When installing the refrigeration circuit of freon installations, use only special copper pipes, intended for refrigeration units(i.e. pipes of "refrigeration" quality). Such pipes are marked abroad with the letters "R" or "L".
Pipes are laid along the route specified in the project or wiring diagram. Pipes should be generally horizontal or vertical. The exception is:
- horizontal sections of the suction pipeline, which are performed with a slope of at least 12 mm per 1 m towards the compressor to facilitate the return of oil to it;
- horizontal sections of the discharge pipeline, which are performed with a slope of at least 12 mm per 1 m towards the condenser.
If the height of the ascending section is more than 7.5 meters, then a second oil sling loop. In general, oil lifting loops should be installed every 7.5 meters of the ascending section of the suction (discharge) section (see Figure 3.15). At the same time, it is desirable that the lengths of ascending sections, especially liquid ones, be as short as possible in order to avoid significant pressure losses in them.
The length of the ascending sections of pipelines more than 30 meters is not recommended.
In the manufacture oil lifting loop it should be borne in mind that its dimensions should be as small as possible. It is best to use one U-fitting or two elbow fittings as an oil lifting loop (see fig. 3.16). In the manufacture oil lifting loop by bending the pipe, and also, if necessary, reducing the diameter of the ascending section of the pipeline, the requirement should be observed that the length L is not more than 8 diameters of the connected pipelines (Fig. 3.17).
For installations with multiple air coolers (evaporators) located at different levels with respect to the compressor, the recommended installation options for pipelines with oil lifting loops are shown in fig. 3.18. Option (a) in fig. 3.18 can only be used if there is a liquid separator and the compressor is located below , in other cases option (b) must be used.
In those cases when during the operation of the installation it is possible to turn off one or more air coolers located below the compressor, and this can lead to a drop in flow in the common ascending suction pipeline by more than 40%, it is necessary to make the common ascending pipeline in the form of 2 pipes (see Fig. 3.19). In this case, the diameter of the smaller pipe (A) is chosen in such a way that when minimum flow the flow velocity in it was not less than 8 m/s and not more than 15 m/s, and the diameter of the larger pipe (B) is determined from the condition of maintaining the flow velocity in the range from 8 m/s to 15 m/s in both pipes at maximum flow .
With a level difference of more than 7.5 meters, twin pipelines must be installed in each section with a height of not more than 7.5 m, strictly observing the requirements of fig. 3.19. To obtain reliable solder joints, it is recommended to use standard fittings different configuration(See Figure 3.20).
When installing the refrigeration circuit pipelines it is recommended to lay using special supports (suspensions) with clamps. When laying the suction and liquid lines together, the suction pipelines are first installed and the liquid pipelines are installed in parallel with them. Supports and hangers must be installed in increments of 1.3 to 1.5 meters. The presence of supports (suspensions) should also prevent dampening of the walls along which non-thermal insulated suction lines. Various design options supports (suspensions) and recommendations on the place of their fastening are shown in fig. 3.21, 3.22.
In the process of acceptance testing, over and over again, one has to deal with errors made during the design and installation copper pipes piping for freon air conditioning systems. Using the accumulated experience, as well as relying on the requirements normative documents, we tried to combine the basic rules for organizing copper pipeline routes within the framework of this article.
It will be about the organization of routes, and not about the rules for installing copper pipelines. Consideration will be given to the placement of pipes, their relative position, problems of choosing the diameter of freon pipelines, the need for oil lifting loops, compensators, etc. We will bypass the rules for installing a particular pipeline, the connection technology and other details. At the same time, issues of a larger and more general view of the construction of copper traces will be raised, and some practical problems will be considered.
Mainly given material concerns freon air conditioning systems, whether traditional split systems, multi-zone air conditioning systems or precision air conditioners. At the same time, we will not touch on the installation of water pipes in chiller systems and the installation of relatively short freon pipelines inside refrigeration machines.
Regulatory documentation for the design and installation of copper pipelines
Among normative documentation concerning the installation of copper pipelines, we distinguish the following two standards:
- STO NOSTROY 2.23.1-2011 "Installation and commissioning of evaporative and compressor-condensing units household systems air conditioning in buildings and structures”;
- SP 40-108-2004 "Design and installation internal systems water supply and heating of buildings from copper pipes.
The first document describes the installation of copper pipes in relation to vapor compression air conditioning systems, and the second - in relation to heating and water supply systems, however, many of the requirements from them are applicable to air conditioning systems.
