# Building Simulation

Online ISSN: 1996-8744
Print ISSN: 1996-3599
Publications
According to the Intergovernmental Panel on Climate Change the buildings sector has the largest mitigation potential for CO2 emissions. Especially in office buildings, where internal heat loads and a relatively high occupant density occur at the same time with solar heat gains, overheating has become a common problem. In Europe the adaptive thermal comfort model according to EN 15251 provides a method to evaluate thermal comfort in naturally ventilated buildings. However, especially in the context of the climate change and the occurrence of heat waves within the last decade, the question arises, how thermal comfort can be maintained without additional cooling, especially in warm climates. In this paper a parametric study for a typical cellular naturally ventilated office room has been conducted, using the building simulation software EnergyPlus. It is based on the Mediterranean climate of Athens, Greece. Adaptive thermal comfort is evaluated according to EN 15251. Variations refer to different building design priorities, and they consider the variability of occupant behaviour and internal heat loads by using an ideal and worst case scenario. The influence of heat waves is considered by comparing measured temperatures for an average and an exceptionally hot year within the last decade. Since the use of building controls for shading affects thermal as well as visual comfort, daylighting and view are evaluated as well. Conclusions are drawn regarding the influence and interaction of building design, occupants and heat waves on comfort and greenhouse gas emissions in naturally ventilated offices, and related optimisation potential. Keywordsbuilding design-occupant behaviour-heat waves-greenhouse gas emissions-EN 15251 adaptive thermal comfort-visual comfort

The continuous process of urban transformation, as well as the changes that take place within the built environments themselves, interfere in the ventilation dynamic. This happened to Vila 37 - in Rio de Janeiro city - where the houses had to grow vertically, and were consequently swallowed by other urban volumes. Aiming to analyze the changes that took place in these confined ventilation spaces, house number VI was evaluated. Simulations using wind-capture was carried out in an attempt to increase and promote better ventilation. The analysis starts by solving the air circulation problem to determine the wind fields by using a mixed stabilized finite element method that is applied to the full Navier-Stokes equations. The computational simulation results of the original situation were compared with the results of the new scenario. The computational results suggest that the use of these strategies presents a good potential to provide ventilation with low environmental and economic costs. Keywordssustainable solutions-natural ventilation-computational modeling-wind-capture-finite element method

Three dimensional mixed convection in an ice rink heated by radiant heaters was simulated numerically using the standard k-ε model with wall functions. This large building was first modelled under steady state conditions by considering or not surface-to-surface radiation between the internal surfaces and with the radiant heaters ON or OFF. After those four basic scenarios the transient behaviour was modelled by considering that the radiant heaters are thermostatically controlled. Results indicate the usefulness of the computational fluid dynamic (CFD) technique as a powerful tool which provides a detailed description of the flow and temperature fields as well as the heat fluxes into the ice. The most important results are: The agreement between calculated values and some measured values is fairly good. The velocity and temperature distributions are definitely three-dimensional. In a large part of the ice rink the air is essentially stagnant and significant air velocities can only be found above the spectator stands and near the ceiling above the ice; analogously, significant turbulent kinetic energy is found only in these same regions. The radiant heat flux into the ice is significantly higher than the convective one. When the radiant heaters are turned ON the temperatures of the inside surfaces of the building envelope and of the air increase; as a result, the heat flux reaching the ice increases significantly.

The present article reports on a ventilation system that uses impinging air jets to remove a portion of the heat generated in DC/AC converter towers. Each tower is a vertical stack of electronic components used in the power conversion. Airflow from the ventilation system enters the room through inlet ports located on the ground at two opposite sides of the DC/AC converter towers. The existing ventilation system circulates sufficient airflow in terms of the total heating load; however, elevated temperatures were reported within the towers due to poor air circulation. A numerical study has been conducted to investigate steady three-dimensional (3-D) turbulent mixed (combined free and forced) convection air cooling of vertical stacks of heat-generating blocks simulating typical towers in two valve halls of a DC/AC power converter station. The simulation results include the magnitudes of the net airflows for all the inter-block gaps, the maximum temperature in each gap, and the flow structure represented by streamlines at various locations of the 3-D domain. The location of the inlet, the inlet size and aspect ratio, and the location on the tower at which the airflow was aimed were varied parametrically to improve the ventilation relative to the existing design. These results demonstrate that, for fixed inlet mass flow rate, all the towers’ heat generating surfaces can be kept under 60°C via simple modifications of the variables used in the parametric study. Keywordsthree dimensional-turbulent mixed convection-enhanced ventilation-DC/AC power converter station

This paper presents the results of a number of case studies concerning measurement and simulation of room acoustical parameters in both historical and contemporary instances of bath spaces. Historical instances of such spaces are, in our study, traditional hammam (bath) buildings in Mediterranean and north-African countries (Algeria, Morocco, Syria). Modern instances include a modern hammam, a spa, and an indoor swimming pool in central Europe (Austria). The analysis is based on data obtained from measurements and simulations of pertinent indicators of room acoustic quality in such spaces. The results of the analysis permit the identification of certain salient features of room acoustics in highly humid spaces and corresponding technical challenges (e.g., excessive reverberation and high noise exposure). Moreover, the results allow for the statistically grounded estimation of uncertainties in simulation of room acoustics in architectural spaces.

Ventilation provides a more comfortable thermal environment for occupants inside of buildings. The growing demand for electricity has encouraged research focused on natural ventilation. In this study, we analyze the thermal comfort in an office room with varied window opening dimensions using the computational fluid dynamics (CFD) technique. We created a 3-dimensional model room with windows on adjacent walls and an atmospheric zone. The flow equations were solved using the control volume method. Steady k-ɛ turbulence model and incompressible fluid flow of constant property have been considered, neglecting the variation due to temperature. We examined the effects of the window openings’ area and aspect ratio on thermal comfort. The CFD code was compared with the network model and its discrepancy value was less than 8%. Air temperatures along the various midlines of the room were predicted and compared for a range of window sizes. We identified the room areas occupied by the low temperature zone at various planes. Finally, we determined the predicted mean vote (PMV) contours at the midplane to identify the comfort zone. Areas other than the room corners and the areas nearest to the windowless walls are identified as the most comfort zone. Results from this study indicate the optimum window opening area and aspect ratio for maintaining thermal comfort in an office room.

