Fuente: Hella. Fuente: Norwegian University of Science and Technology. Fuente: ResearchGate. Fuente: Landmark University. Fuente: Department of Energy. If you found this list useful, do not forget to share it on your social networks. Do you want more Trades books in PDF format? Here we present our complete selection of Refrigeration books:. Read Download. Sam C. Kalla and J. Usmani Fuente: ResearchGate. Here ends our selection of free Refrigeration books in PDF format.
We hope you liked it and already have your next book! Trades Books in PDF. Do you want to read about another topic? A dry—wet boundary divides the dry and wet surfaces. A condensate drain pan is necessary for a dry—wet coil. This coil becomes a sensible cooling—dry coil, and the humidity ratio of the conditioned air wa remains constant during the sensible cooling process.
Water Heating Coil The construction of a water heating coil is similar to that of a water cooling coil except that in water heating coils hot water is supplied instead of chilled water and there are usually fewer rows, only 2, 3, and 4 rows, than in water cooling coils. Steam Heating Coil In a steam heating coil, latent heat of condensation is released when steam is condensed into liquid to heat the air flowing over the coil, as shown in Figure 9.
Steam enters at one end of the coil, and the condensate comes out from the opposite end. For more even distribution, a baffle plate is often installed after the steam inlet. Steam heating coils are usually made of copper, steel, or sometimes stainless steel. For a steam coil, the coil core inside the casing should expand or contract freely. The coil core is also pitched toward the outlet to facilitate condensate drainage.
Coil Accessories and Servicing Coil accessories include air vents, drain valves, isolation valves, pressure relief valves, flow metering valves, balancing valves, thermometers, pressure gauge taps, condensate drain taps, and even distribution baffles. They are employed depending on the size of the system and operating and serving requirements.
Coil cleanliness is important for proper operation. If a medium-efficiency air filter is installed upstream of the coil, dirt accumulation is often not a problem.
If a low-efficiency filter is employed, dirt accumu- lation may block the air passage and significantly increase the pressure drop across the coil. Coils should normally be inspected and cleaned every 3 months in urban areas when low-efficiency filters are used. Drain pans should be cleaned every month to prevent buildup of bacteria and microorganisms. Outdoor air should be guided by a baffle plate and flow in an opposite direction to the recirculating air stream so that they can be thoroughly mixed without stratification.
Run the chilled water pump for the idle coil with a water velocity of 2. A better method is to drain the water completely. For a hot water coil, it is better to reset the hot water temperature at part-load operation instead of running the system intermittently.
A steam heating coil with inner distributor tubes and outer finned heating tubes provides better protection against freeze-up. Air Filters Air Cleaning and Filtration Air cleaning is the process of removing airborne particles from the air. Air cleaning can be classified into air filtration and industrial air cleaning. Industrial air cleaning involves the removal of dust and gaseous contaminants from manufacturing processes as well as from the space air, exhaust air, and flue gas for air pollution control.
In this section, only air filtration is covered. Air filtration involves the removal of airborne particles presented in the conditioned air. The purpose of air filtration is to benefit the health and comfort of the occupants as well as meet the cleanliness requirements of the working area in industrial buildings.
An air filter is a kind of air cleaner that is installed in AHUs, PUs, and other equipment to filter the conditioned air by inertial impaction or interception and to diffuse and settle fine dust particles on the fibrous medium. The filter medium is the fabricated material that performs air filtration.
Test Methods The performance of air filters is usually tested in a test unit that consists of a fan, a test duct, the tested filter, two samplers, a vacuum pump, and other instruments. Three test methods with their own test dusts and procedures are used for the testing of low-, medium-, and high-efficiency air filters. The weight arrestance test is used for low-efficiency air filters to assess their ability to remove coarse dusts. Standard synthetic dusts that are considerably coarser than atmospheric dust are fed to the test unit.
By measuring the weight of dust fed and the weight gain due to the dust collected on the membrane of the sampler after the tested filter, the arrestance can be calculated. The atmospheric dust spot efficiency test is used for medium-efficiency air filters to assess their ability to remove atmospheric dusts. Atmospheric dusts are dusts contained in the outdoor air, the outdoor atmosphere.
