Conjugate mixed-convection numerical analysis is conducted in order to investigate effect of employing different types of window glass on solar heat gain in air-conditioned rooms using mixing air-distribution system. ANSYS Fluent and RNG k-ε turbulence model are utilized. Single- and double-pane clear and tinted window glass are considered with window-to-wall ratio of 0.33. The rate of air change per hour (ACH) is varied in range 5–20. Part of solar radiation absorbed by glass is conducted indoor while solar radiation transmitted through glass heats portion of floor and is released as a heat source to inner space. The numerical model is validated against measurements available under simpler conditions. Results of model application show that airflow pattern and temperature distribution are sensitive to the solar heat gain and, hence, to the type of glass used. It is found that air-conditioning load due to window glass heat gain is reduced by 55% by using double-pane tinted glass compared to using single-pane clear glass. A criterion to distinguish between forced and mixed convection situations in terms of ACH is also developed. In addition, further calculations are made using standard k-ω turbulence model and satisfactory agreement with RNG k-ε model results is obtained.

A numerical study is conducted to simulate flow and heat transfer in shallow cooling ponds. A depth-integrated CFD model, based on the finite-volume method, is developed and applied to calculate detailed velocity and temperature distributions inside the pond. The numerical model is validated by comparing results with temperature measurements available for an experimental cooling pond. The model is used to investigate effect of mass flow rate (m) on pond hydrodynamics and thermal characteristics for cases of without and with internal baffles. The results show that the pressure loss coefficient remains constant, while the pressure drop between pond inlet and outlet increases with increasing m. The heat dissipated from the pond at the air-water interface increases with m despite the decrease in difference between water inlet and outlet temperatures. The pond effective heat-transfer coefficient, pond mean temperature, and water loss by evaporation are determined as a function of m. and relative humidity. The outlet temperature from the pond is determined as a function of pond cooling capacity. Streamline plots show that the flow pattern is independent of m but is strongly dependent on geometric configuration. A single contour map of normalized speed is, therefore, sufficient to describe all speeds inside the pond for different m. It is recommended that m should be as high as possible in order to enhance heat transfer from the pond but this would increase pumping power of cooling water through condenser tubes in which a compromise must be sought.

A numerical model based on the finite-volume method is presented for the determination of heat gain through window glass under time-dependent periodic conditions. The heat gain includes solar transmission and heat conduction to inner space. Model application is made to different climates in KSA; namely, Riyadh, Jeddah, and Abha. Different window orientations are considered using double-pane tinted window glass. Glass solar-optical properties for beam and diffuse radiation are determined as a function of solar incident angle. The ASHRAE clear-sky model is used to calculate the solar radiation. Results show that the peak heat gain in August pertains to the west-facing window with values of 359.3 W/m 2 , 339.4 W/m 2 , and 311.7 W/m 2 for Riyadh, Jeddah and Abha, respectively. Corresponding daily heat gains are 7.67 MJ/m 2 .day, 7.12 MJ/m 2 .day, and 4.39 MJ/m 2 .day, respectively. The daily heat gain is found to be practically equal for the east and west orientations. The north-facing window has the lowest instantaneous and daily heat gain for all cities since the solar heat gain is the lowest for this orientation.

