BUILDING SPACE HEATING THROUGH MODIFIED TROMBE WALL: AN EXPERIMENTAL STUDY

Proceedings of STME-2013 International conference on Smart Technologies for Mechanical Engineering 25-26 Oct 2013

BUILDING SPACE HEATING THROUGH MODIFIED TROMBE WALL: AN EXPERIMENTAL STUDY Shiv Lal* Centre for Energy Studies Indian Institute of Technology Delhi, India E-mail address: [email protected]

P.K. Bhargava Central Building Research Institute Roorkee, CBRI, India Email address: [email protected]

S.C. Kaushik Centre for Energy Studies Indian Institute of Technology Delhi, India E-mail address: [email protected]

Nagesh Babu Balam Central Building Research Institute Roorkee CBRI, India Email address: [email protected]

ABSTRACT This investigation deals with the performance evaluation of modified Trombe wall used for space conditioning. The modified Trombe wall comprises of two parts: (i) black painted mild steel plate of 3mm thickness, used as absorber, and (ii) metallic box of mild steel sheet filled with normal air, which was used as thermal storage. The experiment was conducted during winter season of 2012 at Central Building Research Institute Roorkee. Metallic box increases normal room temperature by 5.0 – 8.5˚C during daytime and by 2.0 -5.0˚C during night times. On the other hand, the metallic plate increases the room temperature by 1-4˚C above ambient air during night time. The ordinary Trombe wall increases the room temperature by 0.4-2˚C during the day time and 2-3˚C during night time temperature. The Experimental room temperature is always higher than the reference room. There is lot of scope for conservation of energy in space heating, and the comfort room temperature can be achieved by metallic plate type or metallic box type solar chimney. Keyword: Trombe wall, space heating, modified Trombe wall 1. INTRODUCTION The utilization of solar energy for space heating is not a new concept though its use is increasing day by day due to expensive conventional energy resources. During the Stone Age, the solar energy was stored by thick stone wall during daytime in many cold regions across the globe which was used for heating purposes during night times. Trombe wall which is extensively used for heating, cooling and ventilation of modern building now days, it has been identified as an alternative for the thick masonry wall which is little bit costly. Trombe wall was developed by Trombe and Michel [1960] at the C.N.R.S. laboratory in France for the first time and thereafter, it was used for heating the buildings by passive mode. There are number of researchers and scientists who have found Trombe wall very useful and effective for both heating and ventilation of

buildings (Bansal 1993; Khedari 2000; Ong and Chow 2003, Darori 2004 and Zhai et al. 2005). Agrawal (1989) reviewed four different passive and active systems which were used extensively in building for natural heating and cooling. The concept of heat storage wall was introduced for heating purposes in the building during winter season initially, which later on also helped to reduce dependence on conventional resources of energy. Kaushik and Kaul (1989) developed a thermal model to study the thermal comfort in building by introducing mixed concrete-water thermal mass storage wall. Parametric study of passive cooling system in building was worked out by Gan (1998). His study revealed that the ventilation rate also increases with increase in the inlet and outlet opening dimensions with respect to the channel width. It was proposed that the interior surface of room wall should be insulated to enhance the ventilation rate in summer so that Trombe wall can be used both for heating and cooling of buildings. Sharma et al. (1989) conducted an experiment on a Trombe wall and found potential application of such a wall in solar passive building architecture in composite climatic conditions. Torcellini and Pless (2004) physically analyzed the Zeon visitor’s Centre and site entrance building situated at NREL wind site. The SEB Trombe wall has claimed as 10-41 cm thick single or double glass, south facing and having 2 -5 cm air gap of between glass cover and absorber surface. The selective coating was used on surface to improve its performance. It was observed after two year’s study that Trombe wall was contributing 20% of the total heating provided to the building with the average efficiency of the wall being 13%. Burek and Habeb (2007) investigated the air flow and thermal efficiency characteristics of both solar chimney and Trombe walls. Chel et al. (2008) estimated the passive heating potential of Trombe wall for honey storage building by using TRNSYS and concluded that the energy conservation up to 3312kWh/year can be achieved by making assumption of a short simple payback period like seven months.

