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Owen, Editor Heather E. Kennedy, Managing Editor Nancy F. The result is that engineers are better able to keep indoor environments safe and productive while protecting and preserving the outdoors for generations to come. This volume includes data and guidance on cooling, freezing, and storing food; industrial and medical applications of refrigeration; and low-temperature refrigeration.
Publications are listed by topic, and full contact information for publishing organizations is included. This volume is published as a bound print volume, in PDF format, and online, in two editions: one using inch-pound I-P units of measurement, the other using the International System of Units SI. Reader comments are enthusiastically invited. Refrigeration Accessories Pressure Control for Refrigerant Condensers Hot-Gas Bypass Arrangements Minimizing Refrigerant Charge in Commercial Systems Refrigerant Retrofitting Temperature Glide In , Thomas Midgley, Jr.
Chlorinated halocarbon refrigerants represent the second generation of refrigerants Calm Concern about the use of halocarbon refrigerants began with a paper by two University of California professors, Frank Rowland and Mario Molina, in which they highlighted the damage chlorine could cause to the ozone layer in the stratosphere. This publication eventually led to the Montreal Protocol Agreement in and its subsequent revisions, which restricted the production and use of chlorinated halocarbon CFC and HCFC refrigerants.
Replacement HFC, third-generation refrigerants were developed following these restrictions Calm This Kigali Agreement marks a commitment from a significant portion of the world to deal with the global warming consequences of HFC gases. As phasedown begins, interest in the future cost and availability of these refrigerants is likely to increase. The latest fluorinated greenhouse gas F-gas regulation in Europe adopted in revised from the initial adoption in aims to reduce HFC refrigerant sales to one-fifth of levels by Some HFCs have already been banned where suitable alternatives are widely available, and all systems require specific maintenance checks, servicing, and refrigerant reclamation when the system is decommissioned.
These early adoption measures were designed as the prelude to a proposed HFC phaseout, and include required service practices; leak inspection; charge monitoring and record keeping; system retrofit and retirement plans; and refrigerant distributor, wholesaler, and reclaimer prohibitions. However, HFOs are classed as mildly flammable, which is an obvious barrier to adoption. Oil management; gas and liquid separation; subcooling, superheating, desuperheating, and piping of refrigerant liquid, gas, and two-phase flow are all part of refrigeration.
Applications include air conditioning, commercial refrigeration, and industrial refrigeration. This chapter focuses on systems that use halocarbons halogenated hydrocarbons as refrigerants. The most commonly used halogen refrigerants are chlorine Cl and fluorine F. Halocarbon refrigerants are classified into four groups: chlorofluorocarbons CFCs , which contain carbon, chlorine, and fluorine; hydrochlorofluorocarbons HCFCs , which consist of carbon, hydrogen, chlorine, and fluorine; hydrofluorocarbons HFCs , which contain carbon, hydrogen, and fluorine; and hydrofluoroolefins HFOs , which are HFC refrigerants derived from an alkene olefin; i.
A successful refrigeration system depends on good piping design and an understanding of the required accessories. This chapter covers the fundamentals of piping and system design as well as guidance on new design considerations in light of increasing regulation on halocarbon refrigeration systems.
Hydrocarbon refrigerant pipe friction data can be found in petroleum industry handbooks. For information on refrigeration load, see Chapter The main refrigerants used then were ammonia R , chloromethane R , and sulfur dioxide R , all of which have some The preparation of this chapter is assigned to TC Environmental Protection Agency EPA , and Underwriters Laboratories UL will need to reach a coordinated agreement to allow broad use of these fourth-generation refrigerants before local and state codes will be in a position to allow their use.
HFC refrigeration systems are still widely used and will continue to be used during the transition to natural or other reduced-GWP refrigerants, so many owners, engineers, and manufacturers seek to reduce charge and build tighter systems to reduce the total system charge on site and ensure that less refrigerant is released into the atmosphere. Table 1 in Chapter 3 lists commonly used refrigerants and their corresponding GWP values.
Also, using indirect and cascade systems to reduce the total amount of refrigerant has become increasingly popular. These systems also reduce the possibility for leakage because large amounts of interconnecting piping between the compressors and the heat load are replaced mainly with glycol or CO2 piping.
See Chapter 9 for more information on refrigerant containment, recovery, recycling, and reclamation. However, some ordinances require heavier piping and other features. The designer should know the specific requirements of the installation site. The rated internal working pressure for Type L copper tubing decreases with 1 increasing metal operating temperature, 2 increasing tubing size OD , and 3 increasing temperature of joining method.
Hot methods used to join drawn pipe e. Particular attention should be paid when specifying copper in conjunction with newer, high-pressure refrigerants e. Concentration calculations, based on the amount of refrigerant in the system and the volume of the space where it is installed, are needed to identify what safety features are required by the appropriate codes.
Whenever allowable concentration limits of the refrigerant may be exceeded in occupied spaces, additional safety measures e. Note that, because halocarbon refrigerants are heavier than air, leak detection sensors should be placed at lower elevations in the space typically mm from the floor.
Refrigerant Line Velocities Economics, pressure drop, noise, and oil entrainment establish feasible design velocities in refrigerant lines Table 1. Higher gas velocities are sometimes found in relatively short suction lines on comfort air-conditioning or other applications where the operating time is only to h per year and where low initial cost of the Fig.
