The increasing demand for air conditioning in commercial buildings imposes a serious threat to Europe's CO2 reduction targets. Architects and engineers are therefore in a key position to help reduce the impact of buildings on the environment by taking appropriate decisions concerning the design of the building and the associated heating, ventilation and air conditioning (HVAC) system. The thesis studies the effect of a number of building and HVAC system related design factors on the energy performance of a notional air-conditioned office building employing either a variable air volume (VAV) system with terminal re-heaters, or a four-pipe fan coil unit (FCU) system with fresh air supply from a central plant, using mainly a dynamic simulation tool and the response surface methodology. The evaluation of the energy performance of the HVAC systems is for two types of climate, using typical weather data for London (UK) and Athens (Greece). It has been found that the design variables associated with the solar radiation through the transparent building elements and the internal heat gains should be the main concern of the building designer. On the other hand, the HVAC system engineer should give emphasis to the parameters associated with the plant performance and operation, as well as the temperature control set-points. It has been shown that it is possible to reduce the carbon emissions of the base case scenario by up to 88% depending on the HVAC system and the climate for which it is simulated. The carbon savings, however, are reduced by up to 22% where humidification is provided. This reduction differs depending on the HVAC system and the climatic conditions. The VAV system is more energy efficient than the FCU system, mainly due to the exploitation of the free cooling capacity of the outdoor air. The difference in carbon emissions between the two systems drops when both of them are simulated for the Athens as opposed to the London typical weather conditions. It has been found that it is possible to turn the carbon scales in favour of the FCU system when humidification to a high RH set-point is provided throughout the year, since the adjustment of the RH of the air is particularly energy wasteful for the VAV system.

Background: People spend most of their time indoors, in buildings such as schools and offices, as well as their homes. Recent interest in Indoor Air Quality (IAQ) suggests that the contribution of outdoor pollutants and indoor airborne particulate and gaseous pollutants may be responsible for the aggregation of a number of respiratory illnesses. Because of these possible health implications, it is important to understand the characteristics of each air pollutant inside/outside (I/O) the building and the variables affecting the degree of exposure to them. Objectives: This was achieved by long-term monitoring of a range of pollutants at two contrasting building types and locations within London. The transfer of pollutants(NOX, NO2, O3 and PMs) and particulate toxicity (PMTSP) within I/O sources over a wide range of meteorological condition, occupancy and seasonality was then characterised. Results 1 (Case 1): At naturally ventilated school building (urban background), paired long term monitoring revealed that the indoor gaseous pollutant concentration reacted differently according to occupancy and seasonality. Due to the fact that indoor NO concentration in the classroom was possibly dominated by indoor source, its presence was also believed to play an important role of reducing O3 in the classroom which mainly came attributed from outdoors during summer time. The increment of indoor larger (PM10) and coarse particle (PM2.5 – 10) was attributed when the building was actively used and identified to be linked from the certain type of classroom activity. However, a greater proportion of indoor PM2.5 was contributed from outdoors. Results 2 (Case 2): In contrast, a different pattern of diurnal variation profiles was observed in the mechanically ventilated office building (roadside site). An extreme indoor concentration of indoor NOX and NO2 monitored during rush hour on working-days were explained by the outdoor penetration. An extension study (building improvement) showed a clear reduction pattern in PM concentration; however it did not solve the high NO2 problem. Results 3: The novel time series of oxidative potential (OP) dataset established in this study highlightedaclear difference between the two sites. Indoor OP metrics in the roadside building recorded higher depletion rates compared to the urban background site. At urban background site, when indoor OP dataset were categorised and group as building occupancy and seasonal dependent, the indoor PM OP antioxidants metrics was found to have a higher depletion rate during occupied period and was observed during winter time, which particularly in particulate mass metric. At roadside site, interestingly, a significant decrease in PM-induced antioxidant depletion indoors, observed after the door upgrade. This study demonstrated that PM OP analysis from both internal and external sources is a useful tool for illustrating any changes in sources in the transfer of pollutants into a building. Conclusion: These monitoring results reveal the complexity of internal-external air quality relationship within building envelopes referring to ventilation type and location specificity. The ingress of outdoor pollution contribution in poor IAQ were also driven by other factors such as urban building orientation, the wide range of building occupancy and different set of ventilation types.

