What is Passive house?

Dr. Wolfgang Feist

Usually a house is equipped with a powerful heating system and often with air conditioners to maintain a comfortable temperature all year round. Due to rising energy costs, the operation of such a house becomes increasingly expensive.

Did you know that you can do without active home heating even in the coldest winter months?

The first Passive house in the world

In 1988 the German scientists Bo Adamson and Dr. Wolfgang Feist developed the passive house concept and built the world’s first passive house in 1991 in Darmstadt, Germany.

These scientists developed the Passive House construction standards and established the following criteria:

1. Sufficient thermal insulation

This can be compared with a high-quality jacket in winter, which keeps you warm without a heater.

4. High-quality triple pane insulated glazing

They serve as large solar collectors that help to heat the house in winter.

2. Fully hermetic

A passive house does not have even the slightest gaps through which warm air could escape.

5. Correct location of the building

The house should be located so that the sun heats it through the large windows in winter, while in summer a shadow is formed under a special window overhang to prevent the house from heating up.

3. Without thermal bridges

A thermal bridge is a heat leak through which heat escapes the building via construction elements.

6. Air ventilation with recovery

Ventilation ensures that the air in the house is always fresh and clean all year round, while preventing the escape of heat from the building.

THE RESULT: a house in which a comfortable indoor climate can be maintained without active heating or cooling systems.

Where does the heat come from then?

A passive house requires approximately 90% less heating energy than a standard house. The remaining 10% comes from:

body heat of the house inhabitants;
solar radiation through windows;
heat released by household appliances, lighting, and TV set;
a ventilation system that keeps the air evenly warm;
a decorative wood-burning fireplace or small electric radiators.

What is “passive” in a Passive House?

The heating system: a passive house requires no “active” heating since it maintains the heat using solar radiation, as well as heat emitted by domestic equipment and the house inhabitants – the so-called “passive” energy. Thanks to the excellent heat insulation, triple pane windows and high-efficiency ventilation unit with heat recovery, a passive house cools down very slowly, like a vacuum flask, and only during the short days of winter requires a little auxiliary heat, such as by using a fireplace or small electric radiator.

The basic elements of a passive house

Excellent thermal insulation

Thick walls which ensure that heat is retained indoors are one of the primary construction elements of any passive or high energy-efficiency building. To optimise the use of resources and to reduce the volume of the walls, we use a wood-framed panel system that provides maximum strength and structural efficiency with minimal material consumption. Cellulose heat insulation has been filled between the I-beam struts of the frame, and on the outside the wall has been additionally insulated using ecological wood fibre boards, thus obtaining an unparalleled thermal insulation layer with a 57-cm thickness and the heat transfer coefficient U=0.07 W/(m2K). In addition to plaster, OSB (wood fibre) boards are used in the walls. Wall panels are designed to avoid the so-called thermal bridges, while the assembly technology allows for obtaining a high-quality structure with very tight joints.

Fully hermetic

The passive house envelope needs to be especially well sealed because otherwise the outdoor air will be heated. The warm indoor air always tries to escape from the house through gaps, which can cause condensation and mould build-up in unsealed areas. Air flow can also cause draughts and cold air zones near the floor. Heat insulation materials are not usually airtight, so this envelope needs to be designed and built separately. In wooden structures, composite wooden boards are normally used, with joints sealed using tape. It is essential that the airtight envelope be seamless and not accidentally damaged by other construction workers (e.g. electricians). All utility outlets (even the power sockets) that cross the envelope must be sealed using special materials. The passive house heat insulation and an airtight layer must be checked using the special blower door method and an infrared camera.

Without thermal bridges

Heat can escape the house not only through cracks in the building, but also through materials with high thermal conductivity. A thermal bridge can be formed, for example, by improperly constructing a balcony on the second floor, the roof, or external and internal corners of the building wall. A passive house may not contain thermal bridges because they reduce the indoor surface temperature, cause a risk of moisture damage occurring and significantly increase the heat loss. Engineers have different methods to prevent thermal bridging. The main rules are: do not breach the thermal insulation envelope, choose a rational shape for the building and build the windows into the heat insulation layer.

Correctly placed airtight triple-glazed windows

One of the basic principles of passive construction is correct orientation of the house and its glazed areas to make use of the most of solar energy. Passive solar energy through the glazing can offset 40% of the heat loss of the building, so the windows (and also glazed front doors) are some of the core elements of the passive house. The best commercially available windows should be chosen for a passive house, usually with very high-quality triple glazing. The panes need to be additionally sealed and set in specially designed frames without thermal bridges. Such windows will let more heat in than out of the room; therefore, in summer the house should be protected against overheating using solar protectors, shutters, roof overhangs or other solutions. The windows of a passive house must not be equipped with the additional ventilation systems sometimes offered by window manufacturers. Airtight windows should not be a cause for concern because air quality is ensured by the innovative mechanical ventilation system.

Efficient air ventilation

A ventilation system is recommended in every home, but in a passive house it is essential. The air ventilation device allows the house to be provided with fresh air without opening the windows. The passive house is airtight and air exchange in it takes place almost exclusively through the ventilation system. By using the air heat exchanger built into the ventilation system, it is possible to recover up to 93% of the heat from the air that is released from the building. A small electric heater is installed in the ventilation system that heats up the air slightly when required to ensure a steady air temperature of +20° C. In summer the system operates in reverse and cools the incoming fresh air to ensure a comfortable microclimate indoors throughout the year. The air in the room needs not only to be warm, but also clean. For good air quality, one person requires at least 30 cubic metres of fresh air per hour. If there are 5 people living in the house, the ventilation equipment will supply 150 cubic metres of fresh air per hour.

Small auxiliary heating system

A passive house requires no “active” heating, since it maintains the heat using solar radiation, as well as heat emitted by domestic equipment and the house inhabitants – the so-called “passive” energy. In addition, the ventilation system warms the incoming fresh air to a temperature of +20° C. Despite this, the Latvian winter weather requires a small heating system.

For SINERGO houses, we offer a RIKA Vitra wood-burning fireplace specially designed for passive houses. It should be lit only during the months with the lowest level of light for two hours per day and the consumption of fuel for a 120 m² house will not exceed 1.5 m³ per year!

To avoid having to light the fireplace, we offer to install low-powered (375 W) decorative electric heaters in each of the rooms.

Solar batteries

The principle of the passive house is to use freely available renewable energy sources, such as solar energy, as much as possible. The principle of operation for solar batteries is simple – the obtained energy is used to run the domestic equipment necessary at the given moment, including the ventilation system, water heating, and partially also for heating. If the electrical power consumption of the moment is greater than solar power produced, then extra electricity is purchased from the grid, but if the solar power produced is higher, then the excess energy is fed into the grid.

The use of solar cells can produce as much electrical power as is required to compensate the average yearly electrical house heating costs.

Passive House requirements

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

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

Passive House buildings are planned, optimised and verified with the Passive House Planning Package (PHPP).

All of the above criteria are achieved through intelligent design and implementation of the 5 Passive House principles: thermal bridge free design, superior windows, ventilation with heat recovery, quality insulation and airtight construction.

For more information visit: www.passiv.de