Effect of roof solar reflectance on the building heat gain in a hot climate

The effect of the roof solar reflectance on the thermal performance of a building is often ignored. However, there are significant differences in heat gain from light and dark-coloured roof surfaces. In this paper an equation for the average daily downward heat flow of a sunlit roof is derived. Using building simulation, it is first shown that the thermal mass of the roof does not significantly affect the overall daily heat gain (although it causes a time lag and reduction in peak heat flow). As a consequence the daily heat gain from the roof may be estimated by integrating the equation for the steady-state downward heat transfer over the day. For north Australia the derived equation suggests that a light-coloured roof has about 30% lower total (air temperature difference and solar-driven) heat gain than a dark-coloured one. The effect of aging (change in solar reflectance with time) is considered in the calculations and a relationship between the solar absorptance of new and aged material is suggested. A classification of roof colours with respect to their solar absorptance (dark, medium, light and reflective) is proposed to enable a quick and simple assessment of the effect of roof colour on the heat gain and R-value.     

Effects of roof tile permeability on the thermal performance of ventilated roofs: Analysis of annual performance

This paper shows the results of the second part of an experimental study aimed at analysing the effects of roof tile permeability on the thermal performances of ventilation ducts. Ventilation ducts under the layer of tiles are typically used in south European countries to limit the energy load during the summer period. The results of the first part of the study, carried out by analysing 14 different types of roof, proved that the air permeability of the layer of tiles determines a certain amount of heat to be released, in addition to the release connected with the stack effect, in ventilation ducts which have the same characteristics but are perfectly airtight. However, the study did not completely resolve some issues since it was carried out on a model roof (6 m × 1.5 m) with devices to raise the layer of tiles and to create the ventilation duct but without those building elements which are present in real roofs and are used to stop insects and small animals from entering the ventilation duct. These elements narrow the inlet and outlet and consequently cause important reductions in pressure. Moreover, the measurements were based on data collected for limited periods of time during the summer season.     

多层建筑变制冷剂流量空调室外机安放与其性能的数值研究

基于不可压缩黏性流体N-S方程和K-ε两方程湍流模型,采用有限容积法对某工程变制冷剂流量空调室外机周围流场进行了数值计算,得到了室外机周围的气流速度和温度分布及室外机的进风温度,分析了多层建筑中室外机安放条件对空调系统性能的影响。结果表明,变制冷剂流量空调室外机进、排风口不宜同侧布置,如果因建筑条件限制只能同侧布置时,同一设备阳台上室外机数量应少于4台。根据研究结果及实际建筑条件改进和优化了空调室外机安放设计。     

Experimental testing of cool colored thin layer asphalt and estimation of its potential to improve the urban microclimate

Urban Heat Island refers to the temperature increase in urban areas compared to rural settings, exacerbating the energy consumption of buildings for cooling. The use of highly reflective materials in buildings and urban structures reduces the absorbed solar radiation and contributes to mitigate heat island. This paper presents the results of a study aiming to measure and analyze the solar spectral properties and the thermal performance of 5 color thin layer asphalt samples in comparison to a sample of conventional black asphalt. Computational fluid dynamics (CFD) simulation is used for evaluating the thermal and energy impact of applying the samples in outdoor spaces (roads). The spectrophotometric measurements showed that the colored thin layer asphalt samples are characterized by higher values of solar reflectance compared to the conventional asphalt, which is mainly due to their high near infrared solar reflectance. From the statistical analysis of the surface temperatures it was found that all the colored thin layer asphalt samples demonstrate lower surface temperatures compared to conventional asphalt. The maximum temperature difference recorded was for the off-white sample and was equal to 12 °C. The CFD simulation results show that surface and air temperatures are decreased when applying the color thin layer sample.     

Influence of insulated roof slabs on air conditioned spaces in tropical climatic conditions—A life cycle cost approach

The recent energy crisis and the environment impacts of building industry have led to the active promotion of principles of sustainable development in recent times. Minimization of energy usage is the key to improve sustainability where the actual impact is assessed on the basis of life cycle cost estimates. In this context, the performance of insulated roof slabs which can be used as an alternative to conventional light weight roofs, have been assessed in detail especially with respect to air conditioned buildings. It is shown that insulated roof slabs could have a desirable behaviour with respect to life cycle performance in addition to providing other benefits such as cyclone resistance and higher robustness to the building.     

