Setting and adjusting a water underfloor heating

Recommendation points

• Typical connection schemes
• Temperature regime
• System filling rules
• Working with collector flow meters
• Automatic and manual temperature equalization

In order for water underfloor heating to work as expected, it is necessary not only to strictly follow the rules of the installation process and use the appropriate materials. Today we will talk about setting up the operation of heating loops and the principles of debugging the operating modes of a warm floor.

Typical connection schemes

Water floor heating is rarely used as the only source of heating. Heating only due to floor heating is permissible only in regions with a mild climate, or in rooms with a large area, where heat removal is not limited to furniture, interior items or low thermal conductivity of the floor covering. Almost always it is necessary to combine radiator circuits, hot water preparation devices and underfloor heating loops in one heating system.

Typical scheme of a combined heating system with connecting radiators and underfloor heating circuits. This is the most technologically advanced and highly customizable option, but it also requires a significant initial investment. 1 – heating boiler; 2 – safety group, circulation pump, expansion tank; 3 – manifold for separate two-pipe connection of radiators according to the “star” scheme; 4 – heating radiators; 5 – underfloor heating collector, includes: bypass, three-way valve, thermostatic head, circulation pump, combs for connecting underfloor heating circuits with reducers and flow meters; 6 – underfloor heating contours

There are a fairly large number of variations in the design of the boiler room piping, while in each individual case there are different principles of operation of the hydraulic system. However, if you do not take into account the extremely specific options, then there are only five ways to coordinate the operation of heating devices of various types:

1. Parallel connection of the underfloor heating collector to the mains of the heating unit. The place of the tie-in into the line must be carried out before the connection point of the radiator network, the supply of the coolant is provided by an additional circulation pump.
2. Combining by the type of primary and secondary rings. The main line, wrapped in a ring, has several flow inlets in the supply part, the flow rate of the coolant in the connected circuits decreases with distance from the heating source. Flow balancing is performed by selecting the pump flow and limiting the flow by regulators.
3. Connection to the extreme point of the coplanar collector. The movement of the coolant in the underfloor heating loops is provided by a common pump located in the generator section, while the system is balanced according to the principle of priority flow.
4. The connection via a low loss header is ideal for a large number of heating devices, significant differences in flow rates in the circuits and a significant length of underfloor heating loops. This option also uses a coplanar manifold, while a hydraulic arrow is necessary to eliminate the pressure drop that interferes with the correct operation of circulation pumps..
5. Local parallel connection of the loop through the unibox. This option is well suited for joining a warm floor loop of a short length, for example, if you need to heat the floor only in the bathroom.

The easiest option for connecting the underfloor heating circuit to a radiator heating system with a coolant temperature of 70-80 ° C. 1 – line with supply and return of the high-temperature circuit; 2 – floor heating contour; 3 – unbox.

It must be remembered that the nature of the underfloor heating operation can also vary depending on the installation pattern of the coil. The “snail” scheme is considered optimal, in which the tubes are laid in pairs, which means that the entire area is heated almost evenly. If the warm floor is arranged in a “snake” or “labyrinth”, then the formation of colder and warmer zones is practically guaranteed. This drawback can be eliminated, including due to the correct setting.

Temperature regime

Before proceeding with the adjustment of the warm floor, it is extremely important to establish a clear idea of ​​the purpose for which it is being performed. According to the principle of operation, a water heated floor is fundamentally different from other heating devices. The main difference is the operating temperature of the coolant. If the supply to the radiator network is carried out at temperatures up to 80 ° C, then the heating of the coolant entering the underfloor heating coil is limited to 40–42 ° C. This need is due to considerations of comfort and safety. In normal mode, the temperature on the floor surface fluctuates in the range of 22-26 ° С, stronger heating causes unpleasant sensations.

There are two ways to control the temperature of heating a liquid underfloor heating. The first of them involves controlling the temperature on the supply line of the collector by mixing in a portion of the cooled coolant from the return. Technically, this solution is realized by installing a three-way valve with a push-acting RTL thermostatic head. The difference between such a head and a radiator head is that it relies on the temperature of the coolant, not air, in operation. With this method of regulation, the flow rate in the loops remains constant, only the temperature of the coolant changes with a small amplitude.

