Background
Buildings report for 40% of the total major energy use worldwide [1]. International Energy Agency mentions that if no energy efficient developments are used in the building segment, energy use may raise by 50% in 2050 [2].
World climatic zones can be differentiated into zones of latitude. Countries with hot climates utilize extra energy per capita due to high demand for air-conditioning. These countries lie within equatorial climate, hot and dry or humid summers, which lie in 40°N and 40°S of latitudes [3]. Along with climate, modern design, particularly for commercial buildings demands for glass facades. This causes elevated cooling demand in summers in urban areas. This results in the heat island effect that is related with global warming. To achieve thermal comfort, and the accessibility of low-cost air-conditioning systems, the use of air conditioners has improved, mainly in the developing countries. The IEA report predicts that the global energy demand in buildings would raise by 60% between 2007 and 2050 which is equal to almost twice the carbon dioxide (CO2) emissions from 8.1 Gt [4] of CO2 to 15.2 Gt CO2 [5]. The same study mentions that the buildings sector play an significant role in use of more sustainable energy in future by the use of low or zero-carbon techniques that would save up to 5.8 Gt CO2 emissions.
The building envelop or facade, is the community face of a building, and has thus a huge impact on the view of the building. From an energy point of view, the envelope acts as a mediator between the internal and the external environment. The facade can lessen solar heat gain, thus contributing in reducing heating/cooling loads, and improving distribution of daylight.
Shading devices are one of the important aspect of many energy-efficient building design strategies. In particular, buildings that use passive solar heating or day lighting often depend on well-designed sun control and shading devices.
During hot months, external window shading prevent unnecessary solar radiation from entering a space. Shading devices can be elements such as awnings, overhangs, etc. Some shading devices reflect light like light shelves, which bounce natural light for day lighting deep into building interiors. The important factor in design of shading devices is the orientation of a particular building facade. For example, simple fixed overhangs are very effective at shading south-facing windows in the summer when sun angles are high. However, the same horizontal device is ineffective at blocking low early morning or afternoon sun from entering east and west-facing windows during peak heat gain periods in the summer.
There are many different reasons to control the amount of sunlight that is entered into a building. In warm and sunny climates excess solar gain may result in high cooling energy consumption; in cold and temperate climates winter sun entering south-facing windows can positively contribute to passive solar heating; and in all climates scheming and diffusing natural light will improve overall day lighting. Ingenious sun control and shading devices can noticeably reduce building high heat gain and cooling necessities and develop the natural lighting quality of building interiors. Sun control and solar shading devices can also improve user visual comfort by controlling glare and reducing contrast ratios. Shading devices offer the chance of differentiating one building facade from another. This can offer architectural interest and human scale to an otherwise ordinary design
During cooling seasons, external window shading is an brilliant way to avoid unwanted solar heat gain from entering a conditioned space. Shading can be provided by natural landscaping or by building elements such as awnings, overhangs, and trellises. Some shading devices can also function as reflectors, called light shelves, which bounce natural light for day lighting deep into building interiors. The design of useful shading devices will depend on the solar orientation of a particular building facade. For example, simple overhangs are very effective at shading south-facing windows in the summer when sun angles are high. However, the same horizontal device is useless at avoiding low afternoon sun from entering west-facing windows during peak heat gain periods in the summer.
Exterior shading devices are particularly effective in conjunction with clear glass facades. However, high performance glazing is now available that have very low shading coefficients (SC). When specified, these new glass products reduce the need for exterior shading devices. In the summer, peak sun angles occur at the solstice on June 21, remember that an overhang sized shade the window in April
World climatic zones can be differentiated into zones of latitude. Countries with hot climates utilize extra energy per capita due to high demand for air-conditioning. These countries lie within equatorial climate, hot and dry or humid summers, which lie in 40°N and 40°S of latitudes [3]. Along with climate, modern design, particularly for commercial buildings demands for glass facades. This causes elevated cooling demand in summers in urban areas. This results in the heat island effect that is related with global warming. To achieve thermal comfort, and the accessibility of low-cost air-conditioning systems, the use of air conditioners has improved, mainly in the developing countries. The IEA report predicts that the global energy demand in buildings would raise by 60% between 2007 and 2050 which is equal to almost twice the carbon dioxide (CO2) emissions from 8.1 Gt [4] of CO2 to 15.2 Gt CO2 [5]. The same study mentions that the buildings sector play an significant role in use of more sustainable energy in future by the use of low or zero-carbon techniques that would save up to 5.8 Gt CO2 emissions.
