part e : evacuation and dehydration

Evacuation and Dehydration

Section 1 Part E Issue 7.7 : 12/19 of 24

Part E : Evacuation and Dehydration Contents

1. Introduction ................................................................................................................... 2 2. Definitions ..................................................................................................................... 2

2.1. Evacuation ............................................................................................................................... 2 2.2. Complete Packaged Refrigeration Systems ............................................................................ 2 2.3. Site Erected Refrigeration Systems ......................................................................................... 3

3. Principles of Evacuation ................................................................................................ 3 3.1. Evacuation and Moisture Removal Method ............................................................................. 4 3.2. Vacuum Pressure Units ........................................................................................................... 5

4. Equipment for Evacuation ............................................................................................. 6 4.1. Vacuum Pressure Gauge ......................................................................................................... 6 4.2. Vacuum Pump ......................................................................................................................... 7 4.3. Connection Lines ................................................................................................................... 10 4.4. Charging Nitrogen Gas .......................................................................................................... 10

5. Personnel Permitted to Evacuate the System ............................................................ 10 6. Personal Protection ..................................................................................................... 10 7. Before Evacuation Takes Place .................................................................................. 11

7.1. Preparing the Plant for Evacuation ........................................................................................ 11 7.2. Preparing the Vacuum Pump for Operation ........................................................................... 11

8. Evacuation Procedures ............................................................................................... 12 8.1. Evacuation Procedure for Complete Packaged Refrigeration Systems ................................. 12 8.2. Evacuation Procedure for Site Erected Refrigeration Systems .............................................. 14 8.3. Pressure Rise Test ................................................................................................................ 17

9. Test Certification ......................................................................................................... 17 10. Faults and Remedies .................................................................................................. 17

10.1. Failure to Obtain the Required Vacuum ................................................................................. 17 10.2. Fault Condition – Moisture in the System .............................................................................. 18

10.2.1. Small Amounts of Moisture Present in the System ......................................................... 18 10.2.2. Free-water Present in the System ................................................................................... 19

10.3. Moisture Removal - System Cleaning Procedures................................................................. 19 10.4. Low Temperature Moisture Trap (Cold Trap) ......................................................................... 20

11. Disposal of Contaminated Oil and Refrigerant ........................................................... 20 12. References for Further Information ............................................................................. 22 13. Appendix 1 System Pressure Test and Evacuation Certificate .................................. 23

List of Figures Fig 1(e) Types of Vacuum Gauge ........................................................................................................... 6 Fig 2(e) Typical Vacuum Pump .............................................................................................................. 7 Fig 3(e) Gas Ballast Operation ............................................................................................................... 9 Fig 4(e) Saturated Vapour Curve for Water .......................................................................................... 16 Fig 5(e) Low Temperature Moisture Trap (Cold Trap) .......................................................................... 21

List of Tables Table 1(e) Minimum Vacuum Pressure Needed to Achieve Moisture Removal ..................................... 4 Table 2(e) Pressure Unit Conversions .................................................................................................... 5 Table 3(e) Suggested Vacuum Pump Displacement/System Cooling Capacity ..................................... 8 Table 4(e) References For Further Information .................................................................................... 22

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Part E Section 1 of 24 Issue 7.7 : 12/19

1. Introduction This publication describes the evacuation procedure used to remove air and moisture present within the primary refrigeration system. Evacuation and dehydration must be carried out:

During Commissioning As part of the installation and commissioning process, after Installation (described in Part C) and Tightness Testing (described in Part D). The procedures described in Part C : Installation are intended to minimise the amount of water vapour entering the system. Provided these procedures have been adhered too and tightness testing has been carried out correctly, evacuation should not be a lengthy process. During Operation After opening up the system for maintenance or repair. As part of the drying out procedure after free-water or an aqueous solution has accidentally entered the system, for example, a leaking shell and tube condenser or an evaporator used for liquid cooling.

Time spent on correct evacuation and dehydration is time well spent. If this process is not carried out properly, trouble may occur later which would impose a time penalty more than the few hours necessary to ensure proper evacuation.

NOTE: Remember that evacuation is an essential procedure and should NEVER be bypassed or foreshortened. Failure to evacuate the plant properly may invalidate the guarantee on the compressor. Refer to the compressor operator’s manual in Section 2 of the plant instruction manual.

2. Definitions For the purpose of this publication, the following definitions apply.

2.1. Evacuation The process of using a vacuum pump to remove the air from the system, dehydrating at the same time by reducing the air pressure until it is low enough for water to boil at ambient temperature.

2.2. Complete Packaged Refrigeration Systems A complete refrigeration plant: compressor, condenser, evaporator and interconnecting pipework, supplied already assembled (packaged) on a skid. The plant is strength and tightness tested at the factory, evacuated and shipped with a holding charge of dry nitrogen to prevent the ingress of air and moisture. Pressure gauges are fitted to the plant. If these register a fall in pressure, some or all of the holding charge has escaped. The leak must be traced and cured, and the plant pressure tested again; refer to Part D : Strength and Tightness Testing. Provided the nitrogen holding charge is intact, follow the procedures described in 7.1. Preparing the Plant for Evacuation and 8.1. Evacuation Procedure for Complete Packaged Refrigeration Systems.



2.3. Site Erected Refrigeration Systems The plant is supplied as one or more skid mounted packaged assemblies (compressor package, vessel package etc.), together with other major items (for example, a remote condenser) and auxiliary components for site erection. Skid mounted packaged assemblies are supplied already strength and tightness tested, evacuated and shipped with a holding charge of nitrogen. These assemblies are usually fitted with stop valves at the various connections permitting them to remain isolated during pressure testing and the initial stages of evacuation. If there has been a leak and the holding charge has escaped, or connections are fitted with blank flanges instead of stop valves, the assembly must be subjected to the same strength, tightness testing and evacuation procedures as the rest of the system. Follow the procedures described in 7.1. Preparing the Plant for Evacuation and 8.2. Evacuation Procedure for Site Erected Refrigeration Systems.