Industrial or commercial refrigeration applications, where equipment runs almost continuously, should be designed with low refrigerant velocities for most efficient compressor performance and low equipment operating costs.
An owning and operating cost analysis will reveal the best choice of line sizes. Liquid drain lines from condensers to receivers should be sized for 0. Where calculated velocities exceed 0. Liquid lines from receiver to evaporator should be sized to maintain velocities below 1. To obtain total system flow rate, select the proper rate value and multiply by system capacity. Enter curves using saturated refrigerant temperature at the evaporator outlet and actual liquid temperature entering the liquid feed device including subcooling in condensers and liquid-suction interchanger, if used.
Because Figures 1 and 2 are based on a saturated evaporator temperature, they may indicate slightly higher refrigerant flow rates than are actually in effect when suction vapor is superheated above the conditions mentioned.
Refrigerant flow rates may be reduced approximately 0. Suction-line superheating downstream of the evaporator from line heat gain from external sources should not be used to reduce evaluated mass flow, because it increases volumetric flow rate and line velocity per unit of evaporator capacity, but not mass flow rate. It should be considered when evaluating suction-line size for satisfactory oil return up risers. Suction gas superheating from use of a liquid-suction heat exchanger has an effect on oil return similar to that of suction-line superheating.
This can be seen in Figures 1 and 2 because the reduced temperature of the liquid supplied to the evaporator feed valve has been taken into account Superheat caused by heat in a space not intended to be cooled is always detrimental because the volumetric flow rate increases with no compensating gain in refrigerating effect.
Although smaller pipes may be cheaper, they inflict higher operating costs for the life of the system because of excessive pressure drop. However, there are diminishing efficiency benefits when moving to larger pipe sizes, and it is necessary to strike a balance. When considering safety, remember that rated working pressures for any pipe material decrease as pipe diameters increase.
It is also important to understand that any brazed copper piping will be weakened by the annealing that occurs during brazing. Typically, two separate working pressures are published for copper: one for annealed copper and one for drawn copper. Drawn copper working pressures should only be used if and when pipes are fitted together without brazing i. Pressure Drop Considerations Suction- and discharge-line pressure drops cause loss of compressor capacity and increased power usage.
Excessive liquid-line pressure drops can cause liquid refrigerant to flash, resulting in faulty expansion valve operation. Refrigeration systems are designed so that friction pressure losses do not exceed a pressure differential equivalent to a corresponding change in the saturation boiling temperature. The primary measure for determining pressure drops is a given change in saturation temperature. Pressure drop calculations are determined as normal pressure loss associated with a change in saturation temperature of the refrigerant.
Typically, the refrigeration system is sized for pressure losses of 1 K or less for each segment of the discharge, suction, and liquid lines.
Liquid Lines. Pressure drop should not be so large as to cause gas formation in the liquid line, insufficient liquid pressure at the liquid feed device, or both. Systems are normally designed so that pressure drop in the liquid line from friction is not greater than that corresponding to about a 0. See Tables 3 to 9 for liquid-line sizing information. Liquid subcooling is the only method of overcoming liquid line pressure loss to guarantee liquid at the expansion device in the evaporator. If subcooling is insufficient, flashing occurs in the liquid line and degrades system efficiency.
Friction pressure drops in the liquid line are caused by accessories such as solenoid valves, filter-driers, and hand valves, as well as by the actual pipe and fittings between the receiver outlet and the refrigerant feed device at the evaporator.
Liquid-line risers are a source of pressure loss and add to the total loss of the liquid line. Loss caused by risers is approximately Total loss is the sum of all friction losses plus pressure loss from liquid risers. Example 1 shows the process of determining liquid-line size and checking for total subcooling required. Example 1. Capacity is 14 kW, and the liquid line is 50 m equivalent length with a riser of 6 m.
Determine the liquidline size and total required subcooling. Use the equation in Note 3 of Table 3 to compute actual temperature drop. Regardless of the liquid-line routing when flashing occurs, overall efficiency is reduced, and the system may malfunction. The velocity of liquid leaving a partially filled vessel e. As a result, both gas and liquid flow through the line, limiting the rate of liquid flow.
If this factor is not considered, excess operating charges in receivers and flooding of shell-and-tube condensers may result. No specific data are available to precisely size a line leaving a vessel. If the height of liquid above the vena contracta produces the desired velocity, liquid leaves the vessel at the expected rate. Thus, if the level in the vessel falls to one pipe diameter above the bottom of the vessel from which the liquid line leaves, the capacity of copper lines for R at 6.
If the line continues down from the receiver, the value of h increases. For a kW capacity with R, the line from the bottom of the receiver should be about 79 mm. After a drop of mm, a reduction to 54 mm is satisfactory. Suction lines are more critical than liquid and discharge lines from a design and construction standpoint. Refrigerant lines should be sized to 1 provide a minimum pressure drop at full load, 2 return oil from the evaporator to the compressor under minimum load conditions, and 3 prevent oil from draining from an active evaporator into an idle one.
The suction line is normally sized to have a pressure drop from friction no greater than the equivalent of about a 1 K change in saturation temperature. See Tables 3 to 15 for suction line sizing information. Therefore, low-temperature lines must be sized for a very low pressure drop, or higher equivalent temperature losses, with resultant loss in equipment capacity, must be accepted. For very low pressure drops, any suction or hot-gas risers must be sized properly to ensure oil entrainment up the riser so that oil is always returned to the compressor.
