Improvements of building envelope using passive cooling techniques to reduce the cooling load in hot‐dry regions

In developed countries, the buildings are responsible for massive energy consumption. When the construction is based on the use of nonsustainable methods, the buildings were dependent on the active systems, for ensuring a maximal indoor comfort. This has increased energy consumption and related greenhouse gas emissions. In this study, a reduction technique of cooling load and power consumption in buildings is proposed. This technique involves the combination of three passive cooling techniques, thermal insulation, phase change materials (PCMs), and electrochromic double glazing. These techniques are applied through simulation software “DesignBuilder” to a building envelope model in various areas like walls, roofs, and glazing. For this purpose, a standard building model is compared with 16 other cases that incorporated the passive cooling techniques for determining the effectiveness of the proposed method. The results show that a combination of PCMs, thermal insulation, and double glazing can reduce the cooling load from 70.37 to 50.53 kW and the energy consumption from 1.51 to 0.90 kWh/m ².     

Thermal energy storage in building integrated thermal systems: A review. Part 2. Integration as passive system

Energy consumption trends in residential and commercial buildings show a significant increase in recent decades. One of the key points for reducing energy consumption in buildings is to decrease the energy demand. Buildings envelopes are not just a structure they also provide protection from outdoor weather conditions always taking into account the local climate. Thermal energy storage has been used and applied to the building structure by taking advantage of sensible heat storage of materials with high thermal mass. But in recent years, researchers have focused their studies on the implementation of latent heat storage materials that if well incorporated could have high potential in energy demand reduction without occupying the space required by sensible storage. The aim of this study is to review the thermal energy storage passive systems that have been integrated in building components such as walls, ceilings or floors, and to classify them depending on their component integration.     

A case study for influence of building thermal insulation on cooling load and air-conditioning system in the hot and humid regions

Ensuring the effective thermal insulation in regions, where the cooling requirement of building with respect to heating requirement is dominant, is very important from the aspect of energy economy. In this study, the influence of thermal insulation on the building cooling load and the cooling system in case of air-conditioning by an all-air central air-conditioning system was evaluated for a sample building located in Adana, based on the results of three different types of insulation (A, B and C-type buildings) according to the energy efficiency index defined in the Thermal Insulation Regulation used in Turkey. The operating costs of the air-conditioning system were calculated using cooling bin numbers. Life-cycle cost analysis was carried out utilizing the present-worth cost method. Results showed that both the initial and the operating costs of the air-conditioning system were reduced considerably for all three insulation thicknesses. However, the optimum results in view of economic measurements were obtained for a C-type building. The thickness of thermal insulation for the buildings in the southern Turkey should be determined according to the guidelines for a C-type building.     

A numerical simulation tool for predicting the impact of outdoor thermal environment on building energy performance

A building affects its surrounding environment, and conversely its indoor environment is influenced by its surroundings. In order to obtain a more accurate prediction of the indoor thermal environment, it is necessary to consider the interactions between the indoor and outdoor thermal environments. However, there is still a lack of numerical simulation tools available for predicting the interactions between indoor and outdoor microclimate that take into account the influences of outdoor spatial conditions (such as building forms and tree shapes) and various urban surface materials. This present paper presents a simulation tool for predicting the effect of outdoor thermal environment on building thermal performance (heating/cooling loads, indoor temperature) in an urban block consisting of several buildings, trees, and other structures. The simulation tool is a 3D CAD-based design tool, which makes it possible to reproduce the spatial forms of buildings and constructed surface materials in detail. The outdoor thermal environment is evaluated in terms of external surface temperature and mean radiant temperature (MRT). Simulated results of these temperatures can be visualized on a color 3D display. Building heating/cooling loads and indoor air temperature (internal surface temperature) can also be simulated. In this study, a simulation methodology is described, and a sensitivity analysis is conducted for a wooden detached house under different outdoor conditions (building coverage, adjacent building height, surrounding with trees or no-trees). Simulation results show that the simulation tool developed in this study is capable of quantifying the influences of outdoor configurations and surface materials on both indoor and outdoor environments.     

