Improving PAQ and comfort conditions in Spanish office buildings with passive climate control

Some researchers have demonstrated that passive moisture transfer between indoor air and hygroscopic structures has the potential to moderate variations of indoor air relative humidity and, thus, to improve comfort and PAQ [Simonson CJ, Salonvaara M, Ojalen T. The effect of structures on indoor humidity-possibility to improve comfort and perceived air quality. Indoor Air 2002; 12: 243–51; Simonson CJ, Salonvaara M, Ojalen T. Improving indoor climate and comfort with wooden structures. Espoo 2001. Technical Research Centre of Finland, VTT Publications 431.200p+app 91p]. The main objective of this study is to show the internal wall coating effect on indoor air conditions and, as a consequence of this, in comfort conditions and PAQ.     

Hygrothermische Wirkungen von Raum‐ und Außenoberflächen

The hygrothermal effect of inside and outside building envelope surfaces. In the past the protection of building constructions under outdoor and indoor climate conditions was one of the most important subjects building physics. Nowadays the energy balance and the hygrothermal performance of building envelopes are current topics. This paper deals with the coupled heat and moisture transfer on the internal and external envelope surfaces. By means of numerical simulation and laboratory investigation the influence of the internal surface of exterior walls on the indoor air humidity is demonstrated. The influence of evaporation cooling on the energy transfer in winter time and during the warm season requires investigations on dewing and driving. It depends on the hygroscopic parameters of the outside wall coating. The effect of infrared reflecting coating is determined. It is shown in which way heat sources integrated in exterior walls could be a possibility to avoid microbiological growth on building envelopes.     

Hygrothermal behavior modeling of the hygroscopic envelopes of buildings: A dynamic co-simulation approach

High levels of humidity in buildings lead to building pathologies. Moisture also has an impact on the indoor air quality and the hygrothermal comfort of the building’s occupants. To better assess these pathologies, it is necessary to take into account the heat and moisture transfer between the building envelope and its indoor ambience. In this work, a new methodology was developed to predict the overall behavior of buildings, which combines two simulation tools: COMSOL Multiphysics© and TRNSYS. The first software is used for the modeling of heat, air and moisture transfer in multilayer porous walls (HAM model: Heat, Air and Moisture transfer), and the second is used to simulate the hygrothermal behavior of the building (BES model: Building Energy Simulation). The combined software applications dynamically solve the mass and energy conservation equations of the two physical models. The HAM-BES coupling efficiency was verified. In this paper, the use of a coupled (HAM-BES) co-simulation for the prediction of the hygrothermal behavior of building envelopes is discussed. Furthermore, the effect of the 2D HAM modeling on relative humidity variations within the building ambience is shown. The results confirm the importance of the HAM modeling in the envelope on the hygrothermal behavior and energy demand of buildings.     

Coupling of thermal mass and natural ventilation in buildings

The coupling of thermal mass and natural ventilation is important to passive building design. Thermal mass can be classified as external thermal mass and internal thermal mass. Due to great diurnal variation of ambient air temperature and solar radiation intensity, heat transfer through building envelopes, which is called external thermal mass, is a complex and unsteady process. Indoor furniture are internal thermal mass, affecting the indoor air temperature through the process of absorbing and releasing heat. In this paper, a heat balance model coupling the external and internal thermal mass, natural ventilation rate and indoor air temperature for naturally ventilated building is developed. In this model, the inner surface temperature of building envelopes is obtained based on the harmonic response method. The effect of external and internal thermal mass on indoor air temperature for six external walls is discussed of different configurations including lightweight and heavy structures with and without external/internal insulation. Based on this model, a simple tool is developed to estimate the indoor air temperature for certain external and internal thermal mass and to determine the internal thermal mass needed to maintain required indoor air temperature for certain external wall for naturally ventilated building.     

Evaluating the effect of building construction periods on household dampness/mold and childhood diseases corresponding to different energy efficiency design requirements

Despite concerns about building dampness and children’ health, few studies have examined the effects of building energy efficiency standards. This study explored the connections between self-reported household dampness and children’ adverse health outcomes across buildings corresponding to construction periods (pre-2001, 2001-2010, post-2010). Significant differences of dampness-related indicators were found between buildings; the prevalence was remarkable in pre-2001 buildings. The prevalence of lifetime-ever doctor-diagnosed diseases for children was significantly associated with building dampness (adjust odd ratios > 1), but was not affected by construction periods. The hygrothermal performance for a typical residence was simulated, varying in U-values of envelopes and air change rates. The simulated performance improvement increased indoor temperatures in 2001-2010 and post-2010 buildings. The frequency with higher indoor relative humidity was higher in pre-2001 buildings, leading to the highest values for maximum mold index (M_max) on wall surface, especially in winter. Compared to buildings in 2001-2010, increased insulation and lower air change rate led to a relatively higher relative humidity in post-2010 buildings, adversely increasing the M_max values. The findings addressed the positive and negative role of building standard development, which help suggesting appropriate environmental and design solutions to trade-off energy savings and dampness/mold risk in residences.     

