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  • 1.
    Cehlin, Mathias
    et al.
    KTH, Superseded Departments, Built Environment.
    Moshfegh, B
    Numerical and Experimental Investigation of Airflows and Temperature Patterns of a Low-Velocity Diffuser2002In: Proceedings of 9th International Conference on Indoor Air Quality and Climate, 2002, p. 765-770Conference paper (Refereed)
    Abstract [en]

    In this article, four turbulence models are studied to capture the flow and temperature behavior of the air close to a low-velocity diffuser for displacement ventilation. Turbulence is modeled by means of one zero-equation model and three different two-equation models, i.e. the LVEL, the RNG, the Standard k-e, and the Chen-Kim model. They are evaluated for their performance in predicting the air flow patterns and temperature profiles close to the diffuser. The models are validated with measurements performed both with traditional point measuring techniques and a whole-field measurement method. The prediction of the velocity and the temperature by the three two-equation models is generally satisfactory. The predictions from the RNG and the Chen-Kim model were almost the same and slightly different than the standard k-e model. The RNG model and the Standard k-e model are computationally much more stable than the Chen-Kim model.

  • 2.
    Cehlin, Mathias
    et al.
    KTH, Superseded Departments, Built Environment.
    Moshfegh, B
    Sandberg, M
    Measurements of Air Temperatures Close to a Low-Velocity Diffuser in Displacement Ventilation Using Infrared Camera2002In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 34, p. 687-698Article in journal (Refereed)
    Abstract [en]

    The near zone of supply air diffusers is very critical for the indoor climate. Complaints of draft are often associated with low-velocity diffusers in displacement ventilation because the air is discharged directly into the occupied zone. Today, the knowledge of the near zone of these air supply diffusers is insufficient, causing an increased need for better measuring methods and representation of the occupied zone.

    A whole-field measuring technique has been developed by the authors for visualization of air temperatures and airflow patterns over a large cross-section. In this particular whole-field method, air temperatures are measured with an infrared camera and a measuring screen placed in the airflow. The technique is applicable to most laboratory and field test environments. It offers several advantages over traditional techniques; for example, it can record real-time images within large areas and capture transient events.

    The purpose of this study was to conduct a parameter and error analysis of the proposed whole-field measuring method applied to a flow from a low-velocity diffuser in displacement ventilation. A model of the energy balance, for a solid measuring screen, was used for analyzing the influence of different parameters on the accuracy of the method. The analysis was performed with respect to the convective heat transfer coefficient, emissivity, screen temperature and surrounding surface temperatures.

    Theoretically, the temperature difference between the screen and the ambient air was found to be 0.2–2.4 °C for the specific delimitation in the investigation. However, after applying correction the maximum uncertainty of the predicted air temperature was found to vary between 0.62 and 0.98 °C, due to uncertainties in estimating parameters used in the correction. The maximum uncertainty can be reduced to a great extent by estimating the convective heat transfer coefficient more accurately and using a screen with rather low emissivity.

  • 3.
    Cehlin, Mathias
    et al.
    KTH, Superseded Departments, Built Environment.
    Moshfegh, B
    Sandberg, M
    Visualization and Measuring of Air Temperatures Based on Infrared2000In: Proceedings of the 7th International Conference on Air Distribution in Rooms, 2000, p. 339-347Conference paper (Refereed)
  • 4.
    Hed, Göran
    KTH, Superseded Departments, Built Environment.
    Service life planning carried out in a building project2003In: International journal of low energy and sustainable buildings, ISSN 1403-2147, Vol. 3Article in journal (Other academic)
  • 5.
    Hed, Göran
    KTH, Superseded Departments, Built Environment.
    Service Life Planning in Building Design1998In: CIB World Building Congress 1998, 1998, p. 201-209Conference paper (Other academic)
  • 6.
    Hed, Göran
    KTH, Superseded Departments, Built Environment.
    Service life planning of building components1999In: 8th International Conference on Durability of Building Materials and Components: Vol. 2, 1999Conference paper (Refereed)
  • 7.
    Hed, Göran
    KTH, Superseded Departments, Built Environment.
    Use of phase change material for change of thermal inertia of buildings2004In: 6th Expert Meeting and Workshop of Annex 17, 2004Conference paper (Other academic)
    Abstract [en]

    Phase change materials can be used to change the thermal inertia of buildings. In this paper a simulation program is presented where the use of the material is investigated in a night cooling system. The phase change material that is used is Glauber’s salt mixed with a gel, enclosed in aluminium pouches. The melting point is 24°C. The aluminium pouches, which are approximately 10 mm thick are placed in an air heat exchanger. The crystallisation takes place during night where cool night air is let in to the building and into the material, the cool air is thereafter released into the building during the day.

