Energy and cost evaluation of thermal bridge correction in Mediterranean climate

In the cold climate of continental Europe the correction of thermal bridges in buildings is a mandatory issue, as in these areas they produce not only heat losses but frequently also condensation and mould growth.In mild Mediterranean climate thermal bridges also cause an increase in energy consumption, but usually do not present condensation effects. In Italy, the current regulations for new buildings only recommend but do not impose the thermal bridge correction, which usually needs extra costs during construction and refurbishment phases.This paper presents a study on the effects of thermal bridges for two building types (terraced houses and semi-detached houses) and three current envelope solutions in Italian climate, which may be considered representative of mild Mediterranean climate. The buildings are characterised by reinforced concrete frameworks and clay block walls; the thermal performance of the envelopes complies with Italian regulations for new constructions. In a first step the impact of thermal bridges on both heating and cooling energy demand is studied; then the economic convenience of correcting such thermal bridges is assessed by calculating the discounted payback period referred to the additional costs of construction and refurbishment.     

Embodied and operational carbon dioxide emissions from housing: A case study on the effects of thermal mass and climate change

A 100-year lifecycle carbon dioxide (CO₂) emissions analysis is reported for a two-bedroom, 65 m² floor area, semi-detached house in south-east England. How the balance between the embodied (ECO₂) and operational CO₂ emissions of the building are affected by the inclusion of thermal mass and the impacts of climate change is quantified. Four ‘weights’ of thermal mass were considered, ranging from lightweight timber frame to very heavyweight concrete construction. For each case, total ECO₂ quantities were calculated and predictions for operational CO₂ emissions obtained from a 100-year dynamic thermal modelling simulation under a medium-high emissions climate change scenario for south-east England. At the start of the lifecycle, the dwellings were passively cooled in summer, but air conditioning was installed when overheating reached a certain threshold. The inclusion of thermal mass delayed the year in the lifecycle when this occurred, due to the better passive control of summertime overheating. Operational heating and cooling energy needs were also found to decrease with increasing thermal mass due to the beneficial effects of fabric energy storage. The calculated initial ECO₂ was higher in the heavier weight cases, by up to 15% (4.93 t) of the lightweight case value, but these difference were offset early in the lifecycle due to the savings in operational CO₂ emissions, with total savings of up to 17% (35.7 t) in lifecycle CO₂ found for the heaviest weight case.     

Advanced wood-frame construction details in Canada

This paper investigates how durability, energy efficiency and indoor air quality can be improved through proper detailing. The energy implications of air-tight construction are evaluated for terrace and semi-detached houses.     

Impact of constructional energy‐saving measures on radon levels indoors

Energy‐efficient building refurbishment has the aim of saving energy and thus reducing CO₂ emissions. Increased energy efficiency of a building often implies reduced air exchange. Together with other indoor air quality problems, this may lead to an increase in indoor radon concentration (Rn‐222). In order to investigate the extent of this problem, measurements of radon concentration in energy‐efficient refurbished and low‐energy houses (passive houses) were carried out. Track etch detectors were exposed in each type of building over a period of 1 year. A reference sample of non‐refurbished non‐passive buildings was drawn from the National Radon Database for comparison. Buildings were selected that have the same radon relevant properties and were built on comparable geological subsoil like those investigated. The reference sample was compiled in such a way that the measured values from the rooms on the ground floor of the refurbished and passive houses were each assigned a measured value from the database. The statistical analysis shows that the houses refurbished for energy efficiency have a wider distribution of radon concentrations indoors than the non‐refurbished ones. Both the mean value and the median of the radon concentration have nearly doubled in buildings refurbished for energy efficiency. The difference is statistically significant. On the other hand, there is no significant difference between the distributions of passive houses and houses not refurbished for energy efficiency.     

Energy efficient demand controlled ventilation in single family houses

This paper presents a strategy for a simple demand controlled ventilation system for single family houses where all sensors and controls are located in the air handling unit. The strategy is based on sensing CO₂-concentration and moisture content in the outdoor air and exhaust air. The CO₂-concentration is used to ensure adequate ventilation during occupancy and the moisture content is used to ensure adequate removal of moisture produced in the house. The ventilation rate can be switched between two flow rates: a high rate and a low rate. The high flow rate is based on existing requirements in the Danish building regulations and the low flow rate is based on minimum requirements in indoor air quality standards. Measurements were performed on an existing single family house where the controls were installed on the existing mechanical ventilation system. The results showed that the ventilation can be reduced to the low rate 37% of the time without significant changes in the CO₂-concentration and moisture level in the house. In theory this gives a 35% saving on electric energy for fans.     

