Development of the timber-glass upgrade module for the purpose of its installation on energy-inefficient buildings in the refurbishment process

The current research study presents the development of the upgrade module consisting of a timber frame structure with the optimal glazing size in the east-, south- and west-oriented façades for the purpose of energy-efficient refurbishment of the existing energy-inefficient buildings. Such construction module could open the way to simple installation onto the existing residential, public or office buildings of various shapes and ensure better energy performance of the refurbished buildings. The optimal glazing size of the east-, south- and west-oriented façades of the module with the optimal shape is determined by the glazing-to-wall area ratio where the sum total of the annual energy need for heating and cooling of the module is minimal. The sum of the annual energy is defined through an extensive parametric numerical analysis including variations regarding the module’s aspect ratio, the thermal transmittance of its envelope and the glazing size in its east-, south- and west-oriented façades. A parametric analysis carried out in the previously described manner leads to analytic functional dependence between the energy consumption and the module’s design parameters. It is therefore possible to make a fairly simple preliminary estimate of the annual energy need, in addition to defining the optimal floor plan shape of the module along with the optimal proportion of glazing in its east-, south- and west-oriented façades. The optimal proportion of glazing varies from 24 to 91% in the south-oriented façade, from 7 to 43% in the east and from 9 to 55% in the west façade, at the thermal transmittance of the thermal envelope 0.100 W/(m² K). The variation in the optimal glazing proportion of the module with the thermal transmittance of the thermal envelope 0.165 W/(m² K) ranges from 14 to 85% in the east, from 28 to 97% in the south and from 16 to 68% in the west-oriented façade. The presented research study permits a choice of the optimal module design with respect to baseline characteristics of the existing building and allows for a more systematic as well as energy-efficient refurbishment process.     

Energy performance analysis of a dormitory building based on different orientations and seasonal variations of leaf area index

The aim of this research is to investigate the effectiveness of vertical vegetation in terms of energy savings for a residential facility situated at KAIST campus. The research has been established through analyzing different building orientations to find out the most suitable combination of vegetation and orientation for reduced heating and cooling energy consumption. A simulation model has been developed where leaf area index, one of the contributing plant physiological parameters for improving building thermal performance, has been incorporated as per seasonal variations. This allowed observing thermal performance patterns of green wall throughout the year. Approximately 60 % savings in heating energy and 31 % increase in overall energy efficiency were achieved with the non-insulated studied building case, and the results showed extreme weather conditions lead to greater energy savings in winter. In cooling season, plant layers were found to be less effective in terms of facade thermal performance especially during relatively higher temperature period, with an average of 17 % cooling energy savings. The North-oriented green wall was observed to be the most effective in increasing heating energy efficiency, while the East-oriented wall was observed to be greatest in cooling energy savings. A higher LAI value proved to be beneficial in improving both heating and cooling energy performance for the studied building.     

An experimental study of façade-integrated photovoltaic/water-heating system

The worldwide fast development of building-integrated solar technology has prompted the design alternatives of fixing the solar panels on the building façades. How to make full use of an integrative system to achieve the best energy performance can be an important area in the technology promotion. Hybrid solar system applying in buildings has the advantage of increasing the energy output per unit installed collector area. This paper describes an experimental study of a centralized photovoltaic and hot water collector wall system that can serve as a water pre-heating system. Collectors are mounted at vertical facades. Different operating modes were performed with measurements in different seasons. Natural water circulation was found more preferable than forced circulation in this hybrid solar collector system. The thermal efficiency was found 38.9% at zero reduced temperature, and the corresponding electricity conversion efficiency was 8.56%, during the late summer of Hong Kong. With the PVT wall, the space thermal loads can be much reduced both in summer and winter, leading to substantial energy savings. Suggestions were given on how to further improve the system performance.     

Experimental study on flame height and temperature profile of buoyant window spill plume from an under-ventilated compartment fire

Fire experiments were carried out in a scale model, consisting of an 0.8 m cubic fire compartment with six window like geometries and an attached 3 m (wide) × 5 m (high) façade wall. A propane porous gas burner with controlled fuel supply rate was the fire source. Gas temperature profiles were measured inside the compartment and near the façade wall. The outside spill flame heights were recorded by a CCD Digital camera. Temperature and flame heights are correlated with heat release rate and the window geometry using physically non-dimensional analysis. The steady gas temperatures inside the compartment are determined by an overall energy balance between the heat release rate inside the compartment and the wall conduction and opening radiation heat losses using an effective overall heat loss coefficient. Flame heights on the façade are non-dimensionally correlated by the excess fuel heat release rate outside the enclosure and a characteristic length scale for the window. These results agree with previous results in the literature. Vertical gas temperatures near the façade wall outside the enclosure are non-dimensionally correlated with the total convective heat flow rate above the flames and the same characteristic window length scale as the flame height, with the additional necessary determination of a virtual origin of the convective flow above the flame. These results and correlations are new and a significant improvement over previous results in the literature.     

