Basic Of Refrigeration And Air Conditioning PdfBy Sophie P. In and pdf 23.04.2021 at 16:33 5 min read
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- What Is The Basic Refrigeration Cycle?
- The Basic Refrigeration Cycle
- Air-Conditioning and Refrigeration. Mechanical Engineering Handbook
The work of energy transfer is traditionally driven by mechanical means, but can also be driven by heat, magnetism , electricity , laser , or other means. Refrigeration has many applications, including household refrigerators , industrial freezers , cryogenics , and air conditioning. Heat pumps may use the heat output of the refrigeration process, and also may be designed to be reversible, but are otherwise similar to air conditioning units.
What Is The Basic Refrigeration Cycle?
Log In Sign Up. Download Free PDF. Air-Conditioning and Refrigeration. Mechanical Engineering Handbook. Pawan Gupta. Download PDF. A short summary of this paper. Wang, S. Wang 9. The com- bination of these processes is equivalent to the functions performed by air-conditioning. They are often called comfort air-conditioning systems. In manufacturing buildings, air-conditioning systems are provided for product processing, or for the health and comfort of workers as well as processing, and are called processing air-conditioning systems.
Based on their size, construction, and operating characteristics, air-conditioning systems can be classified as the following. Individual Room or Individual Systems. An individual air-conditioning system normally employs either a single, self-contained, packaged room air conditioner installed in a window or through a wall or separate indoor and outdoor units to serve an individual room, as shown in Figure 9.
Space-Conditioning Systems or Space Systems. These systems have their air-conditioning—cooling, heating, and filtration—performed predominantly in or above the conditioned space, as shown in Figure 9. Outdoor air is supplied by a separate outdoor ventilation system. Unitary Packaged Systems or Packaged Systems. These systems are installed with either a single self- contained, factory-assembled packaged unit PU or two split units: an indoor air handler, normally with ductwork, and an outdoor condensing unit with refrigeration compressor s and condenser, as shown in Figure 9.
In a packaged system, air is cooled mainly by direct expansion of refrigerant in coils called DX coils and heated by gas furnace, electric heating, or a heat pump effect, which is the reverse of a refrigeration cycle.
Central Hydronic or Central Systems. A central system uses chilled water or hot water from a central plant to cool and heat the air at the coils in an air handling unit AHU as shown in Figure 9. For energy transport, the heat capacity of water is about times greater than that of air. Central systems are built-up systems assembled and installed on the site.
Packaged systems are comprised of only air system, refrigeration, heating, and control systems. Both central and space-conditioning systems consist of the following. Air Systems. Its function is to condition the air, distribute it, and control the indoor environment according to requirements. The primary equipment in an air system is an AHU or air handler; both of these include fan, coils, filters, dampers, humidifiers optional , supply and return ductwork, supply outlets and return inlets, and controls.
Water Systems. These systems include chilled water, hot water, and condenser water systems. A water system consists of pumps, piping work, and accessories. The water system is sometimes called the water side of a central or space-conditioning system.
Central Plant Refrigeration and Heating Systems. The refrigeration system in the central plant of a central system is usually in the form of a chiller package with an outdoor condensing unit. The refrigeration system is also called the refrigeration side of a central system. A boiler and accessories make up the heating system in a central plant for a central system, and a direct-fired gas furnace is often the heating system in the air handler of a rooftop packaged system.
Control Systems. Control systems usually consist of sensors, a microprocessor-based direct digital controller DDC , a control device, control elements, personal computer PC , and communication network. Part of the cooled floor area has been counted for both individual and packaged systems. The sum of the floor areas for these three systems therefore exceeds the total cooled area of 57, million ft2. There are two types of air-conditioning projects: design- bid and design-build.
A design-bid project separates the design engineering consultant and installation contractors responsibilities. In a design-build project, the design is also done by the installation contractor.
A design-build project is usually a small project or a project having insufficient time to go through normal bidding procedures. Air-conditioning design is a process of selecting the optimum system, subsystem, equipment, and components from various alternatives and preparing the drawings and specifications. Design determines the basic operating characteristics of a system.
After an air-conditioning system is designed and constructed, it is difficult and expensive to change its basic characteristics. The foundation of a successful project is teamwork and coordination between designer, contractor, and operator and between mechanical engineer, electrical engineer, facility operator, architect, and structural engineer. Field experience is helpful to the designer. Before beginning the design process it is advisable to visit similar projects that have operated for more than 2 years and talk with the operator to investigate actual performance.
