Glossary

Glossary 
AECBThe Sustainable Building Association, formerly known as the Association for Environment Conscious Building.
BreathableThe ability of a material or building assembly to allow water vapour through it by diffusion.
BREEAMBuilding Research Establishment Environmental Assessment Method.
Certified Passivhaus DesignerAn individual who has trained (taken a Passivhaus-Institut [PHI]-recognised Certified European Passive House (CEPH] course and PHI CEPH examination) and qualified in the principles and methodology needed to design a Passivhaus. It is also possible to gain Certified Passivhaus Designer status by designing and building a Certified Passivhaus building, although this is generally seen as a harder and potentially riskier way to become a Certified Designer.
Chi-value ()Similar to psi-value (w), this measures the rate at which heat passes through a material that penetrates another material at a point, where the penetrating material conducts heat better than the surrounding material: for example, a metal bolt, used to mount a balcony, that passes through an external wall. In a Passivhaus chi-value is used to measure heat loss in a point thermal bridge. It is measured in W/K (watts per kelvin).
DiffusionThe thermal motion - movement driven by temperature - of all liquid and gas particles. The speed of the motion depends on the temperature and the particle size. Diffusion explains how particles move from a place of higher concentration to one of lower concentration (across a vapour pressure differential or gradient), but it also occurs, more slowly, where there is no pressure differential.
DuctsThe pipes that run between the building's thermal envelope and the MVHR unit and between the MVHR unit and the various supply and extract points within the building. The intake duct (sometimes referred to as the 'ambient' duct) takes fresh air from outside into the MVHR. The supply duct takes that air (now containing the heat recovered by the MVHR unit) to supply vents in the living room and bedrooms. The extract duct takes old air from the bathroom(s) and kitchen back to the MVHR unit. The exhaust duct takes the now-cold air back outside.
EnerPHitThe Passivhaus Institut's energy performance standard for retrofits. It allows a maximum annual space heat demand higher than that of Classic Passive House and an upper airtightness limit of 1.0ach. There is also the component method. Note the moisture criteria of the full Passive House Certification must still be met.
Home Energy Rating System (HERS)A measure of (primarily) energy efficiency; mainly used in the USA. A HERS index of 100 means a home meets the code standard that is based on a standard US house; a HERS index of 70 means the home is 30-per-cent better than the code standard. The report generated advises on potential improvements to an existing property.
HygroscopicityThe property of a material to absorb, retain and release moisture from the ambient air. Materials that readily do this are often described as hygroscopic.
Indoor air quality (IAQ)The quality of air within buildings, in regard to both health and comfort. Indoor air often contains a complex mixture of contaminants and common pollutants, including smoke, volatile organic compounds (VOCs) and moulds. The level of carbon dioxide (CO) in indoor air also relates to IAQ, and is an accepted marker for the wider mix of potential indoor air pollutants. ASHRAE issues guidelines on acceptable IAQ.
Internal heat gainsThe heat gains in a building from its occupants and the use of appliances within the thermal envelope. See energy balance. Interstitial condensation Condensation that occurs within a building assembly, when warm moist air (generally from inside a heated building in winter) penetrates into the assembly, meets a cold surface and condenses.
Form factorThe ratio of the external area of the thermal envelope to the treated floor area (TFA). Form factor is a measure of how compact the build design is. It is broadly similar to the area:volume ratio.
Lambda valuealso known as k-value A measure of thermal conductivity, measured in W/mK (watts per metre [depth) per degree kelvin). The inverse is the R-value.
Leadership in Energy and Environmental Design (LEED)A US sustainability rating system, broad-based and internationally recognised.
Mechanical ventilation with heat recovery (MVHR)Also known as heat recovery ventilation (HRV) or comfort ventilation A whole-house ventilation system that takes out heat from the old (exhaust) air and gives it to the new (intake) air. Fresh air is delivered to living areas (e.g. living room and bedrooms) and extracted from kitchens and bathrooms. MVHR units do not supply new heat into the supplied air. However, a supply duct radiator can be used to add heat to the new air after it leaves the MVHR unit.