3. Principles of Evacuation Evacuation not only removes all the air from the system but also evaporates and removes any moisture that may be present. The principle underlying this is the fact that water is a refrigerant (R718) and like any other refrigerant has an exact pressure/temperature relationship. For example, at standard atmospheric pressure, 760 mm Hg, water boils in an open vessel at 100 °C, while at 2 mm Hg absolute its boiling point is reduced to -11 °C. Hence, by using a vacuum pump to reduce the pressure in the system, any free-water can be induced to boil (evaporate). However, the system remains full of saturated water vapour at whatever pressure exists at the time. The water content can be further reduced by breaking the vacuum with oxygen-free grade nitrogen to atmospheric pressure, then re-evacuating to say 2 mm Hg absolute, thereby reducing the volume of water vapour to 2/760, that is 1/380 of the volume before the vapour was diluted by introducing the nitrogen. As the water evaporates, the temperature falls. To keep the water boiling and prevent it from freezing, it is important to maintain an adequate difference between ambient temperature and the boiling point of the water vapour removed by the vacuum pump; this consideration is especially important during the early stages of evacuation. Even with system pressures of 2 mm Hg absolute and below, an ambient temperature of at least 5 °C is necessary. If the ambient temperature is too low, efforts must be made to increase it by warming the surroundings. Obviously, this will be impractical if the plant is installed outdoors. To be completely effective, evacuation must continue until the system pressure has fallen to 2 mm Hg absolute or below, and this pressure must be sustainable with the vacuum pump switched off. Pressures of this order cannot be achieved unless a suitable vacuum pump of the ‘gas ballast’ type is used; refer to 4.2. Vacuum Pump. To monitor these pressures it is necessary to use a barometrically compensated pressure gauge, designed to be accurate at low pressures; refer to 4.1. Vacuum Pressure Gauge.



3.1. Evacuation and Moisture Removal Method Once the integrity of the pipe work has been confirmed, by carrying out a strength and tightness test using Oxygen Free Nitrogen (OFN) in line with BS EN378:2016, the system will need to be evacuated to remove moisture and air from it. It is generally good practice to evacuate to below 1 mm Hg (1 torr) to remove air and moisture in a system. However, there may be circumstances when it is necessary to carry out a calculation to ensure that the evacuation has achieved an effective vacuum: (a) First measure the air temperature surrounding the refrigerant pipe

work both internally and externally, make a note the coldest temperature measurement (usually outside), connect gauges and a vacuum pump to the system and set it to run.

(b) As pressure starts to drop inside the pipework so does the boiling point of water and during evacuation ideally the pressure will reduce efficiently to allow any moisture inside the pipework to turn into steam and be drawn out by the vacuum pump.

(c) In order to achieve moisture removal from the pipe work, the pressure reading on the vacuum gauge must be lower than the boiling point of water from the coldest ambient temperature reading that was taken earlier.

The Table 1(e) can be used to work out the vacuum pressure needed to achieve moisture removal. For example at 10 °C ambient no moisture would be removed until a vacuum of 9.29 mm Hg (9.3 torr) is achieved.

Temp °C mm Hg Pressure torr

100 762 762

90 534 534

80 361 361

70 237 237

60 149 149

50 94 94

40 56 56

30 32 32

20 18 18

10 9.3 9.3

0 4.6 4.6

-10 1.73 1.73

-20 0.83 0.83

-30 0.29 0.29

Table 1(e) Minimum Vacuum Pressure Needed to Achieve Moisture Removal

NOTE: Moisture removal will only start once a vacuum below the equivalent temperature in the table level is achieved.



(d) With the vacuum below the table figure, periodically isolate the vacuum pump from the pipe work that the vacuum pump is connected to the service gauges are the easiest point. Check, if the pressure increases, this is an indication of moisture still being present. The moisture will evaporate (turn into vapour) and expand inside the pipe work resulting in loss of the vacuum. In this case continue evacuating the system and then check again periodically until the vacuum holds.

(e) If after completing the above there is still a pressure increase, the pipe work should be pressurised to 10 psig (0.7 barg) using oxygen free nitrogen. The nitrogen will aid moisture absorption which can then be safely vented.

(f) There is no set time limit for dehydration, when the moisture from the system has been successfully removed and the system holds a vacuum where the gauge pressure reading is less than the boiling point of water for the coldest point of the installation. At this point it is safe to introduce refrigerant and start the commissioning process.

3.2. Vacuum Pressure Units For purposes of standardisation and reference comparisons, atmospheric pressure at sea level has been universally accepted and established at 101325 Pascal (1.01325 bar) which is the equivalent to the pressure exerted by a column of mercury 760 mm Hg.

Unit of Pressure Bar (Pascal x 105)

Standard Atmosphere (atm)

Millibar (m bar)

torr Millimetre of Mercury (mm Hg)

Bar (Pascal x 105) 1 0.986923 1000 750.06168 750.06168

Standard Atmosphere (atm)

1.01325 1 1013.25 760 760

Millibar (m bar) 0.001 0.000986923 1 0.750062 0.750062

Millimetre of Mercury (mm Hg)

0.00133322 0.00131579 1.33322 1 1

Table 2(e) Pressure Unit Conversions

The fundamental SI unit of pressure is the Pascal and the derived unit is the bar (1 bar = Pascal x 105). However, the millimetre of mercury (mm Hg) is still widely used as a working unit in the vacuum field. Other pressure units are not recommended for use in vacuum work. Table 2(e) shows conversion factors to other units.



4. Equipment for Evacuation The following items of equipment are required for evacuation:

4.1. Vacuum Pressure Gauge The digital vacuum pressure gauge has largely replaced the traditional Bourdon gauge for vacuum pressure measurement; a typical example of both types is illustrated in Fig 1(e).

