Roof Surface Temperature Research Articles

Numerical analysis of phase change materials/wood–plastic composite roof module system for improving thermal performance

Using phase change materials (PCMs) to store and release latent heat is one of the most efficient and reliable ways to reduce energy consumption. In this study, a PCM/wood–plastic composite (WPC) roof module system with PCM inserted into a hollow layer of WPC is proposed to reduce building roof surface temperature and improve building energy performance and indoor thermal comfort. A thermal performance evaluation showed that the roof surface temperature can be greatly reduced by increasing reflectivity. However, increasing reflectance can increase heating load and cause freezing-related problems in winter because surface temperature is greatly reduced. The application of the PCM/WPC roof module system reduced surface temperature by 7.37°C in the summer. As the thickness of PCM increased, the surface temperature decreased; however, the variation was not constant. PCM with a phase change temperature of 30°C was most effective in reducing surface temperature, while PCM with a phase change temperature of 20°C was most effective in improving building energy performance and thermal comfort. This is because the PCM is applied to the outer face of the building. Therefore, the type and thickness of PCM should be selected considering reflectance, application purpose, and economic efficiency.

PCM cool roof systems for mitigating urban heat island - an experimental and numerical analysis

The purpose of this study is to develop a “PCM cool roof system”, and to evaluate its performance by applying the PCM cool roof system to the roof envelop. The study methods and procedures are as follows: First, the optimal PCM and finish materials were selected utilizing the indoor artificial climate chamber. Second, the PCM cool roof system was applied to the testbed, and the changes in surface temperatures were measured to determine the effect on the reduction of the heat island phenomenon. Third, the air currents in Gangdong-gu Seoul Korea were analyzed through a numerical analysis based on the data derived from the testbed to verify the reduction in the UHI. The experimental groups were set to A: WPC, B: WPC+PCM, and the control group to C: PCM cool roof system in the testbed experiment. The experimental environments were divided into winter, intermediate, and summer periods to increase the performance evaluation reliability in Seoul, where there are four distinct seasons. The study results showed that all seasons saw an effect of a reduction of roof surface temperatures when using the PCM cool roof system. The maximum temperature difference for each season was 2.5 °C in winter, 4.7 °C in intermediate season, and 5.7 °C in summer. The a numerical analysis results showed that the reduction in roof surface temperature due to the "PCM cool roof system" was effective in the mitigation of the heat island phenomenon.

Experimental study on thermal performance of roof and floor capillary radiant heating systems

This research picks up the bedroom and study of a residential building in Chengdu as the research object. The temperature variations in the supply water of the room, the surface temperature of roof and floor, and the indoor air is analysed when the capillary ends were located on the roof and the floor respectively. Furthermore, the internal mechanism of the different heating environments of the two heating modes is revealed by analysing the heat flux density. The results show that: under the same water supply temperature and flow rate, the thermal response time of the roof radiant heating is shorter and the stability of the surface temperature of the floor radiant heating is better due to the different thickness of the capillary network. The floor heating room has more uniform distribution and better comfort. The heat transfer characteristics of the roof and floor surface are different, and the variation of the radiation and convection heat transfer amount are also different. The heat flux density of the roof increases faster and the maximum value can be reached in only 60 minutes, while the floor needs 156 minutes. The roof heating is about 4.36% higher than the floor heating in the proportion of radiation heat exchange. Thus, roof radiant heating is preferred for intermittent heating. This paper provides a reference when designing the end of the residential heating systems.

Thermal comfort evaluation of an existing glazed airport terminal in Thailand

The indoor thermal comfort of an existing glazed and air-conditioned airport terminal in Thailand was assessed by objective and subjective assessments and analyses. The environmental variables examined included internal and external air temperatures, internal glazed roof surface temperatures, relative humidity and illuminance over the departure lounge. The objective measurements were reviewed against the subjective results of a questionnaire-based survey. It was found that the internal air temperatures remained stable within the space. Slightly high indoor air temperatures normally occurred between 1200 and 1700 h, corresponding to higher afternoon outdoor temperatures. The internal glazed roof surface temperatures were recorded as 40°C by around midday. As a result, the operative temperature within the space, exceeded the American Society of Heating, Refrigerating and Air-conditioning Engineers’ 55 standard of 26°C, which led technically to overheating and thermal discomfort. The measured results were in fair agreement with the subjective survey results. The overall comfort vote and perception found the occupants to be slightly uncomfortable and dissatisfied. However, to resolve these problems, the proposed solution for large glazed air-conditioned airport terminals in the tropics would be to provide suitable external or internal sunshades, which are the most applicable and flexible methods in all climates.