Untreated atmospheric dusts are fed to the test unit. Air samples taken before and after the tested filter are drawn through from identical fiber filter-paper targets. By measuring the light transmission of these discolored white filter papers, the efficiency of the filter can be calculated. The DOP penetration and efficiency test or simply DOP test is used to assess high-efficiency filters removing dusts particles of 0.
According to U. By measuring the concentration of these particles in the air stream upstream and downstream of the tested filter using an electronic particle counter or laser spectrometer, the penetration and efficiency of the air filter can be calculated. These filters are usually in panels as shown in Figure 9.
Their thickness varies from 1 to 4 in. Activated Detergents may be used to wash off dusts so that the filter media can be cleaned and reused — they are therefore called viscous and reusable. The filter medium is discarded when its final pressure drop is reached — dry and disposable. The face velocity of the panel filter is usually between and fpm. The initial pressure drop varies from 0. WG and the final pressure drop from 0. They are usually dry and disposable.
Air velocity through the medium is 6 to 90 fpm. Face velocity of the air filter is about fpm to match the face velocity of the coil in AHUs and PUs. WG and final pressure drop from 0. Its filter media are made of glass fibers of submicrometer diameter in the form of pleated paper mats. The medium is dry and disposable. The surface area of the HEPA filter may be 50 times its face area, and its rated face velocity varies from to fpm, normally at a pressure drop of 0.
WG for clean filters. The final pressure drop is 0. Sealing of the filter pack within its frame and sealing between the frame and the gaskets are critical factors that affect the penetration and efficiency of the HEPA filter.
Both its sealing and filter media are more efficient than those of a HEPA filter. Activated Carbon Filters These filters are widely used to remove objectional odors and irritating gaseous airborne particulates, typically 0. Adsorption is physical conden- sation of gas or vapor on the surface of an activated substance like activated carbon. Activated substances are extremely porous.
One pound of activated carbon contains 5,, ft2 of internal surface. Activated carbon in the form of granules or pellets is made of coal, coconut shells, or petroleum residues and is placed in trays to form activated carbon beds as shown in Figure 9.
Low-efficiency prefilters are used for protection. When air flows through the carbon beds at a face velocity of to fpm, the corresponding pressure drop is 0.
Humidifiers A humidifier adds moisture to the air. For comfort air-conditioning systems, a steam humidifier with a separator as shown in Figure 9. Steam is supplied to a jacketed distribution manifold. It enters a separating chamber with its condensate. Steam then flows through a control valve, throttles to a pressure slightly above atmospheric, and enters a dry chamber.
Due to the high temperature in the surrounding separating chamber, the steam is superheated. Dry steam is then discharged into the ambient air stream through the orifices on the inner steam discharge tubes.
For an air system of cold air supply with humidity control during winter mode operation, an air washer is economical for large-capacity humidification in many industrial applications. An air washer is a humidifier, a cooler, a dehumidifier, and an air cleaner.
An air washer usually has an outer casing, two banks of spraying nozzles, one bank of guide baffles at the entrance, one bank of eliminators at the exit, a water tank, a circulating pump, a water filter, and other accessories as shown in Figure 9.
Outer casing, baffles, and eliminators are often made of plastics or sometimes stainless steel. An eccentric inlet connected to the discharge chamber of the spraying nozzle gives centrifugal force to the water stream and atomizes the spraying water. Water is supplied to the spraying nozzle at a pressure of 15 to 30 psig. The distance between two spraying banks is 3 to 4.
The air velocity inside an air washer is usually to fpm. The cooling and heating capacities of an AHU can be varied by using coils of different numbers of rows and fin densities. The size of a PU is determined by its cooling capacity. Normally, the volume flow rate per ton of cooling capacity in PUs is to cfm. In most packaged units whose supply fans have belt drives, the fan speed can be selected so that the volume flow rate is varied and external pressure is met.
