Impact of thermal insulation on energy consumption in buildings

Abstract

Keywords: Buildings; Energy Consumption; Heat Loss; Thermal Comfort; Thermal Gain; Thermal Insulation; Renovation

Introduction

Globally, buildings are the largest energy consumer, accounting for 36% of final energy consumption and 40% of primary energy consumption worldwide [1-3], making them the second biggest emitter of greenhouse gases. Shockingly, its annual CO2 emissions have risen by an average of 1% per year since 2010. Most building regulations worldwide focus on reducing energy consumption [2]. Thermal insulation is mandatory in buildings, it effectively reduces energy consumption in heating and cooling [2-7]. Insulation has been shown to be effective in numerous research [8-11]. Dombayci [12]

investigated the environmental impact of optimal insulation thickness for exterior walls in Denizli, Turkey, using expanded polystyrene as an insulating material. Results showed that using optimal insulation thickness reduces energy consumption by 46.6%, leading to lower CO2 and SO2 emissions. Mishra et al. [13] discussed energy saving in different types of building walls: Brick, concrete, and stone, using optimum insulation thickness. They selected expanded and extruded polystyrene as insulation materials. They found that the optimum insulation thickness ranged from 5.2 to 7.4 cm, while energy saving varied from 2560 to 5510 Rs/m². Khoukhi and Tahat [14] investigated the relationship between temperature and thermal

*Corresponding author. *E-mail address: bessaih.rachid@gmail.com This paper was recommended for publication in revised form by Editor-in-Chief Ahmet Selim Dalkılıç Published by Yıldız Technical University Press, İstanbul, Turkey Copyright 2021, Yıldız Technical University. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).

conductivity of polystyrene at various densities. Results indicated that high temperature leads to elevated thermal conductivity, and lower material density produces higher thermal conductivity. Yucel et al. [15] applied experimental tests on expanded polystyrene as an insulating and construction material which are homogeneous or close to homogeneous, grainy, multilayer, or porous. The panel method was used for experimental studies in compliance with standards. Findings proved that expanded polystyrene is affected by cell material composition changes. Fang et al. [16] conducted a comparative study between two experimental chambers - one designed with an external thermal insulation system for walls, hollow brick, and double-glazed windows “energy efficient,” the other based on general building design in the 1980s and 1990s, consisting of brick and single-glazed windows (“basic” chamber). According to the study, an “energy efficient” thermally insulated chamber offered more comfortable conditions, was less affected by the outside environment, and saved up to 23.5% in air conditioning energy consumption compared with a “basic” chamber. Paraschiv et al. [3] also discovered that thermal insulation of exterior walls could reduce energy consumption by 13% -16%, depending on external temperature variations. Many studies focus on improving thermal insulation in buildings, thus increasing thermal efficiency and saving more energy, especially when this energy source is non-renewable [17]. Kalbasi and Afrand [18] reported finding that adding phase change material (PCM) or thermal insulation in buildings effectively minimized energy consumption. Results showed that adding PCM to walls is better in summer, while insulation is preferable in winter. Furthermore, applying a combination of insulation and PCM worked well than either of them separately. Boobalakrishnan et al. [19] set out to reduce indoor temperature in metal roofs of single-story industrial buildings. They performed a comparative experimental investigation of two modes, the first without PCM in the roof (Plain Roof) and the second with encapsulated paraffin as PCM within the roof (PCM Roof). Findings showed that the second mode was preferable, reducing average daily indoor temperature by 5°C and peak indoor temperature by 9.5°C. Moreover, there is considerable interest in using phase change materials (PCM) in building construction, as they help to reduce energy consumption [20-24]. Aerogels are an eco-friendly material derived from gelled materials, offering an excellent insulating solution without any cost increase [25]. Bashir et al. [26] investigated aerogel and its use as thermal insulation material towards the sustainable design of residential buildings in tropical climates of Nigeria. They modelled a residential building using conventional materials, then modified it by applying aerogel on various surfaces of model. Their

results indicated that it had a greater influence when aerogel was inserted in attic and floor slabs. Average indoor air temperatures and operating temperature were reduced by over 6%, energy consumption was cut by over 15% [27-32]. These indicate that using aerogel in buildings is a promising solution to improve thermal insulation efficiency. It is interesting to use bio-based materials as thermal insulators since they are highly hygroscopic and renewable which can be used as an alternative to conventional materials for reducing energy consumption in buildings [33-37]. Mathews et al. [38] made thermal insulation panels from recycled cardboard and various biodegradable binders (corn starch, lime, and clay). Results suggested that the fabricated panels have good thermal conductivity due to their porosity and can be used as building insulation. Adding thermal insulation to older houses can increase their energy efficiency, provide thermal comfort, and minimize energy consumption. To ensure that renovation complies with building standards, it is important to consider the climatic and ecological conditions of buildings and the financial resources available when selecting the appropriate type of insulation. This paper examines the application of Algerian Thermal Regulations (DTR C 3.2/4) to a house in Oued Athmania-Mila. The aim is to determine whether or not the home complies with the regulation and to opt for renovation by adding thermal insulation in areas of high thermal loss and gain. The Regulatory Technical Document DTR C3.2/4 CNERIB 2016 defines the general building regulations for thermal design (heating and cooling), and energy needs assessment for winter and summer periods. TRNSYS software is used to simulate house temperatures throughout the year, and DesignBuilder software is utilised to find out the energy requirements of this house. After renovation, temperature values are also measured to demonstrate thermal insulation’s effect on energy consumption.