Digital Vacuum Gauge

Barometrically Compensated (Capsule) Dial Gauge

Fig 1(e) Types of Vacuum Gauge

The digital vacuum gauge offers improved accuracy across the gauge’s pressure range compared with a Bourdon gauge. If a Bourdon gauge is used it must be of the barometrically compensated (capsule) type to measure the degree of vacuum required for satisfactory evacuation. It is essential to use a vacuum gauge with a range of at least 0.5 to 9.0 millimetre of mercury (mm Hg). If the range is only 0.5 to 1.0 mm Hg it is impossible to determine if the failure to obtain the required vacuum is caused by a leak or by the presence of water vapour in the system. To verify the accuracy of the vacuum pressure gauge and therefore rely on the pressure reading, the gauge must be provided with a current calibration certificate.



4.2. Vacuum Pump A vacuum pump creates a void toward which the system pressure flows. As pressure decreases in the system during evacuation, flow also decreases. Therefore, it is IMPOSSIBLE to increase the pressure or flow through a gauge port by using a larger pump.

Fig 2(e) Typical Vacuum Pump

Most vacuum pumps are of the twin rotary blade type having one, two or three stages, depending on the degree of vacuum required, the whole mechanism usually being oil sealed.

WARNING If the plant is located in a Zone 2 hazardous area, the vacuum pump must be Zone 2 compliant.

When selecting a vacuum pump for refrigeration work, it is important to remember that the pump must not only be capable of producing the required vacuum, but must also maintain that vacuum for long periods. The pump must also have the facility to handle relatively large quantities of moisture in vapour form, plus the various refrigerant gases, which are condensable. During the compression portion of the vacuum pump cycle such vapours will often condense into liquids. When the discharge valve lifts, the vapour is forced into the oil in the oil bath. This liquid cannot escape from the oil and will re-enter the oil feed and then re-evaporate on the vacuum side of the pump, thus affecting the degree of vacuum that can be obtained.



Condensation in the oil bath can be prevented to some extent by using a vacuum pump fitted with a ‘gas ballast’ facility. This provision introduces air at atmospheric pressure, through a non-return valve, into the volume between the moving rotor and the pump discharge valve during the compression portion of the cycle. When this volume is compressed before expulsion, the discharge valve lifts before the partial pressure of the vapour component is sufficient to cause condensation. The principle of operation is illustrated in Fig 3(e). It must be appreciated that the gas ballast facility cannot be used during the final stages of evacuation if the degree of vacuum required is to be maintained. If a great deal of moisture has to be removed, the vacuum pump oil bath may become contaminated even if a gas ballast facility is fitted. Once this has occurred, the oil in the bath must be changed. Even if the oil does not show any visual signs of contamination (milky appearance), frequent oil changes are necessary to maintain maximum pumping efficiency. The oil used in the vacuum pump should be that recommended by the pump manufacturer. It is important to consider the displacement of the vacuum pump. A small displacement pump will take forever to achieve a deep vacuum on a large system. On the other hand, a large pump may reduce the pressure in a small system so quickly that moisture will ‘snap-freeze’ making it much more difficult to remove. Table 3(e) provides a general guide to vacuum pump displacement for a range of system cooling capacities. For large, site erected plants always use two or more vacuum pumps.

System Cooling Capacity (kW) Suggested Vacuum Pump Displacement

cfm m3/h

Up to 35 1.2 2.05

35 to 100 4.0 6.8

100 to 175 6.0 10.2

175 to 250 10.0 17.0

250 to 350 18.0 30.6

>350 Use two or more vacuum pumps

1 cubic feet per minute (cfm) = 1.70 m3/h.

Table 3(e) Suggested Vacuum Pump Displacement/System Cooling Capacity



Induction With gas ballast valve ‘2’ open, non-return valve ‘3’ is closed as the gas in the exhaust area is above atmospheric pressure. Gas and vapour enter the pump. The compression space is sealed off when the vane rotates past the suction inlet.

Gas Ballast When the discharge outlet is uncovered, the pressure behind non-return valve ‘3’ falls below atmospheric , allowing the valve to open and introduce air into the compression cycle.

Compression and Exhaust The mixture of gas and vapour from the system, plus air admitted through the gas ballast valve, is compressed as the vane rotates. Non-return valve ‘3’ closes when the pressure rises above atmospheric. Finally, the pressure rises sufficient to lift discharge valve ‘4’ and exhaust the gas/vapour mixture.

1. Air inlet 2. Gas ballast valve (open) 3. Non-return valve 4. Discharge valve 5. Gas/vapour inlet

Gas/vapour

Air

Fig 3(e) Gas Ballast Operation

4

5

3

1

2

4

5

3

1

2

4

5

3

1

2



4.3. Connection Lines A well-maintained vacuum pump should have a high pumping efficiency down to pressures of 1 mm Hg and below, possibly as high as 85 % to 90 %. However, some of this efficiency can be lost if the connecting lines between the vacuum pump and the system are too small. For this reason, make connecting line(s) as short as possible and of at least 10 mm OD. A 5 mm OD pipe has 15 times the pressure drop of a 10 mm OD line of the same wall thickness. Connect the vacuum pump to two points on the system: one on the high pressure side and one on the low pressure side. An effective vacuum may not be obtainable by trying to draw the vapour through the compressor. If two or more vacuum pumps are used connect them individually, one on the high side of the system, one on the low side. Use connections on the system with the largest effective diameter, at least as large as the diameter of the connecting lines.

4.4. Charging Nitrogen Gas It is suggested to use dry, oxygen-free nitrogen (99.9 % minimum purity) to break the vacuum, by doing so it is possible to obtain a lower vacuum on re-evacuation. The method of connecting and disconnecting cylinders of nitrogen to the system, including the use of the pressure regulator when charging nitrogen, are described in Part D : Strength and Tightness Testing.

WARNING Nitrogen MUST NOT, under any circumstances, be charged into a system without the use of a suitable pressure reducing regulator. When charging nitrogen into an evacuated system, do not allow the nitrogen to enter too quickly, otherwise there is a risk of brittle fracture resulting from the low temperatures created by the expanding gases.