Selected equipment in a size larger always means a waste of energy and investment. It raises the pressure of refrigerant so that it can be condensed into liquid, throttled, and evaporated into vapor to produce the refrigeration effect.
It also provides the motive force to circulate the refrigerant through condenser, expansion valve, and evaporator. According to the compression process, refrigeration compressors can be divided into positive dis- placement and nonpositive displacement compressors.
A positive displacement compressor increases the pressure of the refrigerant by reducing the internal volume of the compression chamber. Reciprocating, scroll, rotary, and screw compressors are all positive displacement compressors.
The centrifugal com- pressor is the only type of nonpositive displacement refrigeration compressor widely used in refrigeration systems today.
Currently used refrigeration compressors are reciprocating, scroll, screw, rotary, and centrifugal compressors. Reciprocating Compressors In a reciprocating compressor, as shown in Figure 9. The refrigeration capacity of a reciprocating compressor is a fraction of a ton to about tons. Refrigerants R and Ra are widely used in comfort and processing systems and sometimes R- in industrial applications.
The maximum compression ratio Rcom for a single-stage reciprocating compressor is about 7. Capacity control of reciprocating compressor including: on-off and cylinder unloader in which discharge gas is in short cut and return to the suction chamber. Although reciprocating compressors are still widely used today in small and medium-sized refriger- ation systems, they have little room for significant improvement and will be gradually replaced by scroll and screw compressors.
Scroll Compressors A scroll compressor consists of two identical spiral scrolls assembled opposite to each other, as shown in Figure 9. One of the scrolls is fixed, and the other moves in an orbit around the motor shaft whose amplitude equals the radius of the orbit.
The two scrolls are in contact at several points and therefore form a series of pockets. Vapor refrigerant enters the space between two scrolls through lateral openings. The lateral openings are then sealed and the formation of the two trapped vapor pockets indicates the end of the suction process.
The vapor is compressed and the discharge process begins when the trapped gaseous pockets open to the discharge port. Compressed hot gas is then discharged through this opening to the discharge line. In a scroll compressor, the scrolls touch each other with sufficient force to form a seal but not enough to cause wear. The upper limit of the refrigeration capacity of currently manufactured scroll compressors is 60 tons.
A scroll compressor also has only about half as many parts as a reciprocating compressor at the same refrigeration capacity. Few components result in higher reliability and efficiency. A scroll compressor also operates more smoothly and is quieter. Rotary Compressors Small rotary compressors for room air conditioners and refrigerators have a capacity up to 4 tons. There are two types of rotary compressors: rolling piston and rotating vane.
A typical rolling piston rotary compressor is shown in Figure 9. A rolling piston mounted on an eccentric shaft is kept in contact with a fixed vane that slides in a slot. Vapor refrigerant enters the compression chamber and is compressed by the eccentric motion of the roller. When the rolling piston contacts the top housing, hot gas is squeezed out from the discharge valve. Screw Compressors These are also called helical rotary compressors.
Screw compressors can be classified into single-screw compressors, in which there is a single helical rotor and two star wheels, and twin-screw compressors. Twin-screw compressors are widely used. A typical twin-screw compressor, as shown in Figure 9. Normally, the male rotor is the driver. Twin-screw compressors are often direct driven and of hermetic type. Vapor refrigerant is extracted into the interlobe space when the lobes are separated at the suction port.
During the successive rotations of the rotor, the volume of the trapped vapor is compressed. When the interlobe space is in contact with the discharge port, the compressed hot gas discharges through the outlet. Oil injection effectively cools the rotors and results in a lower discharge temperature. Oil also provides a sealing effect and lubrication.
A small clearance of 0. The refrigeration capacity of twin-screw compressors is 50 to tons. The compression ratio of a twin-screw compressor can be up to R and Ra are the most widely used refrigerants in comfort systems. Continuous and stepless capacity control is provided by moving a sliding valve toward the discharge port, which opens a shortcut recirculating passage to the suction port. Twin-screw compressors are more efficient than reciprocating compressors. The low noise and vibra- tion of the twin-screw compressor together with its positive displacement compression results in more applications today.