Description Of House

The house is located in Hammam Grouz Oued Athmania-Mila in northeastern Algeria, with dimensions 6 m, 11 m, and 3.2 m (width, length, height). It consists of three chambers (kitchen, living room, room), see Table

1. Its geographical coordinates are 36°14’09 N6°17’25 E,

Altitude is 729 m. See Figure 1. - The house’s walls comprise six layers. See Figure 2 and Table 2. - The ceiling has three layers. See Figure 3 and Table 2. - The ground consists of one layer. See Figure 4 and Table 2.

Table 1. Dimensions of the house before renovation Location Kitchen

Table 2. Components and properties of construction materials before renovation Name

Numerical Analysis

Evaluation of Energy Needs During Winter Total loss of a dwelling Equations 1 to 9 were taken from the Regulatory Technical Document C3.2/4 [39]. Total losses L for a dwelling containing several thermal volumes are given by: L=∑ Li

Transmission losses (LT)i of a volume i are given by: (LT)i= (Ls)i + (Lli)i + (Lgr)i + (Luh)i

Regulatory verification The losses by transmission LT of the dwelling must be checked: LT ≤ 1.05 × Lref

Heating power installed The heating power Q required for a dwelling is given by: Q = (t,bi – t,bo) × [(1+ Max (Cr, Cin)) × LT + ((1+Cr) × LR)]

- t,bi= 21 [°C]. - t,bo= -2 [°C]. - Cr= 0 (dimensionless) is an estimated ratio of heat losses due to the possible piping network. - Cin=0.1 (dimensionless) represents an overpower coefficient. Assessment of Energy Needs During Summer Total thermal gain AT= (C∆as × As) + AREN

- C∆as=1.05 is the increasing coefficient of sensible gains. Regulatory verification The sum of the thermal gain through the glazed walls and the overhead opaque walls must be verified in July at 3 p.m., for an interior dry temperature of 27°C, the equation below: APO (15h) + AV (15h) ≤ 1.05 Aref (15h)

Simulation Models During this study, two simulator packages are used: DesignBuilder and TRNSYS, where: DesignBuilder is software with a graphical interface for dynamic simulation and thermal modelling of buildings. Figure 5 Visualization of the house in DesignBuilder. TRNSYS software simulates building’s energy consumption using weather data generated by the meteorological software Meteonorm [40,41]. See Figure 6.

Results And Discussion

Numerical Results Numerical analysis (Equations 1 to 9) revealed that our building did not comply with Algerian Building Thermal Regulations DTR. This necessitated a home renovation. To achieve thermoregulation, good thermal insulation was applied to the ceiling and the floor to reduce losses in winter and thermal gain in summer. Three new layers were added to the ceiling (0.12 m polystyrene HD 23, 0.01 m aluminum, and 0.013 m plasterboard), see Figure 7. Two layers

Figure 7. Thermal insulation layers of the ceiling. (a): Fixing two-layer polystyrene of thickness 4 cm of each layer below the ceiling. (b): Attachment of the last 4 cm polystyrene layer with 1 cm aluminum layer.

Table 3. Construction materials of roof and ground after renovation Designation

on the floor (0.04 m polystyrene, 0.04 m cement screed) see Figure 8. The properties of additive insulation materials were described in Table 3. Figure 9 illustrates loss variations (Luh, Lli, Ls, Lgr, LR, LT, Ltot) before and after the home’s renovation during the winter period. The renovation results are starkly evident, with a 77% reduction in ground losses and a 59% reduction in surface losses (ceiling and walls), leading to a more than twofold drop in total losses. Thermal losses are influenced

by environmental conditions surrounding the building (temperature, wind, humidity, etc.), so the appropriate design minimizes this effect. Therefore, thermal insulation is an effective energy-saving measure that significantly reduces thermal losses and ensures greater thermal comfort regardless of external climatic conditions. Figure 10 shows thermal gain before and after house renovation during summer. It should be noted that the changes in thermal gain occurred only at the APO level

Figure 9. Thermal losses of a building during winter before and after renovation.