NZGBCNew Zealand Green Building Council https://www.nzgbc.org.nz/
Parts per million (ppm)Used to measure atmospheric concentrations of pollutants and other gases, including carbon dioxide (CO2).
Passivhaus Institut (PHI)The independent foundation established in Germany in 1996 to develop, promote and protect the Passivhaus standard. Known as the Passive House Institute in English-speaking countries.
Passivhaus Planning Package (PHPP)The energymodelling design tool created by the Passivhaus Institut (PHI) to accurately predict energy performance. It is the basis for designing and certifying Passive House, PHI Low Energy Buildings and EnerPHit builds.
Off-gassingThe evaporation of volatile chemicals (including volatile organic compounds [VOCs]) at atmospheric pressure and room temperature.
Thermal bypassA type of thermal bridge caused by air movement in the insulation layer or around it (like a road bypass).
Relative humidity (RH)How much water vapour there is in a bit of air compared to the maximum before there is condensation. This varies significantly with temperature. Note above 70% RH it is difficult to prevent mould growth on surfaces which are typically colder than the air in the building.
SpacerThe dividing strip along the edge of a double or triple-glazed unit that separates each pane. Warm edge spacers are made from material or materials with a lower conductivity. The energy performance of a spacer is measured by its psi-value (v).
Specific heat capacity
The amount of heat required to change the temperature of a unit of a material by a given amount. (In standard metric units, it is the number of joules required to raise 1 gram of the material by 1 degree kelvin.) Specific heat capacity is a measure of a material's thermal mass.
Thermal conductivityalso known as conductivity A material's ability to transmit heat, measured by the lambda value. Unlike U-value, the lambda value of a material remains the same irrespective of the thickness of the material. Lambda values do sometimes vary with temperature.
Thermal envelopeThe surfaces that contains the building's conditioned spaces. This includes the floor area and for Passive House tools such as PHPP is always the external surface. This means the bottom of the insulation below the concrete slab to the top of the insulation in the ceiling.
Thermal massThe ability of a body of material to absorb, store and subsequently release heat (due to its specific heat capacity and its mass).
Thermal resistivityalso known as resistivity (but not to be confused with vapour resistivity - see vapour permeability) A material's ability to resist the passage of heat. It is the mathematical inverse of thermal conductivity.
Treated floor area (TFA)A convention for measuring usable internal floor area within the thermal envelope of a building.
U-value measure of the ease with which a material or building assembly allows heat to pass through it; in other words, how good an insulator it is. The lower the U-value, the better the insulator. The U-value is used to measure how much heat loss there is in a wall, roof, floor or window, and is measured in W/m2K (watts per square metre per degree kelvin).
Passive House Planning Package (PHPP)The Excel software tool which is used to build an energy model of buildings and determines if they meet the Passive House Institutes building standards.
Vapour barrier also known as vapour-closed A material that is nearly-impermeable to water vapour, e.g. aluminium foil.
Vapour-openA material that is permeable to water vapour, e.g. a 'breathable' or 'breather' membrane (these are both airtight and liquid-moisture-tight but vapour-open).
Vapour permeabilityThe degree to which a material facilitates the passage of water vapour through it, measured by four different values: vapour resistivity (r-value; units: MNs/gm – meganewton seconds per gram metre); vapour resistance (G-value; units: MNs/g - meganewton seconds per gram); water vapour resistance factor (u-value; no units); equivalent air layer thickness (Sd-value; units: m - metres).
Window scheduleA list of all the windows in a building with dimensions.
KKelvin, temperature unit. One degree kelvin = one degree Celsius.
Km/WKelvin metres per watt. The unit of thermal resistivity.
kWhKilowatt hour, a unit of energy. Typical NZ 2kW roll around heater used for one hour would use 2kWh (2,000W) of energy. 1kWh = 3.6MJ (megajoules).
kWh/m2.aKilowatt hours per square metre per annum. Measures energy used annually per square metre of usable or treated floor area (TFA). This is one of the key units of measure in Passivhaus. By defining energy use in terms of each square metre of floor area, it allows us to make a meaningful comparison of the energy use of buildings of different sizes. See annual [specific] space heat demand.
kWpKilowatt peak. A measure of the maximum power output of photovoltaic (solar) panels.
m3/hrCubic metres (of air) per hour. The unit of measure used to describe ventilation rates. Passivhaus ventilation calculations are based on providing 30m3 per person per hour. This rate is necessary to keep carbon dioxide (CO2) levels well below 1000 parts per million (ppm).
