As the global temperatures rise, regions particularly close to equator are warming up quickly. Cities like Karachi and Mumbai, Dhaka in the 90’s use to see only very few days a year, when the temperature rose above 40°C. In the recent years, the temperatures soared past 45 °C for dozens of days not only during the summer but across the meteorological Autumn and Spring. In light of this it is worthwhile exploring some other cooling methods other than the traditional cooling methods that use energy guzzling air conditioners.
A lot of work needs to be done on the modern building construction methods. The pressure on housing because of huge demand has lead to building being constructed with very low thermal inertia i.e. there are dwelling with far too much metal used. The increase in metal be it in the bars or the window frames lowers the heat capacity of the building. As a result, buildings get hotter during the summer and much cooler during the winter. Houses built with mud and clay on the other hand tend to remain cooler during the scorching heat. Similarly, high ceilings also help improve the temperature of the dwellings. The hotter air tends to rise and stay adjacent to the ceiling, while the cooler air remains at the level of occupants.
Three cheap alternatives to air-conditioners are listed below
Hybrid Solar Air conditioner
Air conditioners work by pressurizing the refrigerant as part of its closed loop cycle. Once the refrigerant is pressurized, it also heats up in the process. The pressure increase is achieved by means of a compressor. The heat build-up because of pressurization is removed by passing it through a heat exchanger which allows the refrigerant to loose its heat to the outside. The refrigerant at this point is much higher in temperature than the ambient.
The refrigerant is than pushed through a throttle valve, which not only reduces the pressure but also the temperature. This happens because of sudden gas expansion. The very cool refrigerant in tubes is transported to the inside unit of the air conditioner which is placed in the room needed to be cooled. A fan in the inside unit blows air past the tubes. As a result we get cool air.
A hybrid solar air conditioner heats up the refrigerant just before it enters the compressor. It should be noted that heat also raises the pressure of refrigerant. Therefore, the compressor, which is the main energy guzzler in an air-conditioners, does not have to work as much with the refrigerant pre-pressurized. It has been reported that Hybrid Solar Air conditioners can reduce energy consumption from 30-50%.
Because the addition of solar collector reduces the compressor activation time, it also saves the compressor from wear and tear and makes it last much longer.
Some useful information on Hybrid Solar Air conditioners can be obtained from this link. They are only slightly higher in price compared to normal air conditioners, but can provide great energy savings and much reduced maintenance cost.
Arid regions that are not close to a large body of water (seas, lakes) have much less moisture in the air and hence much less humidity. One advantage of arid, semi arid and even subtropical climate is that dry air can be cooled by the process of evaporation. The devices used for this process are called Evaporative coolers. They are extremely cheap as they consist of fans blowing air through pads that soaked in water. The water absorbs the heat from the air and evaporates leaving the cools air to fill the room. The drier the air, the more effective evaporative coolers are. In the subcontinent evaporative coolers are often simply referred as “Room coolers”. They utilize mats of dry Vetiver grass (“Khas” in Urdu/Hindi) instead of synthetic pads as a medium to hold water that allows the exchange of heat with the hot air.
The disadvantage of these coolers is their inefficiency when moisture is already present in the air. Furthermore, their constant use can add significant amount of moisture in the building fabric therefore they should be used only where good ventilation is available.
Peltier Air conditioners
Peltier Air conditioners are solid state air conditioners that make use of the Peltier effect and produce cooling. Compared to normal air conditioners they are very inefficient. They are an option only for small spaces and closets. However because they require a DC input, they can be directly coupled with a PV panel to create a very small air conditioning unit.
The Peltier Air conditioners are adequate for cooling a room but may provide enough cooling air for you to fall asleep on a hot summers night. Off the shelf units are available in various sizes and are often used for cooling data centres and server cabinets. They have also been used for cooling dog houses. They are available in the market for as low as $50 and can even be assembled in-home very easily and cheaply.
In hot and humid climates, it is often the high humidity that creates the most discomfort as opposed to the heat. Moisture can be now easily removed through dehumidifiers that also use the Peltier effect. A small size dehumidifier (720 W) can remove up to half a litre (500 ml) of water a day.
Also worth mentioning is the Ranque-Hilsch Vortex tube. This uses compressed air as an input. The compressed air is allowed to enter the tube from a circumferential inlet. This allows the compressed air to spin. The spinning vortex and expansion of the air splits it into two streams. One with a very high internal energy (hot stream) and one with very low internal energy (cold stream). Being more energetic, the hot stream spins around the circumference of the tube and is bled-off at one end (which has a circumferential opening). The cold air stream is made to rebound and is bled at the other end.
Vortex tubes are very inefficient, and can be purchased for 100 to 200 USD. They are solid state devices that will last a lifetime. Vortex tubes can be used for spot cooling rather than air conditioning.
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