Redesigning Urban Open Spaces Based on Bioclimatic Criteria: Two squares in Thessaloniki, Greece

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1 Redesigning Urn Open Spces Bsed on Bioclimtic Criteri: Two squres in Thessloniki, Greece KLEO AXARLI 1, ANGELIKI CHATZIDIMITRIOU 2 1 Deprtment of Architecture, Aristotle University of Thessloniki, Thessloniki, Greece 2 Deprtment of Civil Engineering, Aristotle University of Thessloniki, Thessloniki, Greece ABSTRACT: In the frmework of ntionl level pln for the improvement of urn open spces sed on ioclimtic criteri, redesign project for two pulic squres, in the cmpus of the Aristotle University of Thessloniki, in Greece (40 0 N.), hs een proposed. The proposl hs een evluted in terms of microclimte improvement, pedestrins therml comfort nd uilding energy svings in hot summer conditions. The proposed interventions include vriety of shding cnopies, the ddition of diverse types of trees, low vegettion s well s green wlls, wter elements such s ponds, fountins nd wet pvements, replcement of most hrd pvements with pervious surfces nd nturl soil nd replcement of the remining pvements y cool mterils of high ledo nd high emissivity. The effects of the proposed redevelopment on ir nd surfce tempertures nd on therml indices were exmined y compring microclimte simultions of current nd proposed conditions using the ENVI-met v3.1etv softwre, for two mid summer dys (typicl nd extremely hot). Simultion results reveled, men ir temperture reduction of 2.6 o C nd 1.7 o C in the two squres nd men surfce temperture reduction of pproximtely 14 o C nd 18 o C during extreme conditions. In ddition, 36% nd 34% improvement on pedestrin comfort ws reveled sed on the men PMV indices reduction on typicl summer dy, s well s 32% nd 26% reduction of the cooling degree hours dily sum, in typicl summer conditions, indicting significnt svings on cooling energy demnd of the surrounding uildings. Keywords: urn open spces, microclimte, simultions, outdoor comfort, energy svings INTRODUCTION The urn climte is comintion of the microclimtes tht develop in the streets nd the open spces etween uildings, depend on the chrcteristics of their immedite surroundings, morphologicl, physicl nd functionl fetures, nd often form the urn het islnd [1]. Mny studies hve presented the effects of uilding morphology, surfce mterils, vegettion nd wter in the urn microclimtes [2-9]. An ttempt to utilize urn design to restrict het islnds nd improve the urn environment in Greek cities hs een initited y the Greek Ministry of Environment in collortion with the Centre for Renewle Energy Sources, with ntionl level pln for the redevelopment of urn res focusing on open spces microclimtes, pedestrin comfort nd energy svings in uildings: the Bioclimtic improvement progrm for pulic open spces. The progrm clled for proposls for the redesign of urn open spces to meet specific requirements for ir nd surfce temperture reductions, cooling degree hours reductions, therml comfort enhncement nd wind field improvement in the summer period. In prticulr the gols to e chieved y the redevelopment were re weighted verge ir nd surfce temperture reductions y 1.5 o C nd 5 o C respectively t noon of the hottest dy of the yer, 20% cooling degree hours men dily sum (6:00-20:00) reduction nd 15% men dily (10:00-18:00) improvement of therml comfort indices on typiclly wrm summer dy. Site selection would focus on thermlly nd climticlly degrded res in highly populted dense urn centers. In this frmework the Aristotle University of Thessloniki proposed project on the redevelopment of two usy squres in the university cmpus which re considered downgrded in terms microclimte nd therml comfort, ll yer round nd especilly in the summer period. The microclimte improvement of the squres would hve significnt effects oth on the comfort of numerous pedestrins using or pssing through the res nd on the therml lods of the surrounding uildings. THE SITES Two pulic squres in the cmpus of Aristotle University of Thessloniki (lt. Ν40 ο ), nmed Chemistry squre (Fig.1) nd Administrtion squre (Fig.2) ecuse of the neighoring uildings, were selected for redevelopment sed on ioclimtic criteri. The first

