techniques to reduce the energy consumption in building in...
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TECHNIQUES TO REDUCE THE ENERGY CONSUMPTION IN BUILDING IN HOT ARID REJOIN
Prof. Dr. Ghanim Kadhem Abdul Sada Mechanical Engineering Dept. / Al Mustansiriya University Baghdad IRAQ
ABSTRAC:
The sun is powerful energy source. Earlycultures were adapted to using the sun totemper their indoor climates. They choseorientations, design and materials thatexploited this powerful energy source. Nowdays the unnecessary energy consumption bybuildings has become a matter of concern andcriticism. The researchers and otherprofessionals have begun a search for a moreacceptable and responsible design of thebuildings .
The Iraqi climate is extremely hot and aridzone covers a belt between 29 ºto 36 º N, Theenergy required for air conditioning the Iraqibuildings is about 60% of the entire energyconsumption in buildings .
This research deals with the possibility ofusing different technics for the reducingenergy consumption in building by blocking oreliminates the effect of direct solar radiation insummer season.
The results show that thermal conductivity oflocal insulation materials are very low, so thatis consider a good insulation materials for Iraqbuildings .The energy transmission through theroof surface is about 4%. This systemreducing energy consumption in buildingduring summer season which is the cooling isdominated in Iraq.
Keywords: passive system, insulationmaterials, water spray system,
1. INTRODUCTION
In hot climates in earlier day man had toprotect himself against the temperature risebecause there was no possibility to cool hisliving space by any artificial means , Thus intraditional houses local materials were oftencombine with suitable house design in orderto maintain a good shelter against the hostileenvironment [1].
There were always foresight solutions thatbrought the indoor environment to the humancomfort level or to acceptable conditions. Thisneed for keeping the indoor condition withinthe comfortable level by natural means is call“ passive cooling systems” .Passive coolingrefers to technologies or design features usedto cool buildings naturally. The term “passive”implies that energy-consuming mechanicalcomponents like pumps and fans are not used[2].
The problems of maintaining suitable indoorcomfort conditions can be solved by studyingthe effect of design variations on the thermalperformance of the building . This can bedone by examining both the old methods ofconstruction and design .
In hot climate such as Iraq ( lat. 29- 36 N) ischaracterized by a long hot summer season,and short cold season. Therefore the coolingsystems is required over the hot summerperiod . Hence the cooling demand isdominate in Iraq [3]. It is important to protectthe building envelope against the directincident of solar radiation .
The buildings in Iraq are built from brickswalls and concrete flat roofs, Which are actsas a solar collectors [4].The exterior surface ofthe roofs of the buildings are exposed to solarradiation so that most solar radiation absorbedby roofs ,therefore emitted heat to the interiorliving spaces of the buildings.
There are techniques for cooling the buildingsby using passive systems. Passive coolingrefers to technologies or design features usedto cool buildings naturally. Passive coolingbuilding design attempts to integrate principlesof Physics into the building exterior envelopeto slow heat transfer into a building, by usingthermal insulation to reduce the heat transferthrough the wall and roofs or by using waterspray upon the exterior roof surfaces.
The usage of passive cooling techniques inmodern buildings however, can often eliminatethe need for mechanical cooling or at leastsignificantly reduce the size and cost of theequipment.
This study deal with different insulationmaterials were added to the south face ofwalls surface, as well as water spray systemupon the exterior roof surface to minimize theeffect of incident solar radiation upon the roofsand wall surfaces.
The results show that thermal conductivity oflocal insulation materials are very low, so thatis consider a good insulation materials for Iraqbuildings .The energy transmission through theroof surface is about 4%. This systemreducing energy consumption in buildingduring summer season which is the cooling isdominated in Iraq.
2.THERMAL INSULATION MATERIAL
Many experiments are done to measure thethermal conductivity of different localmaterials at different conditions; such aspapyrus , and palm leaves . The thermalconductivity of papyrus material was (0.059W/ m. k). Therefor the thermal conductivity ofpapyrus is low ,so that these materials considera good thermal insulation as well as low cost.