Selection of copper pipe diameters
The choice of the diameter of copper pipes is carried out on the basis of catalogs and programs for calculating equipment for air conditioning. In split systems, the diameter of the pipes is selected according to the connecting pipes of the indoor and outdoor units. In the case of multi-zone systems, it is most correct to use calculation programs. Precision air conditioners use manufacturer's recommendations. However, with a long freon route, there may be non-standard situations not specified in the technical documentation.
In general, to ensure the return of oil from the circuit to the compressor crankcase and acceptable pressure losses, the flow velocity in the gas line should be at least 4 meters per second for horizontal sections and at least 6 meters per second for ascending sections. To avoid the occurrence of unacceptable high level noise, the maximum allowable gas flow velocity is limited to 15 meters per second.
The flow rate of the refrigerant in the liquid phase is much lower and is limited by the potential destruction of valves. The maximum speed of the liquid phase is no more than 1.2 meters per second.
On high elevations with long runs, the internal diameter of the liquid line should be chosen so that the pressure drop in it and the pressure of the liquid column (in the case of an ascending pipeline) does not lead to boiling of the liquid at the end of the line.
In precision air conditioning systems, where the length of the route can reach and exceed 50 meters, vertical sections of gas lines of underestimated diameter are often accepted, as a rule, by one standard size (by 1/8”).
We also note that often the calculated equivalent length of pipelines exceeds the limit specified by the manufacturer. In this case, it is recommended to coordinate the actual route with the manufacturer of air conditioners. It is usually found that the excess length is permissible by up to 50% maximum length the route specified in the directories. In this case, the manufacturer indicates the required diameters of the pipelines and the percentage of underestimation of the cooling capacity. According to experience, the understatement does not exceed 10% and is not decisive.
Oil lifting loops
Oil lifting loops are installed in the presence of vertical sections with a length of 3 meters or more. For higher lifts, the hinges should be installed every 3.5 meters. At the same time, in top point a reverse oil lifting loop is installed.
But even here there are exceptions. When agreeing on a non-standard route, the manufacturer may either recommend installing an additional oil lifting loop, or abandon the extra ones. In particular, in the conditions of a long route, in order to optimize the hydraulic resistance, it was recommended to abandon the reverse upper loop. In another project, due to the specific conditions on the rise of about 3.5 meters, they were obliged to install two hinges.
The oil lifting loop is an additional hydraulic resistance and must be taken into account when calculating the equivalent route length.
When manufacturing an oil lifting loop, it should be borne in mind that its dimensions should be as small as possible. The length of the loop should not exceed 8 diameters of the copper pipeline.
Fixing copper pipes
Rice. 1. Scheme of fastening pipelines in one of the projects,
of which fastening the clamp directly to the pipe
not obvious, which has been the subject of controversy
In terms of fastening copper pipelines, the most common mistake is fastening with clamps through insulation, supposedly to reduce the vibration effect on fasteners. Controversial situations in this matter can also be caused by insufficiently detailed drawing of the sketch in the project (Fig. 1).
In fact, two-piece metal plumbing clamps, twisted with screws and having rubber sealing inserts, should be used to fasten the pipes. It is they who will provide the necessary damping of vibrations. Clamps must be attached to the pipe, not to the insulation, must be of the appropriate size and provide a rigid fastening of the route to the surface (wall, ceiling).
The choice of distances between the fastenings of pipelines from solid copper pipes is generally calculated according to the method presented in Appendix D of the document SP 40-108-2004. To this method should be used if non-standard piping is used or if controversial situations. In practice, specific recommendations are more often used.
So, recommendations for the distance between the supports of copper pipelines are given in Table. 1. The distance between the fastenings of horizontal pipelines from semi-solid and soft pipes can be taken less by 10 and 20%, respectively. More if needed exact values distances between fasteners horizontal pipelines should be determined by calculation. At least one fastener must be installed on the riser, regardless of the height of the floor.
Table 1 Distance between copper piping supports
Note that the data from Table 1 approximately coincide with the graph shown in Fig. 1 p. 3.5.1 SP 40-108-2004. However, we have adapted the data of this standard for the pipelines used in air conditioning systems of relatively small diameter.
Thermal expansion compensators
thermal expansion various types
(a - L-shaped, b - O-shaped, c - U-shaped)
for copper pipelines
A question that often baffles engineers and installers is the need to install expansion joints, the choice of their type.
