CHAPTER 2RELATED LITERATURE

HISTORYIn the 1840s, physician and inventor Dr. John Gorrie of Florida proposed the idea of cooling cities to relieve residents of "the evils of high temperatures." Gorrie believed that cooling was the key to avoiding diseases like malaria and making patients more comfortable, but his rudimentary system for cooling hospital rooms required iceto be shipped to Florida from frozen lakes and streams in the northern United States.To get around this expensive logistical challenge,Gorrie began experimenting with the concept of artificial cooling. Hedesigneda machine that created ice using a compressor powered by a horse, water, wind-driven sails or steam andwas granted a patent for it in 1851. Although Gorrie was unsuccessful at bringing his patented technology to the marketplace -- primarily due to the death of his chief financial backer -- his invention laid the foundation for modern air conditioning and refrigeration.http://energy.gov/articles/history-air-conditioningThe first modern air conditioner was invented in 1902 by Willis Haviland Carrier, a skilled engineer who began experimenting with the laws of humidity control to solve an application problem at a printing plant in Brooklyn, NY. Borrowing from the concepts of mechanical refrigeration established in earlier years, Carriers system sent air through coils filled with cold water, cooling the air while at the same time removing moisture to control room humidity. In 1933, the Carrier Air Conditioning Company of America developed an air conditioner using a belt-driven condensing unit and associated blower, mechanical controls, and evaporator coil, and this device became the model in the growing U.S. marketplace for air-cooling systems.https://www.asme.org/engineering-topics/articles/technology-and-society/global-cooling-the-history-of-air-conditioning

IMPORTANCE

The primary objective of air-conditioning is to provide comfortable conditions of the people. From the thermal standpoint, the body is inefficient machine but a remarkably good regulator of its temperature. The human body receives full in the form of food, converts a fraction of the energy in the fuel into work, and rejects in the remainder as heat. It is the continuous process of heat rejection, which requires a thermal balance. The generation of heat occurs in cells throughout the body, and the circulatory system carries this heat to the skin, where it is released to the environment. In a steady-state heat balance, the heat energy produced by metabolism equals the rate of heat transferred from the body by convention, radiation, evaporation and respiration. If the metabolism rate is not balanced momentarily by the sum of the transfer of heat, the body temperature will change slightly.

Most people felt restless and uncomfortable if heat wrapped up the body. Concentration is destroyed and work is not organized.The heat-transfer coefficient depends upon the air velocity across the body and consequently also upon the position of the person and orientation to the air current.Based on the discussion made by W.F. Stoecker which are properly dished out in his book Refrigeration and Air-conditioning, the skin temperature is controllable to a certain extent by the temperature-regulating mechanism of the body covered by clothing. The clothing temperature will normally lie somewhere between the skin and the air temperature, unless lowered because it is wet and is evaporating moisture.The human body is an adaptable organism. With long-term conditioning the body can function under quite extreme thermal conditions. Variations in outdoor temperature and humidity, however, go beyond the normal limits of adaptability, and it becomes necessary to provide modified conditions indoors in order to maintain a healthy, comfortable environment.The body is continuously generating heat, which must be dissipated to maintain a constant body temperature.For a person at rest of doing light in a conditioned space, the body dissipates heat primarily by convection (carried away by the surrounding air) and radiation (to surrounding surfaces that are at a lower temperature than the body temperature).

Most of the air-conditioning units in service provide comfort air conditioning, the purpose of which is to supply comfortable conditions for people. Summer cooling systems have become a standard utility in large buildings throughout the world. Even in climates where summer temperatures are not high, large buildings may have cooled in order to remove the heat generated internally by people, lights, and other electrical equipment. In hot climates, the existence of summer cooling systems is the difference between workers performing effectively and not.