5. Personnel Permitted to Evacuate the System In accordance with BS EN 13313 : 2010, only authorised competent personnel are allowed to work on the refrigeration plant. Within the UK, companies who service, maintain or install refrigeration, air conditioning and heat pump systems must be certified by one of the following organisations:

• Bureau Veritas; • Quidos; • Refcom.

This indicates adequate training has recently been received. Any person rendering assistance or under training must be supervised by the authorised competent person who has responsibility for safety. A permit to work system must be introduced when the plant is commissioned and rigorously enforced thereafter.

6. Personal Protection Personnel carrying out the evacuation procedure must wear the appropriate personal protective equipment. In addition to normal work wear and safety footwear, this should include safety goggles, gloves and a hard hat.



7. Before Evacuation Takes Place Do the following before evacuating the plant.

7.1. Preparing the Plant for Evacuation (a) Check the ambient temperature, ideally it should be above 15 °C.

A temperature of at least 5 °C is necessary to effectively dehydrate the system. For every 5 °C below 15 °C reduce the target vacuum by 0.5 mm Hg. NOTE: It is pointless trying to evacuate the system in ambient temperatures below 5 °C and should not be attempted. Increasing the ambient temperature will reduce the time taken to achieve the required vacuum and means that water is less likely to freeze-out when the pressure is reduced. If the plant is located indoors, use an indirect heat source, radiant heaters for example, to warm the surroundings and raise the ambient temperature. Do not directly heat system components as this could cause damage.

(b) The evacuation process may produce temperatures below freezing. If the system has already been commissioned and incorporates shell and tube or plate heat exchangers, the water and/or secondary refrigerant side of these vessels should be isolated and drained down before the evacuation process begins.

(c) Apart from stop valves isolating parts of the plant which have already been pressure tested and evacuated by the manufacturer and contain a holding charge of nitrogen (site erected refrigeration systems only), open all valves throughout the system except for any valve located between the system and atmosphere; for example, charging, drain and purge valves. Check that no part of the system is isolated by a solenoid valve, non-return valve, back-pressure valve or other flow control device. Jack-open solenoid valves/electronic valves or use a magnetic coil valve lifter.

(d) Electrical components that must be left powered-up during the evacuation procedure, e.g. heaters, should be labelled accordingly.

(e) If the system is fitted with a filter/drier, now is the time to fit the filter/drier cores.

7.2. Preparing the Vacuum Pump for Operation The vacuum pump(s) must be of the ‘gas ballast’ type; refer to 4.2. Vacuum Pump.

(g) Connect the vacuum pump to valved connections on the high and low pressure sides of the system using connecting lines of at least 10 mm OD; refer to 4.3. Connection Lines. Suggested points to connect the lines are as follows:

• Evacuating valve(s); • Charging valve(s); • Purge valve(s) on vessels and heat exchangers

(refrigerant side); • Compressor discharge gauge valve.

If there is a choice of connections, use those with the largest effective diameter.



Using two or more vacuum pumps on a large installation can substantially reduce the time required to evacuate the system; refer to Table 3(e). Connect each pump individually, one on the high side of the system, one on the low side.

(h) Start the pump and run for at least 30 minutes on full gas ballast to thoroughly warm the pump and remove moisture from the oil bath. If there is any doubt about the condition of the oil, i.e. milky appearance, drain and refill with fresh oil of the grade recommended by the pump manufacturer. Dispose of waste oil as described in 11. Disposal of Contaminated Oil. NOTE: Vacuum pump oils are very hygroscopic. Keep spare oil in properly sealed containers.

(i) Disconnect the line at the pump. Fit a vacuum gauge between the line and the pump inlet connection. Use a digital vacuum gauge or a calibrated, barometrically compensated, absolute pressure gauge; refer to 4.1. Vacuum Pressure Gauge.

(j) Restart the pump. Operate the pump, hot, to achieve the lowest possible pressure, ideally 0.5 mm Hg. Shut the isolation valve and stop the pump and watch for a rise in pressure. If this should occur there is a leak or the pump is faulty (worn). Check connections for tightness.

(k) Remove the vacuum gauge from the line and remake the connection(s) to the system.

(l) Connect the vacuum gauge to a valved connection on the system as far as possible from the vacuum pump connection(s). Do not fit the gauge to the vacuum pump or in the lines connecting the pump to the system. If the plant is very large use two gauges located as far apart as possible, one on the high side of the system and one on the low side.

8. Evacuation Procedures The vacuum pump should quickly remove most of the air from the system, removing the moisture takes much longer. The length of time required to remove the moisture depends on the ambient temperature and the displacement and condition of the vacuum pump used. The following procedures refer to refrigeration systems fitted with open drive or semi-hermetic refrigeration compressors.

WARNING The electrical insulation of a semi-hermetic compressor must NEVER be tested (Megger test) while the compressor is under vacuum.

If free-water is present in the system, follow the procedures described in 10. Faults and Remedies before evacuating.

8.1. Evacuation Procedure for Complete Packaged Refrigeration Systems The following procedure refers to complete package units, already strength and tightness tested, supplied with a holding charge of nitrogen. For site erected systems refer to 8.2.

NOTE: If you have not already done so read parts 1. to 5., then read through the following procedure before starting work, commencing with steps 7.1. and 7.2. Ideally, the ambient temperature should be >15.0 °C. Do not attempt evacuation if the ambient temperature is below 5.0 °C.

(a) Open a purge valve to release the holding charge of nitrogen to the atmosphere outside the plant room.



(b) Start the vacuum pump, then open the isolating valves between the pump and the system. While the pump is running, keep a check on the condition of the oil in the oil bath. If the oil turns milky, drain and refill with fresh oil of the grade recommended by the pump manufacturer.

(c) With the vacuum pump running, the pressure in the system should fall, stabilise whilst the moisture evaporates, and eventually continue to fall until a pressure of around 3.0 mm Hg at 15.0 °C ambient has been achieved (2.0 mm Hg at 5.0 °C). Close the gas ballast valve to allow the pump to pull the system down to better than 1.0 mm Hg. Note the pressure achieved and the ambient temperature.

