If there is a large temperature difference between the boiler supply and return, the temperature on the walls of the boiler combustion chamber approaches the “dew point” temperature and condensation may form. It is known that during the combustion of fuel various gases are released, including CO 2; if this gas combines with the “dew” that has fallen on the walls of the boiler, an acid is formed that corrodes the “water jacket” of the boiler furnace. As a result, the boiler can quickly fail. To prevent dew, it is necessary to design the heating system so that the temperature difference between the supply and return is not too large. This is usually achieved by heating the return coolant and/or including a hot water supply boiler in the heating system with soft priority.

To heat the coolant between the return and the boiler supply, a bypass is made and a circulation pump is installed on it. The power of the recirculation pump is usually chosen as 1/3 of the power of the main circulation pump (sum of pumps) (Fig. 41). To ensure that the main circulation pump does not “press” the recirculation circuit into reverse side, a check valve is installed behind the recirculation pump.

Rice. 41. Return heating

Another way to heat the return is to install a hot water boiler in close proximity to the boiler. The boiler is “placed” on a short heating ring and positioned in such a way that hot water from the boiler after the main distribution manifold immediately went into the boiler, and from it returned back to the boiler. However, if the need for hot water is small, then both a recirculation ring with a pump and a heating ring with a boiler are installed in the heating system. With proper calculation, the recirculation pump ring can be replaced with a system with three- or four-way mixers (Fig. 42).

Rice. 42. Heating the return using three- or four-way mixers On the pages “Regulation equipment of heating systems” almost all technically significant devices and engineering solutions present in classic heating schemes. When designing heating systems on real construction sites, they must be fully or partially included in the design of heating systems, but this does not mean that exactly the heating fittings that are indicated on these pages of the site should be included in a specific project. For example, at the recharge unit you can install shut-off valves with built-in check valves, or you can install these devices separately. Instead of mesh filters, you can install dirt filters. You can install an air separator on the supply pipelines, or you can not install it, but instead install automatic air vents in all problem areas. You can install a deslimer on the return line, or you can simply equip the collectors with drains. Adjustment of the coolant temperature for “warm floor” circuits can be done with qualitative adjustment using three- and four-way mixers, or quantitative adjustment can be made by installing a two-way valve with thermostatic head. Circulation pumps can be installed on a common supply pipe or vice versa, on the return pipe. The number of pumps and their location may also vary.

After installing the heating system, you need to configure temperature regime. This procedure must be carried out in accordance with existing standards.

The coolant temperature requirements are set out in regulatory documents, which establish the design, installation and use engineering systems residential and public buildings. They are described in the State Building Codes and Rules:

• DBN (V. 2.5-39 Heat networks);
• SNiP 2.04.05 “Heating, ventilation and air conditioning.”

For the calculated supply water temperature, the figure is taken that is equal to the water temperature at the outlet of the boiler, according to its passport data.

For individual heating deciding what the coolant temperature should be should take into account the following factors:

1. Start and end heating season By average daily temperature outside +8 °C for 3 days;
2. The average temperature inside heated premises of housing, communal and public importance should be 20 °C, and for industrial buildings 16 °C;
3. Average design temperature must comply with the requirements of DBN V.2.2-10, DBN V.2.2.-4, DSanPiN 5.5.2.008, SP No. 3231-85.

According to SNiP 2.04.05 “Heating, ventilation and air conditioning” (clause 3.20), the coolant limit values ​​are as follows:

Depending on the external factors, the water temperature in the heating system can be from 30 to 90 °C. When heated above 90 °C, dust and paintwork. For these reasons sanitary standards more heating is prohibited.

For calculation optimal performance Special graphs and tables can be used that define the norms depending on the season:

• With an average reading outside the window of 0 °C, the supply for radiators with different wiring is set at 40 to 45 °C, and the return temperature at 35 to 38 °C;
• At -20 °C, the supply is heated from 67 to 77 °C, and the return rate should be from 53 to 55 °C;
• At -40 °C outside the window, all heating devices are set to the maximum permissible values. On the supply side it is from 95 to 105 °C, and on the return side it is 70 °C.