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More recently, Jaber and Ajib (2011) optimized a Trombe wall for Mediterranean region by using life cycle cost criterion and results were simulated by TRNSYS and concluded that the optimum Trombe wall area ratio from thermal and economical point of view should be 37%. This optimum ratio has reduced life cycle cost (LCC) by 2.4% and CO2 is reduced annually by 445 kg. In the present investigation we have designed a Modified Trombe wall/solar chimney for building space heating in winter season at CBRI Roorkee with the concept of increasing the wall temperature by application of metallic sheet. This will lead to develop an approach for designing a Trombe wall in cold region of India and in North hemisphere. 2. System Description The built up modified Trombe wall/ solar chimney is designed for a specific room having 16.253 m3 volume situated at CBRI Roorkee, India [Latitude 29º 51’ and Longitude 77º 53’ at 274 m mean sea level] as illustrated in Figure 1. The design was based on 4.0 ACH at annual average solar insolation about 400W/m2. The area of inlet and exit vent was kept same as 0.09 m2. The vertical gap between inlet and exit vent from the center point is about 2.85 m. There is a vast gap in available literature on application of a metallic absorber for space heating through the solar chimney. This modified solar chimney / Trombe wall is capable to accommodate the effect of metallic plate and metallic box type absorber. Another important feature introduced in this system is, as hinged glass cover frame from the center by which it can be tilted to any angle. This feature gives an optimum tilt angle to increase the performance and reduce the back flow in the chimney which is essential in summer season, which generates stack’s effect and measurable flow. To control the space heating and ventilation features of a building, two hinged dampers are provided at the top of the frame. The modified Trombe wall constructed in two parts, in the first one, a metallic sheet (3 mm thickness) is fixed over a wooden frame 0.9 m x 2.55m x 0.045m, and the second part is made of metallic box having equal dimension to wooden frame as shown in Figure 2. To assess the temperature profile of the designed Trombe wall, thermo-couple was placed at different positions (see Figure. 2). The plan of experimental room, reference room and thermocouple position in same is shown in Figure 3. Both the plate and water wall are painted by nickel chrome black paint for increasing the absorptivity up to 80%.

Figure 1: Modified Trombe wall for building space heating

Figure 2: Orthographic view and dimensions of modified Trombe wall

Figure 3: Plan of Experimental and reference room 3.

Instrumentation and Measurement

The experimental study was conducted during winter season of year 2012. The global and diffuse solar radiations incident on a horizontal surface were measured by Solar Pyranometer (Modle: SP Lite2 type; Make: Eppley, Netherlands), and (Modle: SP Lite2 type; Make: Kipp&Zonen, Netherlands) respectively is shown in Figure 4 (a, b). Calibrated T-type thermocouples connected to a multi-channel temperature data logger (Digitec, India) was used to measure the air temperatures and data logger for solar insolation and temperature recording are shown in Figure 4(c, d). Total experimental uncertainties of different parameters measured during the experimental work on the modified Trombe wall/ solar chimney.

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4.2 Comparative study of simple and modified Trombe wall The temperature profile of simple and modified Trombe wall is depicted in Figure 5. The figure reveals that the ambient air temperature found lower from 6:00 PM to 9:00AM and it is found higher than the reference room temperature for other periods. The lowest ambient air temperature was observed as 3.2˚C (Below 4˚C freezing started) at 7:30 AM on 10th December and on other days also, ambient air temperature was recorded lowest in morning hours. The space heating effect through Trombe wall is shown in Figure 6 and 7.

Figure 4: Measuring equipment (Pyranometer and data logger) 4. Result and Discussions: 4.1 Observation and measurement of Environmental Parameter: The environmental parameters such as global, diffuse solar radiation, and ambient air temperature were monitored for twenty five days in December 6-30, 2012. The typical day of December is on 10th day of the month as suggested by (Duffy and Beckman, 1980). The Figure 5 reveals the relation between global, diffuse solar radiation, and ambient air temperature of typical day of December month. It was found that the maximum global radiation was about 576.25 W/m2 at 12:00 hours, whereas the maximum diffuse solar radiation was about 109.34 W/m2 at 11:00 hours. As far as the ambient air temperature is concern, it was maximum as 20.1˚C at 13:00 hours and minimum as 3.2˚C at 7:00 hours.

