Carsten Petersdorff 1231 Concept

In high-performance houses, while the heat demand is reduced to a very low level and occurs during only a few months of the year, it does not decrease to zero. Certainly, a significant part of the space heating and major part of the hot water demand can be covered by solar energy. However, to cover 100 per cent of the demand would be economic nonsense. Such a system would be grossly over-dimensioned most of the year, having to dispose of heat. A backup heating system to cover the peaks is essential. Burning a fossil fuel is a proven means of providing this backup. Due to the small absolute quantities of fuel consumed, the environmental impact is negligible. Especially in high-performance houses, the following should be considered:

• Connection costs: because the absolute amount of heat required is so small, the fixed costs must be kept minimal, including the investment cost, the connection to networks, fuel storage, and maintenance, operational and administrative costs.

• Low peak demand: the peak demand capacity for high-performance homes decreases with lower heating energy demand to levels of a few kW. 10 W/m2 is typical for space heating peak demand in a high-performance house. Even this, though very small, only occurs during the coldest, sunless hours of the year. The majority of space heating systems on the market are oversized for such small demands. For domestic water heating, the peak can be kept small according to the size of the storage tank.

• Losses in heating and auxiliary systems: with lower total energy consumption, energy losses in heating systems and auxiliary systems become increasingly important. Thermal storage and heating devices should be installed within the heated space of the building as far as possible so that energy losses contribute to the heating. Pumps and control systems need to have no or low standby losses and must show good part-load efficiency.

• Hot water: energy demand for DHW remains at the same level (approximately 700 kWh/a per person), while space heating demand is cut to a fraction in high-performance buildings. Accordingly, the proportion of energy required for DHW becomes important.

The term fossil fuel applies to energy carriers that were formed from plant and animal organisms some millions of years ago. During their lifetime, these life forms absorbed carbon dioxide (CO2) from their environment and now store carbon in underground reservoirs in the form of natural gas, crude oil and coal. Burning fossil fuels releases the stored chemical energy, while emitting CO2 again.

The reserves of fossil fuels are, by definition, limited. Estimates suggest that all economic reserves of oil will last approximately 40 years under the current consumption rate. For gas, the reserves are estimated to last some 60 years, while the coal resources are predicted to last for some 170 years, as seen in Table 12.3.1. With increasing demand - for example, from developing countries - these times will be proportionally shorter.

Guide to Alternative Fuels

Guide to Alternative Fuels

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