Worldwide energy demand in buildings represents about 40-50% of the total energy consumption. In hot climates, such as Middle East and North Africa (MENA) countries, about 30% of the national power demand is used for HVAC applications in buildings. This has led to escalation in power demand in buildings for indoor air-cooling and high energy bills. This is exacerbated further by the widespread adoption of energy intensive and commercially dominant vapour compression air conditioning systems as the technology of choice. This research aims to address the potential of novel designs of evaporative cooling systems for space cooling and thermal comfort in buildings with reduced water and energy consumption, and low environmental impact as an alternative to vapour compression where climatically is suitable. High water consumption rates and low cooling effectiveness are some of the issues affecting the performance of existing Indirect Evaporative Coolers (IEC). A new configuration of IEC combining heat pipe heat exchanger and porous ceramic tubes is investigated in this work. The proposed cooler configuration is based on the concept of regenerative IEC system, this system incorporates heat pipes as passive heat transfer elements and porous ceramic tubes as wet medium mounted on the condenser side of the exchanger. The design of the cooler was carried out with consideration for size of the airflows channels, heat pipes for heat transfer, and porous ceramic tubes properties for water evaporation. A mathematical formulation of heat and mass transfer equations was used to develop a computer model to design and optimise the cooling system. Furthermore, a test rig was built to test a laboratory scale cooling unit, evaluate the performance and validate the simulation. The simulation results reveal that the Wet-bulb (WB) effectiveness of the cooler ranged from 0.524 to 1.053, the COP ranged from 6.33 to 17.01, and water consumption rates of the cooler were around 0.875-1.55 (l/kWh) of cooling capacity. Whereas, the experimental performance parameters of the cooler show the WB effectiveness was in the range of 0.422-0.908 for all test conditions, the COP was 4.62-13.16, and water consumption rates varied 0.841-2.82 (l/kWh) of cooling capacity. A good agreement was obtained between the experiments data and numerical results, the maximum errors between measured and computed results was around 3.94% and 4.51% of supply air temperature and humidity, respectively, while the discrepancy was in the range of 8.67-12.90% of the WB effectiveness. The impact of operational and design parameters on the cooler performance was evaluated in a parametric study using the developed numerical model. It was found that increasing the inlet air temperature, decreasing the inlet air flow rate, and/or increasing the working-to-inlet air flow ratio, results in improving the effectiveness and supply air temperature. Whereas, increasing the inlet air wet-bulb temperature depression, increasing the inlet air flow rate, and/or minimising the working-to-inlet air flow ratio leads to enhancing the cooling output and COP of the cooler. Additionally, increasing the thickness and/or the radius of ceramic tube causes a decline of cooler thermal performance. Therefore, it is recommended to operate the cooler at inlet air velocity of 2-2.5 m⁄s, 50% flow ratio of working-to-inlet air, and inlet air relative humidity below 35% for best results of supply air temperature, WB effectiveness, and COP. Whereas, for desert climate conditions, it is recommended to increase the number of heat pipe rows to 20 to insure sufficient cooling effectivity and performance that meet comfort levels. Finally, a brief economic assessment of the cooler annual operational performance for a case study was carried out, this IEC system provide sufficient cooling effectiveness to the conditioned space with significantly low power consumption compared to traditional air conditioner with annual saving of 77.60% of operational costs, and also substantially contribute to minimise CO2 emissions by saving about 86% of electricity consumption.

In many dry desert climates such as in Kuwait, the summer season is long with a mean daily maximum temperature of 45°C. A round 80% of total electricity generation is consumed by air-conditioning systems in domestic buildings. A hybrid cooling technique to reduce the domestic cooling demand would have both environmental and economic benefits for Kuwait. A passive cooling technique, which assists the situation, is ground cooling. In this thesis a thermal model of an earth air heat exchanger (EAHE) has been developed to calculate the pre-cooling of ventilation air that can be achieved for a building through use of a buried pipe below ground surface.