Optimal values ​​in an individual heating system

H2_2

Heating system helps to avoid many problems that arise with centralized network, A optimal temperature The coolant can be adjusted according to the season. In the case of individual heating, the concept of standards includes the heat transfer of a heating device per unit area of ​​​​the room where this device is located. The thermal regime in this situation is ensured design features heating devices.

It is important to ensure that the coolant in the network does not cool below 70 °C. The optimal temperature is considered to be 80 °C. WITH gas boiler It is easier to control heating because manufacturers limit the ability to heat the coolant to 90 °C. Using sensors to regulate the gas supply, the heating of the coolant can be adjusted.

It is a little more difficult with solid fuel devices; they do not regulate the heating of the liquid, and can easily turn it into steam. And it is impossible to reduce the heat from coal or wood by turning the knob in such a situation. Control of heating of the coolant is quite conditional with high errors and is carried out by rotary thermostats and mechanical dampers.

Electric boilers allow you to smoothly regulate the heating of the coolant from 30 to 90 °C. They are equipped with an excellent overheat protection system.

Single-pipe and double-pipe lines

The design features of one-pipe and two-pipe heating networks determine different standards for heating the coolant.

For example, for a single-pipe main the maximum norm is 105 °C, and for a two-pipe main it is 95 °C, while the difference between the return and supply should be respectively: 105 - 70 °C and 95 - 70 °C.

Coordination of coolant and boiler temperatures

Regulators help coordinate the temperature of the coolant and the boiler. These are devices that create automatic control and adjustment of return and supply temperatures.

The return temperature depends on the amount of liquid passing through it. Regulators cover the liquid supply and increase the difference between the return and supply to the level required, and the necessary indicators are installed on the sensor.

If the flow needs to be increased, a boost pump can be added to the network, which is controlled by a regulator. To reduce feed heating, use “ cold start": that part of the liquid that passed through the network is again transported from the return to the inlet.

The regulator redistributes the supply and return flows according to the data collected by the sensor and ensures strict temperature standards heating networks.

Ways to reduce heat loss

The above information will help to be used for correct calculation coolant temperature standards and will tell you how to determine situations when you need to use a regulator.

But it is important to remember that the temperature in the room is affected not only by the temperature of the coolant, street air and wind strength. The degree of insulation of the facade, doors and windows in the house should also be taken into account.

To reduce heat loss from your home, you need to worry about its maximum thermal insulation. Insulated walls, sealed doors, metal-plastic windows will help reduce heat loss. This will also reduce heating costs.

First, let's look at a simple diagram:

In the diagram we see a boiler, two pipes, an expansion tank and a group of heating radiators. The red pipe through which hot water flows from the boiler to the radiators is called DIRECT. And the lower (blue) pipe along which more cold water comes back, that’s what’s called REVERSE. Knowing that when heated, all bodies expand (including water), an expansion tank is built into our system. It performs two functions at once: it is a reserve of water to replenish the system and excess water goes into it during expansion from heating. Water in this system is a coolant and therefore must circulate from the boiler to the radiators and back. Either a pump or, under certain conditions, the force of earth's gravity can force it to circulate. If everything is clear with the pump, then with gravity many may have difficulties and questions. We have dedicated a separate topic to them. For a deeper understanding of the process, let's look at the numbers. For example, the heat loss of a house is 10 kW. The operating mode of the heating system is stable, that is, the system neither warms up nor cools down. The temperature in the house does not rise or fall. This means that 10 kW is generated by the boiler and 10 kW is dissipated by the radiators. From school course physicists, we know that to heat 1 kg of water by 1 degree we will need 4.19 kJ of heat. If we heat 1 kg of water by 1 degree every second, then we will need power

Q=4.19*1(kg)*1(deg)/1(sec)=4.19 kW.