Thermal bridges in building walls are usually caused by mortar joints between insulated building blocks and by the presence of concrete columns and beams within the building envelope. These bridges create an easy path for heat transmission and therefore increase air-conditioning loads. In this study, the effects of mortar joints only on cooling and heating loads in a typical two-story villa in Riyadh are investigated using whole building energy analysis. All loads found in the villa, which broadly include ventilation, transmission, solar and internal loads, are considered with schedules based on local lifestyles. The thermal bridging effect of mortar joints is simulated by reducing wall thermal resistance by a percentage that depends on the bridges to wall area ratio (TB area ratio or A(mj)/A(tot)) and the nominal thermal insulation thickness (L-ins). These percentage reductions are obtained from a correlation developed by using a rigorous 2D dynamic model of heat transmission through walls with mortar joints. The reduction in thermal resistance is achieved through minor reductions in insulation thickness, thereby keeping the thermal mass of the wall essentially unchanged. Results indicate that yearly and monthly cooling loads increase almost linearly with the thermal bridge to wall area ratio. The increase in the villa's yearly loads varies from about 3% for A(mj)/A(tot) = 0.02 to about 11% for A(mj)/A(tot) = 0.08. The monthly increase is not uniform over the year and reaches a maximum in August, where it ranges from 5% for A(mj)/A(tot) = 0.02 to 15% for A(mj)/A(tot) = 0.08. In winter, results show that yearly heating loads are generally very small compared to cooling loads and that heating is only needed in December, January and February, starting from late night to late morning. Monthly heating loads increase with the thermal bridge area ratio; however, the variation is not as linear as observed in cooling loads. The present results highlight the importance of reducing or eliminating thermal bridging effects resulting from mortar joints in walls by maintaining the continuity of the insulation layer in order to reduce energy consumption in air-conditioned buildings.

•Optimum wall R-values are determined for different climatic regions in Saudi Arabia.•Optimum R-values are obtained using dynamic heat transfer and economic models.•Optimum R-values for Riyadh and Jeddah regions range from 2 to 2.9 m2.K/W.•Optimum R-values for Abha region range from 1.34 to 1.99 m2.K/W.•Payback periods using optimum insulation thickness range from 3 to 10 years.

In this study, the problem of brine discharge into sea is studied numerically. A 3D model for the heat and brine dispersion in the vicinity of discharge and intake ports is developed using Fluent package. The flow is taken turbulent and the fluid properties are considered variable with salinity and temperature. The results are expressed in terms of streamlines, isotherms, and salinity contours as well as velocity, temperature, and salinity profiles. These results give the excess temperature and salinity relative to the nominal values of the free stream. Effect of discharge mass flow rate on patterns of temperature and salinity contours is presented and analyzed. It is observed in particular that for the different simulations undertaken, the excess temperature and salinity can be important and the intake is always affected by the discharge conditions.

The main goal of this work is to assess the possible impacts of an existing desalination plant on the marine environment under various discharge conditions. Assessment is made through the determination, by using mathematical modeling, of the excess salinity and temperature distributions over the nominal seawater values as caused by the desalination plant effluent discharge. This chapter presents first a review of brine discharge models and studies followed by a rigorous numerical analysis study of a typical discharge problem into the Arabian Gulf. The mathematical formulation centers on the concept of shallow water equations in which the 3-D problem is reduced to an equivalent 2-D one by integrating the governing equations over the depth of flow. Appropriate boundary conditions, seabed friction, wind stress, and heat transfer correlations for thermal exchange at water-air interface are used. After validating the numerical model, it is applied to determine the salinity and temperature distributions in shallow coastal waters resulting from effluent discharge from an existing desalination plant situated on the Arabian Gulf. Parametric studies of the effects of a number of influential conditions are carried out by using the actual seabed topography and plant discharge and intake port locations. Effects of sea current magnitude and direction and plant discharge flow rate are in particular presented and analyzed. Possible plant discharge-intake port interactions were predicted with varying degrees of influence. The results presented indicated such interactions and quantified values of salinity and temperature at the plant intake port.

Effects of type of masonry material and surface absorptivity to solar radiation on critical thermal mass thickness in insulated building walls are investigated for a fixed wall nominal thermal resistance (R-n-value). The concepts of "thermal-mass energy-savings potential" (Delta) and "critical thermal mass thickness" (L-mas,L-cr), developed in a previous study, are utilized to determine the thermal mass thickness required for a desired percentage energy savings. Transmission loads are calculated under the climatic data of Riyadh, assuming steady periodic conditions, by using a previously validated computer model. Effects of masonry materials are investigated by using solid and hollow concrete blocks, while surface absorptivity (lambda) influence is studied for lambda = 0.4 and 0.2. Walls are considered where thermal mass is located on the inside or on the outside relative to insulation layer. Thermal mass thickness is varied between 0 and 50 cm while keeping R-n-value constant. The results show that for a given critical thermal mass thickness, higher energy savings potential is obtained with: (i) walls with solid concrete blocks, (ii) walls with lower surface absorptivity, and (iii) walls with inside thermal mass. Charts are developed for L-mas,L-cr versus Delta under the different conditions for the benefit of building envelope designers. (c) 2012 Elsevier Ltd. All rights reserved.

