Evaluation of a prototype active building envelope window-system

Active building envelope systems represent a new enclosure technology that uses solar energy to compensate for passive heat losses or gains through building envelopes. In ABE systems, energy obtained from solar radiation is converted into electrical energy by using photovoltaic cells. This electrical energy is subsequently used to power a series of solid-state thermoelectric modules, which can control the flow of heat through the enclosure. In order to assess the practical feasibility of ABE systems, we have developed a prototype ABE window-system and an outdoor testing room. A testing system was developed to measure the ABE system's temperatures, solar radiation, current and voltage. Theoretical and experimental results are presented and compared. Finally, the performance of the ABE window-system was evaluated.     

Effect of the thermal conductivity of building materials on the steady-state thermal behaviour of underground building envelopes

Using a mathematical model of heat transfer of basement, the calculation area is divided into eight rectangles according to the interzone temperature profile estimation (ITPE) technology, and the solution obtained for all the parts by the separation of variables technique. During the solution, the Fourier coefficients are determined by the continuity of the heat flux and boundary conditions, as a result, a system of linear equation group including 14N$14N$ equations has been obtained. The effect of building materials on the temperature and heat flux for the building envelope has been evaluated by calculating the temperature and heat flux for three buildings built with different building materials. The results show that the highest relative error in heat flux among the three envelopes built with various non-insulation material is 27.8%, which indicates the thermal conductivity of the building materials is an important factor of the heat transfer of the envelope.     

Study on thermal performance of semi-transparent building-integrated photovoltaic glazings

This paper presents a one-dimensional transient heat transfer model, the Semi-transparent Photovoltaic module Heat Gain (SPVHG) model, for evaluating the heat gain of semi-transparent photovoltaic modules for building-integrated applications. The energy that is transmitted, absorbed and reflected in each element of the building-integrated photovoltaic (BIPV) modules such as solar cells and glass layers were considered in detail in the SPVHG model. Solar radiation model for inclined surface has been incorporated into the SPVHG model. The model is applicable to photovoltaic (PV) modules that have different orientations and inclinations. The annual total heat gain was evaluated by using the SPVHG model. The impacts of different parameters of the PV module were investigated. It was found that solar heat gain is the major component of the total heat gain. The area of solar cell in the PV module has significant effect on the total heat gain. However, the solar cell energy efficiency and the PV module's thickness have only a little influence on the total heat gain. The model was also validated by laboratory tests by using a calorimeter box apparatus and an adjustable solar simulator. The test results showed that the simulation model predicts the actual situation well.     

Modeling of the hygrothermal absorption and desorption for underground building envelopes

The hygrothermal storage characteristics of an underground building envelope have discernible effects on the heat and humidity of the indoor environment. To predict the hygrothermal storage capacity, it is necessary to accurately calculate the transient heat and moisture flux through the envelope. This paper describes the development of a new hygrothermal model described with relative humidity and temperature based on the results of existing researches. The moisture model fully states actual moisture transfer process involving both vapor diffusion and liquid water migration in porous building envelopes. Verified using the results calculated by the mathematical model of Mendes et al., the new hygrothermal model can accurately predict the heat and moisture transfer of building envelopes. Hygrothermal absorption and desorption of three types of common underground building envelopes in Chengdu region in China are analyzed by using the new model. The results show that the hygrothermal absorption and desorption of underground building envelopes must be considered when the heat and moisture environment is controlled by HVAC. Taking account of these factors can reduce air-conditioning equipment capacity and save running energy.     

