Performance evaluation of displacement ventilation system combined with a novel evaporative cooled ceiling for a typical office in the city of Beirut

Size: px

Start display at page:

Download "Performance evaluation of displacement ventilation system combined with a novel evaporative cooled ceiling for a typical office in the city of Beirut"

Ezra Stokes
5 years ago
Views:

1 Avilble online t ScienceDirect Energy Procedi 75 (2015 ) The 7 th Interntionl Conference on Applied Energy ICAE2015 Performnce evlution of displcement ventiltion system combined with novel evportive cooled ceiling for typicl office in the city of Beirut Mrim Itni, Kmel Ghli, Nesreen Ghddr * Deprtment of Mechnicl Engineering, Americn University of Beirut, Beirut , Lebnon Abstrct The study investigtes by modeling the performnce of displcement ventiltion (DV) ided with Novel Evportive Cooled Ceiling, Misotsenko cycle (M-cycle). The proposed system will increse the lod removl of the DV system beyond the 40 W/m 2 limit with no dditionl energy consumption. Predictive mthemticl models of the conditioned spce nd the evportive cooled ceiling will be developed to study the energy performnce of the suggested combined system for typicl offices of Beirut. The study identifies different vlues of supply ir reltive humidity t certin supply flow rte nd temperture while meeting spce lod, indoor ir qulity, nd therml comfort. The proposed system resulted in cooling lod removl cpcity enhncements of 18.65%, 44.3% nd 72.25% t supply ir reltive humidity of 90%, 50% nd 10⁰C respectively. The results indicted better performnce t lower supply ir reltive humidity The Authors. Published by Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license ( 2015The Author. Published by Elsevier Ltd. Peer-review Selection nd/or under responsibility peer-review of under Applied responsibility Energy Innovtion of ICAE Institute Keywords:Displcement ventiltion; Misotsenko cycle; indoor ir qulity; mthemticl modeling 1. Introduction Humn beings currently spend 90% of their time in buildings nd 60% of world-wide energy produced is spent in residentil buildings [1], hence the need to reduce energy consumption. One of the promising ir conditioning systems considered to provide both therml comfort nd ir qulity with low energy consumption is displcement ventiltion (DV) [2] nd [3], but the mjor issue bout this system is the limit of low cooling lods of bout 40 W/m 2. For this reson reserchers hve suggested using the chilled ceiling displcement ventiltion (CC/DV) system to increse the lod removl of DV systems up to 100 * Corresponding uthor. Tel.: ; fx: E-mil ddress: frh@ub.edu.lb. (N.Ghddr) The Authors. Published by Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsibility of Applied Energy Innovtion Institute doi: /j.egypro

2 Mrim Itni et l. / Energy Procedi 75 ( 2015 ) W/m 2. However, this enhncement in lod removl cme t the expense of dditionl energy consumption. So pssive wys need to be used to enhnce the performnce of the DV system nd increse its lod removl using evportive cooling of the ceiling. In this study, the chilled ceiling model incorportes Misotsenko cycle (M-cycle) by pssing the DV upper ir through novel evportive chnnel to lower the temperture of the ceiling nd ssist in removing dditionl spce sensible lod. Nomenclture chnnel height (m) het lod (W/m 2 ) T temperture ( C) X humidity rtio (kg/kg) X* humidity rtio of sturted ir (kg/kg) z position (m) α convective het trnsfer coefficient (W/m 2.K) αm mss trnsfer coefficient (m/s) K e1, K e2 effective therml conductivity of the het trnsfer plte nd ceiling (W/m.K) e1, e2 effective thickness of the het trnsfer plte nd ceiling (m) Subscripts d dry chnnel p het trnsfer plte r room s1, s2 wter bsorbing sheet e1, e2 effective vlue corresponding to the trnsfer plte nd the ceiling w wet chnnel 2. Performnce nlysis of displcement ventiltion system combined with novel evportive cooled ceiling 2.1. Description of the proposed system Cool supply ir enters t floor level nd picks the lod from the spce s shown in Fig 1(). After tht the ir is directed towrd the ceiling where it psses in dry chnnel nd gets cooled down without gining ny humidity. Then it psses in counter flow mnner through the wet chnnel where it gins humidity through the evportion of wter nd decreses the temperture of the ceiling s shown in Fig 1(b). The office, locted in Beirut, hs n 8.2 m 2 floor re nd height of 2.8 m. It consists of one exposed wll on the south fcde. The remining wlls long with the floor re prtitioned with conditioned spces. The internl het in the office hs sensible lod of 40 W/m 2.

