Question: What is a Passivehouse?
Answer: First of all, the most graphic description: I live in a 90 square meter, three-room apartment in the Passivehouse. In 2006, I have paid 188 EUR for all the heat energy, that is for heating the house, for heating the water (but not for the water itself) and for the gas for cooking. We pay this amount not per month, but for the whole year! It is clear that, one can save around 1000 EUR per year by living in a passivehouse rather than living in a new conventional house.Andreas Delleske, Resident of "Wohnen & Arbeiten"
Definition of Passivehouse
There are two widespread descriptions:
- A passivehouse is a passively heated house, thus there is no active heating system like a central heating system. The sun, isolation, inner gains and such suffice to keep the temperature in the house at a comfortable level during the winter.
- A Passivehouse has a heating energy consumption under 15 kWh per square meter per year (not including warm water, electricity and so on.)
How will a Passivehouse be constructed?
A construction engineer of a passivehouse must as a general rule, incorporate five important "elements" or basic interrelations:
- A very good heat insulation:
In modern new buildings, the architects, owners, stress analysts and house technicians already have to deal with heat insulation. In most cases, 12 to 16 cm heat insulation is adequate, for example from mineral wool, expanded polystyrene (a brand name is Styropor), cork or cellulose flakes (old paper). The strength of these isolation measures is usually doubled in passive houses.
- Very good windows:
Without the great improvement in window engineering technology in the last 10 years, passivehouses would not have been feasible or would not have been as cost-effective. We use triple-glazed windows. These windows are also special because two of the six glass surfaces are coated with heat-reflective material.
- South orientation
An often underestimated factor is the areal orientation of the buildings in the territory: A big facade of the passivehouse must face south, the principal axis of the houses also may not lie from north to south, but east to west. Because of the 4 big linden trees in front of the house, Fraunhofer-Institute for Solar Energy Systems had to carry out a computer simulation, which could give us assurance that the passivehouse would still function.
- The Ventilation System
When the walls, the windows, the floor and the spreads are very well heat-insulated, biggest heat-loss occurs via ventilation (also the natural air change through leakages). Normally, heat loss through air makes up only around 10-20% of the total heat loss. However, minimizing the heat loss via air is very important in passivehouses. While doing this, one must also make sure that there is enough fresh air to breathe in the house. In order to achieve this, as a general rule, one needs mechanical ventilation, ventilators and a heat exchanger. The heat exchanger makes sure that the air in the rooms is exchanged every two hours and that the exiting air delivers its warmth to the entering air. Thereby, 80% of the heat loss via air is eliminated, the warmth stays in the house. A convenient secondary effect of this system is that there is no mold problem in the passivehouses; passivehouses are compulsorily very good aired. On the other hand, the air flow is so weak that one can not get a feeling of infiltration or cooling.
- Inner Returns (Internal gains)
The so called "inner returns" are certainly not direct gains but gains that one thinks about while constructing a passivehouse. While cooking, showering and using electrical devices, one adds to the warmth in the house which helps to keep the inner temperature at a warmer degree. We, as humans also emit around 100 Watt heat energy per person.
For comparison: A 15 meter square room in the house with huge windows, (when it is 12 °C outside), has a maximum heating need of around 400 Watt. On the coldest days of the year, two people and four candles alone will suffice to stoke the room.