A cool roof keeps the building cool by reflecting the incident sunlight and by emitting heat retained by the building. This will reduce load on the air conditioner and chiller units installed inside the building. In non-ac buildings, inside temperature drops by a few degrees making it comfortable for the occupants…
A few proposed cool roofing solutions (in the 2018 article)
- Cool Roof Coatings (White Roof): A simple limestone whitewash provides good reflection at reasonable cost. Good quality reflective coatings are also available, which are costly but provide better performance.
- Tiling Solutions (White Roof): Flat roofs can be covered with white glazed tiles. Alternatively, a raised sloped roof can be constructed, supported by metal columns. Glazed tiles placed on the metal roof will reflect the sunlight. The building roof is available for all activities.
- Metal Roofs: Metal roofs have high reflectivity but are very poor in terms of thermal emittance. This can be improved by applying cool roof paints on the metal surface.
- Earthen Pot Insulation System: In this traditional method, roofs and walls are covered with upside down earthen pots. This traps air between roof and top surface of the pots, thus providing thermal insulation.
- Green Roofs: Green Roofs can be designed to have basic plant cover or a garden. Large potted plants and shrubs could be kept on the roof. Alternatively, spreading earth on plastic sheets can be used to grow plants. Watering, drainage, seepage, daily maintenance etc., should be carefully planned. However, it adds extra weight to the building structure, which should be taken into account while planning Green Roofs.
- Solar Panels: Installing Solar Panels is another good option. However, the initial cost is much higher than Cool Roof solutions. Big advantage is, it provides good regular income with a payback period of a few years.
Another simple solution that can be added to the above list
- Sprinkler: Sprinklers used in the gardens can be installed on the roof top. These will water the roof surface at regular intervals. The building will get cooled due to evaporation of water.
Proposed balloon based cool roof design (new idea) for commercial buildings
Figure 1 shows a building in which Balloon based Cool Roof design has been implemented. A typical building front view shows three floors of the building. On the terrace, big advertisement balloons are mounted. Terrace view shows the arrangement of balloons which covers the whole roof. On many commercial buildings, equipment such as condensers, water tanks etc are installed. In those areas balloons can be avoided.
An advertisement balloon is a big balloon filled with Helium gas. These balloons are several feet in diameter and height and are made from thick PVC fabric. The fabric contains UV inhibitor to eliminate fading, for outdoor use. Such balloons could be inflated and deflated multiple times. Hooks have to be fixed on the roof surface in locations where the balloons are to be installed. Using harness, the balloons are tied to these hooks.
The harness is very short and hence these balloons almost touch the roof surface. Additional harness could be attached to the top surface of the ballons and tied to roof. This will restrict the movement of balloons during strong winds. Finally, cylinders containing helium gas will have to be maintained at a safe location.
Advantages of proposed design
Balloons do not put any load on the building structure. No danger of seepage or damage to the roof surface unlike in the Green Roof case.
No structural design changes or additional constructions are required. Few hooks are required to be fixed to the roof surface. Also, plastic pipes will be required for inflating the balloons from the Helium cylinders.
Balloons could be inflated or deflated automatically sitting inside the building itself. There is no need to send staff to the terrace frequently.
After initial installation, there is no need to frequently move any material etc., to the terrace.
These balloons can be used for advertisement, which will generate regular income with a payback period of few years. Advertisements could be given on all four sides of the building.
There is a large gap between reflecting surface (top surface of the balloon) and the roof to be cooled. Hence, cooling effect is better than other solutions.
Similarly, reflecting surface is not in contact with the roof top, hence there is no conduction of heat to the roof.
The installation and maintenance can be outsourced to an advertisement agency. They will install the balloons and maintain them. Income from advertisement can be shared.
Balloons extend length of shade produced by the building on the ground. This extra shade will keep the area surrounding the building relatively cooler.
It is very cost effective. Replacement of damaged balloons is fairly easy.
The above costing is just for guidelines only and costs are approximate. The total investment required for a roof of size 60 ft x 36 ft, is about 10 Lakh rupees. Assuming modest income of Rs 50,000 per month from advertisement, the payback period will be less than 2 years. The system pays back by itself while providing significant savings in the electricity bills due to reduction in load on the ACs.
Conclusions
Proposed Balloon-based Cool Roof design offers several advantages. No major structural change or construction is required. It does not put any load on the building structure. It needs very less maintenance. No movement of men or material on day-to-day basis. Whenever required, the roof can be made available just by deflating the balloons. Large gap between the reflecting surface and roof surface provides more effective cooling. Extended shade due to ballons provides cooling around the building throughout the day. It provides space for advertisement, which can generate good revenue. Lastly, it can be easily outsourced to an advertisement agency with monthly revenue.
Vijay Deshpande has done PhD from IIT Kanpur in Electrical Engineering. He has worked in several companies in India. He worked as Technology Specialist and retired from Honeywell India. His current interests include working on cost effective Cooling Techniques and also on Solar Photovoltaic Systems. He has published several research papers in International Journals and published many articles in leading magazines.
