Thermal testing and numerical simulation of a prototype cell using light wallboards coupling vacuum isolation panels and phase change material

doi:10.1016/j.enbuild.2005.11.002

Energy and Buildings

Volume 38, Issue 6, June 2006, Pages 673-681

https://doi.org/10.1016/j.enbuild.2005.11.002 Get rights and content

Abstract

Light envelopes are more and more frequently used in modern buildings but they do not present sufficient thermal inertia. A solution to increase this inertia is to incorporate a phase change material (PCM) in this envelope. This paper presents the performance of a test-cell with a new structure of light wallboards containing PCMs submitted to climatic variation and a comparison is made with a test-cell without PCMs. To improve the wallboard efficiency a vacuum insulation panel (VIP) was associated to the PCM panel. This new structure allows the apparent heat capacity of the building to be increased, the solar energy transmitted by windows to be stored without raising the indoor cell temperature, and the thickness of the wallboard to be decreased compared with that of traditional wallboards. An experimental study was carried out by measuring temperature and heat fluxes on and through the wallboards. The indoor temperature, which has a special importance for occupants, was also measured.

A numerical simulation with the TRNSYS software was carried out in adding a new module representing the new wallboard. It showed a good agreement with experimental results. This new tool will allow users to simulate the thermal behaviour of buildings having walls with PCMs.

Introduction

The building sector has become (together with the industrial sector) the world dominant energy consumer with 28% of the overall energy consumption [1]. In western countries and in France in particular, this proportion reaches 45% [2] and most of this consumption comes from heating and air-conditioning systems which ensure thermal comfort of occupants. This comfort depends on the desired physiological state for which people can have the feeling of heat or cold. This comfort feeling is, in part, controlled by heat exchange between the body and the environment. For example, the atmosphere can be felt comfortable when there are few variations of temperature in space, from one place or one room to another, or in time either during the day or from a season to another. Moreover, if the air temperature is an important parameter, the wall temperature has also an influence on the comfort feeling [3].

Thermal comfort can be obtained by passive or active means. The passive means are primarily related to thermal storage in the structure of buildings. The active means relate to the transfer of the energy, stored or not, with mechanical or thermal systems.

The buildings with a traditional structure have a large thermal inertia (sensible heat storage) and supply natural air conditioning in the rooms. In the commercial sector, the trend is to decrease the wall thickness to reduce the weight and then the transport costs and the construction time. Latent heat storage by incorporating a phase change material (PCM) into some building materials is an attractive way to compensate for the small storage capacity of most existing modern buildings which use light construction as well as of buildings of the next generation.

Reviews of principles, of available PCMs and current or expected applications were made by a significant number of authors and we can cite the publications of Hasnain [4] and Zalba et al. [5]. Concerning the use of PCM in building materials, a methodology for choosing a PCM has been developed by Peippo et al. [6] for passive solar heating and criteria of choice were given by Gu et al. for thermal energy recovery with air-conditioning systems [7].

After having studied a wall with PCM, several authors studied the performances of these PCM wallboards in cells tests and compared the experimental results with those obtained by numerical simulation. Others carried out only numerical simulations on a whole building or on a part of the building. Kondo et al. [8] developed and tested a wall with PCM. They also studied cells test and developed a simulation program to study the possibility of controlling the fluctuations of temperature. Kissock et al. [9] realized tests on low-size cells with walls manufactured by impregnation of a mixture of hydrocarbon alkyl. These authors compared the results obtained on a reference cell and the cell with PCM. They used wallboards impregnated by paraffin based PCMs and analysed numerically and experimentally a mock-up simulating a house. Peippo et al. presented a method to determine the optimal thickness of a wallboard with PCM [6].

Scalat et al. [10] carried out tests on a room having walls and partitions with PCM. They compared their results with those obtained on an adjacent identical room with conventional walls.

Athienitis et al. [11] made an extensive experimental study as well as a numerical simulation on a cell test on scale 1. The walls had their interior layer made of plasterboard containing approximately 25% in weight of a PCM (butyl stearate). They showed that the use of the PCM could lead to a reduction of 4 °C of the indoor temperature.

The house of BASF [12] has a new lining which contains 10–25% of paraffin particles which can store the latent heat. The wax is incorporated in microcapsules which can be easily incorporated in the concrete and the plaster. The energy consumption per square meter of this house requires only three litres of fuel per annum. This concept also makes it possible to reduce the CO₂ emission of 80%.