Computational studies of two- and three-dimensional, turbulent recirculating flows within mechanically-ventilated enclosures are reported. Two principal cases are examined: (i) two-dimensional offset jets: and (ii) three-dimensional flow induced in rooms by supply jets emanating from low or high side-wall registers. The calculations were undertaken using iterative finite-domain proceedures which solve the conservation equations for mass, momentum and enthalpy, together with additional transport equations for the turbulent kinetic energy and its dissipation rate . The effect of buoyancy waS. explicitly accounted for when modelling these equations, in order that they could be employed to simulate buoyant flow in ventilated rooms. Computations of the mean velocity, temperature and convective heat transfer distribution are reported, and compared with experimental data where available. A modified version of the two-dimensional elliptic code of Pun and Spalding (1977) was employed to simulate the offset jet case. These involve the discharge of a turbulent jet parallel to a flat surface and eventually attaching to it. The investigations covered a wide range of offset ratio (3.5-32.4). and the computed flow properties are compared with measurements from several sources. These comparisons show good agreement downstream of the reattachment point, while some discrepancies are evident upstream from this location. The differences therefore occur mainly in the recirculating flow region, and are believed to arise from shortcoming in the starting profiles, the turbulance model and the treatment of the near-wall flow. A three-dimensional elliptic finite-domain code was developed to simulate the complex, jet-induced flow within rectangular enclosures. The code was verified using both laminar and turbulent flow test cases on simpler geometries. Comparisons with the measurements and predictions reported by previous researchers were employed for this purpose. Subsequentlyr the ventilated room simulations were undertaken using three different ventilation arrangements with thermal conditions corresponding to isothermall non-buoyant (constant property) and buoyancy'affected flows. The computations were again compared with experimental and numerical predictions of previous researchers. This comparison displayed generally good agreement with these sources. A study of the flow and convective heat exchange within a warm-air heated rom, for which buoyancy effects are significant# is also reported in a bound paper (Alamdari, Hammonda nd Mohammad, 1986) for three different heat loads. Its aim to assess the balance between accuracy and economy provided by the present higher-level method compared with the intermediate-level convection model of Alamdari and Hammond (1982) when used to supply building thermal simulation programs with accurate convection heat transfer data. The computed results of both models were compared, and indicate that the intermediate-level is a valuable alternative source that can satisfy the needs of building thermal modellers. It provides resonable accuracy at a very modest cost in computing terms.

Water-filled heat stores present a convenient, relatively inexpensive means of optimising the use of diminishing gas stocks for the central-heating of buildings. The British Gas Corporation recently launched a series of central-heating units with storage, for use in the domestic sector, whose benefits include: - reduced boiler size, more efficient boiler operation, load-levelling at the hours of peak gas demand. This thesis is divided into three parts. Part I examines the inherent advantage of a with-storage, domestic, central-heating system over a conventional system, by means of two simple computer-simulation programs. A minimum efficiency advantage of about 5% is anticipated; the variation of this advantage with the values of certain key parameters has been assessed. Part II is an interim report of a full-scale field trial in the commercial sector; a large (3.3m3) store was fitted in the heating system of a London school, and its performance during the first weeks of its operation is presented here. Returning to the domestic sector, Part III presents a study of the use of two integral heat exchangers in the storage vessels of the above domestic units, whereby hot water can be drawn instantaneously. An attempt to optimise this domestic hot-water facility has been made.

A hierarchy of interacting and interdependent approaches have been developed for calculating internal surface convective heat transfer coefficients within mechanically-ventilated rooms. A 'high-level' computer code is developed for non-bucyant and buoyant flow based on the 'elliptic' code of Pun and Spalding (1977), in which 'upwind' finite-difference approximations to the governing partial-differential equations for continuity, momentum and thermal energy are formulated in terms of 'primitive' pressure-velocity variables. Closure of these time-averaged, elliptic equations is obtained via transport equations for both the turbulence kinetic energy and its dissipation rate. The high-level code solves the difference equations for a predetermined size, staggered grid in an iterative 'line-by-line' manner using a guess-and-correct procedure. An 'intermediate-level' computer code (the ROOM-CHT program) has also been developed for the above purpose, which employs 'informed' estimates of the flow and thermal field based on the known mean flow properties of wall-jets. The corresponding heat transfer distribution across the room surface is calculated using wall-jet profile analysis or improved data correlations for bucyancy-driven convection as appropriate. Caqputations are presented for a room into which air is injected through a low or high side wall register. The supply of air governed by both cyclic and modulating control was examined. The intermediate-level code is advocated as being the most appropriate for meeting the requirements of dynamic building thermal models. This code was verified by comparison with the high-level code and with experimental measurements. The oomputed heat transfer coefficients from the intermediate-level code were found to be in good agreement with that of the high-level code. Both indicate significantly higher values than those which would be obtained from established design guides. These high values suggest errors in building thermal models based on guide data, including substantial under-estimation of preheat times.

