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Steady state and transient simulation of a radiant heating system
Full text linkRadiant heating generally addresses all heat emission systems that have a share of radiant heat emission greater than 50 %, compared to a convector or fan coil where the heat is transferred mainly by means of convection. Recently, so-called infrared-heating systems are increasingly discussed as a cost-effective heating system. Relative small areas with high surface temperatures of typically up to 120 °C are used. In order to investigate in detail radiant heating systems, building models able to reproduce accurately the occurring physics phenomena are required. Physics-detailed steady state and transient room models have been developed in Matlab®. The required view factors for the radiative exchange between all surfaces and between each surface and a sphere representing a person are calculated using COMSOL®. Moreover, the thermal comfort in different positions of the room has been evaluated.
1. Introduction
The implementation of the concept of NZEB (Kurnitski et al. (2013) will lead to a further reduction of the heating demand of new buildings. Also the heating demand of the building stock will decrease by applying deep renovation. The technology to achieve very low energy demands is available since about 25 years, when the first Passive House was built in Darmstadt, Germany Feist (2016). Technology and products have been further improved since then and cost-effectiveness has been significantly improved. However, in order to improve the economic feasibility of these very efficient buildings, cost-effective heating systems are required. In parallel the share of renewable energies (such as PV or wind) in the electric grid will further increase. Both these developments make electric heating interesting again in spite of the fact that, because of thermodynamic principles, electricity should not be used for heating
The benchmark of the SIMULINK open library ALMABuild for dynamic modelling of buildings
No full textNowadays, European Directives and National laws impose more and more strict limits on the primary
energy consumption of buildings, pushing towards a new generation of energy saving buildings named Near Zero
Energy Buildings (NZEB). In order to achieve an important reduction of the primary energy consumptions in
NZEB the use of renewable energy, which gives a discontinuous contribution during the day and the season, is
strongly encouraged; due to the typical unsteady behaviour of renewable energies, for an accurate analysis of
the behaviour of NZEB it becomes important to study the dynamic interactions between the building and the
adopted HVAC system. A dynamic analysis of the energy performances of NZEB can be obtained by using
specific dynamic simulation software (i.e. TRNSYS, ESP-r, Energy Plus, MODELICA, DesignBuilder) or by using
a customized approach based on the use of SIMULINK. In the past, some open block libraries made in
SIMULINK have been proposed for the dynamic analysis of HVAC system. However, a weak point of these
libraries is the creation of the building model. In fact, no fully satisfactory SIMULINK blocks for the accurate
modelling of a whole building have been presented up to now; in many cases, the user is called to add manually
all the envelope elements by setting the thermo-physical properties of each element and connecting each
element to the others. In this way, the modelling of a building becomes not only time consuming but it becomes
an activity characterized by a significant probability to make mistakes during the manual construction of the whole
model. For this reasons, in this paper a new SIMULINK library, named ALMABuild, for the dynamic modelling of
the energy behaviour of a building is presented. The strength point of ALMABuild is that the user is driven
towards the modelling of the building by means of a series of Graphical User Interfaces (GUI). In this paper the
main results obtained during the benchmark of this library, following the BESTEST procedure, are discussed and
the main advantages achieved by using GUIs for the creation of the dynamic building model are described
NUMERICAL EVALUATION OF THE INFLUENCE OF SIZE AND POSITION OF RADIANT AND CONVECTIVE HEAT EMISSION SYSTEM ON THE MAIN INDOOR COMFORT PARAMETERS
Full text linkRadiant heating is increasingly used and the interest in these systems is still increasing because of their low
initial cost and capability in providing ideal comfort conditions coupled with low energy consumptions. In this
system, thermal radiation covers more than 50% of the total heat exchanged and it becomes important to study in
which way the position and the size of the radiant heater within a room influences the indoor comfort. By using
conventional dynamic simulation codes in which the room energy balance is solved with a simplified approach,
detailed information about the optimal position and geometry of the radiant heaters cannot be obtained. In fact,
for the optimization of radiant heating systems it becomes mandatory to introduce a more detailed approach for
the analysis of the heat transferred by radiation among the different surfaces in which radiation physics is
correctly reproduced and this is out of the scope of the commercial dynamic software. In this work a model for the
prediction of the radiant heat flux among the surfaces of a room having different temperatures is described. The
radiation exchange was modelled by means of the net radiation approach. The calculation of the view factors
among the surfaces is obtained by using Matlab. In the paper the effects obtained by adopting different sizes and
positions of radiant and convective heaters in a room on the indoor comfort parameters are analyzed. In addition,
it is shown in which way different envelopes with different thermal insulation levels can influence the distribution
of the operative temperature in the room, the local comfort and the energy demand
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The “Hardware-in-the loop” approach for the experimental test of an innovative dual-source heat pump
No full textIn this paper the lay-out and the main operative features of the new climatic room of the Applied Thermal Engineering Laboratory of the University of Bologna designed for experimental tests on small and medium commercial and innovative heat pumps following the “Hardware in the loop” approach are described and discussed. After the description of the main components of the test rig and its control loop, the main characteristics of the climatic room are presented by means of a series of dynamic simulations obtained by using both TRNSYS 17 and SIMULINK. The double-modelling enables to make a more precise prediction of the behaviour of the thermal loop during dynamic working conditions. The climatic chamber is a room with a volume of 60 m3 and reduced heat losses where commercial or innovative heat pumps having a nominal thermal power lower than 15 kW can be tested under operative conditions which reproduce the real behaviour of a thermal plant. The heat pump can work between two external thermal reservoirs (i.e. air and ground) which can vary their temperature in time reproducing the evolution of the real climatic data (i.e. external air) or of the ground ( by means of a vertical borehole heat exchanger) and one internal reservoir (i.e water) which varies its temperature on the basis of the trend of the building loads (i.e. return water). The hydronic loop of the climatic room is designed in order to reproduce exactly the time dependent trend of the external air during a specific day in a specific site and the trend of the return water temperature due to the instantaneous building loads, obtained with the help of a dynamic simulation software applied to a specific building. In this way the room allows to test the heat pump under realistic conditions in order to obtain information about its performances adopting a specific control logic. As an example, this paper shows in which way the climatic room will be used in the frame of the HEGOS project for the optimisation of the control system adopted for a heat pump able to use two external thermal reservoirs (i.e. air and ground)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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