Thermal energy storage in building integrated thermal systems: A review. Part 1. active storage systems

Energy consumed by heating, ventilation and air conditioning systems (HVAC) in buildings represents an important part of the global energy consumed in Europe. Thermal energy storage is considered as a promising technology to improve the energy efficiency of these systems, and if incorporated in the building envelope the energy demand can be reduced. Many studies are on applications of thermal energy storage in buildings, but few consider their integration in the building. The inclusion of thermal storage in a functional and constructive way could promote these systems in the commercial and residential building sector, as well as providing user-friendly tools to architects and engineers to help implementation at the design stage. The aim of this paper is to review and identify thermal storage building integrated systems and to classify them depending on the location of the thermal storage system.     

Analytical periodic solution for the study of thermal performance and optimum insulation thickness of building walls in Tunisia

In Tunisia, the energy consumption in the building sector is rapidly increasing. Recently, very high electric energy consumption, used for air-conditioning loads, is reached during summer days. Insulation of building walls is recently applied with an insulation layer thickness typically ranging between 4 cm and 5 cm, regardless of the climatic conditions, type and cost of insulation material and other economic parameters. In the present study, an optimum insulation thickness is determined under steady periodic conditions. An analytical method, based on Complex Finite Fourier Transform (CFFT), is extended to rigorously estimate the yearly cooling transmission loads for two types of insulation materials and two typical wall structures. Estimated loads are used as inputs to a life-cycle cost analysis in order to determine the optimum thickness of the insulation layer. Results show that, the most profitable case is the stone/brick sandwich wall and expanded polystyrene for insulation, with an optimum thickness of 5.7 cm. In this case, energy savings up to 58% are achieved with a payback period of 3.11 years. The thermal performance of the walls under optimal conditions is also investigated. Then, comparison of the present study with the degree-days method is performed for different values of indoor design temperature.     

Sustainable thermal energy storage technologies for buildings: A review

Energy management in buildings is indispensable which would control the energy use as well as the cost involved while maintaining comfort conditions and requirements in indoor environments. Energy management is intensely coupled with energy efficiency and increasing of which would provide a cost-effective pathway for reducing greenhouse gas emissions. In recent years, the magnitude of energy consumption in buildings seems to crest from the normal demand and that has to be carefully addressed through implementing energy conservative and energy management techniques. In the class of having several energy efficient schemes, thermal energy storage (TES) technologies for buildings are increasingly attractive among architects and engineers. In the scenario of growing energy demand worldwide, the possibility of improving the energy efficiency of TES systems can be achieved from break-through research efforts. The prime intention of this paper is to review the potential research studies pertaining to a variety of latent heat energy storage (LHES) and cool thermal energy storage (CTES) systems solely dedicated for building heating, cooling and air conditioning (A/C) applications. Technical revelations regarding the integration and performance evaluation of heat storage materials in building fabric elements as well as using separate heat storage facility to satisfy the space thermal load demand have been gleaned from numerous research contributions and presented. Emphasis is also given on advanced heat storage materials produced using micro and nanoparticles to realize their improved heat transfer characteristics which would eventually enhance the overall performance of these TES systems. Furthermore, the sustainable aspects of these TES systems to gain the Leadership in Energy and Environmental Design (LEED) credentials for low carbon/high performance buildings are signified.     

Optimal roof structure with multilayer cooling function materials for building energy saving

