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  • 1.
    Blomqvist, Claes
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    Distribution of Ventilation Air and Heat by Buoyancy Forces inside Buildings: An Experimental Study2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The main task of the ventilation system in a building is to maintain the air quality and (together with the heating or cooling system) the thermal climate at an acceptable level within the building. This means that a sufficient amount of ventilation air at the appropriate temperature and quality must be supplied to satisfy thermal comfort and air quality demands and that this air is distributed to the parts of the building where people reside. Air movements caused by buoyancy forces can determine the distribution of ventilation air within buildings. The purpose of this thesis is to advance the state of knowledge of buoyancydriven air movements within buildings and to determine their importance both for ventilation air distribution and the maintenance of thermal comfort and air quality in buildings. The work is focused on studying thermally-driven air movements through large openings, both horizontal and vertical (i.e. doorways). The properties of a special type of thermally-driven currents, so called gravity currents, have also been explored.

    Large vertical openings like doorways are important for air exchange between rooms within a building. Air movements through doorways separating rooms with different air temperatures are often bidirectional and the buoyancy-driven flow rates are often greater than those caused by the mechanical ventilation system alone. Bidirectional flows through doorways can effectively spread contaminants, for example, from a kitchen or a hospital rooms, yet the results of this study indicate that the conversion of a thermally-driven bidirectional flow to a unidirectional flow via an increase of the mechanically forced flow rate requires forced flows that are more than three times greater than the thermally-driven flows. Experiments conducted in this project indicate that the resistance to buoyancy-driven flows in horizontal openings is significantly greater than that in vertical openings. Model tests have shown, however, that this problem may be mitigated if a simple model of a staircase located in the centre of the room (being ventilated) is linked to the horizontal ventilation opening. Gravity currents in rooms occur in connection with so called displacement ventilation as cool gravity currents propagate along the floor that are driven by the density difference of the ventilation air and the ambient, warmer air within the room. As these gravity currents easily pass obstacles and to a certain extent are self-controlling, they can effectively distribute the cool air within rooms in a building.

    Likewise, warm gravity currents occur when warmer air introduced in a room rises and spreads along the ceiling plane. One application where warm gravity currents may be used to advantage is when converting buildings from electric heating to district hot water heating thus, avoiding the introduction of an expensive hydronic heating system. This report includes a full-scale laboratory study of the basic properties of thermally-driven warm air gravity currents in a residential building and examines the possibilities of using the resulting air movements for the distribution of ventilation air as well as heat. Results from laboratory tests show that this conversion method may prove effective if certain conditions on the layout of the building are fulfilled.

  • 2.
    Blomqvist, Claes
    et al.
    KTH, Tidigare Institutioner                               , Byggvetenskap.
    Sandberg, Mats
    Högskolan i Gävle, Avdelningen för inomhusmiljö.
    A Note on Air Movements through Horizontal Openings in Buildings2002Inngår i: The 8th International Conference on Air Distribution in Rooms: Inividual Controlled Environment, 2002Konferansepaper (Fagfellevurdert)
  • 3.
    Blomqvist, Claes
    et al.
    KTH, Tidigare Institutioner                               , Byggvetenskap.
    Sandberg, Mats
    Högskolan i Gävle.
    Air Movements through Horizontal Openings in Buildings – A Model Study2004Inngår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 3, nr 1, s. 1-10Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 4.
    Blomqvist, Claes
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    Sandberg, Mats
    Högskolan i Gävle, Avdelningen för inomhusmiljö.
    Conversion of electric heating in buildings An unconventional alternative2008Inngår i: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 40, nr 12, s. 2188-2195Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To decrease the electric energy used for heating buildings it has become desirable to convert direct electrical heating to other heat sources. This paper reports on a study of the possibility of using an unconventional method for conversion to avoid installing an expensive hydronic system. The conversion method combines the ventilation and heating systems and uses air instead of water for distribution of heat within the building, taking advantage of thermal forces and the special properties of gravity currents. Full-scale tests have been carried out in a test apartment inside a laboratory hall where the conditions could be controlled. Temperatures and efficiency of ventilation have been measured to ensure that the demands with respect to thermal climate and air exchange were fulfilled. The results show that it is possible to use the method for heating and ventilation when converting the heating system, but further work has to be done to develop a detailed solution that works in practice. (C) 2008 Elsevier B.V. All rights reserved.

