Temperature chart of the heating system. Determining the values ​​of the standard temperature of the return network water in off-design mode

Looking through the statistics of visits to our blog, I noticed that search phrases such as, for example, appear very often “What should be the temperature of the coolant at minus 5 outside?”. Decided to post the old one. schedule quality regulation heat supply according to the average daily outdoor temperature. I want to warn those who, on the basis of these figures, will try to sort out relations with the housing department or heating networks: the heating schedules for each individual settlement are different (I wrote about this in an article). Work on this schedule heating network in Ufa (Bashkiria).

I also want to draw attention to the fact that regulation occurs according to average daily outside temperature, so if, for example, outside at night minus 15 degrees, and during the day minus 5, then the coolant temperature will be maintained in accordance with the schedule minus 10 o C.

As a rule, the following temperature charts are used: 150/70 , 130/70 , 115/70 , 105/70 , 95/70 . The schedule is selected depending on the specific local conditions. House heating systems operate according to schedules 105/70 and 95/70. According to schedules 150, 130 and 115/70, main heat networks operate.

Let's look at an example of how to use the chart. Suppose the temperature outside is minus 10 degrees. Heating networks operate according to the temperature schedule 130/70 , which means at -10 o С the temperature of the heat carrier in the supply pipeline of the heating network must be 85,6 degrees, in the supply pipeline of the heating system - 70.8 o C with a schedule of 105/70 or 65.3 about C on a 95/70 schedule. The temperature of the water after the heating system must be 51,7 about S.

As a rule, the temperature values ​​in the supply pipeline of heat networks are rounded off when setting the heat source. For example, according to the schedule, it should be 85.6 ° C, and 87 degrees are set at the CHP or boiler house.

Temperature outdoor air Tnv, o C	Temperature network water in the supply pipeline T1, about C			Water temperature in the supply pipe of the heating system T3, about C		Water temperature after heating system T2, about C
	150	130	115	105	95
8	53,2	50,2	46,4	43,4	41,2	35,8
7	55,7	52,3	48,2	45,0	42,7	36,8
6	58,1	54,4	50,0	46,6	44,1	37,7
5	60,5	56,5	51,8	48,2	45,5	38,7
4	62,9	58,5	53,5	49,8	46,9	39,6
3	65,3	60,5	55,3	51,4	48,3	40,6
2	67,7	62,6	57,0	52,9	49,7	41,5
1	70,0	64,5	58,8	54,5	51,0	42,4
0	72,4	66,5	60,5	56,0	52,4	43,3
-1	74,7	68,5	62,2	57,5	53,7	44,2
-2	77,0	70,4	63,8	59,0	55,0	45,0
-3	79,3	72,4	65,5	60,5	56,3	45,9
-4	81,6	74,3	67,2	62,0	57,6	46,7
-5	83,9	76,2	68,8	63,5	58,9	47,6
-6	86,2	78,1	70,4	65,0	60,2	48,4
-7	88,5	80,0	72,1	66,4	61,5	49,2
-8	90,8	81,9	73,7	67,9	62,8	50,1
-9	93,0	83,8	75,3	69,3	64,0	50,9
-10	95,3	85,6	76,9	70,8	65,3	51,7
-11	97,6	87,5	78,5	72,2	66,6	52,5
-12	99,8	89,3	80,1	73,6	67,8	53,3
-13	102,0	91,2	81,7	75,0	69,0	54,0
-14	104,3	93,0	83,3	76,4	70,3	54,8
-15	106,5	94,8	84,8	77,9	71,5	55,6
-16	108,7	96,6	86,4	79,3	72,7	56,3
-17	110,9	98,4	87,9	80,7	73,9	57,1
-18	113,1	100,2	89,5	82,0	75,1	57,9
-19	115,3	102,0	91,0	83,4	76,3	58,6
-20	117,5	103,8	92,6	84,8	77,5	59,4
-21	119,7	105,6	94,1	86,2	78,7	60,1
-22	121,9	107,4	95,6	87,6	79,9	60,8
-23	124,1	109,2	97,1	88,9	81,1	61,6
-24	126,3	110,9	98,6	90,3	82,3	62,3
-25	128,5	112,7	100,2	91,6	83,5	63,0
-26	130,6	114,4	101,7	93,0	84,6	63,7
-27	132,8	116,2	103,2	94,3	85,8	64,4
-28	135,0	117,9	104,7	95,7	87,0	65,1
-29	137,1	119,7	106,1	97,0	88,1	65,8
-30	139,3	121,4	107,6	98,4	89,3	66,5
-31	141,4	123,1	109,1	99,7	90,4	67,2
-32	143,6	124,9	110,6	101,0	94,6	67,9
-33	145,7	126,6	112,1	102,4	92,7	68,6
-34	147,9	128,3	113,5	103,7	93,9	69,3
-35	150,0	130,0	115,0	105,0	95,0	70,0

