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of the system can be ensured. Another option to lower the primary energy consumption is the use of electricity from renewable energy sources, possibly generated locally. Considered from a wider

Figure 3: Comparison of the calculated difference in cumulative costs of the two hot water supply systems studied, over a period of 30 years for three scenarios on energy price developments. The calculations are based on price levels in The Netherlands and adjusted to net present values.

generation of electricity is potentially accompanied by large energy losses. In the Netherlands, the overall amount of electricity produced – both from renewable and non- renewable resources – currently accounts to 50.4% of the primary fossil fuel input attributed to electricity production.2

perspective, the DSS concept fits within the much-discussed society-wide transition towards a more sustainable energy supply system. This transition is expected to be accompanied by an increased use of electricity as energy carrier, induced by the increasing exploitation of renewable energy resources, such as wind and solar energy. The DSS concept thus conforms to the anticipated future energy infrastructure. Already, hospitals are experiencing an increasing electrification of the energy supply. The development of the all-electric hospital is well underway and could be accelerated by the DSS concept. An energy supply system, that is entirely based on electric energy, is potentially lean, clean and future-proof while offering a high level of comfort.

Energy costs The difference in energy costs between the two systems depends on local prices for gas and electricity. Per unit

Yet, even

when these generation losses are taken into account, the primary energy consumption of the system based on the DSS concept is still smaller than that of the centralised system, as shown in Figure 2. Both concepts offer opportunities to lower

the primary energy consumption. In a centralised system, the water could be preheated by using waste heat from other centralised systems or applying a thermal solar collector or heat pump. For these solutions, high temperatures and continuous circulation are still required. Further, a backup system needs to be available in case the water temperature drops too low. The DSS concept, on the other hand, may be combined with wastewater heat recovery, integrated in sink or shower drains. This enables preheating the feed water to the water heater and thereby lowering the energy consumption. Obviously, wastewater heat recovery should only be applied if the safety


energy content electricity is generally more expensive than gas; in the Netherlands, for example, electricity is currently more than twice as expensive as gas. Yet, in our calculations the energy content of the electricity consumed by the system based on the DSS concept is only 40% of the energy content of the gas consumed by the centralised system. This means that, considering the energy prices in the Netherlands, the system based on the DSS concept will result in lower energy costs than the centralised system. Even more important when considering life cycle costs, are future price developments. Along with gas reserves and geopolitical issues, gas prices are subject to uncertainty and fluctuations. Since electricity can be produced in many ways, electricity prices are likely to be more stable. Moreover, electricity prices are expected to drop if technology advances, especially when the energy transition is progressing. To demonstrate the effect of these

developments, the difference in cumulative costs of the two systems over a period of 30 years was calculated, based on three scenarios on energy price developments. The total costs includes material cost, installation, energy cost and maintenance, based on price


levels in the Netherlands and adjusted to net present values. The result of the calculations is shown in Figure 3. Electric water heaters are expected to have a shorter lifetime than the other components in both systems, which is visible in the chart by a sudden increase in costs after 15 years. The chart shows that, when gas prices increase at a higher rate than electricity prices, as in scenario 1, the cumulative costs after 30 years are expected to be lower for the system based on the DSS concept than for the centralised system. This is also the case when the gas and electricity price developments are equal, as in scenario 2. Only if electricity prices exhibit a sharp increase compared to gas prices, as in scenario 3, the DSS concept is expected to lead to higher cumulative costs than the centralised system.

Conclusion The conventional centralised hot water system as currently applied in most hospitals has several disadvantages with respect to safety, control and energy consumption. These disadvantages do not apply to a system based on decentralised hot water generation, using electric instantaneous water heaters. Calculations have shown that the energy losses in a centralised system are substantial and, in the building under study, account for over 65% of the energy consumption of the entire system. In contrast, a system based on the DSS

concept results in minimal building-related energy losses. Even when accounting for energy losses during electricity generation from mostly non-renewable resources, the primary energy consumption is smaller for the system based on the DSS concept than for the centralised system. In addition, using electricity rather than gas, the DSS concept conforms to an anticipated future energy infrastructure based on electricity generated from renewable resources. Depending on local price levels, the DSS concept can also be highly beneficial in terms of life cycle costs.

References 1 World Health Organization, 2007, Legionella and the prevention of legionellosis. ISBN 92 4 156297 8.

2 Centraal Bureau voor de Statistiek, 2014, Rendementen en CO2

-emissie van elektriciteitproductie in Nederland, update 2012.

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