Calculation of freon pipelines. Designing a freon route for kkb. What to consider when designing a freon route
When designing refrigeration units, it may be necessary to place the evaporative-compressor unit on the ground floor or in the basement, and the air-cooled condenser on the roof of the building. In such cases, special attention must be paid right choice the diameter and configuration of the discharge line to circulate the lubricating oil in the system.
In freon refrigeration units, unlike ammonia units, lubricating oil dissolves in freon, is carried away with the discharge vapor from the compressor, and can accumulate in various places of the pipeline system. In order for the oil leaving the compressor to rise through the discharge pipeline to the condenser, a siphon loop is installed on the horizontal section of the pipeline before going to the vertical section, in which oil accumulates. The size of the loop in the horizontal direction should be as small as possible. Usually it is made from bends bent at an angle of 90 °. Freon vapors passing through the siphon "crush" the oil accumulated there and carry it up the pipeline.
In refrigeration units with a constant (unregulated) cooling capacity, the speed of freon movement in the pipe does not change. In such installations, if the height of the vertical section is 2.5 m or less, the siphon may not be installed. At a height of more than 2.5 m, a siphon is installed at the beginning of the riser and additional siphons (oil-lifting loops) every 5-7 m, and the horizontal section of the pipeline is mounted with a slope towards the vertical riser.
The diameter of the discharge pipeline is determined by the formula:
Where: V=G/ρ- freon volume flow, m 3 / s; ρ, kg / m 3 - freon density; G- mass consumption of freon (kg / s) - G A \u003d Q 0 / (i 1 "" + i 4), the value of which is determined using the diagram i-lg p for the freon used in the installation at known (given) cooling capacity ( Q0), evaporation temperature ( t o) and condensation temperature ( t k).
If the refrigeration compressor is equipped with a cooling capacity control system (for example, from 100% to 25%), then when it decreases and, consequently, the flow rate and freon velocity in the ascending discharge pipeline decrease to a minimum value (8 m / s), the oil rise will stop. Therefore, in refrigeration units with adjustable compressor capacity, the ascending section of the pipeline (riser) is made of two parallel branches (Fig. 1).
Scheme refrigeration plant
At maximum performance of the installation, freon vapor and oil rise through both pipelines. At minimum performance and, consequently, the speed of freon movement in the main branch ( B ) oil accumulates in the siphon, preventing the movement of freon through this pipeline. In this case the rise of freon and oil will be carried out only through the pipeline BUT .
The calculation of the injection twin pipeline begins with the determination of the diameter of this pipeline. Since the cooling capacity is known for it (for example, 0.25 Q km) and the required freon vapor velocity (8 m/s), the required pipeline diameter is determined by formula (1), after which, according to the catalog copper pipes pipelines select a pipe whose diameter is closest to the value obtained by calculation.
Main branch pipeline diameter d B determined from the condition that at the maximum performance of the installation, when freon rises along both parallel branches, the hydraulic losses in the branches are the same:
G A + G B = G km (2)
Δr A = Δr B (3)
Where: λ - coefficient of hydraulic friction; ζ - coefficient of local losses.
From fig. 1 shows that the lengths of the sections, the number and nature of local resistances in both branches are approximately the same. That's why
Where
Problem solution example determining the diameters of the discharge pipelines of the refrigeration machine.
Determine the diameters of the discharge pipelines of the refrigeration machine for cooling water in the air conditioning system, taking into account the following initial data:
capacity control range .................................100-25%;
refrigerant ............................................................... ..............R 410A;
boiling temperature................................................ ...........to = 5 °C;
condensing temperature .................................................................. ....tk = 45 °C.
cooling load .................................................................. .........320 kW;
The dimensions and configuration of pipelines are shown in Fig.1.
p(for freon R 410A) is shown in fig. one.
Freon R410A parameters at the nodal points of the cycle are shown in Table 1.
Refrigeration cycle diagram in i-lg diagram p(for freon R404A)
Table 1
Freon R410A parameters at the key points of the refrigeration cycle(table to Fig. 2)
| points | Temperature, ° С |
Pressure, Bar |
Enthalpy, kJ/kg |
Density, |
| 1 | 10 | 9,30 | 289 | 34,6 |
| 1"" | 5 | 9,30 | 131 | 34,6 |
| 2 | 75 | 27,2 | 331 | 88,5 |
| 3 | 43 | 27,2 | 131 | 960 |
| 4 | 5 | 9,30 | 131 | - |
Solution.
Determining the diameters of pipelines, we start with the pipeline BUT , for which it is known that the speed of freon in it must be at least 6 m / s, and the freon consumption must be minimal, i.e., at Q 0 \u003d 0.25 Q km= 0.25 x 320 = 80 kW.
1) specific cooling capacity at boiling point t 0 \u003d 5 ° С:
q 0 = 289 - 131 = 158 kJ/kg;
2) the total mass flow rate of freon in pipelines (in the discharge pipe of the compressor):
G km \u003d Q o, km / q 0 \u003d 320/158 \u003d 2.025 kg / s;
3) mass flow of freon in the pipeline BUT :
G A \u003d 0.25 x 2.025 \u003d 0.506 kg / s.
Determine the diameter of the pipeline BUT :
In 1952 he received a diploma from Moscow State Technical University. Bauman (Moscow) and was sent for distribution to the Ural Compressor Plant.
In 1954, upon his return to Moscow, he went to work at MRMK Refrigeration Equipment. Then the labor activity was continued at the All-Union Scientific Research Refrigeration Institute (VNIHI) as a senior researcher.
In 1970 he defended his dissertation and received the degree of Candidate of Technical Sciences.
Later he worked in design organizations in the direction related to the design of refrigeration and air conditioning systems, at the same time taught and translated technical literature from in English.