Where pipe size must be reduced to provide sufficient gas velocity to entrain oil up vertical risers at partial loads, greater pressure drops are imposed at full load. These can usually be compensated for by oversizing the horizontal and down run lines and components. Table capacities are in kilowatts of refrigeration. Multiply table capacities by the following factors for other condensing temperatures. Water-cooled condensers, where receiver ambient temperature may be higher than refrigerant condensing temperature, fall into this category.
Applications with very little subcooling or very long lines may require a larger line. Review maximum working pressure allowances for the pipe material used before selecting pipe sizes to ensure the pipe is properly rated for system working and design pressures.
Halocarbon Refrigeration Systems 1. Condensing 2. Discharge Lines. Pressure loss in hot-gas lines increases the required compressor power per unit of refrigeration and decreases compressor capacity. Pressure drop is minimized by generously sizing lines for low friction losses, but still maintaining refrigerant line velocities to entrain and carry oil along at all loading conditions. Pressure drop is normally designed not to exceed the equivalent of a 1 K change in saturation temperature.
Recommended sizing tables are based on a 0. Location and Arrangement of Piping Refrigerant lines should be as short and direct as possible to minimize tubing and refrigerant requirements and pressure drops. Plan piping for a minimum number of joints using as few elbows and other fittings as possible, but provide sufficient flexibility to absorb compressor vibration and stresses caused by thermal expansion and contraction. Arrange refrigerant piping so that normal inspection and servicing of the compressor and other equipment is not hindered.
Do not obstruct the view of the oil-level sight glass or run piping so that it interferes with removing compressor cylinder heads, end bells, access plates, or any internal parts.
Suction-line piping to the compressor should be arranged so that it will not interfere with removal of the compressor for servicing. Provide adequate clearance between pipe and adjacent walls and hangers or between pipes for insulation installation.
Use sleeves that are sized to allow installation of both pipe and insulation through floors, walls, or ceilings. Set these sleeves before pouring concrete or erecting brickwork. Run piping so that it does not interfere with passages or obstruct headroom, windows, and doors. Protection Against Damage to Piping Protection against damage is necessary, particularly for small lines, which have a false appearance of strength. Where traffic is heavy, provide protection against impact from carelessly handled hand trucks, overhanging loads, ladders, and fork trucks.
Piping Insulation All piping joints and fittings should be thoroughly leak tested before insulation is sealed. Suction lines should be insulated to prevent sweating and heat gain. Insulation covering lines on which moisture can condense or lines subjected to outdoor conditions must be vapor sealed to prevent any moisture travel through the insulation or condensation in the insulation.
Many commercially available types are provided with an integral waterproof jacket for this purpose. Although the liquid line ordinarily does not require insulation, suction and liquid lines can be insulated as a unit on installations where the two lines are clamped together.
When it passes through a warmer area, the liquid line should be insulated to minimize heat gain. Hot-gas discharge lines usually are not insulated; however, they should be insulated if necessary to prevent injury from hightemperature surfaces, or if the heat dissipated is objectionable e. In this case, discharge lines upstream of the heat reclaim heat exchanger should be insulated. Downstream lines between the heat reclaim heat exchanger and condenser do not need to be insulated unless necessary to prevent the refrigerant from condensing prematurely.
Also, indoor hot-gas discharge line insulation does not need a tight vapor seal because moisture condensation is not an issue.
All joints and fittings should be covered, but it is not advisable to do so until the system has been thoroughly leak tested. See Chapter 10 for additional information. Vibration and Noise in Piping Vibration transmitted through or generated in refrigerant piping and the resulting objectionable noise can be eliminated or minimized by proper piping design and support.
In refrigeration applications, piping vibration can be caused by rigid connection of the refrigerant piping to a reciprocating compressor.
Vibration effects are evident in all lines directly connected to the compressor or condensing unit. It is thus impossible to eliminate vibration in piping; it is only possible to mitigate its effects. Flexible metal hose is sometimes used to absorb vibration transmission along smaller pipe sizes.
For maximum effectiveness, it should be installed parallel to the crankshaft. In some cases, two isolators may be required, one in the horizontal line and the other in the vertical line at the compressor.
A rigid brace on the end of the flexible hose away from the compressor is required to prevent vibration of the hot-gas line beyond the hose. Flexible metal hose is not as efficient in absorbing vibration on larger pipes because it is not actually flexible unless the ratio of length to diameter is relatively great. In practice, the length is often limited, so flexibility is reduced in larger sizes. This problem is best solved by using flexible piping and isolation hangers where the piping is secured to the structure.
When piping passes through walls, through floors, or inside furring, it must not touch any part of the building and must be supported only by the hangers provided to avoid transmitting vibration to the building ; this eliminates the possibility of walls or ceilings acting as sounding boards or diaphragms. When piping is erected where access is difficult after installation, it should be supported by isolation hangers. Vibration and noise from a piping system can also be caused by gas pulsations from the compressor operation or from turbulence in the gas, which increases at high velocities.
It is usually more apparent in the discharge line than in other parts of the system. When gas pulsations caused by the compressor create vibration and noise, they have a characteristic frequency that is a function of the number of gas discharges by the compressor on each revolution. This frequency is not necessarily equal to the number of cylinders, because on some compressors two pistons operate together. It is also varied by the angular displacement of the cylinders, such as in V-type compressors.
