Talking about solar air conditioning and its advantages is great. However, there are certain considerations that you have to think about before considering installation of a solar air conditioning. After all, you may not need to spend that much money to buy a solar air conditioner.
For argument sake, take an existing 4 story building as your model since the rate of return on initial investment is faster compared to a single story building and assume your area is a hot climate with average temperature 35 deg C.
With such temperature, your building would act as a heat radiating furnace! Surprised I believe? Definitely, your existing building absorbs heat during the day and in turn you switch on your conventional air conditioner in order to bring the temperature down. Why?
The building was never designed to be energy efficient from the first place and you spend your money on cooling to stay comfortable.
If this is the case in your building, then installing a solar air conditioner for cooling the building is worthless and you would be throwing your money away! What should you do?
Whether you’re considering solar air conditioning or not and your building is not an energy efficient building, you should think about the following:
- In any building that is not thermally insulated to grade A, B or C there is a great loss of heat externally and internally. As the sun rises over the horizon, its rays strikes the walls facing the sun of your building and heats the external wall surfaces constantly to a great degree almost till noon time. Then the other half of the building gets its fair share of sun rays till the sun sets.
- The heat generated would be absorbed by the walls' building material and this heat gets transferred towards the internal surfaces of the walls. The internal walls start to radiate heat to the building internal atmosphere making you feel hot. In turn, you switch on your air conditioner to overcome this discomfort.
- Similarly, if the building’s roof was not thermally insulated it would absorb much more heat than the building’s walls, and the top floor would be the hottest since it is exposed to sun’s rays from more than one area compared to the other floors.
- The air conditioner acts as a temporary relief till sun set. Then the cooling cycle starts to reverse during night time. However, it takes building material a long time to cool down for you to switch off the air condition (that depends on the area where you live in).
In the past, conventional and commercial buildings were not built to be energy efficient. However, it is possible to upgrade the thermal insulation level of a building and make it energy efficient.
How to Thermally Insulate a Building?
Each building has external and internal wall surfaces and both needs to be thermally insulated for the building to become energy efficient. In addition the roof needs to be thermally insulated as well.
Thermal Insulation of the External Walls:
The external walls can be insulated with 50mm high density Polyurethane boards that get fixed on the external walls of the building. However, Polyurethane is a soft material and needs to be protected from external atmospheric effects and that can be achieved using fiberglass boards or Aluminum cladding to make it rigid. Then the boards need to be painted with white color reflective paint to repel sun rays.
Thermal Insulation of the Internal Walls:
The internal walls can be insulated with high density Polyurethane boards of less than 50mm, gypsum boards or wooden boards. Then you paint it whatever color you may chose.
Thermal Insulation of the Roof:
Before insulating the roof, you may need to consider applying water proofing materials to prevent rain water from seeping through or getting soaked if trapped below the insulated roof. The external roof can be insulated with 50mm high density Polyurethane boards then a second layer of fiberglass or similar material can be applied to make the roof rigid. Finally paint the roof with white color reflective paint to repel sun rays.
Note that if you are going to install solar thermal panels for solar air conditioning, then you could reduce the insulation level since the solar panels are going to prevent sun rays from directly hitting the roof top material.
The roof is the most exposed area to the sun and is responsible for most of the heat generated that gets radiated to the inside of a building.
Thermal Insulation of the Ceiling:
By convention hot air rises up and colder air falls down since hot air is lighter than cold air. Therefore, the ceiling will become hot. If you are not going to install solar panels on the roof you may achieve higher insulation level by installing false ceiling. This is optional and can be done at a later stage if you choose to.
There are other areas in the building that you need to look after in order to achieve higher insulation to make your building energy efficient, such as the external windows and doors.
Glass Window and Solar Air Conditioning.
As for windows, if the glass windows are single glassing, then it is easy for the energy to pass in either direction. In normal buildings single glass windows are in most cases around 4mm thick. On a sunny day, if you touch the glass window you may feel it hot, and during winter time, if you touch the glass you may feel it cold. Then what is the solution?
There are three solutions that you may consider; each has a cost impact more than the others and other advantages as explained below:
- For hot climates, the cheapest solution would be to use a good quality non-removable thin reflective film that has a self adhesive surface. You can get pasted easily on glass windows or have a specialist do it for you. It is similar to the one used for cars with tinted windows. However, that only reflects the sun’s rays and won’t prevent transfer of energy to the outside atmosphere.
- The other solution would be to change the windows and make them double glassing. That is having two glass layers with vacuum in between (this is the same idea as in vacuum tubes used for solar water heating).
With this solution, not only will you prevent heat loss to the external or to the internal atmosphere, but the vacuumed glass windows will reduce the noise level greatly and prevent noise from penetrating to the inside of the building. (Noise will not travel in vacuum)
- In a hot climate you may apply the thin reflective film on the double glassing windows to get the ultimate protection from sun rays.
Over and above, make sure that the windows that are going to install are air tight when closed completely. This will tremendously reduce energy loss in either direction as you would see for the externally exposed doors of the dwelling.
Thermal Insulation of External Doors.
Usually in any dwelling there must be a main entrance door. Others may have more than the main entrance door. Regardless of the material used for the externally exposed doors, there are certain gaps that sometimes could allow energy transfer during summer or winter time.
Check your external doors if they close tightly and are not warped. If a problem exists, you may get a good quality single rubber gasket with a single side adhesive surface and paste it around the top and the side of the door.
In addition, check the bottom part of the door to see how big is the gap between the floor and the bottom of the door. If the gap is too big and it allows a lot of energy to escape to the outside atmosphere, then you have one of two solutions that you may consider:
- Fix a rubber sealing strip under the door along the width of the door (it has a metal strip on top and a rubber strip on the bottom).
- Fix a long tile along the door width to seal the gap under the door.