2 one is lrge rectngulr re of 17000m 2 locted ner the NW corner of the cmpus nd open on the NW side djcent to street with hevy trffic nd dense prt of the city centre. Almost ll of the re is covered with hrd pvement, severl lrge nd smll trees re scttered on the sides ner the uildings nd the street nd fountin is locted in the centre. The second is smller squre re of pproximtely 6500m 2 situted in the hert of the cmpus, open on the SE side which is djcent to the min street cross the cmpus nd ner mjor rtery of the city. Hlf of the re is locted ove n underground cr prking spce nd covered y hrd surfces, nd the other hlf is lso used s prking re ut contins trees nd low vegettion s well. these open spces with hrd pvements overexposed to solr rdition lmost ll dy, lck of shding devices nd minimum vegettion, present uncomfortle conditions for pedestrins who use or wlk through these res especilly during dytime in the summer period. The surrounding uildings re lso severely ffected y high tempertures in the summer period resulting in high cooling lods, extended use of ir conditioning nd further degrdtion of the microclimte of the two squres. CLIMATE DATA AND MICROCLIMATE An overview of the climtic conditions in the university cmpus is otined y dt from AUTh meteorologicl sttion [10], during the summer of 2007 which ws period of very high tempertures. In prticulr the mximum ir temperture in July rose ove 43 o C nd the men monthly vlue ws 28 o C. Men reltive humidity in the re fluctuted etween 25% nd 88% nd men wind velocity ws 1.5m/s with mximum vlue of 6m/s indicting possile need for wind shelter. Mximum solr rdition in the fternoon hours in July fluctuted etween 1099 nd 896W/m 2 with men monthly vlue of 989W/m 2. According to the project requirements, the sites were exmined for two specific dys: the 21 st of July which ws considered typiclly wrm summer dy, nd the 25 th of July s the hottest dy in the specific period (Tle 1). Figure 1. Existing conditions in the lrge squre Tle 1. Climte dt for typiclly wrm summer dy nd the hottest dy of the yer in Thessloniki Thessloniki climte dt Typicl summer dy 21 JULY 2007 Hottest dy of the yer 25 JULY 2007 Tir ( o C) Tir.mx ( o C) RH (%) Wind velocity Wind direction SW NW Source of dt A.U.Th. A.U.Th. A.U.Th. irport irport Figure 2. Existing conditions in the smll squre Both squres re extremely usy spces, mostly due to their loction nd use of the neighouring uildings. The lrge one is one of the mjor entrnce points to the cmpus surrounded y highly populted schools; the other in is the dministrtive centre of the university nd ner the centrl lirry. Both res re key meeting points nd venues for vrious events. However currently The cmpus meteorologicl sttion is locted in vegetted re therefore presents etter conditions thn those ctully oserved in the two squres where different microclimtes develop. Simultions of the existing conditions using the sttion s climte dt s input, show ir tempertures up to 36.3 o C nd 35.7 o C in the lrge nd the smll squre respectively on typiclly wrm dy, nd the surfce tempertures up to 52.5 o C nd 57.6 o C respectively on the wrmest summer dy. Are