3 1730 Mrim Itni et l. / Energy Procedi 75 ( 2015 ) Mthemticl modeling To predict the performnce of the combined system, mthemticl model for the DV system nd the evportive cooled ceiling re needed DV Model The widely used DV plume-multi-lyer therml spce model of Ayoub et l. [4] is dopted. The DV model predicts indoor ir temperture for given internl lods nd outdoor mbient conditions, under certin supply ir conditions Evportive Cooled Ceiling Model To predict the ceiling temperture different energy nd mss blnce equtions were developed using the study of Miyzki et l. [5]. Energy blnce for the ir in the dry nd wet chnnels dt ρ C u =α T-T dz d d pd d d d p d dt ρ C u =α T-T +α T -T dz w w pw w w w1 s1 w w2 s2 w (1) (2) The right term of eqution 1 nd 2 represent the net convective het flow in the dry nd wet chnnels respectively. The left hnd side of eqution 1 represents the het exchnge in the dry chnnel. The left hnd side of eqution 2 represents the het exchnge with the two sides of the wet chnnel. Fig. 1. () Schemtic of the combined ir conditioning system; (b) Schemtic of the ceiling M-cycle

4 Mrim Itni et l. / Energy Procedi 75 ( 2015 ) Energy blnce of the two wter sheets Ke1 T-T +α T-T +ρα h X -X =0 e1 * p s1 w1 w s1 d m1 fg w w Ke2 T-T +α T-T +ρα h X -X =0 e2 * c s2 w2 w s2 d m2 fg w w (3) (4) In eqution 3, the upper wter sheet exchnges het with the plte nd exchnges sensible nd ltent het trnsfer with the flowing ir. Similrly, in eqution 4 the lower wter sheet exchnges conduction het trnsfer with the ceiling plte nd sensible nd ltent het with the flowing ir. Mss blnce of the ir in the wet chnnel dx ρ u =ρ α +α X -X dz * w d w w d m1 m2 w w (5) The right hnd side of eqution 5 represents the net convective flow of moisture in the wet chnnel nd the left hnd side represents the moisture exchnges with the two wter sheets of the wet chnnel. Energy blnce of the ceiling nd the plte seprting the wet nd dry chnnels K e2 T s2 -T c +α r T-T r c +q R =0 e2 K α T-T + T -T =0 e1 d d p s1 d e1 (6) (7) The ceiling exchnges het with the wter sheet of the wet chnnel in eqution 6 s well s convective nd rditive het trnsfer with the spce. The first left term in eqution 7 represents the het trnsfer with the dry ir nd the second term represents the conductive het flow with the wter sheet Integrted model sequence of opertion In order to solve the system of equtions for the verticl temperture distribution in the spce nd the system cpcity for lod removl, the required inputs re the ir supply flow rte nd temperture, the outdoor wether conditions such s solr rdition nd mbient conditions nd the internl het lods, where the softwre used to solve the equtions is Mtlb. Internl surfce tempertures found by the DV model will be used by the evportive cooled ceiling model to clculte the lod subjected to the ceiling nd updte the ceiling temperture. Then, the updted tempertures re used to solve for the energy blnce of ech ir lyer. This shows tht the solution requires solving the different models itertively, in order to get t ech time step the different vribles nd updte them until convergence is reched. The coupled mss nd energy equtions re discretized into lgebric equtions using the finite volume method. Once convergence is reched the temperture distribution in the spce is determined s well s

