- System Description
- Application area
- Hydraulic data
- Boiler room piping
- Piping system
- Radiator fittings
One of the most interesting topics in heat engineering is heating systems with an associated two-pipe coolant supply, referred to among the masters as the Tichelman scheme. Their device is really unique: the system practically does not require balancing, is characterized by stable operation, but at the same time it also has a number of disadvantages.
In professional circles, the Tichelman loop is called a two-pipe heating system with a passing movement of the coolant. This name fully reflects the essence and principle of operation, the distinctive features are best seen against the background of a two-pipe system with a reverse movement of the coolant, which is familiar to almost everyone.
Imagine a radiator network deployed in a straight line. In the classical scheme, the heating unit is located at the beginning of this row, from it along the entire network follow two pipes for supplying hot and returning cold coolant, respectively. At the same time, each radiator is a kind of shunt, therefore, the more the heating device is removed from the heating unit, the higher the hydraulic resistance in the loop of its connection.
1 – Two-pipe connection diagram for radiators with a countercurrent coolant in the supply and return; 2 – wiring diagram Tichelman loop with passing connection
If we roll a row of radiators into a ring, then both of its edges will adjoin the heat unit. In this case, it is much more profitable to make sure that the return pipeline does not direct the coolant back to the boiler room, but continues to follow the chain, that is, along the way. In other words, the supply pipe follows from the heating unit and ends at the extreme radiator, in turn, the return pipe originates from the first radiator and goes to the boiler room. The same principle can be implemented even if the radiators are located linearly in space, simply from the place where the extreme radiator is inserted into the return pipe, the pipe unfolds to return the cooled coolant. At the same time, in a certain area, the heating system will be three-pipe, so the Tichelman loop is also sometimes called.
Tichelman loop with the placement of radiators around the perimeter of the building. From each radiator, the total length of the supply and return pipes is approximately the same. 1 – heating boiler; 2 – security group; 3 – heating radiators; 4 – supply pipe; 5 – return pipe; 6 – circulation pump; 7 – expansion tank
But why are such complications necessary? If you carefully study the diagram, it turns out that the sum of the lengths of the supply and return pipelines for each radiator is the same. Hence the conclusion: the hydraulic resistance of each individual connection loop is equivalent to the rest of the sections, that is, the system simply does not need balancing.
However, the temptation to avoid hydraulically adjusting the system should not lead to hasty rash decisions. The two-pipe associated system is characterized by high material consumption, therefore its installation is not justified in all cases.
Let us consider such a concept as the degree of “pressing” of the heating device when balancing a two-pipe return system. By underestimating the nominal passage at the connection point of the first few radiators, it is possible to reduce the flow rate of the coolant in them, thereby reducing the pressure drop, so that sufficient pressure remains in the subsequent sections of the network. If the radiator network consists of a large number of heating devices located at a great distance from each other, the flow on the initial radiators will have to be limited to such an extent that the flow in them will not be enough for normal heat release. This forces the use of pumps with a higher capacity, which is why a noticeable noise is generated in the flow of the coolant in individual nodes. In general, we can say that the device of a two-pipe passing system is justified only when the number of radiators is more than 8-10 with a total length of the pipeline strings over 70 m.
The material consumption of the Tichelman system increases significantly if it is impossible to wrap the radiator network in a ring, that is, to place the heating pipeline strictly along the perimeter of the building. This is usually hampered by doorways and glazing fronts to the floor. In such cases, it is necessary to mount an additional pipe through which the coolant will return to the boiler room, and since the total length of an arbitrarily taken loop increases by at least half, to increase the nominal line bore or pump performance. In principle, it is possible to avoid additional costs due to the device of the collector (beam) system, however, it is better to first perform a comparative calculation of the material consumption.
The operation of the system based on the Tichelman loop principle is highly stable. This fact is clearly demonstrated by the hydraulic calculation data, but this requires compliance with a number of installation rules..
The main functional element of such a system is the hydraulic pump. It creates pressure at the outlet, that is, at the supply, and a vacuum at the inlet – return. Numerically, the value of both values decreases with distance from the pump, and the drop in pressure does not occur linearly, it is described by the quadratic value of the dynamic pressure. This pattern can be traced both for the supply line and for the return line, conventionally, the fall can be described using the example of a pipeline 100 m long:
Distance from the pump in the direction of movement of the coolant (m) Supply pressure (% of nominal) Return vacuum (% of nominal) Radiator pressure drop ten 90% five % 95% 20 75% 20 % 95% thirty 55% 35% 90% 50 45% 40% 85% 60 40% 45% 85% 70 35% 55% 90% 80 20 % 75% 95% 90 five % 90% 95%
This is averaged data, but even from them it can be seen that with an apparent uniformity, the pressure loss in the middle of the radiator network is slightly higher than at the edges. Indeed, due to the proportional change in pressure and vacuum in each radiator, almost the same pressure difference in each heating device is maintained, however, for the correct and stable operation of the Tichelman loop, a number of rules should be observed, which will be discussed further.