Transfer function model and frequency domain validation of moisture sorption in air-conditioned buildings

Moisture transfer in building components and furnishings has significant effect on indoor air humidity and latent cooling load. Many mathematical models and calculation methods have been proposed to evaluate this effect. Simple but accurate models are what the users expect. Investigation shows that the one-dimensional linear moisture transfer model, which uses the vapor pressure as the unique driving potential, is both very simple and well match the real moisture transfer characteristics of most air-conditioned buildings. Frequency analysis shows completely consistent characteristics between the transfer function model of moisture sorption by interior surface materials and the one-dimensional linear moisture transfer model through the entire wall within the frequency range that should be concerned. It also shows that the moisture penetration across the wall is neglectable. The transfer function model of moisture sorption by interior surface materials is not only very simple but also has satisfactory accuracy to evaluate the moisture transfer effect of buildings on indoor air humidity and latent cooling load.     

浅埋工程围护结构全年动态传热计算

浅埋地下工程围护结构三维非稳态传热由于受到工程埋深、几何型式、室外气象参数、室内周期性变化空气以及围护结构热特性参数等的影响而显得尤为复杂。将室内空气对围护结构传热的影响综合考虑，基于FLUENT商业软件采用耦合传热计算方法对三维非稳态传热进行数值求解。通过这一方法可以得到围护结构全年动态传热量，并可反求室内空气与围护结构的对流换热系数。     

近零能耗建筑中相变建筑材料的研究进展

近零能耗建筑是采用被动式建筑设计和主动式节能技术、以最低的能源设备功耗获得舒适室内环境的建筑.相变建筑材料的使用可以提高建筑围护结构的热惰性,减少室内温度的波动,降低供暖、空调设备的容量,同时能与太阳能、空气能等可再生能源相结合,降低建筑设备能耗.从不同围护结构的角度介绍了相变建筑材料的分类与特点,综述了国内外相变围护...     

Reducing energy peak consumption with passive climate control methods

In recent years, European electrical consumption in buildings is experiencing a marked increase, rising to values above design conditions. Consequently, power cuts occur in different periods, such as during the early morning hours in winter and the last hours of occupation in summer. To solve this problem, passive methods could help to reduce energy peaks. Specifically, internal wall coverings were applied to define the moisture-buffering capacity of permeable coverings in indoor air. These permeable coverings improved the indoor partial vapour pressure and, as a result, the ambience acceptability and local thermal comfort, despite the use of an air barrier and less permeable coverings, when compared with other authors. The daily periods in which internal coverings work are clearly defined, and give us an understanding of the peak energy consumption at different times. In particular, peak reductions of 20% and 4% in the energy consumption for indoor air conditioning, respectively during the summer and winter seasons, were obtained with permeable coverings. Permeable coverings have been demonstrated to be an effective solution as a passive control method for indoor air conditions, especially in the summer season and, consequently, are an energy saving technique.     

Modelling of heat and moisture transfer in buildings: I. Model program

The overall objective of this work is to develop an accurate model for predicting heat and moisture transfer in buildings including building envelopes and indoor air. The model is based on the fundamental thermodynamic relations. Darcy’s law, Fick’s law and Fourier’s law are used in describing the transfer equations. The resultant nonlinear system of partial differential equations is discretised in space by the finite element method. The time marching scheme, Crank–Nicolson scheme, is used to advance the solution in time. The final numerical solution provides transient temperature and moisture distributions in building envelopes as well as temperature and moisture content for building’s indoor air subject to outdoor weather conditions described as temperature, relative humidity, solar radiation and wind speed. A series measurements were conducted in order to investigate the model performance. The simulated values were compared against the actual measured values. A good agreement was obtained.     

A new virtual sphere method for estimating the role of thermal mass in natural ventilated buildings

The role of thermal mass is very important in natural ventilated buildings. Thermal mass can be classified as external thermal mass and internal thermal mass. In this paper, a heat balance model for naturally ventilated building is developed. The effect of external thermal mass is introduced by harmonic response method, and the effect of internal thermal mass is calculated by virtual sphere method which can lump different shapes and types into one virtual sphere. The effective convection heat transfer coefficient is presented to represents the effect of uneven distribution of internal thermal mass temperature. Through comparison with Li's model [1] and numerical calculation, it was found that the model is more suitable than the others, especially in estimating decrement factor of indoor air temperature. The errors of time lag become smaller when the fluctuation of indoor air temperature is smaller. Based on the model, a simple tool is developed to evaluate the indoor air temperature and required internal thermal mass for certain naturally ventilated buildings.     

