Glossary/ Abbreviations
Please find below a brief explanation of various terms and abbreviations used on this website:
Air Exchange Rate: Either m3/h or in fractions of the total volume of the house per hour. You need a certain rate of air changes for health reasons (fresh air, counter-act summer overheating) and to avoid excess moisture in the home, but excessive and/or uncontrolled air changes means loss of energy.
Air leakage: is the uncontrolled movement of air in to and out of a building which is not for the specific and planned purpose of exhausting stale air or bringing in fresh air.
Air tightness testing: See Pressure test.
BREEAM: BRE Environmental Assessment Method. It is the widely used environmental assessment method for buildings, which takes a wide range of sustainable aspects into consideration. It sets standards for best practice in sustainable design and is a measure used to describe a building's environmental performance.
BREDEM: Building Research Establishment Domestic Energy Model. Estimating cooking, lights, appliances and hot water use and working out heating demands using RDSAP or SAP.
BRE Digest 398: Study paper referred to by the Scottish planning offices in regards to the specification of MVHR systems.
Carbon footprint: a measure of the impact our activities have on the environment through CO2 emissions. It relates to the amount of greenhouse gases produced in our day-to-day lives through burning fossil fuels for electricity, heating and transportation etc. The carbon footprint is a measurement of all greenhouse gases we individually produce and has units of tonnes (or kg) of carbon dioxide equivalent.
CHP: Combined Heat and Power. A replacement for boilers with economic and environmental benefits, simultaneously producing heat and power.
COP: Consumption over Production. E.g. a COP of 3.5 means that (at e.g. at 10ºC outside temperature and DHW temperature of 40ºC) the device (e.g. heat pump) will use 1kW for every 3.5kW put out.
CPSU: Combined Primary Storage Units – a boiler with a thermal store all in the same casing.
CSH: Code for Sustainable Homes. Valid in England, Wales and Northern Ireland.
DER: Dwelling Emission Rate (annual CO2 per sqm) due to space heating, water heating, ventilation and internal lighting minus any CO2 emissons saved by any generation of electricity.
DHW: Domestic hot water.
EI: Environmental Impact rating. Based on estimated annual CO2 emmissions per sqm due to space heating, hot water heating, ventilation and internal lighting – minus any CO2 emissions saved by any generation of electricity. Figure between 1 and 100+, rounded to the next integer, with the higher the number the better the standard. EI rating of 100 corresponds to zero net CO2 emissions. May also be expressed in bands (like SAP).
Embodied energy: Energy used to produce a building material, including its transport.
EPBD: Energy Performance in Buildings Directive. EU requirement for each EU member state to implement:
• A national methodology for calculating the energy performance of buildings.
• Minimum energy standards for new buildings.
• Minimum energy standards fo most existing buildings, when they are renovated.
• Certification of the energy performance of buildings.
• Regular inspections of large boilers and air conditioning systems.
EPC: Energy Performance Certificate. Issued by the OCDEA. Energy rating ”as built” (i.e. including actual – not planned – figures and components). Benchmark or energy performance & recommendations for cost effective improvement of energy performance. To be included in the HIP.
ER: The Energy Rating (ER) value is calculated using a formula that balances a product's U-value with its potential solar heat gain coefficient (SHGC) and its airtightness. The higher the number, the more energy efficient the product.
Fuel poverty: Households with energy costs that exceed 10% of their income.
FSK: Mark that indentifies sustainably grown timber.
G-value: Solar heat gain coefficient (SHGC). Measure of the solar heat passing through a window, which can be harvested for heating up a dwelling. The value is influenced by the panes of glass and coating, which absorb and reflect heat. E.g. a g-value of 0.6 means that 60% of heat passes through the glass/ window.
GHX: Ground heat exchanger, used to pre-warm the intake air for MVHR systems in winter and pre-cool it in summer. For domestic application often a 30-50m duct of 200mm - 250mm diameter is used. Special attention has to be paid to the drainage of condensed water.
HRV: Heat Recovery Ventilation, see MVHR.
Heat exchanger: Used in MVHR systems to transfer heat from the extract air to the supply air; also used to transfer heat from heat pumps or solar collectors to heating systems and domestic hot water.
Heat load: this measures the capacity of the space heating system required to maintain comfortable indoor temperatures at any one time, specified in Watts per square metre of treated floor area, or W/m2. For a house with, for example 110m2 treated floor space, if the annual space heat requirement is at the maximum of 15kWh/(m2a), the energy consumption for heating would be 1,650 KWh over an entire year. See space heat requirement.
Heat pump: A device extracting heat from a source of a lower level of temperature (e.g. outside air or ground) and ”pumping it up” to a higher, more useful level for space heating and DHW (domestic hot water). With some, the process can be reversed to extract heat from the building (air conditioning).
Standard form of heat pumps are ground source heat pumps and air source heat pumps
HIP: Home Information Pack. Since 14 December 2007 every home put on the market, no matter what size, must have a Home Information Pack. It brings together valuable information at the start of the process - such as a sale statement, local searches and evidence of title. The Pack also includes an Energy Performance Certificate with advice on how to cut CO2 emissions and fuel bills.
Lambda (λ): The Lambda value is the intrinsic figure for the thermal conductivity of a material. The unit is W/(mK). If the figure high, e.g. 220W/(mK) for aluminium, then the material is a good conductor of heat. If it is low, e.g. 0.035W/(mK) for silk, then the material makes a good thermal insulation.