Changes in Temperature and Moisture Content of an Extensive-Type Green Roof

Green roofs ought to be perceived as ensuring a wide-ranging contribution to the sustainable urban environment. The aim of the study was; (1) to investigate and analyse the differences in the surface temperature between four models of green roofs of the extensive type and a conventional roof (covered with bitumen) under the conditions of a continental climate; (2) to assess the influence of environmental parameters (climatic water balance, air temperature, relative humidity, moisture content in the profile) on changes in the temperature of the extensive type green roof profile (substrate and vegetation mat). The study (1) was carried out during the period of June–December 2016 using a thermal imaging camera. As a result, the greatest differences in temperature were noted in June and July, with a maximum difference between the temporary surface temperature of a green roof and a conventional roof of up to 24 °C. The (2) study was conducted on a green roof profile with sedum plant vegetation. The measured parameters were: the temperature of the surface, the temperature and humidity at depths of 3 cm and 15 cm, and active radiation in the photosynthesis process (PAR). As the result, the range of daily changes in the surface temperatures and the vegetation mat were higher than the range of changes in the air temperature. Atmospheric precipitation decreased the thermal gradient in the soil, as well as the temperature fluctuations in the course of a day as a result of the increase in humidity following a rainfall. During the summer period, over the course of a day, the surface temperature was 5 °C higher than the air temperature. The largest correlation was obtained between the air temperature and the temperature of the surface as well as the temperature of the structural layers.

Estimates of cooling effect and energy savings for a cool white coating used on the roof of scale model buildings

The solar reflectance and thermal emittance of uninsulated scale model buildings in Beijing were measured in the laboratory and the actual outdoor environment. The solar reflectance index (SRI), roof surface temperature and energy savings were estimated using DOE roof saving calculator. The roof albedo measured in the field tests is independent of the inverted pyranometer height. A 0.493 increase in solar reflectance (laboratory measurements) yields SRI increase by 67.5, roof surface temperature reduction by 25.5 °C, annual peak demand reduction by 0.1 kWm-2yr-1, and annual net energy savings by 6.8 kWhm-2yr-1, while a 0.459 increase in roof albedo (laboratory measurements) generates SRI increase by 62.3, roof surface temperature reduction by 23.5 °C, annual peak demand reduction by 0.1 kWm-2yr-1, and annual net energy savings by 6.4 kWhm-2yr-1. At the city scale, these savings would reduce emissions from China’s power plants by 60 kton CO2, 1.1 kton NOx, 2.1 kton SO2 and 19.4 kton carbon dust for the laboratory tests and by 56.6 kton CO2, 1.0 kton NOx, 2.0 kton SO2 and 18.3 kton carbon dust for the field tests.

Thermal and energy performance of two distinct green roofs: Temporal pattern and underlying factors in a subtropical climate

This study evaluated and compared the longterm thermal and energy performance of two distinct large-scale green roofs in a humid subtropical city of China. One is an extensive sedum roof (EGR), and the other is an intensive one (IGR) with much deeper soil layer, higher plant diversity and more complex biomass structure. Roof surface temperature (Ts), air temperature at heights of 10 and 150 cm (T10, T150), roof heat flux, and cooling/heating load were analyzed for the green roofs and a control bare roof on hourly, daily, and seasonal basis over an entire year. The two green roofs displayed a similar and consistent performance pattern across the year, characterized by cooling of the roof surface during the day and warming of it at night, and, conversely, warming of the ambient air during the day and cooling of it at night. IGR was more effective than EGR in decreasing daytime and nocturnal Ts, cooling the ambient air, and cutting the summer cooling load, but it added more heating load to the building in winter. Findings from the research suggest that green roofs do not always function in favorable ways for urban heat island (UHI) mitigation and energy conservation but may actually have adverse impacts under certain weather conditions. Despite having a much more complex structure, IGR did not seem to outperform EGR commensurately in thermal benefits. The results can shed light on green-roof design and management for optimization of thermal and energy performance in subtropical areas.