The refrigerant in air conditioning systems generally has a temperature in the range from 5 to 75 °C (more accurate values \u200b\u200bdepend on which elements of the refrigeration circuit are located between the pipelines in question). Temperature environment while changing in the range from –35 to +35 °C. Specific calculated temperature differences are taken depending on where the pipeline in question is located, indoors or outdoors, and between which elements of the refrigeration circuit (for example, the temperature between the compressor and the condenser is in the range from 50 to 75 ° C, and between the expansion valve and the evaporator - in the range from 5 to 15 °C).
Traditionally, U-shaped and L-shaped expansion joints are used in construction. The calculation of the compensating capacity of U-shaped and L-shaped elements of pipelines is carried out according to the formula (see the diagram in Figure 2)
where
L to - departure of the compensator, m;
L - linear deformation of the pipeline section with a change in air temperature during installation and operation, m;
A is the coefficient of elasticity of copper pipes, A = 33.
Linear deformation is determined by the formula
L is the length of the deformable section of the pipeline at the installation temperature, m;
t - temperature difference between the temperature of the pipeline in various modes during operation, °C;
- coefficient of linear expansion of copper, equal to 16.6 10 -6 1/°C.
For example, we calculate the required free distance L k from the movable support of the pipeline d = 28 mm (0.028 m) before the turn, the so-called departure of the L-shaped compensator at a distance to the nearest fixed support L = 10 m. The pipe section is located indoors (pipeline temperature at idle chiller 25 °C) between chiller and remote condenser ( working temperature pipeline 70 °C), i.e. t = 70–25 = 45 °C.
By the formula we find:
L \u003d L t \u003d 16.6 10 -6 10 45 \u003d 0.0075 m.
Thus, a distance of 500 mm is quite enough to compensate for the thermal expansion of the copper pipeline. We emphasize once again that L is the distance to the fixed support of the pipeline, L to is the distance to the movable support of the pipeline.
In the absence of turns and the use of a U-shaped compensator, we find that for every 10 meters of a straight section, a half-meter compensator is required. If the width of the corridor or other geometric characteristics of the pipeline laying site do not allow the installation of an expansion joint with an overhang of 500 mm, expansion joints should be installed more frequently. In this case, the dependence, as can be seen from the formulas, is quadratic. If the distance between the compensators is reduced by 4 times, the expansion joint will become shorter by only 2 times.
To quickly determine the offset of the compensator, it is convenient to use the table. 2.
Table 2. Departure of the compensator L k (mm) depending on the diameter and elongation of the pipeline
| Pipeline diameter, mm | Elongation L, mm | |||
| 5 | 10 | 15 | 20 | |
| 12 | 256 | 361 | 443 | 511 |
| 15 | 286 | 404 | 495 | 572 |
| 18 | 313 | 443 | 542 | 626 |
| 22 | 346 | 489 | 599 | 692 |
| 28 | 390 | 552 | 676 | 781 |
| 35 | 437 | 617 | 756 | 873 |
| 42 | 478 | 676 | 828 | 956 |
| 54 | 542 | 767 | 939 | 1 084 |
| 64 | 590 | 835 | 1 022 | 1 181 |
| 76 | 643 | 910 | 1 114 | 1 287 |
| 89 | 696 | 984 | 1 206 | 1 392 |
| 108 | 767 | 1 084 | 1 328 | 1 534 |
| 133 | 851 | 1 203 | 1 474 | 1 702 |
| 159 | 930 | 1 316 | 1 612 | 1 861 |
| 219 | 1 092 | 1 544 | 1 891 | 2 184 |
| 267 | 1 206 | 1 705 | 2 088 | 2 411 |
Finally, we note that there should be only one fixed support between the two compensators.
Potential locations where compensators may be required are, of course, those where there is the greatest temperature difference between the operating and non-operating modes of the air conditioner. Because the hottest refrigerant flows between the compressor and condenser, and the hottest low temperature typical for outdoor areas in winter, the most critical are the outdoor sections of pipelines in chiller systems with remote condensers, and in precision air conditioning systems - when using indoor cabinet air conditioners and a remote condenser.
A similar situation occurred at one of the facilities, where remote condensers had to be installed on a frame 8 meters from the building. At such a distance, with a temperature difference exceeding 100 °C, there was only one branch and a rigid fastening of the pipeline. Over time, a pipe bend appeared in one of the fixtures, and a leak appeared six months after the system was put into operation. Three systems, mounted parallel to each other, had the same defect and required emergency repairs with a change in the configuration of the route, the introduction of compensators, repeated pressure testing and refilling of the circuit.