If our boiler has a power of 10 kW, then it can heat per second 10/4.2 = 2.4 kilograms of water by 1 degree, or 1 kilogram of water by 2.4 degrees, or 100 grams of water (not vodka) by 24 degrees. The formula for boiler power looks like this:

Qcat=4.19*G*(Tout-Tin) (kW),

Where
G - water flow through the boiler kg/sec
Tout - water temperature at the outlet of the boiler (direct T can be used)
Twh - water temperature at the boiler inlet (reverse temperature is possible)
Radiators dissipate heat and the amount of heat they give off depends on the heat transfer coefficient, the surface area of ​​the radiator and the temperature difference between the radiator wall and the air in the room. The formula looks like this:

Qrad=k*F*(Trad-Tvozd),

Where
k-heat transfer coefficient. The value for household radiators is practically constant and equal to k = 10 watts/(sq meter * deg).
F - total area of ​​radiators (in sq. meters)
Trad-average radiator wall temperature
Тair is the air temperature in the room.
Under stable operation of our system, the equality will always be satisfied

Qcat=Qrad

Let's take a closer look at the operation of radiators using calculations and numbers.
Let's say the total area of ​​their fins is 20 square meters (which approximately corresponds to 100 ribs). Our 10 kW = 10000 W, these radiators will deliver at a temperature difference of

dT=10000/(10*20)=50 degrees

If the room temperature is 20 degrees, then the average temperature of the radiator surface will be

20+50=70 degrees.

In the case when our radiators have a large area, for example 25 square meters(about 125 ribs) then

dT=10000/(10*25)=40 degrees.

And the average surface temperature will be

20+40=60 degrees.

Hence the conclusion: If you want to make a low-temperature heating system, do not skimp on radiators. The average temperature is the arithmetic mean between the temperatures at the radiator inlet and outlet.

Tsr=(Tstraight+Tobr)/2;

The temperature difference between forward and return is also an important value and characterizes the circulation of water through the radiators.

dT=Tstraight-Tobr;

We remember that

Q=4.19*G*(Tpr-Tobr)=4.19*G*dT

At a constant power, an increase in water flow through the device will lead to a decrease in dT, and vice versa, with a decrease in flow, dT will increase. If we ask that dT in our system is 10 degrees, then in the first case when Tav = 70 degrees, after simple calculations we get Tpr = 75 degrees and Tobr = 65 degrees. The water flow through the boiler is

G=Q/(4.19*dT)=10/(4.19*10)=0.24 kg/sec.

If we reduce the water flow exactly by half, and leave the boiler power the same, then the temperature difference dT will double. In the previous example, we set dT to 10 degrees, now with a decrease in flow rate it will become dT=20 degrees. With a constant Tav = 70, we get Tpr-80 degrees and Tobr = 60 degrees. As you can see, a decrease in water flow entails an increase in the flow temperature and a decrease in the return temperature. In cases where the flow rate decreases to a certain critical value, we can observe boiling of water in the system. (boiling point = 100 degrees) Water can also boil when there is an excess of boiler power. This phenomenon is extremely undesirable and very dangerous, therefore a well-designed and thought-out system, competent selection of equipment and high-quality installation eliminates this phenomenon.
As we can see from the example, the temperature regime of the heating system depends on the power that needs to be transferred to the room, the area of ​​​​the radiators and the coolant flow. The volume of coolant poured into the system does not play any role when its operation is stable. The only thing that volume affects is the dynamics of the system, that is, the time of heating and cooling. The larger it is, the longer the heating time and the longer the cooling time, which is undoubtedly a plus in some cases. It remains to consider the operation of the system in these modes.
Let's return to our example with a 10 kW boiler and radiators with 100 fins with 20 square meters of area. The pump sets the flow rate to G=0.24 kg/sec. Let's set the system capacity to 240 liters.
For example, the owners arrived at the house after a long absence and started heating it. During their absence, the house cooled down to 5 degrees, as did the water in the heating system. By turning on the pump, we will create water circulation in the system, but until the boiler is ignited, the forward and return temperatures will be the same and equal to 5 degrees. After igniting the boiler and reaching a power of 10 kW, the picture will be as follows: The water temperature at the entrance to the boiler will be 5 degrees, at the exit from the boiler 15 degrees, the temperature at the entrance to the radiators will be 15 degrees, and at the exit from them a little less than 15.( At such temperatures, radiators emit practically nothing) All this will continue for 1000 seconds until the pump pumps all the water through the system and the return flow reaches the boiler with a temperature of almost 15 degrees. After this, the boiler will produce 25 degrees, and the radiators will return water to the boiler with a temperature of just under 25 (approximately 23-24 degrees). And so again for 1000 seconds.
Eventually the system will warm up to 75 degrees at the outlet, and the radiators will return 65 degrees and the system will go into stable mode. If the system had 120 liters rather than 240, the system would have warmed up 2 times faster. If the boiler is extinguished and the system is hot, the cooling process will begin. That is, the system will release the accumulated heat to the house. It is clear that the larger the volume of coolant, the longer this process will take. When operating solid fuel boilers, this allows you to extend the time between additional loads. Most often, this role is taken on by, to whom we have dedicated a separate topic. Like various types heating systems.