Noise resulting from gas pulsations is usually objectionable only when the piping system amplifies the pulsation by resonance. On single-compressor systems, resonance can be reduced by changing the size or length of the resonating line or by installing a properly sized hot-gas muffler in the discharge line immediately after the compressor discharge valve. On a paralleled compressor system, a harmonic frequency from the different speeds of multiple compressors may be apparent.
This noise can sometimes be reduced by installing mufflers. Sucsaturated evaporator outlet temperature. Liquid capacity kW based Temp. Thermophysical properties and viscosity data based on calculations 20 1.
For brazed Type L copper tubing larger than 28 mm OD for discharge 40 1. Multiply table 50 0. Discharge Line 0. SucNotes: saturated evaporator outlet temperature. Nominal Line OD, mm 1. When noise is caused by turbulence and isolating the line is not effective enough, installing a larger-diameter pipe to reduce gas velocity is sometimes helpful. Also, changing to a line of heavier wall or from copper to steel to change the pipe natural frequency may help.
Equivalent Lengths of Valves and Fittings Refrigerant line capacity tables are based on unit pressure drop per metre length of straight pipe, or per combination of straight pipe, fittings, and valves with friction drop equivalent to a metre of straight pipe. Generally, pressure drop through valves and fittings is determined by establishing the equivalent straight length of pipe of the same size with the same friction drop.
Line sizing tables can then be used directly. Tables 16 to 18 give equivalent lengths of straight pipe for various fittings and valves, based on nominal pipe sizes. The following example shows the use of various tables and charts to size refrigerant lines. Capacities in the tables are based on the refrigerant flow that develops a friction loss, per metre of equivalent pipe length, corresponding to a 0. The capacities shown for liquid lines are for pressure losses corresponding to 0.
Tables 10 to 15 show capacities for the same refrigerants based on reduced suction line pressure loss corresponding to 0. These tables may be used when designing system piping to minimize suction line pressure drop. The refrigerant line sizing capacity tables are based on the Darcy-Weisbach relation and friction factors as computed by the Colebrook function Colebrook , Tubing roughness height is 1.
Viscosity extrapolations and adjustments for pressures other than Discharge gas superheat was 45 K for Ra and 60 K for R The refrigerant cycle for determining capacity is based on saturated gas leaving the evaporator.
The calculations neglect the presence of oil and assume nonpulsating flow. Table 16 Example 2. Suction line is copper tubing, with 15 m of straight pipe and six long-radius elbows. Straight pipe length Six 50 mm long-radius elbows at 1. This temperature drop is too large; therefore, the 54 mm tube is recommended. This file is licensed to Osama Khayata [email protected]. Nominal Pipe or Tube Size, mm 10 15 20 25 32 40 50 65 80 90 Note: Enter table for losses at smallest diameter d.
For valve losses of short pattern plug cocks above mm, check with manufacturer. All compressors lose some lubricating oil during normal operation. Because oil inevitably leaves the compressor with the discharge gas, systems using halocarbon refrigerants must return this oil at the same rate at which it leaves Cooper Oil that leaves the compressor or oil separator reaches the condenser and dissolves in the liquid refrigerant, enabling it to pass readily through the liquid line to the evaporator.
In the evaporator, the refrigerant evaporates, and the liquid phase becomes enriched in oil. The concentration of refrigerant in the oil depends on the evaporator temperature and types of refrigerant and oil used. Oil separated in the evaporator is returned to the compressor by gravity or by drag forces of the returning gas. One of the most difficult problems in low-temperature refrigeration systems using halocarbon refrigerants is returning lubrication oil from the evaporator to the compressors.
Except for most centrifugal compressors and rarely used nonlubricated compressors, refrigerant continuously carries oil into the discharge line from the compressor. Most of this oil can be removed from the stream by an oil separator and returned to the compressor. Oil that finds its way into the system must be managed. Oil mixes well with halocarbon refrigerants at higher temperatures.
As temperature decreases, miscibility is reduced, and some oil separates to form an oil-rich layer near the top of the liquid level in a flooded evaporator.
If the temperature is very low, the oil becomes a gummy mass that prevents refrigerant controls from functioning, blocks flow passages, and fouls heat transfer surfaces.
Proper oil management is often key to a properly functioning system. Low-temperature systems using hot-gas defrost can also be designed to sweep oil out of the circuit each time the system defrosts. This reduces the possibility of oil coating the evaporator surface and hindering heat transfer. Flooded evaporators can promote oil contamination of the evaporator charge because they may only return dry refrigerant vapor back to the system.
Skimming systems must sample the oil-rich layer floating in the drum, a heat source must distill the refrigerant, and the oil must be returned to the compressor. Because flooded halocarbon systems can be elaborate, some designers avoid them. System Capacity Reduction. Using automatic capacity control on compressors requires careful analysis and design. The compressor can load and unload as it modulates with system load requirements through a considerable range of capacity.
System piping must be designed to return oil at the lowest loading, yet not impose excessive pressure drops in the piping and equipment at full load. Oil Return up Suction Risers. Many refrigeration piping systems contain a suction riser because the evaporator is at a lower level than the compressor. Oil circulating in the system can return up gas risers only by being transported by returning gas or by auxiliary means such as a trap and pump.
The minimum conditions for oil transport correlate with buoyancy forces i. The principal criteria determining the transport of oil are gas velocity, gas density, and pipe inside diameter. Greater gas velocities are required as temperature drops and the gas becomes less dense.
