Reinforced Cement Concrete Roof Research Articles

A detailed investigation on thermal performance and energy savings of cool roof systems for composite climates of India

ABSTRACT The rising worldwide temperatures leading to a spike in air conditioning to ensure thermal comfort in buildings is the root cause of the increase in energy demand in India's building sector. The roof of a building significantly adds to the heat gained on the top floor, accounting for 50–60% of the total heat gain. One sustainable way to reduce this heat gain is via cool roofing technology. Through examination and dynamic simulations with the Energy-Plus-based Design Builder software tool, this study explores different cool roof solutions. An experimental setup of a Reinforced Cement Concrete (RCC) roof with cement plaster, solar reflective paint, solar reflective tiles, and earthen pots have been created on the institute campus. Recordings were taken during the peak summer days and peak winter days, alongside simulations carried out to determine various factors such as Albedo, Surface Temperatures, Air Temperatures, Diurnal Heat Ingress, and the Building's Thermal Energy Consumption. The experiments have demonstrated that cool roof layers can considerably improve interior thermal comfort by minimizing heat transfer, which maintains a constant temperature over the bottom surface of the roof. By reducing heat gain by 33–71%, they can save energy by 21-26% compared to traditional RCC roof slab.

Thermal Analysis of Building Roofs with Latent Heat Storage for Reduction in Energy Consumption and CO2 Emissions: An Experimental and Numerical Research

In green energy buildings, air conditioning charges can be lowered through careful planning of the building’s envelope. This article investigates several strategically designed phase change material (PCM) roof envelopes for savings on air conditioning prices, CO2 emission abatement, and payback timeframes in hot–arid and warm-temperate climates, taking into account unsteady heat transfer characteristics, cooling, and heating degree–hours. This is accomplished by using six different PCMs–RCC (reinforced cement concrete) roof envelope cases (RCC roof with PCM layer on the outer side, RCC roof with PCM layer on the center (middle), RCC roof with PCM layer on the inside, RCC roof with PCM layers placed on the outside and center, RCC roof with PCM layers placed on the center and inside, and RCC roof with PCM layers placed on the outer side and inside) with three PCMs (FS29 (form stable mixture), HS29 (hydrated salt), and OM29 (organic mixture)). PCM thermophysical characteristics are experimentally measured. The analytical results are experimentally validated. In hot–arid and warm-temperate regions, the layer of PCM installed on the outside of the RCC with HS29 saved the most on air conditioning expenses, at 6.29 and 6.61 $/m2, respectively. They also reported the greatest carbon mitigation of 300.55 kg of CO2/year and 281.58 kg of CO2/year with the faster payback periods. PCM roof envelopes are the most energy-efficient option for green buildings.

Experimental and numerical investigation on phase change material filled reinforced cement concrete roof slab for mitigating the heat transfer

ABSTRACT In this paper, a phase change material (PCM) filled rooftop is proposed to reduce heat transfer from the roof. Experiments are conducted to compare the thermal characteristics of residential buildings with bare reinforced cement concrete roof (RCC) top without PCM and PCM filled RCC rooftop in the summer season. Aluminum panels containing macro encapsulated PCM, which occupies around 66% of the total roof slab area, are employed in one of the building rooftops. They store the heat energy in the form of latent heat and thus reduce the heat transfer into the building. In the RCC roof slab of thickness 0.152 m, 0.051 m is allotted for storing PCM and the remaining 0.101 m ensures adequate strength of the roof slab. The comparisons of thermal behavior between the buildings of bare and PCM integrated RCC roofs reveal that the PCM integrated roof reduced the heat transfer into the building vis-à-vis bare roof building. The PCM integrated roof diminished the heat flux to a maximum of 53% compared to the non-PCM roof on the day when the maximum temperature was recorded (18 May 2021) during the experimental periods. In PCM filled roof, an average reduction of 2°C in the room temperature is achieved as compared to that of a non-PCM filled roof.

