Indoor thermal comfort assessment using different constructive solutions incorporating PCM

doi:10.1016/j.apenergy.2017.09.032

Applied Energy

Volume 208, 15 December 2017, Pages 1208-1221

https://doi.org/10.1016/j.apenergy.2017.09.032 Get rights and content

Highlights

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The overheating rate reduction using PCM solutions.
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Thermal dynamic simulation of a department building: comfort and energy analyses.
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Building features optimization, aiming the energy reduction during the building use.
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Economic analysis to estimate the payback period for the PCM constructive solutions.

Abstract

Sustainable energy and thermal retrofit design of buildings or districts has a strong global impact in the viewpoint of economies and energy-efficiency perspectives. Several aspects such as architectonic design, building materials, construction technology, mechanical systems and outdoor climate determines the thermal behaviour of buildings and their ability to provide indoor thermal comfort to occupants. The use of geothermal energy and phase change materials (PCMs) in the construction systems are an opportunity that may attenuate indoor air temperature fluctuation as well as overheating risk. This paper presents the results of a study on indoor thermal comfort and energy efficiency regarding the PCM’s positive role when applied to new constructive solutions, inside a building with a geothermal system linked to the air conditioning system. The PCM study was based on real and simulated investigations in two rooms of a new university department at the Aveiro campus. Higrothermal monitoring (indoor air temperature) of two rooms in which one of them has PCM panels incorporated into gypsum board partition wall and into a suspended ceiling. The scope was driven to investigate the potential of these solutions for overheating mitigation. The numerical study was conducted by using an evolutionary algorithm coupled with the software EnergyPlus® used in simulations. In the scope of this optimization process, constructive solutions with the incorporation of different types of PCM with different melting temperatures and enthalpy, and different flow rates of natural ventilation were combined to investigate the potential and the payback time of these novel solutions.

The results for the room measurements show that the indoor thermal comfort of the rooms, present long periods of discomfort namely in overheating. However, it was proved that the PCM application in one of the rooms lead to an overheating reduction of 7.23% representing a PCM efficiency of 35.49%. After the optimization process an overheating reduction of about 34% was attained by the use of PCM in one of the rooms. Regarding the economic analysis of the use of the PCM for cooling demand reduction, a payback time of 18 years was attained.

Introduction

Assessing a building with a high level of indoor thermal comfort achieved by passive techniques is the first step to design a low energy building. Indoor thermal comfort becomes a more challenging issue when the indoor spaces are offices or classrooms, with more concerns related to user’s productivity and concentration. Recently the thermal comfort assessment in schools has been receiving more attention by researchers with the publication of studies in this field [1], [2], [3], [4], [5], [6]. Some of them depict the relationship between the user’s performance (including students and teachers) and the indoor thermal comfort conditions [7], [8], [9], [10], [11], [12], [13].

The use of phase change materials (PCMs) in constructive solutions and geothermal systems linked to the active systems for cooling and heating, may be a suitable passive strategy for overheating reduction and to provide better indoor thermal comfort. Several studies have been developed around PCM applications [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29] and integration into buildings, however full-scale applications, real data monitoring in scholar buildings are not easily found in the existing scientific literature. Applications with PCM in different domains have been also studied by other authors, focusing on the integration with refrigeration systems [30] and condensing micro-CHP [31].

The studies regarding real case studies with the use of geothermal energy in schools and other service building are in exponential grow. The ground source heat pump systems usually offer great advantages on the energy efficiency level, over the traditional systems [32], [33], [34], [35]. Additionally, it is important to refer that several authors have proven that these systems in general, have a better energy performance when applied in moderate climates [36], [37], [38]. Note, that the presented study was developed around the PCM effect on the constructive solutions however, a description regarding the system for heating and cooling of the building was made.