Please do not focus on the diagram at the beginning of the post - it does not correspond to the data from the table.

Calculation of the temperature graph

The method for calculating the temperature graph is described in the reference book (Chapter 4, p. 4.4, p. 153,).

This is quite laborious and long process, since for each outdoor temperature several values ​​\u200b\u200bmust be considered: T 1, T 3, T 2, etc.

To our joy, we have a computer and a MS Excel spreadsheet. A colleague at work shared with me a ready-made table for calculating the temperature graph. She was once made by his wife, who worked as an engineer for a group of regimes in thermal networks.

In order for Excel to calculate and build a graph, it is enough to enter several initial values:

• design temperature in the supply pipeline of the heating network T 1
• design temperature in the return pipeline of the heating network T 2
• design temperature in the supply pipe of the heating system T 3
• Outside temperature T n.v.
• Indoor temperature T v.p.
• coefficient " n» (it is usually not changed and is equal to 0.25)
• Minimum and maximum cut of the temperature graph Cut min, Cut max.

Everything. nothing more is required of you. The results of the calculations will be in the first table of the sheet. It is highlighted in bold.

The charts will also be rebuilt for the new values.

The table also considers the temperature of direct network water, taking into account wind speed.

The heat load for heating and ventilation varies depending on the outdoor temperature. The heat consumption for hot water supply does not depend on the outdoor temperature. Under these conditions, it is necessary to adjust the parameters and flow of the coolant in accordance with the actual needs of subscribers.

4.1. Temperature chart of network water

In the presence of a heterogeneous load (heating, ventilation and hot water supply) in the general heat network, the calculation and construction of the temperature graph of network water is carried out according to the prevailing heat load and for the most common scheme for connecting subscriber installations. As a rule, the heating load is predominant. The preferred system for regulating the heat load is quality control, when the change in the heat load for heating with a change in the outside air temperature is carried out by changing the temperature of the network water at a constant flow rate. Such regulation is carried out at the heat source.

The calculated temperatures of the network water in the supply and return pipelines (- the temperatures of the coolant in the supply and return pipelines and in the heating system with its dependent connection, respectively) on the heat source collectors correspond to the calculated outdoor air temperature and are set when designing the heat supply system, for example, 150/70, 130/70 etc. If thermal load homogeneous, in particular, heating, then in the entire range of outdoor temperatures it is possible to carry out high-quality regulation. In this case, the heat load is directly proportional to the temperature of the coolant in the supply pipeline and inversely proportional to the outdoor air temperature. Therefore, on the temperature graph, the dependences of the temperatures of the network water in the supply and return pipelines are depicted with a uniform load and high-quality regulation by straight lines. Behind starting point these lines take the outside air temperature +20 0 C (+18), when the heat load is zero. Then the temperature of the network water in the supply and return pipelines will also be +20 0 С (+18). The endpoints will be respectively . With dependent connection of the heating system, there will be a third straight line on the graph connecting the starting point with the calculated temperature.

If there is a load of hot water supply (DHW), the temperature of the water in the supply pipeline cannot be reduced below 60 0 С when connecting hot water systems in an open circuit and below 70 0 C when connected via closed scheme, since the temperature of the water in the water fittings should be from 55 0 С to 65 0 С, and in hot water heat exchanger about 10 0 С is lost. Thus, a cut-off is made on the temperature graph, as shown in Figs. 4 and 5. On the control graph of a closed heat supply system, the outdoor temperature corresponding to the cut-off, area of ​​quantitative regulation I. Zone III appears on the regulation chart of an open heat supply system in the zone of qualitative regulation, when the water temperature in the return pipeline reaches 60 0 C and water is taken away for hot water supply only from it.

