Trane TRG-TRC012-EN manuale d’uso

Air Conditioning Clinic Helical-Rotary W ater Chillers One of the Equipment Series TRG-TRC012-EN[...]

Helical-Rotary W ater Chillers One of the Equipment Series A publication of The T rane Company— W orldwide Applied Systems Group[...]

Preface © 1999 American Standard Inc. All rights reserved TRG-TRC012-EN ii The T rane Company believes that it’ s incumbent on manufacturers to serve the industry by regularly disseminating information gathered through laboratory research, testing programs and field experience. The T rane Air Conditioning Clinic series is one means of knowledge [...]

TRG-TRC012-EN iii Contents Introduction ............................................................ 1 period one Components ........................................................... 3 Compressor ............................................................. 4 Oil Separator ............................................................ 8 Condenser .[...]

iv TRG-TRC012-EN[...]

TRG-TRC012-EN 1 notes Introduction W ater chillers are used in a variety of air conditioning and process cooling applications. They are used to make cold water that can be transported throughout a facility using pumps and pipes. This cold water can be passed through the tubes of coils in order to cool the air in an air conditioning application or i[...]

2 TRG-TRC012-EN notes Introduction W ater chillers using the vapor-compression refrigeration cycle vary by the type of compressor used. Reciprocating and scroll compressors are typically used in smaller chillers. Helical-rotary (or screw) compressors are typically used in medium-sized chillers. Centrifugal compressors are typically used in larger c[...]

TRG-TRC012-EN 3 notes period one Components Many of the components of the helical-rotary water chiller are similar to those of other chiller types. This particular helical-rotary water chiller makes use of a shell-and-tube evaporator where refrigerant evaporates inside the shell and water flows inside tubes. The compressor is a twin-rotor , helical[...]

4 TRG-TRC012-EN notes period one Components Compressor The helical-rotary chiller uses 2 screw-like rotors to perform the compression process. The rotors are meshed and fit, with very close tolerances, within a housing. Only the male rotor is driven by the compressor motor . The lobes of the male rotor engage and drive the female rotor , causing th[...]

TRG-TRC012-EN 5 period one Components notes In the operation of the helical-rotary compressor , refrigerant vapor enters the compressor housing through the intake port . The intake port in this example is at the top of the compressor housing. The entering refrigerant vapor is at a low , suction pressure and fills the grooves or pockets formed by th[...]

6 TRG-TRC012-EN notes period one Components Viewing the compressor from the side shows that after the pockets of refrigerant travel to the right past the intake port area, the vapor , still at suction pressure, is confined within the pockets by the compressor housing. Viewing the compressor from the top shows that rotation of the meshed rotor lobes[...]

TRG-TRC012-EN 7 period one Components notes Continued rotation of the rotors causes the meshing point to travel toward the discharge end of the compressor , driving the trapped refrigerant vapor ahead of it. This action progressively reduces the volume of the pockets, compressing the refrigerant. Finally , when the pockets of refrigerant reach the [...]

8 TRG-TRC012-EN notes period one Components Oil Separator The oil leaves the compressor entrained within the discharged refrigerant vapor . The oil is recovered from the discharged refrigerant by an oil separator , which can have an efficiency of greater than 99%. The separator consists of a vertical cylinder surrounding an exit passageway . As the[...]

TRG-TRC012-EN 9 period one Components notes operation and is, therefore, constantly moving to lower pressure areas of the chiller . In this system, oil flows in 2 distinct paths, each performing a separate function: 1) bearing lubrication and cooling and 2) rotor oil injection. Oil leaves the sump and passes through an oil filter and master solenoi[...]

10 TRG-TRC012-EN notes period one Components Cooling water flows first through the lower tubes of the condenser and then through the upper tubes. This produces a nearly constant temperature difference between the downward moving refrigerant and the tube surfaces, resulting in a uniform heat transfer rate within the tube bundle. Subcooled liquid ref[...]

TRG-TRC012-EN 11 period one Components notes Expansion Device An expansion device is used to maintain the pressure difference between the high-pressure (condenser) and low-pressure (evaporator) sides of the system, as established by the compressor . This pressure difference allows the evaporator temperature to be low enough to absorb heat from the [...]

