The main feature for which a closed heating system differs from an open one is its isolation from environmental exposure. In such a scheme include a circulation pump that stimulates the movement of the coolant. The scheme is devoid of many of the drawbacks of an open heating circuit.
All about the pros and cons of closed heating schemes you will learn by reading the article proposed by us. It thoroughly analyzed the options for the device, the specificity of the assembly and operation of closed-type systems. An example of a hydraulic calculation is given for independent masters.
The information provided for review is based on building codes. To optimize the perception of a difficult topic, the text is supplemented with useful diagrams, photo selections and video tutorials.
The content of the article:
- The principle of operation of the closed type system
- Air protection
Hydraulic calculation for a closed system
- Rules for calculating the flow of coolant
- Selection of the circulation pump
- How to calculate the expansion tank?
- Tank selection criteria
Selection of the optimal scheme
- Single pipe heating system
- Two-pipe heating system
- Conclusions and useful video on the topic
The principle of operation of the closed type system
Temperature expansions in a closed system are compensated by using a membrane expansion tank filled with water during heating. When cooled, the water from the tank goes back into the system, thereby maintaining a constant pressure in the circuit.
The pressure generated in the closed heating circuit during installation is transmitted to the entire system. The circulation of the coolant is forced, therefore this system is volatile. Without circulation pump there will be no movement of heated water through the pipes to the instruments and back to the heat generator.
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The main difference of a closed type heating system from an open counterpart is the presence of a membrane expansion tank that prevents direct contact of the coolant with the atmosphere.
In domestic traditions, the expansion tank for heating circuits is produced in red. On sale you can find gray and white imported versions
When using a closed expansion tank, expansion chamber, evaporation of the water circulating along the contour is prevented, the formation of deposits on the inner walls of pipes and devices is reduced
As a result of the absence of evaporation and minimization of deposits on the internal surfaces of devices, pipes, valves, the load on the boiler and the pump is reduced, which significantly extends their service life.
Closed options for the construction of heating systems are used with all types of boilers operating on the available types of fuel
In a closed system, it is mandatory to include a safety group consisting of a pressure safety valve, a vent valve and a pressure gauge
The closed expansion tank is selected so that its volume provides space for the expansion of the heated coolant
Expansion units are installed both in the newly constructed heating systems and in the upgraded versions with pump circulation of the coolant
Specificity of a closed heating circuit
Expansion tank for heating systems
Advantages of a closed system
Sparing equipment conditions
Closed circuit in tandem with boilers
Security group in a closed circuit
Rules for the selection of a closed tank
Suitable type of systems to install
The main elements of the closed loop:
- air vent valve;
- thermostatic valve;
- expansion tank not in contact with the atmosphere;
- balancing valve;
- ball valve;
- pump filter;
- safety valve;
- pressure gauge;
- fittings, fasteners.
If the power supply at home is carried out smoothly, then the closed system works efficiently. Often the design is complemented by “warm floors”, increasing its efficiency and heat transfer.
This arrangement allows you to not adhere to a certain diameter of the pipeline, to reduce the cost of purchasing materials and not to have a pipeline on a slope, which simplifies installation. Liquid with low temperature must come to the pump, otherwise its operation is impossible.
The closed-loop heating circuit includes some parts that are used in other types of systems.
This option has one negative nuance - whereas with a constant slope, the heating also works with the absence of power supply, then with a strictly horizontal position of the pipeline, the closed system does not works. Compensates for this lack of high efficiency and a number of positive aspects compared with other types of heating systems.
Installation is relatively simple and is possible in any area. It is not necessary to warm the pipeline, the heating is very fast, if there is a thermostat in the circuit, then the temperature mode can be set. If the system is arranged correctly, then there is no loss of coolant, therefore there are no reasons for its replenishment.
The undoubted advantage of the closed type heating system is that the temperature difference between the supply and return flow makes it possible to increase the operational life of the boiler. The pipeline in a closed loop is less susceptible to corrosion. It is possible to download to the circuit antifreeze instead of waterwhen heating has to be turned off in the winter for a long time.
The most commonly used closed-type systems are water-based, although non-freezing liquids, steam, and gases that have the required characteristics can also perform the function of the coolant.
Theoretically, the air should not flow into a closed heating system, but in fact it is still there. Its accumulation is observed at the time when the pipes and batteries are filled with water. The second reason may be depressurization of the joints.
As a result of the appearance of air plugs, the heat transfer of the system is reduced. To combat this phenomenon in the system include special valves and valves for air release.
