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.

Hot water thermal energy stores have the potential to improve and extend the performance of many kinds of energy system. Waperature stratification in the store is likely to affect the system's efficiency. A basic but accurate computer model of the hot water store under various inlet flow conditions is a requisite means of assesiing promising applications of hot water storage by system computer simulation techniques. A microprocessor-controlled test facility has been constructed to evaluate the performance of a 3m 3 hot water store under a wide range of inlet flow conditions, using a temperature step input approach. Three types of inlet/outlet ports have been examined: horizontal, vertical and distributors. The results show that two distinct regions evolve within the store: a fully-mixed region adjacent to the inlet port and a region of smooth 'plug-flow' in the remaining volume of the store. The performance of the store is shown to be defined by the initial depth of the fully-mixed region which in turn is seen to be closely related to the buoyancy and momentum fluxes of the inlet flow. The behAviour of the store and the evident correlations have enabled a one-dimensional computer model of the store to be developed, taking into account the turbulent mixing, vertical heat conduction and heat losses to the surrounding areas. The model has been successfully validated against the results from the step input experiments. The model has been integrated into a computer simulated central heating system which incorporates a hot water store. Predictions have been made, using the simulation, of the energy savings which may be achieved with the use of storage in comparison to a conventional system, and an assessment has been made of the economic viability of the application.

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.

The development and use of thermal models is an integral part of the design process in existing buildings due for refurbishment. Energy predictions for existing buildings are often based on models which assume thermal property values of the building construction elements. However, once built, the actual thermal properties may differ significantly from their estimated values. Possible reasons include thermal bridging, material distortion and moisture content, sub-standard construction on-site and unavailability of construction details. The uncertainties can be reduced if the modelling process can also make use of operational measurements, such as the fuel use and internal temperatures, which have been recorded in the building during operation. To make use of operational data, performance-based models can be used. Performance-based models rely on measured data for the development of the model s architecture and for informing the estimation of the model parameters that would otherwise be based on the modeller s assumptions of the building s characteristics. One solution to the challenge of using performance-based models for existing buildings is to use the Lumped Parameter modelling approach. The Lumped Parameter modelling technique is often used for performance-based modelling of existing buildings due to the moderate knowledge of the building s physical properties required and the limited operational data needed for model training. This thesis investigates the potential of performance-based modelling techniques for existing UK domestic buildings, based on the Lumped Parameter thermal modelling technique, and the use of measured operational data to inform the model structure and parameters. Operational data have been collected in 20 homes as part of the REFIT project, an EPSRC-funded research project on Smart Meters and Smart Homes (REFIT, 2016). This thesis explores 11 houses from the REFIT dataset and, in particular, the temperature, gas and electricity measurements from the participating households, and develops whole-house and sub-system performance-based models using the Lumped Parameter technique. The suitability of simple performance-based Lumped Parameter models in representing typical UK domestic buildings using mainstream operational data such as temperatures and gas consumption measurements is explored. This thesis concludes on the adequacy of the operational data as measured. High correlations (>0.9) between whole-house average indoor temperatures and individual room air temperature measurements prove the use of averages adequate for representing the main rooms of the houses, whereas individual representation of the house s main rooms in use in the same model can prove challenging. A similar result is observed for whole-house radiator representation and the individual radiators. The relationships between the operational data is explored to inform the model structure and to identify collinearity and multi collinearity in the measurements. In terms of whole-house modelling, when using constraints for the parameter values during the model calibration to the measured data the resulting model parameters can be realistic and a good agreement to the measured data can be achieved (on average an RMSE of 1.03 for air temperature). The most significant parameters affecting the mean value of internal air temperatures are the external envelope resistance Re, the non-inertia elements (e.g. windows and doors) resistance, the window area for solar gains, boiler efficiency and the infiltration rate. The indoor air and internal element heat capacitance had the greatest impact on the swing in the internal air temperature (a 75% decrease in the capacitance value resulted in a 190.70% increase in the standard deviation value on average across the 11 houses). The building envelope heat capacitance and the envelope node positioning were the two parameters with the least impact on the model goodness of fit (a 75% decrease in capacitance and a value of 0.9 in envelope node positioning resulted in a 2.57% and 6.68% increase respectively in the RMSE on average across all 11 houses). Finally, the heating system representation using the Lumped Parameter model showed that the whole-house gas consumption data at the meter level, consisting of gas used for space heating as well as other purposes, is inadequate to drive the heating system model. A temperature threshold (e.g. of 1oC) indicating model overprediction can be used to remove the time-stamps of mixed use gas consumption from the model calibration. The heating system model can then be used to quantify gas consumption for space heating and non-space heating uses. In the 11 houses under study, 82.96% of the total gas consumption served for space heating, with 17.04% serving for other non-space heating purposes.

