Reduced the Cooling Load and Improved Insulation Effect on Iraqi Buildings Using the Geothermal Energy Storage Phenomenon

A numerical study has been done on Iraqi buildings (Baghdad) on 21


1-Introduction:
Geothermal energy has long been used for bathing, heating, and cooking since the beginning of recorded history.Low-temperature systems such as hot springs were used by the ancient Japanese, Greeks, and Romans, who enjoyed the recreational and therapeutic values of geothermally-heated spaces and bath houses Duffield,W.,et.al.[1].The geothermal heating and cooling system takes advantage of the fact that the ground a depth of several meters remain at a near constant temperature, so; in mid-winter it is warmer than the air, and in midsummer it is cooler Lund J. W., et.al.
[2].Shen L.S. and Ramsey J. W., 1988 [3] developed a twodimensional finite difference numerical model to study coupled soil heat and moisture flow around an earth-sheltered construction.Simulations of a basement wall backfilled with sand and a clay loam were performed.Deru, M., 2003 [4] investigated the ground-coupled heat and moisture transfer from buildings, and developed results and tools to improve energy simulation of ground-coupled heat transfer.He found that basement walls are sensitive to the conditions (temperature and humidity) at the surface.Basement floors are relatively unaffected by short-term variations at the surface, but they are closely tied the deep ground conditions.Compared winannual simulations from the heat-andmoisture-transfer model the heattransfer model produced agreeable results when an appropriate value for soil thermal properties was chosen.The value of the solar irradiation at the surface of the earth on a clear day is given by ASHRAE Handbook [5,6].There are many workers dealing with how to determine the temperature distribution in the soil due to heat flow in the soil Takakura T., Jordan,et.al. [7], Davies J.B. [8] and Novak M.D. [9], consider that the thermal conductivity does not change with temperature.Other workers take into consideration the variation thermal conductivity in the soil Sepaskhah A.R.et.al. [10] and Eshel A. et.al.[11].Wierenga P. J. et.al.[12]suggest models to calculate the underground temperature by measuring the temperature change at the soil surface and the thermal diffusivity which depends on the soil depth and its temperature.Data from Milly P.C.D. [13] on simultaneous heat and mass transfer in onedimensional soil samples indicate that the temperature distribution is not strongly dependent upon moisture content in the particular unsaturated soil used.Most previous studies were for one-dimensional vertical flow region.
In this research a high conductive material (aluminum or copper) flat plate is used as one of the exterior walls layers, but this flat plate is extended downward into the ground (for a certain depth).Its job is to work as a heat dissipater (the upper part) and heat exchanger (the underground part), since it has a higher thermal conductivity than the other building materials, a part of the energy absorbed by the upper part will be exchanged with ground soil (which is at lower temperature) and the building cooling load would be reduced, Fig.
The three-dimensional conduction equation in Cartesian Coordinates is derived by taking a control volume element.Appling the first law of thermodynamics to the element, we get: For the case we have (2-D with no heat generation) equation ( 3) would be; Using numerical analysis to solve Eq. ( 4) and choosing central finite difference formation, and assuming that (dx=dy); yield ( ) Convection is the mode of heat transfer between a solid surface and the adjacent fluid that is in motion, and it involves the combined effects of conduction and fluid motion.It can be obtained from- The total irradiation G t on a surface normal to the sun's rays is made up of normal direct irradiation G ND , diffuse irradiation G d , and reflected irradiation G R are given by [5] Eng.& Technology, Vol.25, No.9, 2007 Reduce the Cooling Load and Improve the Insulation Effect on Iraqi Building Using The Geothermal Energy Storage Phenomenon 1069 Neglecting the coupling of water transfer in the soil with the heat transfer, Wang S.K.
[15], we can assume the following Fourier law of diffusion to govern the soil heat transfer; At the ground-surface the temperature is a function of time (days of year N) and the time of a day (hours), the governing equation is; ( ) The dampening depth (z dp ) is the depth where the variations in soil temperature are 1/e = 0.368 times the temperature variations at the soil surface.The dampening depth is a function of the soil's thermal properties as well as the period of variation considered, ASHRAE Handbook [6]; where ω is the frequency of a temperature fluctuation.For annual fluctuation ω =2π/365 .Note that the dampening depth is 19 times greater for annual variations than it is for daily variations [18].The daily dampening depth, according to [6] for saturated soil is 12.2 cm and for an annual dampening depth, 233 cm.
To predict heat transfer in soil under the conditions of steady and non-steady heat flow requires the knowledge of the basic thermal properties of soil, Noborio K. [17].
The model for the soil thermal conductivity is taken from, De Vries D.A. [16].And it can be determined using Eq. ( 12).i i The volumetric heat capacity C (J/m 3 •K) is calculated as a weighted average of the specific heat capacities C p (J/kg•K) of the soil constituents as shown in Eq. ( 13), the heat capacity of the gases is neglected [14]; There are some cases (nodes) which need a special equations to describe the flow of heat passing through.Considering a point P that is assumed to be the intersection point of four different materials (Fig 3 ) ; where; For P that is assumed to be the intersection point of two different materials (Fig. 4 where; Considering a point P that is assumed to be the intersection point of two different materials and insulated surface (Fig. 5) ; where; Considering a point P that is assumed to be the intersection point of three different materials (Fig. 6) ; Eng. & Technology, Vol.25, No.9, 2007 Reduce the Cooling Load and Improve the Insulation Effect on Iraqi Building Using The Geothermal Energy Storage Phenomenon 1071 where; For external surface with convection subjected to it (Fig. 7); For an external surface with convection and heat flux subjected to it (Fig. 8) ; Considering a point P that represented an external corner point with two insulated sides (Fig. 9) ) Consider point P as an external corner point with one insulated side and a heat flux subjected to the other (Fig. 10) ; Eng. & Technology, Vol.25, No.9, 2007 Reduce the Cooling Load and Improve the Insulation Effect on Iraqi Building Using The Geothermal Energy Storage Phenomenon 1072 Consider point P as an external corner point with one insulated side and convection subjected to the other (Fig. 11); Consider a point P that is a external corner point with one insulated side and the other is subjected to convection and heat flux (Fig. 12);

