## 5 Results and Discussion  
To test the prospective EHS for a real heating scenario, the real heating data for the oil-fired heating on the campus of the 15 November 2016 between 08:42 o'clock and 10:22 o'clock are given to the Heating Mockup, cf. Figure 1. Thereby, the following was selected as the connection variant, because it gives the best result: TEG block 1 and 2 are connected in series and then to MPPT1, whereas TEC block 3 and 4 are also connected in series and supply the fans of Section 1. Thus, in this scenario, a fan control over the duty cycle is not necessary, as the fan velocity will be self-controlled by the energy supported from TEC block 3 and 4. Consequently, the power delivered from TEG block 1 and 2 can be completely considered gained power of the system. The measurements as well as the simulation results are shown in Figure 9, where the upper diagram shows the measured temperatures as well as the set temperature inside the pipe and the lower diagram shows the measured gained power and energy as well as the simulated ones. As there are no additional consumers connected and the fans are directly supplied by TEC block 3 and 4, there is no direct power consumption. In the upper diagram of Figure 9, it is visible that the reproduced inside pipe temperature of the medium fits very well with the set temperature of the medium (which is also the real measured temperature) for temperatures over 80 \({}^{\circ}\)C. However, for lower temperatures there are some overshoots, which are related to the setting options of the hot air blower--it can only be adjusted for temperatures over 80 \({}^{\circ}\)C and due to that fact,  
Figure 8: Simulation model of the thermoelectric EHS at the heating mockup. it turns on briefly and then off again to control lower temperatures. Moreover, it is obvious that the temperatures of the single sections (now, with the attached EHS) are all under 90 \({}^{\circ}\)C, and for the last section the temperatures are approximately 50 \({}^{\circ}\)C. Consequently, the produced power is very low; this is visible in the lower diagram of Figure 9. The maximum gained power is around 2 W, which also matches with the simulation result. Since the oil-fired heating starts about 39 times a day, the daily energy output is approx. 36.4 kJ, which is about 10 Wh a day. Concerning that the number of heating days for this region is on average about 263 days according to [29]; this will be 2.63 kWh per year. To calculate the efficiency of the EHS, Figure 10 represents the system consideration relating to the heat flow rates. The energy balance is given by  
\[0=\dot{Q}_{1}-\dot{Q}_{2}-\dot{Q}_{\text{use}}-\dot{Q}_{\text{ lost}}\, \tag{1}\]  
where \(\dot{Q}_{1}\) is the inflow heat rate, \(\dot{Q}_{2}\) the outflow heat rate, \(\dot{Q}_{\text{use}}\) the useful heat rate and \(\dot{Q}_{\text{ lost}}\) the lost heat rate. With the assumption of no heat losses, the useful heat rate can be calculated by  
\[\dot{Q}_{\text{use}}=\ \dot{Q}_{1}-\dot{Q}_{2}=\dot{m}\cdot c_{p}\cdot(T_{1}-T_{2 })\, \tag{2}\]  
The temperatures \(T_{1}\) and \(T_{2}\) as well as the mass flow rate \(\dot{m}\) are measured or calculated values, whereas the specific heat capacity \(c_{p}\) of the medium can be taken from the simulation. Thus, the useful heat rate here is approx. 560 W at the peaks, cf. Figure 9. The produced power is 2 W and so the efficiency is about 0.36%, according to the following equation:  
\[\eta_{\text{TEG}}=\frac{P_{\text{el}}}{\dot{Q}_{\text{use}}}\, \tag{3}\]  
where \(\eta_{\text{TEG}}\) is the efficiency of the TEG-based EHS and \(P_{\text{el}}\) the produced electrical power. Figure 9: Measurement and simulation data for the heating mockup: heating scenario of the oil-fired heating on campus on 15 November 2016 between 8:42 a.m. and 10:22 a.m., executed on 21 December 2016 at the Heating Mockup. Above: temperature curves of each section as well as the set and real inside pipe temperature at the beginning; below: produced power and energy of the EHS and the corresponding simulation results.