华北地区农村房屋建筑现状以及房屋能耗的调研分析

通过对华北地区农村房屋采取的保温措施情况、需供暖房屋的建筑面积、冬季房屋供暖方式、房屋净高、冬季室内空气品质满意情况、平均温度以及期望温度等方面的调研与分析,发现华北地区农村房屋大部分没有采取良好的保温措施,建筑能耗大、层高过高、室内热舒适性差等问题。针对房屋节能改造和房屋净高的改良提出了合理化的意见,对社会主义新农村的规范化建设以及农村家庭节约能源提供依据,与国家节约能源的政策保持一致。     

Enhanced energy conservation in houses through high performance design

Key design features of high performance houses are investigated for improving energy efficiency in cold climates. Reference dwellings with typical constructions and system designs are compared with high performance houses using the best technology available. The dwellings used for reference are a multi-family apartment building and a single-family detached house, designed according to a mix of Nordic building codes of 2001. The high performance houses designed fulfilled the target requirements of IEA Task 28, Sustainable Solar Housing. Simulations of the buildings are performed using the computer programme DEROB-LTH and results from simulations give the hourly space-heating demand and peak load of the buildings. A comparison of reference houses to high performance solutions shows that the space-heating demand can be reduced by up to 83% for single-family houses and by up to 85% for apartment buildings. The climate data used for all simulations is Stockholm, Sweden. The environmental effects in terms of CO₂ equivalent emissions and use of non-renewable primary energy are quantified for each building type and construction. The energy saving potential of high performance houses in cold climates is demonstrated.     

Optimization of indoor environmental quality and ventilation load in office space by multilevel coupling of building energy simulation and computational fluid dynamics

The fundamentals, implementation, and application of an integrated simulation as an approach for predicting the indoor environmental quality for an open-type office and for quantifying energy saving potential under optimized ventilation are presented in this paper. An integrated simulation procedure based on a building energy simulation and computational fluid dynamics, incorporated with a conceptual model of a CO₂ demand controlled ventilation (DCV) system and proportional integral control of an air conditioning system as the optimization assessment of conceptual model in the occupied zone, was developed. This numerical model quantitatively exhibits energy conservation and represents the non-uniform distribution patterns of airflow properties and CO₂ concentration levels in terms of energy recovery and indoor thermal comfort. By means of an integrated simulation, the long-term energy consumption of heating, ventilation, and air conditioning systems are predicted precisely and dynamically. Relative to a ventilation system with a basic constant air volume supply rate characterized by a fixed outdoor air intake rate from the ceiling supply opening, the optimized CO₂-DCV system coupled with energy recovery ventilators reduced total energy consumption by 29.1% (in summer conditions) and 40.9% (winter).     

The estimation of energy consumption and CO2 emission due to housing construction in Japan

Basic sector classification Input/Output Tables of Japan (Research Committee of International Trade and Industry, Tokyo, Japan, 1988) were applied to quantify the total energy consumption and CO₂ emission including direct and indirect effects due to the construction of various types of houses. As a result, energy consumption for construction is calculated as 8–10 GJ per square meter of floor area for multi-family SRC (steel reinforced concrete) houses, 3 GJ for wooden single-family houses, 4.5 GJ for lightweight steel structure single-family houses. CO₂ emission resulting from construction is 850, 250 and 400 kg/m², respectively.     

上海市节能省地型住宅建设的前景分析与建议

分析了上海市节能省地型住宅建设的现状,指出目前住宅建筑在建设和使用过程中对资源能源的利用效率仍处于相对较低的水平.从节能、节地、节水、节材等四个方面分析了上海市新建住宅节能省地建设的广阔前景,指出节能省地型住宅的推广受到了技术、观念、政策等方面因素的阻碍,并提出了相应的建议.     

