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Theoretical and Experimental Study of Combined System: Chilled Ceiling and Displacement Ventilation

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Theoretical and Experimental Study of Combined System: Chilled Ceiling and Displacement Ventilation Universal Journal of Mechanical Engineering 7(3): 118-138, 2019 http://www.hrpub.org DOI: 10.13189/ujme.2019.070305 Theoretical and Experimental Study of Combined System: Chilled Ceiling and Displacement Ventilation Israa Ali AbdulGhafor1,*, Adnan A. Abdulrasool2, Qasim S. Mehdi2 1Lecturer, Department of Electronic Technique, Middle Technical University, Iraq 2Professor, Department of Mechanical Engineering, Al-Mustansiriya University, Iraq Copyright©2019 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract The present experimental study presents the obtain with using HVAC systems that supply enough of performance of the combine cooling system (chilled quantity of fresh air to the occupied zone whilst effectively ceiling and displacement ventilation). The experimental elimination contaminants. So, HVAC, systems provide study included the effect of different temperatures of suitable air temperature by elimination heat from occupied chilled ceiling of (20 and 16)°C and different supplied air zone while avoid large air temperature gradients and drafts. temperatures of (18, 20, 22 and 24)°C with constant Economic side should be achieved by both thermal and internal load of 1600W and constant supplied air velocity indoor air quality requirements, because the largest energy of 0.75m/s. The theoretical study content studying the air consumption is done by these systems. According to recent flow pattern through occupant zone and temperatures researches more than 40% of total energy used by contours in different directions X, Y and Z at supplied air commercial building is consumption by HAVC systems temperature (18)°C and internal load, mean plate [1]. temperature and supplied air velocity of (1600W, 20°C and 0.75m/s) respectively. The experimental results show that the cooling capacity of air decreases as temperature of 2. Literature Review supplied air increases. At temperature of supplied air increase by 33.3%, the cooling capacity of air decreases by There are many experimental and theoretical (22.7 and 22.54) % for chilled ceiling temperature of (20 investigations were focused on chilled ceiling combined and 16)°C respectively. While cooling capacity of chilled with displacement ventilation with different operation ceiling increases as supplied air temperature increases. At conditions. Jeong and Mumma. (2003),[2] presented an supplied air increases by 33.3%, the cooling capacity of analysis of the enhancement performance of cooling panel chilled ceiling increase by (14 and 15.28)% for chilled capacity when used ventilation. The model was used a ceiling temperatures of (20 and 16)°C respectively. The space with dimensions of 3m (L) x 3m(W) x 3(H)m with theoretical results show that the air velocity and five cooling panel made from aluminum ,dimensions of temperatures contours for supplied air temperature in each one 0.6m(L) x 3m(W). The space model has only one different direction are approximated constant. external wall with small window. The temperature of outdoor is 30 , while temperature inside the space Keywords Combined System, Chilled Ceiling and remains about 26 . The air is introduced to the space by Displacement Ventilation, Theoretical Study of Combined 0.5m(L) x 0.5(W)℃ nozzle diffuser positioned near ceiling. System The velocity of air℃ changed from 2 to 6m/s and temperature of chilled water is varied from 12 to 25 . The results show that when air velocity increases the performance is enhanced from (5 to 35)% at typical ℃design temperature. 1. Introduction The increment of capacity means a reduction in initial cost and area panel required. At a velocity less than 2m/s, the The indoor air quality and thermal comfortable are the effect of ventilation on capacity of cooled panel is small so most necessary condition for the inside environment. the correlation of natural heat transfer coefficient was used Because people remain more time inside environmental, to evaluate the capacity of cooling panel at low velocities. heating, ventilation and air condition (HVAC) systems Ghali et. al. (2016), [3] presented a new method to supply high indoor air quality and thermal comfortable replace cooling ceiling that combined with displacement became very important. High indoor air quality can be ventilation to remove the latent and sensible heat directly. Universal Journal of Mechanical Engineering 7(3): 118-138, 2019 119 The method included a liquid desiccant dehumidification the heat transfer between each other. The plate total area membrane cycle (LDMC) that is modeled mathematically covers about 54% of total area of the ceiling. Plate and to replace cooling ceiling. The combined (LDMC-C) with pipes assembly made from red copper with high thermal displacement ventilation is used in office at Beirut climate. conductivity of 404 W/m.