Field test results show that about 15% to 40% of building heat loss in China is attributable to poor heating systems regulation. The current method for addressing this problem is to install thermostatic radiator valves (TRVs) to the ends of radiators, a method adapted from northern Europe. However, this method has resulted in poor performance from delayed controlling action due to thermal inertia as well as insufficient system control accuracy. This is further compounded by incorrect operation by system users and a lack of financial incentives to regulate the system if users are not billed for their heat consumption. We present a new method for simultaneously heat controlling and metering. The core challenge is to design a control strategy that will maintain the room’s temperature. Thus, we established dynamic heat transfer models for water flow, the radiator and the building so as to obtain the optimal heating strategy. We also simulated the indoor thermal dynamic performance of the heating system with different heating loads, supply water temperatures, and supply water flow rates using three methods: a continuously changing flow rate (Method 1), a step-change flow rate based on temperature deviation (Method 2) and an intelligent step-change flow rate (Method 3) which predicts the duty cycle of the valve in the proceeding period and controls the valve’s on-time. The simulation results indicate the performance of these three methods. For Method 1, as the room temperature is above the set point, the flow rate can be automatically reduced to a level which is proportional to the room temperature deviation. Further, the scale factor of the flow rate is designed according to the +2°C deviation, so it is accepted that the room temperature is higher than the set point by +2°C using this method. However, this low control precision is unsatisfactory. The mean temperature is higher than the set point and greatly affected by the heating load and supply water’s temperature and flow rate. For Method 2, the controlling action is delayed by thermal inertia, the room temperature fluctuates between the highest and lowest levels, and the temperature deviation can be greater than the set value. For Method 3, both the simulation and field test results showed that room temperature deviation was maintained within a ±0.5°C range under the various conditions. This method appears relatively robust and adaptable, and was the best control strategy of the three methods.

The aim of the paper is to present a framework for the optimal control of natural ventilation. To account for the significant crossflow between zones, the notion of ASHRAE-equivalent airflow is proposed which is used to evaluate the quality of ventilation provided to different zones within a building. A model-based predictive control approach is developed which is used to simulate different ventilation strategies and select the most appropriate strategy. To this end, the rationale behind choosing an objective function that captures the goals of a ventilation system is described, and candidate objective functions are discussed. Finally, an illustrative example with an elliptical cross-section building is discussed in detail. The framework for model-predictive control developed in this paper is applicable beyond natural ventilation and high-rise buildings. Keywordsnatural ventilation-control strategy-objective function-ASHRAE-equivalent airflow

The thermal performance of an affordable energy-efficient single-story residential building designated as Tuskegee Healthy House (THH) was simulated by developing a computational model for the house using Visual DOE-4 commercial software. Visual DOE-4 package employs the same calculation engine of the proven DOE-2 building Energy Analysis program. The THH was built from conventional building materials and construction methods according to the southern building codes of the United States. Several energy efficiency and air quality control features were incorporated throughout the THH. The present model was validated by comparison of computed results with power consumption data available from a previous study of the same house. The experimental data were obtained for forced ventilation flow rates of 0, 28.3 L/s and 54.3 L/s. A favorable agreement between the model predictions and experimental data is observed which is indicative of the model’s accuracy. The simulations also show that the heating, ventilation, and air conditioning (HVAC) energy requirement for THH is reduced when forced ventilation is increased during the summer months. However, ventilation during the winter months leads to a rise in THH energy requirement. KeywordsVisual DOE–building simulation–thermal performance–energy efficient

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.

This paper presents findings from a study of the impact of indoor thermal conditions on the productivity of office workers in Thailand. The experiment simulating office working conditions was carried out with a completely randomized design under a variety of indoor thermal conditions over different time periods. In the experiment, subjects performed five simulated tasks: calculation, typing, proof-reading, simple quick reaction, and concentration-needed reaction. Normalized changes in worker productivity associated with those five tasks were measured and analyzed using the analysis of variance technique. In this study, the ranges of thermal conditions resulting in the greatest productivity were calculated by the predicted mean votes (PMVs). The results of this study suggest that the general appropriate PMV value recommended by ISO 7730 is suitable for Thais only in afternoon and evening periods. In addition, it was found that a satisfactory thermal comfort condition for office workers can be achieved by setting the temperatures of air-conditioning systems at 26 °C–28 °C for morning periods and at 24.5 °C–26 °C for afternoon and evening periods. These ranges of temperature settings help maintain and improve the productivity of office workers during morning, afternoon, and evening periods by 18%, 1% to 15%, and 7%, respectively. Keywordsproductivity-thermal condition-predicted mean vote (PMV)-office work simulation-energy conservation-design of experiment

University cafeteria is a kind of building with unique characteristics: there are lots of people dining besides the large cooking area. It is of great importance to study the impact of the cooking generated contaminants on the indoor air quality in the cafeteria since cooking is regarded as the main source of indoor contaminants. This study presents the particulate matter (PM) concentrations measured in three different university cafeterias followed by a series of cases studied with CFD and multizone model simulation. Based on the results, the possible strategies to tackle the indoor air quality (IAQ) problem due to cooking are discussed. It is concluded that using up exhaust, setting up partition between cooking area with other zones and adding scuttles are helpful to reduce the cooking generated particle pollution in the cafeterias. Keywordsindoor air quality (IAQ)-ventilation-particulate matter (PM)-simulation-university cafeteria