Thermal performance assessment of extensive green roofs investigating realistic vegetation-substrate configurations

Green roofing is a sustainable solution for building energy saving, urban heat island mitigation, rainwater management and pollutant absorption. The effectiveness and performance of green roofs depend on layer composition and properties. The uncertainties surrounding green roof performance modeling are mainly related to the vegetation and substrate layer, which are subjected to surrounding climatic conditions. Energy simulation software typically does not use validated models encompassing all possible combinations of vegetation layers and substrates. Therefore, the objective of this research is to investigate different extensive green roof solutions for assessing thermal performance and to provide information on vegetation and substrate layer design. Different simulations executed in EnergyPlus were carried out based on realistic literature data drawn from previous experimental tests conducted on plants and substrates. Several combinations (30 plant-substrate configurations, six vegetative species and five types of substrates) were defined and evaluated. Furthermore, indexes based on the surface temperatures of green roofs were used. Finally, a comprehensive ranking was created based on the scores to identify which extensive green roof combinations offered the highest performance. Greater plant heights, LAI values and leaf reflectivity values improve green roof energy performance in the summer more significantly than substrate modification. During the winter, thermal performance is more heavily dependent on the substrate if succulent vegetation is present, regardless of the substrate used. These results could provide designers with useful data at a preliminary stage for appropriate extensive green roof selection.

Investigation of the thermal performance of coconut fibre composite with aluminium reflector cooling roofs

Global warming and depletion of petroleum resources have made the scientists to focus on new passive cooling techniques to reduce the indoor temperature of residential and commercial buildings. This paper explores the benefits of using coconut fibre composite as a passive cooling roof and quantifies those benefits in terms of heat flow changes through field experiment and compares them to the base case of standard roof in arid regions. The research also focussed on the usage of this material in combination with radiation reflectors such as aluminium and the effect of air gap between coconut fibre composite and aluminium reflector on the energy efficiency of the buildings. Experimental investigation showed a substantial reduction in room air and concrete roof slab temperature of coconut fibre composite with aluminium reflector room in comparison with the conventional roof. A maximum reduction of 5.99 °C (16.59%) and 8.39 °C (23.8%) were observed in room air and roof slab temperature of coconut fibre composite–aluminium roof with an air gap of 40 cm between them. It was also observed that as the air gap between coconut fibre composite and aluminium reflector is increased, the room air and roof slab temperature were reduced due to enhanced convective cooling. Compared to a standard roof, the indoor air temperature of coconut fibre composite roof was reduced by a maximum of 2.2 °C (5.86%), 2.9 °C and 5.99 °C (16.59%) for 0, 20 and 40 cm air gap between the coconut fibre composite and aluminium reflector, respectively. It is convincingly demonstrated that the coconut fibre composite roof with aluminium reflector can significantly affect the indoor air and roof surface temperature of the roofs during the hot summer days.

Impact of post-rainfall evaporation from porous roof tiles on building cooling load in subtropical China

Rainfall occurs frequently in subtropical regions of China, with the subsequent water evaporation from building roofs impacting the thermal performance and the energy consumption of buildings. We proposed a novel simulation method using actual meteorological data to evaluate this impact. New features were developed in EnergyPlus to enable the simulation: (1) an evaporation latent heat flux source term was added to the heat balance equation of the external surface and (2) algorithms for the evaporative cooling module (ECM) were developed and implemented into EnergyPlus. The ECM experimental results showed good agreement with the simulated results. The ECM was used to assess the impact of evaporation from porous roof tiles on the cooling load of a one-floor building in subtropical China. The results show that the evaporation process decreased the maximal values of the external and internal roof surface temperatures by up to 6.4 °C and 3.2 °C, respectively, while the lower internal surface temperature decreased the room accumulated cooling load by up to 14.8% during the hot summer period. The enhanced EnergyPlus capability can be used to evaluate the evaporative cooling performance of roofs with water-storage mediums, as well as to quantify their impact on building cooling loads.