Trends of solar radiation effects on the temperature of vertical surfaces of a modern terrace house

This is a study done to investigate the effects of solar radiation on the wall surface temperature of a modern terrace house. It involves the analysis of the thermal fluctuations of common building materials used for walls or vertical surface areas such as the bricks, glass of the window, and metal doors. A thermal imager and data logging system was used in collecting the data for the Southeast and Northwest façades of the house. The imager gave resourceful data on the thermal heat trend of the walls and their surface temperature. The results show that a lighter wall surface color reduces the temperature of the surface. Furthermore, the bricks, which have a higher density hence a higher absorptivity due to their high capacity for storage of heat, decrease the flow of heat. However, the use of tinted glass on windows increases the surface temperature of the glass area of the wall surface. The metal also shows a high similarity with glass in terms of its thermal performance. In conclusion, the types of material used on wall surfaces have a significant impact on the wall temperature.     

Urban heat island characteristics in London during winter

This paper presents results characterising the urban heat island intensity (UHI) in London during the peak winter season. Most UHI studies focus on the phenomenon during the summer as this is the period when temperature peaks are observed. However, for urban planning mitigation strategies and building energy demand design, the heating season should be also considered, since proposed measures to alleviate the summer UHI might have a negative effect during the winter or intermediate seasons.The study carries out trend and regression analysis by controlling climatic and geographical variations in the data set following a methodology developed for studying summer UHI [Kolokotroni, M., Giridharan, R., 2008. Urban heat island intensity in London: an investigation of the impact of physical characteristics on changes in outdoor air temperature during summer. Solar Energy 82, 986-998]. It was found that average nocturnal UHI of winter periods are of similar magnitude to the summer periods but the peak winter UHI trends are not as regular as summer giving a first indication that the effect of climate and urban parameters is different. The regression analysis in this research uses six on-site variables namely aspect ratio, surface albedo, plan density ratio, green density ratio, fabric density ratio and thermal mass to carry out impact investigation in six data sets, categorised by three geographical location within London and three sky conditions and regional wind velocity. The above variables do not explain the changes in outdoor temperature as much as they did during summer period models. However, unlike summer, the winter climate control models have the same R² indicating that most of changes in outdoor temperature are caused by climate factors and not the on-site variables.     

Investigation of Mixed Convection in a Ventilated Cavity in the Presence of a Heat Conducting Circular Cylinder

The study is aimed to investigate the mixed convective transport within a ventilated square cavity in presence of a heat conducting circular cylinder. The fluid flow is imposed through an opening at the bottom of the left cavity wall and is taken away by a similar opening at the top of the right cavity wall. The cylinder is placed at the center of the cavity. Two cases are considered depending on the thermal conditions of the cavity walls. In the first case, the left and right vertical walls are kept isothermal with different temperatures and the top and bottom horizontal walls are considered as thermally insulated. For the second case, the top and bottom walls are maintained at different constant temperatures and the left and right walls are considered adiabatic. Heat transfer due to forced flow, thermal buoyancy, and conduction within the cylinder are taken into account. Effect of the cylinder size (0.1 ≤ D ≤ 0.5) and the solid–fluid thermal conductivity ratio (0.1 ≤ K ≤ 10) are explored for various values of Richardson number (0 ≤ Ri ≤ 5) at fixed Reynolds (Re = 100) and Prandtl (Pr = 0.71) numbers. The fluid dynamic and thermal transport phenomena are depicted through streamline and isotherm plots. Additionally, the global thermal parameters such as the average Nusselt number and average fluid temperature of the cavity are presented. It is found that the aforementioned parameters have significant influences on the fluid flow and heat transfer characteristics in the cavity.     