Both cool roof and phase change thermal storage are promising technologies in decreasing building energy consumption. Combining these two technologies is likely to further enhance the thermal comfort of the building as well as reduce air condition loads. In this paper, the cooling performance and energy-saving effects of four types of roof (normal roof, phase change material [PCM] roof, cool roof, and cool PCM roof [cool roof coupled with PCM]) were investigated under a simulated sunlight. Experimental results indicate that compared with normal roof, the other three roofs are able to narrow the indoor temperature fluctuation and decrease the heat flow entering into the room. Among them, cool PCM roof gave the best energy-saving effect that can lower the indoor temperature and heat entering into rooms by 6.6°C and 52.9%, respectively. Besides, the PCM location, PCM thickness, and insulation thickness exerted great impacts on the cooling performance of the roof. Placing the PCM on the internal layer beneath the extruded polystyrene (XPS) insulation board can make the indoor temperature 1.2°C lower than that on the middle layer. Although thicker PCM panels or insulation boards can provide a better thermal insulation, 5 mm in PCM thickness and 20 mm in insulation thickness are enough to guarantee the indoor temperature of cool PCM roof system at a comfortable range (22°C-28°C) for a whole day. These findings will give guidance in designing buildings with a light and compact roof structure to decrease energy consumption and improve comfort level.     

Reducing energy use in the buildings sector: measures, costs, and examples

This paper reviews the literature concerning the energy savings that can be achieved through optimized building shape and form, improved building envelopes, improved efficiencies of individual energy-using devices, alternative energy using systems in buildings, and through enlightened occupant behavior and operation of building systems. Cost information is also provided. Both new buildings and retrofits are discussed. Energy-relevant characteristics of the building envelope include window-to-wall ratios, insulation levels of the walls and roof, thermal resistance and solar heat gain coefficient of windows, degree of air tightness to prevent unwanted exchange of air between the inside and outside, and presence or absence of operable windows that connect to pathways for passive ventilation. Provision of a high-performance envelope is the single most important factor in the design of low-energy buildings, not only because it reduces the heating and cooling loads that the mechanical system must satisfy but also because it permits alternative (and low-energy) systems for meeting the reduced loads. In many cases, equipment with significantly greater efficiency than is currently used is available. However, the savings available through better and alternative energy-using systems (such as alternative heating, ventilation, cooling, and lighting systems) are generally much larger than the savings that can be achieved by using more efficient devices (such as boilers, fans, chillers, and lamps). Because improved building envelopes and improved building systems reduce the need for mechanical heating and cooling equipment, buildings with dramatically lower energy use (50–75% savings) often entail no greater construction cost than conventional design while yielding significant annual energy-cost savings.

Development of solar thermal technologies in China

Solar energy is receiving much more attention in building energy systems in recent years. Solar thermal utilization should be based on integration of solar collectors into buildings. The facades of buildings can be important solar collectors, and, therefore, become multifunctional. In addition, solar collectors can be used to enhance the appearance of the facade when considering their aesthetic compatibility. Currently, installation of collectors on the south tilted roofs, south walls, balconies or awnings of buildings are the feasible approaches for integration of solar collectors into buildings. The most well known solar energy demonstration projects in China are introduced in this paper, which cover different integrated approaches, and solar heating and cooling systems. In China's cities, the process of rebuilding apartment roofs from flat to inclined offers the ideal opportunity to carry out solar renovation in combination with roof-integrated collectors. It can be seen from the demonstration projects over the last twenty years, that, solar cooling systems were mainly used in public buildings for either absorption or adsorption. Besides, nearly all solar cooling systems are multifunctional. They have been used to supply heating and hot water in other seasons for the purpose of high solar fraction. In the 11th Five-year research project (duration 2006–2010), the government has encouraged solar energy researchers to study, develop, and break through the key technologies involved in the integration of solar thermal technologies with buildings.     

The analysis of energy consumption of a commercial building in Tianjin,China

According to statistics and field investigation, the energy consumption situation and reality of commercial building is described in this paper. As the first step of large-scale public building energy efficiency supervision system encouraged by central government of China, the energy consumption of several typical commercial buildings and public buildings was analyzed in detail. The main contents of investigation are as follows: basic information of building, operational record of energy consumption equipment, energy consumption of indoor equipments, energy-efficiency assessment of energy consumption systems and equipments, investigation of behavior energy saving, etc. On this basis further analysis and diagnosis including indoor thermal and humid environment, operation state of air-conditioning water system, operation state of air-conditioning duct system and operation management of air-conditioning system were implemented. The results show that the most energy consumption of buildings in this city is commercial buildings, which can reach to about 240 W/m² per year. Further analysis tells that air conditioning systems play the major role of building energy consumption, and building energy saving has great potential in this city. In this paper, the ways of diagnosis work for building energy consumption are also described and discussed. Reasonable test, diagnosis and analysis are meaningful for building energy efficiency retrofit and management.     

