COOLING ENERGY SAVING SYSTEM USING A WATER MIST DEVICE ON WINDOWS

Transcription

1 COOLING ENERGY SAVING SYSTEM USING A WATER MIST DEVICE ON WINDOWS Kybum Jeong Sang-Gon Choi Yuhan College Yuhan College Dept. of Building Services Dept. of Building Services 590 Gyeonginro Sosagu Bucheon 590 Gyeonginro Sosagu Bucheon Gyeonggi Korea Gyeonggi Korea jkb@yuhan.ac.kr tool007@yuhan.ac.kr ABSTRACT 1. INTRODUCTION Many buildings are covered with numerous windowpanes for design impressions, so the proportion of windows to a building s elevation is increasing. Accordingly, the cooling load for solar radiation heat accumulated through a window is getting larger. Moreover, global warming and heat island effect make the outside air temperature increase. In nearly all buildings, cool air is supplied evenly regardless of the direction the space is facing. Consequently, the west side spaces of buildings cannot keep the required cool temperature that tenants need, due to the solar heat coming in through the windows. The water mist system was projected to decrease the solar heat inflow through windows in this study. The experiments were carried out to appraise the performance of the solar heat defending tools. The room temperatures of two disconnected offices were evaluated when using solar heat control devices. The assessment results revealed that the water mist system was advanced to the coated glass and the vertical blinds for the saving of cooling energy The open-air temperature ascends due to Global Warming and heat island effect. Many buildings are enclosed with glass windows as a design impression and the ratio of window to elevation area is growing. As a result, the cooling load for solar radiation heat acquisition through glass windows is getting higher. In most edifices, cooling air is being supplied evenly despite the direction in which the room is facing. Accordingly, the west region spaces of a building cannot maintain the necessary cool temperature that occupants want by reason of the solar heat through windows. Solar heat lessening gadgets like vertical blinds and film coated glass have been used to screen solar gaining increase through the west facing window, but it seemed that those gadgets were not researched. In this study, the water mist system was projected to reduce the solar heat inflow through window systems. The experiments were performed to evaluate the performance of the solar heat protecting gears. The room temperatures of two west

2 facing rooms were measured to evaluate the efficiency of cooling energy for solar heat control devices. 2. EXPERIMENTAL MEASUREMENT 2.1 Water Mist System (a) Supply and mist system at the top The water mist system transports the water to the top of the window and sprayed downward on the surface of the window to block out solar heat and to save cooling energy. Figure 1 and 2 shows the diagram of the water mist system for the windows. The water mist system is installed at the top of the fixed window with a DN15 pipe which is perforated with 1mm holes, 10mm apart. Water is supplied and sprayed on the surface of the window to spread out evenly and to make a consistent layer of water on the plane. The sprayed water that flows downward is collected to the gutter at the bottom of the window, and returns to the water tank. The water supply pump has a 20 liter per minute (LPM) flow capability and 12 meters raise capacity to make constant flow rate at the end of the pipe; hence, to making an equal water layer depth on the whole surface of the windowpane. The water tank has a 50 liters capacity to supply water at the correct temperature uniformly. (b) Collect and return system at the bottom Fig. 2: Photos of water mist system 2.2 Experimental Method Figure 3 shows three measurement poles in the middle of the room to attain the indoor temperatures and measurement probes on each pole are allocated at five points at an equal distance from each other. Five thermocouples are attached on the surface of the glass, thus a total of twenty points from the thermocouples were measured. Data acquisition system NetDAQ was utilized to collect the data every 10 seconds. Fig. 1: Flow of water mist system Two unoccupied offices that have equal conditions in dimension and direction were selected to be evaluated and measured during the hot season from mid July to late August. Typical aluminum framed window system with 5mm double pane glass was selected and this was divided into 2 parts: the fixed window at the top and the sliding window at the bottom. From this window, the use of common double pane glass with no solar heat protection