The building envelop or facade, is the community face of a building, and has thus a huge impact on the view of the building. From an energy point of view, the envelope acts as a mediator between the internal and the external environment. The facade can lessen solar heat gain, thus contributing in reducing heating/cooling loads, and improving distribution of daylight.
Shading devices are one of the important aspect of many energy-efficient building design strategies. In particular, buildings that use passive solar heating or day lighting often depend on well-designed sun control and shading devices.
During hot months, external window shading prevent unnecessary solar radiation from entering a space. Shading devices can be elements such as awnings, overhangs, etc. Some shading devices reflect light like light shelves, which bounce natural light for day lighting deep into building interiors. The important factor in design of shading devices is the orientation of a particular building facade. For example, simple fixed overhangs are very effective at shading south-facing windows in the summer when sun angles are high. However, the same horizontal device is ineffective at blocking low early morning or afternoon sun from entering east and west-facing windows during peak heat gain periods in the summer.
There are many different reasons to control the amount of sunlight that is entered into a building. In warm and sunny climates excess solar gain may result in high cooling energy consumption; in cold and temperate climates winter sun entering south-facing windows can positively contribute to passive solar heating; and in all climates scheming and diffusing natural light will improve overall day lighting. Ingenious sun control and shading devices can noticeably reduce building high heat gain and cooling necessities and develop the natural lighting quality of building interiors. Sun control and solar shading devices can also improve user visual comfort by controlling glare and reducing contrast ratios. Shading devices offer the chance of differentiating one building facade from another. This can offer architectural interest and human scale to an otherwise ordinary design
During cooling seasons, external window shading is an brilliant way to avoid unwanted solar heat gain from entering a conditioned space. Shading can be provided by natural landscaping or by building elements such as awnings, overhangs, and trellises. Some shading devices can also function as reflectors, called light shelves, which bounce natural light for day lighting deep into building interiors. The design of useful shading devices will depend on the solar orientation of a particular building facade. For example, simple overhangs are very effective at shading south-facing windows in the summer when sun angles are high. However, the same horizontal device is useless at avoiding low afternoon sun from entering west-facing windows during peak heat gain periods in the summer.
Exterior shading devices are particularly effective in conjunction with clear glass facades. However, high performance glazing is now available that have very low shading coefficients (SC). When specified, these new glass products reduce the need for exterior shading devices. In the summer, peak sun angles occur at the solstice on June 21, remember that an overhang sized shade the window in April
Literature Review
In the experiment mentioned by Vanaga Ruta, Andra Blumberga, Ritvars Freimanis, Toms Mols, and Dagnija Blumberga, two boxes to be tested were positioned side by side. One was with and one was without the facade module. Both test boxes were placed on the roof to exposed them to the same conditions. Both boxes were instrumented to examine the solar radiation, relative humidity, heat transmission and temperatures in the phase change material. Data collected throughout was analysed and used to regulate simulation mode.
Both the boxes were made from plywood, filled with mineral wool and has a room (22.7 × 12.7 × 12.7 cm) in the centre of the box in reference box. and experimental solar facade module was replaced with mineral wool in the experiment test box.
Fresnel lens: Focal length: 7.1 cm. Effective diameter: 101.6 mm, Transmittance is 0.92. Copper plate: Dimension: 119 mm × 113 mm Copper Rods: Welded to copper plate, Diameter: 5 mm, Distance between rods: 15 mm Phase Change Material: Paraffin Aerogel: Low thermal conductivity and High solar energy transmittance. |
Sectional View of Experiment Box
Experiment Box
Electronics
Solar heat flux: Pyranometer,
Outdoor and Indoor temperature: K-type thermocouple,
Data logged: Campbell Scientific CR1000 data logger.
Outdoor and Indoor temperature: K-type thermocouple,
Data logged: Campbell Scientific CR1000 data logger.
Experimental Results and Discussion
Heat fluxes and temperatures calculated within and on both sides of the module for one day on September 25, 2017. These are presented in Fig. 7. Graph begins from midnight. The solidification of PCM causes latent heat that causes heat flux to both inside and outside. The circulation of heat from PCM to outdoor is more than to indoor. This is due to greater temperature difference.
When the sun rises at 7:05, heat flow from outside to PCM changes direction to become positive. In the meantime heat flux to room begins to fall. Then, it rises again at 1:30 pm. When the solar radiation starts to reduce at 13:22, the heat flux to PCM also reduces till it becomes negative at 4:55 pm. At night solidification of the PCM starts again and latent heat is released at about 11:40 pm and both heat flux to indoor and outdoor rises. But, internal temperature decreases due to heat flow to outdoor is more than to room.