An examination of contemporary office buildings in the warm humid region of Kenya revealed the predominance of highly glazed lightweight buildings that are prone to overheating and rely on costly and unsustainable active climate control systems. In the midst of growing energy demand and a potential deficit in supply, the influx of these poorly designed buildings has intensified the need to explore viable climate-responsive design alternatives suitable to local conditions that can extend occupant comfort and reduce the need for energy intensive environmental control systems. This view is shared by the Kenyan government which has set ambitious targets to develop and enforce national codes for energy efficiency and conservation in buildings by 2030. However, despite the clear and urgent need, research shows that little work has been developed to date that can be applied to the Kenyan context and climate. In this research, ways of improving the thermal comfort and performance of office buildings in the warm humid city of Mombasa (latitude 4°S) were explored. The work was developed through a series of field studies of local vernacular and modern case study buildings and subsequent computer simulations. From this, vernacular Swahili-inspired design strategies were derived and the application of the potentially most significant mitigation strategy to typical local office buildings examined further. Although other work exists elsewhere that may be comparable to parts of this study, this is the first effort that brings together the post occupancy evaluation of buildings in Mombasa, a thorough investigation of the effectiveness of the vernacular strategies found in Swahili architecture, and the validation of the application of these strategies to modern offices. Initial findings derived from a parametric study revealed external shading to be the most effective design strategy as it alleviated solar heat gain transmitted through glazing into buildings, resulting in a significant reduction in discomfort hours. Subsequently, using a series of dynamic computer simulations run for a typical office building in Mombasa, the average monthly solar heat gain coefficient (SHGC) values were derived for a typical year. These previously unavailable latitude (and hemisphere) specific solar path indices were deemed critical in the provision of essential data for effective external shading device design. The findings indicated that low SHGC values of under 0.5 gave the general indication of low percentage of discomfort hours (under 10%). Additionally, estimates of potential annual cooling energy savings of up to 60% were made based on the reduction of SHGC values for shading elements of practicable size. The application of these study findings to two local office buildings revealed that the derived SHGC values and energy estimates provide useful references when considered for similar type office buildings on similar latitudes. For both buildings, it was predicted that energy savings of 15% to 61% could be achieved from the application of suitably sized external shading devices. It was suggested that this type of information would encourage designers to use external shading devices as a method of maintaining thermal comfort, conserving energy and lowering operating costs in office buildings. Finally, recommendations for the incorporation of minimum shading standards in building regulations have been made and presented in a design guidance document.

In hot climates, outside air is too hot during the day. In hot arid climates, low humidity increases discomfort. For comfort, hot air should be cooled before flowing into dwellings and moisture in the moving air increased. For the poor, comfort must be sought cheaply. In places without electricity only 'natural' ventilation is feasible. The air temperature difference between the sunny and the shaded side of a building can be exploited to promote ventilation. Ventilation cooling can be enhanced with an 'evaporative cooling cavity' attached to a dwelling on its shaded side. The cavity has a top external inlet and a bottom internal outlet, and incorporates one or two wet partitions. The air within the cavity, being moist. descends. drawing the outside warm and dry air into the cavity. Evaporation cools the air and raises its humidity. The cool incoming air will reduce inside air temperature and improve comfort. The performance of a typical cavity to induce cooling ventilation by evaporation was investigated theoretically and experimentally with a full scale model. The temperature drop. velocity and relative humidity of the air were measured. The pattern of the air flow in the cavity was observed. The optimum dimensions of the cavity were established. Buoyancy air flow and fan-assisted air flow were analysed in the steady state. Since a convective heat transfer coefficient for air flowing between two parallel vertical surfaces was not found in the literature, appropriate convective heat and surface mass transfer coefficients were derived from measurements. The results show the convective heat transfer coefficient to be independent of the separation of the wet surfaces, and that with separation greater than 3Omm, each wet surface behaves as a 'free' surface. The optimum separation between wet surfaces was assessed, and the water removed by evaporation was determined, and found to be small. The Admittance Method was used to assess comfort. Ventilation and evaporation effectiveness were evaluated. An outlet air velocity of O.3m/s accompanied with a temperature drop of about 6K was achieved. Design proposals for hot arid climates are offered.

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