If no air accumulates in the system, the float of the air vent blocks the exhaust valve. When an airlock accumulates in the float chamber, the float stops holding the exhaust valve, so that air goes outside the device
To minimize the likelihood of air traffic jams, you must follow certain rules when filling a closed system:
- Feed water from the lowest point to the top. To do this, lay the pipes so that the water and the evolved air move in the same direction.
- Leave the taps in the open position and the taps in the closed position to release water. Thus, with a gradual rise of the coolant, the air will escape through the open air vent.
- Close the air vent valve as soon as water starts running through it. Continue the process smoothly until the circuit is completely filled with coolant.
- Start the pump.
If in the heating circuit aluminum radiators, then on each air vent is required. Aluminum, in contact with the coolant, provokes a chemical reaction, accompanied by the release of oxygen. In partially bimetallic radiators, the problem is the same, but much less air is formed.
Automatic air vent is installed at the top. This requirement is explained by the fact that air bubbles in liquid substances always rush up the tube, where they are collected by the device for air exhaust
In the radiators, the 100% bimetallic coolant is not in contact with aluminum, but professionals insist on the presence of an air vent in this case. The specific design of panel radiators made of steel is already being completed in the production process with valves for air release.
On old cast iron radiators, air is removed with a ball valve, other devices are ineffective here.
The critical points in the heating circuit are the bends of the pipes and the upper points of the system; therefore, devices for air exhaust are mounted in these places. In the closed loop apply Mayevsky's cranes or automatic float valves that allow the air vent without human intervention.
In the case of this device there is a polypropylene float connected through a yoke with a slide valve. As the float chamber is filled with air, the float is lowered, and reaching the lower position opens the valve through which air escapes.
In the volume released from gas, water enters, the float rushes up and closes the valve. To prevent debris from entering the latter, it is covered with a protective cap.
The case of both manual and automatic air vent is made of high-quality material that is not susceptible to corrosion. To remove the airlock, the cone is turned against the hour's travel, and the air is released until the hissing stops.
There are modifications where this process takes place differently, but the principle is the same: the float is in the lower position - gas is released; the float is raised - the valve is closed, the air accumulates. The cycle repeats automatically and does not require human presence.
Hydraulic calculation for a closed system
In order not to be mistaken with the selection of pipes for the diameter and power of the pump, the hydraulic calculation of the system is necessary.
The effective operation of the entire system is impossible without taking into account the main 4 points:
- Determine the amount of coolant that must be supplied to the heating devices to ensure the specified heat balance in the house, regardless of the outside temperature.
- Maximum reduction in operating costs.
- Minimizing financial investments, depending on the selected diameter of the pipeline.
- Stable and quiet operation of the system.
Hydraulic calculation will help to solve these problems, allowing you to choose the optimal pipe diameters taking into account economically justified flow rates of the coolant, to determine the hydraulic pressure loss in certain areas, link and balance the branches system. This is a complex and time-consuming, but necessary design phase.
Rules for calculating the flow of coolant
Calculations are possible in the presence of thermal calculation and after the selection of radiators for power. Thermal calculation should contain reasonable data on the amount of thermal energy, loads, heat loss. If this data is not available, then radiator power is taken over the area of the room, but the results of calculations will be less accurate.
Three-dimensional scheme is easy to use. All elements on it are assigned designations, which include the marking and number in order
Start with the scheme. It is better to perform it in axonometric projection and apply all known parameters. Coolant flow rate is determined by the formula:
G = 860q / ∆t kg / h,
where q is the radiator power of kW, ∆t is the temperature difference between the reverse and the flow line. Determining this value, the tables Shevelevyh determine the cross section of the pipe.
To use these tables, the result of the calculations must be converted to liters per second using the formula: GV = G / 3600ρ. Here GV stands for coolant flow in l / s, ρ is the density of water equal to 0.983 kg / l at a temperature of 60 degrees C. From the tables, you can simply pick up the cross-section of the pipe without performing the full calculation.
Shevelevyh tables greatly simplify the calculation. Here are the diameters of plastic and steel pipes, which can be determined by knowing the speed of the coolant and its consumption
The calculation sequence is easier to understand by the example of a simple circuit including a boiler and 10 radiators. The scheme should be divided into sections where the cross section of pipes and coolant flow are constant values.
The first section is a line running from the boiler to the first radiator. The second - the segment between the first and second radiator. The third and subsequent sections emit similarly.
