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  • 1.
    Blomqvist, Claes
    et al.
    KTH, Superseded Departments, Civil and Architectural Engineering.
    Sandberg, Mats
    Högskolan i Gävle.
    Air Movements through Horizontal Openings in Buildings – A Model Study2004In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 3, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    A building contains a number of large openings like doors and staircases. When the temperature of the spaces connected by these openings differs, the difference in density will cause air movements through them. Horizontal air movements through vertical openings in buildings like doors and windows are well investigated while studies of air movements through horizontal openings like stairwells are less frequent and therefore this work is focusing on this case.

    The paper reports on an experimental study of the possibility of using buoyancy forces to distribute air and heat through horizontal openings. The experiments have been carried out in a scale model with water as the operating fluid.

    The result of the study shows that the flow rate through a horizontal opening is roughly half of the flow rate through a vertical opening for the same conditions, probably caused by the more complex flow pattern in the horizontal opening. A staircase below the horizontal opening will guide the flow somewhat and will cause a small increase of the fluid exchange through the opening.

  • 2.
    Cehlin, Mathias
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Sandberg, M
    Computed Tomography for Indoor Applications2006In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 4, no 4, p. 349-364Article in journal (Refereed)
  • 3.
    Einberg, Gery
    et al.
    KTH, Superseded Departments, KTH Syd.
    Holmberg, Sture
    KTH, Superseded Departments, KTH Syd.
    Characteristics of Particles and their Behaviour in Ventilation Air2003In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 2, no 1, p. 45-54Article in journal (Refereed)
    Abstract [en]

    The behaviour of particles in air flow is important for identifying those in various locations in ventilated space. The main reason for this study is to propose a new modelling concept to determine a realistic distribution of particles of different sizes in a space. The goal for this investigation is to divide particles into groups according to their behaviour in air and to improve the existing settling model. The growth of particle aerodynamic diameter in higher relative humidity is also presented. Here, growth of diameter and coagulation is used to determine the control volume concentration. The finite volume method is used to describe the particle concentration in the computational domain. A background to particle properties and theory for calculations are given for this purpose. Results from the literature survey reveal that modelling needs a more systematic approach to cover all sizes of particles with clear classification by behaviour.

  • 4.
    Guha, Jaideep
    et al.
    KTH, School of Technology and Health (STH), Fluid and Climate Technology.
    Holmberg, Sture
    KTH, School of Technology and Health (STH), Fluid and Climate Technology.
    A Numerical and Experimental Evaluation of a Natural Wind Driven Suction Cylinder for Building Ventilation2008In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 7, no 3, p. 197-206Article in journal (Refereed)
    Abstract [en]

    The suction cylinder described in this paper is a device to increase the ventilation flow rate, especially in naturally ventilated buildings. Outdoor wind is the driving force. The principle of operation is the development of a pressure drop created by the relative increase in flow velocity as wind driven air flows through a nozzle. This paper basically describes how this pressure drop and resultant momentum can be used to provide exhaust ventilation. The suction cylinder is particularly designed for natural and hybrid ventilation systems, especially for times when the temperature gradient between inside and outside is not enough to drive stack driven ventilation. A 1-dimensional analytical flow model was derived to establish a relationship between the volume of air entering through the inlet and the volume of air sucked by the suction cylinder. The commercial Computational Fluid Dynamics (CFD) code, Fluent, was used to visualise the flow system inside the suction cylinder. A corresponding wind tunnel experiment was also made. Preliminary results show advantages in using a suction cylinder for building ventilation.