12 TRG-TRC012-EN notes period one Components The orifice plate is another type of expansion device found in helical-rotary chillers. The column of liquid refrigerant creates a head pressure at its base, allowing it to pass through the orifices and undergo a pressure drop equal to the head (H) before it flashes. As the load decreases, less refrigera[...]

TRG-TRC012-EN 13 period one Components notes By removing the vapor portion of the mixture before it gets to the evaporator the separator enhances the effectiveness of the evaporation process. Evaporator In the flooded shell-and-tube evaporator cool, low-pressure liquid refrigerant enters the distribution system inside the shell and is distributed u[...]

14 TRG-TRC012-EN notes period one Components Another type of evaporator found in helical-rotary chillers is the direct expansion (DX) shell-and-tube evaporator . In this type of evaporator the cool, low-pressure liquid refrigerant flows through the tubes and water fills the surrounding shell. As heat is transferred from the water to the refrigerant[...]

TRG-TRC012-EN 15 period one Components notes Controls and Starter A microprocessor -based control panel is provided on the chiller to provide accurate chilled water control as well as monitoring, protection, and adaptive limit functions. These controls monitor the chiller’ s operation and prevent the chiller from operating outside of its limits. [...]

16 TRG-TRC012-EN notes A pressure-enthalpy (p- h ) chart illustrates the refrigeration cycle of the helical- rotary water chiller . But first, lets review the components of the helical-rotary chiller’ s refrigeration cycle... Refrigerant vapor leaves the evaporator and flows to the compressor where it is compressed to a higher pressure and temper[...]

TRG-TRC012-EN 17 period two Refrigeration Cycle notes separated from the mixture and routed directly to the suction side of the compressor and the remaining liquid refrigerant enters the evaporator . In the evaporator , the liquid refrigerant boils as it absorbs heat from water . The resulting vapor is drawn back to the compressor to repeat the cyc[...]

18 TRG-TRC012-EN notes period two Refrigeration Cycle The theoretical vapor -compression refrigeration cycle for a helical-rotary water chiller can be plotted on a pressure-enthalpy chart. The refrigerant leaves the evaporator as saturated vapor ➀ and flows to the suction end of the compressor where it enters the compartment for the suction- gas-[...]

TRG-TRC012-EN 19 period two Refrigeration Cycle notes Manufacturers are continuously improving their designs of helical-rotary water chillers. New chillers need to be designed around the characteristics of the refrigerant. T oday there are 5 strong candidates for use with positive- displacement, helical-rotary chillers. They are HCFC-22, HFC-134a, [...]

20 TRG-TRC012-EN notes period two Refrigeration Cycle T oday the most commonly used refrigerant in helical-rotary chillers is HCFC-22. Due to the scheduled phaseout of HCFC-22, most helical-rotary chillers will be redesigned using HFC refrigerants. Many challenges are encountered when redesigning a chiller to use a refrigerant with different thermo[...]

TRG-TRC012-EN 21 notes period three Compressor Capacity Control The capacity of the helical-rotary compressor presented in this clinic is controlled by a slide valve that is an integral part of the compressor housing. Other helical-rotary compressor designs may use a variety of methods to vary capacity . Some of these methods are similar in functio[...]

22 TRG-TRC012-EN notes period three Compressor Capacity Control At full load, the slide valve is closed. The compressor pumps its maximum volume of refrigerant, discharging it through both the radial and axial ports. At part load, the slide valve modulates toward the open position. The opening created by the valve movement allows refrigerant vapor [...]

TRG-TRC012-EN 23 period three Compressor Capacity Control notes As the slide valve continues to open, further unloading the compressor , its radial discharge port eventually travels past the opening in the compressor housing. Once this occurs, all of the refrigerant vapor being pumped by the compressor is discharged through the axial port in the co[...]

24 TRG-TRC012-EN notes period three Compressor Capacity Control The slide valve is operated by a piston and cylinder assembly . Extension and retraction of the operator shaft positions the slide valve along the compressor rotors. High-pressure refrigerant vapor , controlled by 2 solenoid valves, is fed to or bled from this assembly in order to posi[...]