Dynamic performance of a façade-based solar loop heat pipe water heating system

This paper reported a dedicated study of a novel façade-based solar loop heat pipe (LHP) water heating system using both theoretical and experimental methods. This system employs a modular panel incorporating a unique loop heat pipe that is able to serve as part of the building façade or a decoration layer of the façade, thus creating a façade integrated, low cost, highly efficient and aesthetically appealing solar water heating structure. Taking into account heat balances occurring in different parts of the system, e.g., solar absorber, heat pipes loop, heat exchanger and storage tank, a dedicated computer model was developed to investigate the dynamic performance of the system. An experimental rig was also established to evaluate the performance of such a prototype system through measurement of various operational parameters, e.g., solar radiation, temperatures and flow rates of the heat pipe fluid and water. Through comparison between the testing and modelling results, the model has been approved to be able to give a reasonable accuracy for predicting the performance of the LHP system. Two types of glass covers, i.e., double glazed/evacuated tubes and single-glazing plate, were applied to the prototype. It was found that for both covers, the heat pipe fluid temperature rose dramatically at the start-up operation and afterwards remained a slow but steady growth; while the water temperature remained a steadily growing trend throughout the operational day. The temperature rise of the circulated water at 1.6 l/min of flow rate was around 13.5 °C in the double-glazed/evacuated tubes based system and 10 °C in the single-glazing based system; correspondingly, their average solar conversion efficiencies were 48.8% and 36%, and the COPs were 14 and 10.5 respectively. In overall, the double-glazed/evacuated tubes based system presented a better performance than the single glazing based one.     

Green roofs as passive system for energy savings in buildings during the cooling period: use of rubber crumbs as drainage layer

The building sector is responsible for most of today’s energy and materials consumption. Construction systems such as green roofs can improve the energy performance of buildings, but meanwhile, they themselves should be more sustainable. This research focuses on the study of the benefits, in terms of energy consumption, of an extensive green roof (without insulation layer) in comparison to a conventional flat roof solution (with insulation) under Mediterranean continental climate. Moreover, in order to improve the sustainability of this system, the use of recycled rubber instead of traditional stone materials as drainage material is evaluated as well. For this purpose, the electrical energy consumption of the cooling system and thermal behaviour of three identical experimental cubicles, with only differences on the roof composition, was evaluated during summer period. The results show that a simple extensive green roof 9 cm thickness provides a reduction of 5 % in case of rubber crumbs and 14 % in case of pozzolana, in terms of electrical energy consumption, than a conventional flat roof with an insulation layer of 3 cm polyurethane, even when only the 20 % of the surface is covered by plants. Furthermore, small differences in thermal behaviour were observed when replacing volcanic gravel by recycled rubber crumbs as drainage material.     

Diagnostics of the thermal defects of the walls on the solid-state biogas plant

Energy protection of buildings can be achieved by using suitable construction with minimisation of thermal bridges. This paper is a contribution to the characterisation of the thermal defects and energy efficiency of the envelope on the case study of a solid-state biogas plant. The work specifically concerns the qualitative evaluation of envelope construction details by infrared thermography technique and quantitative evaluation of thermal defects by calculation. Results show that wall constructions of the solid-state biogas plant have an unsuitable engineering solution causing high heat losses. The main problem is the existence of significant numbers of thermal bridges caused by uninsulated bearing steel frames of the façade system, gates, doors and windows.     

Sensitivity study of an opaque ventilated façade in the winter season in different climate zones in Spain

Energy efficient buildings need to take advantage of any renewable energy available. An opaque ventilated façade (OVF) is a kind of façade that absorbs solar energy and transfers it to the ventilation system. This way, the sensible ventilation load of the heating system can be reduced in the winter season. The energy saving of this system depends strongly on the weather variables, mainly solar radiation on the façade, ambient temperature and wind speed. In order to find the most convenient locations where the best OVF efficiency can be obtained, its performance has to be studied along a complete season. For this purpose in this study a sensitivity analysis with the most important weather variables was carried out and the energy saving values in 12 locations in Spain in the winter were evaluated using a numerical model previously validated with experimental data. The results showed that although the most influential weather variable was solar radiation, a combination of high temperatures and low wind speeds can also lead to important energy saving values. It was found that the most convenient locations for installing an OVF were those with low and medium winter severity climates, namely, in the southern and coastal regions of Spain (zones A3, B3, B4, C3 and C4).     