The experience gained was the basis of the popular textbook - "Course and diploma design of refrigeration and air conditioning systems", the 3rd edition of which was published in 1989.
Today, Boris Konstantinovich continues to successfully consult and perform design work (in the ACAD environment), refrigeration units and air conditioning systems, and also provides services for the translation of technical literature and texts from English on the subject of refrigeration units and air conditioning systems.
For individuals and organizations interested in cooperation, personally, with Yavnel B.K., please send requests to.
Thanks.
In the process of acceptance tests, over and over again, one has to deal with errors made in the design and installation of copper pipelines 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. The issues of pipe placement, their relative position, the problem of choosing the diameter of freon pipelines, the need for oil lifting loops, compensators, etc. will be considered. 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.
This material mainly concerns freon air conditioning systems, whether traditional split systems, multi-zone air conditioning systems or precision air conditioners. However, we will not touch on the installation of water pipes in chiller systems and the installation of relatively short freon pipelines inside refrigerators.
Regulatory documentation for the design and installation of copper pipelines
Among the regulatory documentation regarding the installation of copper pipelines, we highlight the following two standards:
- STO NOSTROY 2.23.1-2011 "Installation and commissioning of evaporative and compressor-condenser units of domestic air conditioning systems in buildings and structures";
- SP 40-108-2004 "Design and installation of internal systems for 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, non-standard situations may arise that are not indicated 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 unacceptably high noise levels, the maximum allowed 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, a reverse oil lifting loop is installed at the upper point.
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, and 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. This method should be resorted to in case of using non-standard pipelines or in case of disputes. 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. If necessary, more accurate distances between fasteners on 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 = α L ∆t,
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 different modes during operation, °C;
α - 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 (pipe operating temperature 70°C), i.e. ∆t = 70–25 = 45°C.
By the formula we find:
∆L \u003d α 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 ΔL, 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. Since the hottest refrigerant flows between the compressor and condenser, and the coldest temperature is typical for outdoor areas in winter, the most critical are the outdoor piping 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 the total length of 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 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 hangers, 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 their 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 work. 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 at the design level a height for laying freon lines that is convenient for installation. 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 one above the other various systems, the one in which the heavier gas flows should 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 you have to face in real construction: forgotten expansion joints or expansion joints that do not fit in the corridor due to adjacent engineering systems, erroneous pipe fastening schemes, 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"
A small manual for laying freon pipeline and drainage routes. With details and little tricks. All of them were born and came from, and I really hope they will greatly simplify the installation of ventilation and air conditioning systems.
Any installation of an air conditioner (in our case, the most common option is a split system) begins with the laying of copper pipes for freon circulation. Depending on the model of the air conditioner and its power (in terms of cooling parameters, in KW), copper pipes have different diameters. At the same time, the tube intended for gaseous freon has a larger diameter, and the tube for liquid freon, respectively, is smaller. Since we are dealing with copper, we must always remember that this material is very delicate and easily deformable. Therefore, the laying of tracks must be carried out only by qualified personnel and very carefully. The fact is that damage to copper pipes can cause freon leakage and, as a result, failure of the entire air conditioning system as a whole. This is complicated by the fact that freon does not have a pronounced smell and it is possible to understand exactly where the leak occurs only with the help of a special leak detector device.
So, installation work begins with unwinding the bay copper tube. They have a standard length of 15 meters. .
Important. There are two types of copper tubes: annealed and not. Annealed comes in coils and is easy to bend, unannealed comes in whips and has a rigid structure.
If we are lucky, and the distance between the indoor and outdoor unit is less than 15 meters, the work will only consist in laying one bay (each diameter). If the distance exceeds this footage, then the copper tubes must be soldered together.
After the required length of the copper tube is unwound from the coil, the excess must be cut off. This is done using a special pipe cutter, since when cutting the pipe it does not leave metal chips that can get inside the system. And this is unacceptable. In my practice, there were those who bit the pipes with wire cutters and even cut them off with a grinder! As a result of such installation, the air conditioner will live for a couple of three months and the compressor will break down "for unknown reasons."
Important. After the copper tube is cut to a suitable size, it must be closed with special plastic plugs or simply sealed with plumbing tape.
It's time to isolate the copper traces. For these purposes, special insulation based on foamed rubber is used. It is produced in whips of two meters each and differs in standard sizes for each specific diameter of the copper tube. When pulling the insulation on the pipe, care must be taken not to tear it. Between themselves, the whips, after tightly adjoining each other, are glued together with adhesive tape. Most often, gray plumbing tape is used. Further, a pair of copper pipes prepared in this way (liquid and gas) is mounted in the serviced room. Usually, the routes run in the interceiling space (between the concrete floor and the false ceiling). Also in the composition of the freon pipeline line there is an interconnect cable. It links the internal and outdoor unit. When fastening tracks to a concrete floor, perforated tape is most widely used. It is cut into small pieces and the tubes are pulled for secure fixation.
Important. Excessive force is not allowed when fixing with perforated tape, as this can lead to deformation of a rather plastic and soft copper tube. Also, very strongly compressed insulation loses its thermal insulation properties and condensation may occur in such places.
In laying the copper routes of the freon pipeline, the most difficult place is the passage of holes in the walls, especially in thick monolithic ones. At the same time, rather capricious insulation usually breaks, and this is unacceptable. the places of the tubes where it is not present are frosted over. To avoid this, they resort to a kind of "reinforcement" of the insulation. To do this, along the entire length of the tube (which will pass through the hole), right on top of the insulation, they glue it with dense plumbing tape, which takes on the main “blow”.
That, in fact, is all. The installation of the copper lines of the freon piping is completed. Now it remains only to carefully check the integrity of the insulation and general form the tracks themselves.