Thermal performance of building prototype with different cool roof structures in composite climate

ABSTRACT In the domestic sector, buildings contribute to about 55% of the total energy consumption for space heating and cooling. In this study, an experiment was carried out using a square shape building prototype made up of laminated plywood with Reinforced Cement Concrete (RCC) roof. Surface treatment of four types of reflective paints was applied on the RCC roof slab. Their performance was monitored in the summer season (April and May). Based on the peak temperature of interior and exterior roof layers, several important parameters, such as temperature, indoor thermal amplitude, time lag, decrement factor, thermal damping, thermal performance index, peak degree hours and thermal performance of each roof slab, were analysed. The application of cool roofs (CR-1, CR-2, CR-3, and CR-4) shows a significant reduction in indoor temperature (2.1°C–3.2°C), and indoor thermal amplitude (16.10%–27.94%) compared to a standard RCC roof. The drops in peak temperature of exterior and interior roof layers were 4.8°C–6.8°C and 3.9°C–6.3°C, respectively. A significant improvement was achieved in time lag and decrement factor (3–4 h more than the reinforced concrete roof), with energy savings varying from 10.58% to 13.73%.

Assessing the real-time thermal performance of reinforced cement concrete roof during summer- a study in the warm humid climate of Kerala

Understanding the real-time thermal behaviour of the building envelope is essential to provide comfortable indoor conditions and to develop energy efficient building components. Monitored performance of sloping Reinforced Cement Concrete (RCC) roofs and roof coverings, which is a widely found roofing typology in warm humid climate, are rarely found in published literature. This paper is based on a comparative study of the real-time thermal performance of different types of RCC sloping roofs – exposed, covered using Mangalore pattern tiles, ceramic tiles, concrete tiles, and shingles sheet. Field studies are conducted in naturally ventilated residential buildings with these roof variants, from warm humid climate during summer. The methodology includes (i) Theoretical study to identify significant thermal performance parameters, (ii) Field studies and testing, and (iii) Comparative analysis of case studies. Theoretical study resulted in the identification of simple empirical indices that can express the dynamic thermal behaviour of roof components; they are decrement factor, time lag, thermal performance index, and adaptive thermal comfort index. Field studies show that elevated ceiling temperature and indoor air temperature persists in all the roof types, deeming these roof-covering techniques as inefficient to provide acceptable thermal comfort conditions during summer in a warm humid climate. Among the roof variants, Mangalore pattern tiles exhibited better thermal performance due to their low conductivity, diffusivity, and slightly corrugated profile. The research also provides useful field data as an add-on to the existing knowledge, to aid energy-efficient building design and performance study of roofing materials.

Thermal performance evaluation of traditional walls and roof used in tropical climate using guarded hot box

Buildings provide appropriate thermal comfort for the people residing in it. Buildings provide this thermal comfort via interaction with the external ambient through walls, roof and glazing. As a result, a prior knowledge of the thermal performance of walls, roof and glazing can help estimate the heating or cooling loads on proposed HVAC systems. The purpose of this study is to investigate the thermal performance of walls and roofs commonly used in residential building sector in India. This is done by determination of overall heat transfer coefficient or U-value using guarded hot box test facility. Detailed description into the calibration procedure of the test setup prior to the actual testing has been discussed at first. The overall testing procedure is in accordance with BS EN ISO 8990:1996. Thereafter effect of varying differential air temperature on overall heat transfer coefficient of reinforced cement concrete roof and three types of burnt clay brick wall configurations are studied. From the regression analysis, one can easily evaluate the U-value of the walls and roof for any differential temperature as experienced by buildings in various climatic zones in India.