Figure 4. Temperature graph of the regulation of an open dependent system heat supply

Fig.5 Temperature chart for regulation of a closed independent heat supply system

The presence or absence of a broken line on the regulation graph depends on whether the heat supply system is dependent (Fig. 4) or independent (Fig. 5).

If , then the regulation is rationally carried out according to the joint load on heating and hot water supply. At the same time, the so-called increased temperature control curve is built, which allows compensating increased consumption heat for hot water supply by increasing the temperature difference between the direct and return water in comparison with the control schedule for heating load.

When building elevated schedule heat consumption for hot water supply is taken as a balance:

where is the balance ratio, usually taken equal to 1.2.

The view of the graph is shown in Fig.6.

Figure 6. Increased temperature regulation curve.

In the figure: - temperature of the heat carrier on the collectors of the CHPP; - coolant temperature according to heating schedule; - coolant temperature in heating systems.

Quantities

Connected by the equation

(10)

Here, the calculated temperature difference of network water according to the heating schedule

At the beginning, the value is determined from the equation

. (11)

Temperature tap water after the first stage of the DHW heater where =5…10 o C is the amount of water undercooling in the heater.

4.2. Calculation and scheduling of network water consumption

4.2.1. Estimated consumption of network water for heating:

(12)

where c=4.19 kJ/(kg×K) is the heat capacity of water.

In the zone of qualitative regulation II, the flow rate of the heat carrier for heating is constant, in the zone of quantitative regulation I it drops with an increase in the outdoor temperature to 0 at +20 (18) 0 FROM(Fig. 5 and 6).

4.2.2. Estimated consumption of network water for ventilation:

is determined by (13):

(13)

The nature of the graph of the flow rate for ventilation repeats the course of the graph of the flow rate for heating (Fig. 6 and 7).

4.3.3 Consumption of network water for hot water supply:

In open heat supply networks, the average hourly water consumption for hot water supply will be:

(14)

IN closed systems heat supply, the average hourly consumption for hot water supply is determined by (13, 14).

At parallel circuit water heater connections

(15)

Water temperature after a hot water heater connected in parallel at the break point of the water temperature graph; it is recommended to take = 30 ° С.

With two-stage systems for connecting water heaters

, (16)

where is the water temperature after the first stage of heating at two-stage schemes connection of water heaters, °С.

In relation to the control zones of the temperature graph of the heat supply system, the costs behave as follows.

In the zone of quantitative regulation I, at a constant temperature in the supply pipeline, taking into account the average load on hot water supply, the consumption of network water for hot water supply remains constant both with open and closed heat supply systems (Fig. 5 and 6).

These network water costs are determined as follows.

In the zone of qualitative regulation (II, III - with an open scheme and II - with a closed one), the nature of the curves differs significantly.

With an open circuit in zone II, network water for hot water supply is disassembled from the supply and return pipelines. From the supply pipeline, the network water flow decreases from the maximum value at the outdoor temperature to zero at the outdoor temperature. On the contrary, the flow of network water from the return pipeline varies from zero to a maximum value at the same outdoor temperatures. In zone III, the distribution of network water for hot water supply comes only from the return pipeline and drops somewhat as the water temperature rises from 60 to 70 0 С (Fig. 5).

With a closed scheme for connecting the hot water supply system, heat exchange between the heat supply and hot water supply systems occurs in a single-stage (on the supply line) or in a two-stage (on both lines) heat exchanger. In zone II, the consumption of network water for hot water supply decreases from maximum at to zero at for a two-stage heat exchanger (Fig. 6, solid line) and to the value

(17)

(Fig. 6, dashed line).

Then, for clarity, a graph of the total consumption of network water is plotted (Fig. 7 and 8) according to the condition

. (18)

Figure 7. Graph of costs of an open heat network

Figure 8. Curve of costs of a closed heat network (solid line - two-stage heating hot water: dashed - single-stage).