TRG-TRC012-EN 25 notes period four Maintenance Considerations This period discusses general maintenance requirements of helical-rotary water chillers. Although some of the information applies specifically to the design presented in this clinic, requirements for other helical-rotary chiller designs are also included. Once a helical-rotary chiller is[...]

26 TRG-TRC012-EN notes period four Maintenance Considerations The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has published Guideline 3 titled Reducing Emission of Halogenated Refrigerants in Refrigeration and Air Conditioning Equipment and Systems . This guideline includes a recommended list of data points to[...]

TRG-TRC012-EN 27 period four Maintenance Considerations notes Direct-drive, semi-hermetic compressor designs require no periodic maintenance on the compressor/motor assembly . The compressor contains only 3 main moving parts: the male and female rotors and the slide valve. The semi-hermetic motor eliminates the need for external shaft seals associa[...]

28 TRG-TRC012-EN notes period four Maintenance Considerations Some helical-rotary compressor designs do require periodic maintenance of mechanical system components. This includes oil and refrigerant filter changes, oil strainer changes, and a compressor rotor inspection. Open-motor compressor designs require shaft alignment, coupling inspection, b[...]

TRG-TRC012-EN 29 period four Maintenance Considerations notes determine the level of water treatment required to remove contaminants from the cooling tower water . Scale deposits are best removed by chemical means. The water -cooled condenser is commonly isolated from the rest of the cooling tower water circuit by valves, and a pump circulates clea[...]

30 TRG-TRC012-EN notes period four Maintenance Considerations Refrigerant analysis measures contamination levels and determines suitability for continued use. It can also determine the acceptability of recycled refrigerant for reuse. Refrigerant analysis helps extend the life of the existing charge and ensures that the chiller is operating at peak [...]

TRG-TRC012-EN 31 notes period five Application Considerations There are several considerations to address when applying helical-rotary water chillers, including: ■ Air -cooled or water-cooled condensing ■ Condensing temperature control ■ Constant or variable evaporator water flow ■ Short evaporator water loops ■ Equipment certification st[...]

32 TRG-TRC012-EN notes period five Application Considerations is the elimination of the cooling tower . This eliminates the concerns and maintenance requirements associated with water treatment, makeup water availability and quality , tower mechanical maintenance, freeze protection, and chiller condenser tube cleaning. This reduced maintenance requ[...]

TRG-TRC012-EN 33 period five Application Considerations notes and temperatures that the air -cooled chiller . Generally , air-cooled chillers last 15 to 20 years, while water -cooled chillers last 20 to 25 years. T o summarize the comparison of air -cooled and water-cooled helical-rotary chillers, air -cooled chiller advantages include lower mainte[...]

34 TRG-TRC012-EN notes period five Application Considerations Controlling the refrigerant pressure difference between the evaporator and condenser of a water -cooled chiller is accomplished by varying the temperature or flow rate of the water flowing through the condenser . The following are 5 common methods used to control condensing temperature: [...]

TRG-TRC012-EN 35 period five Application Considerations notes Constant or V ariable Evaporator Water Flow In previous designs, chillers were required to maintain a constant flow rate of water through the evaporator . This requirement has changed due to advances in chiller controls. Increased sensing and control capabilities now allow chiller manufa[...]

36 TRG-TRC012-EN notes period five Application Considerations 1) The water flow rate through the chiller’ s evaporator must stay between the minimum and maximum evaporator bundle flow rates as specified by the chiller manufacturer . These limits depend on the specific details of the actual evaporator bundle, such as the number of tubes, number of[...]

TRG-TRC012-EN 37 period five Application Considerations notes Short water loops may be unavoidable in close-coupled or very small applications, particularly in systems where the load consists of only a few air handlers or processes. T o prevent the effect of a short water loop, a storage tank or large header pipe can be added to the system to incre[...]

38 TRG-TRC012-EN notes period five Application Considerations Equipment Certification Standards The Air Conditioning & Refrigeration Institute (ARI) establishes rating standards for packaged HV AC equipment. ARI also certifies and labels equipment through programs that involve random testing of a manufacturer’ s equipment to verify published [...]