The design of a water based thermal store for use in a domestic central heating system has been investigated theoretically, experimentally and numerically. The transient operation of the store during both the space heating and domestic hot-water modes of operation have been investigated separately. Heat transfer correlations in terms of Nusselt and Rayleigh numbers have been developed in order to predict the natural convection heat transfer coefficient for the outside surface of the horizontal axis finned tube heat exchanger coil located within the store. These heat-transfer correlations can predict the value of the heat transfer coefficient with an accuracy of better than 5% and are in good agreement with existing heat transfer correlations developed for the same geometry of finned tubes and modes of heat transfer. The effect of the water flow rate in the heat exchanger coil on the internal heat transfer coefficient is also investigated. This flow rate should be above 4 litre/minute to achieve a high rate of heat-transfer from the wall of the heat exchanger to the water in the pipe. A detailed investigation of the use of horizontal and vertical baffles to increase the effectiveness of heat delivery in the domestic hot water mode has been carried out. Some improvements can be achieved by the use of a horizontal flat plate located in the middle of the store. This plate, when correctly sized enhances stratification and hence improves the effectiveness of heat recovery. Vertical plate arrangements and a rectangular duct situated around the upper heat exchanger coil were found to be ineffective. However, due to an increased velocity of the water around the heat exchanger, the external heat transfer coefficient of the heat exchanger was increased by 12%. The comparison of experimental observations with computer simulations of the development of the thermocline in the store during the space heating mode of operation showed the presence of a jet in the bottom region of the store at the return inlet. The jet induces a significant amount of mixing in the store which reduces the effectiveness of heat recovery. Correlations in terms of Richardson number and effectiveness of heat delivery have been developed to characterize the effect of this jet. An inlet arrangement designed to achieve a Richardson number exceeding 3 significantly reduces the mixing created by the jet and can increase the amount of heat delivered in the space heating mode by approximately 5%.

Modern development in many Third World countries in the hot regions of the world, have been accompanied by the construction of highly energy-wasteful buildings. The interiors of these buildings have to be mechanically air-conditioned in order to achieve thermal-comfort conditions. The consequence of this, has been the rapid increase in electricity-generating plant capacity to match demand (of which, for example at present in Oman, more than 70% nationally is used for air-conditioning modern, energy inefficient buildings). The aim of this work was to find the most suitable way of stabilising or even reducing the electricity demand in a country like Oman. The first step taken to achieve this aim, was to study and draw out lessons from the vernacular architecture of the different climatic regions in Oman. This has been followed by a literature survey that looks at passive and active natural cooling techniques for buildings in hot climates. Mathematical models were then developed to analyze and compare those passive techniques that are most suitable for an environment like that of Oman. Different ways of reducing the heat gain through the roof were investigated and compared. These include the addition of insulation, shading, air-cooling of the roof when the ambient air temperature is lower than that of the roof, and roof ponds. Roof ponds were found to be the most effective of those techniques analyzed. An improved design of the roof pond (the Water Diode roof pond) that eliminates the need for covering the roof pond during the day and uncovering it at night, was suggested and analyzed. The analysis showed promising results. Mathematical models were also developed to analyze and compare different ways of reducing the heat gain through the walls. These included the use of closed cavities, naturally ventilated cavities, the addition of insulation, and the effect of using brick as compared to concrete block. The analysis suggested that the combination of a Water Diode roof pond and insulated brick wall construction will reduce the heat gain through the envelope of a single room by more than 90%, when compared to a room with un-insulated roof and single-leaf concrete block walls. An empirical validation of the mathematical models was conducted. The results showed a good agreement between the actual and predicted values. An economical analysis of the commonly used roof and wall constructions in Oman, was also conducted. This compared the life-cycle cost of nine different construction techniques, with eight different airconditioning schedules. The result of this analysis showed a clear advantage of using roof insulation, reflective double glazing, and insulated walls with brick outer-leaf and concrete block inner-leaf.

District-heating and/or cooling systems are gradually becoming popular all over the world for heating and/or cooling of large premises. Current conventional practice for the DHC underground distribution networks is to place the supply and the return pipelines side-by-side in air-filled trencRe's. However, t present investigation has shown that by optimising the location of the pipelines, the thermal insulation provided by the air around the pipes can be maximised. This is achieved by placing the hot pipeline above the cold one, the exact position depending upon the temperatures involved. For most purposes, it is recommended that the displacement ratio for the hot pipe is to be at -0.7 or -0.08 and that of the cold pipe at 0.05 or 0.67 for district heating or cooling respectively [i. e. the hot and cold pipes being placed in the upper and lower halves of the trench respectively]. Each chapter is presented in such a way that it can be read independently of the others as far as possible.

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M.Ing. (Mechanical Engineering) / A reversible ground source heat pump, coupled to a municipality water reticulation system, is investigated as an alternative to conventional air source systems for space heating and cooling. The investigation was executed through the development of analytical models that were used for the design of a ground-coupled reversible heat pump and a conventional, also reversible air source system. The models were verified with experimental measurements. The results of the models and measurements indicate that ground source systems are a cost effective alternative.