(d) Having achieved the required pressure, allow the vacuum pump to pump air before it is switched off. Do this by closing the isolating valves on the system, disconnecting one of the lines then switching off the vacuum pump. NOTE: The vacuum pump must never be switched off before it is disconnected from the system, otherwise oil from the pump will be drawn into the system and the vacuum lost. Note the pressure achieved and the ambient temperature.

(e) Leave the plant to stand for at least 6 hours (preferably 24 hours), then check the pressure in the system.

• If the pressure has not risen, proceed to step (g); • If the pressure has risen by a small amount, this may be due

to a rise in ambient temperature; refer to 8.3. If there has been no significant rise in ambient temperature, proceed to step (f).

(f) Determine whether an air leak or moisture in the system is responsible for the rise in pressure by referring to Fig 4(e). If an air leak into the system is indicated, check the compressor shaft seal (open drive compressors only), valve glands (if caps are not fitted) and the vacuum pump connection (this is the only joint that has not been leak tested). Re-evacuate or re-pressure test as necessary.

(g) Break the vacuum by charging dry, oxygen-free nitrogen, via a pressure regulator, to a pressure of 0.15 bar (g); refer to 4.4. Charging Nitrogen Gas. Re-evacuate the system down to ≥0.5 mm Hg on a new system or ≥1.0 mm Hg on an existing system and repeat steps (b) to (f) (triple evacuation). NOTE: Triple evacuation is mandatory for systems fitted with a semi-hermetic compressor, strongly recommended for systems fitted with an open drive compressor.

(h) If the compressor crankcase and/or oil separator reservoir are not already charged with oil, use the vacuum to draw the oil charge into the crankcase/reservoir through the oil drain connection. NOTE: Do not allow the oil charging line to suck air or the vacuum will be lost and moisture will enter the system. Oil must be of the correct type, grade and quantity; refer to Oil for Use in the System in Part H : Operation.



(i) Having successfully evacuated the system, isolate and disconnect the vacuum gauge(es).

(j) Stop valves throughout the system, including solenoid valves, back-pressure valves or other flow control devices, should remain in the open position ready for charging. Do not leave the system under vacuum longer than necessary.

(k) Break the vacuum by charging with refrigerant vapour as described in Part G : Charging With Refrigerant.

(l) Commission the plant as described in Part F : Commissioning. 8.2. Evacuation Procedure for Site Erected Refrigeration Systems

The following procedure refers to a plant supplied as one or more skid mounted packaged assemblies (compressor package, vessel package etc.), together with other major items (for example, a remote condenser) and auxiliary components for site erection. For complete packaged refrigeration systems refer to 8.1. Skid mounted packaged assemblies already strength and tightness tested, evacuated and shipped with a holding charge of nitrogen, are usually fitted with stop valves at the various connections. These packages can remain isolated during pressure testing and the initial stages of evacuation.

NOTE: If you have not already done so read parts 1. to 5., then read through the following procedure before starting work, commencing with steps 7.1. and 7.2. Ideally, the ambient temperature should be >15.0 °C. Do not attempt evacuation if the ambient temperature is below 5.0 °C.

(a) Start the vacuum pump, then open the isolating valves between the pump and the system. While the pump is running, keep a check on the condition of the oil in the oil bath. If the oil turns milky, drain and refill with fresh oil of the grade recommended by the pump manufacturer.

(b) With the vacuum pump running, the pressure in the system should fall, stabilise whilst the moisture evaporates, and eventually continue to fall until a pressure of around 3.0 mm Hg at 15.0 °C ambient has been achieved (2.0 mm Hg at 5.0 °C). Close the gas ballast valve to allow the pump to pull the system down to better than 1.0 mm Hg. Note the pressure achieved and the ambient temperature.

(c) If the system pressure falls, stabilises but does not continue to fall, this could indicate that the system is very wet. This is certainly the case if the vacuum pump oil bath rapidly becomes contaminated with moisture (milky appearance). Disconnect and stop the vacuum pump. Charge dry, oxygen-free nitrogen, via a pressure regulator, to a pressure of to 10 mm Hg then re-evacuate; refer to 4.4. Charging Nitrogen Gas.

(d) Having achieved the required pressure, allow the vacuum pump to pump air before it is switched off. Do this by closing the isolating valves on the system, disconnecting one of the lines then switching off the vacuum pump. NOTE: The vacuum pump must never be switched off before it is disconnected from the system, otherwise oil from the pump will be drawn into the system and the vacuum lost. Record; the pressure achieved and the ambient temperature.



(e) Leave the plant to stand for at least 6 hours (preferably 24 hours), then check the pressure in the system.

• If the pressure has not risen, proceed to step (f); • If the pressure has risen by a small amount, this may be due

to a rise in ambient temperature; refer to 8.3. If there has been no significant rise in ambient temperature, proceed to step (e).

(f) Determine whether an air leak or moisture in the system is responsible for the rise in pressure by referring to Fig 4(e). If an air leak into the system is indicated, check the compressor shaft seal (open drive compressors only), valve glands (if caps are not fitted) and the vacuum pump connection (this is the only joint that has not been leak tested). Re-evacuate or re-pressure test as necessary.

(g) If skid mounted packaged assemblies containing a holding charge of nitrogen were isolated during tightness testing and the first stage of evacuation, open a purge valve to release the holding charge of nitrogen to the atmosphere outside the plant room. Open isolating stop valves as necessary to unite the system.

(h) Repeat steps (c) to (e), this time the system need only be left to stand for 4 hours. Failure to obtain the required pressure can be pin-pointed to a leak in the packaged assemblies isolated during the first stage of evacuation.

(i) Break the vacuum by charging dry, oxygen-free nitrogen, via a pressure regulator, to a pressure of 0.15 bar (g); refer to 4.4. Charging Nitrogen Gas. Re-evacuate the system down to ≥0.5 mm Hg on a new system or ≥1.0 mm Hg on an existing system and repeat steps (a) to (f) (triple evacuation). NOTE: Triple evacuation is mandatory for systems fitted with a semi-hermetic compressor, strongly recommended for systems fitted with an open drive compressor.