Mortar joints which cut across insulation layers in building walls act as thermal bridges that increase transmission loads and reduce wall thermal resistance (R-value). A computer model based on the finite-volume method, which has been previously validated, is used to quantify effects of mortar joints height (Hmj) on thermal performance of building walls under two-dimensional steady-periodic conditions using the climatic data of Riyadh. Results show that for a typical wall with insulation thickness of 75 mm, mortar joints with Hmj = 10 mm (4.8% thermal bridge area) increase peak, daily, and yearly cooling and heating transmission loads by 62%, while the wall R-value decreases by 38% compared to similar wall with no mortar joints (Hmj = 0). The transmissions loads increase by 103% and the R-value decreases by 51% for Hmj = 20 mm (9.1% thermal bridge area). These percentages would drastically increase building air-conditioning loads and energy consumption. Thermal bridges are also shown to appreciably increase the decrement factor causing higher inner surface temperature and transmission load fluctuations. It is strongly recommended that thermal bridging effects should be minimized, if not eliminated, through proper design practices and that, when unavoidably present, must be given due consideration in thermal analysis and must be accounted for.

A CFD study is conducted to simulate turbulent flow and heat-transfer inside mechanically ventilated rooms, using mixing air-distribution system, under forced convection conditions. Air enters room from side wall opening flush with isothermal ceiling and leaves through port in opposite wall flush with floor. Velocity and temperature distributions are determined by using a finite volume method employing the k-epsilon turbulence model. The numerical model is validated by comparing results with available experimental data. Sensitivity of results to turbulent Prandtl number, values of k and epsilon at supply port, and y(+) is examined. The model is then used to investigate effects of supply Reynolds number (Re-d = 4000 to 10,000, where d is supply port height) and room aspect ratio (L/H = 0.5-6) on flow and heat-transfer characteristics within room. Variation of convection coefficient h(x) along ceiling is compared with isolated flat plate correlation. Results show that ceiling averaged convection coefficient (h(av)) increases with Re-d and decreases with L/H. Correlations for h(av) are constructed in terms of Re-d and L/H. Streamline plots show that flow pattern is independent of Re-d but strongly dependent on L/H. A single contour map of speed with values normalized by supply velocity is therefore sufficient to describe all speeds inside the room for different supply Reynolds numbers. Temperature contours illustrate that variation of temperature in the bulk of occupied zone is well within 0.5 degrees C compared to variation of 10 degrees C in region close to ceiling, reflecting good mixing characteristics in occupied zone. (C) 2011 Elsevier Masson SAS. All rights reserved.

The present paper deals with CFD study of flow and thermal characteristics in air-conditioned rooms under turbulent mixed convection conditions. Air enters room from a sidewall slot flush with isothermal ceiling and leaves through a slot in opposite wall flush with floor. Velocity and temperature distributions are determined by a CFD model that has been previously validated by comparison with experimental data. Rigorous dimensional analysis shows that performance of the air-distribution system depends on: supply Reynolds number Re-d, Grashof number Gr(d) (or Archimedes number Ar-d), room aspect ratio L/H, dimensionless heights of supply and return ports (d/H and t/H), where H is room height. For a room with fixed geometry, the effects of Re-d and Gr(d) (or Ar-d) are investigated systematically by varying one parameter at a time. Results show that ceiling average Nusselt number (Nu(d,av)) increases with Re-d and decreases with Gr(d) (or Ar-d). For a given Gr(d), the heat removal index (HRI) increases with Re-d up to Re-d approximate to 9000, then stays practically constant thereafter. For a given Re-d, HRI decreases with increasing Gr(d) (or Ar-d). A criterion for distinction between forced and mixed convection situations is developed, resulting in a critical Archimedes number of 0.11. Results further indicate that Ar-d alone, irrespective of the particular values of Re-d and Gr(d), determines to a reasonable extent Nu(d,av) and HRI when Ar-d is above its critical value. Streamlines and temperature contours are found to be consistent with other results and helped explain them. (C) 2012 Elsevier Masson SAS. All rights reserved.

