EFFECT OF A RADIANT PANEL COOLING SYSTEM ON INDOOR AIR QUALITY OF A CONDITIONED SPACE

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1 EFFECT OF A RADIANT PANEL COOLING SYSTEM ON INDOOR AIR QUALITY OF A CONDITIONED SPACE Dr. E T. Mhamed* and Prf. K. N. Abdalla** *Mechanical Engineering Dept, Faculty f Engineering and Technical Studies, Uniersity f El-imam Elmahdi, P. O. Bx 209 Ksti, Sudan. tigani5@htmail.cm ** Mechanical Engineering Dept, Faculty f Engineering, Khartum Uniersity, P. O. Bx 321 Khartum, Sudan. kamalnasr@yah.cm ABSTRACT This paper discusses the effect f a radiant cling panel system n an indr air quality (IAQ) f a cnditined space. In this study, ceiling radiant cling panel, mechanical entilatin with fan cil unit (FCU) and 100% fresh air are used. Temperature sensrs are lcated at different lcatins inside the cnditined space in rder t sense dry bulb temperatures, relatie humidity t cmpare it with standard ASHRAE cmfrt alues. The present inestigatin indicates that the radiant cling system nt nly impres the indr air quality but als reduces the building energy cnsumptin in the cnditined space. Keywrds: Air cnditining, Ceiling radiant cling panel, Chilled water, Ventilatin system with fan cil unit (Fresh air). INTRODUCTION Air-cnditining systems are designed t cntrl indr temperature and humidity, and t pride fresh, filtered air t building ccupants. The majrity f air-cnditining systems currently in peratin are all-air systems, meaning that they emply air nt nly fr the entilatin task, but als as a heat and humidity transfer medium (Crina Stetui, January 1998). Mechanical heating and cling f indr space has been practiced fr a lng time. The thermal structure at Bath, England and Rme, Italy, represent the first knwn type f large-surface radiant heating system. Anecdtal infrmatin suggests that, arund the same time, the Turks were cling their dwelling by tapping cld rier water and circulating thrugh interstices in wall r flrs (Crina Stetui, January 1998). In early 1990s, interest in the ceiling radiant cling panel (CRCP) began t increase nce the cndensatin issues had been addressed by independent entilatin system designed t meet the entire space latent lad and the required entilatin rate. First f all, the energy cnseratin and indr air quality (IAQ) benefits f the decupled (r hybrid) system began t attract attentin. In additin, it was als indicated that traditinal negatie perceptins n the CRCP system need n lnger bet alid (Jae-Wen Jeng, Stanley A. Mumma, April 2004). Significant energy saings by the radiant cling systems and their relatie adantages (cling panels/chilled beams in cmbinatin with a dedicated utdr air system can reduce cling and entilatin energy cnsumptin by 25 30% relatie t a ariable air lume system) (Kurt w. Rth, Detleft Westphalent, Jn Dieckmann, Sephir D. Hamiltn, William Getzler, July 2002), (E T. Mhamed, July 2009). DESCRIPTION OF THE COOLING SYSTEM In this system the radiant cling panels are attached t the ceiling f the cnditined space. Radiant cling ceiling panels cntain chilled water running thrugh the pipes that are bnded t the nn-isible side f the panels. The panels absrb sensible heat transmitted mainly by thermal radiatin and cnectin frm the cnditined space. The chilled water is then pumped t a chiller, recled and returned t the ceiling again. The entilatin air is dehumidified and cled by fan cil unit frm the same chilled water surce (water chiller). The remal f the exhaust air and 100% fresh air are include. DESIGN DATA FOR THE CONDITIONED SPACE Design data fr the cnditined space is explained in Table (1). Table 1 Design data fr the cnditined space Lcatin Faculty f Engineering, Uniersity f Khartum, Sudan (Latitude 15.7 N) Applicatin System descriptin Office building Ceiling radiant cling panel with 100% fresh air Outside cnditins DBT 45 C & WBT 26 C Inside cnditins DBT 25 C & RH 50% Rm size 4.22m x 2m x 3.05m (height) Occupancy leel Lighting RSH 2 persns 2 flurescent tube Lamps, (1)1200mm,T kW 1 Prceedings f the Tenth Internatinal Cnference Enhanced Building Operatins, Kuwait, Octber 26-28, 2010

