Fariborz Haghighat

Modelling of volatile organic compounds emission from dry building materials

Abstract A numerical and an analytical model were developed to predict the volatile organic compound (VOC) emission rate from dry building materials. Both models consider the mass diffusion process within the material and the mass convection and diffusion processes in the boundary layer. All the parameters, the mass diffusion coefficient of the material, the material/air partition coefficient, and the mass transfer coefficient of the air can be either found in the literature or calculated using known principles. The predictions of the models were validated at two levels: with experimental results from the specially designed test and with predictions made by a CFD model. The results indicated that there was generally good agreement between the model predictions, the experimental results, and the CFD results. The analytical and numerical models then were used to investigate the impact of air velocity on emission rates from dry building materials. Results showed that the impact of air velocity on the VOC emission rate increased as the VOC diffusion coefficient of the material increased. For the material with a diffusion coefficient > 10 −10 m 2 / s , the VOC emission rate increased as the velocity increased; air velocity had significant effect on the VOC emission. For the material with a VOC diffusion coefficient 10 −10 m 2 / s , the VOC emission rate increased as the velocity increased only in the short term; 24 h . In the medium- to long-term time range, the VOC emission rate decreased slightly as the air velocity increased; velocity did not have much impact on these materials. Furthermore, the study also found that the VOC concentration distribution within the material; the VOC emission rate and the VOC concentration in the air were linearly proportional to the initial concentration. However, the normalized emitted mass was not a function of the initial concentration: it was a function of the properties of the VOC and the material.

Material Emission Rates : Literature Review, and the Impact of Indoor Air Temperature and Relative Humidity

Abstract An extensive literature review of research on the impact of indoor air conditions; temperature, relative humidity and surface air velocity on materials emission rates is presented. This paper also presents the results of an experimental work to study the impact of room air temperature and relative humidity on materials emission rates. The results indicate that both the temperature and relative humidity have a significant effect on the emissions from paint and varnish. In the case of varnish, the results were consistent with earlier results. However, the paint results show inconsistent emission behaviour. Further, for both materials, the individual compounds did not necessarily follow the same trend established for the TVOC.

Impact of process design on greenhouse gas (GHG) generation by wastewater treatment plants.

The overall on-site and off-site greenhouse gas emissions by wastewater treatment plants (WWTPs) of food processing industry were estimated by using an elaborate mathematical model. Three different types of treatment processes including aerobic, anaerobic and hybrid anaerobic/aerobic processes were examined in this study. The overall on-site emissions were 1952, 1992, and 2435 kg CO2e/d while the off-site emissions were 1313, 4631, and 5205 kg CO2e/d for the aerobic, anaerobic and hybrid treatment systems, respectively, when treating a wastewater at 2000 kg BOD/d. The on-site biological processes made the highest contribution to GHG emissions in the aerobic treatment system while the highest emissions in anaerobic and hybrid treatment systems were obtained by off-site GHG emissions, mainly due to on-site material usage. Biogas recovery and reuse as fuel cover the total energy needs of the treatment plants for aeration, heating and electricity for all three types of operations, and considerably reduce GHG emissions by 512, 673, and 988 kg CO2e/d from a total of 3265, 6625, and 7640 kg CO2e/d for aerobic, anaerobic, and hybrid treatment systems, respectively. Considering the off-site GHG emissions, aerobic treatment is the least GHG producing type of treatment contrary to what has been reported in the literature.

Zonal Modeling for Simulating Indoor Environment of Buildings: Review, Recent Developments, and Applications

Zonal models are an intermediate approach between computational fluid dynamics and simple nodal models. They have the ability to take into account various phenomena ignored by one-node and multizone models, such as temperature and contaminants distributions, thermal integration with cold façade, draft, asymmetric thermal radiation, and cold or hot floor surfaces. Single and multizone models are inadequate to obtain information required for many applications because the fundamental assumption of heat and mass balance models is that the air in each zone is well stirred with uniform temperature and contaminant concentration. Zonal models are based on an approximate partitioning of a room into a number of subzones and have been used for modeling indoor and outdoor environments. Recently, this approach has been used to predict physical parameters in a number of case studies, including the urban microclimate effects on the building energy demand for the case of a street canyon due to the heat island affect; the combination of a system of stratified air conditioning and natural ventilation for large enclosures; and the prediction of the distribution of indoor air parameters in a space. In this paper, a comprehensive literature review has been carried out that covers the basic principles of zonal models, their development, and their application over the last three decades.

A Procedure for Calculating Thermal Response Factors of Multi-layer Walls State Space Method

Abstract Thermal response factors of building envelopes are fundamental information in the design of thermal systems. The conventional calculating method of these factors is first to calculate the eigenvalues of the system as a function of thermal physical properties and the thickness of materials. The roots finding process is time-consuming and occasionally may lead to micscalculation due to missing one or more roots. in this paper a new approach to calculate these factors based on the state space principle of modern control theory has been proposed. Using this approach through calculation of the state transition matrix of a system, the thermal response factors of a multi-layer wall can be obtained without finding the roots. This method is feasible and easy to use with a sufficient accuracy for engineering applications.