Effects of varying amount and location of thermal mass on dynamic heat-transfer characteristics of insulated building walls with same nominal resistance (R-n-value) are investigated numerically under steady periodic conditions using climatic data of Riyadh. Concepts of "thermal-mass energy-savings potential" (Delta) and "critical thermal-mass thickness" (L-mas,L-cr) are developed and utilized in order to determine thermal mass thickness (L-mas) required for a selected desirable percentage of energy savings. Results show that daily transmission loads are not affected by L-mas for representative days of months in summer and winter. However, for moderate months, daily cooling and heating transmission loads decrease with increasing L-mas and either diminish to zero or be reduced asymptotically to constant values. For all months, peak transmission loads and decrement factor decrease, while time lag increases, with increasing L-mas. For a given L-mas, a wall with outside insulation gives better overall performance than a wall with inside insulation. While R-n-value is constant, wall dynamic resistance (R-d-value) changes and represents actual variations in transmission loads. For Delta in the range 70-99%, L-mas.cr ranges between 6 and 30 cm by using heavyweight concrete. It is found that maximum savings in yearly cooling and heating transmission loads are about 17% and 35%, respectively, as a result of optimizing L-mas for same R-n-value. It is recommended that building walls should contain L-mas.cr that corresponds to high Delta (approximate to 95%) and with insulation placed on outside for applications with continuously operating year-round AC. (C) 2011 Elsevier Ltd. All rights reserved.

Dynamic thermal characteristics of insulated building walls with same thermal mass are studied numerically with optimized insulation thickness under steady periodic conditions using the climatic data of Riyadh. Insulation is effected through use of one, two and three layers of insulation, the locations of which are varied in order to achieve the best performance. Insulation layer(s) thicknesses are optimized by minimizing the total cost of insulation and energy consumption using the present worth method. The results show that the optimum thickness of a single insulation layer is independent of its location in the wall; and that, when more than one insulation layer is used, their total optimum thickness is the same as the optimum thickness of a single layer. As a consequence, walls thermal resistances (R-values) are equal under optimum conditions; however, peak load, time lag, and decrement factor are found to be substantially different. The best overall performance is achieved by a wall with three layers of insulation, each 26-mm-thick, placed at inside, middle and outside followed closely by a wall with two insulation layers, each 39-mm-thick, placed at middle and outside. Comparing performance of the best wall with that of a wall with one layer of insulation, 78-mm-thick, placed on the inside, the following improvements are achieved: 100% increase in time lag from 6h to 12h; 10-fold decrease in decrement factor; 20% decrease in both peak cooling and heating transmission loads, and 1.6% and 3.2% decrease in yearly cooling and heating transmission loads, respectively. It is emphasized that all walls have the same optimized R-value and same thermal mass and therefore all improvements achieved are solely due to the developed distribution of insulation layers.