高原燃油暖风机性能测试与分析

介绍了燃油暖风机的结构及工作原理，对所研制的高原燃油暖风机样机进行了现场冷热态测试，考察了燃烧器的点火启动情况，分析了运行参数、过剩空气系数、大气压力等对机组热效率的影响，并讨论了燃烧室及对流换热面的换热状况，对改进机组性能提出了几点建议。     

Numerical investigation on the ingress of particulate matter from ambient air into the inlet of a building air handling unit

The transportation of ambient particulate matter (PM) from outdoor air into the inlet of a mechanical building ventilation system is poorly understood. No studies have examined the effect commonly used commercial air handling unit (AHU) inlet designs have upon the migration of PM from the ambient environment into the building ventilation system, and implications of this on energy consumption and indoor air quality (IAQ). Through the numerical analysis of commercial AHU inlets, the differences in concentration of PM in ambient air and that within AHUs were determined, more commonly referred to as Aspiration Efficiency (AE %). A 20–50% difference in particle concentrations between ambient air and the in-AHU concentration was observed between forward and rear-facing AHUs relative to ambient wind direction and speed, and at the maximum ventilation flow rate. Furthermore, a decrease in the ventilation flow rates resulted in a significant reduction in PM concentrations entering the rear-facing AHU. Increasing the Stoke number led to lower AE as a continuous decrease was observed for both rear-facing inlets. The findings of this paper show that AHU inlet design has significant implications on IAQ and building energy consumption, and scope exists to design these inlets to impact both aspects positively.     

一种余热驱动溶液调湿新风机组冬季运行研究

测试分析了一种余热驱动溶液调湿新风机组的冬季运行情况,得出了这种机组在冬季工况下的运行性能。在测试数据的基础上,分析了机组的送风参数随热水温度、热水流量和溶液浓度的变化情况。基于这些变化关系,得出了冬季工况下机组送风参数控制的基本原理和方法。     

柜式空调器室内机的试验与优化

就室内机部件对拒式空调器整机性能的影响进行了试验研究，研究结果表明：室内机箱体的风阻最大，其次是蒸发器和进气面板；设计合理的进气面板能在相同气动性能的条件下降低噪声。在此基础上提出了提高整机性能的优化设计方法。     

带冷凝热回收的直流变频恒温恒湿空调机组热湿分控实验研究

基于已有的带冷凝热回收的直流变频恒温恒湿空调机组,提出了一种串级控制的热湿分控方法。为了验证该控制方法的可行性,对机组出风温湿度控制效果和被控房间的温湿度控制效果进行了测试。实验结果表明,采用该控制方法的恒温恒湿机组能满足实验工况下的热湿控制要求,送风温度控制精度为±0.2℃,送风含湿量控制精度为±0.2g/kg,被控房间的干球温度控制精度为±0.04℃,被控房间的露点温度控制精度为±0.02℃。     

The duck curve in a drying pond: The impact of rooftop PV on the Western Australian electricity market transition

Rooftop solar photovoltaics (PV) are significantly influencing the electricity market and system operability in Western Australia. Qualitative methods are used to determine likely impacts and solutions to associated technical and market challenges in this islanded electricity system. Solutions focus on flattening the load curve and addressing minimum system load issues, including via; tariff reform, new ancillary services, automation, storage and energy productivity; targeted markets to match energy supply to the new demand curve; together with enabling technologies such as; improved inverter functionality and control systems. A parsimonious model demonstrates the impacts of rooftop PV on the local mid-day wholesale energy prices.     

A study on the energy consumption unit of subway stations in Korea

As the Korean economy and society continues to develop, the number of subways are expected to increase. This increase will demand greater heating and cooling energy as well as convey a sharp rise in the overall energy consumption. This study aims to develop energy conservation and analysis for subways. This study shows the information, that is, tables, graphs, and charts concerning the trend in energy efficiency in subways between 1999 and 2001. We suggest a practical application for energy conservation methods and efficient energy use based on the investigations and analyses.     

空调机组焓差法制冷量测试系统的研制

介绍了空调机组焓差法制冷量测试系统的总体方案及系统组成，分析了测试系统的工作原理和控制流程，评价了该测试系统的使用效果良好。     

An experimental study on airflow in the cavity of a ventilated roof

The thermal performance of the building envelope is a major requirement for guaranteeing a comfortable and hygienic interior climate. The roof is a part of the building envelope which provides protection from thermal damage incurred by the sun. To improve this protection ability, the use of a ventilated roof can be considered, which has a ventilation layer known as a cavity, beneath the roof cover panel.     