建筑外窗节能分析及能耗损失对策

建筑外窗耗能量占建筑总耗能量的40％左右,文章结合目前常用的窗框材料及玻璃提出减少能耗增加气密性的措施,阐述了建筑外窗节能的各种处理方法。     

Evaluation of four control strategies for building VAV air-conditioning systems

It is necessary to adopt appropriate control strategies to save energy and improve the indoor air quality (IAQ). On the validated TRNSYS simulation platform, four different control strategies are investigated to examine the indoor air temperature, energy consumption, CO₂ concentration and predicted mean vote (PMV) for the variable air volume (VAV) systems in an office building in Shanghai. As an original scheme, Strategy A using constant outdoor air intake fraction shows high energy consumption, low CO₂ concentration and acceptable thermal comfort. By using minimum outdoor air ventilation based on dynamic occupancy detection, Strategy B can provide more than 15% energy saving, acceptable PMV value but high CO₂ concentration in breathing zone. By using indoor air temperature reset, Strategy C presents the most energy savings beyond 20% reduction, low CO₂ concentration but poor thermal comfort. In mild seasons, combining enthalpy-based outdoor airflow economizer cycle with supply air temperature reset, Strategy D can achieve 9.4% energy savings and the lowest CO₂ concentration. Taken together, each strategy covers some strengths as well as some weaknesses. How to comprehensively assess a control strategy for all specific objectives should be considered in future studies.     

One-year Measurement of Indoor Climate and Energy Consumption of Super-insulated Houses in a Mild Climate Region of Japan

Two super-insulated houses were constructed near Sendai City in accordance with the Canadian R-2000 manual (Canadian Home Builders' Assoc., 1987). Shelter performance, thermal environment, air quality and energy consumption of these two houses were investigated for one year. The two super-insulated houses were very airtight compared with other houses. The one-year measurement of room temperature and humidity for one super-insulated house showed that the daily mean temperature for the dining-living room and the master bedroom was 15°C-20°C during the winter and 22°C-28°C during the summer. Absolute humidity for these rooms was less than 5 g/kg (DA) during the winter. The indoor environment of the two super-insulated houses during the heating season was more thermally comfortable, compared with that of ordinary houses in Japan. During the summer, the indoor temperature in these two houses was stable during the day and did not decrease at night even if the outdoor air temperature dropped. The CO₂ concentration in these two houses was lower than that of other airtight houses due to continuous mechanical ventilation. The space heating energy consumption for one super-insulated house was less than that of ordinary houses in Tohoku District in which only the living-dining room was heated.     

Energy and Buildings

Energy is wasted in domestic buildings when rooms that are heated are not occupied. Allowing those rooms to cool reduces the inside-outside temperature difference and therefore rate of heat loss, resulting in an energy saving. This suggests a cost effective way to upgrade an existing modern heating system, especially in older properties where other energy saving possibilities are limited. Assessing the savings achievable requires an analysis of a range of influencing factors, such as house type and age, location and occupancy patterns. Door opening has a major influence due to the impact on air exchange between heated and unheated zones in a house, so this was also considered. Annual simulations were carried out on dynamic models of the thermal and air flow interactions, for all combinations of influencing factors, to compare the potential energy savings of zoned versus non-zoned control. Savings of between 12% and 31% were obtained in the case of a semi-detached house model, and between 8% and 37% for a single storey bungalow. The lar-gest percentage savings occurred in older properties, with inter-connecting doors kept closed, and for the more intermittent types of occupancy. The average saving obtained for both house types was around 20%.     

Energy-efficient terrace houses in Sweden: Simulations and measurements

Reducing energy use in buildings is essential to decrease the environmental impact. Outside Gothenburg in Sweden, 20 terrace houses were built according to the passive house standard and completed in 2001. The goal was to show that it is possible to build passive houses in a Scandinavian climate with very low energy use and to normal costs. The houses are the result of a project including research, design, construction, monitoring and evaluation. The passive house standard means that the space heating peak load should not exceed 10 W/m² living area in order to use supply air heating. This requires low transmission and ventilation losses and the building envelope is therefore highly insulated and very airtight. A mechanical ventilation system with approximately 80% heat recovery is used. The electric resistance heating in the supply air is 900 W per living unit. Solar collectors on the roof provide 40% of the energy needed for the domestic hot water. The monitored delivered energy demand is 68 kWh/m² a. Energy simulations show that main differences between predicted and monitored energy performance concern the household electricity and the space heating demand. Total delivered energy is approximately 40% compared with normal standard in Sweden.     

