本研究主要是利用太陽能來驅動太陽能空氣加熱器，以達到在冬天溫室取暖升溫的效果，實驗除了測試單一太陽能空氣加熱器的效率之外，在冬天的實驗會將太陽能空氣加熱器以串聯、串並聯的方式連接來進行溫室取暖，經由串聯的方式將由溫室內部風扇抽出的空氣經由三組串聯的太陽能空氣加熱器加熱之後再送回溫室，形成一個內循環的空氣流動，進而提升溫室內部空氣溫度，而串並聯的連結方式則是將原本三個太陽能空氣加熱器串聯成一排之外再多增加兩排，將總共九組的太陽能空氣加熱器連結成三排，並以串並聯方式來增加空氣的流量以及溫度，所以串並聯的空氣流量將會是原本串聯的三倍，可以加快溫室暖房的速率。實驗中建有一溫室，內部再分為兩室，一邊為裝有太陽能加熱器的A室，另一邊為未裝有太陽能加熱器的B室，用此兩室做為比較，實驗的結果發現串聯時A室的整體的平均溫度比B室高了7.8℃，而串並聯時A室的平均溫度比B室高了9.9℃，是有效而環保的建築物取暖的方式。

SUMMARY

This study is to use solar energy to drive the solar air heater, in order to increase indoor temperatures in the winter. Not only was the efficiency of the solar air heater tested in this experiment, but the series connection and series-parallel connection of the solar air heater were also performed during winter. The method of series connection was to heat the air that was extracted from the inner greenhouse by the three series connection solar air heater, and then send the air back to the greenhouse. The inner circle air flowing was built then to increase the inner air temperature of the greenhouse. In addition, the method of series-parallel connection was to connect three series connections in a parallel way. This method was to increase the air flow and temperature, so the air flow was three times the single series connection. A greenhouse was built in the experiment and separated into Room A and Room B. The solar air heater was placed in Room A but not in Room B. After the comparison, the average temperature of Room A was 7.8℃ higher than that of Room B in the series connection and the average temperature of Room A was 9.9℃ higher than Room B in the series-parallel connection.
Keywords: solar thermal energy, solar air heater, heating, series connection, series-parallel connection

INTRODUCTION

Humans usually keep warm indoors by stoves or electric heaters in boreal regions, which causes high power consumption and air pollution. Although they have low temperatures in the winter, many areas still have a rich amount of radiation. Studies relating to using solar thermal heating techniques have found that appropriate obstacles could increase the contact area of the absorber plate and the air, thus more efficiently heating the air. The efficiency of the solar air heater could also be different due to the different geometry of the shape; the temperature of the perforated absorber plate performed 27% higher than the flat-type absorber plate because the perforated absorber plate has a wider area for heat transferring and increased disturbance to obtain better heat exchange. The air of the greenhouse was re-heated by the solar air heater in an inner cycle method in the study. This method is not only for human warming but for agricultural temperature controlling as well.

EXPERIMENTAL SETUP

The solar air heater system is composed of the collector、glass、manifold and the number of the vertical fin. The method is to absorb the heat from the sun with the collector to heat up the fin. Inflow-air will branch in a well-distributed way by the manifold, which is placed at the entry and exit of the solar air heater to obtain better efficiency of heat exchange. When the heat is transferred to the fin, the air is heated by the gradual increase in temperature. Two fans were placed inside the greenhouse and connected to the entry and exit of the solar air heater with a PVC pipe. The heated air will redistribute the energy into the greenhouse in an inner cycle way by fans to increase the temperature of the greenhouse. A test of the series connection of the solar air heater was also performed to increase the temperature at the exit. The air temperature at the exit increased more distinctly if the solar air heater applies more series connection. The outdoor greenhouse was covered with double-PEP film which has a black inner layer and a white outer layer. The dimensions are 10 meters in length, 5 meters in width, and 3 meters in height. The greenhouse is separated into two rooms by an inner wall. Room A is placed at the south side of the greenhouse and installed with a solar air heater. Room B is placed at the north side of the greenhouse and is not installed with a solar air heater. The purpose of Rooms A and B is to compare the inner temperature difference of an installed system versus a non-installed system.

RESULTS AND DISCUSSION

The highest sunshine solar power was 1040W/m2 and the efficiency was 63.6% on April 21, 2014.The highest sunshine solar power was 950 W/m2 on December 31, 2013. The overall efficiency of the series solar air heater was 52.4%. The inlet air temperature of the greenhouse was 61.0℃. The air temperature increased by 30.4℃ after the air went through the solar air heater. The temperature difference between Rooms A and B was 7.7℃.The highest sunshine solar power was 938.3 W/m2 on January 11, 2014. The overall efficiency of the series solar air heater was 48.6%. The inlet air temperature of the greenhouse was 61.8℃. The air temperature increased by 28.1℃ after the air went through the solar air heater. The temperature difference between Rooms A and B was 5.3℃.The highest sunshine solar power was 1119 W/m2 on February 20, 2014. The overall efficiency of the series solar air heater was 52.2%. The inlet air temperature of the greenhouse was 65.8℃. This means that the inlet air of the solar air heater can be heated by the series-parallel connected solar air heater. The air temperature increased by 36℃ after the air went through the solar air heater. The temperature difference between Rooms A and B was 9.9℃.The highest sunshine solar power was 1055 W/m2 on February 22, 2014. The overall efficiency of the series solar air heater was 49.1%. The inlet air temperature of the greenhouse was 61.8℃. This means that the inlet air of the solar air heater can be heated by the series-parallel connected solar air heater. The air temperature increased by 32.6℃ after the air went through the solar air heater. The temperature difference between Rooms A and B was 9.4℃.

CONCLUSION

This study shows that the efficiency of a single solar air heater is higher than series connection and series-parallel connection. The temperature increased when air goes through a solar air heater. The temperature difference between air and solar air heater is lower when the air gets closer to the end of the series module. This makes it harder for heat to transfer which causes more heat loss, so the efficiency decreased when the number of series connection increased. In addition, the temperature of the greenhouse increased by 7.8~9.9℃ after heating through the solar air heater.

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