For many installers there is a sin of prejudice. For example, the master considers the single-pipe wiring the best and offers it to all customers - owners of private houses. Such proposals often hide low qualification of the contractor or some kind of benefit. Our task is to consider how a two-pipe heating system works, objectively evaluate the advantages and disadvantages, and give recommendations for choosing a scheme.
How does dual-circuit heating work?
The design of a two-pipe water heating system involves the supply and removal of coolant from each radiator along two separate pipes. Simplified: the battery inlet is connected to the supply line, the output to the return. Through the first pipeline, the heated water from the boiler is distributed to all heating devices, the second pipe collects the cooled coolant and sends it back to the heat generator.
Features of dual-circuit water distribution:
- if all elements of the system are calculated correctly, then each radiator receives a coolant of the same temperature;
- a change in the flow of water through one battery due to adjustment has little effect on the operation of neighboring heating appliances;
- the number of radiators on one branch can reach 40 pcs. provided that the pump capacity and the diameter of the supply pipes provides the estimated water flow.
Note. The number 40 is taken on the basis of practical experience in the design and installation of heating in a production workshop. In country cottages, so many appliances are not connected to one branch, maximum - 10 pcs. If you need to make wiring in a multi-storey building, the heat supply network is divided into several two-pipe circuits.
The movement of water through pipes and batteries is provided in two ways - natural (convection) and forced. There are several options for supplying coolant, so we suggest that you consider each circuit separately.
4 types of 2-pipe systems
Depending on the conditions for laying pipelines and further operation in private homes, the following two-pipe schemes are used:
- Gravity or gravity with the natural circulation of heated water.
- Classic dead end heating system.
- Annular with the accompanying movement of the coolant, it is also the Tichelman loop.
- Radiation with individual heat distribution to radiators from the distribution manifold.
The note. Two-pipe heating can also include underfloor heating. Heating circuits act as batteries, supply pipes and a comb with a mixing unit play the role of pipelines. By design, floor heating is close to the collector circuit.
In a gravity-filled version, the system operates without excessive pressure, the coolant contacts the atmosphere through an open expansion tank. The remaining 3 variants of the schemes are closed, operating under pressure of 1-2.5 Bar and only with forced circulation of hot water. Now we will analyze each scheme using a specific example of a two-story house.
Gravity heating
The principle of operation of the system with the natural movement of the coolant is based on the phenomenon of convection - a hot and less dense liquid tends to rise up the pipe, displaced by heavier cold layers. The boiler heats the water, it becomes lighter and moves through a vertical riser at a speed of 0.1-0.3 m / s, then diverges along the mains and batteries.
Clarification. It is understood that the heated and cooled liquid is within the same closed loop, in this case the heating network of a private house acts as such.
We list the characteristics of the two-pipe gravity system of a two-story building shown in the drawing:
- The way of laying highways is horizontal upper wiring, originating from a common riser. The latter rises from the boiler, at the highest point there is an expansion tank in communication with the atmosphere.
- Horizontal sections are laid with a minimum slope of 3 mm per meter of running line. The feed is tilted towards the radiators, the return to the heat source.
- The diameters of the pipes are increased compared to pressure systems, because they are designed for a low water flow rate.
An important nuance. To realize sustainable gravity flow, pipes of Ø40-50 mm (internal) must be used. The minimum allowable diameter of the distributing and collecting branches - DN25, is placed near the last batteries.
In a one-story house, a similar scheme is used, but with a single connection of radiators. The supply manifold of the upper wiring is laid in the attic or under the ceiling, the reverse - above the floor. It is impossible to make a lower wiring - according to the law of communicating vessels, the coolant will leak into the batteries, but the speed and heating efficiency will drop to a minimum.
Current gravity schemes have become combined thanks to the installation of circulation pumps. The unit is mounted on the bypass, so as not to interfere with the flow of water in the event of a power outage.
Dead end heating branches
The two-pipe closed system of the shoulder (dead-end) type is mounted in most suburban cottages and is often used in new apartment buildings. How the circuit works:
- The radiator network consists of one or more two-pipe branches. The coolant is sent to the heating devices along one highway, and returns along the second.
- The system operates with an overpressure of 1–2.5 Bar, circulation is provided by a pump installed near the boiler.
- The expansion of water is compensated by a membrane-type tank located in the boiler room. The insertion point is on the pipeline in front of the circulation pump (if you look at the fluid flow).