2 RLH Kw BPF 0.12 Other assumptin All walls and ceiling are expsed t the sun, n misture generatin surce except ccupants, entilatin, and infiltratin. Ambient temperature under flr air is 29 C Supply air temperature 12 C Mean panel 15.5 C temperature Panel cling capacity 0.613kW DESCRIPTION OF THE EXPERIMENTAL ROOM The space cnditined under the experimental test is selected as small ffice is shwn in Figure 1 which has dimensins f 4.22 m x 2 m with height f m. All walls f the ffice cnsist f cmmn brick (24 cm thick). The ceiling is made f 12 cm cncrete, 2 cm air gap, 2 cm plyethylene insulatin fam and 0.4 cm plywd. The flr is cnstructed f 39 cm cncrete; 3 cm cement mrtar and 3 cm tile. The 0.95 cm x 0.76 cm windw is made f a single clear glass with thickness f 3 mm where the dr has dimensins f 1.95 m x 0.82 m sft wd (4 cm thick). Fur panels insulated at the tp are used. Each f them has dimensins f 1.3 m x 1.05 m with thickness f 4 mm. The chilled water passes t the fan cil unit t reduce the ambient temperature s as t supply an air temperature f 12 C and then, enters the panel with 14.2 C and exits with 16.8 C. Cling lad f the space was calculated by using cmputer prgram (Matlab) fr transient heat flw (sensible heat lad) thrugh the walls and ceiling. Other heat lads were determined by the standard ASHRAE methd. Then, the ceiling radiant cling panel system was designed. Once the thermdynamic prperties f the air befre and after the cling cil (States O and S Figure 3), the design cling cil lad Q FCU (fresh air FCU capacity) is calculated using equatin belw. Figure 3 thermdynamic prperties f the air befre and after the cling cil f FCU Q FCU q ρ en ( h h ) s q en ( h h ) ( h h ) 0.14( ) qen s QFCU 7kW 2TR VAV SYSTEM WITH 100% FRESH AIR Figure 4 shws VAV system with 100% fresh air. In sme applicatins f air cnditining systems, 100% fresh air is needed t apply such as hspitals (sterilizing and surgery rms) and medicine's factries. Fr sterilizing rms' number f air changes per hur ranges between 15 t 25. In this study the sterilizing rm is used, the number f air changes per hur is selected as Therefre, the entilatin flw rate is calculated as fllws: s (1) Vlume f the cnditined space ACH V& en (2) 3600 Vlume f cnditined space ACH V& en 140l / s Bth supply air and cling cil capacity f VAV system is calculated as belw: Figure 1. Schematic diagram f tested chilled ceiling panel with dedicated utdr air system CRCP/DOAS WITH 100% FRESH AIR Figure 2 explains CRCP/DOAS with 100% fresh air. Figure 2. CRCP/DOAS with 100% fresh air & sup p m ERTH h h R S 3.5 m& sup p 0.22kg / sec l / s V& sup p ( h hs ) FCU capacity m& supp ( h hs ) ( h h ) ( ) V& sup p s FCU capacity m& sup p( h hs ) kW (3) (4) 2 Prceedings f the Tenth Internatinal Cnference Enhanced Building Operatins, Kuwait, Octber 26-28, 2010

3 Figure 4. VAV with 100% fresh air COMPARISON BETWEEN CRCP/DOAS & VAV SYSTEM FOR PEAK POWER DEMAND Table 2 describes cmparisn between CRCP/DOAS & VAV system fr peak pwer demand. Table 2 Cmparisn between CRCP/DOAS & VAV system fr peak pwer demand Design cnsideratin 100% fresh air CRCP system VAV system * Supply air flw rate (l/s) Panel sensible cling lad (kw) Cling cil capacity (kw) Supply fan (kw) Rund windw exhaust fan (kw) Water pump (kw) Ceiling fan capacity (kw) Ttal energy (kw) Pwer saings (kw) Pwer saings % f CRCP er VAV system Figure 5a. Plan iew Figure 5b. Eleatin iew SENSOR'S LOCATIONS INSIDE THE CONDITIONED SPACE Sensr's lcatins inside the cnditined space were explained in Figure 5 and Table 3. Figure 5c. Ismetric iew Figure 5. Cnditined space with sensr's lcatins 3 Prceedings f the Tenth Internatinal Cnference Enhanced Building Operatins, Kuwait, Octber 26-28, 2010

4 Table 3 Lcatin f the sensr's pints inside the ffice Pint Lcatin E1* Center f east wall, 120cm frm flr W1 Center f west wall, 120cm frm flr S1 Center f suth wall, 120cm frm flr N1 Center f nrth wall, 120cm frm flr C1** Center f ceiling radiant panel cling E2*** Perpendicular pint, 25cm away frm center f east wall, 120cm frm flr W2 Perpendicular pint, 25cm away frm center f west wall, 120cm frm flr S2 Perpendicular pint, 25cm away frm center f suth wall, 120cm frm flr N2 Perpendicular pint, 25cm away frm center f nrth wall, 120cm frm flr C2 Office center, 120cm frm flr * Pints E1, W1, S1, and N1 represent inside walls surface temperatures f the ffice. ** Pint C1 indicates panel surface temperature. *** Pints E2, W2, S2 and N2 illustrate perpendicular walls f inside air at the ffice. Figure 7. Inside surface temperature f the east wall at pint E1 (Table 2) RESULTS & DISCUSSIONS Figure 8. Inside surface temperature f the west wall at pint W1 (Table 2) Figure 6. Inside air temperature at ffice center (pint C2) (Table 2) Frm Figure 6 it will be bsered that the inside air temperature f the cnditined space shws unifrm distributin. Temperature lies between 23 C t 26 C. Accrding t ASHRAE, the acceptable cmfrt cnditin temperature aries between 22 C t 25 C in summer. Hence the result in Figure 3 indicates that the panel system gies reasnable perfrmance and prides cmfrtable cnditins. Figure 9. Inside surface temperature f the suth wall at pint S1 (Table 2) 4 Prceedings f the Tenth Internatinal Cnference Enhanced Building Operatins, Kuwait, Octber 26-28, 2010