Higher velocities are also necessary if the pipe diameter increases. Table 19 translates these criteria to minimum refrigeration capacity requirements for oil transport. Suction risers must be sized for minimum system capacity. Oil must be returned to the compressor at the operating condition corresponding to the minimum displacement and minimum suction temperature at which the compressor will operate.
When suction or evaporator pressure regulators are used, suction risers must be sized for actual gas conditions in the riser. For a single compressor with capacity control, the minimum capacity is the lowest capacity at which the unit can operate. For multiple compressors with capacity control, the minimum capacity is the lowest at which the last operating compressor can run. Riser Sizing.
The following example demonstrates the use of Table 19 in establishing maximum riser sizes for satisfactory oil transport down to minimum partial loading. As long as horizontal lines are level or pitched in the direction of the compressor, oil can be transported with normal design velocities.
Because most compressors have multiple capacity-reduction features, gas velocities required to return oil up through vertical suction risers under all load conditions are difficult to maintain. When the suction riser is sized to allow oil return at the minimum operating capacity of the system, pressure drop in this portion of the line may be too great when operating at full load.
If a correctly sized suction riser imposes too great a pressure drop at full load, a double suction riser should be used. Oil movement in the suction lines of multistage systems requires the same design approach as that for single-stage systems. For oil to flow up along a pipe wall, a certain minimum drag of gas flow is required. Drag can be represented by the friction gradient. The following sizing data may be used for ensuring oil return up vertical suction lines for refrigerants other than those listed in Tables 19 and The line size selected should provide a pressure drop equal to or greater than that shown in the chart.
Figure 3 shows two methods of double suction riser construction. Oil return in this arrangement is accomplished at minimum loads, but it does not cause excessive pressure drops at full load.
Sizing and operation of a double suction riser are as follows: 1. Riser A is sized to return oil at minimum load possible. Riser B is sized for satisfactory pressure drop through both risers at full load. The usual method is to size riser B so that the combined cross-sectional area of A and B is equal to or slightly greater than the cross-sectional area of a single pipe sized for acceptable pressure drop at full load without regard for oil return at minimum load.
The combined cross-sectional area, however, should not be greater than the cross-sectional area of a single pipe that would return oil in an upflow riser under maximum load. A trap is introduced between the two risers, as shown in both methods. During part-load operation, gas velocity is not sufficient to return oil through both risers, and the trap gradually fills up with oil until riser B is sealed off.
The gas then travels up riser A only with enough velocity to carry oil along with it back into the horizontal suction main. If this is not done, the trap can accumulate enough oil during part-load operation to lower the compressor crankcase oil level. Note in Figure 3 that riser lines A and B Example 3.
Therefore, 54 mm OD pipe is suitable. Based on Table 19, the next smaller line size should be used for marginal suction risers. When vertical riser sizes are reduced to provide satisfactory minimum gas velocities, pressure drop at full load increases considerably; horizontal lines should be sized to keep total Fig.
For other liquid line temperatures, use correction factors in table at right. Ra computed using ISO 32 ester-based oil. This prevents oil drainage into the risers, which may be idle during part-load operation. The same purpose can be served by running risers horizontally into the main, provided that the main is larger in diameter than either riser.
Often, double suction risers are essential on low-temperature systems that can tolerate very little pressure drop. Any system using these risers should include a suction trap accumulator and a means of returning oil gradually. For systems operating at higher suction temperatures, such as for comfort air conditioning, single suction risers can be sized for oil return at minimum load.
With this low ratio, pressure drop in single suction risers designed for oil return at minimum load is rarely serious at full load. When multiple compressors are used, one or more may shut down while another continues to operate, and the maximum-tominimum ratio becomes much larger. This may make a double suction riser necessary. It is good practice to give some pitch to these lines toward the compressor.
Avoid traps, but when that is impossible, the risers from them are treated the same as those leading from the evaporators. Preventing Oil Trapping in Idle Evaporators. Suction lines should be designed so that oil from an active evaporator does not drain into an idle one. Figure 4A shows multiple evaporators on different floor levels with the compressor above. Each suction line is brought upward and looped into the top of the common suction line to prevent oil from draining into inactive coils.
Figure 4B shows multiple evaporators stacked on the same level, with the compressor above. Oil cannot drain into the lowest evaporator because the common suction line drops below the outlet of the lowest evaporator before entering the suction riser.
Figure 4C shows multiple evaporators on the same level, with the compressor located below. The suction line from each evaporator drops down into the common suction line so that oil cannot drain into an idle evaporator. An alternative arrangement is shown in Figure 4D for cases where the compressor is above the evaporators. Figure 5 shows typical piping for evaporators above and below a common suction line. All horizontal runs should be level or pitched toward the compressor to ensure oil return.
Expansion valve bulbs are located on the suction lines between the evaporator and these traps. The traps serve as drains and help prevent liquid from accumulating under the expansion valve bulbs during compressor off cycles. They are useful only where straight runs or risers are encountered in the suction line leaving the evaporator outlet. Suction Piping Suction piping should be designed so that all compressors run at the same suction pressure and oil is returned in equal proportions.
All suction lines should be brought into a common suction header to return oil to each crankcase as uniformly as possible. Header design can freely pass the suction gas and oil mixture or provide a suction trap for the oil. The header should be run above the level of the compressor suction inlets so oil can drain into the compressors by gravity. Figure 6 shows a pyramidal or yoke-type suction header to maximize pressure and flow equalization at each of three compressor suction inlets piped in parallel.
