Handbook of air conditioning and refrigeration 2nd

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. Although air contaminants may seriously affect human health, they have little effect on the thermo- dynamic properties of moist air. For thermal analysis, moist air may be treated as a binary mixture of dry air and water vapor.

For simplicity, the following assumptions are made during the calculation of the enthalpy of moist air: 1. Their mean values can be taken as 0. In Equation 9. Latent heat of moist air, often represented by whfg0, is the thermal energy associated with the change of state of water vapor. Two moist air samples of similar dew points Tdew at the same atmospheric pressure have the same humidity ratio w and the same partial pressure of water vapor pw.

Liquid water is therefore evaporated into water vapor at the expense of the sensible heat of the moist air. A sling-type psychrometer, as shown in Figure 9. It consists of two mercury-in-glass thermometers. The sensing bulb of one of them is dry and is called the dry bulb. Another sensing bulb is wrapped with a piece of cotton wick, one end of which dips into a water tube.

When unsaturated moist air flows over the surface of the wetted cotton wick, liquid water evaporates from its surface. As it absorbs sensible heat, mainly from the surrounding air, the wet bulb temperature drops. Turning the handle forces the surrounding air to flow over the dry and wet bulbs at an air velocity between to fpm.

Distilled water must be used to wet the cotton wick. According to Threlkeld , for a sling psychrometer whose wet bulb diameter is 1 in. Psychrometric Charts A psychrometric chart is a graphical presentation of the thermodynamic properties of moist air and various air-conditioning processes and air-conditioning cycles.

A psychrometric chart also helps in calculating and analyzing the work and energy transfer of various air-conditioning processes and cycles. Psychrometric charts currently use two kinds of basic coordinates: 1.

In h-w charts, enthalpy h, representing energy, and humidity ratio w, representing mass, are the basic coordinates. T-w charts. In T-w charts, temperature T and humidity ratio w are basic coordinates.

Psychrometric charts published by Carrier Corporation, the Trane Company, etc. Figure 9. Since enthalpy is the basic coordinate, temperature lines are not parallel to each other. The standard atmospheric pressure is Hg at sea level.

Hg, and ft, Both of them are in the normal temperature range. They range from 0 to 0. The moist volume ranges from When pat is given, any additional two of the independent properties determine the state of moist air on the psychrometric chart and the remaining properties. Software using AutoCAD to construct the psychrometric chart and calculate the thermodynamic properties of moist air is available. It can also be linked to the load calculation and energy programs to analyze the characteristics of air-conditioning cycles.

Example 9. Determine the humidity ratio, enthalpy, density, dew point, and thermodynamic wet bulb temperature of the indoor air at design condition.

Solution 1. Since the air-conditioned room is at sea level, a psychrometric chart of standard atmospheric pressure of Plot the state point of the room air at design condition r on the psychrometric chart. Draw a horizontal line toward the humidity ratio scale from point r. Draw a line from point r parallel to the enthalpy line. Draw a line through point r parallel to the moist volume line. Draw a horizontal line to the left from point r. Draw a line through point r parallel to the thermodynamic wet bulb line.

The energy balance and conservation of mass are the two principles used for the analysis and the calculation of the thermodynamic properties of the moist air. Generally, for a single air-conditioning process, heat transfer or mass transfer is positive. However, for calculations that involve several air-conditioning processes, heat supplied to the moist air is taken as positive and heat rejected is negative.

Both processes are aimed at maintaining a desirable space temperature and relative humidity. Also in Equation 9. A sensible heating process adds heat to the moist air in order to increase its temperature; its humidity ratio remains constant, as shown by line 12 in Figure 9.

A sensible heating process occurs when moist air flows over a heating coil. Heat is transferred from the hot water inside the tubes to the moist air. The sensible cooling process occurs when moist air flows through a cooling coil containing chilled water at a temperature equal to or greater than the dew point of the entering moist air. The sensible cooling load can also be calculated from Equation 9. Humidifying and Cooling and Dehumidifying Processes In a humidifying process, water vapor is added to moist air and increases the humidity ratio of the moist air entering the humidifier if the moist air is not saturated.

