by Thomas Lützkendorf

In the past, the demands for a further reduction of the consumption of non-renewable energy sources, and in particular for a significant reduction of greenhouse gas emissions, were described in a relative abstract way. Often, the owners and users of buildings may not realize how great their influence is and how their behaviour can contribute to achieve these goals.

The owners and users of buildings are the ones who ultimately decide on the energy consumption and impact to global and local environment. This happens through

• the choice of an energetic standard either when constructing a new building or when renting/ purchasing an existing building

• the choice of an energy source/ source of energy supply and thus the type and extent of the use of renewable energy sources

• the demand for a specific (living) area

• the demand for a specific level of comfort in winter and summer

• the demand for hot water

• the demand for household electricity in connection with the amount, type and use of household appliances

• the user behaviour and the operational mode

• the type and extent of maintenance and repair

There is a clear relationship between the assessment of constructed assets and the assessment of lifestyles or the demand patterns/ behaviour of its occupants. The quality of buildings and energy supply are not the only important factors for the achievement of climate change objectives, but also the behaviour of their owners and users. From the perspective of the owners and users, the strategies for efficiency, sufficiency and consistency can be usefully combined. This comprises the reduction of energy demand, the improvement of the energy conversion efficiency, reasonable demands for space and comfort level as well as the use of renewable energy, an appropriate behaviour of users and the regular maintenance of building services.

One approach to involve the owners and users of residential buildings is to make them aware of their personal CO₂ footprint. There is an extensive experience in this field and related calculation tools and visual aids are freely available on the Internet see Figure 1 and http://www.nature.org/greenliving/carboncalculator/

Fig.01 : Example for a CO2-calculator from Germany (the current individual CO₂ emissions are compared with a national average) see http://uba.co2-rechner.de/de_DE/

For the situation in Europe the following estimation can be made: The annual per-capita CO₂emissions are around 10 tonnes. Of this total, about 2- 3t CO₂ / capita and year relate to the energy requirements of residential buildings (heating, hot water supply, electricity for lighting, pumps, household appliances). There is a clear need and aim to reduce the total number to 1-2t CO₂ / capita and year. Maintaining the share of the CO₂ emissions associated with energy requirements of residential buildings of the total means that a budget of about 300 – 600 kg CO₂/ capita and year are available for housing (use stage). The idea of a “personal budget” for the greenhouse gas emissions has already been increasingly discussed in the literature. The question arises as to what the level of a budget for the societal need “housing” is, and whether this budget is sufficient taking into account the technologies and options for action already available today.

This goal is realistic and can be achieved even today through the implementation of a series of measures. An evaluation shows that the following measures (selection), when combined, are sufficient for achieving this goal:

• renovation to low energy or passive house standard, or alternatively, complete switch to renewable energy sources when it comes to heating

• limit the living space to about 30 m²/capita

• limit the power consumption to about 500 kWh/ capita and year and predominant use of green power

• use of solar thermal energy for heating water

Fig. 02: Example calculation for the situation in Germany

Fig. 02 shows, by using data from Germany as an example, that it is already possible today to reach a target of less than 300 kg CO₂/ capita and year for “housing”. The example below assumes an average household of 4 persons. The target value can be reached through the combination of different measures:

• The required living space in a multi-family house can be reduced to approx. 30 m² per capita. Currently, the average living space in Germany is about 47 m² per capita. Examples from Europe show that values of 25 – 35m² /capita can also be achieved. Optimised floor plans is a prerequisite among others.

• Builders, buyers or tenants can ask for buildings or apartments with low energy requirements. Such buildings are offered in the market – built as passive houses or energy-efficient houses. Energy efficient buildings are also available as prefabricated houses. A prerequisite is the provision of reliable information on the energy performance of the building – e.g. in the form of an energy passport.

• The remaining energy needs of the building can be covered by efficient systems (condensing technology, heat recovery) and environmentally-friendly energy supply (e.g. solar district heating).

• A reduced consumption of hot water can be achieved through conscious behavior, water-saving fittings and household appliances. A value of 30 liters/person and day is realistic considering an economic use of water.

• The energy consumption for hot water preparation can be reduced through the use of solar thermal heating. Coverage ratios of 50% to 65% can be achieved.

• Electricity consumption for domestic appliances can be reduced through conscious behavior (e.g. avoid standby power consumption) and energy-saving appliances. As a rule, the use of electric tumble-dryers should be avoided.

• Current electricity-related emissions can be reduced through the purchase of green electricity or the integration of a PV system into the building. (The amount of energy required to produce the PV system has to be taken into account in an overall assessment).

The “budget” principle can be expanded by including standards for the limitation of energy consumption and environmental impact of the construction and maintenance of residential buildings – see part 2 of G. Habert in this document. It is clear that the values should be achieved on average level and compensations are possible. However, the perception of the problem and the willingness to take action can only be supported on an individual level. Additionally, the decisions regarding the construction type/method of a building and the selection of building products are taken by the building owner.

Conclusion

By combining a mix of measures to limit the need and demand, to increase efficiency and the use of renewable energy sources, a target of around 300 kg CO2eq. /capita and year for “housing” (heating, preparation of hot water and household electricity consumption) can be achieved in Europe.

As a way of collecting and awarding relevant examples, a campaign is proposed having its focus on (North) Europe “How to live with a budget of 300 kg CO₂/ capita and year?”.