The temperature from the first to the last device gradually decreases. If in the first section the heat energy is 10 kW, then when the first radiator passes, the coolant gives it some heat and the heat lost is reduced by 1 kW, etc.
Calculate the flow of coolant can be according to the formula:
Q = (3.6xQuch) / (cx (tr-to))
Here Quch is the heat load of the section, c is the specific heat capacity of water, having a constant value of 4.2. kJ / kg x s., tr is the temperature of the hot coolant at the inlet, to is the temperature of the cooled coolant at output
The optimal speed of the hot coolant through the pipeline is from 0.2 to 0.7 m / s. At a lower value, air plugs will appear in the system. This parameter is affected by the material of the product, the roughness inside the pipe.
Both open and closed heating circuits use pipes made of black and stainless steel, copper, polypropylene, polyethylene of various modifications, polybutylene, etc.
When the coolant velocity in the recommended limits, 0.2-0.7 m / s, in the polymer pipeline there will be pressure losses of 45 to 280 Pa / m, and in steel pipes - from 48 to 480 Pa / m.
The internal diameter of the pipe at the site (dвн) is determined based on the heat flux and the difference inlet and outlet temperatures (∆tco = 20 degrees С for a 2-pipe heating scheme) or flow heat carrier. For this there is a special table:
According to this table, knowing the temperature difference between the inlet and outlet, as well as the flow rate, it is easy to determine the internal diameter of the pipe
To select a circuit, one and two-pipe schemes should be considered separately. In the first case, the riser with the greatest amount of equipment is calculated, and in the second, the loaded contour. The length of the plot taken from the plan, made to scale.
Performing accurate hydraulic calculation is only possible for a specialist of the relevant profile. There are special programs that allow you to perform all calculations relating to thermal and hydraulic characteristics, which can be used when heating system design for your home.
Selection of the circulation pump
The purpose of the calculation is to obtain the pressure value that the pump must develop to run water through the system. To do this, use the formula:
P = Rl + Z
- P is the pressure loss in the pipeline in Pa;
- R is the resistivity of friction in Pa / m;
- l is the length of the pipe in the calculated area in m;
- Z - pressure loss on the "narrow" areas in Pa.
These calculations are simplified by the same Shevelevs tables, from which it is possible to find the resistance to friction, only 1000i will have to be recalculated for a specific pipe length. So, if the diameter of the inner tube is 15 mm, the length of the section is 5 m, and 1000i = 28.8, then Rl = 28.8 x 5/1000 = 0.144 Bar. Finding the values of Rl for each plot, they are summarized.
The value of pressure loss Z for both the boiler and radiators is in the passport. For other resistances, experts advise taking 20% of Rl, followed by summing up the results for individual sections and multiplying by a factor of 1.3. The result is the desired pump head. For single and 2-pipe systems, the calculation is the same.
The pump is installed so that its shaft is horizontal, otherwise it will not avoid the formation of air plugs. It is mounted on American women, so that, if necessary, it is easy to remove
In the case when pump pick up according to the existing boiler, the formula is used: Q = N / (t2-t1), where N is the heating unit power in W, t2 and t1 is the coolant temperature at the outlet from the boiler and at the return, respectively.
How to calculate the expansion tank?
The calculation is reduced to the determination of the magnitude by which the volume of the coolant will increase during its heating from the average room temperature + 20 degrees C to the working temperature - from 50 to 80 degrees. These calculations are not easy, but there is another way to solve the problem: professionals advise choosing a tank with a volume equal to 1/10 of the total amount of fluid in the system.
The expansion tank is a very important element of the system. Excess coolant, taken by him at the time of expansion of the latter, save the pipeline and taps from tearing
You can find out these data from the equipment passports, where the capacity of the water jacket of the boiler and 1 section of the radiator is indicated. Then calculate the cross-sectional area of pipes of different diameters and multiply by the appropriate length.
The results are summarized, the data from passports are added to them, and from the total they take 10%. If the entire system holds 200 liters of coolant, then an expansion tank with a volume of 20 liters is needed.
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If there is no desire to delve into complex calculations, the expansion tank for heating circuits up to 150 liters is selected so that its total capacity does not exceed 10% of the total heat carrier volume
Expansion tanks of disc type are produced without membrane. The volume of devices from 6 to 12 liters, occupy a minimum of space in a small boiler room
Vertically oriented membrane tanks with a volume of 6 to 35 liters are produced without supporting legs. In devices up to 18 liters the membrane cannot be replaced.
