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- Hed, Göran, et al.
(författare)
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Mathematical modelling of PCM air heat exchanger
- 2006
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788 .- 1872-6178. ; 38:2, s. 82-89
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Tidskriftsartikel (refereegranskat)abstract
- In order to cool a room with a cold night air phase change material, PCM, is stored in an air heat exchanger. During night the PCM crystallises, energy is released. During daytime air is circulated in the unit, energy is absorbed and the indoor air is cooled. The characteristic of PCM is that there is an increase of the specific heat over a limited temperature span. This is the principle that is used in the design of the PCM air heat exchanger unit. The action of a PCM storage unit will act differently depending of the thermal properties of the material. In an ideal material the phase transition occurs at a given temperature. On the market, compounds containing PCM are available which, in order to create a suitable melting temperature, are mixtures of different products. In these materials, the transition from liquid to solid takes place over a temperature span, i.e. the specific heat varies with the temperature. This can be represented by a c(p)(T) curve, specific heat as a function of the temperature. In this paper, the development of a mathematical model of the PCM air heat exchanger is presented. Considerations are taken to different shapes of the cp(T) curve. The mathematical model is verified with measurement on a prototype heat exchanger. The development of the equipment is part of the CRAFT project Changeable Thermal Inertia Dry Enclosures (C-TIDE) the possibility of use of phase change materials integrated into a building is explored.
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- Hed, Göran, 1954-
(författare)
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Service life estimations in the design of a PCM based night cooling system
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of Phase Change Material, PCM, to change the thermal inertia of lightweight buildings is investigated in the CRAFT project C-TIDE. It is a joint project with Italian and Swedish partners, representing both industry and research. PCMs are materials where the phase change enthalpy can be used for thermal storage. The Swedish application is a night ventilation system where cold night air is used to solidify the PCM. The PCM is melted in the day with warm indoor air and thereby the indoor air is cooled. The system is intended for light weight buildings with an overproduction of heat during daytime. In the thesis, the results of experiments and numerical simulations of the application are presented. The theoretical background in order design the heat exchanger and applying the installation in thermal simulation software is presented. An extensive program is set up, in order to develop test methods and carry tests to evaluate the performance over time of the PCM. Testing procedures are set up according to ISO standards concerning service life testing. The tests are focused on the change over time of the Thermal Storage Capacity (TSC) in different temperature spans. Measurements are carried out on large samples with a water bath calorimeter. The service life estimation of a material is based on the performance of one or more critical properties over time. When the performances of these properties are below the performance requirements, the material has reached its service life. The critical properties of the PCM are evaluated by simulation of the application. The performance requirements of the material are set up according to general requirements of PCM and requirements according to building legislation. The critical properties of a PCM are the transition temperature, the melting temperature range and the TSC in the operative temperature interval. The critical property of the application is its energy efficiency. The results of the study show that the night cooling system will lower the indoor air temperature during daytime. It also shows that the tested PCM does not have a clear phase change, but an increased specific heat in the operative temperature interval. Increasing the amount of material, used in the application, can compensate this. Finally, the tested PCM is thermally stable and the service life of the product is within the range of the design lives of the building services. It is essential to for all designers to know the performance over time of the properties of PCMs. Therefore it is desirable that standardized testing methods of PCM are established and standardized classification systems of PCMs are developed.
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- Hed, Göran, et al.
(författare)
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Service life testing of PCM based components in buildings
- 2005
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Ingår i: 10DBMC International Conference of Building Materials and Components. ; , s. 253-260
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the CRAFT project C-TIDE (Changeable Thermal Inertia Dry Enclosures) the possibility of changing the thermal inertia of lightweight buildings with PCM, Phase Change Material, is explored. The project is performed in collaboration with Italian and Swedish partners representing both the industry and research. Lightweight buildings represent a well-established technology in Sweden. In Italy this technology is entering the market. A problem is the overheating of the building during the hot season, especially in warm climate but also in Nordic climate during summer. This project deals mainly with this problem. A crucial issue of the use of these materials is the performance over time data of the phase change material that are used in the building. An extensive program is set up to perform long time testing of the thermal properties of the materials that were used in the project. The long time testing programme of the materials was established to correspond with the governing procedure set up by ISO 15686-2 "Buildings and consructed assets– Service life planning – Part 2: Service life prediction procedures". This paper describes the framework of the testing procedure, the set-up of the testing equipment and preliminary results of the tests.
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| 10. |
- Hed, Göran
(författare)
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Use of phase change material for change of thermal inertia of buildings
- 2004
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Ingår i: 6th Expert Meeting and Workshop of Annex 17.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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