結合再生能源之淨零碳空調系統實驗分析與研究

Abstract

本研究依據台灣濕熱氣候條件，發展出一套結合再生能源之複合空調系統，並以達成零碳或淨零碳空調系統為目標，本論文分為吸附除溼轉輪冷卻系統開發測試及淨零碳空調系統研究與節能分析兩大部分。首先，本研究開發一套結合淺層溫能及太陽熱能之吸附除溼轉輪冷卻系統來處理外氣負荷，可避免傳統空調系統因冷凝除濕及再熱過程中造成的能源浪費，並提高除溼性能及改善傳統除溼轉輪系統供風溫度過高之問題。此套系統採用20~22oC淺層溫能預冷外氣及處理空氣吸附除溼後的降溫，可提高系統冷卻能力及除溼性能，太陽熱能用於再生除溼材料。量測結果表明，於夏季外氣乾球溫度33.3oC及露點溫度28.0oC情況下，傳統除溼轉輪系統與本研究所開發之系統的能源因數值(Energy Factor, E.F)分別為0.99 kg kW-1hr-1及3.73 kg kW-1hr-1，節能效益可達73%。此外，本研究分別採用淺層地下水溫能及淺層地埋熱交換器兩種不同形式系統進行測試，結果顯示系統皆具可行性，可依系統安裝場域選擇適當的淺層溫能系統。 第二部分為淨零碳空調系統研究與節能分析，系統的組成包含一結合太陽熱能及淺層溫能吸附除溼轉輪冷卻系統、雙效地源熱泵系統、淺層溫能系統及太陽熱能系統，並以宜蘭一面積22.1 m2及高度5.5 m大小之房間作為測試場域，進行實驗量測與性能分析。本系統將外氣負荷及室內負荷分開處理，使用結合太陽熱能及淺層溫能吸附除溼轉輪冷卻系統處理外氣，並設計出四種不同操作模式，可依外氣條件選擇最節能之操作模式；室內負荷由一風機盤管組處理，可依室內負荷需求選擇通入冰水、20~22oC淺層溫能水或熱水，風機盤管組所使用之熱水及冰水分別由雙效地源熱泵製熱模式及製冷模式提供，因外氣潛熱負荷已由除溼轉輪系統處理，風機盤管組僅需處理室內負荷，冰水溫度可設定為14~17oC，較傳統空調冰水設定溫度7~12oC高，故有較佳的製冷COP，可有效降低壓縮機耗能。於外氣乾球及露點溫度分別為28.0oC及24.5oC時，使用此套系統可使室內乾球及露點溫度維持在24.0oC及20.0oC的熱舒適範圍內，且二氧化碳濃度保持在1000ppm以下，系統持續運轉7小時的耗電量，可較傳統空調系統節能63.7%。本論文亦針對宜蘭氣候進行整年運轉分析，當系統每日運轉時間為8:00至20:00的情況下，整年有41.3%的時間不需啟動地源熱泵；於4~11月冷卻負荷較大期間，有19.0%的時間不需啟動地源熱泵。本研究所開發之空調系統，已將耗電需求大幅降低，提高零碳空調系統的可行性，未來可搭配創能及儲能系統，朝零碳空調之目標邁進。

This study developed a hybrid air conditioning system integrated with renewable energy according to the hot and humid climate in Taiwan, so that it can achieve the goal of zero-carbon or net zero-carbon air conditioning systems. This study contains two parts, including the development of a desiccant wheel cooling system and the investigation of a net zero-carbon air conditioning system. First, a desiccant wheel cooling system combined with shallow geothermal energy and solar thermal energy was developed, which was used to handle the outdoor air. It can rule out the energy waste of low dew point temperature of evaporator cooling coil and subsequent reheating. Shallow geothermal energy water, at about 20~22oC, can precool outdoor air and cool the processed air after adsorption dehumidification. Solar thermal energy is used to provide heating source for the regeneration of desiccant wheel system. The cooling capacity and dehumidification performance can enhance. Results show that the energy factor (E.F) of the conventional desiccant wheel system and the developed system under the condition of 33.0oC dry bulb temperature and 28.0oC dew point temperature is 0.99 kg kW-1hr-1 and 3.73kg kW-1hr-1, respectively. The energy savings is up to 73%. Moreover, this study applied two different shallow geothermal energy systems, which are shallow geothermal groundwater system and shallow geothermal earth-to-air heat exchanger system, to conduct the experiments. Results present that the all different shallow geothermal systems are feasible, and it can choose suitable shallow geothermal systems based on the environmental condition of installation sites. The second part is the experimental investigation and energy-saving analysis of a net zero-carbon air conditioning system, which consists of a desiccant wheel cooling system combined with shallow geothermal energy and solar thermal energy, a ground source heat pump system, a shallow geothermal energy system, and a solar thermal energy system. Experimental investigation and performance analysis were conducted in a room with an area of 22.1 m2 and a height of 5.5 m. This net zero-carbon air conditioning system handles the outdoor air load and indoor load, respectively. The outdoor air load is processed by a desiccant wheel cooling system combined with shallow geothermal energy and solar thermal energy. Four outdoor air operation modes were designed, and the system could work with the most energy-saving mode on the basis of the outdoor air condition. A fan coil was utilized to control the indoor load. The fan coil could use chilled water, 20~22oC shallow geothermal energy water, or hot water in accordance with the indoor load. The chilled water and the hot water were provided by the cooling mode and heating mode of a ground source heat pump, respectively. Because the outdoor air latent load was processed by a desiccant wheel, the fan coil merely controls the indoor load. Thus, the design chilled water temperature could be higher than conventionally used. In this system, the design chilled water temperature is at about 14 ~17oC. Compared to 7~12oC design chilled water temperature conventional air conditioning systems used, this system has a higher coefficient of performance and a lower required power consumption. When the outdoor condition is 28.0oC dry bulb temperature and 24.5oC dew point temperature, this system could provide satisfactory thermal comfort for indoor environment and maintain indoor at about 24.0oC dry bulb temperature and at about 20.0 oC dew point temperature. Moreover, the concentration of indoor carbon dioxide can keep below 1000 ppm. For a continuous operation for seven hours, this system can save 63.7% power consumption compared with conventional air conditioning systems. This study also performed a full-year operation analysis of the developed net zero-carbon air conditioning system based on the climate in Yilan County, Taiwan. The daily operating time of the system is from 8:00 a.m. to 20:00 p.m. Result shows that the ground source heat pump system was not needed in 41.3% of a full-year operating times. For the cooling period from April to September, the ground source heat pump was stopped in 19.0 % operating times. The developed net zero-carbon air conditioning system in this study has decreased effectively the system power consumption and has enhanced the feasibility of zero-carbon air conditioning system. The future work will combine the developed system with power generation systems and energy storage systems to achieve the goal of zero-carbon air conditioning systems.