Centrifugal Compressors A centrifugal compressor is a turbomachine and is similar to a centrifugal fan. A hermetic centrifugal compressor has an outer casing with one, two, or even three impellers internally connected in series and is driven by a motor directly or by a gear train. At the entrance to the first-stage impeller are inlet guide vanes positioned at a specific opening to adjust refrigerant flow and therefore the capacity of the centrifugal compressor.
The total pressure rise in a centrifugal compressor, often called head lift, in psi, is due to the conversion of the velocity pressure into static pressure.
Although the compression ratio Rcom of a single-stage centrifugal compressor using R and R seldom exceeds 4, two or three impellers connected in series satisfy most of the requirements in comfort systems.
Centrifugal compressors need high peripheral velocity and rotating speeds up to 50, rpm to produce such a discharge velocity. It is not economical to manufacture small centrifugal compressors. The available refrigeration capacity for centrifugal compressors ranges from to 10, tons. Centrifugal compressors have higher volume flow per unit refrigeration capacity output than positive displacement compressors. Centrifugal compres- sors are efficient and reliable.
Their volumetric efficiency almost equals 1. They are the most widely used refrigeration compressors in large air-conditioning systems. Refrigeration Condensers A refrigeration condenser or simply a condenser is a heat exchanger in which hot gaseous refrigerant is condensed into liquid and the latent heat of condensation is rejected to the atmospheric air, surface water, or well water.
In a condenser, hot gas is first desuperheated, then condensed into liquid, and finally subcooled. ARI Standard specifies the following for evaporators and condensers: Field fouling allowance 0. Air-Cooled Condensers In an air-cooled condenser, air is used to absorb the latent heat of condensation released during desuperheating, condensation, and subcooling. An air-cooled condenser consists of a condenser coil, a subcooling coil, condenser fans, dampers, and controls as shown in Figure 9.
There are refrigeration circuits in the condensing coil. Con- densing coils are usually made of copper tubes and aluminum fins. A condensing coil usually has only two to three rows due to the low pressure drop of the propeller-type condenser fans.
A subcooling coil is located at a lower level and is connected to the condensing coil. Hot gas from the compressor enters the condensing coil from the top. When the condensate increases, part of the condensing area can be used as a subcooling area.
A receiver is necessary only when the liquid refrigerant cannot all be stored in the condensing and subcooling coils during the shut-down period in winter. Cooling air is drawn through the coils by a condenser fan s for even distribution. Condenser fans are often propeller fans for their low pressure and large volume flow rate. A damper s may be installed to adjust the volume flow of cooling air. The corresponding cooling air temperature difference — cooling air leaving temperature minus outdoor temperature Tca.
The condenser temperature difference CTD for an air-cooled condenser is defined as the difference between the saturated condensing temperature corresponding to the pressure at the inlet and the air intake temperature, or Tcon. Air-cooled condensers are rated at a specific CTD, depending on the evaporating temperature of the refrigeration system Tev in which the air-cooled condenser is installed. For a refrigeration system having a lower Tev, it is more economical to equip a larger condenser with a smaller CTD.
The clearance should not be less than the width of the condensing coil. If pcon drops below a certain value because of a lower outdoor temperature, the expansion valve in a reciprocating vapor compression system may not operate properly. Water-Cooled Condensers In a water-cooled condenser, latent heat of condensation released from the refrigerant during conden- sation is extracted by water.
This cooling water, often called condenser water, is taken directly from river, lake, sea, underground well water or a cooling tower. Two types of water-cooled condensers are widely used for air-conditioning and refrigeration: double- tube condensers and horizontal shell-and-tube condensers.
A double-tube condenser consists of two tubes, one inside the other. Condenser water is pumped through the inner tube and refrigerant flows within the space between the inner and outer tubes in a counterflow arrangement. Because of its limited condensing area, the double-tube condenser is used only in small refrigeration systems. Hot gas from the compressor enters the top inlet and is distributed along the baffle to fill the shell.