Figure 6: Full day Variation of Different temperatures for average day of Dec 2012

Figure 7: Comparison of experimental room, reference room and ambient air temperature

Figure 5: Solar radiation for the average day of December, 2012

The experimental room temperature was observed higher than the ambient air and reference room temperature that is because of low losses and more heat stored during day time. The reference room temperature (without wall heating) was found lower than the ambient air temperature during day time, but the experimental room temperature was found approximately 2-9˚C

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higher for various set up times. The difference between room and ambient temperatures in least morning hours was recorded higher as compared to other median times. Experimental room temperatures were recorded 1.5-8˚C higher with reference room in peak winter season. The temperature of black masonry wall (simple Trombe wall) was recorded lower than the both metal plate and metallic box. And as a result of that the room temperature increases in order of wall, metal plate and metallic box which is clearly shown in Figure 8. It was observed that, the higher the absorber temperature, more the convective effect. On the other hand the output air temperature through Trombe wall was found higher for metallic box as compared to others.

Figure 8: Comparison of Simple black masonry wall, MS plate, and MS box data in Trombe wall

4.3 Temperature variation according to height of absorber The temperature is not constant throughout the entire height of absorber plate which is clearly shown in Figure 9. It reveals that, the lower temperature found at the lowest end of absorber because absorber plate end is in contact with room temperature. On other hand the temperature at height of 2.55m reduces slightly from the maximum temperature (at 1.8m) because this end also is in contact with room air and hot air bends (eddy formation at the corner of 90 degree bend). It expressed that the air flow temperature increases with increase in chimney height.

4.4 Error and uncertainty analysis There is chance of error or uncertainties during the experiments and this may be due to, instrumentation (data logger, memory, electronic circuit, transmitters, wire resistance etc.), type of junction and sensor, climate condition, calibration method, method of observation and testing methods for evaluation. The total experimental uncertainties of different parameters measured during the experiment on modified Trombe wall were presented in Table 1. Table 1: Uncertainties of the experimental parameters Parameters Units Uncertainty Uncertainty in the temperature ˚C measurement (T-type thermocouples used) Uncertainty in the solar energy W/m2 measurement

5. Conclusions: The effect of metallic plate and metallic box on space heating of building in peak winter season was evaluated. It was found that the technology introduced in modified Trombe wall having better performance as compared to conventional Trombe wall. The experimental results were compared with reference room where no external space heating is provided. After inducing metallic box in Trombe wall the temperature during night time was higher by 5-10˚C corresponding to ambient air temperature. On the other hand, during the day time the room temperature was 2-5˚C higher than ambient air temperature. The conventional Trombe wall gives higher temperature by 0.42˚C during day time whereas; it was 2-3˚C during night time corresponding to ambient air. The metallic plate heating effect gives the 1-4˚C temperature above ambient air temperature during night time and 2-3˚C during day time. The experimental room temperature recorded 1.5-8˚C higher with reference room in peak winter season. These technologies found suitable for producing the comfort room temperature. On the other hand metallic plate temperature increases with increase in solar radiation and accumulated heat was enough to produce chimney effect, the air temperature inside the chimney was increased from lower side to upper side. The plate temperature found higher at the upper stage as compared to lower and middle stage, it clearly indicates convective heat transfer at upper level is less than the lower side. The temperature of air near to metallic plate is higher and it decreases towards glazing side but near to glazing air temperature is slightly higher. The air extracts convective heat from both plate and glazing.

Figure 9: Temperature variation according to height of absorber plate at 12:00 hour on typical day

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ACKNOWLEDGMENTS The author (Shiv Lal) gratefully acknowledges University College of Engineering, Rajasthan Technical University, Kota, Rajasthan (India) and IIT Delhi (India), for sponsorship under quality improvement program of government of India.

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