Initiation of a project by owner or developer 2. Organizing a design team 3. Determining the design criteria and indoor environmental parameters 4. Calculation of cooling and heating loads 5. Selection of systems, subsystems, and their components 6.
Preparation of schematic layouts; sizing of piping and ductwork 7. Preparation of contract documents: drawings and specifications 8. Competitive biddings by various contractors; evaluation of bids; negotiations and modifications 9.
Advice on awarding of contract Monitoring, supervision, and inspection of installation; reviewing shop drawings Supervision of commissioning Modification of drawings to the as-built condition; preparation of the operation and maintenance manual Handing over to the property management for operation Design Documents Drawings and specifications are legal documents of a construction contract.
Drawings and specifi- cations complement each other. Drawings should clearly and completely show, define, and present the work.
Adequate plan and sectional views should be drawn. More often, isometric drawings are used to show the flow diagrams for water or the supply, return, and exhaust air. Specifications include the legal contract between the owner and the contractor, installer, or vendor and the technical specifications, which describe in detail what kind of material and equipment should be used and how they are to be installed.
It includes 16 divisions. The Mechanical division is divided into the following: Section No. Title Air Distribution Controls Testing, Adjusting, and Balancing Each section includes general considerations, equipment and material, and field installation. There are two types of specifications: the performance specification, which depends mainly on the required performance criteria, and the or-equal specification, which specifies the wanted vendor.
Spec- ifications should be written in simple, direct, and clear language without repetition. Computer-Aided Design and Drafting With the wide acceptance of the PC and the availability of numerous types of engineering software, the use of computer-aided drafting CAD and computer-aided design and drafting CADD has increased greatly in recent years.
Drafting software used to reproduce architectural drawings is the foundation of CADD. Automated CAD AutoCAD is the leading personal computer-based drafting tool software used in architectural and engineering design firms.
Both of them convert the single-line duct layout drawn with CAD to two-dimensional 2D double-line drawings with fittings, terminals, and diffusers. Software for piping system design and analysis can also be integrated with CAD. The most widely used software for load calculations and energy analysis is Department of Energy DOE Product categories include selection, configuration, performance, price, and maintenance schedule.
Product manufacturers provide software including data and CAD drawings for their specific product. Federal and local codes must be followed. The designer should be thoroughly familiar with relevant codes. However, for design criteria or performance that has not been covered in the codes, whether the ASHRAE Standard is followed or violated is the vital criterion, as was the case in a recent indoor air quality lawsuit against a designer and contractor.
The lower atmosphere, or homosphere, is composed of moist air, that is, a mixture of dry air and water vapor. Psychrometrics is the science of studying the thermodynamic properties of moist air.
It is widely used to illustrate and analyze the change in properties and the thermal characteristics of the air-conditioning process and cycles. The composition of dry air varies slightly at different geographic locations and from time to time. The approximate composition of dry air by volume is nitrogen, The variation of water vapor has a critical influence on the characteristics of moist air. National Bureau of Standards. According to Nelson et al.
Therefore, ideal gas equations are used in the development and calculation of psychrometric formulations in this handbook.
The Basic Refrigeration Cycle
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Air-Conditioning and Refrigeration. Mechanical Engineering Handbook
One very important part of all HVAC systems is the basic refrigeration cycle. It contains four major components: the compressor, condenser, expansion device, and evaporator. The system pipes refrigerant through these four components in a loop, giving the cycle its name and keeping your home cool! The refrigerant in your system starts as vapour in the first component of the cycle, the compressor.
This process is accompanied by an increase in Entropy along with a drop in pressure due to which volume increases and a part of the liquid is vaporized, thus cooling the liquid. Real gases produce a substantial decrease in temperature under certain condition, which corresponds to a certain initial low temperature and high pressure of the gas. Cooling is produced of one junction of two dissimilar metals if a current is passed through them. The phenomenon is called the Peltier effect.
Mechanical refrigeration is accomplished by continuously circulating, evaporating, and condensing a fixed supply of refrigerant in a closed system. Evaporation occurs at a low temperature and low pressure while condensation occurs at a high temperature and high pressure. Thus, it is possible to transfer heat from an area of low temperature i.