Finally, another factor that should be taken into account when calculating and designing thermal expansion compensators, especially U-shaped ones, is a significant increase in the equivalent length of the freon circuit due to the additional length of the pipeline and four bends. If a total length the route reaches critical values (and if we are talking about the need to use compensators, the length of the route is obviously rather big), then the final scheme should be agreed with the manufacturer, indicating all the compensators. In some cases, by joint efforts it is possible to develop the most optimal solution.
Routes of air conditioning systems should be laid hidden in furrows, channels and shafts, trays and on suspensions, while hidden laying should provide access to detachable connections and fittings by arranging doors and removable shields, on the surface of which there should be no sharp protrusions. Also, when laying hidden pipelines at the locations of collapsible connections and fittings, service hatches or removable shields should be provided.
Vertical sections should be monolithic only in exceptional cases. Basically, it is advisable to place them in channels, niches, furrows, as well as behind decorative panels.
In any case, the hidden laying of copper pipelines must be carried out in a casing (for example, in corrugated polyethylene pipes Oh). Application corrugated pipes PVC is not allowed. Prior to sealing the places for laying pipelines, it is necessary to carry out an executive scheme for the installation of this section and conduct hydraulic tests.
Open laying of copper pipes is allowed in places that exclude them mechanical damage. Open areas can be covered with decorative elements.
The laying of pipelines through walls without sleeves, it must be said, is almost never observed. Nevertheless, we recall that for the passage through building structures, it is necessary to provide sleeves (cases), for example, from polyethylene pipes. The inner diameter of the sleeve should be 5–10 mm larger than the outer diameter of the pipe being laid. The gap between the pipe and the case must be sealed with a soft waterproof material that allows the pipe to move along the longitudinal axis.
When installing copper pipes, you should use a tool specially designed for this - rolling, pipe bender, press.
Quite a few useful information about the installation of freon pipelines can be obtained from experienced installers of air conditioning systems. It is especially important to transfer this information to designers, since one of the problems of the design industry is its isolation from installation. As a result, solutions that are difficult to implement in practice are included in projects. As they say, paper will endure everything. Easy to draw, hard to execute.
By the way, that is why all advanced training courses at the APIC Training and Consulting Center are conducted by teachers with experience in the field of construction and installation works. Even for management and design specialties, teachers from the field of implementation are invited to ensure a comprehensive perception of the industry by students.
So, one of the basic rules is to provide a gasket height that is convenient for installation at the design level. freon lines. The distance to the ceiling and to the false ceiling is recommended to be at least 200 mm. When hanging pipes on studs, the most comfortable lengths of the latter are from 200 to 600 mm. Shorter studs are difficult to work with. Longer studs are also inconvenient to install and can wobble.
When installing pipelines in a tray, do not suspend the tray from the ceiling closer than 200 mm. Moreover, it is recommended to leave about 400 mm from the tray to the ceiling for comfortable pipe soldering.
It is most convenient to lay outdoor routes in trays. If the slope allows, then in trays with a lid. If not, the pipes are protected in a different way.
An invariable problem of many objects is the lack of marking. One of the most common remarks when working in the field of architectural or technical supervision is to mark the cables and pipelines of the air conditioning system. For ease of operation and subsequent maintenance of the system, it is recommended to mark cables and pipes every 5 meters of length, as well as before and after building structures. The marking should use the system number, type of pipeline.
When installing various pipelines one above the other on the same plane (wall), it is necessary to install below the one that is most likely to form condensate during operation. In the case of parallel laying of two gas lines of different systems one above the other, the one in which the heavier gas flows must be installed below.
Conclusion
When designing and installing large facilities with many air conditioning systems and long routes, special attention should be paid to the organization of freon pipeline routes. This approach to developing a common piping policy will save time both at the design and installation stages. In addition, this approach allows you to avoid a lot of errors that have to be encountered in real construction: forgotten expansion joints or expansion joints that do not fit in the corridor due to adjacent engineering systems, erroneous schemes fastening of pipes, incorrect calculations of the equivalent length of the pipeline.
As the implementation experience has shown, taking into account these tips and recommendations really gives a positive effect at the stage of installing air conditioning systems, significantly reduces the number of questions during installation and the number of situations when it is urgently required to find a solution to a complex problem.
Yury Khomutsky, technical editor of the magazine "Climate World"
Loss of refrigerant pressure in the pipes of the refrigeration circuit reduces the efficiency of the refrigeration machine, reducing its cooling and heating capacity. Therefore, it is necessary to strive to reduce pressure losses in the tubes.
Since the evaporating and condensing temperatures depend on pressure (almost linearly), pressure losses are often measured by condensing or evaporating temperature losses in °C.