Strategy to control indoor temperature for redevelopment of slum dwellings

The present paper focuses on developing a strategy to control the indoor temperature in slum dwellings under redevelopment. The proposed framework aims at improving the building planning and appropriate selection of construction materials along with controlled cost with respect to currently adopted practices. The proposed strategy is elaborated with a case study in Nagpur, India. A single storey, four-room model was planned as per the National Building Code of India. The performance of the model building was evaluated by using energy simulation software TRNSYS. The cellular light-weight bricks used in the construction were made with bio briquette ash (BBA), which is a locally available waste material. Instead of using the conventional reinforced cement concrete (RCC) roof, aluminium and sawdust were suggested as a reflecting-cum-insulating material. To improve the temperature control in model homes, installation of a reflecting-cum-insulating material was conducted, consisting of aluminium and sawdust, over the conventional RCC roof. The model building constructed with these new materials was compared with that built with conventional fly ash bricks and RCC roof. Results show that the proposed model building improved the efficiency of indoor temperature control by 23% and, at the same time, reduced the cost by 13%. The present concept will contribute to the redevelopment of slum dwellings to deliver cost-effective dwelling units that provide occupants with acceptable thermal comfort.

Development of thermally insulated sustainable building model

Appropriate construction materials with low thermal conductivity are required to control excess heat gain in building surfaces exposed to hot climates. This paper elaborates on the development and application of three sustainable building materials, namely hollow bricks using construction waste, double-glazed windows insulated with ultraviolet (UV) rejection film and reflecting/insulating roof treatment material. The physical, mechanical and thermal properties of the developed materials were investigated. To investigate the thermal performance experimentally, two small-scale models were developed over the study area. A two-room model (M1) built with fly ash brick, double-glazed (plain glass) windows with UV rejection film (W1) and a conventional reinforced cement concrete roof was compared with another two-room model (M2) built with construction waste bricks, double-glazed (commercial glass) windows with UV rejection film (W2) and a reinforced cement concrete roof that underwent a reflecting/insulating treatment. The results showed that the thermal transmittance of the wall and the roof of model M2 was reduced by 73% and 25% respectively compared with the wall and roof of model M1. Temperature analyses revealed that the west and east rooms of M2 were respectively 2·3% and 5·0% cooler than those of M1.

Heat transfer analysis in PCM-filled RCC roof for thermal management

We analyzed of heat transmission across three roof structures ; bare RCC (reinforced cement concrete) roof, RCC roof with weathering coarse and RCC roof with PCM (phase change material) above RCC. A transient numerical procedure was developed. ANSYS-Fluent 12 finite volume method based software was used for solving the problem. The numerical procedure was validated against the available experimental data. The simulation was carried out on 365 days of the year for these three roofs. The PCM melted from 8 h to 18 h and solidified during the rest of the day. From March to August, the net heat entering into the room per day is positive, thus more and more PCM melts and becomes liquid. The liquid portion of PCM increases from March to August, during September to February, there is a net heat rejection per day, thus the melted PCM becomes solid progressively, and at the end of February, almost all PCM has become solid. Thus there is a melting cycle on a daily basis and over the year. It takes care of all the external climatic variations and keeps the roof bottom surface temperature almost constant and close to room air temperature. On yearly basis, about 56% reduction in heat transmission into the room is obtained with PCM roof when compared to the conventional weathering coarse laid roof.

Experimental evaluation of insulation materials for walls and roofs and their impact on indoor thermal comfort under composite climate

Better insulation having low thermal conductivity is a significant contributor for new construction and retrofitting existing buildings, when the emphasis is on energy efficiency. The objective of the study is to determine the impact of the thermal insulation materials in buildings enabling effective energy savings with minimal occupation of space. Although, the Energy Conservation Building Code (ECBC), India defines the prescriptive and mandatory requirements for the U-factor and R-value but the way to achieve these values is left to the designer and there is no published data on these values. To accomplish these objectives, the experiments for computation of thermal resistance and over all heat transfer coefficients have been carried out by measuring the thermal conductivity of the various types of materials available in the Indian market having different thicknesses by Automatic Guarded Hot Plate Apparatus. One hundred and twelve combinations of wall and roof sections have been computed and compared with different thicknesses of insulating materials for determining U-factor and R-value to satisfy ECBC requirements. The results of the study show that 50 mm thick Elastospray with conventional roof and wall satisfy the ECBC requirements whereas, other insulation materials require higher thickness to fulfill the recommended values. To validate the results, two prototype buildings are constructed at CSIR–CBRI campus; one with conventional burnt clay brick wall, reinforced cement concrete roof and 50 mm thick outside thermal insulation and the other without insulation. The results of the winter and summer season for six months are presented.