Latent heat cells: High-performance thermal stores, which operate with phase changing material. Ideal for small units or where there is not much space for a heat store (can e.g. be placed in the corner of a roof).
MVHR: Mechanical Ventilation with Heat Recovery, also called HRV. Controlled exchange of air which requires a high standard of air tightness. Up to 90+% of energy can be recovered that would otherwise be lost in during the air exchange process.
NHER: National Home Energy Rating. A figure between 0 (= a tent with an electric fire) and 20 (= Significant local generation of electricity, zero running costs), based on annual fuel running costs per sqm and using standard occupancy conditions and deflated three year average fuel prices. Fully authorised to deliver SAP ratings. Includes SAP plus cooking and appliances but on actual location. Most new homes are around 9.
OCDER: On Construction Domestic Energy Assessor. Only one authorised to issue EPC's.
Part F ...of Building Regulations. Requirements for Northern Ireland to meet Energy Performance levels.
Part L1A ...of the English Building Regulations. Requirements for England and Wales to meet Energy Performance levels.
PH: Passive House or Passivhaus. A concept of building to an extremely high level of insulation and airtightnes, developed by Dr. Feist from Germany. Average energy saving on space heating compared to a standard house is 80-90%!
PHI: The German Passivhaus Institute.
PEA: Predicted Energy Assessment. Issued by the Plan Assessor. For new homes sold from plan; to be included in the HIP and to be replaced by ”as built” EPC within 15 working days of completion.
PHPP: Passivhaus Planning Package. A very accurate energy assessment tool for consultants and architects. It goes along with the design process of the building and is used in the certification process of passive houses.
PHVP: Passivhaus Pre-Planning. The simplified version of PHPP, including (more) standard values to get approximate results in the planning phase.
Plan assessor: Certified / authorised to assess plans for new buildings and issue PAEs as well as giving advice on energy performance improvements.
Pressure test: Also called air permeability test. This measures the air tightness of a building (m3/h at 50Pa) and is needed for the EPC. The Building Regulations 2006 standard is 10 m3/hr/m2
Psi (Ψ): The PSi-value is related to the lambda-value (also in W/(mK)), but in this case it denotes the thermal conductivity of an assembly of materials, e.g. the edge of a window glazing panel, where glass sheets, one or more spacers and the window frame, with one or more different material, come together. It describes therfore the thermal bridging of that detail. The higher the figure, the higher the heat loss through that detail. Figures of 0.01W/(mK) and smaller are considered "thermal-bridge-free" and this is what detailed planning of a Passive House is aiming for. In some special cases (e.g. for detais where a well-insulated wall meets a well-insulated floor slab), the value might go even below 0, i.e. negative.
PV: Photovoltaic. Generation of electrical power from (sun) light.
Phase changing material: Material that absorbs heat to a certain temperature and releases heat at a certain temperature. Used to store heat e.g. during sunshine and release the heat again when the temperatures drop. E.g. paraffin is a phase chaning material, which has a 4 times better heat storage capacity than water. Used in heat storage cells or plaster board. See latent heat cells and thermal mass.
RDSAP: Reduced Data SAP. Survey system used to produce EPCs for existing homes.
Radon: a naturally occurring radioactive gas formed as a result of the radioactive decay of uranium, which is more or less present in all rocks and soils. It can accumulate in buildings and can be harmful to the health of the inhabitants. Constant ventilation, e.g. through MVHR systems, decreases the accumulation of radon gas drastically.
Renewable energies: Thermal and electrical energy derived from sources other than fossil fuels (oil, gas and coal).
R-value: The R value or R-value is a measure of thermal resistance of materials. The R-value is independant of the thickness of the material. The higher the R-Value number, the more insulative the product is. R-value is the reciprocal of U-value.
SAP: Standard Assessment Procedure for new homes. Independed of location (using a ”standard location”) and including lights, heating and hot water but not cooking and appliances. Rating scale is from 1 to 100+ with the higher the number the lower the fuel running costs. 100 corresponds to zero running costs, so the rating can be over 100 if surplus energy is exported. SAP rating provides the basis for the ECPs, which place the rating on an A-G scale (similar to what you would find on white goods).
Section 6 ...of Building Regulations. Requirements for Scotland to meet Energy Performance levels.
SHGC: Solar heat gain coefficient; see G-value.
Solar heating: Generation of hot water (and in some cases additional space heating) through sunlight.
Space Heat Requirement: this measures the amount of energy that is needed to maintain a comfortable indoor temperature, specified in kilowatt hours per square metre of treated floor area per year, or kWh/(m2a). See heat load.
TER: Target Emission Rate (CO2). The DER must not exceed the TER for a notional dwelling of the same size and shape.
Thermal envelope: In contrast to the building envelope. It sets the boundaries for the insulation and airtightness line between the inside and outside of a building. E.g. a cold loft is outside the thermal envelope.
Thermal imaging: Survey which detects thermal losses through a buildings fabric.
Thermal mass: The capacity of the structure of a building to store heat. Helps to level out indoor temperatures and reduces the risk of overheating in summer. Concrete, stone or phase-changing materials all have a high thermal mass.
Thermal store: Used to store heat for hot water and/or space heating.
Treated floor area: The internal area of the building, which is heated. Roof spaces below 1m height are not included and from 1-2m they are included only 50%.
URN: Unique Reference Number. All property assessments are identified by an URN.
U-value: A measure of the rate of heat transfer through a building component, such as window or wall by the means of convection, conduction and radiation. Units = W/(m2K). The smaller the u-value, the better the insulation.