Broad tanks from 35 to 700 l are installed on basic legs. By structure, all membrane varieties are no different.
Simplified version of the selection of tank
Non-membrane Expansion Tanks
Expansion Tanks with Membrane
Expansion tanks for large systems
Tank selection criteria
Make expansion tanks of steel. Inside there is a membrane dividing the capacity into 2 compartments. The first is filled with gas, and the second is filled with coolant. When the temperature rises and the water rushes from the system into the tank, then under its pressure the gas is compressed. Due to the presence of gas in the tank, the coolant cannot occupy the entire volume.
Capacity of broad tanks happens different. This parameter is selected so that when the pressure in the system reaches its peak, the water does not rise above the set level. As a tank protection against overflow, a safety valve is included in the design. Normal filling of the tank - from 60 to 30%.
The optimal solution is to install the expansion tank in a place where the system has the least bends. The best place for him is a straight section in front of the pump.
Selection of the optimal scheme
At the device of heating in a private house, two types of schemes are used: single and 2-pipe. If you compare them, the latter is more efficient. Their main difference in the methods of connecting radiators to pipelines. In a two-pipe system, an indispensable element of the heating circuit is the individual riser, according to which the cooled coolant is returned to the boiler.
Installation of a single pipe system is simpler and less costly in financial terms. The closed loop of this system combines both supply and return pipelines.
Single pipe heating system
In one and 2-storey houses with a small area, the one-pipe contour scheme has proven itself well. heating of the closed type, which represents the layout of 1 pipe and a number of radiators connected to it consistently.
It is sometimes popularly called "Leningrad". The coolant returns heat to the radiator, returns to the supply pipe, and then passes through the next battery. The last radiators get less heat.
When installing a single-pipe system, you can make 2 options for the movement of the coolant - passing and dead-end. In the first case, the system can be balanced, but in the second there is no
The advantage of this scheme is called economical installation - the material and time is spent less than on a 2-pipe system. In case of failure of a single radiator, the rest will work in normal mode when using the bypass.
The possibilities of the one-pipe scheme are limited - it cannot be started in stages, the radiators warm up unevenly, therefore sections should be added to the last in the chain. So that the coolant does not cool so quickly, it is necessary to increase the diameter of the pipes. It is recommended to connect no more than 5 radiators for each floor.
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In the one-pipe schemes of heating systems, the devices are connected to the main pipe, carrying out both the supply and removal of coolant
Coolant in monotube systems sequentially flows from one heater to another, loses 1–3º of operating temperature along the way.
Single pipe systems with horizontal wiring require the use of a circulation pump. Devices are necessarily equipped with air vent
Systems with the natural movement of the coolant along the heating circuit can be only with the upper wiring
Monotube systems are easy to assemble, require a minimum of pipes and fittings for construction, which has a positive effect on the amount invested in the device
In one-pipe schemes do not use complex technical devices for high-quality temperature balancing, the owners of the systems have fewer reasons for carrying out unplanned repairs.
Temperature regulation in monotube systems is carried out in quantitative terms - the flow of coolant tritely decreases by turning the tap
A significant disadvantage of one-pipe systems is that with a decrease in coolant flow in one battery its reduced quantity will be supplied to the following devices, i.e. only the whole circuit can be regulated, not a single one device
The principle of the construction of a single pipe system
Specificity of coolant movement
Single pipe system with top wiring
The advantages of ease of installation
Advantages of long-term operation
Principle of temperature control
Negative side of one pipe
Two types of systems are known: horizontal and vertical. In a one-story building, a horizontal view of the heating system is laid both above and below the floor. It is recommended to install the batteries on the same level, and the horizontal supply pipe with a slight bias in the course of the coolant.
In case of vertical distribution, water from the boiler rises upwards along the central riser, enters the pipeline, is distributed among the individual risers, and from them - along radiators. Cooling down, the liquid goes down along the same riser, passing through all the devices there, turns out to be in the return pipeline, and from it the pump pumps it back to the boiler.
The single-pipe vertical system includes the main riser and a number of separate, expansion tank, supply pipe, batteries, air collector, return pipe, pump. The system with displaced sections is used more often, where 3-way valves are used to adjust the heating of radiators.
Having chosen the closed type of the heating system, the installation is carried out in the following sequence:
- Install the boiler. Most often for him a place is allocated on the basement or ground floor of the house.
- Connect to the inlet and outlet pipes of the boiler pipe, diluted them around the perimeter of all premises. Connections are selected depending on the material of the main pipes.