  • 5.
    Blomqvist, Claes
    et al.
    KTH, Tidigare Institutioner                               , Byggvetenskap.
    Sandberg, Mats
    KTH, Tidigare Institutioner                               , Byggvetenskap.
    Measurements and Control of Air Movements within a Building1997Inngår i: 18th AIVC Conference: Ventilation and Cooling, 1997, s. 427-436Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    There are a number of methods available concerning with distribution of air in buildings. Within control research, one can find new control algorithms which have not yet been used in practice. These new algorithms open the possibility of developing and implementing of new demand controlled ventilation systems.

    In a building the internal air motions are due both to differences in temperature and pressure differences caused by the ventilation system. Therefore, one fundamental question is to what extent it s possible to control the air motions within a building using fan powered ventilation in combination with temperature control.

    The aims of this paper is to report on measurements done to examine the influence of temperature differences between rooms on the air exchange through open doors in a building and to explore the use of modern control technique to minimise the temperature difference.

    The result of the measurements shows that even very small (0.1-0.2°C) temperature differences between rooms cause bi-directional air flows in the doorways of a magnitude that exceed the flow rates caused by the mechanical ventilation system. Therefore it is necessary to control the temperatures in the rooms to make it possible for the ventilation system to distribute the air to those parts of the building where it is needed.

  • 6.
    Blomqvist, Claes
    et al.
    KTH, Tidigare Institutioner                               , Byggvetenskap.
    Sandberg, Mats
    Högskolan i Gävle, Avdelningen för inomhusmiljö.
    Spread of Gravity Currents within a Multi-Room Building2000Inngår i: The 7th International Conference on Air Distribution in Rooms: Ventilation for Health and Sustainable Environment, 2000Konferansepaper (Fagfellevurdert)
  • 7.
    Blomqvist, Claes
    et al.
    KTH, Tidigare Institutioner                               , Byggvetenskap.
    Sandberg, Mats
    KTH, Tidigare Institutioner                               , Byggvetenskap.
    To what extent can one with mechanical ventilation control the air motions within a building1996Inngår i: ROOMVENT'96: 5th International Conference on Air Distribution in Rooms, 1996, s. 265-272Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    There are a number of methods available concerning with air distribution in buildings. Within control research, one can find new control algorithms which have not been used in practice yet. These new algorithms open the possibility of developing and implementing of new demand controlled ventilation systems.

    In a building the internal air motions are due both to differences in temperature and due to pressure differences induced by the ventilation system. Therefore, one fundamental question is to what extent one can with fan powered ventilation control the air motions within a building.

    The aims of this paper is to report on development of methods to study the air motions in a multi room residence apartment using various combinations of exhaust and supply air management. The experimental work includes measurements of air flow rates in door openings in both directions and use of various tracer gas methods to determine the supply air flow to each room, and identifying flow paths.

    In an accompanying paper (Björsell 1996) is reported on the results from a simulation of the performance of different control algorithms.

  • 8.
    Blomqvist, Claes
    et al.
    KTH, Tidigare Institutioner                               , Byggvetenskap.
    Sandberg, Mats
    Högskolan i Gävle, Avdelningen för inomhusmiljö.
    Transition from Bi-directional to Unidirectional Flow in a Doorway1998Inngår i: ROOMVENT '98 : proceedings: 6th International Conference on Air Distribution in Rooms, 1998, s. 539-546Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The air flow in a doorway is governed by density difference caused by temperature difference and pressure difference caused by mechanical ventilation. Tests have been carried out in a unique indoor test house where the room to room to temperature difference could be controlled very accurately with a new control system. In addition to these tests some tests were carried out in a scale model with water as the operating fluid. Two main criteria of unidirectional flow in a doorway have been explored:

     

    1a.     The recorded mean velocity is unidirectional

    1b.     The neutral height is equal to the height of the door

    2.       Unidirectional flow in the sense that

     

    there is no transfer of contaminant from one room to another. To explore condition one the velocity profile in the doorway have been recorded by transversing the door opening. Condition two has been explored by using tracer gas technique.

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