How to enhance thermal energy storage effect of PCM in roofs with varying solar reflectance: Experimental and numerical assessment of a new roof system for passive cooling in different climate conditions

In last decades, the effectiveness of thermal energy storage (TES) systems for energy efficiency has been widely studied when integrated to building envelope, often as latent strategy by means of Phase Change Materials (PCM). In this view, the present study investigates the dynamic thermal performance of an innovative cool polyurethane-based membrane with PCMs inclusion for roofing applications. Such membranes were developed in previous works when the new composite material was characterized in terms of thermal-optical and morphological properties, when integrating PCMs with transition point at 25 °C and 55 °C. In this work, such materials is finally implemented into a roof multilayer structure, and additional experimental tests are carried out in a dedicated environmental simulation chamber, where the thermal performance of the novel lightweight roof stratigraphy is investigated. To this aim, two types of membranes for roofing applications, i.e. the innovative proposed cool membrane and a more traditional dark bitumen membrane, are considered. These two roof configurations are tested with and without the integration of PCMs, with varying the melting temperature range, in two different climate boundary conditions, i.e. Mediterranean climate of Rome, Italy, and Hot desert climate of Abu Dhabi, UAE. Moreover, numerical analysis of the roof thermal behavior is carried out through transient heat transfer calculation. Therefore, the two roof configurations are simulated and compared, in the same selected climate conditions and with varying PCMs.Findings of coupled experimental tests and numerical analysis show that the combination of cool membrane and PCMs with suitable melting temperature range allows to significantly reduce the roof surface temperatures and, therefore, the heat flux through the roof. In detail, results of numerical analysis demonstrate how in Rome the integration of PCMs with melting point around 25 °C and 45 °C in the cool and the dark roof membrane, respectively, has a great effect in reducing the external roof surface temperature. On the contrary, in Abu Dhabi, the configuration allowing the higher inward heat flux reduction is represented by the integration of PCMs with melting point around 35 °C and 55 °C in the cool and dark membrane, respectively. On the other hand, experimental tests show how the inclusion of a PCM layer with melting point around 25 °C and 31 °C under the cool and dark coating membrane, respectively, allows the best thermal performance in both climate conditions. Therefore, this work showed the promising effectiveness of PCMs inclusion to improve the thermal performance of waterproof membranes for roofing applications. However, as demonstrated, the selection of the proper PCM melting temperature should be operated by taking into account not only the climate conditions, but especially the roofing medium and the position in the roof stratigraphy where thermal energy storage materials are integrated. In fact, roof coating thermal behavior is largely influenced by its thermal-optical properties, e.g. solar reflectance and thermal emittance.

Thermal-cooling performance of subtropical green roof with deep substrate and woodland vegetation

As building-integrated vegetation, green roofs can improve thermal performance of buildings and their ambience. Research efforts tended to focus on thermal behavior of extensive green roofs outside the tropics, with inadequate attention on intensive type and tropical region. Using detailed microclimatic monitoring, this study investigated the thermal behavior of a native-woodland intensive green roof in subtropical Hong Kong. Three summer weather days denoting sunny, cloudy and rainy were chosen from long-term monitoring data for comparison with a nearby bare control roof. Shading and evapotranspiration by the woodland canopy respectively reduced roof surface temperature and air temperature by latent-heat absorption. The most notable maximum surface and air cooling, respectively at 19.80 °C and 6.21 °C, was achieved in daytime sunny condition, with cooling effect extending into nighttime. Surface cooling was mainly governed by daily pattern of solar irradiance, whereas air cooling was more pronounced nearer ground surface except in nighttime period on rainy days. Slight near-surface air warming occurred in rainy nighttime. The woodland vegetation filtered 90% of the incoming short-wave radiation during most of the daytime, serving as an insolation filter which contributed to surface cooling. The substrate experienced net heat loss in cloudy and rainy weather, exporting its antecedent stored heat. At 0.5 m substrate depth, the temperature stayed at a stable level, suggesting restricted heat exchange in subsoil. With appropriate design and regular maintenance, an intensive green roof with dense woodland canopy and 1-m substrate could provide effective above-ground and soil cooling and buffer against outdoor-to-indoor heat ingress.