  • 5. Heiselberg, P.
    et al.
    Sandberg, Mats G.
    KTH Research School, University of Gävle.
    Evaluation of discharge coefficients for window openings in wind driven natural ventilation2006In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 5, no 1, p. 43-52Article in journal (Refereed)
    Abstract [en]

    This paper describes the classical approach for calculation of wind driven airflow through large openings in buildings and discusses the fulfilment of the limiting assumptions. It is demonstrated that the limiting assumptions are not fulfilled for large openings in buildings for cross ventilation, and therefore, the classical approach is not appropriate for prediction of airflow through large openings in buildings in the cross ventilation case. Using the approach for real openings and estimating the discharge coefficient for window openings has also not been very successful. The discharge coefficient cannot be regarded as a constant and it is very difficult to estimate correct values resulting in less accuracy of prediction of natural ventilation.

  • 6. Jansson, Anders
    et al.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering (name changed to Building Service and Energy Systems 2012-03-01).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Sundh, Jon
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Söderberg, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Ultrafine Particle Formation from Wear2010In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 9, no 1, p. 83-88Article in journal (Refereed)
    Abstract [en]

    Much attention is given to the consequences of airborne particles on human health and well-being. Wear is one source of airborne particles and contributions in the urban environments from wheel-to-rail contacts and disc brakes cannot be neglected. Traditionally, mechanical wear has been associated with the generation of particles of diameters of some microns. However, the research described has found ultrafine particle generation from wear processes. Particle generation from wear was measured under controlled laboratory conditions. The wear was created through sliding contact in a tribometer (type "pin-on-disc") with different materials and with different sliding velocities and pressures, to represent rail traffic and automobile disc braking. Particle concentrations and size distributions in the air were determined for particle diameters from 10 nm up to more than 10 mu m. For most materials and conditions three particle size modes were found: one at 50-100 nm, one at a few hundred nm and one at a few mu m particle diameter.

  • 7.
    Kobayashi, Tomohiro
    et al.
    University of Gävle, KTH Research School.
    Sagara, K.
    Yamanaka, T.
    Kotani, H.
    Sandberg, Mats G.
    University of Gävle, KTH Research School.
    Wind driven flow through openings: Analysis of the stream tube2006In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 4, no 4, p. 323-336Article in journal (Refereed)
    Abstract [en]

    Wind approaching a building provided with openings on the windward and leeward sides has a choice, either it flows through the openings or flows around and above the building. This choice gives rise to a dominant stream tube containing the fluid flowing through the openings. In this paper the stream tube is analysed based on wind tunnel measurements and CFD simulation. A house model with dimensions 120 mm (Width)× 120 mm (Height)× 180 mm (Length) was provided with rectangular openings of equal size located opposite each other. The end walls were thin giving rise to a sharp edged opening. The size of the openings expressed as the porosity (opening area divided by the façade area) was 1.3 %, 5.2 %, 11.6 %, 20.7 % and 46.5 %. In the wind tunnel, velocity including velocity fluctuations and pressure were measured along the centre line through the openings. In the CFD prediction it was possible to visualize the stream tube by the method of "flying particles". This made it possible to explore the change in shape of the stream tube and to calculate the cross-sections of the stream tube at different positions and to know the total pressure distribution within the stream tube cross section. Finally, the discharge coefficient based on stream tube analysis was compared to that from a conventional chamber method.

  • 8. Kobayashi, Tomohiro
    et al.
    Sagara, Kazunobu
    Yamanaka, Toshio
    Kotani, Hisashi
    Takeda, Shogo
    Sandberg, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Stream Tube based Analysis of Problems in Prediction of Cross-Ventilation Rate2009In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 7, no 4, p. 321-334Article in journal (Refereed)
    Abstract [en]

