Improvement of thermal inertia effect in buildings using shape stabilized PCM wallboard based on the enthalpy-temperature function

Highlights

• SSPCM was applied to building energy saving to improve heat storage performance.

• Enthalpy–temperature function was used to model 22 types of SSPCM.

• The average annual building energy reduced by 5 % when SSPCM was applied.

• Peak summer temperature reduced by 4.1 ℃ after maintaining thermal inertia of SSPCM.

Abstract

The use of phase change material as an efficient way to use building energy has recently been discovered as this material occupies 40 % of the total carbon emissions through energy used in the building sector. In order to apply phase change materials to buildings, phase stabilization must first be achieved; some researchers have developed shape-stabilized phase change material (SSPCM). In this study, the enthalpy-temperature function based on the thermal properties of 22 types of SSPCMs were analyzed and applied to a dynamic energy simulation program. The SSPCM was applied to improve the low heat storage performance of wooden buildings along with building energy savings. The SSPCM was applied to the inner side of a 20-mm-thick external wall in a case study concerning the inside and outside of an external wall. An analysis of the annual energy consumption of buildings showed that applying SSPCM resulted in average savings of 5 %. To confirm the improvement in the heat storage performance of buildings, the indoor temperature behavior during the heating and cooling periods was analyzed. Maintaining the thermal inertia of SSPCM was found to have reduced the peak temperature in summer by 4.1 °C.

Introduction

With the rapid growth of population and urbanization, global energy consumption increases, especially in buildings, with energy consumption accounting for 40 % of the total industry (Kasaeian, bahrami, Pourfayaz, Khodabandeh, & Yan, 2017; Wang, Wu, Wu, & Zhao, 2018). Along with energy consumption, efforts are being made to reduce Greenhouse Gas (GHG) emissions by 2030 after the Paris Agreement on climate change (Ari & Sari, 2017). Building materials used in buildings account for 42 % of the carbon footprint of a building's life cycle (Kofoworola & Gheewala, 2008); therefore, the use of building materials with low embodied carbon can contribute significantly to carbon emission reduction. Reinforced concrete is the most commonly used building material in the world and 10 billion tonnes are used annually (Meyer, 2009). For sustainable cities, consideration should be given to the reduction of carbon from the material unit at construction stage (Omer & Noguchi, 2019), through which materials can efficiently use the thermal energy required for buildings and reduce the amount of energy required for total heating and cooling energy (Díaz-López, Carpio, Martín-Morales, & Zamorano, 2019). Thus, effective use of energy needed for buildings at the building level can save energy and eventually expand to the city level (Marquez-Ballesteros, Mora-López, Lloret-Gallego, Sumper, & Sidrach-de-Cardona, 2019). In recent years, studies have been under way to reduce carbon emissions at the construction stage by using eco-friendly materials that have lower embodied carbon than conventional reinforced concrete such as wood. Grönvall et al. analyzed the total carbon content of each building through life cycle assessment (LCA) of wooden framed buildings and concrete framed buildings and found that the concrete buildings had 354 kg CO₂e/m² and the wooden buildings had 225 kg CO₂e/m² of carbon emissions respectively (Grönvall, Lundquist, & Pedersen Bergli, 2014). In terms of carbon emissions, wood is an excellent building material compared to concrete; however, wood has lower heat capacity than concrete due to its low density and specific heat (Asdrubali et al., 2017). When the thermal capacity of a building is low, it cannot cope with the changes in climate and maintain a constant indoor air temperature. Recently, studies on carbon emission reduction through reductions in building energy have been conducted along with those on improvement in the thermal storage performance of buildings. Among the three main types of heat storage systems—sensible storage, latent heat storage, and thermochemical storage—latent heat storage systems using phase change materials (PCMs) are the most actively researched type for application to buildings (Kunkel et al., 2018). PCMs are energy-dense materials that use latent heat storage during phase transition processes. PCMs are used to obtain a melting point between 20 °C and 30 °C for a typical building temperature range. Phase change materials are majorly classified as organic, inorganic, and eutectic. Organic PCMs such as paraffinic series is safe, reliable, predictable, inexpensive, non-corrosive and chemically stable and possesses extremely low thermal conductivity (0.1–0.3 W/m K) (Sharma, Ganesan, Tyagi, Metselaar, & Sandaran, 2015). However, inorganic PCMs such as hydrated salts has high latent heat (254 kJ/kg) but it is highly prone to phase segregation and subcooling. The corrosion of salt on metal container is also a concern (Farrell, Norton, & Kennedy, 2006). Therefore, organic PCM types are mainly used in latent heat storage systems as they have good compatibility and are recyclable with other materials, exhibit no supercoiling, have a high heat of fusion, and are available in a large temperature range (Nematpour Keshteli & Sheikholeslami, 2019). Thus, research on latent heat thermal energy storage (LHTES) using PCMs is progressing steadily. Some researchers use a method of vacuum impregnating PCM using a porous material as a PCM container and thermal performance enhancement. This phase stabilization technique is called shape-stabilization PCM (SSPCM), and researchers have developed phase stable PCM by vacuum-impregnating organic PCM with porous material. Chung et al. prepared SSPCM by the vacuum impregnation method with n-octadecane, a type of organic paraffin PCM, on expanded vermiculite and expanded perlite, which are porous nanoclay materials (Chung, Jeong, Yu, & Kim, 2014). Kim et al. prepared SSPCM by vacuum impregnating n-octadecane on exfoliated graphite nanoplatelets (xGnP), which is porous and a nano sized carbon material to improve the thermal conductivity and heat storage efficiency (Kim, Paek, Jeong, Lee, & Kim, 2014). They analyzed the thermal performance of the developed SSPCM such as latent heat, phase change range, and thermal conductivity. The shape-stabilized PCMs can be applied to various building parts to reduce energy consumption in buildings, interior walls, exterior walls, ceilings, roofs, and floors. Fabrizio Ascione et al. applied a PCM to a building in the form of a wallboard and confirmed the cooling energy reduction effect from 3 % to 7.2 % depending on the climate zone (Ascione, Bianco, De Masi, de’ Rossi, & Vanoli, 2014). Sage-Lauck and Sailor studied the application of PCM to the interior walls of a building, showing that it can provide a higher thermal comfort level and confirming that approximately 50 % of the uncomfortable time is reduced when applying PCM (Sage-Lauck & Sailor, 2014). Kośny et al. confirmed that 70–80 % of the peak load in attics is reduced when a PCM is applied (Kosny et al., 2010). Saffari et al. reported 10–15 % annual energy savings when applying a 10 mm PCM with a phase change temperature of 27 °C to walls and ceilings (Saffari, de Gracia, Ushak, & Cabeza, 2016). However, research on building energy savings through PCM is still focused on stabilizing PCM techniques. In addition, it remains in the stage of analyzing thermal performance of developed SSPCM. To study real applications, energy analysis based on the thermal properties of the manufactured SSPCM should be performed. In this study, the analysis of building energy savings when applied to SSPCM manufactured by vacuum impregnation and improvement in the thermal storage performance of wooden houses were analyzed through dynamic simulation. The research methodology flowchart of this work is shown in Fig. 1.