buildings, warehouses, or retail i.e. convenience stores, ‘big box stores, shopping malls, etc.

Cost-optimal level: Cost-optimal level means the energy performance level which leads to the lowest cost during the estimated economic lifecycle [EPBD, recast, 2010/31/EC]

Deep Retrofit: We define deep retrofit as an investment in energy efficiency which saves the homeowner 40% or more on energy bills. A deep retrofit investment will generally involve a combination of roof and wall insulation, a new renewable or highly efficient heating system, and heating controls. [Thinking Deeper – Financing Options for Home Retrofit, Joseph Curtin & Josephine McGuire, 2011]

District heating/cooling: means the distribution of thermal energy in the form of steam, hot water or chilled liquids, from a central source of production through a network to multiple buildings or sites, for the use of space or process heating or cooling [EPBD, 2010/31/EC]

Energy audit: a systematic procedure to obtain adequate knowledge of the existing energy consumption profile of a building or group of buildings, of an industrial operation and/or installation or of a private or public service, identify and quantify cost-effective energy savings opportunities, and report the findings [ESD, 2006/32/EC]

Energy consumption: The amount of energy consumed in the form in which it is acquired by the user. The term excludes electrical generation and distribution losses.

Energy performance certificate: a certificate recognised by the Member State or a legal person designated by it, which includes the energy performance of a building calculated according to a methodology based on the general framework set out in the Annex of Directive 2002/91/EC [EPBD, 2002/91/EC]

Energy performance of a building: the amount of energy actually consumed or estimated to meet the different needs associated with a standardised use of the building, which may include, inter alia, heating, hot water heating, cooling, ventilation and lighting. This amount shall be reflected in one or more numeric indicators which have been calculated, taking into account insulation, technical and installation characteristics, design and positioning in relation to climatic aspects, solar exposure and influence of neighbouring structures, own-energy generation and other factors, including indoor climate, that influence the energy demand [EPBD, 2002/91/EC]

Energy service company (ESCO): a natural or legal person that delivers energy services and/or other energy efficiency improvement measures in a user’s facility or premises, and accepts some degree of financial risk in so doing. The payment for the services delivered is based (either wholly or in part) on the achievement of energy efficiency improvements and on the meeting of the other agreed performance criteria [ESD, 2006/32/EC]

Final energy: Energy supplied that is available to the consumer to be converted into useful energy (e.g. electricity at the wall outlet). [Intergovernmental Panel on Climate Change, IPCC]

Heat pump: a device or installation that extracts heat at low temperature from air, water or earth and supplies the heat to the building [EPBD, 2002/91/EC]

Nearly zero energy building: a building that has very high energy performance, as determined in accordance with Annex I of the EPBD recast. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby [EPBD recast, 2010/31/EC]

Pay as You Save Scheme (PAYS): A method of financing dwelling energy retrofit improvements. The debt on capital cost for energy retrofit improvements is charged on the property or directly to the energy utility supplier meter in a dwelling by way of a legal charge on the energy bill (PAYS tariff) or property tax. The capital cost is then offset by the accrued energy savings, either on the energy bill or in the form of a carbon credit reduction to the rate of property tax.

Payback time/period: the length of time required to recover the cost of an investment

Primary energy: Energy from renewable and non-renewable sources which has not undergone any conversion or transformation process

Public building: building owned or occupied by any public body

Residential building: A structure used primarily as a dwelling for one or more households. Residential buildings include single-family houses (detached houses, semi-detached houses, terraced houses (or alternatively row houses) and multi-family houses (or apartment blocks) which includes apartments/flats

Thermal Bridging: Fundamental of heat transfer that occurs in building envelopes when materials with high thermal conductivity (also called noninsulating material), such as steel, timber and concrete create pathways for heat loss that bypass thermal insulation.

Thermal Conductivity: the property of a material to conduct heat.

U-Value: U-value is the measure of the rate of heat loss through a material. It represents the amount of heat lost through one square meter of the material for every degree difference in temperature either side of the material. It is indicated in units of Watts per meter Squared per Degree Kelvin or W/m²K

Ventilation: Ventilation is the controlled supply of outside fresh air to a building by natural and/or mechanical systems.

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