What constitutes a passive house


A passive house is a building standard, which is both environmentally friendly and energy efficient, comfortable and economical. It is not a brand, rather it represents an open building concept, which has proven itself in the practice.   

 

Requirements

 

According to Passivhausinstituts Darmstadt there are 5 criteria, which have to be met in order for a house to be certified as passive:

- maximum annual consumption of energy for heating of 15kWh/m2 (energy content of 1,5 l diesel);

- maximum annual heat loading of 10 W/m2. The passive house should also even in the coldest days of the winter to be heated by the supply of fresh air (with maximum temperature of 52°C);

- maximum annual energy consumption for heating, including hot water and electricity, of 120kWh/m2;

- comfort during the summer season: days with temperature  >25°C less than 10%;

- excellent air tightness (result from Blower-Door Test < 0,6/h).

House, which have covered these criteria are called “passive” because they meet the majority of their needs for heat energy from passive sources (solar energy, emitted heat from occupants and appliances). The end result should be a positive perception of the premises and the climate in them, accompanied by a low energy consumption. The passive house is not a result from a newly construction, but a building standard, which sets certain requirements for the architecture, the technique and the ecology, and it is not limited to certain types of buildings. The requirements of this standard can be met through the renovation of the building.

 

Principle of functioning

 

A typical passive house possesses the indicated in the graph constructive signs. Deviations are permissible and possible to any of the indicated places, as much as the indicated principle of functioning is not disturbed.

In a passive house, through special thermal insulation of the walls, windows and the roof is achieved recuperation above the average of the thermal energy emitted by the occupants and household appliances. The mounted intelligent ventilation system also prevents heat losses and regulates the supply of fresh air in the building as it gives to the air the heat energy of the used air before discharging it. The supplied fresh air in the building usually is warmed initially in a terrestrial heat exchanger. A very important part of the passive house is its extremely good air tightness, as well as the shape of the building. Only on extremely cold days is allowed part of the energy, needed for heating, to be supplied by standard heating systems (central and gas heating, diesel heaters, wood heaters, solar heating systems, etc.). 

 

Thermal insulation

 

The main part of the energy saving in passive houses is achieved by reducing the heat loss from thermal conductivity (through the surrounding elements) and from ventilation. This is achieved through a very good thermal insulation of all surrounding surfaces (roof, basement walls, foundation, windows), to a great extend large, dense sealing of the house and controlled ventilation of the premises by recuperating the heat energy, contained in the discharged air. Thermal bridges and leaky connections are not allowed.

The windows in the average passive houses are usually with triple glazing, they have selective layers from each side, bordering with the space between the glass panels, which are filled with argon (rarely krypton). Even though windows from this type have worse thermal insulation properties than the well-insulated walls, if they are placed in a non-cloudy south part of the building – they neutralize their worse characteristics by the passing through them solar energy, thus achieving a positive energy balance in winter. 

 

Ventilation

 

The cladding of the buildings, especially the newly build ones, nowadays are very air-tightened. Consequently at closed windows the natural air exchange is not carried out. For this reason, today massively ventilation equipment is being build (in non-passive buildings too), with the scope to discharge the exhausted air and water vapor and to guarantee a pleasant indoor climate.

In order to reduce the heat losses, the passive houses require controlled ventilation of the premises, accompanied by a heat exchange. Each 1 to 4 hours, all the air in the building is changed. At, required for this, minimal air flow movements in the air, currents or noises are not perceived. The fresh, filtered and pre-heated air is fed into the bedrooms and living rooms, and from there through holes (usually above or in the doors) is transferred in the hallways, kitchens, bathrooms and toilets. From there it is sucked back and transmitted through channels to the heat exchanger (where it gives from 80% to 95% of its thermal energy to the fresh air, without mixing with it), and then it is discharged outside.

 

Heating

 

Much of the needs of heating in a passive house are satisfied by the interior (from the emitted heat from people and equipment) and from the solar energy (passing through the windows). The rest can be satisfied in any way (gas heating, central heating, heat pump, thermal solar heating, heating on pellets or diesel, etc.). It is important to respect the limit of maximum 15kWh for 1m2  heated living space for 1 year. At greater density of occupation (less living space per occupant) this heating is done by supplementary heating of the freshly supplied air by a conventional heater. At bigger passive houses the additional heating is done similar to the ordinary building, it is performed by static heating devices, but with smaller dimensions. 

 

Climate comfort: constant interior temperature

The most important and special feature of a passive house is the constant interior temperature. This applies to the individual premises viewed throughout the year and in one day. The interior temperature in a passive house changes very slowly – when the heating is off it decreases with less than 5°С per day (in winter when there is not sunshine). All walls and floors have the same temperature, as this applied for the walls in the basement too, if it is included in the thermal cladding of the building. Cold walls and floors do not exist, which excludes the formation of mold. In the summer the heat insulation and the presence of terrestrial heat exchanger ensure that the house will remain pleasantly cold without the need for air conditioning.

The interior temperature, however, is not perceived by everyone as comfortable. Very often is desired a self-temperature regulation (for example colder in the bedroom or warmer in the bathroom). In a passive house this is achieved very difficult and it involves additional costs (for example separate floor heating).

 

Climate comfort: air quality

The controlled ventilation in a passive house provides a better air quality in the building than the one of the outside air (through filters). The rapidly heating of the air in the passive houses is not possible due to the slow (for comfort reasons) exchange of the air (0,4/h– 1,0/h). The additional ventilation and aeration are always possible but unnecessary in general.

 

Construction costs

 

The practice shows that a newly build passive house is about 5% to 15% more expensive than the same, build in a conventional way. At refurbishment of old buildings, the additional costs for them to become passive is somewhere in the range of 12% to 18%. The energy saved from heating in the passive houses is around 75% in comparison with that in a conventional built by the currents building standards.

 

The increased costs

 

The increasing construction cost is caused by:

- especially good thermal insulation (costs for thermal insulation material)

- additional costs caused by increased external surfaces (more difficult works and more details)

- ventilation system with heat exchange

- very good windows with triple glass layer

- increased demands on the air-tightness of the building

- expensive individual solutions (for example flaps for pets)

 

Reduced costs

 

The reduction in the construction costs in a passive house is caused by:

- lack of chimneys (more living space and maintenance costs)

- very rarely are needed heaters, wall and floor heating and the related to the equipment  

- lack of a boiler room and fuel storage

- lower costs for preparation of hot water and maintenance of heating equipment

 

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