(j) If the compressor crankcase and/or oil separator reservoir are not already charged with oil, use the vacuum to draw the oil charge into the crankcase/reservoir through the oil drain connection. NOTE: Do not allow the oil charging line to suck air or the vacuum will be lost and moisture will enter the system. Oil must be of the correct type, grade and quantity; refer to Oil for Use in the System in Part H : Operation.

(k) Having successfully evacuated the system, isolate and disconnect the vacuum gauge(es).

(l) Stop valves throughout the system, including solenoid valves, back-pressure valves or other flow control devices, should remain in the open position ready for charging. Do not leave the system under vacuum longer than necessary.

(m) Break the vacuum by charging with refrigerant vapour as described in Part G : Charging With Refrigerant.

(n) Insulate refrigerant lines as required. Insulation thicknesses are shown on the plant schematic flow diagram.

(o) Commission the plant as described in Part F : Commissioning.



Failure to Obtain a Vacuum - Checking if Moisture or Air is Present During the evacuation process, as the pressure falls, any water vapour that may be present may ‘snap-freeze’ and remain behind in the system. This may occur if the evacuation process is carried out too quickly, a vacuum pump with a very large displacement is used on a small system and/or the ambient temperature is too low. After the system has been evacuated and left to stand, this frozen or subcooled water will evaporate, increase the pressure in the system and give the false impression of an air leak. It is a simple matter to check whether air or moisture is responsible for the rise in pressure by referring to the saturated vapour curve for water illustrated above. • If the values of system pressure and ambient temperature plotted on the graph intersect ON or BELOW the

curve, then the rise in pressure is due to moisture in the system. The more moisture present, the nearer the point of intersection to the curve. In this case, evacuate again to 2 mm Hg.

• If the values of system pressure and ambient temperature plotted on the graph intersect ABOVE the curve, then the rise in pressure is due to a leak allowing air to enter the system. The pneumatic testing procedures described in Part D : Strength and Tightness Testing must be repeated and the evacuation and standing test reapplied.

Fig 4(e) Saturated Vapour Curve for Water

-10

-5

0

5

10

15

20

25

2 4 6 8 10 12 14 16 18 20 22

Ambi

ent T

empe

ratu

re (°

C)

Pressure (mm Hg abs)

Air Leak

Moisture Present



8.3. Pressure Rise Test After evacuation, with the required vacuum achieved, ambient temperature, date and time must be recorded. Isolate the system and leave it to stand for at least 6 hours (preferably 24 hours). If there is no indicated rise in pressure after this time the system is tight. If there is a rise in pressure this may be due to a rise in ambient temperature. Use the following equation to calculate the revised pressure:

P1/T1 = P2/T2 Where: P1 = System pressure after evacuation (torr). T1 = Ambient temperature after evacuation (K). P2 = System pressure present at the end of the standing period (torr). T2 = Ambient temperature present at the end of the standing period (K).

Example: P1 = 1.5 mm Hg T1 = 12 °C + 273 = 285 K T2 = 20 °C + 273 = 293 K P2 = P1 x T2/T1 = (1.5 x 293)/285 = 1.54210 mm Hg

The expected pressure deviation due to a rise in ambient temperature of 8 °C over the standing period is equal to 1.54210 – 1.50010, a rise of 0.04200 mm Hg.

9. Test Certification After evacuation has been carried out and proved satisfactory, the competent person must add the date, test pressures and witness identity signature or stamp to the test pressure certificate. This information must be available for transfer to any subsequent certificate produced by Quality Control personnel. Test certification must be retained as a permanent record. Refer to System Pressure Test and Evacuation Certificate JEH-C5-025 or 13. Appendix 1 System Pressure Test and Evacuation Certificate.

10. Faults and Remedies 10.1. Failure to Obtain the Required Vacuum

Taking an excessively long time to pull the vacuum, failure to achieve the required vacuum or difficulty in holding the vacuum, depends upon the following factors:

• Size of the plant. Not surprisingly, large plants take longer to evacuate than small ones. Try to match vacuum pump displacement to the volume of the system. On a large plant, use two or more vacuum pumps;

• Pipes connecting the system to the vacuum pump(s) are too small. Use pipes of the largest practical diameter, certainly no smaller than the connection on the pump; refer to 4.3. Connection Lines;

• Defective vacuum pump or vacuum pressure gauge. Refer to the manufacturer’s instructions;

• Ambient temperature too low. An ambient temperature of at least 5 °C is necessary to effectively dehydrate the system. Use an indirect heat source, radiant heaters for example, to warm the surroundings and raise the ambient temperature;

• Part of the system isolated. Check that stop valves, solenoid valves, back-pressure valves and other flow control devices are fully open;



• Moisture in the system or air leaks; refer to Failure to Obtain a Vacuum - Checking if Moisture or Air is Present in Fig 4(e). A number of air leaks would suggest that the tightness testing procedure was not thoroughly carried out as described in Part D : Strength and Tightness Testing;

• If a system using HCFC, HFC or HFO refrigerant is already charged with oil, refrigerant in solution with the lubricating oil will be released as the pressure falls.

10.2. Fault Condition – Moisture in the System Atmospheric air always contains moisture. Moisture in the system will have a detrimental effect as follows:

Acids Moisture reacts with the lubricating oil to form acids. Similar reactions can occur with the system HCFC, HFC or HFO refrigerant. If the system contains copper lines or components made from copper-based alloys, these acids dissolve or leach out the copper which is deposited on surfaces inside the system (copper plating). Acids degrade the lubricating oil leading to poor lubrication and the formation of oil sludge. Corrosion Corrosion of ferrous components inside the system. Rust deposits. Ice Moisture forms ice crystals at cold spots, i.e. where there is a pressure drop: at the expansion valve, refrigerant filter/drier. Can also result in the deposition of ice on the evaporator heat exchange surfaces. Semi-hermetic Compressor Moisture and acids attack/degrade the motor insulation material leading to a burnout.