Active thermal insulators: Finite elements modeling and parametric study of thermoelectric modules integrated into a double pane glazing system

Active thermal insulators (ATI) represent a new thermal control technology that uses solar energy to compensate for the passive heat losses or gains in building envelopes. This effect is accomplished by integrating photovoltaic (PV) and thermoelectric (TE) systems into a wall assembly. A parametric study is presented considering the implementation of TE-modules into the air cavity of a double pane glazing system. The main objectives of this study are to explore design configurations that maximize the coefficient of performance (COP) of the TE-heat pump units, and maximize the ability of the system to perform as a heating and cooling system for use in buildings. A finite elements model (FEM) was developed and experimentally validated to calculate the steady-state heat transfer for the ATI-system. A parametric study was undertaken to determine: (i) suitable TE-modules for this application, (ii) the optimal spreading of the TE-heat pumps, and (iii) the composition of the double glazing unit. The results of our study indicate that the system can be properly designed for heating purposes, however, a more optimal design will need to be realized in order to make the approach effective for cooling applications.     

New equipment for testing steady and transient thermal performance of multilayered building envelopes with PCM

Thermal properties of the different building envelopes, such as thermal transmittance in steady state, heat storage capacity and dynamic thermal responses, must be taken into account during the design phase of buildings. The evaluation and measurement of these parameters in multilayered samples are difficult because of the irregular morphology of the used materials and the difficulty in providing the well-controlled environment needed for the measurements. A new equipment has been designed to measure the thermal response and heat capacity of composite walls of different materials simulating real building envelopes.The equipment presented in this paper was used to test the improvement in the thermal response of a building envelope due to the incorporation of PCM. This study is focused on wood structural panels attached to a gypsum board, which is either impregnated or not with PCM. The four edges of the composite sample are properly insulated to ensure one-dimensional heat flow. The two faces of the sample are exposed to controlled environments heated and cooled by copper coils with thermo stated water supplied by water baths. The measured surface heat fluxes at both surfaces of the sample and temperature distribution in the sample provide accurate assessment to thermal mass and dynamic response of the composite wall, while the steady state measurements provide an accurate estimate of its effective thermal transmittance.     

Analysis of the condensation risk on exterior surface of building envelopes

The main sources of moisture on building façades are rain and condensation. Being moisture a prerequisite for the development of microbial growth it is of great interest to identify and analyse the factors responsible for these wetting mechanisms. The development of the microbial vegetation, in addition of being potentially damaging to the building envelope, creates a visual nuisance. This work aims to study the external environment conditions favourable for exterior surface condensation of buildings. The risk for occurrence of surface condensation depends mainly on the surface energy balance and on the moisture content of the ambient air. Because external surface temperature of buildings are very sensitive to convective and radiative exchanges, the investigation has been conducted analysing both convective and radiative heat transfer coefficients for a wide range of scenarios covering different climate sensitivities and building envelope qualities. The analysis has shown that convection and the moisture content of the air play a key role in the occurrence of surface condensations on building façades.     

Climate classifications and building energy use implications in China

Cluster analysis of summer and winter discomfort in terms of heat and cold stresses based on 102-year (1901-2002) weather data in China was conducted. Five bioclimate zones were identified. These were compared with the corresponding thermal and solar zoning classifications. Bio-I and Bio-II tended to locate largely within severe cold and cold climates in the north with excellent solar availability (annual clearness index K_t generally exceeding 0.5). Bio-III and Bio-IV covered mostly the hot summer and cold winter and mild climate zones. Despite the relatively low K_t in winter, passive solar heating should be able to meet a significant proportion of the heating requirements. Bio-V covered the hot summer and warmer winter region, where heat stress and hence cooling requirement dominated. Decreasing trends in the zone-average annual cumulative cold stress during the 102-year period were observed for all five zones. There was, however, no distinct pattern for the heat stress and the changes tended to be more subtle. These indicate that climate change during the 20^th century affected winter discomfort (especially in colder climates in the north) more than the summer discomfort. This could have significant implications for energy use in buildings if such trends persist.     