The paper presents the setpoint control for air heating in a church to minimize moisture related mechanical stress in wooden interior parts, with the focus on the preservation of a monumental organ. The setpoint operation of the heating, ventilation, and air conditioning (HVAC) system is evaluated by simulation using MatLab, COMSOL and Simulink models. The main model components are presented and combined in a single integrated Simulink model: (1) a HAMBase Simulink building model for simulating the indoor temperature and relative humidity, (2) a COMSOL partial differential equation model for simulating detailed dynamic moisture transport and related mechanical stresses in the monumental wood (organ) and (3) a Simulink controller model. The main advantage of the integrated model is that it directly simulates the impact of HVAC control setpoint strategies on the indoor climate and the related mechanical stresses in wooden objects, like a monumental organ. As control strategy the limited indoor air temperature changing rate is discussed. Recommendations from international literature suggest that a limitation of the relative humidity changing rate of 2 to 5RH%/h will preserve the interior of churches. This study shows that a limitation of indoor air relative humidity changing rate of 2RH%/h can reduce mechanical stresses by a factor of 2.5, compared to maximum capacity heating. Keywordsheating–church–organ–wood–stress–simulation

Humidity of indoor air is an important factor influencing the air quality and energy consumption of buildings as well as durability of building components. Indoor humidity depends on several factors, such as moisture sources, air change, sorption in materials and possible condensation. Since all these phenomena are strongly dependent on each other, numerical predictions of indoor humidity need to be integrated into combined heat and airflow simulation tools. The purpose of a recent international collaborative project, IEA ECBCS Annex 41, has been to advance development in modelling the integral heat, air and moisture transfer processes that take place in “whole buildings” by considering all relevant parts of its constituents. It is believed that full understanding of these processes for the whole building is absolutely crucial for future energy optimization of buildings, as this cannot take place without a coherent and complete description of all hygrothermal processes. This paper will illustrate some of the modelling work that has taken place within the project and present some of the simulation tools used.

This paper presents a new concept in energy-saving equipment, namely, a regional air-conditioning mechanism (RACM). The RACM system is constructed with an inlet and an outlet in a main duct centered in a cylindrical housing. The RACM produces an airflow circulation cell for satisfying the thermal comfort demands of users, and can potentially be energy-saving. This study targets two areas: (1) study the effect of cool air inlet velocity (V inlet), negative outlet pressure (P out), and distance between floor surface and outlet port (L 2) of an airflow circulation cell, and (2) determine their suitable adjustments for creating a better method for using computational fluid dynamics (CFD). Experimental platforms were set up to test the validity of a simulation model, and the tested results showed good agreement with simulation. In the study, nine simulated case studies divided into three groups with various values of V inlet, P out, and L 2 were analyzed. Case four of group two, V inlet = 0.3 m/s, P out = −2 Pa, and L 2 = 0.5 m, yielded the lowest energy consumption and the highest level of thermal comfort demands. Group one, in which P out, and L 2 were fixed for all case studies, except values of V inlet, resulted in the most sensitive in terms of vertical temperature distribution along the body of a sedentary occupant in the room. The two thermal regions of the tested environment, i.e., occupied zone and the rest of the room, evidently experienced different temperatures in the simulated room. It was concluded that the RACM is a potential candidate for portable air-conditioning in enclosed spaces. Keywordssimulation analysis-energy-saving-regional air-conditioning-thermal comfort demands-airflow circulation cell

This article introduces a liquid desiccant fresh air processor. Its driving force is low-grade heat (heat obtained from 65 – 75°C hot water). Inside the processor, the air is dehumidified by the evaporative cooling energy of the indoor exhaust air. A four-stage structure is used to increase the efficiency of the combined sensible and latent heat recovery from the exhaust air. A mathematical model of the fresh air processor was set up using Simulink®. A liquid desiccant fresh air processor was constructed and tested for outside air conditions of 29.1 – 33.6°C, 13.7 – 16.7g/kg humidity ratio, and supply air conditions of 23.6 – 24.2°C, 7.4 – 8.6g/kg humidity ratio. The average measured COP f was 1.6 (cold production divided by latent heat removed) for the range of conditions tested. The corresponding average COP sys of the system including the regenerator was 1.3 (cold production divided by heat input). The detailed operating parameters of each part of the test unit were also measured. The test data was compared with the simulated performance. The characteristic coefficients (such as the volumetric mass transfer coefficient of the air-water evaporative cooling module, etc.) in the mathematical model were modified to calibrate the model output to the measured data. The calibrated simulation model was used to investigate the control strategy of the fresh air processor. The flow rate of the strong solution into the unit and the number of operation stages may be controlled separately or together to meet different indoor air requirements at different outdoor conditions. The hot water driven liquid desiccant air conditioning system was compared with a typical vapor compression system with an average COP of 4.5; the pump and fan power of the proposed system was 40% of the combined chiller, pump, and fan consumption. We achieved savings of over 30% of the power consumption compared with the traditional system under the designed outdoor air conditions.

This paper presents an overview of the development and evaluation of integrated heat, air and moisture modeling using the SimuLink/COMSOL simulation environment for simulating dynamic heat, air and moisture processes in buildings and systems. Most of the models are successfully verified (by analytical solutions or by comparison with other simulation results) and/or validated (by experimental data). Overall it is concluded that the SimuLink/COMSOL simulation environment is capable of solving a large range of integrated heat, air and moisture problems. Furthermore, it seems promising in accurately solving modeling problems that are caused by the presence of different time scales and/or lumped/distributed parameters.

A full-scale test room is used to investigate experimentally and numerically the velocity and temperature fields in the case of a mechanical ventilation. Detailed fields are measured for three cases of ventilation air temperature: an isothermal case, a hot case, and a cold case. The experimental data are used to test two turbulence models: a first order k-ε realizable turbulence model and a second order quadratic RSM (Reynolds Stress Model) turbulence model. The RSM model predicts the temperature and velocity fields better than the k-ε turbulence model. In particular, global values of velocity and temperature coming from experiments are in good agreement with the RSM turbulence model. This conclusion is confirmed using a turbulence analysis based on Lumley triangles. Keywordsbuilding room–full-scale experiment–CFD–ventilation–turbulence models