Hot gas is then desuperheated, condensed, subcooled into liquid, and discharged into the liquid line at the bottom outlet. Usually one sixth of the volume is filled with subcooled liquid refrigerant. Condenser water enters the condenser from the bottom for effective subcooling.
After extracting heat from the gaseous refrigerant, condenser water is discharged at a higher level. Two-pass or three-pass water flow arrangements are usually used in shell-and-tube water-cooled condensers. The two-pass arrangement means that water flows from one end to the opposite end and returns to the original end.
Two-pass is the standard setup. In a shell-and-tube water-cooled condenser, the condensing temperature Tcon depends mainly on the entering temperature of condenser water Tce, the condenser area, the fouling factor, and the configuration of the copper tube. Evaporative Condenser An evaporative condenser uses the evaporation of water spray on the outer surface of the condensing tubes to remove the latent heat of condensation of refrigerant during condensation.
An evaporative condenser consists of a condensing coil, a subcooling coil, a water spray, an induced draft or sometimes forced draft fan, a circulating water pump, a water eliminator, a water basin, an outer casing, and controls as shown in Figure 9.
The condensing coil is usually made of bare copper, steel, or sometimes stainless steel tubing. The evaporation of a fraction of condenser water from the saturated air film removes the sensible and latent heat rejected by the refrigerant. The rest of the spray falls and is collected by the basin.
Air enters from the inlet just above the basin. It flows through the condensing coil at a face velocity of to fpm, the water spray bank, and the eliminator. After air absorbs the evaporated water vapor, it is extracted by the fan and discharged at the top outlet. The water circulation rate is about 1. An evaporative condenser is actually a combination of a water-cooled condenser and a cooling tower. It is usually located on the rooftop and should be as near the compressor as possible.
Clean tube surface and good maintenance are critical factors for evaporative condensers. An evaporative condenser also needs low ambient control similar as in an air-cooled condenser. Comparison of Air-Cooled, Water-Cooled, and Evaporative Condensers An air-cooled condenser has the highest condensing temperature Tcon and therefore the highest compres- sor power input.
An evaporative condenser has the lowest Tcon and is most energy efficient. An evaporative condenser also consumes less water and pump power. The drawback of evaporative condensers is that the rejected heat from the interior zone is difficult to recover and use as winter heating for perimeter zones and more maintenance is required. Evaporators and Refrigerant Flow Control Devices An evaporator is a heat exchanger in which the liquid refrigerant is vaporized and extracts heat from the surrounding air, chilled water, brine, or other substance to produce a refrigeration effect.
Evaporators used in air-conditioning can be classified according to the combination of the medium to be cooled and the type of refrigerant feed, as the following. Direct expansion DX coils are air coolers, and the refrigerant is fed according to its degree of superheat after vaporization. DX coils were covered earlier. Direct expansion ice makers or liquid overfeed ice makers are such that liquid refrigerant is forced through the copper tubes or the hollow inner part of a plate heat exchanger and vaporized.
The refrig- eration effect freezes the water in the glycol-water that flows over the outside surface of the tubes or the plate heat exchanger. In direct expansion ice makers, liquid refrigerant completely vaporizes inside the copper tubes, and the superheated vapor is extracted by the compressor.
In liquid overfeed ice makers, liquid refrigerant floods and wets the inner surface of the copper tubes or the hollow plate heat exchanger.
Only part of the liquid refrigerant is vaporized. The rest is returned to a receiver and pumped to the copper tubes or plate heat exchanger again at a circulation rate two to several times greater than the evaporation rate. Flooded shell-and-tube liquid coolers, or simply flooded liquid coolers, are such that refrigerant floods and wets all the boiling surfaces and results in high heat transfer coefficients. A flooded shell-and-tube liquid cooler is similar in construction to a shell-and-tube water-cooled condenser, except that its liquid refrigeration inlet is at the bottom and the vapor outlet is at the top.
