In this case study, a district with district heating and district cooling network is partially supplied by solar thermal collectors. The entire planning process can be carried out in the nPro tool: From the demand calculation, to the pipe dimensioning, to the design of the components in the energy center and the solar thermal collectors.

District

An energy supply for an exemplary district with 6 buildings is planned. The location of the districts is assumed to be Berlin (Germany).

Figure 1: District with the 6 buildings to be supplied. The energy center is located in building A.

Demand analysis

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 solar thermal collectors) strongly depend on the daytime and season.

Table 1: Overview of the building demands in the district

Building	Usage	Floor area	Space heating	Domestic hot water	Space cooling	Electricity
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.

Figure 2: Heat demand profile at the energy center

Wärmebedarfsprofil an der Energiezentrale als Heatmap

Figure 3: Heat demands at the energy center shown as a heat map

Figure 4: Cooling demand profile at the energy center

Strombedarfsprofil an der Energiezentrale als Heatmap

Figure 5: Electricity demand of the district shown as heat map

Pipe dimensioning

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.

Table 2: Assumptions 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 %
Diversity factor	0.9	0.9
Temperature spread	20 K	10 K
Pipe roughness	0.1 mm	0.1 mm

Figure 6 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.

Figure 6: Pressure drop in the flow and return of the heat network line supplying buildings B, C and D for three different pipe diameters.

The optimized pipe diameters for the heating (red) and district cooling network (grey) for this district are shown in Figure 7.

Figure 7: Pipe dimensioning of the heating (red) and district cooling network (grey).

In the nPro tool, pipe diameters for heating, cooling, and 5GDHC (anergy) networks can be determined and optimized.

Design of the energy center

In this district, the heating and cooling supply is supported by solar thermal collectors. For the design, it is assumed that at the energy center a connection to an existing district heating network is available to cover base heat load. Heat from solar thermal collectors is used directly in the district and, it is possible to feed surplus heat into the district heating network. The heat generation from solar thermal collectors is shown for incident angles of 60° and 15° in Figures 8a and 8b, respectively.

Figure 8a: Heat generation by solar thermal collectors (60° incident angle) over the course of the year

Figure 8b: Heat generation by solar thermal collectors (15° incident angle) over the course of the year

Figure 9 shows the operation of the energy supply system optimized by nPro. The cooling loads are covered by compression chillers. The optimal solar thermal area is 5000 m², which is the maximum installable area for this district. The solar thermal collectors produce 442 kWh of heat per m² of collector area per year. 24.3% of the heat demands in the district are met by the solar thermal collectors, and the remaining 75.7% are met by the external district heating connection. The electricity to cover the building demands and the compression chillers is purchased directly from the power grid. Figure 10 shows the heat purchased from the external district heating network. It can be seen that in summer, almost no more heat needs to be imported from the external district heating network due to the solar thermal system and the heat storage.

Figure 9: Optimized energy system with solar thermal collectors and heat storage

Figure 10: Heat import from the external district heating network. Due to the solar thermal system, almost no heat needs to be imported from the external district heating network in summer.

The operation of the thermal storage (Figure 11) shows that the storage is charged in the afternoon hours in summer and discharged in the evening/night hours. nPro also provides an economic analysis of the energy supply system. Figure 12 shows the evolution of the net present value over the lifetime of the system. A positive net present value at the end of the project life indicates that the investment pays off. The environmental analysis in nPro shows that the CO₂ emissions of this district are 4365 tons per year.

Figure 11: Operation of the heat storage: The storage is mainly used in summer to utilize surplus heat from solar thermal energy in the evening and night hours.