Study on the performance of a solar assisted air source heat pump system for building heating

This paper proposed a new solar assisted air source heat pump system with flexible operational modes to improve the performance of the heating system. A mathematical model was established on the solar assisted air source heat pump system for building heating with a heating capacity of 10 kW, and an air source heat pump unit was developed to validate the model. The effect of the solar collector area on the performance of the system running in Nanjing was studied. The results showed that the COP of the heat pump unit was enhanced with the increase of the solar radiation density during the typical sunny day in the heating season. In addition, the COP also increased in proportion to the solar collector area. Compared with the case when the solar collector area was 0 m², the COP increase of the heat pump and the energy-saving rate were 11.22% and 24% respectively when the solar collector area was 40 m². Meanwhile, the solar equivalent generation power efficiency could reach 11.8%.     

Energetic and exergetic analysis and assessment of a thermal energy storage (TES) unit for building applications

The main objective of this study is to investigate the energetic and exergetic performances of a latent energy storage system in both charging (solidification) and discharging (melting) processes. A shell-and-tube TES unit was designed, constructed and tested in Dokuz Eylul University, Izmir, Turkey. This experimental unit basically consisted of a heat exchanger section, a measurement system and flow control systems. For the charging mode, the inlet temperatures varied to be −5 °C, −10 °C and −15 °C, while the volumetric flow rates changed to be 2 l/min, 4 l/min and 8 l/min. The experiments were performed for three different tube materials, copper, steel and PE32 and two various shell diameters of 114 mm and 190 mm to investigate the tube material and shell diameter effects on energetic and exergetic efficiencies. It may be concluded that for the charging period, the exergetic efficiency increased with the increase in the inlet temperature and flow rate. For discharging period, irreversibility increased as the temperature difference between the melting temperature of the PCM and the inlet temperature of the heat transfer fluid (HTF) increased and hence the exergy efficiency increased.     

Efficiency analysis of a solar photovoltaic array coupled with an electrolyser power unit: a case study

Hydrogen as an energy carrier is one of the most potential candidates for clean energy and can be produced by water electrolysis. The use of 10?kW photovoltaic arrays for supplying a 5?kW electrolyser which consists of 10 series-connected electrolyser stacks and a 28% alkaline (KOH) solution electrolyte has been investigated at the Taleghan renewable energies site in Iran. The hydrogen produced by the electrolyser provides energy for the 1?kW polymer electrolyte membrane fuel cell, which meets the load when the solar energy is insufficient. Variations of the solar radiation intensity, the hydrogen production rate, the solar hydrogen efficiency and the overall efficiency of the solar hydrogen energy unit were monitored in detail. The overall energy efficiency was found to range from 0.93% to 5.01%. The obtained results demonstrate the great potential of such a power system for producing and storing energy in a solar-belt country like Iran.     

The effects of rooftop garden on energy consumption of a commercial building in Singapore

DOE-2 energy simulation program was used to determine the effects of rooftop garden on the annual energy consumption, cooling load and roof thermal transfer value (RTTV) of a five-story hypothetical commercial building in Singapore. The thermal resistances (R-values) of turfing, shrubs and trees were estimated using data from site measurements, and the effects on the building energy consumption of a rooftop garden with these three types of plants were simulated. Two soil types with different soil thickness on the building roof were also simulated. The results showed that the installation of rooftop garden on the five-story commercial building can result in a saving of 0.6–14.5% in the annual energy consumption, and shrubs was found to be most effective in reducing building energy consumption. The results also revealed that the increase of soil thickness would further reduce the building energy consumption and the moisture content of soil can affect the outcome quite substantially.     

Proposal for a new hybrid control strategy of a solar desiccant evaporative cooling air handling unit

Correctly controlled solar desiccant evaporative cooling is an interesting option for achieving savings in building air-conditioning consumption. The operation of this system (open loop cooling cycle) is strongly influenced by indoor and outdoor air conditions. This influence is characterized using numerical simulations. First the air conditioned room and the cooling system are simulated using a validated model of the desiccant wheel. Then the influence of each parameter of the desiccant air handling unit is evaluated. The third step is to assess the system cooling power for each operating mode with fluctuating outdoor and indoor air conditions. This allows for making relevant choices for a new control strategy taking into account both indoor and outdoor air conditions. This control strategy is tested for a whole cooling season and compared to a reference compression system with promising results, allowing for energy savings of about 40% for French climate.     

Evaluation of faults impacts on energy consumption and indoor air quality on an air handling unit

The effects of faults on an air handling unit (AHU) are often poorly evaluated (assuming indoor air quality (IAQ) problems), and under-estimated in consumption balances. Based on an experimental site, this paper presents a quantitative study of some different faults that can appear on AHUs.