If heating installers or sellers are trying to stick a "hydrostrel" about which I broadcast earlier, then here two options, either they want to make more money on the sale of unnecessary equipment and installation, or she really needed.
In this case, especially recently, progressive plumbers try not to use it, but find hydraulic arrow replacement in the form "primary and secondary ring". If you have not read the article about the "hydraulic separator" on the channel, then it is advisable to read it here, and then come back here to continue the educational program.
Primary heating ring, what is it?
In fact, this is a closed pipe through which the coolant moves thanks to the pump. In the illustration below, you can see it.
If you add consumers to it in the form of an indirect hot water heating boiler, a radiator network, underfloor heating and others, then each branch is considered a secondary ring.
The distance between the supply, taking the coolant from the primary ring and the return flow, returning the cooled one the coolant in the primary ring should be minimal so that the difference in pressure between supply and return is "imperceptible". This is usually four diameters of the primary ring pipe.
The first consumer in the direction of movement of the coolant in the primary ring must be the highest temperature, for example here, a boiler for indirect hot water heating (red line), but in fact it is better for it to make another connection, but not the point. Next is the radiator network (red-green line). Warm floors (green-blue branch) are next because they do not require high temperature.
From this it follows that each subsequent circuit will receive a lower temperature.
Note, in a conventional classic circuit with a hydraulic arrow, the boiler pump must be more efficient than all those taken in the circuits. And in the primary-secondary rings, the boiler pump in terms of flow rate must be greater than the most powerful one on any of the individual circuits.
Typically, in an overclocked system, the temperature drop between the circuits is 3-5 degrees. In contrast to the standard hydraulic arrow, where each consumer receives the same temperature, in this system of rings there is a drop in temperature for each subsequent consumer. And yes, this short interval between the flow and return of the circuit is a small hydraulic arrow.
As a result, the primary and secondary rings require very accurate calculations, while it is imperative that the installation of the system must be carried out by the same person who calculated, or by his company. So that in case of force majeure, you could find the extreme one. Mounting rings is more labor-intensive for a specialist than installing a hydraulic arrow. Therefore, the end consumer will pay more to the specialist for his work. It is more difficult to modernize, that is, add new consumers to a system with rings. Therefore, it is necessary to know which contours are needed by the end of construction work.
In fact, that the hydraulic arrow, that the primary-secondary rings act as a pressure divider, so that the circulation pumps do not "tyr" the coolant from each other or interfere with the correct operation.