Criteria for use of groundwater as renewable energy source in geothermal heat pump systems for building heating/cooling purposes

Environmental protection measures are conducted directly by the use of renewable energy sources. The energy development of cities in Europe is aimed at the sustainable use of renewable energy sources in order to achieve the substitution of fossil fuels and the reduction of the hazardous gas emission into the atmosphere. Geothermal resources of medium and low enthalpy in Europe being used for obtaining heat energy are providing about 6600 MW_t, currently having the growth trend of 50 MW_t annually. The use of geothermal low enthalpy, namely of subgeothermal groundwater resources, has even higher annual growth rate, and if such a trend is kept till the year 2010, the produced energy will amount about 8000 MW_t. Criteria of the groundwater use as a hydrogeothermal energy resource in heat pumps are complex, and they deal with aspects of incoming temperatures and groundwater quantities. The precise limit temperature of groundwater that would separate the direct use of geothermal energy (only by the use of heat exchangers), and indirectly by the use of a heat pump has not been determined in the professional and scientific practice of Serbia so far. Taking into account that relatively small number of new flat is being built in Serbia nowadays, if we want to save energy it is necessary to carry out the energy reconstruction of the existing flats whose number is estimated to be more than 2.8 million. By the application of subgeothermal energy and the use of heat pumps, energy consumption would be significantly reduced.     

浅谈对建筑工程中常用之规范条文的认识

本文对建筑工程中常用的规范条文进行剖析，引导工程技术人员在理解应用规范条文时应以概念着手，理性解析，逐步过渡到熟练掌握应用。本文的作用在于试图消除咬文嚼字式的理解方法，消除仅以文字表面的表象化理解方法，理清概念，真正理性的、合理的把握规范条文的实质。     

Effect of building integrated photovoltaics on microclimate of urban canopy layer

Building integrated photovoltaics (BIPV) has potential of becoming the mainstream of renewable energy in the urban environment. BIPV has significant influence on the thermal performance of building envelope and changes radiation energy balance by adding or replacing conventional building elements in urban areas. PTEBU model was developed to evaluate the effect of photovoltaic (PV) system on the microclimate of urban canopy layer. PTEBU model consists of four sub-models: PV thermal model, PV electrical performance model, building energy consumption model, and urban canyon energy budget model. PTEBU model is forced with temperature, wind speed, and solar radiation above the roof level and incorporates detailed data of PV system and urban canyon in Tianjin, China. The simulation results show that PV roof and PV façade with ventilated air gap significantly change the building surface temperature and sensible heat flux density, but the air temperature of urban canyon with PV module varies little compared with the urban canyon of no PV. The PV module also changes the magnitude and pattern of diurnal variation of the storage heat flux and the net radiation for the urban canyon with PV increase slightly. The increase in the PV conversion efficiency not only improves the PV power output, but also reduces the urban canyon air temperature.     

Experimental and numerical investigation on thermal and electrical performance of a building integrated photovoltaic-thermal collector system

An experimentally validated computational fluid dynamics (CFD) model of a novel building integrated photovoltaic-thermal (BIPV/T) collector is studied to determine the effect of active heat recovery on cell efficiency and to determine the effectiveness of the device as a solar hot water heater. Parametric analysis indicates that cell efficiency can be raised by 5.3% and that water temperatures suitable for domestic hot water use are possible. Thermal and combined (thermal plus electrical) efficiencies reach 19% and 34.9%, respectively. A new correlation is developed relating electrical efficiency to collector inlet water temperature, ambient air temperature and insolation that allows cell efficiency to be calculated directly.     

Optimization of the form of a building on an oval base

The aim of this work is to analyze the possibility of optimizing an abstract, symmetrical with respect to the north–south axis form of a building with vertical walls and windows, and constant volume and height. The external south partitions of the building are walls with whole windowpanes. The heat losses through walls, floors, roof and the gain of solar radiation through transparent partitions with respect to their direct correlation with the shape of building form are next taken into consideration. The gain of solar energy for the north part of the building have been disregarded.     

