What is a Passive House?
A Passive House is a building that has compared to conventional buildings a decreased use of energy
- use of energy
The required thermal heat of customary new Residential Buildings is according to EnEV 2009 about 70 kWh/m²a. A Passive House consumes less than 15 kWh/m²a which is just 20 % of the conventional value.
The expenditures for the heating of drinking water as well as losses determined by the system are not considered in both statements but are approximately even.
an ideal user comfort. This is because of:
- user comfort
The wellness is significantly dependent on the surface temperatures of the members. The higher the level of insulation, the higher and more consistent the surface temperature of all members is.
Man perceive a consistent emission of heat of all adjacent members as comfortable. The smaller the difference in temperature of the members, the better man feel. Just with the high standard of Passive Houses this aspiration is achieved via a difference in temperature of 2.5 Kelvin.
Due to the consistent surface temperature the temperature layering in a room is not as distinct as in a conventianal building. If a sitting person is considered the difference between ear and ankle, beeing the temperature sensors of the human body, is less than 2 Kelvin which increses the wellness.
- a high level of insulation
To reduce the need of thermal heat of a building the primary goal is to minimise heat flows to outside air, unheated rooms and soil. One premise of Passive Houses is therefore to limit the overall heat tranfer coefficient of opaque members like walls, ceilings, roofs or floors to a maximum of 0,15 W/m²K and for windows and doors to a maximum of 0,8 W/m²K. This resembles an insulation thickness of ~24 cm. Windows would need to have triple glazing and optimized glass holder as well as sash.
Due to the high insulation level the surface temperature of the members rises. The heating does therefore not have to compensate for 'weak' areas. So the heating surfaces do not need to be arranged at windows or within floors. Where exactly the heat is caried in is not important.
If the level of insulation is rising the inertia to cool down rises as well. Because of that the time interval of heating is not necessary to be adjusted to the time interval of usage.
For information to wellness please see 'user comfort'
- detailed solutions mostly without heat bridges
A higher level of insulation increases the influence of heat bridges. To ensure the decreased energy needs of Passive Houses a detailed consideration of heat bridges is essential. This can be done with the aid of FEM-calculations - complex numerical procedures, according to DIN EN ISO 10211 - 3.1.1 - or in some cases with standardised detailed solutions. The final aim of Passive Houses is a structure without heat bridges!
- an efficient orientation and utilisation of solar entries
It is important to use the insolation as efficient as possible to obtain a good energy balance. On the one hand, windows cause design related large heat losses due to transmission, on the other hand it is possible to optimise the usable insolation by a smart arrangement of the building. To do so it is needed to analyse the presence of shadow casting objects for every window. The calculations are influenced by
• shadows cast by other buildings, trees or mountains
• shadows cast by ledges of the building itself or the scuncheon
• shadows cast by balconies, roofs or lintels above to window
If a Passive House is designed well the heat losses through south windows during winter is smaller than the solar entries. The window itself works as a heating!
- the airtightness of the cladding
The airtightness is unavoidable because of the following - prevention of damage of memebers.
Reasoning - If humid, warm inside air streams into a member it condenses and damages the member.
Prevention of infiltration and draughts
Reasoning - It is possible that cold outside air streams through leakages into the building and leads to draughts and cold floors.
Reducing of heat losses due to ventilation
Reasoning - The less unchecked air flows there are, the smaller are the heat losses.
Improvement of acoustic protection
On these grounds the airtightness is also demanded by the German Energy Saving Ordinance. There are appropriate boundry values which can be determined by the Blower-Door-Test. These values are stricter if the building is supposed to be a Passive House.
To achieve airtighness of buildings a considerable amount of detailed planning is necessary. Examples are
• connections
• penetrations
• appropriate materials
- a venitaltion system which has a high grade of heat provision
A sufficient supply of fresh air is needed to ensure a high quality of the inside air. The ventilation system can remove moistures rising from the bathroom or kitchen and regulate the pollutant concentration, including CO2. Due to the airtightness required by law a ventilation system is inevitable as ventilation using windows can not ensure this function.
Disadvantages of ventilation using windows are
• high and uncheckable energy losses
•cooling of adjacent members, possibly leading to damaging
• it is not independent from the user
• ventilation of interior rooms impossible
• high acoustic emissions
Ventilation systems with heat recovery warm the incoming outside air with the help of the inside air and therefore reduce heat losses due to ventilation to a minimum.
The efficiency, the wellness in the rooms and the hygiene of the channel system and apparatus is guaranteed by a well-engineered ventilation concept.
With Passive Houses it is also possible to cover the thermal conditioning of the rooms with the ventilation system. This is not mandatory but has the advatage that no heating surfaces, lines or pumps need to be installed
- the construction form
Principally many designs are possible for Passive Houses. The larger the percentage of the cladding, due to for example dormers, ledges or bays, the bigger the compensation via the level of insulation of exterior members is. This can lead especially at smaller building to inefficient and nonsensical insulation thicknesses.