Cases study
In this study we take an Iraqi wall that is constructed of cement, brick,

Results and discussion
In all cases it is obvious that a reduction in the heat flow inside the air-conditioned space takes place.Figs.(15,16) show that the insulation and the plate reduce the cooling load and does not change its distribution (cases 2, 3, 4), and when is used the insulation with plate the load reduces and its distribution changes.Also from these figures one can see that the arrangement of the plate and the insulation affects the reduction in the cooling load and its distribution.These figures show that case (6) gives uniform load in the eastern and southern walls and case (7) gives more reduction in the cooling load but not uniform as case (6).Figs.(17,18) represent the outside temperatures of the eastern and the southern walls, and when comparing case (3) and case (6) one can see that the plate success in reducing the temperature that increased when using insulation at on outside surface.Also from these figures one can see that the efficiency of the plate increases as the temperature of the wall surface increases, and for this reason the plate at the eastern wall reduces the temperature more than at the southern wall.
For the normal wall (case 1) the inside surface temperature is varying.The temperature distribution at the inside surface of the two walls (Figs.19 and 20) is to very similar to the heat passing through distribution system with a maximum value at (12 P.M) and a minimum value at (12 A.M) for the southern wall and a maximum value at (10 P.M) and a minimum value at (10 A.M) for the eastern wall.Through day time between (31 and 33˚C) for the southern wall and between (32 and 34.5˚C) for the eastern wall, which leads to non-homogenous temperature distribution inside the room and uncomfortable condition for people inside it.While for case (7) the variation is amount is less than 1 C for both south and east oriented walls.The temperature of the inside surface of the eastern wall is higher than that of the southern wall with; 1˚C for cases 2,3,4,5 and 6, while for case (7) the temperature difference drops to 0.5˚C which gives a better condition of human comfort.
From the same figures it can be seen that when which is placed close to the inside surface affects the temperature distribution and gives good results.Figures (21and 22) show the temperature difference between the average temperatures of the upper and lower parts of the plate for each hour and for four cases.The high fluctuation in the temperature difference for the case is due to the position of the plate on the outside surface of the wall which made the upper part of the plate highly and quickly effective by the changes in the outdoor conditions while the lower part of the plate remains approximately at the same average temperature due to the effect of the surrounding soil.In case (7) the plate is positioned near the inside surface of the wall with an insulation material right after it, this position made the plate less affected by the changes of the outdoor conditions and helped to maintain a certain amount of temperature difference between the two parts.Fig. (23) shows the total heat passing-in for the entire day (24 hours) for each case.From this figure it can be seen that when using insulation as an inner layer of the wall, cases (2,5 and 7), the plate in case (5) reduces the cooling load by (8 %) compared with case (2) (for both southern and eastern walls) but in case (7) the plate reduces the cooling load by (40% and 41.3 %) compared with case (2) (for southern and eastern walls respectively).And when using insulation as an outer layer of the wall, cases (3 and 5), the plate reduces the cooling load by (14.5% and 15.8 %).This figure shows that (14)  shows the case study presented in this work.For more details about the present work see Aslan[20].
Eng. & Technology, Vol.25, No.9, 2007    Reduce the Cooling Load and Improve the Insulation Effect on Iraqi Building Using The Geothermal Energy Storage Phenomenon 10682-TheoryHeat transfer is energy in transient, which occurs as a result of a temperature gradient or difference.This temperature difference is thought of as a driving force that causes heat to flow.Heat transfer occurs in three basic mechanisms or modes: conduction, convection, and radiation.The key to maintaining a comfortable temperature in a building is to reduce the heat transfer out of the building in the winter and reduce heat transfer into the building in the summer, Novak M.D. [9].The flow of heat through porous media such as soils can be important for many engineering structures.The two major modes of energy transfer in soils are conduction and convection.It has been found that the relative proportions of these modes of energy transfer are a function of grain size, with conduction occurring predominantly in fine-grained soils and convection in coarse-grained soils, Farouki, O.T. [19].The Fourier's law of conduction, ASHRAE Handbook [5through a wall Fig. (1); ref , and t ref are time lags from an arbitrary date and time (Jan. 1 st , 12 p.m) to the date and time at which T s =T avg , and they are taken to be N ref =105 (April 15 th ), t ref =15 (3 p.m), Cruse R.M. [18].While the underground soil initial temperature is a function of depth and time; Figure (13) Wall arrangements

Figure ( 22 )
Figure (22)  Tempereture difference between the upper and the lower parts of the plate for southern wall