A standard for energy efficient houses
House energy efficiency can be demonstrated with the PassivHaus Standard in Europe which is a very rigorous system that creates ultra-low energy-use houses which are able to dispense with conventional heating systems – although heat is often distributed through the low-volume heat recovery ventilation system that is required to maintain air quality.
This standard is being used voluntarily in many places throughout Europe including Germany and Sweden, which have colder winter climates than New Zealand.
To achieve the Passivhaus standards, a number of techniques and technologies are used in combination:
Passive solar design
The Standard follows passive solar building design techniques. Where possible buildings are compact in shape to reduce their surface area, with windows oriented towards the north (or south in the northern hemisphere) to maximise passive solar gain. However, the use of solar gain is secondary to minimising the overall energy requirements. Some internal thermal mass is normally incorporated to reduce summer peak temperatures, maintain stable winter temperatures, and prevent possible over-heating in spring or autumn before normal solar shading becomes effective.
Passivhaus buildings employ ‘super-insulation’ to significantly reduce the heat transfer through the walls, roof and floor compared to conventional buildings. Special attention is given to eliminating thermal bridges (timber frames for example).
Advanced window technology
Windows (including the frame) are manufactured with exceptionally high R-values (heat flow resistance). These normally combine triple-pane insulated glazing with air-seals and specially developed thermally-broken window frames.
Building envelopes under the Passivhaus standard are required to be extremely airtight compared to conventional construction. Air barriers, careful sealing of every construction joint in the building envelope, and sealing of all service penetrations through it are all used to achieve this.
Airtightness minimises the amount of warm (or cool) air that can pass through the structure, enabling the mechanical ventilation system to recover the heat before discharging the air externally.
Mechanical heat recovery ventilation systems, with a heat recovery rate of over 80%, are employed to maintain air quality, and to recover sufficient heat to dispense with a conventional central heating system. All ventilation ducts are insulated and sealed against leakage.
In addition to using passive solar gain, Passivhaus buildings make extensive use of their intrinsic heat from internal sources – such as waste heat from lighting, appliances and other electrical devices (but not dedicated heaters) – as well as body heat from the people and animals inside the building. Together with the comprehensive energy conservation measures taken, this means that a conventional central heating system is not necessary beyond the recovery of heat by the heat recovery ventilation unit if the heating load is kept under 10W/m².
Lighting and electrical appliances
To minimise the total primary energy consumption, low-energy lighting (such as compact fluorescent lamps), and high-efficiency electrical appliances are normally used.