The calculated consumption of network water in a two-pipe network in open and closed heat supply systems, necessary for the hydraulic calculation of the heat network, is determined by the formula (19):

. (19)

Coefficient that takes into account the share of the average water consumption in the regulation of the heating load, taken from the following considerations:

· open system: 100 or more MW =0.6, less than 100MW, =0.8;

· closed system: 100 and more MW =1.0, less than 100MW, =1.2.

When regulating according to the combined load of heating and hot water supply with an adjusted control schedule, the coefficient is taken equal to 0.

When designing heat networks, the task of hydraulic calculation includes determining the diameters of pipelines and the pressure drop in sections and in general along the main. The calculation is carried out in two stages: preliminary and verification.

5.1. Procedure for hydraulic calculation

The initial data for the calculation are: calculation scheme (see Fig. 1); estimated costs of network water by sections; the type and number of local resistances in each section.

One of the main parameters that determine the hydraulic resistance is the speed of water in pipelines. In main networks, the water speed is recommended to be taken within l¸2 m / s, and in distribution pipelines - 3¸5 m / s.

At the first, preliminary, stage, the estimated diameter of the pipeline is determined according to the accepted values ​​of the water velocity w and specific pressure drop. For main pipelines, the value £ 80 Pa/m, for distribution networks and branches =100¸300 Pa/m. The nominal diameter of the section under consideration is determined using a nomogram for the hydraulic calculation of the pipeline (Appendix P) according to the water flow rate and the accepted specific pressure drop. Since the intersection point on the nomogram does not fall on any line of the standard diameter, it is necessary to move up or down along the flow line until it intersects with the line of the standard diameter. If you move up, then a smaller standard diameter is selected, but the actual specific linear resistance turns out to be larger, and if you move down, then the diameter is larger, and the resistance is smaller. Usually, in sections of the pipeline close to the heat source, they switch to larger diameters, and closer to the end of the pipeline, to smaller ones. It is also necessary to ensure that the water velocity in the pipeline section does not go beyond the specified limits. The obtained actual values ​​of specific linear resistance and water velocity are entered in Table 2.

table 2

Hydraulic calculation of the heating network

Continuation of table 2

Hydraulic calculation of the heating network

By calculation scheme and the selected pipeline route, the types and number of local resistances are determined: fittings, bends, compensators, etc. According to Appendix P8, depending on the nominal diameter and type of local resistances, the equivalent length of local resistances is determined and entered in Table 2. The estimated length of the pipeline section is determined by summing the actual and equivalent length.

The pressure drop in the design section is calculated by formula (20), Pa:

(20)

where is the length of the calculated section, m;

The total equivalent length of local resistances in a given section.

The pressure loss in the section will be:

where \u003d 975 kg / m 3 - the density of water at a temperature of 100 ° C;

g\u003d 9.81 m / s 2 - free fall acceleration.

The obtained values ​​are entered in the columns of the verification calculation (Table 2). All sections of the highway are calculated similarly.

The calculation of branches is carried out in the same way as a section of the main line, with a given pressure drop (head), determined after constructing a piezometric graph as the difference in pressure in the supply and return lines at the point of connection of the branch.

Also, as for the main line, for a specific calculated branch, the length of pipelines is measured from the branch point to the farthest consumer (subscriber) - l resp., m. For this branch with a length l resp. preliminary specific linear pressure drop, Pa/m:

(22)

where ; Z- experimental coefficient of local resistance for branches (for conduits Z\u003d 0.03¸0.05); G resp.- estimated flow rate of the coolant at the initial section of the branch, kg/s; - the difference between the available pressure drop on the branch and the required pressure drop at the last subscriber, Pa; - the actual length of the branch in a two-pipe version.

At complex scheme distribution networks, a branch is divided into sections similar to the division into sections of the main network.

4.2. Building a piezometric graph

The piezometric graph is built on the basis of hydraulic calculation (Table 2). The piezometric graph of the network allows you to establish the mutual correspondence of the terrain, the height of subscriber systems and pressure losses in pipelines. According to the piezometric graph, it is possible to determine the pressure at any point in the network, the available pressure at the branch points and at the input to the subscriber systems, as well as adjust the connection schemes of the subscriber systems and the existing pressures in the forward and reverse mains of the network.