The extent to which these symptoms are exhibited depends on the amount of air/moisture contamination. Small amounts of moisture may show few symptoms and the moisture can usually be easily be removed. Large amounts of moisture, especially free-water, will result in serious loss of performance (reduced COP) and system failure.

10.2.1. Small Amounts of Moisture Present in the System Air and, therefore, moisture may be present within the system because:

• Air/moisture have accumulated in the system over a prolonged period of operation, evident by the liquid line sight-glass/moisture indicator colour indication changing from ‘dry’ to ‘caution’ or ‘danger’. Trace and rectify the cause of air/moisture ingress. Remove the moisture by changing the liquid line filter/drier cores. If necessary, purge air from the system at the condenser. Use a recovery/pump-out unit and a recovery cylinder for purging HCFC or HFC refrigerants, use a purge apparatus for ammonia;

• System tightness testing has not be properly carried out during commissioning, allowing air/moisture to enter via a leaking connection, repeat the tightness testing procedure; refer to Part D : Strength and Tightness Testing;

• Moisture has been left behind because evacuation procedures were not properly carried out.



Repeat the evacuation procedure; refer to 8. Evacuation Procedures. 10.2.2. Free-water Present in the System

Free-water in the system will make itself apparent in the following ways: • If the system is opened up, water droplets or puddles may

be present. There may be evidence of copper plating and oil sludge. Acids may be present;

• Refrigerant flow may be restricted. Water will freeze out at the regulator and prevent liquid refrigerant entering the evaporator;

• Moisture indicator colour rapid change to ‘danger’ warning. An oil analysis indicates very high moisture levels;

• If the system is fitted with a semi-hermetic compressor, the high levels of moisture may have resulted in a motor burnout.

If the system contains much free-water, for example, from a leaking shell and tube condenser, after repair to the condenser, it is essential to remove as much of this water as possible, before attempting to evacuate the system. This will reduce the time required to dehydrate the system.

10.3. Moisture Removal - System Cleaning Procedures If the system is contaminated with significant amounts of moisture, the following instructions are a general guide to correcting the condition and returning the plant to operation. Maintenance procedures must be reviewed to ensure that there is no recurrence; refer to Part J : Maintenance. The first step is to identify and remedy the cause of the leak before cleaning the system and removing the moisture. Simply to evacuate will allow more air and moisture to enter, and possibly free-water if the problem is caused by a leaking water cooled condenser or evaporator used for liquid cooling. The action to be taken depends on the extent of the moisture ingress. If the system is fitted with a semi-hermetic compressor, the presence of large amounts of moisture may already have resulted in a motor burnout. Take an oil sample and check the acid number; follow the procedures described in publication 2-250 Semi-hermetic Compressor Motor Burnout. For systems fitted with an open drive compressor, check for oil sludging, copper plating, corrosion etc. It will be necessary to remove the refrigerant and oil charges (recycle, do not reuse), then dismantle, clean and dry pipework and recondition/replace line components; sometimes replacement is the more cost-effective option. Propitiatory flushing/cleaning agents can be used. There are two main types: solvent based, the residue cannot be removed by dehydration, or hydrofluoroolefin (HFO) based which can. Examples are:

• Honeywell Solvents Solstice® PF-C; • DiversiTech Pro-Flush; • Nu-Calgon Rx11-Flush; • Advanced Engineering Endoflush Refrigerant Flushing Fluid.

Do not inject the solvent into the compressor itself. Only the supporting refrigeration system should be flushed. Follow the manufacturer’s instruction regarding use and safe disposal. After cleaning, pipelines can dried by blowing through with oxygen-free, nitrogen; refer to 4.4 Charging Nitrogen Gas. Dry out heat exchange vessels in two stages.



First Stage Use oxygen-free, nitrogen to raise the pressure (do not exceed the vessel’s maximum allowable pressure), then release the pressure quickly, preferably by opening a full-flow valve (globe valve); release the nitrogen to the atmosphere outside the plant room. Much of the water will become entrained in the nitrogen and will be removed; repeat this procedure as necessary until there is no evidence of free-water escaping with the nitrogen. Second Stage Attach a hot air blower to the vessel. The construction of the vessel will dictate the precise mode of connection, however, flexible pipes will make this job easier. How long it is necessary to use the blower depends on the quantity of moisture still remaining in the vessel. The process can be speeded up by purging with oxygen-free, nitrogen and checking the humidity of the nitrogen leaving the vessel; refer to 4.4.Charging Nitrogen Gas.

Finally, with the compressor rebuilt (if necessary), reassemble reconditioned/new line components and pipework using new gaskets and ‘O’ rings. Fit a new oil filter element and new cores to the refrigerant filter/drier. The system must now be strength and tightness tested; refer to Part D : Strength and Tightness Testing. Only then should the system be evacuated as described in 8. Evacuation Procedures, charged with fresh oil and refrigerant (not recovered) and recommissioned.

10.4. Low Temperature Moisture Trap (Cold Trap) Despite removing as much moisture as possible as described in 10.3, a significant amount of moisture may still be present within the system, too much moisture for the vacuum pump alone to deal with or the life of the pump may be significantly reduced if it is used under these conditions. In these cases the use of a low temperature moisture trap (cold trap) should be considered, installed between the system and the vacuum pump as illustrated in Fig 5(e); the evaporator coil inside the trap is cooled to approximately -20 °C by a separate small condensing unit. Water vapour present in the air drawn from the system by the vacuum pump condenses and freezes on the cold surface of the evaporator coil inside the trap, limiting the amount of moisture absorbed by the vacuum pump oil and prolonging the life of the pump. The trap will slowly become less effective as more and more frost accumulates on the coil and will eventually need to be isolated, defrosted and dried off before reuse.