The villages in the south of Iraq are build thewalls and roofs from papyrus. The confortableconduction inside door of these houses areaccepted conditions without using airconditions units.
3.WATER SPRAY ROOF SYSTEM
Water spray roof system (WSRS) is anintegrated roof surface, provides a means tocool the roof surface and eliminate the effectof solar radiation which is incident uponexternal roof surface causing increase the heatgain transfer to inside living space. WSRS issuitable for hot and dry climates such as Iraqand other hot arid reigns.
WSRS consisting of a piping grid andconventional water spray nozzles is installedon the roof surface as shown in figure (1), andconnected to water pumping , to sprayer water,over the external roof surface and kept it wet.
Experimental work has been done in BaghdadIraq (Lat 33°N) for two hot days (7 & 8) July .The roof of the building is divided in to two
zones one zone is wet surface and the otherzone is dry surface.
4. RESULTS AND DISCUSSIONS -
The results show that the papyrus insulationmaterial is used upon the roofs and south wallssurface of houses building reduces the heatflow inside the living space from 98 W / m2
for un insulated roof to 17 W / m2, insulatedroof by papyrus,25 mm thickness.
The results of this experimental work of waterspray system are shown in the followingfigures.
Fig (1) show the incident solar radiation on ahorizontal surface on Baghdad (lat.33°N ) fortwo days 7 & 8 July .These days are choosebecause the maximum amount of solarradiation in this month which measured inBaghdad. Figures. (2) & (3) shown the threecurves, these are dry surface temperature,ambient temperature and wet surfacetemperature. Note from the figures that whenusing water spray the roof surface temperaturedecreases, from 51°C to 23.5°C The decreasein wet surface temperature due to present ofwater upon the roof, which are reduce theintensity of solar radiation incident on the roofas well as the evaporation of water absorbedheat from roof surface.
The temperature of water spray is 23°C. Fig(4) shown the amount of heat transfer throughthe roof to indoor living space. The heattransfer is reduced about 96%, when usingwater spray roof system.
5. CONCLUSIONS
Many conclusions can be drawn from thisstudy which can be summarized as follows.1-The local thermal insulation materials areavailable in Iraq such as papyrus palm leaves,good insulation with low cost.2- The roofs in Iraq's building working as solarcollectors.3- Minimized the effect of solar radiation uponthe roofs surfaces by using water spray roofsystem.4- Hence the heat transfer from outdoor toindoor through the roofs is small. Hence largemoment of energy will be saved with usingwater spray roof system.5- This method WSRS gives good indicationto use it in building in hot arid rejoins.
6.REFERENCES :-
(1)Inaam Amen Al bazaz ” The use of solarenergy in buildings” M.Sc thesis Baghdaduniversity .1990.(2) Muthana l. Abdullah” The effect of localinsulation in building” M.Sc thesisMustansiriya university.2002.(3) Abdulsada G. K “Appropriate techniquesmodel to minimize environments impacts ofbuilding” (paper summated to ISES solarworld congress 2006 .Florence Italy ).(4) Abdulsada G.K. “ Minimizing effect the
impact of enlivenment upon residencebuilding
in hot arid regions (Iraq) " 8 UTEG10, Clean
Energy congress 2010 Turkish”
(5) Iraq Meteorological Organization“Climatic ATLS of Iraq”.1993
Fig. 1: Water spray system
Fig. 1 : show the incident solar radiation on a horizontal surface measured In Baghdad lat. 33°N ref. [5].
Fig. 2 : show the effect of using water spray roof system on the temperature of roof surface in Baghdad on 7 July
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Fig. 3 : show the effect of using water spray roof system on the temperature of roof surface in Baghdad on 8 July .
Fig. 4 : show heat gain through the roof with and without water spray roof system.
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