MNs/gmMeganewton seconds per gram metre. The unit of measure of vapour resistivity (r-value). See vapour permeability.
PaPascal, pressure units. Building leakage is measured for Passive House at 50Pa. Note that 33 kilometers per hour wind hitting the side of a house produces 50Pa. 1Pa is 1 newton per square metre.
WWatt, a unit of power. For example, a typ. Led might be 10W and a hair dryer 3kW (kilowatts, i.e. 1,000W). 1W = 1 joule per second.
W/KWatts per degree kelvin (temperature difference between inside and outside the thermal envelope). Used to quantify chi-value (V) in point thermal bridges.
Certified Passive House Designer or ConsultantAn individual who has passed the PHI Darmstadt, Germany exam and has therby demonstrated a level of knowledge about Passive House design and analysis. You can also become a Certified Passive House Designer by doing the majority of the Passive House design for a Certified Passive House or PHI Low Energy Building - hard but an be done.
Accedited Passive House CertifierAn individual who has been accredited by PHI in Darmstadt, Germany to carry out building certification reviews and award the PHI certification certificate (and plaque of course). Any size or type of building can be certified by any accredited Passive House Certifier.
kWh/m2/yearKilowatt hours per square metre per year. Measures energy used over the whole year per square metre of usable or treated floor area (TFA).
W/m2
Heating or cooling load (power) divided by the TFA of the building.
Space Specific Heating Demand (kWh/m2/year)
This is the amount of heat required to keep the home within the acceptable, comfortable temperature range, expressed as the amount of kilowatt hours per square metre per year. (This is approximately 5-30% of the heating demand of a modern house built only to the Building Code minimum.)
Space Specific Heating Load (W/m2)The power used by a heater of sufficient size to maintain the comfortable temperature on the coldest days. A 300m2 Passive House can typically rely on a single plug in roll-around 3kW heater.
Frequency of Overheating
A certified Passive House must not overheat — defined as 25º C or above — for more than 10 % of the time. Note this can assume night and window ventilation so if the building is modeled with more ventilation than you use in practice it can overheat more than this.
TFA
Treated floor area is a measure of the useful floor area inside the conditioned area of the home. It excludes stairways and wall thickness (both exterior and interior).
Form factor
A ratio arrived at by dividing the total external surface area of the thermal envelope (including the floor slab area) by the treated floor area. A big building will have a lower form factor than a smaller one. A simpler shape will also have a lower form factor than a more complex shape. The lower the number, the less insulation needed in the same climate.
Air leakage
A crucial measure of building quality and major benefit of Passive House certification. Measured via a blower door test done toward the end of construction and verifies that the building will perform as modelled. It can be used as a proxy measure of the quality of building construction.
PER demand
Primary Energy Renewable demand measures total energy usage in the house (not just energy for heating and cooling) and includes (a) the power lost to the grid as power is carried from the power station to the home and (b) storage losses (as if the grid were fully renewable). Excess solar power generated in summer needs to be stored for winter use. PER demand is expressed on a per square metre basis per year. To calculate it for a specific house, multiple the PER demand by the building’s TFA. A certified Passive House must be below specified maximums, which depend on the degree to which power consumed comes from renewable sources generated on site.
PE demand
Primary Energy demand has been superseded by PER demand but you’ll see it referenced in older case studies and it can still be used on new buildings as well. It measures total energy usage in the house (not just energy for heating and cooling) and includes the power lost to the grid as electricity is carried from the power station to the home and the losses in converting non-renewable fuels to electricity. Buildings are required to be below 120 kWh/m2/year if they certify using PE demand.
RE generation
Measures the total amount of renewable energy generated onsite divided by the buildings footprint (not TFA). This threshold is relevant to Passive House Plus and Passive House Premium builds