Energy-saving potentials of some local trees

The energy-saving potentials of some common tropical trees are presented. The experimental setup consists of a tree and sixteen (16) 0.05 cm by 0.05 cm dry wood of height 3 m which served as a stake. Each of the dry woods has two 0.001-mm-thick galvanized steel plates (0.3 cm by 0.3 cm), which served as the heated surface, nailed at heights of 1.3 and 2.6 m from the ground level. The plates are insulated at the back side with plywood, thus leaving only one side exposed to the direct effect of solar heating. The woods were installed at equal distances from the tree trunk such that the uncovered sides of the plates face east, west, north, and south. Temperatures of the plate at 1-h intervals were recorded from 08:00 and 17:00 h and subsequently used to compute energy absorbed by each plate. Four trees, Dogon Yaro (Azadirachta indica.), mango (Mangifera indica), velvet tamarind (Dialium indum), and oil bean (Pentacletra macrophylla), were used for the study. Results obtained showed that a reduction in solar space heating by up to 79 % can be achieved, depending on the position of the tree relative to the building. This corresponds to a saving in energy of up to 1050 kWh/year or 22 % of the annual energy consumption in a typical average residential building in Nigeria. Thus, proper tree planting is recommended for reduced residential energy consumption.     

Building integration of concentrating systems for solar cooling applications

The high energy consumption in buildings in Mediterranean countries, especially in the spring and summer months due to the extensive use of air conditioning, requires immediate actions to minimise energy costs and environmental impact given the current energy crisis. Solar cooling systems offer an attractive solution, but the main drawbacks of this type of systems are the low efficiency of the currently used single-effect absorption chillers and the large areas of thermal collectors needed to produce the thermal energy. These large solar installations make difficult their building integration. A way to overcome these difficulties is the use of high efficient integrated solar concentrator systems able to achieve temperatures around 150 °C that could be used to activate the more energy efficient double-effect absorption chillers. In the frame of this concept, in the present work a comparison between two cooling systems for a specific three-floor building, with and without solar concentration, is performed. The first is a conventional system which consists of evacuated tube collectors feeding a single-effect absorption chiller. On the other hand, a Fresnel reflective solar concentrating system, integrated on the building façade, is coupled to a double-effect absorption chiller. The results show an important reduction of the solar collectors absorber area in the concentrating system compared with the standard solar thermal installation. However, the solar concentrating system requires a large aperture area. In addition, the rejected heat in the double-effect chiller is lower, implying that the investment and operation costs of the solar concentrating cooling system can be reduced significantly.     

Experimental performance of a Fresnel-transmission PVT concentrator for building-façade integration

A building-façade integrated concentrating photovoltaic-thermal system has been designed, constructed and experimentally characterised. Comparative performances with a non-concentration reference unit have been conducted to analyse the differential outputs. The concentrating system consists of double-side reflective strips which concentrate the incident beam towards a static photovoltaic-thermal receiver. The reflectors are placed vertically at the façade and track the sun by rotating axially. The concentrating reflector outperforms the reference one in both, thermal and electrical power. The thermal output of the concentration module almost doubles the reference one and the electrical power registered is more than 4.5 times in the case of the concentrating configuration.     

Performance analysis of phase-change material storage unit for both heating and cooling of buildings

Utilisation of solar energy and the night ambient (cool) temperatures are the passive ways of heating and cooling of buildings. Intermittent and time-dependent nature of these sources makes thermal energy storage vital for efficient and continuous operation of these heating and cooling techniques. Latent heat thermal energy storage by phase-change materials (PCMs) is preferred over other storage techniques due to its high-energy storage density and isothermal storage process. The current study was aimed to evaluate the performance of the air-based PCM storage unit utilising solar energy and cool ambient night temperatures for comfort heating and cooling of a building in dry-cold and dry-hot climates. The performance of the studied PCM storage unit was maximised when the melting point of the PCM was ～29°C in summer and 21°C during winter season. The appropriate melting point was ～27.5°C for all-the-year-round performance. At lower melting points than 27.5°C, declination in the cooling capacity of the storage unit was more profound as compared to the improvement in the heating capacity. Also, it was concluded that the melting point of the PCM that provided maximum cooling during summer season could be used for winter heating also but not vice versa.     