Large-scale humidification of moist air is usually performed by steam injection, evaporation from a water spray, atomizing water, a wetted medium, or submerged heating elements. Some details of their construction and characteristics are covered in a later section. Dry steam in a steam injection humidifying process is often supplied from the main steam line to a grid-type humidifier and injected into the moist air directly through small holes at a pressure slightly above atmospheric, as shown by line 12 in Figure 9.

The slight inclination at the top of line 12 is due to the high temperature of the steam. When moist air flows through an air washer, the moist air is humidified and approaches saturation. The humidity ratio of the moist air is increased while its temperature is reduced.

The cooling effect of this adiabatic saturation process is called evaporative cooling. Because of the fan power heat gain, duct heat gain, and other heat gains providing the latent heat of vaporization, some evaporation takes place due to the heat transfer to the water drops, and the humidity ratio increases further. Such evaporation of oversaturated drops is often a process with an increase of both humidity ratio and enthalpy of moist air.

For an air washer, ww may vary from 0. For a pulverizing fan without an eliminator, ww may be up to 0. Cooling and Dehumidifying Process In a cooling and dehumidifying process, both the humidity ratio and temperature of moist air decrease.

Some water vapor is condensed in the form of liquid water, called a condensate. This process is shown by curve m cc on the psychrometric chart in Figure 9. Here m represents the entering mixture of outdoor and recirculating air and cc the conditioned air leaving the cooling coil. Three types of heat exchangers are used in a cooling and dehumidifying process: 1 water cooling coil as shown in Figure 9. SHRc is shown by the slope of the straight line joining points m and cc.

The relative humidity of moist air leaving the water cooling coil or DX coil depends mainly on the outer surface area of the coil including pipe and fins. Since the AHU or PU is well insulated, the heat transfer between the mixing chamber and ambient air is small and is usually neglected. The cold conditioned air is denoted by subscript cc, the heated air ch, and the bypass air by. Equations 9. Air-Conditioning Cycle and Operating Modes An air-conditioning cycle comprises several air-conditioning processes that are connected in a sequential order.

An air-conditioning cycle determines the operating performance of the air system in an air- conditioning system. The working substance to condition air may be chilled or hot water, refrigerant, desiccant, etc. Each type of air system has its own air-conditioning cycle. An air- conditioning cycle with all outdoor air is an open cycle.

An air-conditioning cycle that conditions the mixture of recirculating and outdoor air, supplies it, recirculates part of the return air, and mixes it again with outdoor air is a closed cycle. The air economizer mode saves energy use for refrigeration.

Continuous modes operate 24 hr a day and 7 days a week. Examples are systems that serve hospital wards and refrigerated warehouses. An intermittently operated mode usually shuts down once or several times within a hr operating cycle. Such systems serve offices, class rooms, retail stores, etc. The hr day-and-night cycle of an intermittently operated system can again be divided into: 1. Cool-down or warm-up period. When the space is not occupied and the space air temperature is higher or lower than the predetermined value, the space air should be cooled down or warmed up before the space is occupied.

Conditioning period. The air-conditioning system is operated during the occupied period to maintain the required indoor environment. Nighttime shut-down period. The air system or terminal is shut down or only partly operating to maintain a set-back temperature.

Summer, winter, air economizer, and continuously operating modes consist of full-load design load and part-load operations.

Part load occurs when the system load is less than the design load. The capacity of the equipment is selected to meet summer and winter system design loads as well as system loads in all operating modes. A single zone is a conditioned space for which a single controller is used to maintain a unique indoor operating parameter, probably indoor temperature. A basic air-conditioning cycle is the operating cycle of a basic air-conditioning system. In summer mode at design load, recirculating air from the conditioned space, a worship hall, enters the packaged unit through the return grill at point ru.

It is mixed with the required minimum amount of outdoor air at point o for acceptable indoor air quality and energy saving. The mixture m is then cooled and dehumidified to point cc at the DX coil, and the conditioned air is supplied to the hall through the supply fan, supply duct, and ceiling diffuser.

Supply air then absorbs the sensible and latent load from the space, becoming the space air r. Recirculating air enters the packaged unit again and forms a closed cycle.

Return air is the air returned from the space. Part of the return air is exhausted to balance the outdoor air intake and infiltration. The summer mode operating cycle consists of the following processes: 1. Sensible heating process, represented by line r ru, due to the return system gain qr. In this packaged system, the return system heat gain is small and neglected.

