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Domestic hot water demands in districts

The demand for domestic hot water can play a decisive role in the planning of district heating networks, as it exists all year round and has only a low seasonal dependency.

How large is the domestic hot water demand?

The useful energy demand for domestic hot water is set at a flat rate of 12.5 kWh/m²a for residential buildings in the German Energy Saving Ordinance (ENEV) 2014. In the Austrian thermal insulation standard ÖNORM B 8110-5, a flat rate of 35 Wh/m²/day is applied for residential buildings, which corresponds to 12.8 kWh/m²a for 365 days. For offices, the area-specific domestic hot water demand is usually significantly lower. According to ÖNORM B 8110-5, this is half that of residential buildings, i.e. 6.4 kWh/m²a. For hospitals, it is about twice as high (25.6 kWh/m²a). It should be noted that distribution losses within a building are about as large as the actual useful demands, so that heat generation for domestic hot water for a residential building is about 25 kWh/m²a.

Table 1: Domestic hot water for different buildingy types (without distribution losses).
Building type Domestic hot water demand
Residential 12,5 kWh/m²
School 3 kWh/m²
Office 8 kWh/m²
Hospital > 30 kWh/m²
The nPro tool provides specific domestic hot water requirements for different building types for orientation purposes, including literature values from statistical surveys and national standards.

Simulation und calculation

Stochastic simulations can be used to determine demand profiles. These simulations model user behavior in detail and are based on so-called tap profiles. The disadvantage of these simulations is that very extensive input data is required, e.g. occupant presence profiles (partly derivable from age and occupational activity). These data are usually not available at an early planning stage of districts. It is therefore often appropriate to use experience-based data from the literature as a basis for estimating the demand for domestic hot water. In this way, the total requirements for domestic hot water are sufficiently accurate in a first approximation. With the help of typical usage profiles, hourly resolved demand profiles can also be generated.


  1. Energieeinsparverordnung (ENEV) 2014.
  2. Wärmeschutznorm ÖNORM B 8110-5 (Österreich)

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