A new test cell for the evaluation of thermo-physical performance of facades building components

How do the new building façade components work under real climatic conditions? The question is especially related to the dynamic behaviour of new and complex components such as the ventilated walls, the Phase Change Material, or others that use nano-technologies and aerogels. One of the objectives of the undergoing research activity, named Abitare Mediterraneo, is the evaluation of their thermal behaviour through the use of an outdoor test cell, in order to reproduce under the real external conditions the performance of these components, and consequently define the main thermal parameters such as the attenuation factor and the thermal inertia, characterising the component; moreover, the results will be used to write new algorithms for dynamic simulation tools allowing an appropriate evaluation of the complex behaviour of the whole building at a real scale condition. The new test cell is realised in Florence, Italy. The design starts from the study of the experience of the existing PASSYS test cells, overtaking the main weakness of the building structure and of the heat-flux sensors.     

Numerical study of thermal characteristics of double skin facade system with middle shade

Architectural shade is an effective method for improving building energy efficiency. A new shade combined with the double skin façade (DSF) system, called middle shade (MS), was introduced and developed for buildings. In this paper, a 3D dynamic simulation was conducted to analyze the influence of MS combined with DSF on the indoor thermal characteristics. The research on MS for DSF involves the temperature, the ventilation rate, the velocity distribution of the air flow duct, and the indoor temperature. The results show that the angle and position of the shade in the three seasons are different, and different conditions effectively enhance the indoor thermal characteristics. In summer, the appearance of MS in DSF makes the indoor temperature significantly lower. The indoor temperature is obviously lower than that of the air flow duct, and the temperature of the air flow duct is less affected by MS. The influence of the position of blinds on indoor temperature and ventilation rate is greater than the influence of the angle of blinds. According to the climate characteristics of winter and transition season, in winter, early spring, and late autumn, the indoor temperature decreases with the increase of the position of blinds at daytime, but the opposite is true at night. The results found in this paper can provide reference for the design and use of MS combined with DSF in hot summer and cold winter zone.     

Performance analysis of two combined cycle power plants with different steam injection system design

A thermal analysis of two combined cycle power plants is performed. The steam injection system in the combustion chamber constitutes the main difference between the two designs. For the first power plant (design 1) the injected steam is generated in the HRSG. While for second power plant (design 2) this steam is provided using a heat recovery system installed at the compressor outlet. The steam turbine cycle engenders two pressure extraction levels connected to open feed-water heaters. The steam injection in the combustion chamber improves the overall combined cycle efficiency if this steam is generated outside the HRSG.The increase of the ambient temperature affects the overall cycle efficiency.The optimum thermal efficiency, for any temperature value during the year, may be obtained for suitable margin of steam injection ratio. The second design presents better overall efficiency then the first one. In winter season (T_am = 15 °C), the overall cycle efficiency is about 54.45% for a range of steam injection ratio within 11.8 and 14%. While in summer season (T_am = 35 °C) and for the same cycle efficiency, the required range of steam injection ratio is between 18.5 and 18.8%.     

Comparison of theoretical and real energy yield of direct DC-power usage of a Photovoltaic Façade system

Multifunctional façade components have nowadays become a significant research topic as a step towards developing energy-efficient buildings. This paper presents the performance evaluation of an experimental setup of a real fully decentralized façade-integrated photovoltaic (PV) system installed in a prototype façade, for direct DC power use. The goal of this evaluation was to test the system's ability to fulfill a pre-designed daily electrical load of 925Wh corresponding to a three-people office space under 100% decentralization. This was achieved by studying the operation under different weather conditions and the impact of the system design and components on its overall output. The evaluation of both the actual and theoretical system outputs indicates poor actual system performance in terms of low energy yield and unacceptable load fulfillment factor, which did not exceed 0.95. At the same time it revealed underutilized system potential which could be exploited theoretically with a proper system configuration. The results in this paper conclude that decentralized façade integrated PV systems can completely satisfy their designated applications if properly-designed and implemented, and provides a methodology which could be used in designing similar systems. Satisfactory fulfillment is shown to be achieved by having 30% additional PV and 9 times bigger storage capacities in this system.     

Experimental validation of an improved concept of building integrated photovoltaic panels

Recent progress in the implementation of the Energy Performance of Buildings Directive resulted in a significant increase of rooftop PV installations in European buildings. In certain cases the PV installation is extended to cover also south- or west-facing walls byair cooled Building Integrated PV panels (BIPV). The cooling effect maintains a highconversion efficiency of the panels and the heated air may be exploited by the HVAC or service water heating system. Sizing and design of the double façade system is critical to its energetic performance.In this paper, the transient thermal behavior of the basic structural module of a double-skin photovoltaic façade is experimentally investigated in real insolation conditions.Theresults are employed in the validation and further improvement of integration of a BIPV concept to the HVAC system of a building.