The main reason behind this is the temperature difference between PCM and the room temperature. At night while the latent heat is discharged during solidification process, PCM temperature is roughly stable but indoor temperature decreases. Thus, the temperature difference rises. Heat flux from PCM to the room rises due to latent heat and temperature difference. PCM temperature begin to rise after heat flux when the sun's heat enters PCM at and PCM starts to melt. At the start temperature difference is reducing leading to decreased heat flux and then the temperature difference is growing due to a lag caused by PCM melting. Then, the heat flux starts to reduce as room temperature is reaching to PCM temperature.
Dynamic performance of the room temperature and heat flux in the reference box is different from box with module. Heat flux in the reference box corresponds with the late solar radiation and at its highest peak is approximately four times less than in the module. The room temperature in the reference box is different from the module between 0.5 °C during the day touching this value at 14:30 and 5 °C during the night at 7:50 which shows the effect of the thermal energy buildup in the PCM. The time delay between solar radiation and the PCM temperature is 3.5 h and between the PCM temperature and indoor temperature it is 45 min. In the reference box indoor temperature peak is delayed from the solar radiation peak for 4 h. The temperature decreases and then begins to increase. This is due the solidification process when PCM is release latent heat and heat flux increases. Heat cannot be removed right away. Thus, the PCM temperature is going up leading to cooling. Heat flux rises more quickly to the outside than to inside because of high temperature difference between PCM and outdoor. When the heat flux to room began to rise, the solidification temperature settles about +21.6 °C. Solidification do not take place at the melting point and it is well shown by the hysteresis effect of PCM.
When the sun rises at 7:05, heat flow from outside to PCM changes direction to become positive. In the meantime heat flux to room begins to fall. Then, it rises again at 1:30 pm. When the solar radiation starts to reduce at 13:22, the heat flux to PCM also reduces till it becomes negative at 4:55 pm. At night solidification of the PCM starts again and latent heat is released at about 11:40 pm and both heat flux to indoor and outdoor rises. But, internal temperature decreases due to heat flow to outdoor is more than to room.
The main reason behind this is the temperature difference between PCM and the room temperature. At night while the latent heat is discharged during solidification process, PCM temperature is roughly stable but indoor temperature decreases. Thus, the temperature difference rises. Heat flux from PCM to the room rises due to latent heat and temperature difference. PCM temperature begin to rise after heat flux when the sun's heat enters PCM at and PCM starts to melt. At the start temperature difference is reducing leading to decreased heat flux and then the temperature difference is growing due to a lag caused by PCM melting. Then, the heat flux starts to reduce as room temperature is reaching to PCM temperature.
Dynamic performance of the room temperature and heat flux in the reference box is different from box with module. Heat flux in the reference box corresponds with the late solar radiation and at its highest peak is approximately four times less than in the module. The room temperature in the reference box is different from the module between 0.5 °C during the day touching this value at 14:30 and 5 °C during the night at 7:50 which shows the effect of the thermal energy buildup in the PCM. The time delay between solar radiation and the PCM temperature is 3.5 h and between the PCM temperature and indoor temperature it is 45 min. In the reference box indoor temperature peak is delayed from the solar radiation peak for 4 h. The temperature decreases and then begins to increase. This is due the solidification process when PCM is release latent heat and heat flux increases. Heat cannot be removed right away. Thus, the PCM temperature is going up leading to cooling. Heat flux rises more quickly to the outside than to inside because of high temperature difference between PCM and outdoor. When the heat flux to room began to rise, the solidification temperature settles about +21.6 °C. Solidification do not take place at the melting point and it is well shown by the hysteresis effect of PCM.
Sources
- Modernising building energy codes, International Energy Agency (2013)
- Transition to sustainable buildings, strategies and opportunities to 2050, International Energy Agency (2013)
- Meteorological OfficeMeteorological Office: Meteorological Glossary.
- (6th ed.), HMSO, London (1991)
- H.S. Brown, P.J. VergragtBounded socio-technical experiments as agents of systemic change: the case of a zero-energy residential building
- Technological Forecasting and Social Change, 75 (2008), pp. 107-130
- Energy Technology Perspectives 2010: Senarios & Strategies to 2050
- International Energy Agency, France (2010)
- Vanaga, Ruta, Andra Blumberga, Ritvars Freimanis, Toms Mols, and Dagnija Blumberga. “Solar Facade Module for Nearly Zero Energy Building.” Energy 157 (August 15, 2018): 1025–1034.