    The airflow rate of a building ventilated by wind is usually predicted by using the wind pressure coefficients obtained for a sealed building and discharge coefficients based on measuring the airflow characteristics through an opening in a sealed chamber (chamber method). This can result in the underestimation of wind driven flow through large openings located on opposite sides of a room. In this paper, the discharge coefficient, based on the chamber method, and the actual condition of cross-ventilation are calculated and compared with each other by means of stream tube analysis. The driving pressure based on wind pressure coefficients obtained from a sealed building are also compared with those based on pressures inside the stream tube of the actual flow field representing a porous rather than sealed building. A building model of dimensions 120 mm (width)x120 mm (height)x180 mm (length) was used for the analyses. The size of openings, expressed as the porosity (opening area divided by facade area), was 11.6 %, 20.7 % and 46.5 %. These models were analyzed by CFD simulation and the stream tubes caught by the opening were determined. From the analysis the errors in discharge coefficient and wind pressure coefficient were identified. Finally, the flow rate based on these discharge coefficients and driving pressures were calculated and compared. It is shown that the effect of the underestimation of the discharge coefficients by the chamber method is significant for all cases of porosity studied in this paper. Moreover, it is shown that the use of wind pressure coefficients is not appropriate for the case of extremely large openings.

  • 9.
    Myrefelt, Sonny
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Functional Availability of Climate and Ventilation Systems2005In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 4, no 2, p. 133-142Article in journal (Refereed)
    Abstract [en]

    Functional availability is used to quantify the probability of a system's capability both to be in an operational state and, at the same time, maintain the intended levels of the functions. The purpose of the work described in this paper is to determine if functional availability can be used for the evaluation of performance procurement contracts. This study involved making measurements in an office building over eight consecutive periods during July and August. This monitoring showed that the HVAC-system did not perform as well as it should and that, in each case, the system functional availability was found to be below 0.7 (sometimes much less). This meant that the performance criteria studied were attained for less than 70% of the monitoring time. Although there was no contract regarding the level of functional availability, it is evident that the situation was not acceptable. In this building, only the operational staff handled the malfunctions and they were unable to secure desirable conditions. Using the functional availability as an active tool, during the whole building process, helps all of those involved to focus on functions. This, in turn, should increase co-operation to reach these aims. This study showed that the use of functional availability could form a basis for determining how well functions are maintained. However, there is still much work needed before it can be used for performance procurement contracts.

  • 10.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Do Train Tunnels Need Ventilation Systems?2010In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 9, no 1, p. 89-92Article in journal (Refereed)
    Abstract [en]

    A planned new train tunnel under the central parts of Stockholm was intended to be ventilated by natural ventilation and the movement of the trains. However, the amount of heat generated by the trains is so high that natural ventilation would give abnormal temperatures and velocities in the tunnel and at the stations. The heat adsorbed by the rock surrounding the tunnel can be neglected in comparison with the amount transported by air. Some of the problems with the ventilation system are described and also the problems with dust generation by the trains and the exposure to dust at the stations by the passengers. The final decision was to use glass walls at the stations to separate the ventilation for the tunnel from that for the stations.

  • 11.
    Sattari, Amir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Service and Energy Systems. KTH/HiG.
    Sandberg, Mats
    HiG.
    PIV Study of Ventilation Quality in Certain Occupied Regions of a Two-Dimensional Room Model with Rapidly Varying Flow Rates2013In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 12, no 2, p. 187-194Article in journal (Refereed)
    Abstract [en]

    The use of supply jet flows is the most common type of air distribution for general ventilation. Usually the supply flow rate is constant or slowly varying (VAV-systems) to cope with a varying load. A novel air distribution method, with the potential to reduce stagnation and to increase the ventilation efficiency, is to introduce rapid flow variations (pulsations). This paper reports on a fundamental study of this type of air distribution. The purpose of the study was to explore the effect of flow variations on stagnant zones and the levels of the turbulent kinetic energy and the relative turbulence intensity. A small scale room model is used that consists of an enclosure with a ventilation supply at the bottom and an extract at the top of the opposite wall. Water was used as an operating fluid and the model had a design which mainly generated a two-dimensional flow. The size of the model made it possible to investigate the two-dimensional velocity vector field using the Particle Image Velocimetry (PIV) method in regions corresponding to occupied regions. Further post processing was conducted from the resulting vector fields. The comparison between cases of constant inflow and pulsated inflow (flow variations with frequency of 0.5 Hz) was conducted for three domains: two belonging to the far-field occupied zone and one belonging to the near-field, downstream of the supply wall jet.            