Auswirkungen der Baurestfeuchte auf Innenklima und Holzfeuchte bei Holz‐Mischbauweisen

Effects of the build‐in‐moisture on indoor climate and wood moisture of timber mixed construction Within the scope of the competence center “wood technology” the Holzforschung Austria deals with the combination of prefabricated timber elements in the building shell with concrete construction parts for high rise buildings. In addition to the design of construction details a one‐zone model has been created – in close collaboration with the Technical University of Vienna – to analyze the effects of residual humidity on the internal climate and on the moisture content of the timber elements. The simulated drying properties of the concrete elements are consistent with the results of the analysis of the Verein der Österreichischen Zementfabrikanten in matters of drying time and change of moisture content. In addition to the variation of the beginning and progress of construction work and the behavior of air conditioning three different exterior wall constructions – one timber frame construction with OSB and one with PE as vapour barrier and a construction with solid timber boards without vapour barrier have been analysed.     

Increasing the indoor humidity levels in buildings with ventilation systems: Simulation aided design in case of passive houses

In modern societies, people spend about 90 percent of their time inside buildings. The challenge of building physics is to ensure that buildings are planned, constructed and built to provide a comfortable and healthy working and living environment. As construction style has changed during recent years, the planning phase has to be much more precise and the need of simulation programs that respond to every little change arises. An increasing problem in Austria is the indoor humidity. In the field of renovated buildings with airtight new building envelopes, mould growth due to high indoor relative humidity (RH) is a persistent problem. On the other hand, in recently realized Austrian passive houses with an air treatment system, the low humidity level of the indoor air is a problem with which scientists have been struggling for some time. It has been observed in numerous measurements and it is also easily computationally detectable that in winter period the indoor relative humidity level often drops below 30% RH. Low and high relative humidity levels have negative effects on the comfort feeling and health of the occupants of the dwelling and should therefore be avoided. However, it is expensive to increase or decrease the humidity in houses mechanically. Therefore, the existing room moisture should be used sensibly in buildings with a ventilation system. In buildings with a high indoor humidity it is necessary to adjust the ventilation depended on moisture production. This paper focuses on low indoor humidity and presents some different methods by which the indoor relative humidity can be regulated. The effects of adapting parameters such as ventilation rate and buffering material in the dwelling were clearly reflected in the measured temperature and relative humidity. “BuildOpt_VIE” software developed at the Vienna University of Technology was used for the dynamic building simulation in this study.     

Moisture buffering capacity of hygroscopic building materials: Experimental facilities and energy impact

Research into dynamic moisture storage in hygroscopic building materials has renewed interest in the moisture buffering capacity of building materials and shown the potential for these materials to improve indoor humidity, thermal comfort and indoor air quality in buildings. This paper complements previous research by estimating the effect of hygroscopic materials on energy consumptions in buildings. The results show that it may be possible to reduce heating and cooling energy consumption by up to 5% and 30%, respectively, when applying hygroscopic materials with well-controlled HVAC systems. The paper also describes two different experimental facilities that can be used to measure accurately the moisture buffering capacity of hygroscopic building materials. These facilities provide different convective transfer coefficients between the hygroscopic material and ambient air, ranging from natural convection in small, sealed jars to fully developed laminar and turbulent forced convection. The paper presents a numerical model and property data for spruce plywood which will be used in a companion paper [O.F. Osanyintola, P. Talukdar, C.J. Simonson, Effect of initial conditions, boundary conditions and thickness on the moisture buffering capacity of spruce plywood, Energy and Buildings (2006), doi:10.1016/j.enbuild.2006.03.024.] to provide additional insight into the design of an experiment to measure the moisture buffering capacity of hygroscopic materials.     

Investigation of air quality,comfort parameters and effectiveness for two floor-level air supply systems in classrooms

The method of distributing the outdoor air in classrooms has a major impact on indoor air quality and thermal comfort of pupils. In a previous study, ([11] Karimipanah T, Sandberg M, Awbi HB. A comparative study of different air distribution systems in a classroom. In: Proceedings of Roomvent 2000, vol. II, Reading, UK, 2000. p. 1013–18; [13] Karimipanah T, Sandberg M, Awbi HB, Blomqvist C. Effectiveness of confluent jets ventilation system for classrooms. In: Idoor Air 2005, Beijing, China, 2005 (to be presented).) presented results for four and two types of air distribution systems tested in a purpose built classroom with simulated occupancy as well as computational fluid dynamics (CFD) modelling.     