URBAN HEAT ISLAND MITIGATION USING GREEN ROOF APPROACH

In urban environments, vegetation has largely been replaced by impervious and often dark surfaces. These conditions contribute to an Urban Heat Island (UHI) effect. This phenomenon is demonstrated in many cities and produced effects such as higher atmospheric temperatures, intensive precipitation, excessive solar radiation and increasing air pollution. Therefore, reducing the surface temperature of roofs in a building may play an important role in improving the conventional roof surfaces with green roofs that offer much lower temperatures throughout a day to reach their thermal performance and reduce the absorption of solar radiation. Thus, this study is focused on determining the effectiveness of the existing green roof in reducing the ambient temperature and humidity of the air above it by comparison with conventional open roof top without vegetation. This study also aims to evaluate the potential of green roof to reduce the air pollutants in improving air quality in urban cities. As a result, by adopting green roof system, it has reduced temperature during the hottest hour in a day at 1230 hour (hr) by 4.3°C when compared to open roof. Green roof has also recorded higher percentage of humidity compared to open roof. Most importantly, it was proven through this study that green roof has the potential of absorbing pollutants in the air by reducing the concentrations of Sulphur dioxide (SO2), Ammonia (NH3), Nitrogen dioxide (NO2), Ozone (O3) and Carbon monoxide (CO) compared to open roof. Thus, green roofs can be considered to be one of the effective methods to mitigate UHI effects in urban cities.

Study on Air Film Formation Mechanism and Cooling in Large-Span Air-Conditioning Plant Rooms without Natural Wind

Large-span air-conditioning plant rooms have a large roof area and suffer from serious solar radiation in summer. The outside roof surface temperature is very high, so cooling load of roof occupies a large proportion in the envelope structure cooling load of large-span air-conditioning plant rooms. Based on the Coanda airfoil air induction unit, the author combined with exhaust air in large-span air-conditioning plant rooms to design the roof air film cooling system of large-span air-conditioning plant rooms. The adherence air film formed on the outside surface takes away heat on the outside surface of the roof, so as to reduce outside roof surface temperature of the roof, decrease heat transfer temperature difference between inside and outside roof surfaces of, and reduce roof cooling cold. Furthermore, the mathematical model and numerical simulation method of considering fluid-structure interaction for heat transfer and influences of solar radiation on air film formation of outside surface and cooling were constructed. Moreover, the numerical simulation method was conducted the validation of effectiveness. Also, the author discussed the air film formation mechanism and air film cooling ability of outside surface in large-span air-conditioning plant rooms without natural wind, developed a new air film cooling technology for the roof of large-span air-conditioning plant rooms, and supplemented the existing roof cooling technology.

Thermal Behavior of a Building Provided With Phase-Change Materials on the Roof and Exposed to Solar Radiation

This paper evaluates the effectiveness of phase change materials (PCMs) for the improvement of summer thermal comfort in lightweight buildings. Experiments have been carried out using PCM in the form of DuPont Energain wallboards in combination with a roof. Two factors influencing the effectiveness of PCM (thickness and location of PCM layer) have been investigated. An experimental study was carried out using two identical test cavities submitted to Casablanca weather. Thermal performance such as the roof surface temperatures and heat flux densities, through the envelope, have been studied. The results indicated that, compared with reference room (without PCM), the thermal storage allows solar radiation to be stored and released up to 6–7 h after solar irradiation; this has effects on both the reduction of daily temperature swings (up to 2 °C) and heat flux (more than 88%). It has been proved that the PCM with a thickness of 10.52 mm on the outer face of the roof has good thermal insulation effect and energy efficiency potential.

Surface temperature analysis of an extensive green roof for the mitigation of urban heat island in southern mediterranean climate

Green roofs have recently been regarded as useful tools to mitigate the Urban Heat Island (UHI) phenomenon, being capable of substantially reducing the roof surface temperature. In this context the paper aims to present an extensive analysis of the surface temperature of an experimental green roof located in southern Italy. The surface thermal performance of both green and traditional roof was analysed in a very concise manner through proper defined indexes. The results of the analysis showed how the traditional roof in June reached a peak of 74.3°C with a daily excursion of 51.5°C whereas green roofs were able to produce a surface temperature from 0.57 to 0.63 times lower. The results also showed that in winter the vegetated roof could significantly reduce the daily temperature excursion compared to the reference membrane, indicating a reduction of the heat losses of the indoor spaces toward the external environment. Finally, a statistical comparison in terms of probability density distributions revealed that the dynamic thermal behaviour of the three different green layerings in both seasons was remarkably similar, proving the ability of vegetated roofs to maintain limited temperature variation in the whole year, thus containing heat losses in winter and overheating in summer.