Flooded liquid coolers can provide larger evaporating surface area and need minimal space. They are widely used in large central air-conditioning systems. Currently used refrigerant flow control devices include thermostatic expansion valves, float valves, multiple orifices, and capillary tubes.
A thermostatic expansion valve is usually installed just prior to the refrigerant distributor in DX coils and direct-expansion ice makers. A thermostatic expansion valve consists of a valve body, a valve pin, a spring, a diaphragm, and a sensing bulb near the outlet of the DX coil, as shown in Figure 9.
The sensing bulb is connected to the upper part of the diaphragm by a connecting tube. When the liquid refrigerant passes through the opening of the thermostatic expansion valve, its pressure is reduced to the evaporating pressure. Liquid and a small fraction of vaporized refrigerant then flow through the distributor and enter various refrigerant circuits.
If the refrigeration load of the DX coil increases, more liquid refrigerant evaporizes. This increases the degree of superheat of the leaving vapor at the outlet and the temperature of the sensing bulb. A higher bulb temperature exerts a higher saturated pressure on the top of the diaphragm. The valve pin then moves downward and widens the opening. More liquid refrigerant is allowed to enter the DX coil to match the increase of refrigeration load.
If the refrigeration load drops, the degree of superheat at the outlet and the temperature of the sensing bulb both drop, and the valve opening is narrower.
The refrigeration feed decreases accordingly. Its value can also be adjusted manually by varying the spring tension. A float valve is a valve in which a float is used to regulate the valve opening to maintain a specific liquid refrigerant level.
A lower liquid level causes a lower valve pin and therefore a wider opening and vice versa. In a centrifugal refrigeration system, two or more orifice plates, multiple orifices, are sometimes installed in the liquid line between the condenser and the flash cooler and between the flash cooler and the flooded liquid cooler to throttle their pressure as well as to regulate the refrigerant feed.
A capillary tube, sometimes called a restrictor tube, is a fixed length of small-diameter tubing installed between the condenser and the evaporator to throttle the refrigerant pressure from pcon to pev and to meter the refrigerant flow to the evaporator.
Capillary tubes are usually made of copper. The inside diameter Dcap is 0. Capillary tubes are especially suitable for a heat pump system in which the refrigerant flow may be reversed.
Evaporative Coolers An evaporative cooling system is an air-conditioning system in which air is cooled evaporatively. It consists of evaporative coolers, fan s , filters, dampers, controls, and others. A mixing box is optional.
An evaporative cooler could be a stand-alone cooler or installed in an air system as a component. There are three types of evaporative coolers: 1 direct evaporative coolers, 2 indirect evaporative coolers, and 3 indirect—direct evaporative coolers. Direct Evaporative Cooler In a direct evaporative cooler, the air stream to be cooled directly contacts the water spray or wetted medium as shown in Figure 9.
Evaporative pads made of wooden fibers with necessary treatment at a thickness of 2 in. The direct evaporation process 12 takes place along the thermodynamic wet bulb line on the psychro- metric chart. Subscript ae indicates the entering air and al the leaving air. Indirect Evaporative Coolers In an indirect evaporative cooler, the cooled-air stream to be cooled is separated from a wetted surface by a flat plate or tube wall as shown in Figure 9.
A wet-air stream flows over the wetted surface so that liquid water is evaporated and extracts heat from the cooled-air stream through the flat plate or tube wall. The cooled-air stream is in contact with the wetted surface indirectly. The core part of an indirect evaporative cooler is a plate heat exchanger.
It is made of thin polyvinyl chloride plates 0. As in a direct evaporative cooler, there are also fan s , water sprays, circulating pump, air intake, dampers, controls, etc. An indirect evaporative cooling process is represented by a horizontal line on a psychrometric chart, which shows that humidity ratio remains constant. If the space air is extracted and used as the wet air intake, the wet air will be exhausted at point x at nearly saturated state.