The piezometric graph is plotted on a scale in coordinates L-H (L- track length, m; H- pressure, m). The point is taken as the origin of coordinates 0 corresponding to the setting network pumps(Fig. 6). To the right of the dot 0 along the axis L (I-I line, mark 0.0) a route profile is drawn in accordance with the terrain along the main highway and branches. Here it is assumed that the path profile coincides with the terrain. At simple scheme heat supply and a small number of subscriber inputs (no more than 20) on branches and mains, the heights of buildings (subscriber systems) are plotted. Y-axis from point 0 head is given in meters.

The construction of a piezometric graph begins with a hydrostatic mode, when there is no water circulation in the system, and the entire heat supply system, including heating systems or heat exchangers of heating systems, is filled with water with a temperature of up to 100 ° C. Static pressure in the heating network H st provided by feed pumps. line static head S-S on the graph is carried out from the condition of strength cast iron radiators, i.e. 60 m. The static pressure must be higher than the height of the buildings connected to the heat supply system, and also ensure that the water in the heating network does not boil. If at least one of the conditions for subscriber inputs is not met, it is necessary to provide for the division of the heating network into zones with the maintenance of its own static pressure in each zone.

The required head of modern network pumps is within 10¸25 m from the condition of suppressing cavitation at the suction to the pump, and the total head of the make-up pumps H st=40¸60 m. Given value

H st is plotted along the H axis from point 0 to A. From point A, the construction of a piezometric graph for the return line in dynamic mode begins, based on this hydraulic calculation. From point A, the length of the first calculated section 0 - I (0 I) is plotted. Further along the H axis, the calculated value of hydraulic losses Δ H I is plotted (point 0 1 ). Performing the described actions, we determine successively all points of the piezometric graph of the return line (points 0 , 0 1 , 0 2 etc.).

From last point piezometric curve of the return line (point 0 4 ) the required available head is deposited at last subscriber DH ab » 15¸20 m with an elevator or DH ab » 10m +H zd- with elevatorless connection (point P 4). The piezometric graph of a straight line is built from the point P 4 in reverse order along the network sections. Connecting all found points ( А,0 1 ,0 2 , ...) we obtain a piezometric graph of the return line. With proper calculations and construction, the piezometric graph should be straight. At the point P, corresponding to the location of the heat source, the pressure loss in the network heaters is deposited upwards DH P=10¸20 m or in a hot water boiler DH P=15¸30 m.

Figure 9. Piezometric graph and heat network diagram:

I - network pump; II - make-up pump; III - heat treatment plant; IV - pressure regulator; V - make-up tank.

5. SELECTION OF SCHEMES FOR CONNECTING SUBSCRIBER HEATING SYSTEMS TO THE HEAT NETWORK

The piezometric graph allows you to choose the scheme for connecting subscriber units to the heating network, taking into account the available pressure drop and restrictions on overpressure in pipelines.

On fig. 10 shows the schemes for connecting subscriber heating systems to the heating network. Schemes (a), (b) and (c) are dependent connections. Scheme (a) is used when there is a central or group heating point, where the heat carrier with the required parameters is prepared and only the pressure needs to be adjusted in front of the heating system. Fig.10b - elevator scheme connection is used provided that the pressure in the return line does not exceed the allowable for local heating systems, and the available pressure at the input is sufficient for the operation of the elevator (15¸18 m).

If the pressure in the return line does not exceed the allowable one, and the available pressure is insufficient for the operation of the elevator, apply dependent schema with a mixing pump (Fig. 10c).

If the pressure in the return line in static or dynamic mode exceeds the allowable pressure for local heating systems, an independent scheme is used with the installation of a water-to-water heat exchanger (Fig. 10d).

Designations on the diagram:

PC - peak boiler; TP - heating heater; CH - network pump; PN - make-up pump; РР – flow regulator; D - diaphragm; B - air vent (Maevsky crane); E - elevator; H - mixing pump; RT - temperature controller; TO - heat exchanger of the heating system; CN - circulation pump; RB - expansion tank.

