@@ -58,22 +58,37 @@ The detailed input parameters can be found in the 3bhes\_1U.prj file, they are a
### TESPy
A one-way pipeline network system was constructed in TESPy to be coupled with the OGS model.
The TESPy software developed by Francesco Witte is capable of simulating coupled thermal-hydraulic status of a network, which is composed of pre-defined components including pipes, heat exchangers, and different types of turbo machinery.
Here, the TESPy software developed by Francesco Witte is employed to simulate the coupled thermal-hydraulic status of a pipe network, which is composed of pre-defined components including pipes, heat exchangers, and different types of turbo machinery.
Interested readers may refer to the online documentation of TESPy for the detailed introduction of the software.
The TESPy version 0.3.2 is used in this benchmark.
Figure 1 illustrates the basic configuration of the entire network.
Two different pipe network setup were constructed for this benchmakr.
* A one-way pipe network (see Figure 1a)
In this setup, the refrigerant flow rate in the network is pre-defined by the user.
After being lifted by the pump, the refrigerant inflow will be divided into 3 branches by the splitter and then flow into each BHEs.
Because of the pipe network configuration, the inflow temperature on each BHE will be the same.
Because of this configuration, the inflow temperature on each BHE will be the same.
The refrigerant flowing out of the BHEs array will be firstly mixed at the merging point and then extracted for the heat extraction through the heat pump.
After that, the refrigerant will flow out from the network.
For the boundary condition, a constant thermal load of 3750 $W$ is imposed on the heat pump for the entire simulation period, which means an average specific heat extraction rate on each BHE with 25 $W/m$.
The fluid enthalpy value at the splitter point is set to be equal to the sink point enthalpy, such that means all the consumed heat on the heat pump is supplied by the BHEs array.
For the boundary condition, a constant thermal load of 3750 $W$ is imposed on the heat pump for the entire simulation period. which means an average specific heat extraction rate on each BHE with 25 $W/m$.
The fluid enthalpy value at the splitter point is set to be equal to the sink point enthalpy, that means all the consumed heat on the heat pump is supplied by the BHEs array.
The setup for a closed-loop network model is illustrated in Figure 1b.
Compared to the configuration in the one-way network, the refrigerant in the closed loop network is circulating through the entire system.
In this case, the flow rate will be automatically adjusted by the water pump in each time step, as its pressure head is directly linked to the flow rate. Subsequently, the flow rate is determined by the pressure losses in the BHE array.
@@ -84,6 +99,14 @@ This imbalance leads to a lower outflow temperature from the BHE \#2, which is s
Compared to the decrease of the heat extraction rate on the centre BHE \#2, the rates on the other two BHEs located at the out sides was gradually increasing.
It indicates that the heat extraction rate is shifting from the centre BHE towards the outer BHEs over the heating season.
In comparision to the one-way setup, the closed-loop network shows a slightly different behaviour.
The evolution of inflow refrigerant temperature and flow rate entering the BHE array is shown in Figure 5.
With the decreasing of the working fluid temperature over the time, the system flow rate dereases gradually.
Figure 6 depicts the thermal load shifting phenomenon with the closed-loop model.
Except for the thermal shifiting behavior among the BHEs, the averaged heat extraction rate of all BHEs (black line) increases slightly over the time.
This is due to the fact that additional energy is required to compensate the hydraulic loss of the pipe.
Figure 2: Evolution of the soil temperature located at the 1 m distance away from each BHE
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@@ -96,28 +119,14 @@ Figure 3: Evolution of the inflow and outflow refrigerant temperature of each BH
Figure 4: Evolution of the heat extraction rate of each BHE
### Closed loop networt model
The one-way network model used in this example can be replaced by a closed loop network model which illustrated in Figure 5.
Compared to the configuration in the one-way network, The refrigerant in the closed loop network is circulating through the entire system.
In this case, the system flow rate will be automatically adjusted by the water pump in each time step, in order to guarantee the energy balance on every point within the system.
The evolution of inflow refrigerant temperature and flow rate entering the BHE array is shown in Figure 6.
With the decreasing of the working fluid temperature over the time, the system flow rate dereases gradually accordingly.
Figure 7 depicts the thermal load shifting phenomenon with closed loop network model.
Except for the thermal shifiting behavior among the BHEs, the averaged heat extraction rate of all BHEs (black line) increases slightly over the time.
It indicates that more energy is required to be extracted on the BHE array, since the hydraulic loss within the pipe increases due to the decrease of the system flow rate.
Figure 7: Evolution of the heat extraction rate of each BHE with close loop network model
Figure 6: Evolution of the heat extraction rate of each BHE with close loop network model
## References
[1] Diersch, H. J., Bauer, D., Heidemann, W., Rühaak, W., & Schätzl, P. (2011). Finite element modeling of borehole heat exchanger systems: Part 1. Fundamentals. Computers & Geosciences, 37(8), 1122-1135.
