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Wed Feb 17, 2016



Puzzled by what makes a Passive House? Baffled by building envelopes? Take a sharp intake of breath when you hear the term ‘airtightness’? Don’t worry! The jargon describing Passive House principles and technologies is simpler than it sounds...

ACH - Air changes per hour, a measure of the air volume added to or removed from a space such as a room or building. See Airtightness.
 
Airtightness - The resistance to inward or outward air leakage through unintentional leakage points or areas in the building envelope. The Passive House target for the number of times the building’s whole interior air volume is transferred is 0.6ACH (Air Changes Per Hour). This is 10 times tighter than UK regulations.
 
Building Envelope - All the elements of the outer shell of a building that maintain a dry, heated or cooled indoor environment, enabling its climate control. 
 
EnerPHit - The Passive House Institute’s standard for retrofit projects, less onerous than that for new builds because it is often more difficult for older buildings to achieve the Passive House standard. EnerPHit demands airtightness of 1.0ACH (as opposed to 0.6ACH) and space heating demand of 25kWh/m² per year (as opposed to 15kWh/m² per year).  
 
ERV - Energy recovery ventilator. Exchanges the energy contained in air exhausted from a building and uses this to heat or cool the building’s incoming outdoor ventilation air. 
 
HRV - Heat recovery ventilation. A technology that ventilates a building while also recovering heat from extracted air. Typically extracts warm, damp air from ‘wet’ rooms such as kitchens and bathrooms and uses it to heat cool fresh incoming air before feeding it to living spaces such as living rooms and bedrooms. Typically saves 10 times the energy it requires for operation.  Also referred to as MVHR. 
 
International Passive House Association (iPHA) - The international network for Passivhaus knowledge, working to promote Passive House worldwide. http://www.passivehouse-international.org/
 
MVHR - Mechanical ventilation with heat recovery. MVHR systems transfer heat from stale outgoing air to the fresh incoming air, providing fresh air and improved climate control while also making the building more energy efficient by reducing heating and cooling requirements. See also HRV.
 
Enthalpy Exchanger - The Zehnder Enthalpy Exchanger, designed to maintain comfortable moisture levels within a home, recovers thermal energy and humidity energy from the stale air extracted from ‘wet’ rooms such as kitchens and bathrooms. 
 
Passipedia - iPHA’s wiki-based Passive House resource.
 
Passive House - A construction concept and voluntary standard, internationally recognised, for energy efficient architecture. Passive Houses make use of “passive” heating and cooling technologies to stay at a comfortable temperature with consistent fresh air throughout the building all year-round with minimal energy inputs. 

Passivhaus Institut - An independent research institute founded in 1996 under the leadership of Dr Wolfgang Feist, co-inventor of Passive House. http://passiv.de/en/
 
Passivhaus Trust - Independent, non-profit organisation that provides leadership in the UK for the adoption of the Passive House standard and methodology. www.passivhaustrust.org.uk
 
Passive House Certification - Certification processes to ensure the quality of any official Passive House buildings, practitioners, products and components. 
 
Passive House Standard  - The criteria a building must meet to be considered a Passive House.
  • Space heating energy demand must not exceed 15kWh per square metre of net living space or 10 W per square-metre peak demand.  
  • Primary energy demand must not exceed 120kWh per square metre of treated floor area per year.  
  • Airtightness must ensure the building leaks no more air than 0.6 times the house volume per hour at 50 Pascals air pressure (ACH50).
  • Thermal comfort must be met for all living areas year-round with not more than 10% of the hours in any given year above 25⁰ C.  
 
PHPP - Passive House Planning Package for the planning, optimisation and verification of Passive House buildings. Spreadsheet-based modelling software used to calculate energy balance and design. 

Thermal Envelope - The thermal control layer between the house interior and exterior, separating the inside climate from the outside. 
 
Thermal performance - Heat loss. Commonly quantified in the construction industry as a U-value or R-value.   
 
Wh/m²/yr - Kilowatt hours (unit of energy) used per square-metre of liveable floor area per year. A typical UK house might use around 278kWh/m²/yr, of which around 140kWh/m²/yr would be for space heating. In Passive Houses a target of 15k Wh/m²/yr is set as a maximum energy demand for space heating, achieved by minimising heat lost from the building. 
 
ZEB - A net zero-energy building, where the total amount of energy used annually by the building is equal to the amount of renewable energy created on the site. 





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