The heat generated from an air-conditioning equipment or other thermal loads is distributed throughout a room by a three-dimensional airflow. This three-dimensional airflow creates a three-dimensional heat distribution in a room. To better understand building performance, we must integrate this spatial distribution into building simulations. Thus, three-dimensional computational fluid dynamics (CFD) analysis is necessary in design process because most conventional building energy simulations still employ a temperature that is averaged across the space of a room. However, usually only a few cases of CFD analyses are executable in real design process because of the large computational load they require. This paper presents a new, simplified method to calculate heat transport phenomena in rooms, based on a few cases of CFD analysis, and to integrate data into a nodal analysis. This method can be used to calculate an indoor environment, including the spatial distribution of temperature, with a computational load that is much lighter than it is in a simulation using CFD alone. Furthermore, in terms of precision, it is a far more reliable method than the conventional simulation, which assumes the perfect mixing of heat in a room. In the paper, we apply this method to simulate the control of air conditioning. Ordinarily, the reproduction of the phenomena shown in the calculation examples requires substantial manpower and costly computing resources for experimentation or CFD analysis. With our calculation method, it is possible to reproduce the same calculation results in a very short time with a PC. And we checked the potential to the practical use through a verification calculation with CFD analysis. Keywordsresponse factor-CFD-temperature distribution-air-conditioning control-thermal environment

Use of a HEPA (high efficiency particulate air) filter in a room is believed to assist in reducing the risk of transmission of infectious diseases through removing the particles or large droplets to which pathogens may be attached. Use of a portable HEPA filter(s) in hospital wards is hypothesized to increase the effective ventilation rate (for particles only). Use of a portable HEPA filter is also hypothesized to increase the effective airflow rate of the general ward to the standard of an isolation ward for emerging infection diseases. This may be a good solution for housing patients when the number of beds in an isolation ward is insufficient. An experiment was conducted in a full scale experimental ward with a dimension of 6.7 m × 6 m × 2.7 m and 6 beds to test these hypotheses for a portable HEPA filter. The removal efficiency for different size particles was measured at different locations. The influence of the portable HEPA air cleaner on the airflow pattern was also studied through smoke visualization and computational fluid dynamics (CFD) simulations. Results show that the HEPA filter can effectively decrease the particle concentration level. The effective air change rate achieved by the HEPA filter (for particle removal only) is from 2.7 to 5.6 ACH in the ward. The strong supply air jet from the portable HEPA filter interacted with the room airflow pattern and became dominate, introducing global airflow mixing in the room. Background noise levels were also measured and noise level in the room increased when the maximum airflow of the filter was used. Keywordsparticle-portable HEPA filter-hospital ward

The assessment of building thermal comfort quality in the Mediterranean context necessitates detailed information concerning local air speed and temperature inside the space. We have extended the three-dimensional zonal model ZAER (Zonal AERial model) to enable predictions of air flow pattern and thermal distributions between and within rooms. Numerical simulations from the new program have been compared with data obtained from measurements on the experimental cell Minibat (CETHIL, INSA Lyon laboratory) and with the prediction of another zonal model as well as a computational fluid dynamics (CFD) tool. The comparison indicates that this new program is an effective model for predicting air flow and temperature distribution in a partitioned building. By coupling ZAER with a thermal comfort model, we study the influence of a passive solar component belonging to a south-oriented room upon the winter thermal comfort of an unconditioned Tunisian dwelling. The obtained results show that this simulation tool has the potential to describe realistically the thermal comfort within a dwelling, and that a Trombe wall can be a useful heating component to improve thermal winter comfort in the Tunisian context, even in another room.

Building indoor air quality (IAQ) has received growing attentions lately because of the extended time people spend indoors and the increasing reports of health problems related to poor indoor environments. Recent alarms to potential terrorist attacks with airborne chemical and biological agents (CBA) have further highlighted the research needs on building vulnerability and protection. To maintain a healthful and safe indoor environment, it is crucial to identify contaminant source locations, strengths, and release histories. Accurate and prompt identification of contaminant sources can ensure that the contaminant sources can be quickly removed and contaminated spaces can be effectively isolated and cleaned. This paper introduces a probability concept based prediction method—the adjoint probability method-that can track potential indoor airborne contaminant sources with limited sensor outputs. The paper describes the principles of the method and presents the general modeling algorithm and procedure that can be implemented with current computational fluid dynamics (CFD) or multi-zone airflow models. The study demonstrates the application of the method for identifying airborne pollutant source locations in two realistic indoor environments with few sensor measurement outputs. The numerical simulations verify the feasibility and accuracy of the method for indoor pollutant tracking applications, which forms a good foundation for developing an intelligent and integrated indoor environment management system that can promptly respond to indoor pollution episodes with effective detection, analysis, and control.

In an effort to improve building energy and indoor air quality models, relations to describe the airflow characteristics of back-draft dampers were determined. In particular, two equations were developed to represent the relationship between pressure drop and airflow rate for one-blade and multi-blade back-draft dampers. The equation for multi-blade dampers was validated by comparing the predicted results with available Air Movement and Control Association (AMCA) 500-D test data. The results showed that these two equations can be used to model the airflow characteristics of back-draft dampers. Keywordsback-draft damper-building modeling-airflow characteristics-pressure drop-airflow rate

There is a wide variety of thermal analyses that can be used to characterize the thermal behavior of a wall under certain outdoor conditions. The selection of a particular wall configuration for a building project involves not only the outdoor climate, but also the whole building characteristics, orientation, percentage of glazed areas, occupation periods, lifestyles, etc. In this paper we apply common available methods for wall thermal analysis to two particular wall types, a massive brick wall and an insulated brick wall, in order to compare the information given by each method and to evaluate how these methods can help in the selection of a certain type of wall. The studied methods include the estimation of the wall time lag and decrement factor, the harmonically heated slab model, the Athanassouli’s method, and numerical simulations. The study was performed for the walls of a residence for university students and it was built in La Pampa (Argentina). Once the building was finished, the transient thermal behavior of two walls was monitored during one summer week. The experimental results are presented and the fitting with the thermal behavior predicted by each method is discussed. The thermal comfort indicators PMV (predicted mean vote) and PPD (predicted percentage of dissatisfied) were calculated for two flats, at ground floor and first floor respectively.