Impact of psycho-social factors on perception of the indoor air environment studies in 12 office buildings

Abstract The main function of a mechanically ventilated office building is to provide a healthy and comfortable working environment for occupants, while maintaining minimum energy consumption. Twelve mechanically ventilated buildings were selected. They varied greatly in surface area, number of floors, occupant density, and building use. The indoor air quality, thermal comfort, energy consumption, and perception of occupants were investigated in these buildings. A total of 877 subjects participated in the questionnaire survey during the hot summer months of June, July, and August, and during the cold winter months of January, February, and March. The questions included in the questionnaire dealt with health, environmental sensitivity, work area satisfaction, personal control of the workstations environment, and job satisfaction. Measured parameters concerning the quality of indoor air included ventilation rate, concentration of TVOC, CO 2 , CO, RH, and formaldehyde. The thermal comfort parameters included room air, mean radiant, plane radiant asymmetry, and dew point temperatures, as well as air velocity and turbulence intensity. Monthly energy consumption data was also gathered for each building. Ventilation performance, in terms of air flow rate and indoor air quality, was compared with the ASHRAE Standard 62-89R (Ventilation for Acceptable Indoor Air Quality. Atlanta: American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. U.S.A. [1] ). The measured and calculated thermal environmental results were also compared with the ASHRAE Standard 55-92 (Thermal Environmental Conditions for Human Occupancy. Atlanta: American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. U.S.A. [2] ). CO 2 and CO levels satisfied the recommended limits. The outdoor airflow rate was half that recommended in only one building. The formaldehyde and TVOC levels were moderately higher than suggested comfort levels. However, more than 56% of the occupants rated dissatisfaction with the indoor air quality. Only 63% of the indoor climatic observations fell within the ASHRAE Standard 55-92 summer comfort zone; 27% in the winter. However, only 69% of those surveyed agreed with the comfort zones. More symptoms were reported by workers who perceived IAQ to be poor. Positive relationships were observed between the job satisfaction and satisfaction with office air quality, ventilation, work area temperature, and ratings of work area environment. However, job dissatisfaction did not correlate with symptom reports. The occupants were more dissatisfied with IAQ when they preferred more air movement. In other words, the higher the perceived air movement, the greater the satisfaction with IAQ.

Development and validation of a zonal model — POMA

Abstract This paper reports the development of a simplified numerical model, Pressurized zOnal Model with Air-diffuser (POMA), which is able to predict the airflow pattern and thermal distributions within a room. POMA model is based on the conservation of mass and energy. Jet characteristic equations were introduced in the model to generalize its application to mechanically ventilated buildings. POMAs prediction was compared with the experimental results and with the prediction of another zonal model as well as a CFD model. Comparisons were made for both natural and force ventilation cases, and in the case of force ventilation the comparison was done for cross-ventilation and a linear ceiling jet. The good agreements between results of POMA model and those of a CFD model and experimental data demonstrated that POMA model was a practical tool for ventilation system design.

The influence of turbulent wind on air change rates—a modelling approach

Abstract Turbulence in wind-induced pressures on a building envelope causes fluctuating air infiltration. The resultant airflows are influenced both by building characteristics, the resistance of the openings to flow, the inertia of the air mass in the openings and the compressibility of room air, and by frequency characteristics of wind pressures, their power spectra and the correlation among them. A new approach using the spectrum analysis technique is proposed to model the pulsating flows through openings of a building. The governing equations for fluctuating airflow behaviour are obtained from the pressure/force balance between the turbulence pressure differences across openings and the forces required to overcome the flow resistance and inertia of air. The proposed approach is applied to a single-zone enclosure with a single opening and with two openings, and can be easily extended to multi-zone buildings.

Wastewater treatment in the pulp-and-paper industry: A review of treatment processes and the associated greenhouse gas emission.

Pulp-and-paper mills produce various types of contaminants and a significant amount of wastewater depending on the type of processes used in the plant. Since the generated wastewaters can be potentially polluting and very dangerous, they should be treated in wastewater treatment plants before being released to the environment. This paper reviews different wastewater treatment processes used in the pulp-and-paper industry and compares them with respect to their contaminant removal efficiencies and the extent of greenhouse gas (GHG) emission. It also evaluates the impact of operating parameters on the performance of different treatment processes. Two mathematical models were used to estimate GHG emission in common biological treatment processes used in the pulp-and-paper industry. Nutrient removal processes and sludge treatment are discussed and their associated GHG emissions are calculated. Although both aerobic and anaerobic biological processes are appropriate for wastewater treatment, their combination known as hybrid processes showed a better contaminant removal capacity at higher efficiencies under optimized operating conditions with reduced GHG emission and energy costs.

Removal of pharmaceuticals from water by homo/heterogonous Fenton-type processes – A review

The presence of emerging contaminants such as pharmaceuticals in natural waters has raised increasing concern due to their frequent appearance and persistence in the aquatic ecosystem and the threat to health and safety of aquatic life, even at trace concentrations. Conventional water treatment processes are known to be generally inadequate for the elimination of these persistent contaminants. Therefore, the use of advanced oxidation processes (AOPs) which are able to efficiently oxidize organic pollutants has attracted a great amount of attention. The main limitation of AOPs lies in their high operating costs associated with the consumption of energy and chemicals. Fenton-based processes, which utilize nontoxic and common reagents and potentially can exploit solar energy, will considerably reduce the removal cost of recalcitrant contaminants. The disadvantages of homogeneous Fenton processes, such as the generation of high amounts of iron-containing sludge and limited operational range of pH, have prompted much attention to the use of heterogeneous Fenton processes. In this review, the impacts of some controlling parameters including the H2O2 and catalyst dosage, solution pH, initial contaminants concentrations, temperature, type of catalyst, intensity of irradiation, reaction time and feeding mode on the removal efficiencies of hetero/homogeneous Fenton processes are discussed. In addition, the combination of Fenton-type processes with biological systems as the pre/post treatment stages in pilot-scale operations is considered. The reported experimental results obtained by using Fenton and photo-Fenton processes for the elimination of pharmaceutical contaminants are also compiled and evaluated.