An indirect evaporative cooler could be so energy efficient as to provide evaporative cooling with an EER up to 50 instead of 9 to 12 for a reciprocating compression refrigeration system. Direct—Indirect Evaporative Cooler. A direct—indirect evaporative cooler is a two-stage evaporating cooler, as shown in Figure 9. Operating Characteristics. For a direct evaporative cooler, face velocity is usually less than fpm to reduce drift carryover. For an indirect evaporative cooler, face velocity vs is usually between to fpm.
A higher vs results at a greater air-side pressure drop. Scofield et al. In the direct cooler, conditioned air was further cooled to a dry bulb of Because the installation cost of an indirect—direct cooler is higher than that of refrigeration, cost analysis is required to select the right choice. Chilled water is then used as a cooling medium to cool the air in the cooling coils in AHUs and terminals.
Using common main and branch pipes requires a lengthy changeover from chilled water to hot water or vice versa for a period of several hours. Water systems can also be classified according to their operating characteristics. Closed System In a closed system, water forms a closed loop for water conservation and energy saving when it flows through the coils, chillers, boilers, heaters, or other heat exchangers and water is not exposed to the atmosphere.
Open System In an open system, water is exposed to the atmosphere. Once-Through System In a once-through system, water flows through a heat exchanger s only once without recirculation. Otherwise, brine or glycol-water should be used. The lower Twe, the higher will be the compressor power input.
A pressure loss of 2. Schedule 40 is the standard thickness for a pipe of up to 10 in. For copper tubing, type K is the heaviest, and type L is generally used as the standard for pressure copper tubes. Steel pipes of small diameter are often joined by threaded cast-iron fittings. Steel pipes of diameter 2 in. Not only pipes, but also their joints and fittings should be considered.
During temperature changes, pipes expand and contract. Both operating and shut-down periods should be taken into consideration. Bends like U-, Z-, and L-bends, loops, and sometimes packed expansion joints, bellows, or flexible metal hose mechanical joints are used.
Corrosion, Impurities, and Water Treatments Corrosion is a destructive process caused by a chemical or electrochemical reaction on metal or alloy. In water systems, dissolved impurities cause corrosion and scale and the growth of microbiologicals like algae, bacteria, and fungi.
Scale is the deposit formed on a metal surface by precipitation of the insoluble constituents. In addition to the dissolved solids, unpurified water may contain suspended solids.
Currently used chemicals include crystal modifiers to change the crystal formation of scale and sequestering chemicals. Growth of bacteria, algae, and fungi is usually treated by biocides to prevent the formation of an insulating layer resulting in lower heat transfer as well as restricted water flow. Chlorine and its compounds are effective and widely used. Blow-down is an effective process in water treatment and should be considered as important as chemical treatments. Piping Arrangements Main and Branch Pipes.
In a piping circuit as shown in Figure 9. Reprinted with permission. Chilled or hot water from the coils and heat exchangers is accumulated by the return main pipe through return branch pipes and then returned to the chiller or boiler.
Constant Flow and Variable Flow. In a constant-flow water system, the volume flow rate at any cross- sectional plane of the supply and return mains remains constant during the entire operating period. In a variable-flow water system, the volume flow rate varies when the system load changes during the operating period.
Direct Return and Reverse Return. In a direct return system, the water supplies to and returns from various coils through various piping circuits. Water flow must be adjusted and balanced by using balance valves to provide required design flow rates at design conditions.
In a reverse-return system, as shown in Figure 9. Water flow rates to various coils are easier to balance. In a dual-temperature water system, the piping from the chiller or boiler to the coils can be either a two-pipe system with a supply main and return main as shown in Figure 9.
The two-pipe system needs a changeover from chilled to hot water and vice versa. A four-pipe system is more expensive to install. Generally, a fairly constant-volume water flow is required in the evaporator to protect it from freezing at part load. Current chilled water systems or dual-temperature water systems often adopt a plant-building loop that consists of two piping loops as shown in Figure 9.
The plant loop is operated at constant flow. Building Loop. A building loop BCDEFGHJB contains coils; building circulating water pumps, often variable-speed pumps, one being a standby pump; corresponding pipes and fittings; and control systems.