- Example: for refrigerant R-22 at an evaporating temperature of +5°C, the pressure is 584 kPa. With a pressure loss of 18 kPa, the boiling point will decrease by 1°C.
Suction line losses
With a loss of pressure in the suction line, the compressor operates at a lower inlet pressure than the evaporation pressure in the evaporator of the chiller. Because of this, the flow of refrigerant passing through the compressor is reduced, and the cooling capacity of the air conditioner is reduced. Suction line pressure loss is most critical to chiller operation. With losses equivalent to 1°C, performance is reduced by as much as 4.5%!
Discharge line losses
With a loss of pressure in the discharge line, the compressor has to work with more high pressure than the condensing pressure. At the same time, the performance of the compressor is also reduced. With losses in the discharge line equivalent to 1°C, the performance is reduced by 1.5%.
Liquid Line Loss
Pressure losses in the liquid line have little effect on the cooling capacity of the air conditioner. But they cause the danger of boiling of the refrigerant. This happens for the following reasons:
- due to pressure reduction in the tube, the refrigerant temperature may be higher than the condensing temperature at that pressure.
- the refrigerant heats up due to friction against the walls of the pipes, since the mechanical energy of its movement is converted into heat.
As a result, the refrigerant may begin to boil not in the evaporator, but in the tubes before the regulator. The regulator cannot work stably on a mixture of liquid and vapor refrigerant, since the refrigerant flow through it will greatly decrease. In addition, the cooling capacity will decrease, since not only the air in the room will be cooled, but also the space around the pipeline.
The following pressure losses in the pipes are allowed:
- in the discharge and suction lines - up to 1°С
- in the liquid line - 0.5 - 1°С
Today on the market there areVRF
- systems of original Japanese, Korean and Chinese brands. Even moreVRF
-multiple systemsOEM
manufacturers. Outwardly, they are all very similar and one gets the false impression that allVRF
systems are the same. But "not all yogurts are created equal," as the popular ad said. We are starting a series of articles aimed at studying the technologies for obtaining cold, which are used in modern classroom air conditioners -VRF
-systems. We have already considered the refrigerant subcooling system and its effect on the characteristics of the air conditioner, various layouts of the compressor unit. In this article, we will explore -oil separation system
.
What is the oil in the refrigeration circuit for? For compressor lubrication. And the oil must be in the compressor. In a conventional split system, oil circulates freely along with freon and is evenly distributed throughout the entire refrigeration circuit. At VRF systems the refrigeration circuit is too large, so the first problem faced by manufacturers of VRF systems is a decrease in the oil level in the compressors and their failure due to "oil starvation".
There are two technologies by which refrigerant oil is returned back to the compressor. First, the device is used oil separator(oil separator) in the outdoor unit (picture 1). Oil separators are installed on the compressor discharge pipe between the compressor and the condenser. The oil is carried away from the compressor both in the form of small droplets and in the vapor state, since at temperatures from 80C to 110C the oil partially evaporates. Most of oil settles in the separator and returns through a separate oil pipeline to the compressor crankcase. This device greatly improves the lubrication regime of the compressor and ultimately increases the reliability of the system. From the point of view of the design of the refrigeration circuit, there are systems without oil separators at all, systems with one oil separator for all compressors, systems with an oil separator for each compressor. Perfect option uniform oil distribution is when each compressor has its own oil separator (Fig. 1).
Rice. one . Scheme of the refrigeration circuit VRF - systems with two separators of freon oil.
Designs of separators (oil separators).
The oil in the oil separators is separated from the gaseous refrigerant as a result of a sharp change in direction and a decrease in the speed of the steam (up to 0.7 - 1 m/s). The direction of movement of the gaseous refrigerant is changed with the help of baffles or nozzles installed in a certain way. In this case, the oil separator captures only 40-60% of the oil carried away from the compressor. That's why top scores gives a centrifugal or cyclone oil separator (Fig. 2). The gaseous refrigerant entering the nozzle 1, falling on the guide vanes 4, acquires a rotational motion. Under the action of centrifugal force, oil drops are thrown onto the body and form a film slowly flowing down. The gaseous refrigerant, when leaving the coil, abruptly changes its direction and leaves the oil separator through pipe 2. The separated oil is fenced off from the gas jet by partition 5 to prevent the secondary capture of oil by the refrigerant.
Rice. 2. The design of the centrifugal oil separator.