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Natural ventilation is widely recognised as contributing towards low-energy building design. The requirement to reduce energy usage in new buildings has rejuvenated interest in natural ventilation. This thesis deals with computer modelling of natural displacement ventilation driven either by buoyancy or buoyancy combined with wind forces. Two benchmarks have been developed using computational fluid dynamics (CFD) in order to evaluate the accuracy with which CFD is able to model natural displacement ventilation flow. The first benchmark considers the natural ventilation of a single ventilated space with high and low level openings connected to the exterior driven by combined forces of wind and buoyancy. The second benchmark considers natural ventilation flow in a single space connected to an atrium driven by pure buoyancy. Simulation results of key ventilation parameters (stratification depth, temperature gradient and ventilation flow rate) have been compared with analytical and experimental models and close agreements have been achieved. The two benchmarks are defined using the RNG k-epsilon turbulence model. A pressure boundary is applied onto the ventilation openings directly and a porous medium boundary is used to assist the development of the thermal plume. This method has proved to be robust and the close agreement between the three modelling techniques indicates that CFD is able to model natural ventilation flows in simple geometries with acceptable accuracy and reliability. Using the benchmarks the influences of key CFD modelling parameters and building design issues have been investigated. For example, representing openings, heat source representation, stack height, and air inlet strategies. Natural displacement ventilation of a multi-storey building comprising an atrium is also addressed. Simple analytical models have been developed to describe the key air flow features within the ventilation system.

With the emergence of climate change, the increasing figure of energy consumption for cooling in buildings expresses an urgent need for energy conscious design of new and existing buildings, and there is a significant opportunity for implementation of natural ventilation strategies. The high-energy consumption of the Greek domestic sector, the number of existing multi-storey apartment buildings, the small rate of building retrofitting in Greece and the warm, dry climate of Greece, indicate the potential to achieve significant energy reductions for cooling via natural ventilation. The aim of this research was to evaluate the energy saving potential of natural ventilation solutions for domestic buildings in the Mediterranean climate to deliver summer comfort, and to propose a low-energy refurbishment design guide. The natural ventilation efficiency of an urban multi-storey apartment building in Athens and the potential implementation of advanced natural ventilation strategies, were evaluated using modelling tools. This would provide the knowledge for future energy refurbishments. The building was a representative example of over 4 million buildings in Greece. Several ventilation strategies were implemented in a single apartment (51.4m2) and evaluated in order to enhance the existing single-sided ventilation strategy of the building, including: daytime and nighttime ventilation; cross ventilation strategies; use of a wind-catcher; lightweight dynamic façade with shading system; new internal openings; and passive downdraught evaporative cooling strategies. The ventilation performance of the strategies was investigated over the full cooling period using DTM simulations. Controlled natural ventilation strategies, in response to internal and external air properties, delivered: occupants comfort; ventilation rates increase; and reductions in air temperatures and in CO2 levels. Natural day and night ventilation contributed to significant temperature reductions (up to 7°C) relative to the base-case ventilation strategy. The proposed strategies marginally reduced the hours during the cooling period for which the CO2 levels exceeded the upper acceptable limit for comfort. The strategies also achieved air change rates above the minimum acceptable values for comfort were provided; and therefore occupants comfort was achieved. De-coupled internal-external steady state CFD airflow simulations were performed to predict wind pressures across the building openings, and to predict detailed ventilation rates for a number of climate scenarios. Using CFD it was possible to overcome the limitation of DTM and predict average pressures at the location of the openings, considering the location of the building within its surroundings (both external and internal flow simulations were performed), leading to accurate results. It was predicted that the ventilation performance of the wind catcher was significant relative to the simple single or cross-ventilation strategies. The downdraft evaporative cooling performed best at low ventilation rates providing up to 4°C further temperature reductions. Indoor comfort was provided during windless hours for specific strategies (buoyancy driven); this is significant considering that low wind speeds (below 1m/s) were predicted for 14% of the cooling period. The performance of the strategies varies considerably with regard to both wind speed and direction; these should be considered when retrofitting natural ventilation strategies in existing buildings. The proposed strategies delivered natural cooling and adequate ventilation rates, relative the base-case strategy. The combined wind catcher and dynamic façade strategy performed the best; this combined strategy would be recommended for the Mediterranean sub-climate, and for buildings comparable to the type studied. This should be combined with evaporative cooling strategies particularly during windless hours, and mechanical cooling only when these strategies do not provide sufficient performance. For both the CFD and DTM results, empirical relationships were established with statistical methods between indoor air properties and climate characteristics, which can be used to predict behaviours under conditions that have not been examined using simulations. This assists extrapolation of patterns in ventilation performance, to facilitate design guidance of the natural ventilation strategies for implementation in similar buildings. The established performance of the natural ventilation strategies in the case study building assisted the development of a prototype scenario for similar building designs with comparable climatic context. A low-energy refurbishment design guide for natural ventilation was proposed that provides guidelines and design recommendations. Retrofitting such natural ventilation strategies in existing apartment buildings in similar climates presents a significant opportunity to achieve significant energy consumption reductions.