A differential pressure transmitter is often installed at the farthest end from the building pump between the supply and return mains. The building loop is operated at variable flow.
A short common pipe connects these two loops and combines them into a plant-building loop combination. It is also called a primary-secondary loop, with the plant loop the primary loop and the building loop the secondary loop. The location of the pump in a water system should be arranged so that the pressure at any point in the system is greater than atmospheric pressure to prevent air leaking into the system. The pressure drop across the coils then increases.
As soon as the increase of the pressure differential is sensed by the transmitter, a DDC controller reduces the flow rate of the variable-speed pump to match the reduction of the coil load during part load. The pressure differential transmitter functions similarly to a duct static pressure sensor in a VAV system. Since the plant loop is at constant flow, excess chilled water bypasses the building loop and flows back to the chiller s through the common pipe.
When the reduction of coil loads in the building loop is equal to or greater than the refrigeration capacity of a single chiller, the DDC controller will shut down a chiller and its associated chilled water pump.
The operating characteristics of the hot water in a dual-temperature water system are similar to those in a chilled water system.
Roughly, a 0. The pressure drop across the two-way control valve is considerably reduced as the control valve is only a component of the building loop. It teaches fundamental principles and service techniques needed to install, maintain, diagnose, and service HVACR systems.
Students learn basic concepts and then apply them to increasingly complex systems" Focused on the food service industry, chapters address how HVAC technicians service medium- and low-temperature refrigeration equipment such as walk-ins, reach-ins, refrigerated cases, and ice machines.
Readings also include special features, such as insider tips from seasoned pros on installing, servicing, and troubleshooting commercial equipment. Freshly updated to include the latest industry changes, the third edition adds six full sections of content, as well as helpful illustrations, pictures, and diagrams—including a step-by-step flowchart for quickly diagnosing and addressing the nine most common refrigeration problems you will see on the job.
This textbook provides a concise, systematic treatment of essential theories and practical aspects of refrigeration and air-conditioning systems. It is designed for students pursuing courses in mechanical engineering both at diploma and degree level with a view to equipping them with a fundamental background necessary to understand the latest methodologies used for the design of refrigeration and air-conditioning systems.
After reviewing the physical principles, the text focuses on the refrigeration cycles commonly used in air-conditioning applications in tropical climates. The subject of psychrometry for analysing the various thermodynamic processes in air conditioning is particularly dealt with in considerable detail. This text incorporates such tables and charts so that the students are exposed to solving real-life design problems with the help of ASHRAE Tables.
Finally, the book highlights the features, characteristics and selection criteria of hardware including the control equipment. It also provides the readers with the big picture in respect of the latest developments such as thermal storage air conditioning, desiccant cooling, chilled ceiling cooling, Indoor Air Quality IAQ and thermal comfort. Besides the students, the book would be immensely useful to practising engineers as a ready reference.
Comprehensive introduction to refrigeration and heating. Covers principles, practices and servicing techniques. The text begins by reviewing, in a simple and precise manner, the physical principles of three pillars of Refrigeration and Air Conditioning, namely thermodynamics, heat transfer, and fluid mechanics.
Following an overview of the history of refrigeration, subsequent chapters provide exhaustive coverage of the principles, applications and design of several types of refrigeration systems and their associated components such as compressors, condensers, evaporators, and expansion devices.
Refrigerants too, are studied elaboratively in an exclusive chapter. The second part of the book, beginning with the historical background of air conditioning in Chapter 15, discusses the subject of psychrometrics being at the heart of understanding the design and implementation of air conditioning processes and systems, which are subsequently dealt with in Chapters 16 to It also explains the design practices followed for cooling and heating load calculations.
Each chapter contains several worked-out examples that clarify the material discussed and illustrate the use of basic principles in engineering applications.
Each chapter also ends with a set of few review questions to serve as revision of the material learned. Download Refrigeration and Air Conditioning book written by C. Explains the functions and operations of refrigeration and air conditioning units through an analytical synthesis of the principles of thermodynamics, heat transfer and fluid mechanics.
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