Most thermal properties of construction materials used in the analysis of building performance have been measured under laboratory conditions, using a guarded hot box or hot plate apparatus. As a consequence, these properties seldom reflect the impact of actual conditions (especially moisture content) on the values of thermal conductivity and diffusivity. Hence there is a need to develop techniques that take into account local conditions, and measure building material properties in situ. One option available is the use of a thermal probe. The thermal probe technique is based on creating a line source in a material sample and measuring the temperature rise in the sample in reaction to heat being applied. Obviously the data analysis routines used to calculate thermal conductivity and diffusivity based on the temperature rise observed are crucial to the success of the technique. This work has used transient thermal simulation of a model representing a line source in an infinite material sample to generate a set of numerical data sets to validate analysis routines in conjunction with an experimental thermal probe apparatus. Findings show that by careful application of these routines, a close agreement with simulation input values can be achieved, with errors of less than one percent. This validates the analysis routines and provides a deeper appreciation of the theoretical behaviour of a thermal probe. Keywordsvalidation–thermal probe–analysis routines–transient simulation

In residential building design, areaway can act as an open subsurface space to help improve the living environment in adjacent basement by natural ventilation. To study this particular ventilation phenomenon mainly driven by wind force, the first part of this paper presents an investigation of flow field and pollution dispersion inside areaway space based on a wind tunnel experiment. In the experiment, the measurement of mean velocity, turbulence and concentration as well as the flow visualization were carried out for a rectangular cavity-like areaway model with the width to height (w/h) ratio ranging from 0.3 to 1.0 and the influence of above-ground building has also been investigated. The experimental results reveal quite different airflow patterns characterized with unsteady vortex movement inside the areaway model, which indicates that the w/h ratio and the above-ground building are important factors for ventilating the areaway space. Furthermore, for the purpose of computational fluid dynamics (CFD) model validation, the experimental results of flow fields were compared with the simulation results. The areaway model of w/h = 1 was used for this study and the simulations were performed using large-eddy simulation (LES) and standard k-ε turbulence model. The numerical results show a good agreement with the experimental results when using LES with inflow turbulence. The further investigations with regard to the characteristics of flow field and pollutant removal as well as ventilation performance were also performed by LES. Keywordsareaway-basement-natural ventilation-wind tunnel experiment-large-eddy simulation

This paper aims to investigate the influence of comparative ventilation arrangements (wall-return, locally balanced ceiling-return, and four-way ceiling-return) on the airflow distribution and particle fates within cleanrooms of ISO cleanliness class 7 with various tool coverage ratios (0%, 38%, and 60%). Computational fluid dynamics (CFD) was employed to analyze and compare the influence of the three ventilation arrangements on concentrations for particles of various sizes (diameters ranging from 0.01 to 100 μm) in the cleanrooms. The techniques of Eulerian and Lagrangian in CFD were employed for solving the continuous fluid and tracking the particle trajectory, respectively. The outcomes from this study suggested that particle removal rates for the given cleanrooms were significantly affected by the tool coverage ratios, the design of ventilation, and the particle sizes of concerns. In the cases of heavy tool coverage, the locally balanced ceiling-return ventilation arrangements can minimize the need for the relocation of the production lines and layouts of the production tools in cleanrooms, and may provide viable solutions to effective contamination without compromising contamination effectiveness or efficiency. Keywordscleanroom-particle-CFD-Lagrangian-industrial building

In this paper, the ventilation performances of (1) isothermal street canyons of different building-height-to-street-width (aspect) ratios (h/b) and (2) a ground-heated street canyon of h/b=1 at different Richardson numbers (Ri) are examined numerically by solving the Reynolds-averaged Navier-Stokes (RANS) equations with the use of the Renormalization Group (RNG) k-ɛ turbulence model. The mean ($$\overline {ACH}$$) and turbulent (ACH’) air exchange rates (ACH) are calculated by the eddy-viscosity model instead of the turbulence kinetic energy (TKE) used elsewhere. For the isothermal street canyons, the ACH’ is found to account for 90% of the total ACH for 0.5 ≤ h/b ≤ 2. Similar to the previous large-eddy simulation (LES) and k-ɛ turbulence model, the magnitudes and shapes of the roof-level profiles of mean and fluctuating vertical winds are close to each other for different h/b. This suggests that turbulent mixing is important for the ventilation of isothermal street canyons. For the ground-heated street canyon, both the mean wind and turbulence are strengthened as illustrated by the increasing $$\overline {ACH}$$ and ACH’ with decreasing Ri. A secondary recirculation is developed at the ground-level windward corner that pushes the primary recirculation upward and enhances and ACH as well.

This paper presents the features of Eco-Bat, a computer program developed to assess the environmental impacts of buildings, including construction materials and energy consumed, during its life cycle. The methodology used to evaluate environmental impacts based on a life cycle assessment (LCA) approach, compatible with ISO 14040 standards, is detailed. The data are mainly extracted from an environmental impacts database, Ecoinvent, which contains values for the manufacturing and elimination of numerous materials as well as other processes. Two applications are presented to illustrate the possibilities offered by Eco-Bat. The first one is a comparison of different variants of building facades. The second example shows the analysis of a whole building including its energy consumption. Keywordsenvironmental impacts–life cycle impacts assessment–ecobalance

This paper presents the results of computational experiments where multi-objective algorithms were used to tune a controller for blind movements in a residential building and a room of the LESO (Solar Energy and Building Physics Laboratory) experimental building. The blind controller, which is based on fuzzy logic, was optimized not only in terms of energy consumption but also in terms of thermal comfort. The goal is to show saving potential for intelligent blind controller in a real world example rather than in tailored idealized test rooms. Therefore, a state of the art simulation program with a multi-objective evolutionary algorithm was combined. It was found that with elementary control systems, like schedules for the lighting in a building, almost 40% of the energy could be saved. With the help of more advanced controllers this can be further increased. Also discussed in this paper are the results and the feasibility of implementing such a controller.