5 1732 Mrim Itni et l. / Energy Procedi 75 ( 2015 ) the energy performnce of the system. The convergence condition for the residuls of the different equtions is set to Results nd discussion The models were simulted t supply ir flow rte of 0.14 m 3 /s nd supply ir temperture of 22 C with 10%, 50% nd 90% reltive humidity. Simultions were done for the model when using the DV system lone nd other simultions were done for the model when using the integrted system of the evportive cooled ceiling nd DV system. Then the room temperture ws recorded for the different simultions s well s the totl cooling lod removed by the system. Comprison ws done between the two systems to clculte the improvement in totl lod removl. Fig 3() shows the vrition of the totl lod removed in W/m 2 by the DV system nd the integrted evportive cooled ceiling nd DV system t different supply ir reltive humidity. Results showed the lod removed by the DV system ws 40 W/m 2 nd it ws constnt for the different reltive humidity vlues, however; the lod removed by the integrted system ws mximum nd equl to 68.9 W/m 2 t the lowest reltive humidity of 10% nd it decresed to rech W/m 2 t the highest reltive humidity of 90%. The improvement in sensible lod removl when using the proposed integrted system ws 18.65%, 44.3% nd 72.25% t reltive humidity of 10%, 50% nd 90% respectively. Fig 3(b) shows the vrition of the room ir temperture when using the DV system lone nd then when using the integrted system t different supply ir reltive humidity. The room temperture when using the DV system lone ws 24 C nd it ws not ffected by the chnge in the supply ir reltive humidity. When using the integrted system of the evportive cooled ceiling nd the DV system, the room temperture incresed from 23.4 C to 23.8 C t the reltive humidity of 10% nd 90% respectively. This shows tht the integrted system hs better sensible lod removl t lower supply ir reltive humidity. 4. Conclusion Simultion results showed tht the displcement ventiltion system combined with novel evportive cooled ceiling cn improve the displcement ventiltion cooling cpcity with no dditionl energy consumption. Mthemticl modelling of the proposed system ws performed. Results showed enhncements of the proposed system between 18.65% nd 72.25% t supply ir reltive humidity between 10% nd 90% respectively. Better cooling performnce ws ttined t lower supply ir reltive humidity, which justifies the use of desiccnt dehumidifiction systems to lower the humidity of supply ir before it enters nd cools the spce. Fig. 3. () Totl lod Removl t 10, 50 &90% reltive humidity; (b) Room temperture t 10, 50 &90% reltive humidity

Mrim Itni et l. / Energy Procedi 75 ( 2015 ) 1728 1733 1733 Acknowledgements Authors would like to express their grtitude to the Qtr Chir Fund for the support to conduct this study.

6 Mrim Itni et l. / Energy Procedi 75 ( 2015 ) Acknowledgements Authors would like to express their grtitude to the Qtr Chir Fund for the support to conduct this study. References [1] [2] Jing, Z., Q. Chen, nd A. Moser Indoor irflow with cooling nd rditive/convective het source. ASHRAE Trnsctions 98(1): [3] Mossolly M., N. Ghddr, K. Gli, nd L. Jensen Optimized opertion of combined chilled ceiling displcement ventiltion system using genetic lgorithm. ASHRAE Trnsctions 143(2): [4] Ghli K., N. Ghddr, nd M. Ayoub Chilled Ceiling nd Displcement Ventiltion System: An Opportunity for Energy Sving in Beirut. Interntionl Journl of Energy Reserch, 31: [5] Tkhiko Miyzki, Atsushi Akisw nd Iso Niki The cooling performnce of building integrted evportive cooling system driven by solr energy. Energy nd Buildings, Volume 43, Issue 9, September 2011, Pges Biogrphy Eng. Mrim Itni is reserch ssistnt t Americn University of Beirut working on displcement ventiltion system combined with novel evportive cooled ceiling. She grduted mechnicl engineer from Beirut Arb University in 2013 nd is expected to get her Msters degree from Americn University of Beirut in 2015.

Sensitive Analysis of Passive Dehumidification System using Solar Heat

Sensitive Analysis of Passive Dehumidification System using Solar Heat Sensitive Anlysis of Pssive Dehumidifiction System using Solr Het Hksung Lee 1, Akihito Ozki 2, Myonghyng Lee 3 1 Grdute student, Kyushu University, Fukuok, Jpn 2 Professor, Kyushu University, Fukuok,