Case study: Heating and cooling supply of a district with hydrogen
In this case study, a district with district heating and district cooling network is partially supplied by hydrogen technologies. The entire planning process can be carried out with the nPro tool: From the demand calculation, to the pipe dimensioning, to the design of the components in the energy center.
An energy supply for an exemplary district with 6 buildings is planned. The location of the districts is assumed to be Berlin (Germany).
In a first planning step, the demands for heating, cooling and electricity are determined for each building. It is assumed that all buildings are supplied with space heat and domestic hot water via a district heating networks. Space cooling and process cooling (e.g. server cooling) are covered by a district cooling network. Plug-load demands (e.g. for lighting) and electric demands for e-mobility are the electricity demands of the district. The demand profiles for each of the 6 buildings can be created in nPro with a few clicks. Annual profiles with hourly resolution are of great importance for the calculation of the districts, since renewable sources (here photovoltaics) strongly depend on the daytime and season.
|A||Hotel||20000 m²||1700 MWh||640 MWh||980 MWh||3000 MWh|
|B||Office||18000 m²||1170 MWh||144 MWh||1062 MWh||936 MWh|
|C||Retail||24500 m²||1593 MWh||74 MWh||784 MWh||2352 MWh|
|D||Museum||16500 m²||1073 MWh||83 MWh||578 MWh||859 MWh|
|E||Theater||6700 m²||503 MWh||40 MWh||101 MWh||563 MWh|
|F||Restaurant||2500 m²||188 MWh||125 MWh||50 MWh||358 MWh|
Load at energy hub
After adding all buildings to the district, the load profiles can be displayed in nPro in hourly resolution. Figures 2 to 5 show the demand profiles at the energy center for heating, cooling and electricity.
In nPro, the diameters of the pipes for district heating networks can be dimensioned semi-automatically. In this design example, the assumptions listed in Table 2 are made for the heat network calculation.
|Parameter||District heating||District cooling|
|Relative heat/cold losses||12 %||8 %|
|Pump work (share of heat/cold supply)||1 %||2 %|
|Temperature spread||20 K||10 K|
|Pipe roughness||0.1 mm||0.1 mm|
Figure 7 shows an example of the dimensioning of the supply pipe to buildings B, C and D. In the preliminary design, the nPro tool suggests three pipe diameters for this network section. In this case, these are the diameters DN150, DN200 and DN250. nPro then calculates the maximum pressure drop for each of the suggested diameters, as well as other key figures such as the annual pumping work or maximum flow velocities. Based on this information, the user can select the optimal pipe diameter.
The optimized pipe diameters for the heating (red) and district cooling network (grey) for this district are shown in Figure 8.
Design of the energy center
In this district, the heating and cooling supply is supported by hydrogen technologies. For the design, it is assumed that a 3 MW connection to an existing district heating network is available. The remaining heat is to be covered by an electrolysis process. The electrolyzer to be installed produces hydrogen from surplus PV electricity, which is fed into the natural gas grid. The resulting waste heat is fed into the district heating network. The PV electricity generation is shown in Figure 9.
Figure 10 shows the operation of the energy supply system optimized by nPro. The cooling loads are covered by compression chillers. The optimal PV system capacity is 58800 m², which is the maximum module area that can be installed in this district. 38 % of the electricity required in the district is purchased from the grid. 62 % of the electricity is generated on site by the PV system. The hydrogen feed-in is shown in Figure 11. It can be seen that almost exclusively surplus PV electricity is converted to hydrogen. Overall, 92.1 % of the heat supply is covered by the district heating network. 7.9 % is covered by waste heat from the electrolysis process. The CO2 emissions of this district are 4370 t per year.