11. Disposal of Contaminated Oil and Refrigerant Return oil and refrigerant to the supplier for disposal or recycling. Large industrial suppliers of refrigerant and oil have their own approved recovery scheme so that recovered oil can be returned to the supplier for safe disposal/recycling. Within the UK; refer to J & E Hall International Hazardous Waste Consignment Note HWCN01v111 which acts as a record of waste transfer to enable the site as the waste producer to provide evidence of safe, correct disposal. A description of contents marked on the hazardous waste consignment note must be returned with the recovery container. Conform to local hazardous waste regulations for the removal and disposal of recovered refrigerant and waste oil. In the EU all hazardous waste is assigned a European Waste Catalogue (EWC) Code:

Waste oil. 13 01 01 Recovered refrigerant. 14 06 01



Fig 5(e) Low Temperature Moisture Trap (Cold Trap)

Orifice

Moisture vapour condenses and forms ice on the evaporator coil

Tongue and Groove Flanged Joint

Evaporator Coil (minimum evaporating

temperature –20 °C)

Insulation

Liquid line from condensing unit

From system to be evacuated

To vacuum

pump

Suction line to condensing unit



12. References for Further Information

Organisation and Publication Website

Air Conditioning and Refrigeration Industry Board (ACRIB) Safe Handling of Refrigerants. Guidelines for the Use of Halocarbon Refrigerants in Static Refrigeration and Air Conditioning Systems. ISBN 1-872719-13-9.

www.acrib.org.uk

American Conference of Government Industrial Hygienists (ACGIH) Threshold Limit Values and Biological Exposure Indices 2001 (7th Edition). ISBN 1-882417-43-7. Also available on CD.

www.acgih.org

British Standards Institution (BSI) BS EN 13313:2010 Refrigeration Systems and Heat Pumps. Competence of Personnel.

ISBN 978 0 580 6770 6. BS EN 1089-3:2011 Transportable Gas Cylinders. Gas cylinder identification (excluding LPG).

ISBN 978 0 580 68705 1. BS EN 378-1:2016 Refrigerating systems and heat pumps. Safety and environmental requirements. Basic requirements, definitions, classification and selection criteria.

ISBN 978 0 580 84660 1. BS EN 378-2:2016 Refrigerating systems and heat pumps. Safety and environmental requirements. Design, construction, testing, marking and documentation.

ISBN 978 0 580 54661 8. BS EN 378-3:2016 Refrigerating systems and heat pumps. Safety and environmental requirements. Installation site and personal protection.

ISBN 978 0 580 54662 5. BS EN 378-4:2016 Refrigerating systems and heat pumps. Safety and environmental requirements. Operation, maintenance, repair and recovery.

ISBN 978 0 580 54663 2. BS EN 1089-3: 2011 Transportable Gas Cylinders. Gas Cylinder Identification (Excluding LPG) Colour Coding.

ISBN 978 0 580 68705 1. BS EN 14276-2:2007+A1:2011 Pressure equipment for refrigerating systems and heat pumps. Piping. General requirements.

ISBN 978 0 580 71101 5. BS EN ISO 9712:2012 Non-destructive testing. Qualification and certification of NDT personnel.

ISBN 978 0 580 74535 5.

www.bsigroup.com

Health and Safety Executive (HSE) EH40/2005 Workplace exposure limits. ISBN 978 0 7176 6446 7. GS4 Safety requirements for pressure testing. HSE-53 Respiratory Protective Equipment at Work. ISBN 978 0 7176 6454 2. Pressure Systems Safety Regulations 2000 (published 2014). ISBN 978-0-7176-6644-7.

www.hse.gov.uk

Her Majesty’s Stationery Office (HMSO) COSHH. Control of Substances Hazardous to Health Regulations 2002. Statutory Instrument 2002 No 2677. ISBN 0 11 042919 2. The Pressure Systems and Transportable Gas Containers Regulations 1989. Statutory Instrument 1989 No 2169. ISBN 0 110 98169 3. Health and Safety at Work Act 1974.

www.hmso.gov.uk

Institute of Refrigeration Safety Code for Compression Refrigerating Systems Utilizing Groups A1 & A2 Refrigerants (1999). Code of Practice for the Minimisation of Refrigerant Emissions from Refrigerating Systems.

www.ior.org.uk

J & E Hall International Engineering standard 10 001 Identification of Industrial Gas Cylinder Contents. J & E Hall International Hazardous Waste Consignment Note HWCN01v111.

www.jehall.co.uk

Table 4(e) References For Further Information



13. Appendix 1 System Pressure Test and Evacuation Certificate Certificate Number:

J & E Hall Contract Number:

Client / Customer:

Site Name / Location:

Client / Customer Contract Number:

System Under Test:

System Description:

Reference Drawing Number(s):

Calibrated Gauge Serial Number(s):

Pneumatic Pressure Test with dry,

oxygen-free grade nitrogen

Pressure Applied (bar g)

Ambient Temperature

(ºC)

Test Duration

(h)

Test Date / Initials / Stamp

Engineer Customer Inspector

Low Pressure (LP) Side - Strength Test

Low Pressure (LP) Side - Tightness Test

High Pressure (HP) Side - Strength Test

High Pressure (HP) Side - Tightness Test

Vacuum Achieved (mm Hg)

Ambient Temperature

(ºC)

Test Duration

(h)

Test Date / Inspectors Initials / Stamp

Engineer Customer Inspector

System Evacuation

Rise Test

Vacuum Pump Serial Number



Tests Performed By The system described hereon has been tested in accordance with the requirements of the order and / or drawings relative thereto and the results found to be satisfactory.

Name (print): Position:

Signature: Date:

Company: Competence:

Witnessed on behalf of Client / Customer The system described hereon has been tested in accordance with the requirements of the order and / or drawings relative thereto and the results found to be satisfactory.


Signature: Date:


Certified by The system described hereon has been tested in accordance with the requirements of the order and / or drawings relative thereto and the results found to be satisfactory.


Signature: Date:


part e : evacuation and dehydration

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