Despite the operation of the oil separator, a small part of the oil is nevertheless carried away with freon into the system and gradually accumulates there. To return it, a special mode is used, which is called oil return mode. Its essence is as follows:
The outdoor unit turns on in cooling mode at maximum capacity. All EEV valves in indoor units are fully open. BUT the fans of the indoor units are turned off, so freon in the liquid phase passes through the heat exchanger of the indoor unit without boiling away. The liquid oil in indoor unit, is washed off with liquid freon into the gas pipeline. And then returns to outdoor unit with freon gas at maximum speed.
Refrigeration oil type used in refrigeration systems for lubricating compressors, depends on the type of compressor, its performance, but most importantly, the freon used. Refrigeration cycle oils are classified as either mineral or synthetic. Mineral oil is mainly used with CFC (R 12) and HCFC (R 22) refrigerants and is based on naphthene or paraffin, or a mixture of paraffin and acrylbenzene. HFC refrigerants (R 410A , R 407C ) do not dissolve in mineral oil, therefore synthetic oil is used for them.
crankcase heater. Refrigeration oil mixes with the refrigerant and circulates with it throughout the entire refrigeration cycle. The oil in the compressor crankcase contains some dissolved refrigerant, while the liquid refrigerant in the condenser contains no a large number of dissolved oil. The disadvantage of using soluble oil is the formation of foam. If a refrigerator is turned off for a long period and the oil temperature in the compressor is lower than in the internal circuit, the refrigerant condenses and most of it dissolves in the oil. If the compressor is started in this condition, the pressure in the crankcase drops and the dissolved refrigerant evaporates along with the oil, forming oil foam. This process is called foaming, it leads to the exit of oil from the compressor through the discharge pipe and the deterioration of the lubrication of the compressor. To prevent foaming, a heater is installed on the compressor crankcase of VRF systems so that the temperature of the compressor crankcase is always slightly higher than the ambient temperature (Fig. 3).
Rice. 3. Compressor crankcase heater
Influence of impurities on the operation of the refrigeration circuit.
Process oil (machine oil, assembly oil). If process oil (such as machine oil) enters a system using HFC refrigerant, the oil will separate, causing flocculation and clogging of the capillary tubes.
Water. If water enters the cooling system using HFC refrigerant, then the acidity of the oil increases, destruction occurs polymer materials used in the compressor motor. This leads to destruction and breakdown of the motor insulation, clogging of capillary tubes, etc.
Mechanical debris and dirt. Emerging problems: clogging of filters, capillary tubes. Decomposition and separation of oil. Compressor motor insulation failure.
Air. A consequence of the ingress of a large amount of air (for example, the system was charged without evacuation): abnormal pressure, hyperacidity oil, compressor insulation breakdown.
Impurities of other refrigerants. If a large amount of different types of refrigerants enter the refrigeration system, abnormal operating pressure and temperature will occur. The result is system damage.
Impurities of other refrigeration oils. Many refrigeration oils do not mix with each other and precipitate in the form of flakes. The flakes clog the filters and capillaries, reducing the flow of freon in the system, which leads to overheating of the compressor.
The following situation occurs repeatedly, related to the mode of oil return to the compressors of outdoor units. Mounted VRF-air conditioning system (Fig. 4). Refueling of the system, operating parameters, piping configuration - everything is normal. The only caveat is that some of the indoor units are not mounted, but the load factor of the outdoor unit is acceptable - 80%. However, compressors regularly fail due to jamming. What is the reason?
Rice. 4. Scheme of partial installation of indoor units.
And the reason turned out to be simple: the fact is that branches were prepared for the installation of the missing indoor units. These branches were dead-end "appendices" into which the oil circulating along with freon got into it, but could no longer come out and accumulated. Therefore, the compressor failed due to the usual "oil starvation". To prevent this from happening, on the branches MAXIMUM CLOSE TO THE SPLITTERS it was necessary to put shut-off valves. The oil would then circulate freely in the system and return in oil recovery mode.
Oil lifting loops.
For VRF-systems of Japanese manufacturers there are no requirements for the installation of oil lifting loops. It is believed that the separators and the oil return mode effectively return the oil to the compressor. However, there are no rules without exceptions - on V 5 series MDV systems, it is recommended to install oil lifting loops if the outdoor unit is higher than the indoor unit and the height difference is more than 20 meters (Fig. 5).
Rice. 5. Scheme of the oil lifting loop.
for freonR 410 A oil lifting loops are recommended to be installed every 10 - 20 meters of vertical sections.
for freonsR 22 andR 407C oil lifting loops are recommended to be installed after 5 meters of vertical sections.