Five-year data of measured weather,energy consumption,and time-dependent temperature variations within different exterior wall structures

This paper presents coherent 5-year measured data that have been gathered for analyses of building energy consumption and thermal performance of exterior walls. The data is also very suitable for calculations and simulations of heating and cooling energy need of buildings. The data was collected from six identical test buildings, having exterior walls that are constructed of different building materials. The data include the following: indoor–outdoors temperatures; temperatures at various depths within the northern, southern, eastern, and western exterior wall facades; indoor–outdoors relative humidity, heating energy, wind speed and direction; air tightness, infiltration, and horizontal global solar radiation. A computer system (data logger) was used to monitor, check, calculate, integrate, and save the data acquired from approximately 520 sensors in each test building. Measurements were taken with a time interval of 20 s. The 20 s values were then integrated over a time interval of 30 min and the minimum, maximum, and mean values were subsequently stored to a computer database. Analyses of the results indicated that temperatures within the buildings’ exterior walls are constantly changing and, that occasionally the flow of conduction heat is reversed (i.e. outside–inside) due to solar radiation. For accurate results of temperature distribution and the actual heat losses through building envelopes, none steady-state calculations are essential. Depending on the intensity of solar radiation and the material characteristics of the walls, temperature gradient at the inner surfaces of exterior walls may become milder compared to that of the outer surfaces.     

Moisture performance of building materials: From material characterization to building simulation using the Moisture Buffer Value concept

Predicting the indoor air relative humidity evolution is of great importance to evaluate people thermal comfort, perceived air quality and energy consumption. In building environments, porous materials of the envelope and furniture act on the indoor air humidity by reducing its variations. Solving the physical processes involved inside the porous materials requires the knowledge of the material hygrothermal properties that needs multiple and, for some of them, time-consuming experimental procedures. Recently, both the NORDTEST Project and Japanese Industrial Standard described a new Moisture Buffer Capacity index that accounts for surrounding air vapor concentration variation. The Moisture Buffer Value (MBV) indicates the amount of water vapor that is transported in or out of a material, during a certain period of time, when the vapor concentration of the surrounding air varies. The MBV evaluation requires only one experimental procedure and its value permits a direct comparison of the building materials moisture performance. However, two limitations can be distinguished: first, no relation between the MBV and the usual material hygrothermal properties has been clearly identified and second, no model has been proposed to actually use the MBV in building simulation. The present study aims to solve these two problems. First, the MBV fundamentals are introduced and discussed; followed by its relation with the usual material properties. Then, a lumped model for building simulation, whose parameters can be determined from the MBV experimental procedure, is described. To finish, examples of the use of this MBV-based lumped model for moisture prediction in buildings are presented.     

In situ measuring and evaluating the thermal resistance of building construction

This paper introduces an in situ measuring method for the thermal resistance of buildings, including the test chamber, measuring points’ arrangement, and measurement results, in Nanjing during 2000 and 2001. Three methods for the analysis of in situ data are also presented to determine the thermal resistance of buildings although the R-values evaluated by these methods have smaller values than those of design due to the limitation of field conditions. The synthetic temperature method only requires measuring the heat flow rate on the inside surface of the building construction and both the synthetic indoor and outdoor temperatures. And the surface temperature method just requires testing the heat flow rate on the inside surface of building envelopes and both the inside and outside surface temperatures of building construction. However, the frequency response method introduced in this paper only relates to the mean synthetic indoor and outdoor temperatures and the average inside surface temperatures of the building envelopes. In other words, it is not involved with the heat flow rate, which is difficult to measure. Thus, on this point, the frequency response method is better than the other two methods to evaluate the in situ R-value of buildings.     

Outdoor Air Contaminants and Indoor Air Quality under Transient Conditions

The indoor concentrations of contaminants originating from outdoor sources have been measured and calculated under transient conditions. The results show that contaminants that are supplied to an office building via the ventilation system can reach considerably high concentration levels. The indoor/outdoor concentration ratio and time lag are dependent on the air change rate. In buildings with low air change rates the indoor concentration variations are smoothed out compared to buildings with high air change rates. The results from the theoretical model are compared to the results from both laboratory and field measurements and the model is verified for well mixed conditions in a 20 m³ test chamber. The model can be used to simulate different control strategies for reduction of indoor contaminant concentrations related to outdoor sources. One such control strategy is based on reduction of the outdoor air change rate during periods with peak outdoor contaminant concentrations.     

Transient analysis of an external building cladding

Energy performances and building quality can be achieved by high performance envelopes. In this paper the thermal and mechanical performances of external cladding, applied to a traditional wall, largely used in existing buildings, were investigated by a transient simulation. Result comparison with the thermal performances obtained by simulating the wall without the insulation system showed that external insulation is particularly effective in reducing cooling and heating loads and can also guarantee indoor thermal comfort. Fatigue stresses of the external cladding, investigated by ANSYS simulation, showed that continuous change of the loads over time with limited cyclic stress can cause deterioration of materials.