Figure 10. Thermal gain during summer before and after renovation.

from 1973.62 [W] to 626.46 [W]. This can be explained by the fact that the renovation of the ceiling and floor levels reduced the thermal gain of the opaque walls, which mainly explains the 18% decrease in AT, with no variations in other parameters (Table 4). The thermal gain during the summer period is rather large. This can be attributed to the region’s hot climate, which has a high solar radiation of 323 [W/m²] and receives at least 10 hours of sunshine per day (Fig. 11). Figure 12 demonstrates variation in the calculated heating and cooling power required to maintain thermal comfort in a house before and after renovation. As shown, there is a significant decrease in heating power in the winter of over 55% and cooling power in the summer of 18%. This is explained by the reduction in thermal losses and gains due

to the thermal insulation of the building (Figures 9 and 10). Moreover, the house requires more air-conditioning power 2000 [W] than heating energy after renovation due to the regional climate and considerable heat gains in summer.

(a) Figure 11. Average monthly change. (a) Beam irradiance-DNI, (b) Sunshine duration [h].

Figure 12. Energy needs for heating and cooling (numerical analysis). After renovation, it appeared that the house complied with thermal regulations for buildings during winter and summer (based on equations (4) and (8)). The reason lies in the application of effective insulation (12 cm of polystyrene on the ceiling and 4 cm on the ground), which achieved the objective of this study. Simulation Results Figure 13 shows the results of the TRNSYS software simulation of temperature change in the three chambers (kitchen, living room, and room) over a period of 8760 hours. It is observed that the ambient chamber temperature throughout the year is between 6 and 32°C without heating or cooling. The average room temperature during the cold period is around 14-15°C, while the warm period ranges between 30-32°C. The results of these simulations suggest

Figure 14. Average annual energy consumption for heating and cooling the house. that the house is not thermally comfortable, so heating and air-conditioning are necessary to maintain a comfortable temperature. To achieve this, energy must be consumed to cool and heat the house as seen in Figure 14 which shows the average annual consumption before and after renovation of the dwelling. We find that thermal insulation is the cause of the decrease in annual consumption by more than 500 [kWh]. Figure 15 illustrates results from a simulation using DesignBuilder software, displaying the power required to heat and cool the house before and after renovation. The data demonstrate a 42% and 17% decrease in energy needs

Figure 15. Energy needs for heating and cooling the house using DesignBuilder software.

for heating and cooling the house, respectively. In addition, the accuracy of the DTR-derived calculations of heating and air-conditioning powers was verified. This significant drop is attributed to the building’s superior thermal insulation, which provides maximum comfort while reducing consumption and increasing savings. Implemented Measures After calculating thermal losses and gains for the home, it was insulated with compressed polystyrene, as indicated in Figures 7 and 8. To determine the effectiveness of thermal insulation and confirm the results of this paper, house temperatures were measured and compared to those outside. Two thermometers (IHM-MOINEAU TPM-10, measurement range: - 30/50°C) were used, one installed next to the chamber window at a distance of 1.5 m from floors, another suspended just outside the chamber. Measurements were taken every hour manually, starting at 11:00 a.m. Before using thermometers, we calibrated them with a digital probe thermometer, the difference between them being less than 0.1°C. Temperatures measured inside and outside the building on 14/06/2021 from 11.00 to 19.00 are presented in Figure

16. Clearly, outside temperatures rise gradually until they

reach their maximum at 3:00 p.m., then fall as winds blow across the region. Despite these external changes, internal temperatures remain almost constant at 24± 0.5 °C. This stability is due to thermal insulation applied in this home, which prevents gains from penetrating the interior, thus protecting the building. At 6:00 p.m., the indoor temperature drops to

Conclusion

This study investigated the impact of thermal insulation on the energy consumption of an existing house in northeastern Algeria. This research aimed to verify if the house was compatible with the construction codes of Algerian thermal regulations DTR. A simulation model was also presented using DesignBuilder and TRNSYS software. Results showed that the house did not satisfy the regulations and had considerable thermal losses on the ceiling and floor. Therefore, thermal insulation (0.12 [m] polystyrene HD 23,

Nomenclature

A AI AINF APO AREN As AT AV e K L Lgr Lli LR LS LT Luh Q R t,bi t,bo W ρ

Gain, [W] Internal gain, [W] Gain due to air infiltration, [W] Gain by opaque walls, [W] Sensitive part due to ventilation of premises, [W] Sensible gain, [W] Total thermal gain, [W] Gain through the glazed walls, [W] Thickness, [m] Conductivity, [W/m.K] Losses, [W/°C] Losses through the walls in contact with the ground (low floor), [W/°C]. Losses through the links (thermal bridges), [W/°C]. Losses by air renewal, [W/°C]. Surface losses through common parts of walls in contact with outside, [W/°C]. Transmission losses, [W/°C] Losses through walls in contact with unheated rooms, [W/°C]. Heating power, [W] Resistance, [m²°C/W] Indoor base temperature, [°C] Outdoor base temperature, [°C] Air-conditioning power, [W] density, [Kg/m³]

Subscripts gr Ground i Indoor li Links o Outdoor R Renewal Ref Reference s Surface

Data Availability Statement

The authors confirm that the data that supports the findings of this study are available within the article. Raw data that support the finding of this study are available from the corresponding author, upon reasonable request.

Conflict Of Interest

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Ethics

There are no ethical issues with the publication of this manuscript.

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