3 device, vertical blinds (green color), film coated glass (reflection rate at 30%), water mist system, and chilled water mist system were measured and evaluated. The two offices for the experiment were ventilated well over 8 hours after finishing the measurement to make the two rooms first condition equal for the next experiment. After making the two rooms state uniform, the doors and windows were closed to defend the inlet of outdoor air. Two rooms without occupants and furniture were compared in the clear daytime to promote the effect of solar heat, but only data measured on the same day were compared to avoid the differences of temperature, clouds, and wind in unlike days. (a) Floor plan (b) Section Fig. 3: Measurement points of room temperature 3. RESULTS AND DISCUSSIONS The performance of the solar heat reduction methodsvertical blinds, film coated glass, water mist system, and chilled water mist system were quantified and assessed at two separate offices. The twenty points of room air temperature measured was averaged in the period of noon to 3 PM in which solar heat was the highest during the day. Air temperature measured every 10 seconds was averaged for 15 minutes and these values are shown and compared in figures 4 to Evaluation of Vertical Blinds and Film Coated Glass Figure 4 shows the comparison between vertical blinds and common double pane glass without any solar heat reduction devices on the window while the two rooms were air conditioned. The result concludes that the average room temperature with vertical blinds is lower by 0.7 (range 0.5~1.0) C than the average room temperature without blinds. Thus, vertical blinds can cool down the room temperature by reducing the solar heat through the window. Figure 5 illustrates the comparison between coated glass and common double pane glass without any devices in an air conditioned room. Contrast demonstrates the room temperature with coated glass is lower by 1.3 (range 1.1~1.5) C than the room temperature without coated glass. It indicates that coated film on glass can keep off solar rays, decrease cooling load, and save cooling energy. Figure 6 shows the assessment between vertical blinds and film coated glass. The results illustrates that the case of coated glass is lower by 0.6 (0.5~0.7) C than the case of

4 vertical blinds in room temperature. Coated glass is a little more efficient than the vertical blinds to reduce cooling energy and is validated again in figures 4 and 5. (2.1~2.5) C more than the common double pane glass in room temperature, and was confirmed the best device to save cooling energy. Coated glass can protect from solar heat on the surface of glass before entering the room and reflect the solar heat back, but vertical blinds are only capable of hindering solar heat after it enters the room. Due to these points, vertical blinds are less efficient in defending against solar heat and to save cooling energy. 3.2 Water Mist Device and Chilled Water Mist Device All the cases should be compared at the same time and the same condition, but outdoor environment was different during the experiment period, so they have to be compared relatively. The relative comparisons were analyzed; vertical blinds, coated glass, a water mist system, and a chilled water mist system can reduce more solar heat and is more superior at saving cooling energy in order of increasing efficiency. Figure 7 illustrates the evaluation between the room with a water mist system and a room without a water mist system in an air conditioned environment. This verifies that the case with the water mist system is lower by 1.8 (range 1.6~1.9) C in room temperature than the case of common double pane glass. Therefore, this system was more superior at saving cooling energy in hot seasons. Figure 8 demonstrates that the contrast between the water mist system and coated glass in the air conditioned room setting. The room temperature with the water mist system is lower by 1.1 (range 0.7~1.3) C than the room with coated glass. For that reason, the water mist system is more efficient than the coated glass at diminishing room temperature. In figure 9, we matched up the case with a chilled water mist system which was exposed to a supply of cool water in the pipe of the fan coil unit (FCU) where the water was then transported to the top of the window and sprayed downward compared to the case using common double pane glass. The chilled water mist system can reduce 2.2 Figure 10 illustrates the room temperature distribution contour at the center section of the room according to the solar heat protection device. At the window side of the room, we can contrast the differences of the temperature among four cases. The case of the water mist system is confirmed the most efficient to reduce the solar heat through the window glass. At the middle of the room, the case of common double pane glass (Fig. 10-a) shows the range of 26.0~27.5 C due to the solar heat flood, the water mist system(fig. 10-d) demonstrates the range of 25.0~26.0 C, then this contrast proves that the water mist system is more efficient at reducing solar heat. In the case of common glass, the temperature of the upper part of the room is higher than the temperature of the lower part of the room due to the accumulation of flooded solar heat through the window. In the case with the water mist system, the temperature of the upper part of the room is less than the temperature of the lower part by the effect of the water mist at the upper fixed window. Then the temperature of the lower part is a little high, since this is