- Air is discharged from the network through Mayevsky taps on batteries and an automatic valve as part of the safety group of the heating unit. There is also a manometer and safety valve.
- A common wiring option is the lower horizontal, when both pipes pass under the radiators in an open way.
Comment. If necessary, dead-end lines can be laid without problems in a closed way - in floor screed grooves, behind suspended ceilings or inside walls.
If it is necessary to distribute the coolant into 2 wings of a two-story building, it is divided into 4 separate branches (shoulders) converging to a common riser. It is noteworthy that the length of the lines and the thermal load on the shoulders should not be the same at all. The number of batteries and the laying route is developed taking into account the characteristics of a particular building.
Branches with a different number of radiators are balanced by balancing - limiting the flow of control valves. Valves are always placed at the battery outputs and, if necessary, on the shoulder as a whole. How to properly balance the contours, read on another page of our resource.
Tihelman's Ring
The general principle of operation of this circuit is identical to the dead-end wiring, but the method of distribution and return of the coolant differs in 3 ways:
- Each heating circuit is closed in a ring.
- The battery connection method is as follows: the first radiator in the feed is the last for the return line. Conversely, the final battery of the distribution line becomes the first for return.
- Water in both pipelines moves in one direction, hence the technical name of the system is associated.
The Tichelman loop device involves a horizontal lower wiring - hidden under the floor, less often - open on the walls.Another option: the ring can be made under the ceiling, hidden behind suspended ceilings or in the basement, and pipe pipes to the heaters.
The peculiarity of the ring "hitch" - almost perfect hydraulic balance. Note: on the way to all batteries and back, the coolant travels the same distance. The circuit is able to provide the required water flow for 10 or more radiators with minimal balancing.
The author of the video explains the system well, but does an incorrect comparison - properly balanced branches give out heat no worse than a "ride".
Beam connection method
This most advanced type of two-pipe water heating system includes the following elements:
- heaters - ordinary batteries, floor convectors or individual contours of underfloor heating;
- 2 collectors - supply and return, equipped with flow meters and thermostatic valves;
- individual two-pipe hoses laid from the collector to the heating devices along the shortest path (under the floor or ceiling, in the ceiling).
A collector installed in a convenient location receives and returns water to the boiler along two main highways. Using the valves, the flow rate of the coolant for each battery is adjusted. If you install RTL thermal heads or servos on the manifold valves, you can automatically adjust the climate in any room and building in general.
Pros and cons of two-pipe wiring
For ease of perception, we have combined the advantages and disadvantages of all the above systems in one section. First, we list the key positive points:
- The only advantage of gravity over other schemes is independence from electricity. Prerequisite: you need to select a non-volatile boiler and make strapping without connecting to a house electrical network.
- The shoulder (dead end) system is a worthy alternative to Leningrad and other single-tube wiring. The main advantages are versatility and simplicity, thanks to which the two-pipe heating scheme of a 100-200 m² house can be mounted on its own without problems.
- The main trump cards of the Tichelman loop are hydraulic balance and the ability to provide a large number of radiators with a coolant.
- Collector wiring is the best solution for hidden pipe laying and full automation of heating.
Note. The last 3 circuits are easy to combine with the underfloor heating circuits. It is not always advisable to combine a gravitational radiator network with warm floors - forced circulation in heating circuits is impossible without electricity.
Briefly highlight the general advantages of the beam, incidental and deadlock systems:
- small sections of distribution pipes;
- flexibility in terms of laying, that is, lines can run along various routes - in the floors, along and inside walls, under the ceiling;
- various plastic or metal pipes are suitable for installation: polypropylene, cross-linked polyethylene, metal-plastic, copper and corrugated stainless steel;
- all 2-pipe networks lend themselves well to balancing and thermal regulation.
We note a minor plus of gravity wiring - the ease of filling and removing air without the use of valves and taps (although it is easier to air the system with them). Water is slowly supplied through the nozzle at the lower point, air is gradually displaced from the pipelines into an open expansion tank.
Now about the significant disadvantages:
- The scheme with the natural movement of water is cumbersome and expensive. You will need pipes with an inner diameter of 25 ... 50 mm, mounted with a large slope, ideally - steel. Hidden laying is very difficult - most of the elements will be in sight.
- In the installation and operation of dead-end branches, significant minuses were not found. If the shoulders are very different in length and number of batteries, balance is restored by deep balancing.
- Tichelman's ring lanes always cross doorways. We have to make bypass loops, where air can subsequently accumulate.
