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17.12.2018

Passive energy houses: How do they work and what do they achieve?

Winter has arrived in Germany. When the temperature drops outside, we need to turn up the heating indoors. But with the prices of heating oil and gas continuously increasing for decades, that’s getting more and more expensive. This makes it all the more important to ensure that your own four walls are well insulated. After all, good thermal insulation allows you to save plenty of energy while simultaneously protecting the environment and your wallet. In this regard, ‘passive houses’ are especially efficient by consuming up to 80% less heating energy.

What exactly is a passive house?

Passive houses are ultra-low energy buildings with a heating demand which is well below the maximum permissible consumption for new buildings. There’s no uniform standard in Germany. Instead, the statutory minimum requirements for new buildings are regulated by the EnEV Energy Saving Ordinance, which has been repeatedly amended since 2002.

In 2002, the average heating energy consumption of residential buildings in Germany was about 160 kWh per square metre of energy reference area per year, and a house with consumption below 70 kWh/(m²a) was still considered a low-energy house.

Since then, the bar has been set much higher. The ‘KfW Efficiency House 70’ with consumption below 45 kWh/(m²a) is currently the standard for all new buildings in Germany. Anyone applying for public funding for particularly energy-efficient construction from the KfW reconstruction bank must build an Efficiency House 55 or an Efficiency House 40 Plus and reduce its consumption to below 35 or 25 kWh/(m²a). This corresponds to an annual oil consumption of less than 3 litres per square metre.

The energy savings are mainly achieved by the effective thermal insulation of the roof and the outer walls as well as by insulating the windows and outer doors. Other important factors are the use of renewable energy, such as biomass or solar. Solar energy can be exploited passively by planning, say, sunrooms and conservatories, and actively by installing solar energy systems for hot water and heating as well as heat pumps and photovoltaic systems.

Passive houses are so well insulated that heating systems can be dispensed with. This explains their name: heat from passive sources (e.g. solar radiation, waste heat from household appliances, body heat) is sufficient to maintain a comfortable living temperature. Due to their ideal thermal insulation, passive houses don’t need traditional heating for the winter or any form of cooling in the summer. Although there is a persistent myth that you can’t open the windows in passive houses, that’s not true. And radiators aren’t prohibited of course – it’s just that they don’t usually need to be on. The maximum heating demand for passive houses is no more than15 kWh per square metre of energy reference area per year.

How does a passive house work?

Due to current construction methods with airtight walls, windows and doors, hardly any air exchange takes place. But because an adequate supply of fresh air is essential for well-being, newbuilds now have ventilation systems. A passive house makes use of this and heats up the air in the ventilation system passively in various ways, for instance by means of solar radiation, geothermal heat, or the heat created in the kitchen by cooking. The warm air is then evenly distributed in the house – meaning traditional radiators aren’t required in passive houses.

Costs and benefits of a passive house

Constructing a building as a passive house requires sometimes substantial additional investments of up to €10,000, depending on the size of the building. The good news is that passive houses are supported by subsidy programmes with low-interest loans, repayment subsidies and one-off grants from state institutions such as the KfW reconstruction bank and the BAFA German Office of Economics and Export Control. For example, subsidies under the KfW’s Renewable Energies – Standard 274 (Photovoltaic) programme can be used to install a heat pump and a photovoltaic system. Moreover, over the years these additional investments pay for themselves thanks to the heating costs saved.

Another positive effect of passive houses is the healthier indoor climate. Due to both the better insulation of the outer shell and the ventilation system, the room temperature remains pleasant all year round and there’s almost no chance of mould forming on the walls.

But it’s not just your finances and your health that benefit – the environment does, too. The significantly reduced heating energy demand slashes the CO2 emissions generated by the building permanently. If solar energy systems are fitted to meet outstanding demand and the electricity supply is switched to green power, it’s even possible to run a passive house solely on renewable energy and hence reduce its ecological footprint.

Efficient construction at MediaMarktSaturn

Reducing the operational energy demand of more than 1,000 stores worldwide and cutting their CO2 emissions as a result is one of the key sustainability goals of the MediaMarktSaturn Retail Group. Under its Saving Energy 2.0 initiative, electricity consumption per square metre of retail space has already been reduced by 23% compared to 2011 – and the aim is to lower it by another 15% by the end of 2025. To do so, the group relies on efficient energy management coupled with the continuous modernization of its stores and administrative buildings.