Francis Allard

Night ventilation for building cooling in summer

Abstract This paper presents a two-step analysis of night ventilation as a way of cooling office buildings and providing comfort in summer. Experimental data first allows us to discuss some factors which affect the performance of the technique, to show that significant comfort improvement may be obtained in “well-designed” rooms, and to investigate the energy removal from the building by defining a potential energy efficiency index. Through the use of numerical simulations, we then deal with the useful cooling energy which is offered by night ventilation in the experimental configuration and show that much care has to be taken when the technique is intended to be used in the frame of a mixed-mode cooling system.

Indoor particle pollution: effect of wall textures on particle deposition

Abstract The aim of this study is the experimental determination of deposition constants for several wall textures in order to predict indoor particles concentration. Experiments involved the injection of spherical particles (0.7, 1.0 and 5.0 μm in diameter) in a cubic box whose internal faces are covered by the texture to be tested. Global constants of deposition are determined by regression fitting of the concentration exponential decay curves. Deposition constants are deduced for each orientation from the Crump and Seinfeld theory (J. Aerosol Sci. 12(5) (1981) 405). This decomposition method has been tested for 5.0 μm and then been extended to smaller particles.

Multicriteria analysis of ventilation in summer period

This paper presents a multicriteria analysis of ventilation during summertime in Europe. Multicriteria analysis theories are used to determine the most suitable ventilation strategy on a university building, that is to say to ensure the best possible indoor air quality, thermal comfort of the occupants and the lower energy consumption in case of accelerated diurnal or nocturnal ventilation and/or air conditioning. After defining the possible actions, the criteria of quality regarding thermal comfort, indoor air quality and energy consumption are defined. The possible actions are then assessed relative to each of these three criteria and ranked from the best to the worst ones using two different multicriteria analysis methods.

Measurement of Thermal Comfort and Indoor Air Quality Aboard 43 Flights on Commercial Airlines

This paper reports the results of thermal comfort and indoor air quality measurements aboard aircraft from 43 flights on commercial airlines with a duration of more than 1 h. The measurements were performed continuously during the whole flight (from the departure gate to the arrival gate), and the parameters monitored were temperature, relative humidity and carbon dioxide concentration. The results were then compared with the ASHRAE Standards for the thermal comfort (ASHRAE Standard 55-92) and indoor air quality (ASHRAE Standard 62-89). The evaluation of the indoor air quality was based mainly upon comparison of the carbon dioxide concentrations measured with standards and recommendations for the indoor environment. Overall, the levels of relative humidity were far lower than the limit set by the ASHRAE Standard 55-92. The levels of carbon dioxide on most flights were higher than that recommended by the ASHRAE Standard 62-89. The results of this study, mainly the low level of humidity and high concentrations of carbon dioxide, led us to expect that the crew and the passengers would have been dissatisfied with their degree of thermal comfort and the quality of the air in the cabin. This conclusion is based simply on a comparison of our measurements with the values stated in the ASHRAE Standards. However, we must bear in mind that these were developed for an indoor environment at atmospheric pressure. More research is needed to study the validity of these standards for sub-atmospheric conditions.

Sorption Isotherms of Acetone on Various Building Materials

The physical modelling of Indoor Air Quality (IAQ) suffers a lack of sorption data for the most common Volatile Organic Compounds (VOC) on building materials. This paper deals with an experimental facility that aimed to provide the sorption isotherms of gaseous contaminants on various materials. It was used to determine the sorption isotherms of acetone on chipboard, acrylic paint, and the gypsum core of commercially available gypsum board. After a brief introduction to fundamental principles of sorption, the experimental device is presented in detail. The results are reported and discussed, emphasising the description of the isotherm shapes and the possible partial reversibility of the sorption phenomenon for porous materials. The resulting curves are clearly non linear when dealing with gypsum and chipboard. Moreover, the sorption isotherms of acetone on gypsum were found to be different whether they were determined in the directions of increasing or decreasing concentrations. Many questions remain unresolved about the physico-chemical processes involved, the sorption data to be considered for the purposes of IAQ modelling, and the way to account for the observed phenomenon when modelling the sorption/diffusion contaminant transport in building materials.