The second method of regulation involves limiting the flow rate of the hot coolant in the circuit. In this case, a thermostatic head is also installed, but it is located on the two-way valve, which interrupts the return flow. With this method of regulation, the flow and return are connected by a bypass circuit, the flow through which is regulated by a restriction valve with a pre-calibrated capacity. The principle of such regulation is based on the high inertia of the underfloor heating system. During operation, the coolant is fed into the loops at the nominal temperature of the heating unit, only the total flow rate changes periodically. Thus, the screed is heated cyclically, that is, a significant heat capacity of the accumulating layer is required to smooth out temperature drops..

In both cases, one important rule applies: the thermostatic valve is necessarily based on the return temperature of the loop or collector. The device can have a mechanical or electronic principle of operation, it can even be an ordinary thermometer. The need for the correct location is due to the fact that it is almost impossible to judge the effectiveness of the regulation by the value of the coolant temperature at the supply, because the length of the loops can differ significantly.

System filling rules

It is impossible to adjust the operation of the underfloor heating if the flow rate of the coolant in the loops changes spontaneously. This phenomenon is typical in the presence of air congestion, so the heating system must not only be properly organized technically, but also properly charged..

To fully fill the system, automatic air vents must be installed on both branches of the underfloor heating collector. If the loops are located at a level higher than the collector, the supply connection to the latter must be made through a deaerator. Refueling of the underfloor heating system is carried out separately from other heating circuits, that is, the piping of the generator part and the radiator network must be filled in advance, and the shut-off valves at the collector inputs must be closed. To pour the coolant into the system, a hose from the water supply system or pump is connected to the drain outlet of the supply branch of the collector. Accordingly, to a similar branch of the return branch, you need to connect a hose for bleeding air, the reverse end of which is either brought out into the street or lowered into a container with a volume of 30-40 liters.

The first in the underfloor heating system is filled with the collector and its piping. In this case, the flow meters on the supply line must be completely open, and the regulators on the return line must be closed. Next, you need to consistently fill each loop with a coolant until a clean coolant without air bubbles comes from the bleed hose. The underfloor heating is filled with a minimum flow for uniform squeezing of air from the system. When all the underfloor heating loops are filled, you can put the heating system into operation and balance it.

Working with collector flow meters

Hydraulic balancing of underfloor heating loops consists in regulating the flow rate in each coil. Depending on the length, a different amount of incoming heat carrier may be required in order for it to cool down exactly to the calculated value when passing through the loop. Quantitatively, the required flow is determined as the ratio of the heat load on the loop to the product of the heat capacity of water or other heat carrier by the temperature difference in the supply and return: G = Q / s * (t₁ – t₂).

You can often find recommendations to determine the flow rate of the coolant according to the performance of the circulation pump, that is, to divide its supply in proportion to the ratio of the loop lengths. Such advice should be avoided: besides the fact that the length of each coil is quite difficult to calculate, one of the most important rules is violated – to choose equipment parameters based on the needs of the system, and not vice versa. Attempts to distribute the flow in the described way almost always lead to the fact that the flow in the loops differs significantly from the calculated values, which makes further system tuning impossible..

The flow adjustment itself with flow meters is quite simple. In some models, the throughput is changed by turning the body, in others – by rotating the stem with a special key. The scale on the body of the flow meter indicates the flow rate in liters per minute, you just need to set the appropriate position of the float. Almost always, when the throughput of one flow meter changes, the flow rate in the remaining loops changes, so the adjustment is carried out several times, sequentially calibrating each branch. If such changes are especially pronounced, this indicates a lack of throughput of the control valves through which the collector is connected, or about too low performance of the circulation pump.

Automatic and manual temperature equalization

When adjusting a warm floor by mixing and limiting, the methods for setting the required temperature of the coolant are slightly different. It also matters whether the proportional trim is on-the-fly or manual. The latter is permissible only for the mixing control method and only under the condition that the coolant flow rate in the remaining circuits of the system changes slightly.

Manual adjustment of the three-way valve requires temperature control on the return branch, for which a thermometer well or an overhead temperature probe can be used. Temperature measurements should not be carried out immediately, but based on the length of the loop and the flow rate of the coolant in it. It is necessary to measure the temperature after a time sufficient for 2 or 3 times to renew the coolant in the underfloor heating system. The task of the regulation is to ensure a constant temperature difference of the coolant between the supply and return. At the same time, the temperature difference is determined by the project of the warm floor and is calculated according to the thickness, screed material, as well as the direction and pitch of the coil pipes.

Automatic proportional control is much easier. The main control element is the RTL thermostatic head or the unibox valve. The higher the mark at which the handwheel is set, the higher the temperature of the coolant will be, which is true for both mixing and limiting adjustments..