Application of green blue roof to mitigate heat island phenomena and resilient to climate change in urban areas: A case study from Seoul, Korea

AbstractGreen blue roof has the potential to reduce the surface temperature of the building in the urban areas. Green blue roof is a new innovative low impact development (LID) practice that has exhibited an option to mitigate the heat island phenomena in urban area. This is the modified form of green roof that has ability to store rainwater in vegetation, soil layer and increases the evapotranspiration rate which decreases the temperature of an area. For this purpose, green blue roof is installed at the Cheong-un middle school building roof, Seoul, Korea. During the different time scenarios the surface temperature from the green blue roof and control roof were analyzed and their results were compared with each other. The results revealed that the surface temperature of green blue roof was much less as compared to control roof under same climatic conditions. From the results it is also concluded that surface temperature value of green blue roof was less than 5°C to 9°C as compared to control roof.

An integrative approach for indoor environment quality assessment of large glazed air-conditioned airport terminal in the tropics

The indoor environment quality in large glazed space such as airport terminals affects its users in many ways. The indoor environment quality assessment of such a building was typically conducted objective measurement using measurement and subjective assessment using questionnaire survey. However, limited resources and measurement period imply that would be incomplete and cannot provide accurate results. Computer modelling is thus an additional tool in the integrative approach for indoor environment quality assessment and analysis to improve its comfort and energy performance.Field measurement on the objective variables defined the environment quality and energy consumption, as well as questionnaire survey on the subjective judgment defined the indoor comfort. While the computer modelling was assessed across the air temperature, indoor glazed roof surface temperatures, mean radiant temperatures, operative temperatures and illuminance, to examine the building energy performance across the annual cooling load in 2010.The inner surface temperature over glazed roof were recorded as 56°C due to high level solar penetration, even when the indoor air temperatures over the floor level remain stable within the standard comfort zone. This rose the mean radiant temperature and was considered as main cause for indoor discomfort revealed by the survey. The survey found the employees to be slightly uncomfortable and dissatisfied, particularly in summer. The total energy consumption in 2010 was very high compared against the energy benchmarking. This study confirms that the large proportion of glazed roof is the cause for both overheating and thermal discomfort even with excessive use of the cooling system. In addition, recommendation was made to improve the thermal comfort condition in the large glazed air-conditioned terminal.

Performance of Building Roofs on Energy Efficiency – A Review

The steep increase in energy demand mainly during the summer season for tropical humid climates has gained significant importance in this scarce condition of fossil fuels. This paper presents a review on different roof technologies performed with an aim to reduce the cooling loads during summer thus helping in energy conservation. Firstly it deals with green vegetated roof carried out in regions of hot humid climates. The green roof performance was explored by evaluating its effect on temperature fluctuations and heat fluxes during summer. The results showed that the presence of plants led to a decrease in temperature in the presence of green roof. The water usage and tolerance to stress at times of prolonged drought were also assessed for several types of plants suitable for extensive green roof systems. Other cooling strategies are use of reflective paints also called cool paints. The impacts of the application of reflective paint on a standard bare roof were analyzed by mainly monitoring reduction of roof surface temperature at different case study locations. Further performance of three kinds of cool paints and even cool black paints are studied for going deeper into the facts of cool paint potentials and limitations. Eventually comparative analysis between these two solutions is assessed by taking into account the several parameters that affect the final energy performances.

Energy performance of a medium scale green roof system installed on a commercial building using numerical and experimental data recorded during the cold period of the year

The aim of this study is to investigate the energy performance of a medium scale green roof system installed on a two-story commercial building in Athens, Greece and its possible contribution to the mitigation of the urban heat island phenomenon. For the purpose of this research, in-situ measurements of temperature and humidity took place during the cold period of the year. The surface temperature of the conventional concrete floor of the roof was found to be up to 21.9K higher than the one of the planted area during the day, while at the first hours of the day, the surface temperature of the green roof appeared to be up to 1.6K higher than the one of the cement floor of the roof. Differences of the surface temperatures of the varying plants of the green roof were measured and led to a proposal of an optimum selection among them for the best performance of such a green roof system. Furthermore, simulations for this building were performed by using the EnergyPlus program. It was calculated that, the indoor air temperature, for a non air conditioned status of the building, was decreased up to 1.1K during a typical summer day and was increased up to 0.7K during a typical winter day. Lastly, an overall saving of 15.1% for a whole year on the energy consumption of the building was calculated.