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Air conditioning often referred to as AC is the process of removing heat and moisture from the interior of an occupied space to improve the comfort of occupants. Air conditioning can be used in both domestic and commercial environments. This process is most commonly used to achieve a more comfortable interior environment, typically for humans and animals.
However, air conditioning is also used to cool/dehumidify rooms filled with heat-producing electronic devices, such as computer servers, power amplifiers, and even to display and store artwork.
The Basics Of Air Conditioning
All air conditioners including portable air conditioners and room air conditioners (which are covered in their own reports) as well as central air conditioners (which are covered here) work basically the same way as your refrigerator. They pump heat from one area (in this case, your home's interior) and transfer it to another (the outdoors). An air conditioning system contains several parts:
The evaporator is a winding coil, usually made of copper, which draws out warm air from indoors.
The condenser is a separate coil that releases the collected heat outside. This coil is surrounded by aluminum fins to disperse the heat.
The refrigerant is a liquid that transfers heat from the evaporator to the condenser. It evaporates in the indoor coil, pulling heat out of the air, and turns back to a liquid in the condenser, releasing its heat outdoors.
The compressor is a pump that forces the refrigerant through this network of tubing and fins. This is the part of the system that uses electricity.
In a room air conditioner or a portable air conditioner, all these parts are contained in one compact unit that sits in a window, can be installed through an exterior wall or in the case of portable air conditioners, sits on the floor and is vented to the outside via flexible connecting hoses. Individually, these units are much cheaper than a central air conditioning system and are relatively easy to install.
However, they only have enough power to cool a single room and if you want to cool multiple areas, costs can mount up.
CENTRAL AIR CONDITIONER
A central air conditioner is a major investment for the home. The home owner must make several choices when selecting a central air unit. Choices include brand name of the equipment, energy efficiency of the system, desirable features and the size of the unit.
Types of Central Air Conditioner
There are basically two types of central air conditioner available which are
The Packaged AC Unit
The packaged system is the traditional ducted central air system. New features are now available on packaged units that will save you money. Variable speed blowers and more precise controls are two of the features available on packaged AC systems that will provide energy savings. Saving energy to operate your central air unit is always a welcome windfall.
The Mini-Split System
The mini-split system is a newer concept and does not require ductwork for the air conditioner installation. Local air conditioning contractors can provide you with advice regarding which type of system works best for homes in your region and climate. For example, a mini-split system may be an option to air condition a garage, a room addition or a workshop where ductwork is not easily installed.
Features Of Central Air Conditioner
Quiet Operation
Some homeowners may be concerned about the noise produced by the AC unit. If you need a system that will operate quietly, choices are available for both packaged and mini-split systems. Mini-split systems tend to be more quiet and unobtrusive. However, packaged units are now produced with features that reduce the noise of operation.
Advanced Controls
Today’s AC units offer advanced control features, such as zone control. One of the most popular features of mini-split systems is the zone control feature. Each room or zone is controlled by an individual internal air handler, which will save energy and lower your utility bills.
Variable Speed Systems
New features on packaged systems include variable speed blowers. The variable speed blowers operate at a lower speed when demand on the system is low. When demand is higher, the blower operates at full speed. The lower speed operation saves energy and lowers utility bills during the times when cooling demands are low.
AC Equipment Size
Probably the most important feature when selecting a new air conditioner is the size of the unit. Bigger is not necessarily better when purchasing HVAC equipment. A unit that is too small will not effectively cool the home when the temperatures are high. A unit that is too big will constantly cycle on and off, creating undue wear and tear on system components. A general rule for the size of AC systems is 1 ton of equipment per 550 square feet of living space. However, your HVAC professional will be much more precise in their estimate of the equipment size your home requires. In fact, AC contractors use a mathematical formula to determine the right size of HVAC equipment for a home.
Features to look for in a central air conditioner are those that will save money and reduce energy consumption. When you are considering a new air conditioner installation, be sure to evaluate all the features that are available. Determine which features you value most and make your decision based on the needs of your home and the climate where you live.
Other Features To Look For When Buying An Air Conditioner include:
- A thermal expansion valve and a high-temperature rating (EER) greater than 11.6, for high-efficiency operation when the weather is at its hottest
- A variable speed air handler for new ventilation systems
- A unit that operates quietly
- A fan-only switch, so you can use the unit for nighttime ventilation to substantially reduce air-conditioning costs
- A filter check light to remind you to check the filter after a predetermined number of operating hours
- An automatic-delay fan switch to turn off the fan a few minutes after the compressor turns off.
HEAT EXCHANGER
Heat exchangers used to minimize heat losses from buildings, engines, and machines are sometimes called recuperators or regenerators. These are two quite different things.
A recuperator is typically used to capture heat that would otherwise be lost, for example, as stuffy air is ventilated from a building: cold, incoming fluid is channeled in the opposite direction to warm, outgoing fluid to minimize the heat loss. The two fluids flow through separate channels remain separate and do not mix. Since incoming and outgoing fluids move in opposite directions. A recuperators are examples of counterflow heat exchangers. The heat exchanger in a heat-recovery ventilation (HRV) system is an everyday example of a recuperator.
A regenerator is similar, but the incoming and outgoing fluids move through the same channel in opposite directions and at different times. So the warm fluid will flow out through the regenerator, giving up some of its heat on the way. Later, the cold fluid will flow in through the same channel, back through the regenerator, picking up some of the heat stored there. A regenerator is one of the key parts in a highly efficient form of power called a Stirling engine, in which a piston pushes trapped gas back and forth between a heat source (such as a fire) and a place where the heat is lost ("a sink"). The regenerator reduces the heat that would otherwise be lost as the engine cycles back and forth.
FUNCTIONS OF HEAT EXCHANGER
- A heat exchanger is a device that is used to transfer thermal energy (enthalpy) between two or more fluids, between a solid surface and a fluid, or between solid particulates and a fluid, at different temperatures and in thermal contact.
- In heat exchangers, there are usually no external heat and work interactions. Typical applications involve heating or cooling of a fluid stream of concern and evaporation or condensation of single- or multi component fluid streams.
- In other applications, the objective may be to recover or reject heat, or sterilize, pasteurize, fractionate, distill, concentrate, crystallize, or control a process fluid.
- In a few heat exchangers, the fluids exchanging heat are in direct contact.
- In most heat exchangers, heat transfer between fluids takes place through a separating wall or into and out of a wall in a transient manner.
- In many heat exchangers, the fluids are separated by a heat transfer surface, and ideally they do not mix or leak. Such exchangers are referred to as direct transfer type, or simply recuperators.
- In contrast, exchangers in which there is intermittent heat exchange between the hot and cold fluids—via thermal energy storage and release through the exchanger surface or matrix—are referred to as indirect transfer type, or simply regenerators. Such exchangers usually have fluid leakage from one fluid stream to the other, due to pressure differences and matrix rotation/valve switching. Common examples of heat exchangers are shell-and tube exchangers, automobile radiators, condensers, evaporators, air pre-heaters, and cooling towers.
- If no phase change occurs in any of the fluids in the exchanger, it is sometimes referred to as a sensible heat exchanger. There could be internal thermal energy sources in the exchangers, such as in electric heaters and nuclear fuel elements.
- Combustion and chemical reaction may take place within the exchanger, such as in boilers, fired heaters, and fluidized-bed exchangers.
- Mechanical devices may be used in some exchangers such as in scraped surface exchangers, agitated vessels, and stirred tank reactors. Heat transfer in the separating wall of a recuperator generally takes place by conduction.
- Heat Exchangers are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment.
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