Year round performance

Fig.6 shows the year-round performance of the solar DHW system. In Fig.6 the collector efficiency, the DHW heat load, the solar contribution, the CO2 emission and energy cost are compared. The performance in Fig.6 is expresses for a housing unit. The CO2 emission was calculated from the gas calorific value of 45MJ/m3 and the CO2 emission coefficient of 2.21kg/m3. The energy cost was calculated using the fee structure of the city gas company in Tokyo. The average unit price of the gas is 149JPY/m3. The collector efficiency for the collector area of 20m2 with Case A DHW supply is from 53.0% to 63.4%. It tends to increase according to the storage tank volume is large. The collector efficiency decreases by 3.6%-7.2%, when the collector area increases by 10m2. The considerable difference in the collector efficiency is found when increasing from 0.5m3 to 1.5m3 of the storage tank volume, however there is only few difference when the storage tank volume is more than 2.0m3. The collector efficiency for the collector area of 30m2 and the storage tank volume of 1.0m3 is 53.0% with Case A DHW supply, 49.5% with Case B DHW supply, and 41.6% with Case C DHW supply, respectively. The CO2 emission for collector area of 30m2 and the

image207

Fig.6 Year-round performance from the simulation results expressed for a housing unit.

 

storage tank volume of 1.0m3 is 650kg-CO2/year with Case A DHW supply, 300kg-CO2/year with

 

Case B DHW supply, and 67kg-CO2/year with Case C DHW supply, respectively, for a housing unit.

Relationships of the collector area and the storage tank volume for the solar contribution is shown in Fig.7. The solar contribution increase by 4%-26% when collector area increases by 10m2 in all simulation cases. In addition, the solar contribution increases with larger collector area and larger storage tank volume. The solar contribution only increase

 

by 2.2% when the storage tank volume is increased from 1.0m3 to 1.5m3 in case of the collector area of 20m2 and Case A DHW supply. However, the solar contribution only increase by 6.7% when the storage tank volume is increased from 1.0m3 to 1.5m3 in case of the collector area of 50m2 and Case A DHW supply.

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image209

The comparison of the saved cost of the city gas for a housing unit was shown in Fig.8. The dark bars in Fig.8 show the suitable combinations of the collector area and the storage tank volume judged from the solar contribution. The saved energy cost for the collector area of 30m2 and the storage tank volume of 1.0m3 with Case A DHW supply is estimated to be 19,700JPY/year for a housing unit. The comparison of the installation cost for 10 housing unit is shown in Fig.9. The installation cost for the collector area of 30m2 and the storage tank volume of 1.0m3 with Case A DHW supply should be suppressed 2.0 million JPY when the pay back period of 10 years is assumed. The installation cost should be suppressed 3.0 million JPY when the pay back period of 15 years is assumed. The saved energy cost for the collector area of 20m2 and the storage tank volume of 0.5m3 with Case A DHW is estimated to be 80,000JPY/year, and the installation costs are 8.0 million JPY and 1.2 million JPY for pay back period of 10 and 15 years, respectively.

Fig.9 The installation cost for 10 housing units assuming the pay back periods of 10 and 15 years.

6. Conclusion

The central type of solar DHW supply system for 10 housing units was simulated to examine the relationships of the collector area and the storage tank volume with considering the DHW supply rate. The simulation results showed the followings.

1) The collector efficiency for the collector area of 30m2 varies from 38% to 59% depending on the storage tank volume and the DHW supply rate. The collector efficiency decrease by 3.6%-7.2%, when the collector area increases by 10m2.

2) The suitable storage tank volume is from 1.0m3 to 1.5m3, since the collector efficiency decreases extremely when the storage tank volume is 0.5m3. The efficiency for 2.0m3 is almost same as the case for 1.5m3.

3) The solar contribution for the collector area of 30m2 and the storage tank volume of 1.0m3 is 37.1% with Case A DHW supply, 52.5% with Case B DHW supply, and 74.6% with Case C DHW supply, respectively.

4) The boiler load for the collector area of 30m2 and the storage tank volume of 1.0m3 is 105.9GJ/year with Case A DHW supply, 48.6GJ/year with Case B DHW supply, and 10.8GJ/year with Case C DHW supply, respectively.

5) The installation cost for the collector area of 30m2 and the storage tank volume of 1.0m3 should be suppressed 2.0 million JPY with Case A DHW supply, 1.7 million JPY with Case B DHW supply and 1.0 million JPY with Case C when the pay back period of 10 years. The installation cost for the collector area of 30m2 and the storage tank volume of 1.0m3 should be suppressed 3.0 million JPY with Case A DHW supply, 2.5 million JPY with Case B DHW supply and 1.5 million JPY with Case C when the pay back period of 15 years.

References

[1] T. Kusunoki and M. Udagawa, Planning of Solar Collector Arrangement for Solar DHW Heating Apartment House, Proceedings of JSES/JWEA Joint Conference 2006, pp. 125-128. (In Japanese)

[2] H. Roh and M. Udagawa, Study on Standardization of Solar DHW Heating System for Apartment Houses, Proceedings of JSES/JWEA Joint Conference 2005, pp.79-82. (In Japanese)

[3] M. Udagawa, H. Roh and M. Satoh, Design of Solar DHW System for Apartment Houses, Proceedings of ISES Solar World Congress 2005

[4] M. Udagawa, and M. Satoh, Energy Simulation of Residential Houses Using EESLISM, Proceedings of Building Simulation ‘99, pp.91-98. (In Japanese)

[5] Architectural Institute of Japan, Expended AMeDAS Weather Data, 2005. (In Japanese)

[6] S. Kaneko, M. Udagawa and T. Kusunoki, Design of Solar DHW Heating System for Small Apartment House, Proceedings of JSES/JWEA Joint Conference 2007, pp.213-216. (In Japanese)