Balancing the heating system

Recommendation points

• What is the essence of balancing
• Features of working with different types of wiring
• Computational modeling
• The empirical way
• Debugging in automatic mode

Heating systems of almost all configurations require balancing, the only exception is the wiring along the Tichelman loop. We will consider three possible ways to balance, talk about the advantages, disadvantages and appropriateness of each of the methods, and give practical recommendations..

What is the essence of balancing

Hydraulic heating systems are considered to be the most complex. Their effective work is possible only with a deep understanding of the physical processes hidden from visual observation. The joint operation of all devices should ensure the absorption of the maximum amount of heat by the heat carrier and its uniform distribution over all heating devices of each circuit.

The operating mode of each hydraulic system is based on the relationship of two inversely proportional values: hydraulic resistance and flow capacity. It is they who determine the flow rate of the coolant in each node and part of the system, and therefore the amount of heat supplied to the radiators. In the general case, the calculation of the flow rate for each individual radiator reflects a high degree of unevenness: the further the heating device is from the heating unit, the higher the effect of the hydrodynamic resistance of pipes and branches, respectively, the coolant circulates at a lower speed.

The task of balancing the heating system is to ensure that the flow in each part of the system will have approximately the same intensity even with temporary changes in operating modes. Careful balancing allows you to achieve a state where individual adjustment of the thermostatic heads does not significantly affect other elements of the system. At the same time, the very possibility of balancing should be provided even at the design and installation stage, because to configure the system, both special fittings and technical data for the boiler room equipment are required. In particular, it is obligatory to install shut-off valves on each radiator, in the common people called chokes.

Features of working with different types of wiring

One-pipe heating systems are the easiest to adjust for balancing. This is due to the fact that the total flow through the radiator and the connecting bypass is always the same and does not depend on the throughput of the installed fittings. Therefore, in systems like “Leningradka” work is not so much on balancing the flow, but on the equation for the amount of heat released by the coolant in the radiators. Simply put, the main goal of balancing in this case is to ensure that water flows to the most distant radiator at a sufficiently high temperature..

In two-pipe dead-end systems, a slightly different principle applies. Each radiator of the system is a kind of shunt, the hydraulic resistance of which is lower than that of the rest of the group located further in the direction of the flow. Because of this, a significant part of the coolant flows through the shunt back to the heating unit, while the circulation further through the system has a much lower intensity. In such heating systems, it is necessary to work precisely on equalizing the flow in each radiator by changing the throughput of the fittings.

Two-pipe associated heating systems do not require balancing at all, but at the same time they have a relatively high material consumption. This is the beauty of the Tichelmann loop: the path taken by the coolant in the circuit of each radiator is approximately the same, due to which the equivalence of the flow at each point of the system is automatically maintained. The situation is similar with radiant heating systems and water underfloor heating: the flow is aligned on a common manifold using float flow meters.

Computational modeling

The most constructive and correct method of adjustment is by building a design model of the hydraulic heating system. This can be done in software such as Danfoss CO and Valtec.PRG, or with paid products like AutoSnab 3D. You should not be afraid of paid software: as you will see later, its cost cannot be compared with the cost of special automatic balancing devices, while the calculated design of the hydraulic system will provide a complete picture of the system, its modes of operation and physical processes occurring at each point.

Balancing using software calculations is carried out by building an exact virtual copy of the heating system. In different working environments, the modeling mechanism proceeds with some differences, however, all programs of this kind have a friendly and user-friendly interface. It is very important that the construction is carried out really accurately: with an indication of each fitting, reinforcement element, turns and branches present in the real system. Here’s what you need the initial data:

• boiler passport data: power, efficiency, pressure-flow schedule, working pressure.
• information about the circulation pump: flow rate and head;
• type of coolant;
• material and nominal bore of pipes, temperature of their environment;
• technical information about all shut-off and control valves, local resistance coefficients (LRR) of each element;
• passport data for shut-off valves, the dependence of their capacity on pressure drop and degree of opening.

After building a model of the system, all work is reduced to ensuring the equality of the flow rate of the coolant on each radiator. To do this, artificially underestimate the throughput of shut-off valves on those radiators and circuits where there is a significant increase in flow compared to the rest. When the virtual balancing is completed, Kvs are written out for each radiator – the bandwidth coefficients. Using a table or graph from the valve’s passport, the required number of revolutions of the control rod is determined, after which this data is used to balance the real system in nature..

The empirical way

Of course, it is possible to adjust the heating system with up to ten radiators without preliminary calculation. However, this method is quite laborious and time-consuming. Among other things, with such balancing, it is not possible to provide for a change in flow rate during the operation of the thermostatic heads, which greatly reduces the balancing accuracy.

The manual balancing algorithm is simple, first you need to shut off absolutely all radiators in the system. This is done in order to match as closely as possible the temperature of the coolant at the inlet and outlet from the heating unit. This whole process takes about an hour, while it is necessary to set the circulation pump at maximum speed and make sure that there are no air locks in the system..

The next step is to fully open the shut-off valve on the farthest radiator (often this valve is not installed on the last radiator at all). After 10-15 minutes, the heating temperature of the outermost radiator is measured, and with further balancing it will be used as a reference.

Next, you need to open the shut-off valve on the penultimate radiator. The degree of opening must be such that heating occurs up to the reference temperature and at the same time the heating temperature on the last radiator does not decrease. The line is very thin, and the work is greatly complicated by the inertia of the radiators: after each change in the position of the valve stem, wait at least 15 minutes on an aluminum radiator, and about 30–40 minutes on a cast iron radiator. This is the whole point of manual balancing: moving from the most distant radiator to the very first in the chain, it is necessary to reduce the throughput, ensuring that the same temperature is maintained on each heating device. The adjustment should be carried out very finely and accurately, because a sharp increase in the flow rate in the middle of the circuit will lead to a drop in temperature in its distant part, so it will take another 15–20 minutes to return the system to its original state.

Debugging in automatic mode

There is a kind of middle ground between the two methods described above. Special equipment for automatic balancing of hydraulic heating systems allows adjustment with very high accuracy and in a fairly short time. At the moment, the main technical solution for such purposes is considered to be the “smart” pump Grundfos ALPHA 3, equipped with a removable transmitter, as well as a proprietary application for mobile devices. The average price of a set of equipment is about $ 300.

What is the essence of the undertaking? The pump has a built-in flow meter and can communicate with a smartphone or tablet, where all information is processed. The app works like a guide: it guides the user step by step and indicates which manipulations need to be carried out on different parts of the heating system. At the same time, individual rooms with a specified number of heating devices are saved in the application database, it is possible to select different types of radiators, indicate their power, required heating standards and other data.

The process is extremely simple and fully demonstrates the algorithm of the program. After pairing with the transmitter and preparing for operation, all radiators are disconnected from the system, this is necessary to measure zero flow. The shut-off valves on each radiator are then fully opened in turn. At the same time, the flow meter in the pump notes changes in the flow and determines the maximum throughput of each heating device. After all radiators have been entered into the program database, they are individually adjusted..

The setting of the shut-off valve on the radiators takes place in real time. The application has sound indication for the ability to work in hard-to-reach places. Balancing requires fine adjustment of the shut-off rod to such a position that the current flow in the system equals the value recommended by the program. Upon completion of work with each radiator, the application generates a report, which includes all the heating devices of the system and the flow rate of the coolant in them. After balancing, the ALPHA 3 pump can be removed and replaced with another one with the same performance parameters..