TRG-TRC012-EN 39 period five Application Considerations notes The standard rating conditions used for ARI certification represent typical design temperatures and flow rates for which water -cooled and air-cooled systems are designed. They are not suggestions for good design practice for a given system, they are simply a common rating point. T rends[...]

40 TRG-TRC012-EN notes Let’ s review the main concepts that were covered in this clinic on helical-rotary water chillers. In Period 1, the following components of a helical-rotary water chiller were discussed: compressor , oil separator , oil supply system, condenser , expansion device, liquid/vapor separator , evaporator , starter , and controls[...]

TRG-TRC012-EN 41 period six Review notes In Period 2, the refrigeration cycle of the helical-rotary water chiller was examined on a pressure-enthalpy chart. Also, the performance characteristics of the various refrigerants were compared. In Period 3, the operation of the modulating slide valve was explained. The slide valve is one method by which a[...]

42 TRG-TRC012-EN notes period six Review In Period 4, the general maintenance requirements of a helical-rotary water chiller were discussed, including: ■ Recommended data to be logged daily ■ Required and recommended maintenance of the mechanical components ■ Required and recommended maintenance of the heat transfer surfaces ■ Recommended a[...]

TRG-TRC012-EN 43 period six Review notes For more information, refer to the following references: ■ T rane product catalogs for helical-rotary water chiller products (T rane literature order numbers RLC-DS-1, RLC-DS-2, RLC-DS-4, and RLC-DS-6) ■ W ater-Cooled Series R ® Chiller—Model R THC Mechanical Operation (RLC-EB-16) ■ Series R ® CenT[...]

44 TRG-TRC012-EN Questions for Period 1 1 What components of the helical-rotary compressor are used to compress the refrigerant? 2 What are the 2 functions of the oil supply system presented in this clinic? 3 In a flooded shell-and-tube evaporator , is the refrigerant flowing inside or outside of the tubes? 4 Name 2 types of expansion devices commo[...]

TRG-TRC012-EN 45 Quiz Questions for Period 3 7 At full load, is the slide valve fully closed or fully open? 8 Explain how the slide valve varies the refrigerant flow rate through the helical-rotary compressor . Questions for Period 4 9 What document recommends the data points to be logged daily for each chiller? 10 List 3 advantages to performing a[...]

46 TRG-TRC012-EN 1 Male and female screw rotors 2 Bearing lubrication and cooling, and rotor oil injection 3 Outside of the tubes 4 Electronic expansion valve and orifice plate 5) a) compression b) condensation (desuperheat, condense, subcool) c) expansion d) evaporation 6 Point 1, the suction inlet of the compressor 7 Fully closed 8 At part load, [...]

TRG-TRC012-EN 47 air -cooled condenser A type of condenser that rejects the heat of the refrigerant to air flowing through it. ARI Air Conditioning & Refrigeration Institute ARI Standard 550/590 A publication, titled “Standard for W ater Chilling Packages Using the V apor-Compression Cycle”, used to promote consistent rating and testing met[...]

48 TRG-TRC012-EN Glossary vapor is directed back to the compressor while the liquid refrigerant travels on to the evaporator . oil separator The component of the chiller used to remove oil from the refrigerant vapor after it is discharged from the compressor . This oil is directed back to the compressor . orifice plate A type of expansion device th[...]

NO PO STAG E NEC ES SAR Y IF M AIL ED IN THE UNITED STA TES B USINESS RE PL Y M AIL FIRST -CLASS MAIL LA CROSSE, WI PERMIT NO. 1 1 POST AGE W ILL BE P AID BY ADDRESSEE THE TRANE COMP ANY Attn: Applicat ions Engin eering 3600 P am mel Cr eek R oa d La C ros se W I 546 01-99 85 NO PO STAG E NEC ES SAR Y IF M AIL ED IN THE UNITED STA TES B USINESS RE [...]

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The T rane Company Worldwide Applied Systems Group 3600 Pammel Creek Road La Crosse, WI 54601-7599 www . trane.com An American Standard Company Literature Order Number TRG-TRC012-EN File Number E/A V-FND-TRG-TRC012-899-EN Supersedes 2803-15-888 Stocking Location Inland-La Crosse Since The T rane Company has a policy of continuous product improvemen[...]