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Register a new userSelection of Phase Change Materials (PCMs) for residential air conditioning in summer
اختيار المواد متغيّرة الطور (PCM) من أجل تكييف هواء المنازل في فصل الصيف
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مها احمد( باحث )
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المواد متغيرة الطور (PCM) عبارة عن مواد تمتص كمية كبيرة من الطاقة الحرارية عند تغير الطور صلب/سائل و تقوم بتحريرها عند التصلب. لذلك إحدى استخدامات المواد متغيرة الطور هي تخزين الطاقة الحرارية، حيث يمكن للمواد متغيرة الطور المدمجة مع مواد البناء أن تزيد من العطالة الحرارية للأبنية و أن تخفض الطاقة اللازمة للتدفئة و التكييف. يعتبر هذا مناسباً بشكل خاص للأبنية التجارية التي تكون عادة ذات هيكل خفيف. لكن الإيصالية الحرارية الضعيفة للمواد متغيرة الطور تُعتبر من أهم الخواص التي تحدّ من استخدامها. الهدف من هذه الدراسة هو اقتراح اختيار مواد ذات إيصالية كافية لأن تسمح بتحقيق التكييف خلال فصل الصيف لتحدّ بل لتلغي استخدام الطاقة (الكهربائية أو الوقود) باستخدام جدران حاوية على مواد متغيرة الطور. تتكون الدراسة من جزأين: ـ الجزء الأول يستعرض مشاكل الدراسة، و يبيّن المجال الذي يمكن ضمنه استخدام المواد متغيرة الطور كنظام تكييف سلبي. ـ الجزء الثاني وضع معايير الاختيار التي ستسمح مبدئيّاً باختيار مواد معينة.
The Phase Change Materials (PCM) are materials which absorb a great quantity of energy during the change of phase solid /liquid and relies it during solidification An application of these materials is thermal energy storage. The PCM integrated into materials of the building can reinforce their inertia and reduce the power necessary for the heating and air conditioning. This is particularly true for the buildings of the tertiary sector whose envelope is light. Nevertheless, one of the characteristics which limits the use of the PCM is their low conductivity. The objective of this article is to propose a selection of materials having a conductivity high enough to make it possible to ensure an air conditioning in summer while limiting, even while removing, the use of energy (electricity or fuel) thanks to walls containing these PCMs. This article consists of two parts: - The first part exposes the problems of the study and specifies the context in which the use of a PCM as a passive air conditioning system fits. - The second part fixes the selection criteria which will allow, in a first approach to choose certain materials.
References used
PEETERS, L.F.R., DEAR, R. DE, Hensen, J.L.M. & D'HAESSELEER, W. Thermal comfort in residential buildings: Comfort values and scales for building energy simulation. Applied Energy, 86 (5), 2009, 772-780
AGYENIM, F., The use of enhanced heat transfer phase change materials (PCM) to improve the coefficient of performance (COP) of solar powered LiBr/H2O absorption cooling systems. Renewable Energy, 87, 2016, 229-239
BABY, R., BALAJI, C., Thermal optimization of PCM based pin fin heat sinks: An experimental study, Applied Thermal Engineering, 54, 2013, 65-77
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When the temperature of the external surface of a wall increases, it is important to predict what the thickness of the wall will be so that the internal surface of the wall does not exceed a limit value. We will study, by an analytical method, the ca
se in which the external surface temperature is linearly varying with time in order to determine the time for which the temperature does not exceed a predetermined limit value at a given depth from the surface. Two cases will be considered: the first one is for a wall made of a homogeneous material (e.g. concrete) and the second one is for a wall made up of concrete and phase-changing material whose melting temperature will be selected according to the desired temperature. The results obtained show that a significant delay to reach this temperature can be obtained between the two cases.
Latent heat storage is an economical way to achieve energy
efficiency and improve thermal comfort in buildings.
In this research, the effects of using PCM Wallboards in a
residential apartment envelop located in Homs was studied by PCM
Express so
ftware.
PCM wallboard with 23°C melting temperature was used and
installed on the inner face of the walls and ceiling of the apartment.
This investigation shows that the importance of using PCMs in
buildings envelope, compared with conventional thermal insulation
materials, due to the effectiveness of PCMs materials and storing
and releasing of thermal energy, which contributed to reducing of
thermal loads and improved the internal thermal comfort.
The walls containing phase change materials (PCM) play a significant role in the
air conditioning of buildings. However, one of the characteristics which limits the use
of PCMs is their low conductivity. It is possible to solve this problem by coup
ling a
metal matrix with the PCM. The aim of this study is to determine the optimal size of a
wall which allows a complete change of state, and a homogenization of the temperature
without a too fast change-of-state rate. To study the thermal behavior of the wall, we
have carried out a numerical simulation using the COMSOL® software in considering a
unit cell. To describe the change of state, the method of the equivalent heat capacity
has been used. Paraffin has been chosen as PCM (melting temperature 24.5 °C). The
influence of the nature and the volume fraction of the metal were determined. The case
of honeycombs made of aluminum has been specifically treated.
The objective of this investigation is to study the influence of application of phase
change material (PCM) in solar basin stills for improving its productivity.
The experimental results of this investigation showed that using phase change
materia
l (paraffin wax) in solar basin still improved its daily productivity, which increased
with increasing the mass of phase change material. The highest increase ratio of daily
productivity was 26.3[%] when using 3.5[kg] of phase change material in plastic case, and
it was 34.74[%] when using 4.5[kg] of phase change material (PCM) in metal case.
Also the experimental results of this investigation showed an increase in the period
of working basin still provided with phase change material compared with basin still
without phase change material. This is owing to the latent heat stored in phase change
material, which is emitted to water when solar radiation decreases. This results in longer
period of work for the basin still.
This research was done by using a mathematical modeling for a heat storage tank by
the preparation a mathematical function using MATLAB software for charging and discharging
phase of the storage tank . it was applied partial storage strategy on a d
efault
building located in the city of Palmyra in the Syrian desert. peak cooling load (420 kW)
and storing (1420 kw-h) within a storage tank size of "30m3" So that the store of ice at
night and melting using outer fusion technology (External Melt) in thermal and electrical
peak hours in the next day .
The results showed the feasibility of a thermal modeling of the tank to cover the
air-conditioning load cooling load required ,the results also showed the shift of part of the
electrical daily load of the chiller about (576 Kw-h) with a clear reduction of mechanical
and electrical equipment with the provision of using electrical energy to a summer season
about (1376 kW-h/Season) and improving the daily electrical factor (DLF) achieves stability
of the electric system.
This paper presents the results can be generalized to large projects in the tropics
help in thermal and power consumption peak shift.
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