Physically Based Modelling of the Material and Gaseous Contaminant Interactions in Buildings: Models, Experimental Data and Future Developments

Abstract Although potentially having a significant influence on indoor air quality (IAQ), interactions between building materials and gaseous contaminants have often been neglected or crudely modelled in IAQ simulation tools. During the past 20 years, empirical source and sink models have progressively given way to physically based models; but confusion still remains on their applicability, as well as on the adequate experimental data to input for the model parameters. Thus, demonstration is first made that models relating macroscopically the room air phase and material concentrations through adsorption and desorption constants are not scientifically sound. Instead, elemental models combining diffusion equations and local sorption equilibria should be used. The compilation of sorption and diffusion data presented in the second part of this chapter underlines the fact that such data cannot be considered independently from the mass transport equations used to fit the measurements. As a result, a thorough analysis of diffusion processes in polymers and porous media is presented in order to define and relate the diffusion coefficients. Finally, the last part of the chapter discusses the way in which existing models could be extended to account for the contributions of temperature, multi-component mixtures, humidity and chemical transformations within materials. Still based on fundamental considerations, the proposed methodology consists of implementing new functionalities to describe the temperature dependence of the model parameters, elemental models representing the interactions between gaseous contaminants and water, as well as kinetic models coming from the fields of atmospheric and surface sciences.

Book Review: Computational Fluid Dynamics in Ventilation Design : REHVA Guidebook No 10

Computational Fluid Dynamics in Ventilation Design is a new title in the REHVA guidebook series. This guidebook is written for people who need to use and discuss results based on CFD predictions, and it gives insight into the subject for those who are not used to working with CFD. It is also written for users working with CFD who have to be more aware of how this numerical method is applied in the area of ventilation. The guidebook has, for example, chapters that are very important for CFD quality control in general and for the quality control of ventilation related problems in particular.

Natural ventilation - A new method based on the Walton model applied to cross-ventilated buildings having two large external openings

Abstract In order to provide comfort in a low energy consumption building, it is preferable to use natural ventilation rather than HVAC systems. To achieve this, engineers need tools that predict the heat and mass transfer between the buildings interior and exterior. This paper presents a method implemented in some building software, and the results are compared to CFD. The results show that the knowledge model is not sufficiently well described to identify all the physical phenomena and the relationships between them. A model was developed which introduces a new building-dependent coefficient allowing the use of Waltons model, as extended by Roldan to large external openings, and which better represents the turbulent phenomena near large external openings. The formulation of the mass flow rates was inversed to identify modelling problems. It appears that the discharge coefficient is not the only or best parameter to obtain an indoor static pressure compatible with CFD results, or to calculate more realistic mass flow rates.

Natural Ventilation Potential of Urban Buildings

Abstract The design of a building should provide the flow paths needed for natural ventilation. Therefore, the decision to apply natural ventilation should be taken early in the building design process, when little information is available for airflow estimation. To deal with this lack of data, a semi-qualitative method to assess the potential of an urban site to host a naturally ventilated building is proposed. First, natural ventilation driving forces and constraints are assessed by using comfort criteria, statistical meteorological data and user-provided information. Then, the site of interest is compared to other, well known sites using criteria related to both natural ventilation driving forces and constraints. This method compares and ranks the site within the base sites using a qualitative multicriteria analysis procedure. The result of the comparison shows if the assessed site has a higher potential for application of natural ventilation than a set of known sites.

Optimal settings of residential oil burners

Abstract Residential oil burners are capable of almost complete burning of the fuel oil, without visible smoke, when they are operated to deliver approximately 12% CO 2 in the flue gases. The positions of the air damper and of the combustion nozzle are adjusted at start-up and during operation in order to maximize the combustion efficiency. In practice, one factor at a time is varied, starting with the air damper. However, this method fails to detect the interaction between air excess and nozzle position and results in non-optimal settings. Optimal designed experiments allow obtaining local regression models and statistical analyses indicate if experiment augmentation is required. The air damper and combustion nozzle settings are changed in the direction of local gradient until a second order model that contains the optimal point in its experimental region is obtained. The gain in combustion efficiency thus obtained may be up to 5% as compared with the classical approach.