The physical meaning of the oil lifting loop is reduced to the accumulation of oil before vertical lifting. Oil accumulates in the lower part of the pipe and gradually blocks the opening for the passage of freon. Gaseous freon increases its speed in the free section of the pipeline, while capturing liquid oil. When the pipe section is completely covered with oil, freon pushes the oil out like a plug to the next oil lifting loop.
|
Oil |
HF (father) |
Mobile |
TOTAL PLANETELF |
SUNISO |
Bitzer |
|
|
R12 |
Mineral |
HF 12-16 |
Suniso 3GS, 4GS |
|||
|
R22 |
Mineral, Synthetic |
HF 12-24 |
Mobil Gargoyle Arctic Oil 155, 300, Mobil Gargoyle Arctic SHC 400, Mobil Gargoyle Arctic SHC 200, Mobil EAL Arctic 32,46,68,100 |
LUNARIA SK |
Suniso 3GS, 4GS |
Biltzer B 5.2, Biltzer B100 |
|
R23 |
Synthetic |
Mobil EAL Arctic 32, 46,68,100 |
PLANETELF ACD 68M |
Suniso SL 32, 46,68,100 |
Biltzer BSE 32 |
|
|
R134a |
Synthetic |
Mobil Arctic Assembly Oil 32, |
PLANETELF ACD 32, 46,68,100, PLANETELF PAG |
Suniso SL 32, 46,68,100 |
Biltzer BSE 32 |
|
|
R404a |
Synthetic |
Mobil EAL Arctic 32.46, 68.100 |
PLANETELF ACD 32.46, 68.100 |
Suniso SL 32, 46,68,100 |
Biltzer BSE 32 |
|
|
R406a |
Synthetic |
HF 12-16 |
Mobil Gargoyle Arctic Oil 155,300 |
Suniso 3GS, 4GS |
||
|
R407c |
Synthetic |
Mobil EAL Arctic 32.46, 68.100 |
PLANETELF |
Suniso SL 32, 46,68,100 |
Biltzer BSE 32 |
|
|
R410a |
Synthetic |
Mobil EAL Arctic 32.46, 68.100 |
PLANETELF |
Suniso SL 32, 46,68,100 |
Biltzer BSE 32 |
|
|
R507 |
Synthetic |
Mobil EAL Arctic 22CC, 32, 46,68,100 |
PLANETELF ACD 32.46, 68.100 |
Suniso SL 32, 46,68,100 |
Biltzer BSE 32 |
|
|
R600a |
Mineral |
HF 12-16 |
Mobil Gargoyle Arctic Oil 155, 300 |
Suniso 3GS, 4GS |
Conclusion.
Oil separators are the most important and indispensable element of a quality VRF air conditioning system. Only thanks to the return of freon oil back to the compressor, reliable and trouble-free operation of the VRF system is achieved. Most best option construction, when each compressor is equipped with a SEPARATE separator, because only in this case is achieved a uniform distribution of freon oil in multi-compressor systems.
Brukh Sergey Viktorovich, LLC "Company MEL"
2017-08-15There are original Japanese, Korean and Chinese VRF systems on the market today. More VRF systems from numerous OEMs. Outwardly, they are all very similar, and there is a false impression that all VRF systems are the same. But "not all yogurts are created equal," as the popular ad said. We continue a series of articles aimed at studying the technologies for obtaining cold, which are used in the modern class of air conditioners - VRF systems.
Designs of separators (oil separators)
Oil in oil separators is separated from the gaseous refrigerant as a result of a sharp change in direction and a decrease in the speed of steam movement (up to 0.7-1.0 m/s). The direction of movement of the gaseous refrigerant is changed with the help of baffles or nozzles installed in a certain way. In this case, the oil separator captures only 40-60% of the oil carried away from the compressor. Therefore, a centrifugal or cyclone oil separator gives the best results (Fig. 2). The gaseous refrigerant entering the nozzle 1, falling on the guide vanes 3, acquires a rotational motion. Under the influence of centrifugal force, oil drops are thrown onto the body and form a film slowly flowing down. The gaseous refrigerant, when leaving the coil, abruptly changes its direction and leaves the oil separator through pipe 2. The separated oil is separated from the gas jet by partition 4 in order to prevent the secondary capture of the oil by the refrigerant.
Despite the operation of the separator, a small part of the oil is still carried away with freon into the system and gradually accumulates there. To return it, a special oil return mode is used. Its essence is as follows. The outdoor unit turns on in cooling mode at maximum capacity. All EEV valves in indoor units are fully open. But the fans of the indoor units are turned off, so freon in the liquid phase passes through the heat exchanger of the indoor unit without boiling away. The liquid oil in the indoor unit is flushed with liquid freon into the gas pipeline. And then it returns to the outdoor unit with gaseous freon at maximum speed.