Development of a light envelope leads to study multi-layer walls which incorporate electro-chromic glazing, aerogel and PCM [13] thus reducing heating, cutting overheating and taking advantage of solar radiation.

All these studies showed a lot of potential for development of wallboards containing PCMs. On the other hand, using a vacuum isolation panel (VIP) in a wallboard is another way to get a light structure so reducing thermal losses and improving efficiency. Coupling a VIP with a PCM structure combines the advantages of the two systems. The objective of the present study is to analyze experimentally and by numerical simulation the thermal behaviour of two test-cells, one with thin wallboards containing a PCM and a VIP, the other with wallboards without PCMs.

This study is a part of a larger project and in a previous work a PCM wallboard was developed in order to define a component for the light envelope of buildings [3]. Amongst the criteria of the wallboard definition, four were considered imperative: (i) a melting temperature of about 23 °C, (ii) a high storage heat capacity, (iii) a small thickness and (iv) the lowest cost. Several wallboard types were tested. The chosen solution was commercial plasterboard in polyvinyl chloride (PVC) filled up with a PCM. Several PCM were tested and the selected end product was the polyethylene glycol 600 (PEG 600) whose properties are given in Table 1. This choice results from a compromise between the availability, cost and thermal performance. The main problem of this choice remains the large range of the melting temperatures (21–25 °C). However, tests of others PCMs are in progress to improve the melting temperature control and the heat storage capacity.

Section snippets

Structure

Each test-cell consists of one glazed face and five opaque faces insulated with VIPs. In order to increase thermal inertia, one of them is equipped with five panels containing a PCM. Fig. 1(a and b) presents the structure of wallboards with and without PCMs. For the cell without PCM, the walls are constituted of a VIP sandwiched between a fibre panel and a plywood panel. For the cell with PCM, walls are constituted of a VIP between a fibre panel and a plywood panel, and associated with a panel

Sensors

The test-cells were instrumented using thermocouples and heat flux sensors. The calibration of the sensors has been carried out by the manufacturer and verified at the laboratory before use. These sensors were placed on each face of the walls, in order to measure the heat flux between outside and wall, and between wall and inside. These sensors cover an area of 100 mm × 100 mm for a thickness of approximately 420 μm. Their thermal conductivities are much less that those of the VIPs and, in this

Experimental results and discussion

The simultaneous acquisitions of measurements on the two cells began on 26 August 2003 and are always continuing. To discuss the results, few days were extracted from the data.

Heat flux analysis on the west panel

It is noted that heat fluxes on the external surfaces have the same behaviour, except for the north wall and the floor. As a consequence, only results on the western wall are analyzed. In Fig. 8, Fig. 9 are given the variations of the fluxes during 2 consecutive days on the external side (φ_e) and on the internal side (φ_i) of the walls without and with PCM, respectively. Fluxes have a higher amplitude in the case of the cells with PCM. The heat storage and release of the walls without PCM are

Durability tests

The data recording began on 26 August 2003 and is currently continuing. A data base for more than 20 months has been constituted and certain periods can be compared. As an example, the temperatures for several days of September 2004 are presented in Fig. 9 and have to be compared to those of September 2003 (Fig. 11). It is noted that after 480 thermal cycles, the PCM continues to play its role of thermal absorber. The used PCM (PEG 600) was previously tested for 1000 thermal cycles and no

Numerical simulation

The cells, located outside, are thus subjected to the climatic variations which will constitute the external boundary conditions for the numerical simulation. The thermal behaviour of the test-cells was simulated by using the TRNSYS 15 software with IISiBat [16]. TRNSYS is a “transient system simulation program”. The climatic parameters are the boundary conditions and the targeted results are the indoor temperatures. The TRNSYS software simulates the behaviour (thermal, hydraulic, …) of systems

Conclusion

The objective of this study is the realization of building components incorporating a phase change material coupled with a vacuum insulation panel (VIP) (i) to improve thermal inertia of the walls and comfort inside the buildings and (ii) to build a light envelope.

Two test-cells with super-insulated light wallboards were installed, one of them being equipped with PCM panels. Temperature and heat flux measurements allowed us to characterize the thermal behaviour of the two cells submitted to

Acknowledgments

This work was partly financed by ADEME, Agence De l’Environnement et de la Maîtrise de l’Energie, French Agency for Environment and Energy Management.

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