The present study deals with energy conservation in buildings via reduction of cooling-and-heating transmission loads through walls by optimizing the indoor air-temperature settings. Maximum energy-saving and thermal-comfort are obtained for both yearly- and monthly-fixed thermostat settings. The transmission loads are calculated under the climatic conditions of Riyadh by using a dynamic heat-transfer model based on the finite-volume implicit procedure, which has been validated previously. The study utilizes a basic thermal-comfort chart where indoor air temperatures are selected inside the summer and winter comfort-zones, as a function of relative humidity, in a manner to provide the highest comfort-level while maximizing energy savings. The yearly-fixed thermostat settings range between 21.6 degrees C and 24.1 degrees C (70.9 degrees F and 75.4 degrees F), and those for the optimized monthly-fixed settings range between 20.1 degrees C and 26.2 degrees C (68.2 degrees F and 79.1 degrees F). For the yearly-fixed thermostat settings, the results show that about a 10% reduction in yearly cooling transmission load can be achieved per 1 degrees C increase in thermostat setting. Despite a corresponding increase of about 14% in yearly heating transmission load, a net saving in the yearly total energy cost of about 4% can still be affected per 1 degrees C increase in thermostat setting within the comfort zone. However, much bigger savings are achieved by utilizing an optimized monthly-fixed thermostat setting scheme developed in this study. Savings in energy cost between 26.8% and 33.6% compared with the yearly-fixed settings are obtained depending on the value of yearly-fixed setting. The corresponding reductions in peak loads compared with the yearly-fixed settings range between 13.5% and 25.6% in summer, and between 15.1% and 31.9% in winter depending on the yearly-fixed setting. These percentage savings in energy cost and reductions in peak loads are conservative since the yearly-fixed settings are themselves selected for high annual energy-savings while maintaining a high level of thermal comfort throughout the year. (C) 2007 Elsevier Ltd. All rights reserved.

Rib-slab (Hordi) roofs are commonly used in the construction of buildings in Saudi Arabia. Compared to the traditional solid-slab roofs, Hordi roofs are lighter and have higher thermal and acoustic resistances. Despite their widespread use in recent years, only little information is available regarding their thermal characteristics in general, and none under optimised insulation conditions. The geometrical configuration of the Hordi units is strictly two-dimensional, however, the heat flow across the roof is predominantly one-dimensional. By modeling the layers in a Hordi unit by thermal resistances connected in parallel, an "equivalent" one-dimensional model is obtained for the roof. A finite-volume timedependent implicit procedure, which has been previously validated, is used in conjunction with this model to compute the yearly heat transmission loads for different insulation layer thickness while accounting for solar radiation and long wave radiation exchange with the sky. These loads, calculated under steady periodic conditions using the climatic data of Riyadh, are used in an economic model in order to determine the optimum insulation thickness (L-opt). Three roof configurations are investigated afl with a polystyrene insulation layer. Roof R1 is a traditional solid-slab roof, roof R2 is a rib-slab roof with Hordi units made of polystyrene, and roof R3 is a rib-slab roof with Hordi units made of concrete. Under the conditions of the present study, values of L-opt obtained are: 4.8, 3.7 and 4.2 cm, for R1, R2 and R3, respectively. Under optimum conditions, R2 gives the lowest total cost of insulation and energy consumption over the lifetime of the building, while R3 gives the lowest decrement factor (0.0047) and the longest time lag (13.2 h); R1 is found to be the least favoured roof in these respects. The average R-value for the three roofs is about 2.2 m(2) K/W.

A numerical model based on a two-dimensional finite-volume implicit procedure is utilized for the determination of the thermal performance of Hordi (rib-slab) roofs used in the construction of buildings in Saudi Arabia. The roofs are subjected to periodic change in ambient temperature, solar radiation and nonlinear radiation exchange on the outside surface and to a constant indoor-air-temperature on the inside surface. The investigation is carried out under the climatic conditions of Riyadh for a representative day for July. The daily heat transmission load and dynamic R-value, averaged over a 24-hour period, are compared by using different materials for the Hordi units for the cases without and with an insulation layer. The results show that using insulation materials for the Hordi units, instead of the commonly used building materials, reduces the roof heat transmission load by about 25%. However, the ribs of the reinforced concrete slab act as thermal bridges which significantly reduce the R-value. It is concluded that using low thermal conductivity Hordi units is advantageous but does not, generally, produce sufficient thermal resistance for the uninsulated roofs. It is recommended that the ends of the ribs should be insulated.