Analysis of heat transfer across phase change material filled reinforced cement concrete roof for thermal management

Analysis of heat transmission across three roof structures, namely, bare reinforced cement concrete roof, reinforced cement concrete roof with weathering coarse and reinforced cement concrete roof with phase change material above reinforced cement concrete are analysed. A transient numerical procedure is developed. The numerical procedure is validated against the available experimental data. The simulation is carried out on 365 days of year for these three roofs. The phase change material melts from 8 to 18 h and solidifies during the rest of the day. From March to August, the net heat entering into the room per day is positive, thus more and more phase change material melts and becomes liquid. The liquid portion of phase change material increases from March to August. During September to February, there is a net heat rejection per day, thus the melted phase change material becomes solid progressively, and at the end of February, almost all phase change material has become solid. Thus, there is melting cycle on daily basis and over the year. It takes care of all the external climatic variations and keeps the roof bottom surface temperature almost constant and closes to room air temperature. On yearly basis, about 56% reduction in heat transmission into the room is obtained with phase change material roof when compared to the conventional weathering coarse laid roof.

Estimation of structural vulnerability for flooding using geospatial tools in the rural area of Orissa, India

Vulnerability assessment of natural disasters is a crucial input for risk assessment and management. In the light of increasing frequency of disasters, societies must become more disaster resilient. This research tries to contribute to this aim. For risk assessment, insight is needed into the hazard, the elements at risk and their vulnerabilities. This study focused on the estimation of structural vulnerability due to flood for a number of structural elements at risk in the rural area of Orissa, India (Kendrapara), using a community-based approach together with geospatial analysis tools. Sixty-three households were interviewed about the 2003 floods in 11 villages and 166 elements at risk (buildings) were identified. Two main structural types were identified in the study area, and their vulnerability curves were made by plotting the relationships between flood depth and vulnerability for each structural type. The vulnerability ranges from 0 (no damage) to 1 (collapse/total damage). Structural type-1 is characterized by mud wall/floor material and a roof of paddy straw, and structural type-2 is characterized by reinforced cement concrete (RCC) walls/floor and a RCC roof. The results indicate that structural type-1 is most vulnerable for flooding. Besides flood depth, flood duration is also of major importance. Houses from structural type-1 were totally collapsed after 3 days of inundation. Damage of the houses of structural type-2 began after 10 days of inundation.

Performance of different passive techniques for cooling of buildings in arid regions

Eight identical test structures each having dimensions 1280×610×1100 mm 3 have been fabricated. All the four sides of the test structures were made by using mild steel angle and galvanised steel sheet. The reinforced cement concrete roof was casted over these. The different passive techniques were used over the roof for cooling the environment inside test structures viz. painting of roof with white cement, thermal insulation over the roof, nocturnal cooling i.e. shallow pond with 100 mm water column with 40 mm thick movable thermal insulation over the roof, evaporative cooling i.e. roof is provided with gunny bags soaked with water with the help of a storage tank and dripper for controlling flow of water without any pump, broken white glazed tile pieces stuck over the roof, air void insulation i.e. inverted earthern pots having 100 mm diameter and 125 mm height were provided over the roof, and roof covered with Sania, a local insulating material used over the huts in the arid regions and the controlled unit without any treatment. The evaporative cooling has been found best for conventional roof, but it requires about 50 l/ m 2 water per day, therefore, pieces of white glazed tiles stuck over the roof can be used to reduce heat load from the roof and hence cooling of the environment inside buildings.