The purpose of this study is to use existing simulation tools to quantify the energy savings benefits of integrated control in office buildings. An EnergyPlus medium office benchmark simulation model (V1.0_3.0) developed by the Department of Energy (DOE) was used as a baseline model for this study. The baseline model was modified to examine the energy savings benefits of three possible control strategies compared to a benchmark case across 16 DOE climate zones. Two controllable subsystems were examined: (1) dimming of electric lighting, and (2) controllable window transmission. Simulation cases were run in EnergyPlus V3.0.0 for building window-to-wall ratios (WWR) of 33% and 66%. All three strategies employed electric lighting dimming resulting in lighting energy savings in building perimeter zones ranging from 64% to 84%. Integrated control of electric lighting and window transmission resulted in heating, ventilation, and air conditioning (HVAC) energy savings ranging from −1% to 40%. Control of electric lighting and window transmission with HVAC integration (seasonal schedule of window transmission control) resulted in HVAC energy savings ranging from 3% to 43%. HVAC energy savings decreased moving from warm climates to cold climates and increased when moving from humid, to dry, to marine climates. Keywordsdaylighting-energy conservation-energy management systems-energy efficiency-energy consumption-lighting control systems

Life cycle assessment (LCA) is a powerful tool to identify a building’s environmental impact throughout its life cycle. However, LCA does have limits in practice because it does not consider the economic aspect of project implementation. In order to promote LCA application, a more comprehensive evaluation of building life cycle environmental and economic performance must be performed. To address these issues, we propose life cycle green cost assessment (LCGCA), a method that combines LCA with life cycle costing (LCC). In LCGCA the building’s environmental loads are converted to environmental costs based on the trading price of CO2 certified emission reductions (CERs). These environmental costs are then included into the building life cycle cost. Subsequently an evaluation index of green net present value (GNPV) for LCGCA can be obtained. A governmental office building in Beijing was studied using LCGCA. Several design options were compared and the sensitivity of the CER price was analyzed. The research also shows that conclusions reached by LCGCA may be different from those of traditional LCC, which does not include environmental costs. The application of LCGCA needs the support of environmental policies. A sound environmental tax mechanism is expected to be established in China soon, which will enable LCGCA to be a useful tool to guide sustainable building design efficiently.

A prototypical office building meeting the prescriptive requirements of the 2008 California Building Energy Efficiency Standards (Title 24) was used in EnergyPlus simulations to calculate the energy savings potential of demand controlled ventilation (DCV) in five typical California climates per three design occupancy densities and two minimum ventilation rates. The assumed minimum ventilation rates in offices without DCV, based on two different measurement methods employed in a large survey, were 38 and 13 L/s per occupant. The results of the life cycle cost analysis show DCV is cost effective for office spaces if the typical minimum ventilation rate without DCV is 38 L/s per person, except at the low design occupancy of 10.8 people per 100 m2 in climate zones 3 (north coast) and 6 (south coast). DCV was not found to be cost effective if the typical minimum ventilation rate without DCV is 13 L/s per occupant, except at high design occupancy of 21.5 people per 100 m2 in climate zones 14 (desert) and 16 (mountains). Until the large uncertainties about the base case ventilation rates in offices without DCV are reduced, the case for requiring DCV in general office spaces will be a weak case. Under the Title 24 standard office occupant density of 10.8 people per 100 m2, DCV becomes cost effective when the base case minimum ventilation rate is greater than 42.5, 43.0, 24.0, 19.0, and 18.0 L/s per person for climate zones 3, 6, 12, 14, and 16, respectively. Keywordsbuilding simulation-building energy standard-demand controlled ventilation-energy savings

In order to realize the “design by simulation” concept in the building design, the methodology of applying the building simulation in the building’s conceptual design stage is the main theme discussed in this paper. The conceptual design stage is divided into four sub-stages, and the framework of the design is built by way of the simulation in the conceptual design stage. Moreover, the energy saving potential assessment by the simulation in the preliminary conceptual design stage is also discussed in detail, including the input/output information, the calculation method and procedure, and the requirements and information from architects, etc. The natural ventilation design is used as the first trial in this study, and the difference between the detailed conceptual design and the preliminary conceptual design is also discussed, and the new simulation methodology is further described. The main objective of this paper is to help avoid an incorrect decision in the conceptual design stage, as well as to provide a better base for the energy efficient design in the next stage by means of the building simulation tool.

This paper identifies the “safe ventilation rate” for eliminating airborne viral infection and preventing cross-infection of severe acute respiratory syndrome (SARS) in a hospital-based setting. We used simulation approaches to reproduce three actual cases where groups of hospital occupants reported to be either infected or not infected when SARS patients were hospitalized in nearby rooms. Simulations using both computational fluid dynamics (CFD) and multi-zone models were carried out to understand the dilution level of SARS virus-laden aerosols during these scenarios. We also conducted a series of measurements to validate the simulations. The ventilation rates (dilution level) for infection and non-infection were determined based on these scenarios. The safe ventilation rate for eliminating airborne viral infection is to dilute the air emitted from a SARS patient by 10000 times with clean air. Dilution at lower volumes, specifically 1000 times, is insufficient for protecting non-infected people from SARS exposure and the risk of infection is very high. This study provides a methodology for investigating the necessary ventilation rate from an engineering viewpoint. KeywordsSARS-ventilation rate-simulation-infection

A series of building energy simulation tools are being developed to help the building energy auditor in establishing his diagnosis (including benchmarking and detailed analysis of actual energy consumption) and in evaluating the selected energy conservation opportunities (ECOs). A first simulation tool, dedicated to benchmarking, has been presented in a previous paper. The present paper focuses on the second simulation tool, dedicated to inspection and evaluation of ECOs. This Building-HVAC System global model includes simplified models of building zones and of HVAC (heating, ventilation, and air conditioning) equipment. Only a limited number of easily identifiable parameters are required. The simplicity of the models and the use of an equation solver to run the simulation ensure good robustness and full transparency. The development, the implementation and the application of these models are discussed. Focus is also given to the calibration of the tools to monthly utility bills. Keywordsbuilding modeling-HVAC system modeling-building energy audit-calibration

Occupants of buildings typically operate devices such as windows, shades, luminaires, radiators, and fans to bring about desirable indoor environmental conditions. These control actions can have a significant impact on buildings’ performance (energy use, indoor climate). A better understanding of control-oriented user behavior can not only facilitate more accurate predictions of buildings’ performance, but also support the effective operation of buildings’ service systems. This paper describes a study of control-oriented user behavior (as related to systems for lighting and shading) in three office buildings in Austria. The results specifically shed light on the relationships between control actions and environmental conditions inside and outside buildings.

