Energy saving potentials by optimisation of existing domestic hot water systems

Consideration of single family houses and multiple dwellings with central and decentral supply systems

In order to achieve the political goals of reducing CO2 emissions a decrease in energy consumption in the buildings sector is highly relevant. The sequence of measures is to:

1.    reduce energy demand,
2.    cover the demand efficiently,
3.    cover the demand with renewable energies  and
4.    use demand supportive for the overall energy system.

The supply of domestic hot water currently accounts for about 5% of Germany's final energy demand and over 14% of the final energy demand of private households. In existing domestic hot water supply systems, the energy losses often exceed the useful energy, although these losses can be reduced significantly through low-investment measures.

As part of a state-wide campaign to save energy, conducted by the Consumer Advice Centre North Rhine-Westphalia, FfE prepared a study entitled "Energy saving potentials by optimisation of existing domestic hot water systems".

In this study, firstly possibilities to reduce energy requirements and costs for the provision of domestic hot water were examined regarding their economic viability. Combined with the composition of the domestic hot water supply systems in the building stock in North Rhine-Westphalia (derived from statistical data), it was possible to determine energy and cost-saving potentials for the federal state (see Figure 1).TWW Homepage Grafik1

Figure 1: Energy requirements and losses in North Rhine-Westphalia calculated in the initial state of the domestic hot water supply system and after implementation of economically viable measures to increase efficiency

In the second part of the study, the technical and economic potentials of the use of electricity from a privately owned photovoltaic system were examined. The calculation tool created for this purpose makes it possible to simulate the flexibility of domestic hot water and electricity requirements via a thermal or electricity storage. The results include a visual comparison of the resulting energy costs with and without flexibilisation of the energy consumption (see example in Figure 2).

Details can be found in the final presentation and the project report.

TWW Homepage Grafik2

Figure 2: Comparison of annual energy costs for the provision of domestic electricity and hot water without and with selective personal consumption – Here considered: domestic hot water heat pump with 200 l hot water storage and 4.3 kWh electricity storage.

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