On fig. 11 shows the schemes for connecting the hot water supply system to the heat supply system.

Figure 11. Connection of hot water systems to the heat supply system

6. SELECTION OF PUMPS

6.1. Selection of network pumps

Network pumps are installed on the heat source, their number must be at least two, of which one is standby. The performance of all working pumps is assumed to be equal to the total consumption of network water, taking into account the pump safety factor for performance (1.05-1.1).

The head of the network pumps is determined by the piezometric graph and is equal, m:

H s.n. \u003d H st + DH p + DH o + DH ab,

where H st- head loss at the station, m;

DH n- pressure loss in the supply line, m;

DH ab- available pressure at the subscriber, m ;

dh about- pressure loss in the return line, m.

Pumps are selected for heating and non-heating periods. If there are booster pumps in the network, the pressure of the network pumps is reduced by the pressure of the booster pumps.

6.2. Selection of make-up pumps

The performance of make-up pumps is determined by the amount of network water losses in the heat supply system. In closed systems, network water losses are 0.5% of the volume of water in networks, m 3 / h:

G sub. =0.005×V+G hot water,

where V \u003d Q × (V s + V m)- the volume of water in the heat supply system, m 3; Q - thermal power heat supply systems, MW; V s, V m- specific volumes of network water located in external networks with heating installations and in local systems, m 3 / MW ( V c \u003d 10¸20, V m=25).

Bibliography

1. Aizenberg I.I., Baimachev E.E., Vygonets A.V. and etc. Tutorial degree design for students of the specialty 270109 - TV. - Irkutsk: Irkutsk Press House, 2007, - 104 p.

Economical energy consumption in the heating system can be achieved if certain requirements are met. One of the options is the presence of a temperature chart, which reflects the ratio of the temperature emanating from the heating source to external environment. The value of the values ​​makes 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 CHP. Water is used as a heat carrier. It is heated to a predetermined temperature.

Having passed full cycle through the system, the coolant, already cooled, returns to the source and reheating occurs. Sources are connected to the consumer by thermal networks. As the environment changes temperature regime, thermal energy should be regulated so that the consumer receives the required volume.

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

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

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

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

Dependency graph may vary.

A particular chart has a dependency on:

1. Technical and economic indicators.
2. Equipment for a CHP or boiler room.
3. climate.

High performance of the coolant provides the consumer with a large thermal energy.

An example of a circuit is shown below, where T1 is the temperature of the coolant, Tnv is the outdoor air:

It is also used, the diagram of the returned coolant. A boiler house or CHP according to such a scheme can evaluate the efficiency of the source. It is considered high when the returned liquid arrives cooled.

The stability of the scheme depends on the design values ​​of the liquid flow of high-rise buildings. If the flow rate through the heating circuit increases, the water will return uncooled, as the flow rate will increase. And vice versa, when minimum flow, the return water will be sufficiently cooled.

The supplier's interest is, of course, in the flow of return water in a chilled state. But there are certain limits to reduce the flow, since a decrease leads to losses in the amount of heat. The consumer will begin to lower the internal degree in the apartment, which will lead to a violation building codes and the discomfort of the inhabitants.

What does it depend on?

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

The value of the temperature leaving the boiler room is 90 degrees, so that at minus 23°C, it would be warm in the apartments and have a value of 22°C. Then the return water returns to 70 degrees. These standards are in line with the normal comfortable living in the House.

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

Previously, for 10-storey buildings, a scheme with calculated data of 95-70°C was introduced. The buildings above had their chart 105-70°C. Modern new buildings may have a different scheme, 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?

The control method is selected, then the calculation is made. The calculation-winter and reverse order of water inflow, the amount of outside air, the order at the break point of the diagram are taken into account. There are two diagrams, where one of them considers only heating, the other one considers heating with hot water consumption.

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

The initial 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- return flow of water.
5. T3- the entrance to the building.

We will consider several options for supplying heat with a value of 150, 130 and 115 degrees.

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

The results obtained are brought into a single table for the 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 considered the recommended values, without taking into account the climatic features of the region and the characteristics of the building.