5 due to the solar heat influx through the lower sliding window glass without the water mist system. The water mist system can shield off the solar heat influx throughout the window glass indicating that this system can cool down the temperature of the glass surface and reduce the thermal conduction through the glass. As a result, this system can save cooling energy. The combination of the water mist system with coated glass or vertical blinds can increase the solar heat reduction effect and can save more cooling energy. Fig. 6: Comparison between vertical blinds and film coated glass Fig. 4: Comparison between common glass and vertical blinds Fig. 7: Comparison between water mist systems and common glass Fig.8 Comparison between water mist system Fig. 5: Comparison between common glass and film coated glass and film coated glass

6 4. CONCLUSION Fig.9 Comparison between chilled water mist system and common glass (a) Common glass (b) Vertical blinds (c) Film coated glass (d) Water mist system Fig. 10 Comparison of indoor room temperature distribution contour In most buildings, cooled air is being supplied evenly despite the direction of the room in which it is facing. Accordingly, the west side spaces of a building cannot uphold the necessary cooling temperature that tenants want by reason of the solar heat coming through windows. In this study, the water mist system was projected to decrease the solar heat inflow through the window systems. The experiments were carried out to calculate the performance of the solar heat protecting tools. The room temperatures of two west sided rooms were measured to evaluate the saving efficiency of cooling energy for solar heat control devices. The experimental results are as follows. (1) The room temperature with vertical blinds is lower by 0.7 C than the room temperature without vertical blinds. And the room temperature with coated glass is lower by 1.3 C than the room temperature without coated glass. The data demonstrates that vertical blinds and coated film on glass can prevent solar heat from entering, and can cool down room temperature. (2) The case of the water mist system is lower by 1.8 C in room temperature than the case of common double pane glass with no solar heat protection. Also, the water mist system is lower by 1.1 C than the coated glass. Therefore, the water mist system is better than coated glass and vertical blinds at reducing room temperature. (3) The chilled water mist system heat exchanged with an FCU can reduce the room temperature by 2.2 C more than the common double pane glass, and was confirmed the best device in saving cooling energy.

7 (4) The comparison evaluation illustrates that the chilled water mist system, a regular water mist system, film coated glass, and vertical blinds are superior in order of decreasing efficiency to common double pane glass to cut cooling load in the room. The combination of these systems can augment the solar heat reduction effectively and can save more cooling energy. The water mist system can be utilized to decrease cooling load instead of remodeling cooling equipment that would require a high initial cost. This system can be adopted for structures with many glass windows like atriums to save cooling energy by reduction of solar heat. Only statistics taken on the same day were compared to avoid the differences in temperatures, clouds, and wind on different days. Future research would need more comparisons with plenty of data from long term measurements. (4) Duffie, J. and Beckman, W., Solar engineering of thermal process, John Wiley & Sons, Inc (5) Ha, D., Park, K. and Son, W., Study on the analysis of energy consumption corresponding window area ratio, Proceedings of the Society of Air-Conditioning and Refrigeration Engineers of Korea, Society of Air- Conditioning and Refrigeration Engineers of Korea, 2008 summer, pp (6) Kim, B., A study on thermal environmental and design methods to save energy in small glass-skin commercial buildings, Journal of Asian architecture and Building Engineering, 2004, Vol.3 No.1 (7) Park, Y. and Park, J., A study of energy use impacts by SHGCs of windows in detached house, Korean Journal of Air-Conditioning and Refrigeration Engineering, Society of Air-Conditioning and Refrigeration Engineers of Korea, 2010, v. 22, n.04, pp REFERENCES (1) ASHRAE, ASHRAE Handbook Fundamentals, ASHRAE (2) Choi, D., Choi, G., Kang, J. and Lee, S., The evaluation on thermal window high-tight composition of sliding door and open door, Proceedings of the Society of Air- Conditioning and Refrigeration Engineers of Korea, Society of Air-Conditioning and Refrigeration Engineers of Korea, 2009, pp (3) Choi, G., Kang, J., Yang, K. and Lee, S., A Research on air-tightness and thermal performance of windows system classified by windows type, Proceedings of the Society of Air-Conditioning and Refrigeration Engineers of Korea, Society of Air-Conditioning and Refrigeration Engineers of Korea, 2009, pp