    The building types that are investigated are buildings where there is an overproduction of heat during the daytime such as offices, schools, shopping centres etc.

    In the paper a simulation of three different buildings is presented. A school, an office and a shopping centre. Each building were assigned with different thermal inertia, lightweight, medium weight and heavy weight building. The buildings were simulated with finite difference method. A network model was programmed in Mathcad. Climate data, air temperature and solar radiation on a horisontal surface were from the summer 2002 in Gävle, Sweden. That summer was an unusually hot summer.

    The simulations show that the use of the phase change material has a significant effect on the maximum indoor air temperature during the day. The effects are more apparent in the lightweight buildings than in the heavy weight buildings.

  • 8.
    Mattsson, Magnus
    KTH, Superseded Departments, Built Environment.
    On the efficiency of displacement ventilation1999Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    The efficiency of room ventilation by the displacementprinciple was studied with respect to some influential factors,in particular that of physical activity. The study wasexperimental and performed in two full-scale test rooms, one ofoffice-size and one of classroom-size. Physical activity wasexecuted in these rooms by person simulators and by humans. Theventilation efficiency was quantified by tracer gasmeasurements.

    In the performed tests, the activity of a walking persongenerally proved detrimental to the ventilation efficiency.Particularly the air quality in the occupied zone was impaired,due to down-wash of air in the wake behind the moving person,causing transportation of relatively old and contaminated airfrom the upper part of the room down to lower levels. Itappeared, however, that it takes a rather high level ofphysical activity to completely abolish the displacementeffect. Especially the air quality in the breathing zone ofnon-moving occupants tended to remain significantly better thanat perfect-mixing conditions. Completely mixed room airoccurred nevertheless when the activity was intense, but thedisplacement flow pattern was re-established fairly quicklyafter ceasing of the activity.

    The contaminant distribution showed substantial horizontalvariations in the "classroom". A contaminant released in theoccupied zone was effectively extracted from the room when thesource was situated on the same side of the room as the extractterminal(s), whereas, when situated on the opposite side, thecontaminant accumulated in the upper part of the room. It wasfurther shown that the air supplied from displacement diffuserstends to reach all occupants fairly quickly, also in relativelylarge and densely populated rooms, likeclassrooms.

    The temperature stratification of the room air, andfree-convection currents along the walls are crucial for theappearing air flow pattern and contaminant distribution.Transfer and accumulation of heat in materials tend further tomake the thermal conditions indoors more or less transient atall times. This entails, it was shown, that also theventilation efficiency is time dependent. In tests where peoplesuddenly entered the "classroom", the ventilation efficiencyimproved with time. This generally caused the highestcontaminant exposures to occur at the beginning of the stay inthe room.

    Tests with two different ceiling heights showed lowerventilation efficiency with the higher ceiling, involving ahigher contaminant exposure of the occupants. A walltemperature deviating from that of the indoor air impaired theventilation efficiency, whereas an increase in ventilation rateimproved it. In all test cases in this study, however, the airquality in the breathing zone of seated occupants remainedsignificantly better than that at perfect-mixing conditions–a sports-activity test being the only exception.

    Key words:Displacement ventilation, Ventilationefficiency, Physical activity, Movements, Transient behaviours,Ceiling height, Wall temperature.

  • 9.
    Norberg, Peter
    KTH, Superseded Departments, Built Environment.
    Microclimate measurements in the built environment1998Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Surface moisture plays an important role in thedeterioration of building surfaces. The extent and duration ofsurface moisture is generally impossible to predictfrommeteorological data and consequently direct measurement ofthis quantity is essential,e.g. using the WETCORR method. Thismethod has been developed in Scandinaviaduring the past 25years. From the beginning it was intended for measurementsofinstantaneous atmospheric corrosion rates and TOW (time ofwetness) using corrodingelectrolytic cells. Over the past 15years the method has been extended tomeasurements of surfacemoisture and TOW on building materials in general. To thatend amodified measuring concept has gradually been developed,including an inertelectrolytic cell with electrodes of gold(Au). More recently, the method has also been applied tomeasurements of moisture content (MC) in various materialsusingmodifications of the traditional pin-type electrodes.