The possibility to use full scale models in research studies to characterize solutions is globally an advantage. In the scope of a research project, a constructive solution incorporating PCMs was tested and monitored at real scale in one recently built University department building, referred as CICFANO (in Portuguese “Complexo Interdisciplinar de Ciências Físicas Aplicadas à Nanotecnologia e à Oceanografia”). PCM panels were incorporated into a partition wall and suspended ceiling. Then, the building model was simulated using the software EnergyPlus and calibrated using real data. The PCM effect was evaluated over the indoor thermal comfort comparison in two rooms; with and without PCM incorporated into the constructive solutions. Finally, the payback analysis in regards to the cooling demand was calculated.

Using the knowledge and the results presented in this paper, two constructive solutions containing PCM were tested in a real building and different solutions working in parallel with the building features were optimized and defined. This work allows to optimize the thermal energy transfer between the indoor spaces and the outdoor climate, increasing the indoor thermal comfort and consequently enhancing the energy efficiency of the building, by lowering the use of active systems for heating and cooling. These solutions have the advantage of ensuring good indoor thermal performance for different climatic regions by changing the ventilation system rate to potentiate the efficiency of the PCM. The applied and developed solution can be used into new buildings and as well as into in the existent buildings.

In sum, the first goal of the present study consists in assessing the indoor air temperature comfort as well as the PCM efficiency in the temperature control. The second goal is the optimization of the constructive solutions with PCM, using different commercial based PCM solutions, to attain the optimum indoor comfort conditions and energy efficiency. To achieve the first goal, real data was collected and analysed. To comply with the second goal, dynamic thermal simulation of the department building was carried out using EnergyPlus® 8.3.0 (EP) software.

Section snippets

Methodology

The methodology starts with a hygro-thermal monitoring campaign of the two rooms, used to evaluate the indoor air temperature comfort according to EN 15251 [39]. This data was also used to validate the numerical model. To record temperature and relative humidity, thermo-hygrometer sensors were installed. In the second part of this approach it was carried out resourcing to optimization features using a multi-objective evolutionary algorithm. This step aims to increase the indoor thermal comfort

Building location and general characterization

The university building was constructed in 2012, in the University Campus of the city of Aveiro. It is located approximately at 10 km from the Atlantic coast, in central North of Portugal mainland. This building is representative of the architecture and constructive typology of existing departments, and was built between two adjacent departments with similar geometries (see Fig. 2).

The building has a plan configuration with a rectangular shape, with a gross floor area of 1600 m² (see Fig. 3). It

Indoor air temperature data analysis

This section presents the monitored results of the temperature for the annual period. The temperature curve depicted is an average value of all sensors in the room for the annual period monitored (see Fig. 11).

During the annual monitoring campaign, there were periods in which data collected was lost due to acquisition software error (shown in Fig. 11 as “not monitored”).

The expected behaviour of the PCM is to buffer the temperature swing in the cooling season during the day, to prevent

PCM optimization using a hybrid evolutionary algorithm

The main goal of this section is the overheating reduction optimizing the coupled effect of different PCM solutions and the ventilation rate. Based on the calibrated model and using the weather file collected from INMG (see Section 3.2) all the simulations ran for a yearly period (with an hourly frequency). First the model was simulated using the model resulting from the calibration with the original PCM constructive solutions. The thermal building characterization was evaluated in accordance

Final remarks and conclusions

This study has tackled the overheating and heating demand reduction issue for a university department building. In the experimental work, a layer of PCM was incorporated into the partition wall and ceiling in the form of panels in one room of the building. Two rooms of the building were monitored and the results were provided by the instrumentation plan data collected during a complete year. The thermal comfort and the PCM influence were quantified using the standard EN 15251.

In the numerical

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Indoor thermal comfort assessment using different constructive solutions incorporating PCM

Highlights

Abstract

Introduction

Section snippets

Methodology

Building location and general characterization

Indoor air temperature data analysis

PCM optimization using a hybrid evolutionary algorithm

Final remarks and conclusions

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