A generalized methodology for determining the total heat gain through building envelopes

We present a generalized methodology for determining the annual total heat gain through external walls and proofs of large air-conditioned buildings. The methodology is based on the concept of the overall thermal transfer value (OTTV). Respective OTTV equations for building envelopes and roofs are developed through parametric simulations using the DOE-2 computer code. The equations are valid for buildings having different aspect ratios and wall masses. Appropriate coefficients for heat conduction through fenestrations and opaque walls and solar correction factors for wall facades of different orientations are computed from local weather data. The equations allow building designers to make accurate estimates of the total heat gain for the purpose of evaluating energy-efficient building envelope components and air-conditioning systems and plant options. The methodology is validated using DOE-2 computed heat gain results and can be applied to different classes of buildings, construction types and locations.     

A review of the economical and optimum thermal insulation thickness for building applications

Energy conservation is an increasingly important issue for the residential sector. Therefore, attention towards the thermal performance of building materials, particularly thermal insulation systems for buildings, has grown in recent years. In this study, a literature review on determining the optimum thickness of the thermal insulation material in a building envelope and its effect on energy consumption was carried out. The results, the optimization procedures and the economic analysis methods used in the studies were presented comparatively. Additionally, a practical application on optimizing the insulation thickness was performed, and the effective parameters on the optimum value were investigated.     

Optimum insulation thickness of walls for energy-saving in hot regions of India

In India, the energy consumption in the building sector is rapidly increasing due to improvement in living standards. Effective thermal insulation of building walls is one of the most effective energy conservation measures for heating, ventilation, and air conditioning applications in buildings. In this study, the thermoeconomic optimisation of insulation thickness on walls of buildings is analysed based on degree days. Thermoeconomic parameters such as optimum insulation thickness, annual electrical energy consumption, annual energy cost and payback period is determined for three different insulation materials for the cities located in India. Database on insulation materials for five cities of India are provided.     

Properties and performance of advanced reflective paints to reduce the cooling loads in buildings and mitigate the heat island effect in urban areas

High reflective coatings and paints spread on the roof and walls can be very useful to reduce the cooling loads in buildings to ensure thermal comfort in the built environment. The solar reflectance of construction and cooling materials was measured with a spectrophotometer. A surface temperature monitoring campaign compared the thermal profiles of typical Italian construction materials with an innovative sustainable white paint, obtained with a special mixture of milk and vinegar of very high solar reflectance. Two building-integration cool-roof campaigns were run in the experimental building, Casa Intelligente of ENEA, in which indoor and outdoor air temperature and roof surface temperatures were monitored. This campaign, run in the summer of 2005 and 2006, allowed us to verify the influence of cool roofs to mitigate indoor air temperatures and to compare the behaviour of different cool-roof technologies.     

PCM thermal storage in buildings: A state of art

A comprehensive review of various possible methods for heating and cooling in buildings are discussed in this paper. The thermal performance of various types of systems like PCM trombe wall, PCM wallboards, PCM shutters, PCM building blocks, air-based heating systems, floor heating, ceiling boards, etc., is presented in this paper. All systems have good potential for heating and cooling in building through phase change materials and also very beneficial to reduce the energy demand of the buildings.     

Determination of the economical insulation thickness of building envelopes simultaneously in energy-saving renovation of existing residential buildings

When the energy saving rate of existing residential buildings renovation is determined, the thermal performances of external walls, windows, and roof interact with each other. Therefore, it is necessary to study the determination of economical insulation thickness of building envelopes considering the interaction among building envelope performances. The objective function and its bound of envelope thermal performance optimization in the energy-saving renovation of existing residential buildings in severe cold and cold zones in China were established. It is the conditional extremum problem and can be solved through Lagrange’s method of multipliers to determine the economical insulation thickness of external walls and roofs simultaneously. The method is proved to be feasible by an existing residential building in Beijing. When the same window types are selected, the energy-saving renovation program of the building envelope determined by the Lagrangian optimization method can produce the minimum investment in insulation, minimum investment payback period, and the largest net present value (NPV) of the life cycle.     