This type of construction is recommended for applications of three or more compressors in parallel. For two compressors in parallel, a single feed between the two compressor takeoffs is acceptable. Although not as good for equalizing flow and pressure drops to all compressors, one alternative is to have the suction line from evaporators enter at one end of the header instead of using the yoke arrangement.
The suction header may have to be enlarged to minimize pressure drop and flow turbulence. Return mains from the evaporators should not be connected into the suction header to form crosses with the branch suction lines to the compressors. The header should be full size based on the largest mass flow of the suction line returning to the This file is licensed to Osama Khayata [email protected]. Halocarbon Refrigeration Systems compressors. Takeoffs to the compressors should either be the same size as the suction header or be constructed so that oil will not trap in the suction header.
Branch suction lines to the compressors should not be reduced until the vertical drop is reached. Suction traps are recommended wherever 1 parallel compressors, 2 flooded evaporators, 3 double suction risers, 4 long suction lines, 5 multiple expansion valves, 6 hot-gas defrost, 7 reverse-cycle operation, or 8 suction-pressure regulators are used.
Depending on system size, the suction header may be designed to function as a suction trap. The suction header should be large enough to provide a low-velocity region in the header to allow suction gas and oil to separate. See the section on Low-Pressure Receiver Sizing in Chapter 4 to find recommended velocities for separation.
Suction gas flow for individual compressors should be taken off the top of the suction header. Oil can be returned to the compressor directly or through a vessel equipped with a heater to boil off refrigerant and then allow oil to drain to the compressors or other devices used to feed oil to the compressors.
The suction trap must be sized for effective gas and liquid separation. Adequate liquid volume and a means of disposing of it must be provided. A liquid transfer pump or heater may be used. Chapter 4 has further information on separation and liquid transfer pumps. An oil receiver equipped with a heater effectively evaporates liquid refrigerant accumulated in the suction trap.
It also ensures that each compressor receives its share of oil. Either crankcase float valves or external float switches and solenoid valves can be used to control the oil flow to each compressor. A gravity-feed oil receiver should be elevated to overcome the pressure drop between it and the crankcase.
The oil receiver should be sized so that a malfunction of the oil control mechanism cannot overfill an idle compressor. Figure 7 shows a recommended hookup of multiple compressors, suction trap accumulator , oil receiver, and discharge line oil separators. The oil receiver also provides a reserve supply of oil for compressors where oil in the system outside the compressor varies with system loading.
The heater mechanism should always be submerged. Discharge Piping The piping arrangement in Figure 6 is suggested for discharge piping. The piping must be arranged to prevent refrigerant liquid Fig. A check valve in the discharge line may be necessary to prevent refrigerant and oil from entering the compressor heads by migration.
It is recommended that, after leaving the compressor head, the piping be routed to a lower elevation so that a trap is formed to allow drainback of refrigerant and oil from the discharge line when flow rates are reduced or the compressors are off. If an oil separator is used in the discharge line, it may suffice as the trap for drainback for the discharge line. Avoid using a bullheaded tee at the junction of two compressor branches and the main discharge header: this configuration causes increased turbulence, increased pressure drop, and possible hammering in the line.
When an oil separator is used on multiple-compressor arrangements, oil must be piped to return to the compressors. This can be done in various ways, depending on the oil management system design.
Oil may be returned to an oil receiver that is the supply for control devices feeding oil back to the compressors. Interconnecting Crankcases When two or more compressors are interconnected, a method must be provided to equalize the crankcases. Some compressor designs do not operate correctly with simple equalization of the crankcases. For these systems, it may be necessary to design a positive oil float control system for each compressor crankcase.
A typical system allows oil to collect in a receiver that, in turn, supplies oil to a device that meters it back into the compressor crankcase to maintain a proper oil level Figure 7. Compressor systems that can be equalized should be placed on foundations so that all oil equalizer tapping locations are exactly level.
If crankcase floats as in Figure 7 are not used, an oil equalization line should connect all crankcases to maintain uniform oil levels. The oil equalizer may be run level with the tapping, or, for convenient access to compressors, it may be run at the floor Figure 8. It should never be run at a level higher than that of the tapping.
For the oil equalizer line to work properly, equalize the crankcase pressures by installing a gas equalizer line above the oil level. This line may be run to provide head room Figure 8 or run level with tapping on the compressors.
It should be piped so that oil or liquid refrigerant will not be trapped. Both lines should be the same size as the tapping on the largest compressor and should be valved so that any one machine can be taken out for repair. The piping should be arranged to absorb vibration. Shell-and-tube flooded coolers designed to minimize liquid entrainment in the suction gas require a continuous liquid bleed line Figure 9 installed at some point in the cooler shell below the liquid level to remove trapped oil.
This continuous bleed of refrigerant liquid and oil prevents the oil concentration in the cooler from getting too high. The location of the liquid bleed connection on the shell depends on the refrigerant and oil used. For refrigerants that are highly miscible with the oil, the connection can be anywhere below the liquid level. Refrigerant 22 can have a separate oil-rich phase floating on a refrigerant-rich layer. This becomes more pronounced as evaporating temperature drops.
When R is used with mineral oil, the bleed line is usually taken off the shell just slightly below the liquid level, or there may be more than one valved bleed connection at slightly different levels so that the optimum point can be selected during operation.