谈窗户节能措施

介绍了窗户热量损失的途径及材料的发展趋势，从选择气密性好的窗型、增加玻璃层数、选择节能玻璃品种等方面，提出了提高窗户节能性能的具体措施。     

Life-cycle assessment of post-disaster temporary housing

The estimation of energy consumption and related CO₂ emissions from buildings is increasingly important in life-cycle assessment (LCA) studies that have been applied in the design of more energy-efficient building construction systems and materials. This study undertakes a life-cycle energy analysis (LCEA) and life-cycle CO₂ emissions analysis (LCCO₂A) of two common types of post-disaster temporary houses constructed in Turkey. The proposed model includes building construction, operation and demolition phases to estimate total energy use and CO₂ emissions over 15- and 25-year lifespans for container houses (CH) and prefabricated houses (PH) respectively. Energy efficiency and emission parameters are defined per?m² and on a per capita basis. It is found that the operation phase is dominant in both PH and CH and contributes 86–88% of the primary energy requirements and 95–96% of CO₂ emissions. The embodied energy (EE) of the constructions accounts for 12–14% of the overall life-cycle energy consumption. The results show that life-cycle energy and emissions intensity in CH are higher than those for PH. However, this pattern is reversed when energy requirements are expressed on a per capita basis.     

Potential energy savings achievable by zoned control of individual rooms in UK housing compared to standard central heating controls

Energy is w asted in domestic buildings w hen rooms that are heated are not occupied. Allow ing those rooms to cool reduces the inside-outside temperature difference and therefore rate of heat loss,resulting in an energy saving. This suggests a cost effective w ay to upgrade an existing modern heating system,especially in older properties w here other energy saving possibilities are limited. Assessing the savings achievable requires an analysis of a range of influencing factors,such as house type and age,location and occupancy patterns. Door opening has amajor influence due to the impact on air exchange betw een heated and unheated zones in a house,so this w as also considered.Annual simulations w ere carried out on dynamic models of the thermal and air flow interactions, for all combinations of influencing factors,to compare the potential energy savings of zoned versus non-zoned control. Savings of betw een 12% and31% w ere obtained in the case of a semi-detached house model,and betw een 8% and 37% for a single storey bungalow. The largest percentage savings occurred in older properties,w ith interconnecting doors kept closed,and for the more intermittent types of occupancy. The average saving obtained for both house types w as around 20%.     

Modelling sheltering effects of trees on reducing space heating in office buildings in a windy city

Using statistical weather analysis, computational fluid dynamics and thermal dynamic simulation, a systematic method was developed to assess quantitatively the effects of a shelterbelt on space heating, particularly with regard to the energy consumption and CO₂ emission. It was then applied to estimate the heating loads of two typical office buildings in a windy city located at 57.2North, with and without a shelterbelt. Firstly, the statistical analysis of weather data was carried out to identify the prevailing wind direction during a typical winter heating season in the location. It was to ensure the windbreak planted rightly to maximise its sheltering benefits for the buildings in its leeward. This analysis, which revealed the main weather features in the location, would help to better comprehend the results of the thermal modelling and gain insight of how the load responses to the climate. In the second part, CFD modelling predicted wind reduction due to the shelterbelt under various wind directions. The predicted data were then used to prepare two sets of weather data, the original weather file and the revised one, in which the wind data had taken into account the reduction effect of the windbreak. The third part was a dynamic thermal modelling study where two types of office buildings were selected as the representative offices in Edinburgh for the assessment of sheltering effect on energy saving and CO₂ reduction. The predicted savings over a heating season due to the shelterbelt were in a range of 16–42% and the actual values in space heating were about 2.2 kWh m⁻² for new office buildings and 14.5 kWh m⁻² for offices converted from conventional houses without insulation improvement. These significant savings were due to the local weather that is typically known as long windy winter with many cloudy days.     

Evaluating the potential impact of global warming on the UAE residential buildings – A contribution to reduce the CO2 emissions

There is significant evidence that the world is warming. The International Panel of Climate Change stated that there would be a steady increase in the ambient temperature during the end of the 21st century. This increase will impact the built environment, particularly the requirements of energy used for air-conditioning buildings. This paper discusses issues related to the potential impact of global warming on air-conditioning energy use in the hot climate of the United Arab Emirates. Al-Ain city was chosen for this study. Simulation studies and energy analysis were employed to investigate the energy consumption of buildings and the most effective measures to cope with this impact under different climate scenarios. The paper focuses on residential buildings and concludes that global warming is likely to increase the energy used for cooling buildings by 23.5% if Al-Ain city warms by 5.9 °C. The net CO₂ emissions could increase at around 5.4% over the next few decades. The simulation results show that the energy design measures such as thermal insulation and thermal mass are important to cope with global warming, while window area and glazing system are beneficial and sensitive to climate change, whereas the shading devices are moderate as a building CO₂ emissions saver and insensitive to global warming.