Economical energy consumption in heating system, can be achieved if certain requirements are met. One option is to have a temperature diagram, which reflects the ratio of the temperature emanating from the heating source to the external environment. The values ​​of the values ​​make it possible to optimally distribute heat and hot water to the consumer.

High-rise buildings are connected mainly to central heating. Sources that convey thermal energy, are boiler houses or thermal power plants. Water is used as a coolant. It is heated to a given temperature.

Having gone through a full cycle through the system, the coolant, already cooled, returns to the source and reheats. Sources are connected to consumers by heating networks. Since the environment changes temperature, thermal energy should be adjusted so that the consumer receives the required volume.

Heat regulation from central system can be done in two ways:

1. Quantitative. In this form, the water flow changes, but its temperature remains constant.
2. Qualitative. The temperature of the liquid changes, but its flow does not change.

In our systems, the second regulation option is used, that is, qualitative. Z Here there is a direct relationship between two temperatures: coolant and environment. And the calculation is carried out in such a way as to ensure the heat in the room is 18 degrees and above.

Hence, we can say that the temperature graph of the source is a broken curve. The change in its directions depends on temperature differences (coolant and outside air).

The dependency schedule may vary.

A specific diagram has a dependency on:

1. Technical and economic indicators.
2. CHP or boiler room equipment.
3. Climate.

High coolant values ​​provide the consumer with great thermal energy.

Below is an example of a diagram, where T1 is the coolant temperature, Tnv is the outside air:

A diagram of the returned coolant is also used. A boiler house or thermal power plant can estimate the efficiency of the source using this scheme. It is considered high when the returned liquid arrives chilled.

The stability of the scheme depends on the design values ​​of fluid flow of high-rise buildings. If the flow through the heating circuit increases, the water will return uncooled, as the flow rate will increase. Conversely, with minimal flow, the return water will be sufficiently cooled.

The supplier's interest, of course, is in the supply of return water in a cooled state. But there are certain limits for reducing consumption, since a decrease leads to loss of heat. The consumer’s internal temperature in the apartment will begin to drop, which will lead to violation of building codes and discomfort for ordinary people.

What does it depend on?

The temperature curve depends on two quantities: outside air and coolant. Frosty weather leads to an increase in coolant temperature. When designing a central source, the size of the equipment, building and pipe size are taken into account.

The temperature leaving the boiler room is 90 degrees, so that at minus 23°C, the apartments are warm and have a value of 22°C. Then the return water returns to 70 degrees. Such standards correspond to normal and comfortable living in the house.

Analysis and adjustment of operating modes is carried out using a temperature diagram. For example, the return of liquid with an elevated temperature will indicate high coolant costs. Underestimated data will be considered a consumption deficit.