    This thesis summarises various measurement projects thathave involved theWETCORR method during the past 10 years. Someprojects are entirely focused on the method as such, some aremore concerned with the interaction between themoisture sensorand the environment. In some cases attempts are made tocorrelate TOW with corrosion.

    The limitations of the ISO 9223 standard for estimating TOW(RH>80%, T>0°C) isclearly illustrated. Theshortcomings of the ISO standard become evident in climateswith sub-zero temperatures, in environments with significantdeposition of pollutantsand salt, and in situations where theexchange of radiation between building surfaces and thesurrounding environment creates large temperature differenceswhich in turnmay either promote or inhibit condensation.

    A generalised definition of TOW based on the conductivity ofthe surface electrolyterather than the thickness of themoisture film is proposed. The modified TOW is called time ofconduction or time of corrosion, (TOC). Strict measurement ofTOC requiresthe use of an inert electrolytic sensor andexcitation by AC or pulsed DC withreversing of the polarity.This is different from the present WETCORR technique.Theadoption of the TOC concept opens up the possibility ofdividing time into "wet" and"dry" periods. This is believed tofacilitate for the development of dose-responsefunctions basedon the real physical/chemical processes occurring on materialsurfacesrather than on a parametric approach.

    The WETCORR technique has proven to be very useful also formeasurements of MCin wood, a measurement concept called INWOOD.The general principles andtheoretical considerations for woodmoisture measurements are reviewed, includingthe derivation ofsemi-empirical relationships describing the dependence ofresistivity on MC, temperature and dry density of wood. Thesame technique should be possible to use with almost any porousbuilding material.

  • 10.
    Sjöström, Christer
    KTH, Superseded Departments, Built Environment.
    Materials and Technologies for Sustainable Construction1999In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 32, no 2, p. 158-159Article in journal (Refereed)
    Abstract [en]

    The main themes on which the symposium focused helped address some of the issues related to achieving sustainable construction. Evidently the collectively of the work suggests that this area is in the incipient stages and minor but nonetheless significant contributions have been made towards resolving these complex problems. Maintaining and sustaining the built environment through information integration, assessment and analysis techniques and the use of specifications as well as service life models for building materials, components and assemblies is likely to be an involved yet compelling challenge in the decades to come. Editorial Note This joint CIB/RILEM Symposium was one of the events organised during the CIB World Building Congress 1998 in Gävle, Sweden 7–12 June. As the President of CIB, Prof. C. Sjöström was in charge of the organisation of this congress. The Executive Secretariat of CIB 1998 was the Division of Materials Technology, Centre of Built Environment, Royal Institute of Technology, which is also a RILEM Titular Member.

  • 11.
    Sjöström, Christer
    et al.
    KTH, Superseded Departments, Built Environment.
    Bakens, Wim
    CIB Agenda 21 for Sustainable Construction: why, how and what1999In: Building Research & Information, ISSN 0961-3218, E-ISSN 1466-4321, Vol. 27, no 6, p. 348-354Article in journal (Refereed)
    Abstract [en]

    CIB's efforts to create an Agenda 21 for the construction sector are introduced here. CIB's unique position within the international construction community allowed it to initiate a specific sectorial response to the international agendas raised by Brundtland, Habitat II, Rio and Kyoto. CIB's recognition of the problems in establishing both a framework for sustainable development; how change within industry occurs, along with CIB's past, current and proposed activities meant that CIB was perfectly suited to respond to sustainable development. This CIB-led project resulted in global collaboration and co-ordination to specifically address sustainable development for the construction community. Situated between the broad international agendas and more local and subsectorial agendas, CIB's Agenda 21 is a conceptual framework that serves as an intermediary and provides for comparison and co-ordination. The three principal objectives are: to create a global framework and terminology that will add value to national, regional and sub-sectorial agendas; to create an agenda for CIB activities and for co-ordinating CIB with specialist partner organizations, and to provide a source document for definition of R&D activities.

1 - 11 of 11
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