This chapter does however, attempts to present the importance of air-conditioning to establishments, service areas and institutions. Air conditioning embraces more than cooling. The definition of comfort air conditioning is the process of treating air to control simultaneously its temperature, humidity, cleanliness and distribution to meet the comfort requirements of the occupants of the conditioned space . Air conditioning of medium-sized and large buildings. Most of the air-conditioning units in service provide comfort air conditioning, the purpose of which is to supply comfortable conditions for people. Even in climates where summer temperatures are not high, large buildings may have been cooled in order to remove the heat generated internally by people, lights, and other electrical equipment.Computer rooms. The air conditioning system for computer rooms should control the temperature, humidity, and cleanness of the air. Some electronic components operate in faulty manner if they become too hot, and one means of preventing such localized high temperature in the computer room in the range of 20 to 23C. The electronic components in the computer function favorably at even lower temperatures, but this temperature is a compromise with the lowest comfortable temperature for occupants.

ASHRAE Trans., vol. 85 have elaborated the facts thatheat transfer have developed from a general set of concepts, based on observations of the physical world, the specific models, and laws necessary to solve problems and design systems. Mass and energy are two of the basic concepts from which engineering science grows.As the physical world is extremely complex, it is virtually impossible to describe it precisely. One of the most significant accomplishments of engineering science has been the development of models of physical phenomena, which although they are approximations, provide both a sufficiently accurate description, and a tractable means of solution.http://vicky-vksworld.blogspot.com/2008/11/thesis-on-aircon-improved-version.htmlCHILLED WATERWhile most people have heard of air conditioning, few have heard of water-chilled cooling. This makes it sound scary and new. But in reality,water-chilled coolingand heating have been around since the 70s and can regularly be found in hotels, hospitals and universities, as well as high-heat environments like server farms. While typically only found in commercial environments in the US, worldwide, water chilled technology is increasingly being used in residential buildings as well. Additionally, in some areas, chiller systems are actually mandated and required by local building codes for buildings over a certain square footage due to their superior energy efficiency. If all that hasnt convinced you yet that water-chilled climate control is a real and valuable way to cool your garden, maybe a short explanation of how the system works will ease your mind.

Water-chilled climate control uses water, instead of air, to cool a space. A reservoir holds a water and glycol mixture that is circulated throughout the building through pipes. Inside each room, there are air handlers, which work in the same way as traditional air conditioning. The cold water is run over cooling coils inside the air handler and a fan blows the air from the room over the coils.

Warm water returns from the air handlers back to the initial reservoir of water. Once the overall temperature of the water in the reservoir goes above a certain point, the chillers, located outside the building, turn on. The reservoir water is then run through the chiller, where it is cooled down to the appropriate temperature. A bonus of using water-chilled systems is that the chiller only turns on when the water in the reservoir gets above a certain temperature, chillers are not directly connected to air handlers. This means that as long as that water is within a certain range, the chiller is not running but the air handlers are still able to cool the rooms. This provides significant energy savings. Additionally, because water has 20 times the heat absorption rate of air, it takes much longer for the water mixture to reach a temperature that causes the chiller to turn on that it does for air. Think of it this way, if you are standing outside on a cold day, say 35 degrees out, you will be cold and uncomfortable, but not deathly so, However, if you were to jump into a pool of 35 degree water, you could start to experience hypothermia in as little as 30 minutes. As a bonus, if a chiller needs to be repaired, it is possible to take one chiller out of circulation and still maintain the temperature of your water reservoir, and thus the temperature inside your rooms. This is not possible with traditional air conditioning where each air handler is tied to an individual condenser. It is also important to note that in water-chilled cooling systems, there is no evaporation of water. The system is closed-loop, running water through pipes and back to the reservoir, so no water will be added to your environment. As a bonus, any water that is collected from the condenser can be collected and used to water the plants in your garden, providing water savings as well as energy savings. Overall, water-chilled cooling systems are a great way to control the climate of any building. If you still arent sure if water-cooled climate control is for you, pleasecontact usto get answers to any questions you may have.

http://surna.com/water-chilled-systems-work/