Previously, for 10-story buildings, a scheme with calculated data of 95-70°C was introduced. The buildings above had their own chart of 105-70°C. Modern new buildings may have a different layout, at the discretion of the designer. More often, there are diagrams of 90-70°C, and maybe 80-60°C.

Temperature chart 95-70:

Temperature chart 95-70

How is it calculated?

A control method is selected, then a calculation is made. The design winter and reverse order water inflows, the amount of outside air, the order at the break point of the diagram. There are two diagrams: one of them considers only heating, the second considers heating with consumption hot water.

For an example of calculation, we will use methodological development"Roskommunenergo".

The input data for the heat generating station will be:

1. Tnv– the amount of outside air.
2. TVN- indoor air.
3. T1– coolant from the source.
4. T2– reverse flow of water.
5. T3- entrance to the building.

We will look at several heat supply options with values ​​of 150, 130 and 115 degrees.

At the same time, at the exit they will have 70°C.

The results obtained are compiled into a single table for subsequent construction of the curve:

So we got three various schemes, which can be taken as a basis. It would be more correct to calculate the diagram individually for each system. Here we looked at the recommended values, excluding climatic features region and building characteristics.

To reduce energy consumption, just select a low temperature setting of 70 degrees and uniform heat distribution throughout the heating circuit will be ensured. The boiler should be taken with a power reserve so that the system load does not affect the quality operation of the unit.

Adjustment

Heating regulator

Automatic control is provided by the heating regulator.

It includes the following parts:

1. Computing and matching panel.
2. Actuator on the water supply section.
3. Actuator, which performs the function of mixing liquid from the returned liquid (return).
4. Boost pump and a sensor on the water supply line.
5. Three sensors (on the return line, on the street, inside the building). There may be several of them in the room.

The regulator closes the liquid supply, thereby increasing the value between return and supply to the value specified by the sensors.

To increase the flow, there is a boost pump and a corresponding command from the regulator. The incoming flow is controlled by a "cold bypass". That is, the temperature decreases. Some of the liquid that has circulated along the circuit is sent to the supply.

Sensors collect information and transmit it to control units, resulting in a redistribution of flows that provide a rigid temperature scheme for the heating system.

Sometimes, a computing device is used that combines hot water and heating regulators.

The hot water regulator has more simple diagram management. The hot water sensor regulates the flow of water with a stable value of 50°C.

Advantages of the regulator:

1. The temperature scheme is strictly maintained.
2. Elimination of overheating of the liquid.
3. Fuel efficiency and energy.
4. The consumer, regardless of the distance, receives heat equally.

Table with temperature graph

The operating mode of boilers depends on the environmental weather.

If we take various objects, for example, a factory premises, multi-storey and a private house, all will have an individual thermal diagram.

In the table we show the temperature diagram of the dependence of residential buildings on outside air:

Outdoor temperature	Temperature network water in the supply line	Return water temperature
+10	70	55
+9	70	54
+8	70	53
+7	70	52
+6	70	51
+5	70	50
+4	70	49
+3	70	48
+2	70	47
+1	70	46
0	70	45
-1	72	46
-2	74	47
-3	76	48
-4	79	49
-5	81	50
-6	84	51
-7	86	52
-8	89	53
-9	91	54
-10	93	55
-11	96	56
-12	98	57
-13	100	58
-14	103	59
-15	105	60
-16	107	61
-17	110	62
-18	112	63
-19	114	64
-20	116	65
-21	119	66
-22	121	66
-23	123	67
-24	126	68
-25	128	69
-26	130	70

SNiP

There are certain standards that must be observed in creating projects on heating network and transportation of hot water to the consumer, where the supply of water steam must be carried out at 400°C, at a pressure of 6.3 Bar. It is recommended that the heat supply from the source be released to the consumer with values ​​of 90/70 °C or 115/70 °C.

Regulatory requirements must be met in compliance with the approved documentation with mandatory approval from the Ministry of Construction of the country.