About Passive House

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What is a Passive House?

A Passive House is an energy-efficient building with year-round comfort and good indoor environmental conditions without the use of active space heating or cooling systems. The space heat requirement is reduced by means of passive measures to the point at which there is no longer any need for a conventional heating system; the air supply system essentially suffices to distribute the remaining heat requirement.

A passive house provides very high level of thermal comfort and provision of whole-house even temperature. The concept is based on minimising heat losses and maximising heat gains, thus enabling the use of simple building services. 

The appearance of a passive house does not need to differ from a conventional house and living in it does not require any lifestyle changes. Passive houses are light and bright due to large glazed areas designed to optimise solar gains, as well as healthy buildings in which to live and work due to fresh air supply through the ventilation system. 

The Passivhaus Standard is a construction standard developed by the Passivhaus Institut in Germany (http://www.passiv.de). The Standard can be met using a variety of design strategies, construction methods and technologies and is applicable to any building type.

The 5 key principals of a Passive House.

Thermal insulation
All opaque building components of the exterior envelope of the house must be very well-insulated. For most cool-termperate climates, this means a heat transfer coefficient (U-value) of 0.15 W/(m²K) at the most, i.e. a maximum of 0.15 watts per degree of temperature difference and per square metre of exterior surface are lost.

Passive House windows
The window frames must be well insulated and fitted with low-e glazings filled with argon or krypton to prevent heat transfer. For most cool-termperate climates, this means a U-value of 0.80 W/(m²K) or less, with g-values around 50% (g-value= total solar transmittance, proportion of the solar energy available for the room).

Ventilation heat recovery
Efficient heat recovery ventilation is key, allowing for a good indoor air quality and saving energy. In Passive House, at least 75% of the heat from the exhaust air is transferred to the fresh air again by means of a heat exchanger.

Airtightness of the building
Uncontrolled leakage through gaps must be smaller than 0.6 of the total house volume per hour during a pressure test at 50 Pascal (both pressurised and depressurised).

Absence of thermal bridges
All edges, corners, connections and penetrations must be planned and executed with great care, so that thermal bridges can be avoided. Thermal bridges which cannot be avoided must be minimised as far as possible.

Passive House Requirements

For a building to be considered a Passive House, it must meet the following criteria:

1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.

In climates where active cooling is needed, the Space Cooling Energy Demand requirement roughly matches the heat demand requirements above, with a slight additional allowance for dehumidification.

2. The Primary Energy Demand, the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 120 kWh per square meter of treated floor area per year.

3. In terms of Airtightness, a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states).

4. Thermal comfort must be met for all living areas during winter as well as in summer, with not more than 10 % of the hours in a given year over 25 °C. For a complete overview of general quality requirements.

Benefits of a Passive House.

For many years the Passive House standard has been quietly spreading across Europe, applied both to residential and commercial buildings.  Architects and builders are using such standards to construct buildings that use up to 80% less heating and cooling energy. Lifecycle costs of a passive house building are less than any other “green” method of construction.  Passive houses stay at a comfortable temperature all year round with minimal energy inputs.  High quality insulation keeps the temperature comfortable just where it is needed.  Because of effective insulation heat stays within the building, and all surrounding areas are equally warm.

Consequently there is no radiation heat-loss through the outside walls of a passive house, nor any resulting draughts. Conversely, the heat in summer stays outside and this prevents overheating inside. Because of these factors the room temperature in a passive house remains constant and comfortable throughout the year, ensuring a high standard of comfort and coziness for the occupier. In addition, passive houses have efficient ventilation systems (MVHR) which prevent a build-up of mould and dust and their resultant allergies.  As well as adequate insulation passive house windows have an important role in creating a passive building in that they can reduce heat loss and they allow sunlight to produce heat through the glass also.