The solubility charts in Chapter 12 give specific information. Where the flooded cooler design requires an external surge drum to separate liquid carryover from suction gas off the tube bundle, the richest oil concentration may or may not be in the cooler. In some cases, the surge drum has the highest concentration of oil. Here, the refrigerant and oil bleed connection is taken from the surge drum.
The refrigerant and oil bleed from the cooler by gravity. The bleed sometimes drains into the suction line so oil can be returned to the compressor with the suction gas after the accompanying liquid refrigerant is vaporized in a liquid-suction heat interchanger. Refrigerant Feed Devices For further information on refrigerant feed devices, see Chapter The pilot-operated low-side float control Figure 9 is sometimes selected for flooded systems using halocarbon refrigerants.
Except for small capacities, direct-acting low-side float valves are impractical for these refrigerants. The displacer float controlling a pneumatic valve works well for low-side liquid level control; it allows the cooler level to be adjusted within the instrument without disturbing the piping. High-side float valves are practical only in single-evaporator systems, because distribution problems result when multiple evaporators are used. Float chambers should be located as near the liquid connection on the cooler as possible because a long length of liquid line, even if insulated, can pick up room heat and give an artificial liquid level in the float chamber.
Equalizer lines to the float chamber must be amply sized to minimize the effect of heat transmission. The float chamber and its equalizing lines must be insulated. Each flooded cooler system must have a way of keeping oil concentration in the evaporator low, both to minimize the bleedoff needed to keep oil concentration in the cooler low and to reduce system losses from large stills.
At low temperatures, periodic warm-up of the evaporator allows recovery of oil accumulation in the chiller. If continuous operation is required, dual chillers may be needed to deoil an oil-laden evaporator, or an oil-free compressor may be used.
Figure 10 shows typical piping connections for a multicircuit direct-expansion DX chiller. Each circuit contains its own thermostatic expansion and solenoid valves. One solenoid valve can be wired to close at reduced system capacity. The thermostatic expansion valve bulbs should be located between the cooler and the liquid-suction interchanger, if used. Locating the bulb downstream from the interchanger can cause excessive cycling of the thermostatic expansion valve because the flow of high-pressure liquid through the interchanger ceases when the thermostatic expansion valve closes; consequently, no heat is available from the high-pressure liquid, and the cooler must starve itself to obtain the superheat necessary to open the valve.
When the valve does open, excessive superheat causes it to overfeed until the bulb senses liquid downstream from the interchanger. Therefore, the remote bulb should be positioned between the cooler and the interchanger. Figure 11 shows a typical piping arrangement that has been successful in packaged water chillers with DX coolers.
With this arrangement, automatic recycling pumpdown is needed on the lag compressor to prevent leakage through compressor valves, allowing migration to the cold evaporator circuit. It also prevents liquid from slugging the compressor at start-up.
On larger systems, the limited size of thermostatic expansion valves may require use of a pilot-operated liquid valve controlled by a small thermostatic expansion valve Figure The equalizing Fig. A small solenoid valve in the pilot line shuts off the high side from the low during shutdown. However, the main liquid valve does not open and close instantaneously. The most common ways of arranging DX coils are shown in Figures 13 and The method shown in Figure 14 provides the superheat needed to operate the thermostatic expansion valve and is effective for heat transfer because leaving air contacts the coldest evaporator surface.
This arrangement is advantageous on low-temperature applications, where the coil pressure drop represents an appreciable change in evaporating temperature.
Direct-expansion air coils can be located in any position as long as proper refrigerant distribution and continuous oil removal facilities are provided.
Figure 13 shows top-feed, free-draining piping with a vertical up-airflow coil. In Figure 14, which shows a horizontal-airflow coil, suction is taken off the bottom header connection, providing free oil draining. Many coils are supplied with connections at each end of the suction header so that a free-draining connection can be used regardless of which side of the coil is up; the other end is then capped. In Figure 15, a refrigerant upfeed coil is used with a vertical downflow air arrangement.
Here, the coil design must provide sufficient gas velocity to entrain oil at lowest loadings and to carry it into the suction line. Pumpdown compressor control is desirable on all systems using downfeed or upfeed evaporators, to protect the compressor against Fig.
Thermostatic expansion valve operation and application are described in Chapter Thermostatic expansion valves should be sized carefully to avoid undersizing at full load and oversizing at partial load. The refrigerant pressure drops through the system distributor, coil, condenser, and refrigerant lines, including liquid lifts must be properly evaluated to determine the correct pressure drop available across the valve on which to base the selection.
Variations in condensing pressure greatly affect the pressure available across the valve, and hence its capacity. Oversized thermostatic expansion valves result in cycling that alternates flooding and starving the coil. This occurs because the valve attempts to throttle at a capacity below its capability, which This file is licensed to Osama Khayata [email protected].
They extend to a lower point on the suction line to allow gravity flow. Included in this oil return line is 1 a solenoid valve that is open only while the compressor is running and 2 a metering valve that is adjusted to allow a constant but small-volume return to the suction line. A liquid-line sight glass may be installed downstream from the metering valve to serve as a convenient check on liquid being returned.
Oil can be returned satisfactorily by taking a bleed of refrigerant and oil from the pump discharge Figure 17 and feeding it to the heated oil receiver. If a low-side float is used, a jet ejector can be used to remove oil from the quiescent float chamber.
