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14 декабря, 2021
Fig.3. shows the simulation results of the temperatures of the solar collector, the heat storage tank, the boiler and the DHW use. Fig.4. shows the simulation results of the solar radiation on the collector, the collected solar energy and the DHW heating load. Figs.3 and 4 show the results for the collector tilt angle of 40 degrees and the azimuth of 0 degrees (due south) in Tokyo.
The large differences were not found for the outlet temperatures of the solar collector. The temperatures of the heat storage tank were almost the same. The bottom temperatures of the tank in Cases 2 and 3 were close. The difference in Cases 1 and 3 was about 6 degrees C while the difference in Case 2 and 3 are very small. The temperatures of the DHW supply in Case 1 are lower than Cases 2 and 3, since the flow rate in Case 1 is very small.
The differences in collected solar energy in Case 1 to 3 were small in Fig.4.
Table 2. shows the comparison of the yearly performance. The solar radiations on collector are almost the same. For the collected solar energy, Case 3 with the short time increment is the largest, but almost same as Case 2. The collector efficiencies for Cases 1 to 3 are 36.8 %, 38.6 % and 38.9 %, respectively. For the DHW heat load, Case 1 is the largest. The solar contributions for Cases 1 to 3 are 55.8 %, 60.7 % and 62.5 %, respectively. The results of Cases 2 and 3 are close. Therefore, it was considered that the suitable time increment is 10minutes. Case 1 is different from Cases 2 and 3. However, the simulation with 1 hour increment can be considered that the results may not over estimating the system performance.
Simulation of total system performance in five cities
The detailed system simulation was carried out for 42 combinations of collector tilt angle and azimuth as shown in Table3. for five cities in Japan, Sapporo (43 degrees N), Morioka (39 degrees N), Sendai (38 degrees N), Tokyo (35 degrees N) and Kagoshima (31 degrees N). Five cities were selected to examine the
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average primary energy was less than the case of without solar DHW heating system by 10
GJ. The CO2 emission was around 52 % of the average of the solar DHW system.
Fig.6. shows the comparison of the yearly performance of with the combinations. As the contour, the combination of the collector tilt angle of 40 degree and the azimuth of 0 degree is expressed as 100 %. The results of 100 % are the combination of the collector tilt angle from 30 to 40 degrees and azimuth within 15 degrees. When the collector tilt angle is too low and too high or azimuth is largely deviated from 0 degrees, collector performance is reduced. However, the difference is within 10%.
Table 5. shows the average yearly performance in five cities in Japan. The collector efficiencies are close in each region. In Sapporo, the average temperature of city water was the coldest. Therefore, the DHW heat load is highest in five cities. The solar contributions for DHW heating load in Sapporo, Morioka, Sendai, Tokyo and Kagoshima were 44.3 %, 45.7 %, 51.0 %, 57.0 % and 65.5 %, respectively.
Table 5. Comparison of average yearly performance in five cities
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The boiler heat loads with the solar DHW system in five cities are 9.3 GJ/year, 8.8 GJ/year,7.5GJ/year, 5.8 GJ/year and 4.1 GJ/year, respectively.
The electricity consumption of the collector pump and the boiler were 87 kWh/year and 111kWh/year (278 MJ/year), respectively. The CO2 emissions were reduced to 63.1 %, 62.2 %, 57.5 %, 53.5 % and 47.8 %, respectively.
1) In order to find the suitable time increment in the simulation of the solar DHW system, the results of three time increment cases, 1 hour, 10 minutes and 1 minute were compared. The simulated results of 10 minutes and 1minute time increments were very close.
Therefore, 10 minutes time increment is considered to be the suitable for the solar DHW heating system simulation. However, in case of 1 hour time increment, the simulated result in solar energy contribution was lower than other two cases by 8 % and the auxiliary boiler load was larger by 14 %. This means that the simulation results with 1 hour time increment does not overestimate the system performance.
2) The comparison of the total system performance of the solar DHW heating system for the combination of collector tilt angle and azimuth in Tokyo was carried out. The difference of the system performance was within 15 % when the collector tilt angle is from 10 to 60 degrees and azimuth is within 45 degrees from due south. As the similar results were found for the effect of collector tilt angle and azimuth on the total system performance in other four cities, there are many possible ways of the tilt angle and azimuth of collector in designing the solar DHW system in Japan.
3) The average solar system performance was compared in five cities in Japan. The simulation result showed that the solar contribution for DHW heating load in Sapporo, Morioka, Sendai, Tokyo and Kagoshima were 44.3 %, 45.7 %, 51.0 %, 57.0 % and 65.5 %, respectively. The difference is caused by the in DHW heating load which strongly influenced by the city water temperature.
[1] T. Kusunoki and M. Udagawa, Effect of Hot Water Heating Load in Solar DHW Heating System, Proceedings of JSES/JWEA Joint Conference 2007, pp.217-220. (In Japanese)
[2] T. Aoki and M. Udagawa, Effect of Building Orientation for Overall System Performance of Solar House — Application of EESLISM for solar house design-, Proceedings of ISES RENEWABLE ENERGY 2006.
[3] T. Aoki, M. Udagawa and H. Roh, Optimum Collector Arrangement for Solar Space and Hot Water Heating System, Proceedings of ISES EuroSun2006.
[4] M. Satoh and M. Udagawa, Study on the Simulation Time Increments for Solar DHW Heating Systems, Proceedings of JSES/JWEA Joint Conference 1997, pp. 129-132. (In Japanese)
[5] M. Udagawa, and M. Satoh, Energy Simulation of Residential Houses using EESLISM, Proceedings of Building Simulation ‘99, pp.91-98. (In Japanese)
[6] SHASEJ Report, Estimation of CO2 emission from residential house for validation the reduction effects of heating, cooling and hot water systems, SHASEJ, 2008.3
[7] Architectural Institute of Japan, Expended AMeDAS Weather Data, 2005. (In Japanese)