°C [5],The dimension of each The combined LDMC-C/DV system is consisted of four plate is 60cm(W)x60cm(L) and 150mm pitch according to main subsystems: the liquid desiccant cycle, the DV ASHRAE standards [6]. The remaining space of the area system, the parabolic solar collector and the space thermal. ceiling filled with false plates. The back of each plate is The soiled pipes were used in all system except in covered with insulation made of glass wool which has a dehumidifier and regenerator parts, the pipes made from thermal conductivity 0.04 W/m.°C. The copper tube are porous material. fixed on corrugated panel having a serpentine arrangement The results shown that at temperature of desiccant shape to increase the available time for heat transfer during ceiling decreases by 3°C, the total cooling energy needed water circulation and to enhance the heat transfer when by chiller decreasing by 10%. With the same input compared with straight parallel plate channel. [7]. The parameters of operation, the energy saves by 49% plate that made of red copper was painted from front side compared to the conventional system. The thermal by black color to increase their ability to absorp the heat condition in occupied zone for both new system and from occupied zone. During experimental test the conventional system have same conditions for thermal temperatures along plate were measured using K-type comfort but the slightly difference in operative parameters thermocouple. Twenty seven thermocouples are fixed on like RH. The RH was 68.2% and 73.2% for LDMC and DV the plates and tubes distributed at three plates that are while RH was 50.1% and 70% for conventional system located at different positions. Figure 2 illustrates plate CC/DV. construction stages and the distribution of thermocouples Pomianowski et. al. (2017), [4] developed the on the plates. Also the experimental part content design of numerical model that can expect the air flow and thermal performance of diffuser ventilation combined with chilled pipe network that distribute and collected water from ceiling at design stage. This model is used to estimate the chilled plate. The piping network is shown in figure 3. effects of different design parameters that contain the Figure shows the details of used circuit diagram and U-value of diffuse ceiling panel, plenum depth high of photographs of the piping system. The system consist of plenum. The simulation results show that the effect of one pipe (used as main header) to supply water from the diffuse ceiling for separating the radiant ceiling from the intake source. This pipe is used to supply water for the rest room can be minimized by using chilled ceiling plate application. Another pipe (used as second main header), is with higher U-value and the low plenum height was good used for collection and return water to the source. Reverse for energy efficiency but cause non-uniform in air return circuit design was used to ensure even distribution of distribution that led to draught problem in occupied zone. water without a need to the balance valve. From figure (3) So this system can be used for small offices instead of large can noticed that the length of branches the pipes for office. distribution and combined chilled water were longer than main headers (divided and combined) to avoid irregularities[8]. The pipes network consist of main 3. Experimental Work distribution header with diameter is (25.4mm) that A combined cooling system (chilled ceiling and branching to three branches (19.05mm) then each one displacement ventilation) was installed at room with branching to six branch (12.7mm) for feeding every plate. 3m(L)x4m(W)x3m(H) located at fourth floor on surface of The exit water from each plate is collected by main Mechanical Engineering Department building, Al combine header (25.4mm) through (12.7mm) pipes and Mustansiriya University , Collage of Engineering as shown then to branch (19.05mm). The design consideration the in figure 1. The chilled ceiling consist of corrugated metal choice of all pipes can be seen in item 4.1. The all pipes are plates (made of red copper metal), with copper tube being made of CPVC schedule 80 and covered with two layer of fitted inside it. The tube is fixed in holes made inside the insulate to minimize the heat loss or gain during transfer of plate to increase the contact area between the tube and the water to plates and reduce the noise produce from flowing plate in order to reduce the thermal resistance and increase of water. 120 Theoretical and Experimental Study of Combined System: Chilled Ceiling and Displacement Ventilation Figure 1. The texted room a: The Plate Mold b: The plate finished and its back after cover by glass wool insulation Universal Journal of Mechanical Engineering 7(3): 118-138, 2019 121 c: Thermocouples arrangement Figure 2. The details of plate’s construction a:Digram sketch of top veiw for pipeing network 122 Theoretical and Experimental Study of Combined System: Chilled Ceiling and Displacement Ventilation b: The actual view for combing network pipes c: The actual view for dividing network pipes Figure 3.
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