3 weighted verge PMV vlues on typicl dy indicte very hot conditions in oth cses t ll times nd the men dily vlues (10:00-18:00) rech 6.2 in the lrge squre nd 5.8 in the smll one. Finlly, the Cooling Degree Hours sum on typiclly wrm dy, with se temperture of 26 o C, ws clculted 92.4DH for the lrge squre nd 96.4DH for the smll, lmost doule thn typicl CDH sum for the city of Thessloniki [11], indicting severe consequences on the cooling lods of surrounding uildings. PROPOSED INTERVENTIONS The proposed interventions in the two squres include vriety of shding cnopies, the ddition of diverse types of trees, low vegettion s well s green wlls, wter elements such s ponds, fountins nd wet pvements, replcement of most hrd pvements with pervious surfces nd nturl soil nd replcement of the mterils of the remining pvements with cool mterils which re siclly concrete products of high ledo nd high emissivity. In prticulr the re of soil nd pervious surfces increse y 30% (from 28% to 58%) in the two squres nd cool mterils replce lmost 18% of the existing pvements. 225 new trees re dded, new fountins, wter ponds nd wet pvements re proposed lmost t 5% of the totl re of the squres nd dditionl shding cnopies cover more thn 5% of the spce. In ddition, shding devices re proposed on ll uildings in oth squres, s well s vegetted wll on the uilding locted in the SW prt of the smll squre. Also in ll prking spces of oth squres sphlt is replced y pervious surfces with cole stones nd grss. Figure 3. Proposed interventions in the lrge squre (3d views): shding cnopies (), fountins nd wet pvements () In the lrge squre ( Chemistry squre ) the ddition of 184 new trees (from 88 to 272) nd 600m 2 extr shding cnopies (lmost 4% of the squre) incresed drmticlly the shded res which re essentil to provide comfort in the summer period. Furthermore, fountins in the centrl nd the north prt of the squre re proposed to sprinkle nd keep wet lrge prt of the hrd pvement (750m 2, lmost 5% of the whole re) to induce evportive cooling. In the smll squre ( Administrtion squre ) the underground prking spce restricts the possiilities to increse the mount of trees nd vegettion therefore only 41 new trees re dded (from 28 to 69). To overcome this deficit, 640m 2 of extr shding cnopies re proposed (lmost 10% of the spce) nd 310m 2 of wter ponds (lmost 5% of the squre) nd the mximum possile replcement of hrd pvements with cool mterils.

4 Figure 4. Proposed interventions in the smll squre (3d views): shding cnopies (), wter ponds () The proposl of shding cnopies nd trees ims to reduce surfce tempertures s well s to improve comfort y decresing the mount of solr rdition on pedestrins, ut the trees lso contriute to ir temperture reductions y leves evpotrnspirtion. Low vegettion, soil, pervious surfces nd wet surfces re proposed to decrese oth surfce nd ir tempertures y llowing humidity evportion from the ground while the ddition of fountins nd ponds lso ims for evportive cooling of the ir. Cool mterils re proposed for limit the overheting of ground surfces y reducing solr rdition sorption nd incresing het emission. Shding devices on uildings re proposed to reduce wlls reflectivity nd its effect on the therml conditions nd comfort in oth squres while reducing uilding cooling lods. PROJECT EVALUATION The effects of the proposed redevelopment on ir nd surfce tempertures nd on therml indices were exmined y compring microclimte simultions of current nd proposed conditions (Fig. 6) using the ENVImet v3.1etv softwre[12], for the two mid summer dys (typicl nd extremely hot). Surrounding uildings cooling lod reduction ws estimted y clculting cooling degree hours dily sum from morning to evening (6:00 20:00) with se temperture of 26 o C. Figure 5. Mps of geometric, mteril nd vegettion input dt for current conditions of the lrge () nd smll () squre simultions (ENVI-met), with indiction of nine spots considered for re weighted verges. The comprison of simultion results reveled, men ir temperture reduction of 2.6 o C nd 1.7 o C in the lrge nd the smll squre respectively nd men surfce temperture reduction of pproximtely 14 o C nd 18 o C respectively during extreme conditions, t noon on the hottest dy, July 25 th. These results exceed the project s requirements for 1.5 o C nd 5 o C reductions of ir nd surfce tempertures respectively t noon of the hottest dy of the yer. In ddition, 36% nd 34% improvement on pedestrin comfort ws reveled sed on the men PMV indices reduction on typicl summer dy from morning to fternoon (10:00-18:00) for the lrge nd smll squre respectively, fr exceeding the gols for 15% improvement, s well s 32% nd 26% reduction of the cooling degree hours dily sum, in typicl summer conditions, well ove the requirement for 20% reduction, indicting significnt svings on