Refrigeration oil type
The type of refrigerant oil used in refrigeration systems to lubricate compressors depends on the type of compressor, its performance, but most importantly, on the freon used. Refrigeration cycle oils are classified as either mineral or synthetic.
Mineral oil is mainly used with CFC (R12) and HCFC (R22) refrigerants and is based on naphthene or paraffin, or a mixture of paraffin and acrylbenzene. HFC refrigerants (R410a, R407c) do not dissolve in mineral oil, so synthetic oil is used for them.
crankcase heater
Refrigeration oil mixes with the refrigerant and circulates with it throughout the entire refrigeration cycle. The oil in the compressor crankcase contains some dissolved refrigerant, and the liquid refrigerant in the condenser contains a small amount of dissolved oil. The disadvantage of using the latter is the formation of foam. If the chiller is shut down for an extended period and the oil temperature in the compressor is lower than in the internal circuit, the refrigerant will condense and most of it will dissolve in the oil. If the compressor starts in this state, the pressure in the crankcase drops and the dissolved refrigerant evaporates along with the oil, forming oil foam. This process is called “foaming” and causes oil to escape from the compressor through the discharge pipe and deteriorate compressor lubrication. To prevent foaming, a heater is installed on the compressor crankcase of VRF systems so that the temperature of the compressor crankcase is always slightly higher than the ambient temperature (Fig. 3).
Influence of impurities on the operation of the refrigeration circuit
1. Process oil (machine, assembly oil). If process oil (such as machine oil) enters a system using HFC refrigerant, the oil will separate, forming flocculation and causing clogging of the capillary tubes.
2. Water. If water enters the cooling system using HFC refrigerant, the acidity of the oil increases, and the polymer materials used in the compressor engine are destroyed. This leads to destruction and breakdown of the motor insulation, clogging of capillary tubes, etc.
3. Mechanical debris and dirt. Emerging problems: clogging of filters, capillary tubes. Decomposition and separation of oil. Compressor motor insulation failure.
4. Air. A consequence of the ingress of a large amount of air (for example, the system was filled without evacuation): abnormal pressure, increased acidity of the oil, breakdown of the compressor insulation.
5. Impurities of other refrigerants. If a large amount of different types of refrigerants enter the refrigeration system, abnormal operating pressure and temperature will occur. The consequence of this is damage to the system.
6. Impurities of other refrigeration oils. Many refrigeration oils do not mix with each other and precipitate in the form of flakes. The flakes clog the filters and capillary tubes, reducing the flow of freon in the system, which leads to overheating of the compressor.
The following situation occurs repeatedly, related to the mode of oil return to the compressors of outdoor units. A VRF air conditioning system has been installed (Fig. 4). Refueling of the system, operating parameters, pipeline configuration - everything is normal. The only caveat is that some of the indoor units are not mounted, but the load factor of the outdoor unit is acceptable - 80%. However, compressors regularly fail due to jamming. What is the reason?
And the reason is simple: the fact is that branches were prepared for the installation of the missing indoor units. These branches were dead-end "appendices" into which the oil circulating along with freon got into, but could not go back and accumulated there. Therefore, the compressors failed due to the usual "oil starvation". To prevent this from happening, it was necessary to install shut-off valves on the branches as close as possible to the splitters. The oil would then circulate freely in the system and return in oil recovery mode.
Oil lifting loops
There are no requirements for the installation of oil lifting loops for Japanese VRF systems. It is believed that the separators and the oil return mode effectively return the oil to the compressor. However, there are no rules without exceptions - on V5 series MDV systems, it is recommended to install oil lifting loops if the outdoor unit is higher than the indoor unit and the height difference is more than 20 m (Fig. 5).
The physical meaning of the oil-lifting loop is reduced to the accumulation of oil before the vertical lift. Oil accumulates in the lower part of the pipe and gradually blocks the opening for the passage of freon. Gaseous freon increases its speed in the free section of the pipeline, while capturing the accumulated liquid oil.
When the pipe section is completely covered with oil, freon pushes this oil out like a plug to the next oil lifting loop.
Conclusion
Oil separators are an essential and indispensable element of a quality VRF air conditioning system. Only thanks to the return of freon oil back to the compressor, reliable and trouble-free operation of the VRF system is achieved. The most optimal design option is when each compressor is equipped with a separate separator, since only in this case is a uniform distribution of freon oil in multi-compressor systems achieved.
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