Hollow bricks are widely used to build facades of light weight and high thermal resistance. The air filled voids within the brick configuration elevates the block's thermal resistance. Disturbing the natural flow patterns developed inside the voids affects the blocks overall thermal resistance. This paper presents a numerical study for a section of a masonry brick represented by a baffled squared cavity surrounded by a conductive wall of finite thickness. The baffles are attached to the top and bottom sides dividing the void into three regions. The thermal resistance of the partitioned voids depends on baffles length and location. Short baffle develops a stratified region in the central gap and generates two circulation zones near the upper left and lower right corners. Long baffles, on the other hand, splits the flow into three different convection circulation cells, a cell near each side of the cavity and a third in the central gap. Increasing the baffle height increases the thermal resistance of the partitioned cavity for all gap widths. The highest increase in thermal resistance is 53% over the non baffled voids and is achieved with long baffles when located to divide the cavity into three regions of equal widths. © 2010 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

The thermal comfort in urban canyons of a high density city is a very challenging issue for urban planners and designers, especially in hot humid tropical zone. The present study aims to evaluate the effects of a newly promulgated building construction rules in respect of thermal climate for Dhaka, Bangladesh, a region characterized by high density area with tropical climate. Three different urban canyons from three areas were considered which almost represents the whole city. Measurements were carried out to assess the existing thermal climate in the city canyons. Further, three model canyons were configured according to the new rules of ground coverage, floor area ratio (FAR) and site setback. A three-dimensional numerical model with high spatial and temporal resolution was used to investigate the microclimatic changes within the urban environments. Model calculations were run for a typical summer day. The thermal climate was evaluated based on air temperature T a, surface temperature T s, relative humidity RH, and wind speed in the existing and model canyons. For thermal comfort assessment the temperature humidity index (THI) was considered in this study. The results showed that the outdoor spaces of the study areas are thermally uncomfortable and the new building construction rules hardly improve the conditions in general. However, THI decreases in a canyon where sky view factor (SVF) decreases in the model canyon than the existing one. In addition, the surface temperature T s and air temperature T a do not show the same picture. Furthermore, the wind speed increases in all the model canyons as the site setback allows wind flow uniformly inside the canyons.

A numerical model is developed to assess the static and dynamic operations of a new kind of floor heat emitter. Surface floor heating systems are widely used to achieve better comfort conditions in residential and tertiary building sector. Classical floor heating systems have a low thermal response while the emitting device studied in this paper is highly reactive. It allows comfort enhancement and energy savings. A finite element method based software COMSOL Multiphysics is applied to solve the heat equation. This work focuses on the thermal behaviour of the emitter itself, but does not include a building model. A test bench has been built for this application to verify the numerical model. Both computational and experimental results demonstrate the benefits of this new heating and cooling device. Keywordsheated floor–experimental validation–COMSOL Multiphysics

Ventilation is a main method to control the contaminant dispersion within clean wards. In this paper, we investigated the effects of various ventilation designs of the bathroom in an ISO Class 5 clean ward. Specifically, the contaminant dispersion and particle concentrations corresponding to three different ventilation design schemes were characterized and compared using computational fluid dynamics (CFD) analysis. For each design, we examined airflow and particle concentrations for contaminant sources located at two places (i.e., at the toilet seat and on the floor), respectively. Field test was conducted to compare the measured and simulated air velocities and particle concentrations in a hospital clean ward. The implemented CFD modeling of ventilation effects of various designs in this study has proven to accurately characterize airflow and contaminant control in the ventilated space, and has led to optimizing ventilation for the bathroom in an ISO Class 5 clean ward.

The models for daylighting control are to contend with multi-variant, dynamic, nonlinear components impacted by geographical, environmental and occupancy factors amongst many other things. Conventional techniques for system analysis are not suitable for dealing with blind control systems whose positions are strongly influenced by occupant’s mood, emotions, and perception. This paper attempts to illustrate the effectiveness of using intelligent techniques in the visual environment control domain of the building systems. With the use of adaptive neuro fuzzy inference system (ANFIS), the paper models nonlinear blind position dynamics from the simulated data. The model thus obtained is then used for controller design and validation. Using MATLAB’s fuzzy logic toolbox, the paper also gives the procedure for creating such a model that is capable of maintaining a user-specified illuminance profile. When implemented in an adaptive control scheme, the model could be further tuned online for time-varying dynamics. The article’s ultimate objective is to accentuate the use of soft computing techniques towards significantly improving the effectiveness of control process and help address the problem of control search space reduction when used along with simulation. Keywordsintelligent control-daylighting-blind control-soft computing-Dubai

This paper presents a detailed numerical study, in steady state regime, of the interaction between two dimensional heat transfers by conduction, natural convection and radiation in double hollow bricks formed by two honeycomb walls separated by an air layer. The air motion in all cavities of the system is laminar. The left and right vertical sides of the hollow bricks are considered isothermal and maintained at different constant temperatures. The top and bottom horizontal sides are assumed to be adiabatic. The governing equations are solved using the finite volume method (FVM) and the SIMPLE algorithm. The impact of the thickness of the air layer on the global heat flux through the structure is discussed. The simulation results show that the variation of the overall heat flux through each hollow brick as a function of the temperature difference ΔT between the vertical sides of the system is almost linear for the different types of double hollow bricks considered. This linear thermal behaviour allowed the generation of appropriate overall heat exchange coefficients that permit fast and accurate prediction of heat transfers through the hollow bricks without solving the complex system of equations governing the coupled heat transfers. Comparison of the performance of different types of double hollow bricks is made. Keywordshollow brick-conduction-natural convection-radiation-thermal conductance-numerical simulation