- Install the expansion tank, placing it at the highest point. Simultaneously with this, the security group is mounted, connecting it to the highway via a tee. Perform fixation of the vertical main riser, connect it to the tank.
- Make installation of radiators with the installation of cranes Mayevsky. The best option: bypass and 2 shut-off valves - one at the inlet, the other at the outlet.
- The pump is installed on the site where the cooled coolant enters the boiler, having previously installed a filter in front of its mounting location. The rotor is placed strictly horizontally.
Some masters install a pump with a bypass, so as not to drain water from the system in case of repair or replacement of equipment.
After installation of all elements open the valve, fill the line with coolant, remove the air. It is checked that the air is so completely removed by unscrewing the screw located on the cover of the pump casing. If a liquid is emitted from it, it means that the equipment can be started up, having previously tightened the previously unscrewed central screw.
With proven practice schemes single pipe heating systems and options for the device you can find in another article on our site.
Two-pipe heating system
As in the case of the one-pipe system, there is a horizontal and vertical layout, but there is both a supply and a return line. All radiators heat the same. One type differs from another in that in the first case there is a single riser and all heating devices are connected to it.
Two-pipe schemes are most often found in multi-storey construction, when it is required that one boiler effectively heat the entire building.
The vertical scheme provides for the connection of radiators to the riser, located vertically. Its advantage is that in a multi-storey building, each floor is connected to the riser individually.
A special feature of the two-pipe circuit is the presence of pipes connected to each battery: one straight-through and the second reverse. To connect the heaters there are 2 schemes. One of them is collector, when 2 pipes fit from the collectors to the battery.
The scheme is characterized by complex installation, high material consumption, but in each room you can adjust the temperature.
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The two-pipe scheme for the construction of heating systems assumes that the supply of coolant is made through one pipe, and its withdrawal after cooling is done through another
The use of two pipes can significantly complicate and increase the length of the heating circuits. Systems with upper wiring arrange with both natural and forced movement of the coolant
Systems with lower wiring are most often constructed using a circulation pump. Gravity variants are rare because of the need to install an air vent on each device and bleed off excess air almost every day.
By analogy with one-pipe systems with two pipes are divided into passing and dead-end. In dead-end devices located closer to the boiler, they warm up better.
With the difference in the parameters of the working temperature are struggling by installing thermostats. The change in temperature in one device does not affect the entire circuit.
Pipes and fittings for the construction of a two-pipe network of heating, of course, will need more, but when using polymer products, they can be hidden in building structures
The use of two pipes significantly expands the construction options, although in the assembling of the systems tee circuits are still often used.
It is the two-pipe principle of the device that makes it possible to embody various versions of the beam wiring, which presupposes parallel connection of devices to the distribution manifold. As a result, the length of the pipe is reduced and all radiators get equal in temperature coolant
Features of the two-pipe system
Two-pipe version with top wiring
Heating scheme with lower wiring
Dead-end two-pipe system
Ability to hide pipes
Using the tee scheme
Radial pipe liner
The second - the parallel circuit is simpler. Risers installed around the perimeter of the house, they are connected to radiators. A lounger passes through the whole floor and the risers are connected to it.
The components of such a system are:
- safety valve;
- pressure gauge;
- automatic air vent;
- thermostatic valve;
- balancing device;
Before proceeding with the installation, the issue of the type of energy carrier should be resolved. Next, install the boiler in a separate boiler room or in the basement. The main thing is to ensure good ventilation there. Install the collector, if it is provided by the project and the pump. Adjacent to the boiler, adjusting and measuring equipment.
A line is connected to each future radiator, then the batteries are installed. They hang heaters on special brackets in such a way that 10-12 centimeters remain up to the floor, and 2-5 cm from the walls. Provide locking and regulating devices to openings of devices on an entrance and an exit.
The process of installing a two-pipe system consists of several stages. The first is the installation of the boiler. To the places of installation of batteries, pipes are first brought in and only then radiators are mounted.
After installation of all nodes of the system it is pressed. Professionals should be engaged in it because only they can issue the corresponding document.
Detail features of the device double-pipe heating system described hereThe article presents various schemes and their analysis.
Conclusions and useful video on the topic
This video contains an example of a detailed hydraulic calculation of a 2-pipe closed-type heating system for a 2-storey house in the VALTEC.PRG program:
Here is described in detail about the device one-pipe heating system:
Installation of a closed version of the heating system is possible on its own, but it is impossible to do without expert advice. The key to success is a correctly executed project and high-quality materials.
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