With 50 % of the worlds population dwelling in urban environments and over 70 % of people’s time is spent indoors (at home, work or in vehicles). It is important to understand how the urban area effects the internal-external air exchange for buildings and how this may impact on the occupants, though this will differ depending on location. The urban area is complex, requiring multidisciplinary expertise in order to understand the driving features. Urban areas may be simplified down for study to reduce some of the complexity. The study undertaken at Silsoe, UK, used a full-scale staggered array of nine 6 m3 cubes to gain an understanding of the effects of meteorological variables on the natural ventilation rate and pressure coefficient. After 6 months 8 cubes were removed, leaving the instrumented cube isolated for 2 months. All equipment logged constantly, creating a dataset which covers a wide range of wind directions, wind speeds, temperature differences and atmospheric stabilities making the dataset unique from previous work. Changes in wind direction cause changes in the pressure coefficient for both isolated and array cases. However defining wind direction is difficult for the array due to the complex interaction of obstacle wakes. The relation between reference and local wind directions is non-linear. The flow within the array was dominated by mechanical turbulence generated by the wakes of the array elements, with the local turbulence intensity being 7 to 10 times greater than for an isolated cube. The presence of an opening had no effect on the pressure coefficient when acting as an inlet. Stability was found to have no effect due to the building being low-rise and the effects of turbulence could not be discerned from 30 minute averages for both pressure coefficient and ventilation measurements. The full-scale data were compared to a wind tunnel model of the site. This allowed for increased array sizes to be used. It was found that the length and size of the rows have a non-linear effect on the pressure coefficient of a cube within the array, with a limited array reducing the pressure coefficient by 10 to 50 % ± 5 % depending on measurement location. Pre-existing models predict the pressure coefficient for an isolated cube well, but do not accurately predict the pressure coefficient for a limited array due to the lack of wind direction and shielding terms. This is also true for the full-scale data. The three methods used to predict ventilation rate (tracer gas decay, pressure difference and the volumetric method) were all affected by different variables such as the presence of thermally driven ventilation, wind direction, location of the wind speed measurement and amount of turbulence within the flow. The difference in the volumetric flow methods depended on the wind speed measurement used, highlighting the difficulty in gaining an accurate representation of ventilation rate using wind speed alone, especially in an urban area. All three methods show more agreement for the array cases than for the isolated cube cases. Pre-existing empirical models of urban wind speed (CIBSE), pressure coefficient (ASHRAE and AIVC) and ventilation rate do not capture the dual behaviour of the ratio of local and reference wind speeds found for the array. This dual behaviour is demonstrated for 1, 5, 10, 30 and 60 minute averaging periods. This behaviour is not correlated to changes in wind direction, the turbulence or speed of the oncoming flow or internal-external temperature differences. A combination of frontal area density, sheltering factor, wind speed, wind direction, opening location and temperature differences within a ventilation model is required to accurately predict ventilation rate.