Adiabatic mixing process of recirculating air at point ru and outdoor air at point o in the mixing box, represented by line ru m o. Cooling and dehumidifying process m cc at the DX coil whose coil load determines the cooling capacity of the system calculated from Equation 9.

Sensible heating process related to the supply system heat gain qs. Supply conditioning process line sr. Design Supply Volume Flow Rate Design supply volume flow rate and cooling and heating capacities are primary characteristics of an air- conditioning system. Design supply volume flow rate is used to determine the size of fans, grills, outlets, air-handling units, and packaged units.

For most comfort systems and many processing air-conditioning o systems, design supply volume flow rate V s. Specific heat cpa is usually considered constant. For a given qrs.

The summer cooling load is often greater than the winter heating load, and this is why qrc or qrs. Hg Here V sf. Therefore, [ V sf. From Equation 9. In order to provide the o required mass flow rate of supply air, a greater V sf. At ft above sea level, the o o o o rated supply volume flow rate V r. The result is a lower investment and energy cost.

When an air-conditioning system serves a conditioned space of a single zone, optimum Tcc, Ts, and Twe can be selected. For a conditioned space of multizones, Tcc, Ts, and Twe should be selected to satisfy the lowest requirement. In practice, Ts and Twe are often determined according to previous experience with similar projects.

Three methods are often used to prevent condensation: 1. Increase the thickness of the insulation layer on the outside surface. Adopt a supply outlet that induces more space air. Equip with a terminal that mixes the supply air with the space air or air from the ceiling plenum.

During the cool-down period, due to the high dew point temperature of the plenum air when the air system is started, the supply air temperature must be controlled to prevent condensation. Temperature of supply air at summer design conditions 2. Rated volume flow rate of the supply fan 3. Cooling coil load 4. Possibility of condensation at the outside surface of the insulated branch duct to the supply outlet Solution 1. The state points s and cc are then determined as shown in Figure 9.

Connect line ro. As shown in Figure 9. Condensation will not occur at the outside surface of the branch duct. Basic Air-Conditioning Cycle — Winter Mode When the basic air-conditioning systems are operated in winter mode, their air-conditioning cycles can be classified into the following four categories: Cold Air Supply without Space Humidity Control.

In winter, for a fully occupied worship hall, if the heat loss is less than the space sensible cooling load, a cold air supply is required to offset the space sensible cooling load and maintain a desirable indoor environment as shown by the lower cycle in Figure 9. Usually, a humidifier is not used. The winter cycle of a cold air supply without humidity control consists of the following air-condi- tioning processes: 1.

Adiabatic mixing process of outdoor air and recirculating air o m r. Sensible heating process due to supply fan power heat gain m sf. Because of the smaller temper- ature difference between the air in the ceiling plenum and the supply air inside the supply duct, heat transfer through duct wall in winter can be neglected.

Supply conditioning line sr. Troubleshooting charts. Standard service procedures. New to This Edition: New refrigerants are illustrated EPA-required refrigerant handling procedures are used in exercises and procedures Electronic control troubleshooting procedures Table of Contents: Component Troubleshooting.

Electronic Controls. Start-Up Procedures. Standard Service Procedures. Representative Wiring Diagrams. Safety Procedures. Buy this product. K educators : This link is for individuals purchasing with credit cards or PayPal only. This comprehensive text covers both electric and electronic controls in one book in depth.

Using at-a-glance charts, cross-referenced to specific sections of the text, it encompasses control operation, adjustment, troubleshooting, installation, and use, and provides start-up procedures for different types of units, representative wiring diagrams for some types of equipment, safety procedures, and useful engineering data. Supplies students with all the information needed to properly perform system diagnosis and repair.

Guides students through the proper steps for starting up both new and existing systems and different types of equipment. Presents students with a ready reference of what causes different problems and how to properly repair the equipment. Component Troubleshooting. Electronic Controls. Start-Up Procedures. Standard Service Procedures.

Representative Wiring Diagrams. Get Books. Handbook of Air Conditioning System Design. Authors: Carrier Corporation. Carrier Air Conditioning Company. Handbook of Refrigeration and Air Conditioning.