The steady laminar flow and heat transfer characteristics of a continuously moving vertical sheet of extruded material are studied close to and far downstream from the extrusion slot. Uniform or non-uniform suction/injection is allowed at the surface. The velocity and temperature variations, obtained by a finite-volume method, are used to map out the entire forced, mixed and natural convection regimes. The effects of the Prandtl number (Pr), the buoyancy force parameter (B) and the suction/injection parameter (D) on the friction and heat transfer coefficients are investigated. Comparisons of results with local-similarity method and finite-difference solutions of the boundary layer equations and with exact analytic solutions for asymptotic suction flows show an excellent agreement. The region close to the extrusion slot is characterized as a diffusion dominated region in which NuxRex−1/2 drops sharply with increasing Richardson number (Rix). This is followed by a forced-convection dominated region in which NuxRex−1/2 levels off with increasing Rix until the buoyancy effect sets in. A mixed convection region where increasing buoyancy effect enhances the heat transfer rate follows. Finally, this region is followed downstream by a natural-convection dominated region in which NuxRex−1/2 approaches asymptotically the pure natural convection results. For the case of uniform suction and far downstream from the slot, the boundary layer thickness becomes constant and the heat transfer rate approaches a constant asymptotic suction value independent of the heat convection mode. Critical values of Rix to distinguish the various convection regimes are determined for different Pr, B and D.

A finite-volume implicit procedure is presented for the determination of the thermal performance of two-dimensional composite building roof elements. The elements are subjected to steady periodic change in ambient temperature, solar radiation and non-linear radiation exchange on the outside surface and to a constant indoor-air-temperature on the inside surface. The solar radiation is calculated by the ASHRAE clear-sky model. TEACH-C computer program is utilized to solve the finite-volume equations. The validity and accuracy of the numerical model are checked by comparing results with exact analytical solutions for simpler problems. The model versatility is demonstrated by an application to a “Hordi-type” (rib-slab) structure used in roofs in Saudi Arabia. The climatic data of Riyadh for a representative day for July are employed. The Hordi units used are made of an insulation material to further increase the overall thermal resistance ( R -value) of the roof. Sample results show that the ribs of the reinforced concrete slab act as thermal bridges which degrade the roof R -value appreciably.

The optimum thickness of insulation layers in cavity walls in buildings is determined under steady periodic conditions using the climatic data of Riyadh, Saudi Arabia. Different insulation materials are investigated at different locations in the cavity for a west-facing wall. The yearly cooling and heating transmission loads are calculated by an implicit finite-volume procedure that has been previously validated. These loads are used in an economic model based on the present worth analysis in order to minimize the total cost. Air spaces and insulation layers with different surface conditions and thickness are investigated and compared with the limiting cases with no air space or with no insulation. The results show that the most economical cavity configuration depends on the insulation material used. Under the conditions of the present study, polyurethane board and rock wool are found to be more cost effective when used alongside air spaces, while polystyrene is most cost effective when used with no air space. Among all configurations and insulation materials considered, a 9-cm-thick molded polystyrene layer with no air space is found to be the most economical. Thermal characteristics in the form of yearly transmission loads, and yearly averaged-dynamic R-value, time lag and decrement factor are presented versus insulation thickness.

SYNOPSIS The optimum thickness of an insulation layer in a typical building wall is determined under steady periodic conditions using the climatic data of Riyadh. A finite-volume implicit procedure, which has been previously validated, is used to compute the yearly heat transmission loads for various insulation thicknesses. These loads are input to an economic model, based on the present worth method, in order to minimise the total cost of insulation and energy consumption over the lifetime of the building. Cooling and heating loads are integrated separately over the year and treated with different costs in the economic analysis. The wall yearly transmission loads, yearly-averaged dynamic R-value, time lag and decrement factor are presented versus insulation thickness and compared for different wall orientations. A parametric study is performed to establish the sensitivity of the results to changes in economic parameters. The optimum insulation thickness is found to increase with the cost of electricity, building lifetime and inflation rate; and decrease with increasing cost of insulation material, coefficient of performance of air-conditioning equipment and discount rate. The results also show that the wall orientation has a significant effect on the thermal behaviour but a relatively smaller effect on the total cost and consequently the optimum insulation thickness. The south-facing wall is the most favourite orientation since it gives about 12% lower yearly transmission load and 5% lower total cost compared to the least favourite orientation which is the west-facing wall. Among the insulation materials investigated, molded polystyrene is found to be the most economical type with an optimum thickness of 9.3 cm.