Reduced compressor capacity further aggravates this problem. Systems having multiple coils can use solenoid valves located in the liquid line feeding each evaporator or group of evaporators to close them off individually as compressor capacity is reduced. For information on defrosting, see Chapter Flooded Evaporators Flooded evaporators may be desirable when a small temperature differential is required between the refrigerant and the medium being cooled.
A small temperature differential is advantageous in low-temperature applications. In a flooded evaporator, the coil is kept full of refrigerant when cooling is required. The refrigerant level is generally controlled through a high- or low-side float control. Figure 16 represents a typical arrangement showing a low-side float control, oil return line, and heat interchanger. Circulation of refrigerant through the evaporator depends on gravity and a thermosiphon effect. A mixture of liquid refrigerant and vapor returns to the surge tank, and the vapor flows into the suction line.
A baffle installed in the surge tank helps prevent foam and liquid from entering the suction line. A liquid refrigerant circulating pump Figure 17 provides a more positive way of obtaining a high circulation rate.
Taking the suction line off the top of the surge tank causes difficulties if no special provisions are made for oil return. For this reason, the oil return lines in Figure 16 should be installed. These lines 7. Although a low pressure drop is desired, oversized hot-gas lines can reduce gas velocities to a point where the refrigerant will not transport oil.
Therefore, when using multiple compressors with capacity control, hot-gas risers must transport oil at all possible loadings. Minimum capacities for oil entrainment in hot-gas line risers are shown in Table On multiple-compressor installations, the lowest possible system loading should be calculated and a riser size selected to give at least the minimum capacity indicated in the table for successful oil transport.
In some installations with multiple compressors and with capacity control, a vertical hot-gas line, sized to transport oil at minimum load, has excessive pressure drop at maximum load.
When this problem exists, either a double riser or a single riser with an oil separator can be used. Double Hot-Gas Risers. A double hot-gas riser can be used the same way it is used in a suction line. Figure 18 shows the double riser principle applied to a hot-gas line.
Its operating principle and sizing technique are described in the section on Double Suction Risers. As an alternative, an oil separator in the discharge line just before the riser allows sizing the riser for a low pressure drop. Any oil draining back down the riser accumulates in the oil separator. With large multiple compressors, separator capacity may dictate the use of individual units for each compressor located between the discharge line and the main discharge header.
Additional info preview on request. Individual chapters may also be purchased as digital downloads in PDF format. Ashrae Hvac Fundamentals Handbook. This revised edition presents those chapter updates as originally intended by the cognizant Technical Committees TCs. Comb CC and Worldcat refrigeration titles K lote "In handbook form to be useful to practicing engineers and. Additions and corrections to Handbook volumes in print will be published in the Handbook published the year following their verification and, as soon as verified, on the ASHRAE Internet Web site.
Ashrae handbook of fundamentals. Price Download Download PDF. Compliance to the Design Manual, which promulgates minimum performance design standards for VA owned and leased new buildings and renovated facilities,. With more than 50, members from over nations, ASHRAE is a diverse organization dedicated to advancing the arts and sciences of heating, ventilation, air conditioning and refrigeration to serve humanity and promote a sustainable world.
Today, I will share to everyone. Its more than 1, pages cover basic principles suchas thermodynamics, psychrometrics, and heat transfer, and provide practicalguidance on building envelope, indoor environmental quality, load calculations,duct and piping system design, refrigerants, energy. Spend less. Supersedes Handbook July 16, User-contributed reviews Tags. The following are among significant changes made in the edition of the standard The scope is changed to remove commentary and to more specifically identify occupancies.
The concern with humidity has always been one of preventing static discharge, which everyone has experienced on cold winter days when the air is very dry. Telephone worldwide. Tiu chun. Carlos Martinez. Priced From 49 PDF. This Handbook is considered to be the most comprehensive and authoritative repository of practical knowledge on various topics that form the area of heating, ventilation,. Of data centers cooling is the ashrae operating ranges, because they refer to.
PDF, This Handbook is considered to be the most comprehensive and authoritative repository of practical knowledge on various topics that form the. Most notably, the edition incorporates content in support of the new framework introduced in , which divided the standard into three distinct sections hospital. T his information helps system designers and operators in selecting and using equipment. Featuring pictorial outlines of each fitting, this database is useful to design engineers dealing with a variety of duct.
Samir Rabia. Example 3. Its more than 1, pages cover basic principles such as thermodynamics, psychrometrics, and heat transfer, and provide practical guidance on building envelope, indoor environmental quality, load calculations, duct and piping system design, refrigerants, energy.
The Construction Information Service brings together a comprehensive collection of essential technical documents from a wide range of publishers in one online package. The ASHRAE Technical Committees that prepare these chapters provide new information, clarify existing content, delete obsolete materials, and reorganize chapters to make the Handbook more understandable and easier to use. Print-all or PDF-all into a single file.
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|Adobe photoshop cs6 software download for windows 7||The 11th edition continues in the tradition of previous editions, visit web page easily transportable and. Enio Pedone Bandarra Filho. Pressure loss through any one of the parallel circuits is always equal to that through any of the others, even if it results in filling much of one circuit with liquid while gas passes through another. Handbook Ashrae Org Nov 27, Acces PDF Handbook Ashrae Org Handbook Ashrae Org As recognized, adventure as well as experience virtually lesson, amusement, as with ease as bargain can be gotten by just checking out a asjrae handbook ashrae org furthermore it is not directly done, you could say yes even more more frer less this life, on the. It also ensures that each compressor receives its share of oil.|
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