Boiler room piping
A two-pipe system with a passing movement of the coolant can be either open or closed. As we have already said, the pump is the main functioning element, so its installation cannot be avoided. You should not count on natural circulation even with properly organized upper piping. As we have already said, a typical Tichelmann loop contains 10 or more radiators; it is unlikely that such an arm can be pushed through by gravitational movement alone.
A traditional safety troika is installed at the boiler feed outlet: an automatic air vent, a bleed valve and a pressure gauge. For open systems, the delivery outlet must be arranged in a vertical channel up to the slope formation height, an open expansion tank is installed at the highest point. Further, the supply pipe is directed directly to the distribution network.
One circulation pump is installed on the boiler return, the performance of which is determined by the hydraulic resistance of the entire system. A strainer is located directly in front of the pump, and immediately after the pump there is a tee for connecting an expansion tank and a low point pressure gauge. Also in this place, the filler pipe is displayed.
The boiler room shut-off valves are represented by full bore ball valves, which are installed:
- on both sides of the pump
- at the outlet of the expansion tank
- on the filler pipe
- at the points of connection of the boiler to the main
Additionally, a connecting bypass tube can be installed in the boiler room, in the gap of which an electric normally closed valve is installed, which is triggered when the circulation is stopped. The bypass insert must be carried out before the circulation pump: the bypass is designed to protect against temperature shock and it shunts the boiler heat exchanger from the mains, and not vice versa.
The Tichelman system is also good in that, with a relatively high power of the radiator network, it is possible to operate from a boiler with a built-in complex of hydraulic equipment. However, if it is necessary to coordinate the operation of the radiator network and the warm floor, each arm of the system is equipped with its own circulation pump. If the performance in the shoulders is significantly different, the installation of a hydraulic arrow is necessary.
Both the upper and lower wiring of the Tichelman loop are usually made with PPR pipes. If concealed piping is required, it is recommended to use the PEX system with push-in fittings. If pipes are to be laid in solid substrates, an insulating sheath should be used..
The Tichelman heating system for a one-story house is extremely simple. The coolant supply pipeline runs from the heating unit along the entire radiator network. The nominal nominal pipe diameter remains until the penultimate radiator in the row, after which the transition to the diameter of the radiator connection is made, usually 20 mm polypropylene or 16 mm PEX. The return current pipeline is laid in the same order, but towards the flow, that is, the first radiator in the direction of the hot coolant flow is connected with a reduced diameter.
If the Tichelman system is arranged on several floors, installation of a vertical riser is required. The main supply pipe follows to the highest point from which a branch is made to feed the upper floor. After that, the line turns down, in this section, the feed is cut in for all the lower floors. The common return flow pipeline is performed by analogy with a two-pipe system with an opposite movement of the coolant, that is, it simply acts as a collecting line.
The diameter of the pipes for the Tichelman loop is calculated according to the general methods of heat engineering calculation, based on the choice of the optimal Kvs value of the main pipes. At the same time, it is desirable that a stepwise understatement of the nominal bore does not occur in the direction of movement of the coolant, otherwise the natural balancing of the system will not be so high quality. In systems with a length of distribution pipelines up to 120 m, the nominal bore of the main pipes is considered to be at least 270 mm2, and for pipes connecting radiators – about 130 mm2.
You can often come across the opinion that a two-pipe heating system with a passing movement of the coolant does not need to complete the radiators with control valves. It is believed that this fact supposedly levels out the additional costs for additional pipes and fittings for them. However, the correct operation of the radiators in this case is hardly possible..
Thermostatic heads for radiators in the Tichelmann system must be installed without fail. Without them, it is impossible to customize radiators in different rooms, which is not very comfortable under changing climatic conditions. As for the balancing valves (throttles), the controversy is particularly hot on this score. As mentioned above, even with the passing movement of the coolant, there is a pressure drop across the radiators. With the correct calculation of the system, this phenomenon can be compensated by varying the number of sections in the radiators of different zones. However, if there is even a minimal risk of error, it is best to install control valves on at least the first few radiators at each end..
The Tichelmann loop can also be balanced by static adjustment methods. We are talking about the so-called “washer”. If the local resistance coefficients are predetermined by hydraulic calculations, the control valves can be replaced with inserts that lower the nominal size by a certain amount. Of the simplest options, you can offer self-made O-rings with different inner diameters, which are installed at the radiator threaded connections..