5 cooling energy demnd of the surrounding uildings. Wind field ws lso improved with higher wind velocity t severl spots, the effect of which is reflected in the comfort indices reduction. The re weighted verge vlues of tempertures nd comfort indices for ech squre were clculted sed on hourly simultion results t nine evenly distriuted spots (Fig. 5), where different interventions were pplied. The comprison of spot vlues lso reveled the effects of the vrious interventions seprtely. The highest ir nd surfce temperture reductions re cused y tree shding with replcement of hrd surfces y soil, low vegettion or cool mterils, nd the highest comfort improvement y tree shde nd in some cses y pvement replcement y soil nd vegettion. It ws lso oserved tht cool mterils exposed to solr rdition reduced surfce tempertures ut in some cses cused slight increse of the therml indices (PMV). The effect of wter ponds ws mostly surfce temperture reduction nd comfort improvement due to reduced reflectivity. All wter odies were represented s still wter in the models so the effect of evportion from flowing wter ws only prtly tken into ccount y the softwre clcultions ut the extended replcement of hrd pvements ws simulted not only with mteril chnge ut lso with n increse of soil humidity with mjor effects on ll microclimte vriles. FUTURE ASSESSMENT The project is currently cndidte to ecome prt of wider pln on ntionl level nd in the cse of selection for funding nd construction it will e followed y extensive monitoring studies. Monitoring will include continuous mesurements of ir nd surfce tempertures, wind velocity nd solr rdition in the two squres nd will e used for further evlution of oth the current conditions nd the interventions effects.

6 Figure 6. Air temperture simultion results (ENVI-met) of current () nd proposed () conditions in the smll squre t 1.8m ove ground t noon of the hottest dy.

7 CONCLUSION A redesign project of two pulic squres in the university cmpus in Thessloniki hs een prepred in the frmework of ntionl progrm for the improvement of urn open spces in terms of microclimte conditions, pedestrin comfort nd uilding energy svings in the summer period. The evlution of the proposed interventions with specilised microclimte simultion softwre hs shown tht the improvement in ir nd surfce tempertures, comfort indices nd cooling degree hours dily sums exceeds the redevelopment progrm s requirements. The highest improvements oserved were ttriuted to tree shding nd pvement replcement y soil s well s to soil humidity increse. Further evlution will tke plce in the cse of construction nd my revel more detiled rel scle effects of the design proposls on microclimte nd comfort in nd round the squres. the Mediterrnen climte. PhD thesis, Deprtment of Civil Engineering, Aristotle University of Thessloniki (in Greek). 10. Meteorologicl oservtions of Thessloniki meteorologicl sttion. Annul ed. of the Deprtment of Meteorology & Climtology, AUTh, Vol Technicl Guidelines /2010 (2010). Climte dt of Greek Regions. Technicl Chmer of Greece (in Greek). 12. ENVI-met v.3 Avilile online: www. envi-met.com AKNOWLEDGEMENTS Acknowledgments re due to Aristotle University of Thessloniki for funding the study nd to the design tem prtners Dr I. Tslikides, F. Pppetrou nd M. Goutzimnis. REFERENCES 1. Oke T.R. (1987). Boundry lyer climtes. second ed. Methuen & Co, London. 2. Ynns, S. (2001). Towrd More Sustinle Cities. Solr Energy Journl. Vol. 70 No 3 pp , Elsevier Science Pulishers, Oxford 3. Akri, H., M. Pomerntz nd H. Th (2001). Cool surfces nd shde trees to reduce energy use nd improve ir qulity in urn res. Solr Energy Journl Vol. 70 No 3 pp , Elsevier Science Limited. 4. Oke, T.R. (1989). The micrometeorology of the urn forest, J. Phil. R. Sec. Lnd. B 324 pp Doulos, L., M. Sntmouris nd I. Livd (2004). Pssive cooling of outdoor urn spces. The role of mterils. Solr Energy Volume 77, Issue 2, pp Cdim, P. (2005). Form nd Microclimte: Sptil Confinement nd Het in the Urn Ptio. In proceedings of the 22nd Conference of Pssive nd Low Energy Architecture, Beirut, Lenon, Novemer Alexndri, E. nd P. Jones (2006). Ponds, GreenRoofs, Pergols nd High Aledo Mterils; Which cooling technique for urn spces. In proceedings of the 23rd Conference of Pssive nd Low Energy Architecture, Genev, Switzerlnd 8. Chtzidimitriou, A. nd S. Ynns, (2004). Microclimtic Studies of Urn Open Spces in Northern Greece. In proceedings of 21st PLEA conference, Eindhoven, The Netherlnds. 9. Chtzidimitriou, A. (2012). Evlution of the effect of design prmeters on urn open spces microclimte development nd on therml comfort conditions, during the summer period in