5 Table 3 shws summary f aerage temperature f inside walls surface (Figure 4 t 8) f inside air building. These results cnfirm that, the applicatin f cmputer simulatin in engineering sciences is expected t render reasnable results. AVERAGE TEMPERATURE OF PERPENDICULAR WALLS OF INSIDE AIR AT THE OFFICE BUILDING (EXPERIMENTAL RESULTS) The aerage temperatures f perpendicular walls f inside air at the ffice building which hae been btained during the perid f experimental testing were summarized in Table 4. Figure 10. Inside surface temperature f the nrth wall at pint N1 (Table 2) Table 6 Aerage temperatures f perpendicular walls f inside air at the ffice (experimental wrk) Surfaces f the ffice* Temperature ( C) E W N S C * Pint lcatin: 0.25m frm center f each wall surface and 1.2m (seating leel) frm the flr. Table 6 shws aerage temperatures f perpendicular walls f inside air (Figure 3 and 9 t 12) at the ffice building. It is clear that, these temperatures are clse t inside air design temperature (25 C). Fiure 11. Cmparisn between CRCP/DOAS and VAV system fr peak pwer demand Figure 11 shws a cmparisn between CRCP/DOAS and VAV system fr peak pwer demand thrugh this study. It is clear that frm this figure the CRCP/DOAS system with 100% fresh air can sae mre than 26.1% f input pwer er a VAV system with 100% fresh air. The reasn fr this is that the CRCP/DOAS uses minimum supply air (140l/s) than VAV system ( l/s) in case if 100% fresh air is used in each respectiely. The ther reasn is attributed t the energy used by its pump (19.2W) which is less than by fan (40W) in VAV system. PREDICTED VERSUS EXPERIMENTAL INSIDE WALLS SURFACE TEMPERASTURE Table5 illustrates predicted ersus experimental inside walls surface temperatures f the ffice. Table 5 Predicted s. experimental results f inside walls surface temperatures f the ffice Surface temperature* Predicted ( C) E W N S C Aerage f experimental wrk ( C) CONCLUTIONS Frm the study f the radiant panel system accrding t Khartum climatic cnditins, the fllwing cnclusins can be drawn: The present inestigatin indicated that the radiant cling system impres the human cmfrt (100% fresh air is used). The results btained in this study demnstrate that the ceiling radiant cling panel system creates unifrm temperature distributin inside the cnditined space. Mreer, the predicted inside walls surface temperatures and temperatures f perpendicular walls f inside air are shwn t be in reasnable agreement with thse measured as indicated in the experimental results. The current study shwed that the ceiling radiant cling panel system impres indr air quality (lw nise and minimum supply air are used when cmpared with cnentinal cling system) Electrical serices reductin fr the mechanical equipment can be achieed due t smaller chiller, fans and pumps. REFERENCES Crina Stetui. January Radiant Cling in US Office Buildings: Twards Eliminating the Perceptin Climate Impsed Barriers. Energy and Resurces Grup. Uniersity f Califrnia Berkeley, CA Prceedings f the Tenth Internatinal Cnference Enhanced Building Operatins, Kuwait, Octber 26-28, 2010

6 E T. Mhamed. July Design f a Radiant Panel Cling System fr Summer air cnditining. Ph.D. Thesis, Faculty f Engineering, Uniersity f Khartum, Sudan. Jae-Wen Jeng, Stanley A. Mumma. April Simplified cling capacity estimati mdel fr tp insulated metal ceiling radiant cling panels. pp Kurt w. Rth, Detleft Westphalent, Jn Dieckmann, Sephir D. Hamiltn, William Getzler. July Energy Cnsumptin Characteristic f Cmmercial Building HVAC Systems Vlume III: Energy Saing Ptential. ACRONYMS CRCP DOAS VAV ASHRAE DBT ACH ERTH FCU Ceiling Radiant Cling Panel Dedicated utdr air system Variable air lume American sciety f heating, refrigeratin and air-cnditining engineers Dry bulb temperature Humidity rati Number f air changes per hur fr rm Fan cil unit 6 Prceedings f the Tenth Internatinal Cnference Enhanced Building Operatins, Kuwait, Octber 26-28, 2010