Evaluation on energy and thermal performance for residential envelopes in hot summer and cold winter zone of China

As a result of rapid economic growth in the last several decades, energy issue is becoming more and more important in today’s world because of a possible energy shortage in the future; the usage of residential electricity has increased rapidly in China and building energy efficiency is included as one of the 10 key programs targeting energy efficiency improvement in the 11th Five-Year Plan. In response to the growing concerns about energy conservation in residential buildings and its implications for the environment, systematic evaluation on energy and thermal Performance for residential envelops (EETP) is put forward to assess the energy efficiency of envelop designs and to calculate the energy consumption of cooling and heating systems. Hot summer and cold winter zone of China was selected for EETP analysis because of its rigorous climatic and huge energy consumption. The correlations between EETPs and electricity consumptions in cooling season, heating season, and the whole year were built in Shanghai, Changsha, Shaoguan and Chengdu, which represent A, B, C and D subzone of hot summer and cold winter zone in China, respectively. Illustrations indicate that the algorithm is simple and effective, energy and thermal performance of residential envelopes can be evaluated easily. The maximum allowable values of EETPs were determined when just meeting the compulsory indices of Standard JGJ134-2001, the corresponding allowable EETPs were also gained when achieving different energy-saving degrees on basis of it. EETP method can suggest possible ways to improve the energy efficiency for envelope designs of new building and retrofits of existing buildings and provide governments some useful information for the establishment of new policy on energy efficiency buildings. It has important meanings to carry out sustainable residential building designs with high thermal comfort and low energy consumption.     

Identification of the building parameters that influence heating and cooling energy loads for apartment buildings in hot-humid climates

Identifying the building parameters that significantly impact energy performance is an important step for enabling the reduction of the heating and cooling energy loads of apartment buildings in the design stage. Implementing passive design techniques for these buildings is not a simple task in most dense cities; their energy performance usually depends on uncertainties in the local climate and many building parameters, such as window size, zone height, and features of materials. For this paper, a sensitivity analysis was performed to determine the most significant parameters for buildings in hot-humid climates by considering the design of an existing apartment building in Izmir, Turkey. The Monte Carlo method is selected for sensitivity and uncertainty analyses with the Latin hypercube sampling (LHC) technique. The results show that the sensitivity of parameters in apartment buildings varies based on the purpose of the energy loads and locations in the building, such as the ground, intermediate, and top floors. In addition, the total window area, the heat transfer coefficient (U) and the solar heat gain coefficient (SHGC) of the glazing based on the orientation have the most considerable influence on the energy performance of apartment buildings in hot-humid climates.     

Case study of data-oriented approach for building energy performance investigation

The key parameters that may influence building energy performance is studied by comparing the building energy data of college buildings in two different regions (the USA and China). By introducing data-orientated approach, a study of a set of on-campus building energy demand and consumption is conducted for cooling, heating and electricity. In addition, the heating, ventilation and air conditioning (HVAC) and lighting systems are studied in great detail. The breakdown analyses of the current energy consumption data are used to focus the investigation on critical issues. The analysis shows that the energy consumption of college buildings in the USA can be 3–5 times more than that of college buildings in China. The over-high energy consumption in campus buildings in the USA is mainly caused by operation schedule, system style, cooling and heating counteraction and sensor/actuator faults in the control systems, which also leads to the discussion of energy difference on the concept of “full control” or “local improvement” in building environment control. The study also indicates that the building energy efficiency can only be achieved by adjusting the demand according to natural conditions, encouraging green life behaviors, and developing relative technical solutions coordinated with the thrift culture and human behavior.