The outdoor climate of an area has a significant impact on housing and urban fabric as a whole, and the more extreme a climate, the more necessary it becomes to respond to it. Thus the climate should be regarded as a significant modifier of the built environment; thermal discomfort within building environments is a prevalent and significant issue throughout the developed and developing countries. There is considerable disagreement in the research community concerning whether comfort standards developed in the climate of North America and Europe are appropriate for use in other countries with more extreme climatic conditions. This research focuses on designing for the conditions of thermal comfort in hot dry climate regions. The research reports field surveys in both naturally ventilated (NV) buildings and air-conditioned (AC) buildings in summer season, with reference to Ghadames in Libya. This involves objective measurements and subjective questionnaire study with a view to testing the validity of the established thermal comfort models: Fanger's PMV model and the Adaptive model. It reviews the results from the field survey within those two types of buildings in the summer seasons of 1997 and 1998, which experiences the hot-dry climate of North Africa. It shows how the residents responded to the environmental conditions, social needs, and architectural character such as building design and thermal mass. The method of study and analysis are critically described. The subjective data was collected and tabulated by using questionnaires, which have been widely used and shown to be effective, to determine people's votes through scales modified especially for this purpose. Questionnaires were collected from households of 60 buildings: 30 old NV buildings and 30 new AC buildings involving a total of 270 participants from both types of buildings. The questionnaires compare the significance of the thermal sensation, the thermal comfort, and the preference scales of each type of building. The objective survey consisted of 19 observations of empirical data (in the 9 old NV buildings, and in the 10 AC new buildings) to validate the performance of the current thermal comfort indices. The results show that the PMV model is not valid, unless modified, for predicting the thermal comfort in old buildings, in Ghadames oasis, Libya. Thus a modification is proposed. However, the results from modem air-conditioned buildings have shown that there is good agreement between Fanger's model and the actual mean vote (AMV) values reported by the occupants in these buildings. The results from the present study show also that the neutral temperatures in old and new buildings are 31.6°C and 29.4°C respectively. The adaptive model, which is developed by Auliciems (1983), is shown to be valid, without modification, for predicting the thermal comfort of sedentary occupants in such environments. The results indicate that the construction of residential dwellings using traditional methods is more conducive to the climatic conditions of hot-dry climates and suitable for the cultural requirements and life style of the occupants. Human thermal comfort was assessed using the adaptive model, to show that the climate and personal behaviour have a significant impact on human comfort perception and building design.

Buildings account for 40% of total energy consumption in the UK and more than 55% of this energy is used by heating, ventilation, air-conditioning and refrigeration (HVAC&R) systems. This significant energy demand and the ascending trend in utilising HVAC&R systems together with the global need to impose energy-efficiency measures underline the importance of selecting the most appropriate HVAC&R system in a design process. In the early stages of the design and construction of a building, the design engineer is responsible for considering various systems in the process of HVAC&R systems selection. Although a broad range of simulation tools is developed for performance evaluation of HVAC&R systems, none of them is capable of performing a decision making process for HVAC&R systems selection. Therefore, the contribution of this study to knowledge has been the development of a multiple attribute decision making tool for HVAC&R systems selection for office buildings in the UK. Firstly, a set of reference office buildings was developed as representative of the UK office building stock and one of them was selected for further study. Then, a set of common alternative HVAC&R systems was identified. The reference office building, assumed to be located in London, together with the alternative HVAC&R systems were simulated in the TRNSVS and their technical performance, economic aspects and environmental impacts were assessed. Finally, to choose the most appropriate system among the alternatives a fuzzy multiple attribute decision making method was used to formulate the process of decision making. The scope of this study was further extended by considering 18 climate regions in the UK together with the effect of climate change in the decision making process using the degree-days theory. In addition, the UK Government's electricity decarbonisation plans were integrated to the developed decision making model. Finally, the model was transferred into a computational tool with a user-friendly interface developed in Matlab.

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