Households claiming in most of the industrialised countries about one third of total final energy if the fuel consumption in transport are not included. The household sector itself serves very well to illustrate the extensive possibilities of a much more efficient use of energy. Over the course of the next few articles we are looking behind the wonderful terminology “energy efficiency” and explain in more details what is it in regards to our common daily usage in residential households.
2 Energy services in the common household
The domestic demand of energy services are physically measurable quantities, but do not have the dimensions of energy, and some examples are shown in Table 1.
Table 1: Quantification of energy services
Under ideal conditions, the least of the household demand of energy services have a necessity to spend to their provision of energy flows. Rather, “energy,” comes only into the game that the services used in the energy flows, the system boundary “house” crosses to the outside and becomes the environmental heat (anergy). In the usual terminology, these emerging energy flows are called losses. Ultimately, all of the input energy flows leave the house system as anergy. Evidence would be for example within one year of regular energy remain in the system house, so the internal energy of the house would constantly increase and thus overheat the house. (An increase of potential energy can, as a rough calculation shows, only take place in very small amounts). Ideally, it should therefore be possible to provide the vast majority of household energy services in demand, although not with the use of zero energy (lossless), but with an arbitrarily small external energy supplied electricity.
But a closer analysis of the services shows, it turns out that these are usually to maintain the nonequilibrium are kept. Especially when most of the services as shown in Table 1 the case is. Nonequilibrium can be maintained in two different ways:
- either by creating a dynamic steady state – i.e. acts at the expense of energy balance active effort to meet;
- or by building stationary barriers that work against the passive state change and thus establish the desired state as a new Gleichgwicht.
The first alternative leads to a greater or less actively prepared wrongful energy flow, which then leaves as indicated above, the system boundary as anergy again. The second alternative is possible with consistent implementation, ideally without any active energy.
This is the central argument that explains the fundamental importance of energy efficiency: By consistently avoiding and reducing losses, it is possible to reduce the specific energy per desired energy service to very small values. This finding is now confirmed by practical results in efficiency improvement. Some examples are discussed in the following sections.
3 Breakdown of energy consumption
Figure 1 shows on the left side of the typical distribution of final energy consumption in the average budget for a building, thus today goes a greater proportion (78% or 210 kWh/(m²a) related to the living space) into the building heating. The energy demand for space heating can be considerably reduced in existing [Feist 1998a] as well as new buildings. The current state of the art in high-efficiency buildings give the so-called “passive houses” before. These annual heating demand is typically limited to 10 – 15 kWh/(m²a). This is less than a tenth of the usual consumption of the average old building. With such efficient use of energy for space heating it does loses its dominant role and other energy applications becomes more important.
The figure 1 below describes the cmparison of average energy consumption by con sumption in household, measured consumption of four households in their show homes “Passive House”. Through consistent application of efficiency techniques it was feasible to save 88% of normal energy use. The equipment and comfort are even better than average.
Figure 1: Specific end energy consumption comparision
The fuel used for hot water today counts for about 10% which is 28 kWh/(m²a) of the consumption of a typical household. Also here are significant efficiency improvements possible, whereas today in this area the use of solar and geothermal thermal and wind energy systems are very attractive. Through a combination of renewable enrgy sources and efficient building services as well as energy efficiency appliances the remaining energy requirements will be siginificant reduced with a high level of comfort at about 7 kWh/(m²a).
The electricity consumption for household appliances, power supply and lighting in the average household carries with 31.8 kWh/(m²a) to about 12% of final energy demand. However, it must be kept in the assessment of the electricity consumed in the higher primary energy use of 2.97 kWhPrimär/kWhEnd in mind. Based on the required primary energy use of electricity in the proposed budget takes already today about 27% into account. Even with the current applications are energy efficiency improvements possible, todays existing equipments used in households are mainly old, which have a much lower efficiency than today commercially available efficient household appliances. Field measurements in a sample households have shown that a household with fully-equipped electrical appliances with the most efficient devices on the market available can be maintened with less than 15 kWh (m²a).
On the right side of Figure 1, the resulting distribution of final energy consumption in a household with very high energy efficiency is given. These are average results for the four households (a total of 14 persons) in the passive house (show houses) for the period of 5 years. The specific final energy consumption is compared to the average of exisiting building only by using high-efficiency equipment (including a solar hot water usage) is reduced by 88%. The practical success of the efficiency of technology illustrates well that the basic considerations on the thermodynamics of energy use in homes are properly. The use or the energy required for the provision of energy services can be reduced to an almost vanishing fraction of today’s conventional energy flows.
4 Efficient living space heating – principle of the passive house
….will be continued in part 2