Advancement of solar desiccant cooling system for building use in subtropical Hong Kong

The solar desiccant cooling system (SDCS) had a saving potential of the year-round primary energy consumption as compared to the conventional air-conditioning system for full fresh air application in the subtropical Hong Kong. In order to further enhance its energy efficiency, advancement of the basic SDCS was carried out through a strategy of hybrid design. Six hybrid system alternatives of SDCS were therefore proposed, three for full fresh air design while another three for return air design for the building zone. Year-round performance evaluation of each solar hybrid desiccant cooling system was conducted for typical office application under different climatic and loading conditions. All the six hybrid system alternatives were found technically feasible, with up to 35.2% saving of year-round primary energy consumption against the conventional air-conditioning systems. Among the hybrid alternatives, recommendations were made on the SDCS hybridized with vapour compression refrigeration for full fresh air design; and the SDCS hybridized with vapour absorption refrigeration for return air design, since they had the saving potentials of both primary energy and initial cost. These two hybrid system alternatives used evacuated tubes, a more economical type of solar collectors compared to the PV or PVT panels.     

建筑围护结构传热得热量计算方法的比较

比较了围护结构传热得热量的两种计算方法:周期性反应系数法和传递函数法。与传递函数法相比,周期性反应系数法简化了计算,而且周期性反应系数能反映围护结构对周期性扰量的热响应,可作为评价围护结构热稳定性的指标。推导了传递函数系数与周期性反应系数间的关系式,可根据ASHRAE的数据库RP 626建立典型围护结构周期性反应系数的数据库,从而减少周期性反应系数法的计算量。     

Performance analysis of the building envelope: A case study of the Main Hall,Shinawatra University

The envelope of the Main Hall, Shinawatra University has been designed to provide protection from energy gain. According to initial estimates, the Main Hall could achieve an overall thermal transfer value (OTTV) of 10.16 W/m², which is four times lower than those recommended by the Thai national standard. This study aims to evaluate the actual energy performance of the Main Hall building envelope using field measurements and simulations. The air temperature, surface temperature, and relative humidity were measured at frequent intervals, both indoors and outdoors. Hourly average meteorological data for insolations were utilized in order to calculate the solar gain by light transmission. Based on the empirical data, the energy fluxes through the envelope on eight different orientations were simulated and the average value was found within 7% of the estimated OTTV. Using the same empirical data for the outdoor condition, simulations of other common types of building envelope in Thailand were carried out for comparison. The results of the analysis show that the Main Hall's lightweight and highly insulated building envelope outperforms other commonly used heavyweight envelopes in preventing building energy gain in the hot-humid climate of Thailand. Although the use of the lightweight and highly insulated envelope helps reduce the operating and investment costs of the air conditioning system as well as the cost of building structure, it also increases the investment cost of the envelope substantially. However, the life cycle cost analysis (LCCA) reveals that the life cycle cost (LCC) of the Main Hall envelope is the most economical, and the increased investment cost of the Main Hall envelope requires a discounted payback period of only 3–5 years, depending on the envelope types used in the comparison. Furthermore, it should be noted that greater savings and a more favorable pay back period could be obtained if this highly energy efficient envelope is applied to other typical buildings, especially high-rise structures in urban areas.     

A new approach to compute heat transfer of ground-coupled envelope in building thermal simulation software

This study presents a new approach to compute the heat transfer of ground-coupled envelope quickly and correctly which is suitable for implementation into building thermal simulation software. The heat transfer process is decomposed into three processes which are controlled by ground-coupled envelope surface temperature, outdoor ground surface temperature and the temperature difference of ground-coupled envelope surfaces. The three processes are computed by computing one-dimensional Equivalent Slab, simplifying outdoor temperature as harmonic and computing one-dimensional Extra Partition Wall. Validation indicates that the heat flux of ground-coupled envelope surface computed by the new approach is very close to that computed by Finite Difference Method (FDM) under unsteady boundary conditions. The computing time is much less than that with FDM.