- The beam type wiring requires financial costs for equipment - manifolds with valves and rotameters plus automation equipment. An alternative is to assemble a comb from polypropylene or bronze tees with your own hands.
Addition. To automatically control the heat transfer of batteries during gravity, you will need special radiator valves with an increased bore.
Which scheme is better to choose
The selection of wiring is carried out taking into account many factors - the area and number of storeys of a private house, the allocated budget, the availability of additional systems, the reliability of power supply and so on. We give a number of general recommendations for selection:
- If you plan to collect heating yourself, it is better to stay on a two-pipe shoulder system. She forgives beginners many mistakes and will work, despite the flaws.
- With high requirements for the interior of the rooms, take the collector type of wiring as a basis. You’ll hide the comb in a wall cupboard, and you will separate the lines under the screed. In a two- or three-story mansion, it is advisable to install several combs - one per floor.
- Frequent power outages do not leave a choice - you need to assemble a circuit with natural circulation (gravity flow).
- The Tichelman system is appropriate in buildings with a large area and the number of heating panels. To install a loop in small buildings is impractical from a financial point of view.
- For a small country house or bath, a dead end wiring option with an open piping is perfect.
Tip. Heating cottages for 2-4 small rooms can be arranged using a one-pipe horizontal system with a lower wiring - “Leningrad”.
If it is planned to heat the cottage with radiators, underfloor heating and water heaters, it is worth using a dead-end or collector wiring option. These two schemes are easily combined with other heating equipment.
How to calculate pipe diameter
With the installation of a dead end and collector wiring in a country house with an area of up to 200 m², you can do without rigorous calculations. Take the section of highways and eyeliners according to the recommendations:
- in order to supply coolant to the radiators in the building of 100 squares or less, the Du15 pipeline is sufficient (outer size 20 mm);
- connections to the batteries are made with a cross-section of Du10 (external diameter 15-16 mm);
- in a two-story house of 200 squares, the distributing riser is made with a diameter of Du20-25;
- if the number of radiators on the floor exceeds 5 pcs., divide the system into several branches extending from the riser Ø32 mm.
Tip. The diameters of highways and eyeliners are quite accurately affixed on the examples of schemes above. You can use the specified information when developing a home heating project.
A gravity and ring system is developed according to engineering calculations. If you want to determine the cross-section of the pipes yourself, first calculate the load on the heating of each room, taking into account ventilation, then find out the required flow rate of the coolant according to the formula:
- G is the mass flow rate of heated water in the pipe section that feeds the radiators of a particular room (or group of rooms), kg / h;
- Q - the amount of heat required to heat a given room, W;
- Δt is the calculated temperature difference at the supply and in the return, take 20 ° С.
Example. To warm the second floor to a temperature of +21 ° C, 6000 watts of thermal energy are needed. The heating riser passing through the ceiling should bring 0.86 x 6000/20 = 258 kg / h of hot water from the boiler room.
Knowing the hourly consumption of the coolant, it is not difficult to calculate the cross-section of the supply pipe according to the formula:
- S is the area of the desired pipe section, m²;
- V - volumetric flow rate of hot water, m³ / h;
- ʋ– flow rate of the heat carrier, m / s.
Reference.The velocity of the coolant in pressure systems with a circulation pump is taken from the range 0.3 ... 0.7 m / s. During gravity flow is slower - 0.1 ... 0.3 m / s.
Continuation of the example. The calculated flow rate of 258 kg / h is provided by the pump, we take the water speed of 0.4 m / s. The cross-sectional area of the supply pipe is 0.258 / (3600 x 0.4) = 0.00018 m². We recalculate the cross-section into diameter according to the circle area formula, we get 0.02 m - a Du20 pipe (outer - Ø25 mm).
Note that we neglected the difference in water densities at different temperatures and substituted the mass flow rate into the formula. The error is small, with a handicraft calculation is quite allowed.
Final conclusion
Practice shows that a 2-pipe dead-end system is suitable for heating most medium-sized residential buildings. The technical solution captivates with the simplicity and reasonable cost of installation work. Collector and associated wiring will cost more - the price of equipment and the length of the lines play a role. Take a look at the scheme with the Tichelman loop - distribution pipelines of the same diameter run along the entire perimeter of the building.
A separate conversation is a two-pipe heating system with natural water circulation. In conditions of frequent power outages, it is better not to risk and not to chase the beauty of the interiors, but to mount a non-volatile heating. High initial investments are compensated by heat and low electricity consumption.