Tuesday, February 14, 2012

Solar Air-conditioning

‘Clean Energy and Water Technologies’ (CEWT), will be presenting a series of articles, on how to generate and use various renewable energy sources and use them for our day today applications. These articles will be useful for individual families, businesses and small industries, to effectively use such energy sources. Many nations around the world, have now started realizing the importance of renewable energy; especially after witnessing fluctuating oil prices (oil price hike is caused due to many factors, most of them are beyond our control), the nuclear disaster at Fukashima Nuclear power plant in Japan, global warming and its natural consequences (unusual snow during summer and bush fires in winter etc.), we are now witnessing all over the world. In most of these cases, power failures are due to grid failures. In many countries, Government offer higher tariff for renewable energy, subsidies for cost of renewable energy equipments etc., to encourage people to opt for such energy sources. The most important incentive offered by renewable energy is, ‘a sense of independence’ to the consumer, not to depend on grid power, but to generate their own power, to meet their day to day requirements. Renewable energy is still expensive, but improving technological developments will change this situation. That is why; many industrialized countries in Europe, US and Japan, are now investing heavily in renewable energy industries. In this article we will discuss about ‘Solar air-conditioning’: Solar air-conditioning is a method of cooling space, in buildings, using (PV) photo voltaic solar panels, concentrated PV solar panels, and solar thermal heaters. 1. This can be achieved by generating electricity, using roof top solar panels similar to a system we normally use for lighting, to run a conventional type electrical air-conditioning unit. Individual houses and buildings have to be carefully studied, and systems have to be specifically designed, to get the optimum results. 2. Alternatively, we can use roof top solar water heaters to generate hot water. This hot water can be circulated through an absorption chiller, to generate chilled water. The chilled water will then be circulated through fan coils, mounted on the ceiling of the room, to be cooled. It is a close circuit unit, in which, the fan in the fan coil unit blows air across the fan coil, through which chilled water is circulated at 4.5℃ and returned back to the chiller at 8.5℃. The returning chilled water at 8.5℃ will be chilled again to 4.5℃ in the chiller and returned back to the fan coil unit. This process continues, as long as, we need to keep the room cool, at around 18-20℃. This article will not describe the principles, and methods of absorption chilling, which is a well established industrial practice. The hot water from the solar water heater can additionally be supplemented, from any other waste heat source. For example, if a business or an industry has a diesel operated engine or a generator, with water cooling, and then such water can be supplemented with solar heated water, to supplement the capacity of the airconditioner. Most of the diesel engines operate at an efficiency of around 30-40%, and the balance 60-70% is wasted as waste heat, into atmosphere, as greenhouse emission. Some diesel generators will have a radiator with coolant, or cooling water circulated through a cooling tower, for recirculation. The diesel engine cooling system can be suitable altered, to generate hot water to supplement the solar hot water. In many tropical countries in Asia, power failures or blackouts are common, and many businesses, industries, and beach resorts, have standby diesel generators as a backup power source. These customers can opt for solar air-conditioning that will offer them good savings. A typical 100TR solar air-conditioning unit in a beach resort, using back up diesel power generator cooling water, will be able to recover their investment in less than 5 years. It is economical, because the cost of power using diesel generators is high. In places, where piped natural gas is available, the system can be designed for both heating (during winter) and cooling (during summer), as well as, for back up hot water. The engine will be gas fired, and the waste heat can be used to supplement solar hot water. Alternatively, when the engine is not used, the gas can be used to generate hot water to supplement the solar hot water. The system can be designed in many ways to suit the conditions of the site and the customer’s requirement. In all our applications, we will try to substitute fossil fuel, with 100% renewable energy source, or at least, to supplement the fossil fuel, with renewable energy source, similar to a ‘hybrid car’. Solar energy can also be used to refrigerate critical, life saving medical vials and injectibles, in remote places where there is no grid power.