  • 12.
    Sattari, Ämir
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Service and Energy Systems. Building Technology, Högskolan Dalarna (Dalarna University), Falun, Sweden.
    Particle image velocimetry visualization and measurement of airflow over a wall-mounted radiator2015In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 14, no 3, p. 289-302Article in journal (Refereed)
    Abstract [en]

    A common room-heating technique involves the use of a wall-mounted radiator without forced convection. The cold surrounding air passes adjacent to the warm surfaces of the radiator where it absorbs heat and gains momentum to rise along the wall surface and finally circulate in the entire room. Understanding the properties of heated airflows is important for several purposes. To understand the flow process it is important to identify where the transition from laminar to turbulent flow occurs and to quantify the turbulent fluctuations. With the objective to characterize the airflow in the vicinity of wall surfaces, the local climate over the radiator was visualized and measured using a two-dimensional particle image velocimetry technique. The PIV technique yields 2D vector fields of the flow. The resulting vector maps were properly validated and post-processed using in-house software to provide the average streamlines and other statistical information such as standard deviation, average velocity, and covariance of the entire vector field. The results show that, for a room with a typical heating power, the airflow over the radiator becomes agitated after an ordinate of N = 5 - 6.25 over the radiator upper level, in which N is the dimensionless length based on the thickness of the radiator. Practical problems encountered in near-wall PIV measurements include generating a homogeneous global seeding that makes it possible to study both plume and entraining region, as well as optical problems due to near-surface laser reflection that makes the measurement process more complicated.

  • 13. Wigö, Hans
    Effects of intermittent air velocity on thermal and draught perception during transient temperature conditions2008In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 7, no 1, p. 59-66Article in journal (Refereed)
    Abstract [en]

    : Previous research has shown that air movement has a significant influence on humans' thermal comfort. For persons feeling cool, air movement tends to be perceived as draught, whilst when feeling warm air movements may provide a desired cooling effect. In the transition zone it therefore seems difficult to use constant air velocity as a tool for cooling without creating draught problems. Nevertheless, from an energy saving perspective it appears to be far more efficient to use enhanced convective cooling, induced by the air movement, to cool only the occupants instead of the entire building. One possible way to use air movement as a method to improve thermal comfort without resultant draught problems could be to use intermittent air velocity instead of constant velocity. The present paper reports results from three experiments where subjects have been exposed to velocity variations, showing support for the hypothesis that it is possible to cool humans and reduce the percentage of occupants who are dissatisfied with the room temperature, without creating draught problems, through intermittent cooling.

  • 14. Wigö, Hans
    et al.
    Nilsson, Håkan O.
    Application of a thermal manikin to evaluate heat loss rates from people caused by variations in air velocity and air temperature2004In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 3, no 3Article in journal (Refereed)
    Abstract [en]

    Heat loss monitoring from a thermal manikin was undertaken representing an occupant in a classroom during a lesson period of 80 minutes in which the room temperature was increased from 21 to 24°C for various airflow velocity configurations. A group of subjects was exposed to various conditions of temperature and airflow rate so that the impact of these variations on their surface/skin temperature could be determined. It was found that skin temperature remained stable and close to 34°C for all conditions of exposure. Thus, over the temperature and air velocity range considered, these new findings verified the suitability of using a thermal manikin, set to steady uniform surface temperature, to determine the heat loss characteristics from occupants subjected to intermittent velocity       variation. When the manikin was exposed to a high velocity pulse, the heat loss from the       whole body increased by 10% while the heat loss from exposed areas (hands and face) increased by 20 % (when compared to no velocity pulse). After the 80 minutes monitoring period, the total energy loss from a manikin exposed to velocity variations was 2% higher than when exposed to constant low velocity.

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