This paper describes a two step numerical procedure to determinate empirical transfer function coefficients (TFCs) for vertically heated hollow concrete bricks. For such systems TFCs cannot be generated using the analytical techniques available in the literature such as the z-transfer function method or the space state representation method because of the nonlinear local character of the heat transfer by natural convection and radiation in the air cells of the hollow concrete bricks. The first step of the procedure consists in predicting coupled heat transfer by conduction, convection, and radiation in realistic time varying conditions using a detailed numerical simulation. In the second step, the results of the simulation (the time-varying heat fluxes at the hollow brick surfaces) are used to obtain empirical transfer function coefficients using an identification technique. Transfer function coefficients are generated for three different types of hollow concrete bricks mostly used in practice. It is shown that the empirical transfer function coefficients permit fast and accurate prediction of heat transfer for thermal excitations that differ markedly from those used to generate these coefficients without solving the complex system of equations governing the coupled heat transfer mechanisms.

The paper presents an overview of Multiphysics applications using a Multiphysics modeling package for building physical constructions simulation. The overview includes three main basic transport phenomena for building physical constructions: (1) heat transfer, (2) heat and moisture transfer and (3) heat, air and moisture (HAM) transfer. It is concluded that full 3D transient coupled HAM models for building physical constructions can be build using a Multiphysics modeling package. Regarding the heat transport, neither difficulties nor limitations are expected. Concerning the combined heat and moisture transport the main difficulties are related with the material properties but this seems to be no limitation. Regarding the HAM modeling inside solid constructions, there is at least one limitation: the validation is almost impossible due to limitation of measuring ultra low air velocities of order μm/s. Keywordsheat–air–moisture–modeling–Multiphysics–building–construction

During the design of a new building or retrofitting of an existing one, it is important to reliably assess the indoor humidity levels of the building as it can potentially affect the building envelope durability, occupants’ comfort and health risks associated with mould growth. Simplistic assumptions of indoor humidity profiles, which ignore the dynamic coupling of the indoor environment and building enclosure, may lead to inaccurate conclusions about the indoor environment and moisture performance of the building enclosure. In this paper, a whole-building hygrothermal model called HAMFitPlus, which takes into account the dynamic interactions between building envelope components, mechanical systems and indoor heat and moisture generation mechanisms, is used to assess the indoor humidity condition of an existing occupied house. HAMFitPlus is developed on SimuLink development platform and integrates COMSOL multiphysics with MatLab. The basic input parameters of the model are discussed in detail, and its simulation results are presented. In general, the HAMFitPlus simulation results are in good agreement with the measured data. Keywordscoupled HAM analysis–whole-building hygrothermal modeling–energy efficiency–indoor environment–building envelope performance

Building ventilation code requirements for crawl spaces were reviewed from 1937 to today and though remain largely unchanged, provide designers and builders flexibility in moisture control methods. This study evaluates the current building ventilation code requirements for at-grade and below grade crawl space using computational fluid dynamic (CFD) software with experiment inputs. The research first tested the soil moisture evaporation rate from two monitored crawl spaces in Colorado, US, which produces an average moisture load of 13.75 grains/(ft2·h) (9.6g/(m2·h)) and a maximum load of 42.7 grains/(ft2·h) (29.8g/(m2·h)). The soil moisture evaporation rates identified align well in magnitude with those recorded in the literature, supporting the estimation method used. The experiment reveals that plastic ground cover can effectively reduce the moisture load from the soil by an average of 93%. The study then developed a CFD model of the monitored crawl space to assess the necessity and effectiveness of various ventilation code requirements. The space effective leakage area to the exterior was determined through field pressurization testing and CFD analysis to be approximately 0.26in.2/ft2 of floor area. The CFD predictions, validated with the measured data, verify that the building code requirements for at-grade crawl spaces appear sufficient, but have limitations for below grade crawl spaces. Sealed crawl spaces perform better in humid climates, supporting previous research, and mechanical ventilation is justified for below grade crawl spaces only. The paper provides suggestions for the revisions to the current building code to recognize below grade underfloor spaces.

The paper formulates some fundamental principles of performance-based design (PBD), suggesting a conceptual framework and systematic approach suitable for application in most areas of building design, and in the development of simulation tools and performance test methods required in the design and assessment processes. A schematic algorithm, which has been developed for the common engineering approach, was helpful in identifying the inter-relation with the required knowledge-based databases and tools that are needed for proper implementation of PBD. It is also shown that this schematic algorithm can serve not only as a conceptual model but also as the basic framework for developing or adapting simulation tools that are intended for PBD and assessment. The last part of the paper demonstrates the application of the fundamental approach in several areas of building performance (fire safety, acoustics, moisture safety, indoor air quality, and durability), outlining in each area the main user needs, ensuing performance requirements, and the most significant capabilities required of adequate simulation tools, with an emphasis on input/output.

Building occupancy is an important basic factor in building energy simulation but it is hard to represent due to its temporal and spatial stochastic nature. This paper presents a novel approach for building occupancy simulation based on the Markov chain. In this study, occupancy is handled as the straightforward result of occupant movement processes which occur among the spaces inside and outside a building. By using the Markov chain method to simulate this stochastic movement process, the model can generate the location for each occupant and the zone-level occupancy for the whole building. There is no explicit or implicit constraint to the number of occupants and the number of zones in the model while maintaining a simple and clear set of input parameters. From the case study of an office building, it can be seen that the model can produce realistic occupancy variations in the office building for a typical workday with key statistical properties of occupancy such as the time of morning arrival and night departure, lunch time, periods of intermediate walking-around, etc. Due to simplicity, accuracy and unrestraint, this model is sufficient and practical to simulate occupancy for building energy simulations and stochastic analysis of building heating, ventilation, and air conditioning (HVAC) systems. Keywordsbuilding occupancy–occupant movement–stochastic process–Markov chain–energy simulation

Top-cited authors
• Tsinghua University
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