To reduce power consumption, it is enough to choose a low-temperature order of 70 degrees and uniform distribution of heat throughout the heating circuit will be ensured. The boiler should be taken with a power reserve so that the load of the system does not affect the quality operation of the unit.

Adjustment

Heating regulator

Automatic control is provided by the heating controller.

It includes the following details:

1. Computing and matching panel.
2. Executive device at the water supply line.
3. Executive device, 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 in a room.

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

To increase the flow, there is a booster pump, and the corresponding command from the regulator. The incoming flow is regulated by a "cold bypass". That is, the temperature drops. Some of the liquid that circulates along the circuit is sent to the supply.

Information is taken by sensors and transmitted to control units, as a result of which flows are redistributed, which provide a rigid temperature scheme for the heating system.

Sometimes, a computing device is used, where the DHW and heating regulators are combined.

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

Regulator benefits:

1. The temperature regime is strictly maintained.
2. Exclusion of liquid overheating.
3. Fuel Economy and energy.
4. The consumer, regardless of distance, receives heat equally.

Table with temperature chart

The operating mode of the boilers depends on the weather of the environment.

If we take various objects, for example, a factory building, a multi-storey building and private house, all will have an individual heat chart.

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

Outside temperature	Temperature of network water in the supply pipeline	Temperature of network water in the return pipeline
+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 norms that must be observed in the creation of projects for heating networks and the transportation of hot water to the consumer, where the supply of water vapor must be carried out at 400 ° C, at a pressure of 6.3 bar. The supply of heat from the source is recommended to be released to the consumer with values ​​of 90/70 °C or 115/70 °C.

Regulatory requirements should be followed for compliance with the approved documentation with the obligatory coordination with the Ministry of Construction of the country.

Page 1

The decrease in the return water temperature against the schedule is not limited.

Thus, the first task is to reduce the temperature of the return water from the heating systems at the design point to 60 C.

This scheme gives a very large savings in thermal energy and a decrease in the return water temperature when the heating network is operating with a cutoff schedule for hot water supply, since it allows obtaining a variable temperature at a constant temperature of the network water in the supply line supply air according to the outside temperature.

Many heating networks successfully withstand this limit and even achieve a decrease in the return water temperature below the established schedule, thereby increasing the technical and economic performance of the entire system as a whole.

Energy savings for coolant pumping, fuel savings at CHPPs and a decrease in the return water temperature with three-pulse isodromic control pays for all the costs of bushing automation.

The use of surface condensing boilers and economizers for heating is therefore advisable, provided that the return water temperature is reduced heating system. Accordingly, the average water temperature and, as shown above, the temperature of direct water entering the system also decrease. Therefore, the use of surface condensing boilers and economizers for heating water in heating systems is inevitably associated with a certain excess consumption of metal for the construction of heating systems. Nevertheless, abroad, condensing boilers and economizers are mainly used for heating systems.

Average daily temperature return water from the heating network must not exceed the set value by more than 2 C. The decrease in the return water temperature against the schedule is not limited.

When the return water temperature drops to calculated value some decrease in the flue gas temperature should be expected.

Let's define optimal temperature return water coming from the heating system of the building to the FNKV-1 contact-surface water heater. As the return water temperature tz decreases, the efficiency of gas use in the apparatus increases due to the use of heat released during the condensation of water vapor in the gas combustion products. Therefore, the determination of the value of n is practically necessary.

raw water for chemical water treatment they are taken from the waste circulation conduit at a temperature of 20 - 35 C, which makes it possible to utilize waste heat. A significant increase in the specific output at heat consumption results in a decrease in the temperature of the return water, which is obtained as a result of mixing the return and colder make-up water.

The bellows is the regulating body. With an increase in the temperature of the water leaving the heater, the liquid in the bellows heats up and expands, which leads to a decrease in the valve flow area and a reduction in the network water flow rate, and, consequently, to a decrease in the return water temperature.

Thus, for the considered scheme of proportional control of the temperature in the room, it is always necessary to provide automatic protection against freezing of heaters. According to this scheme, a manometric temperature sensor is installed in the return water pipeline after the heater and is adjusted to a temperature of 25 - 30 C. When the return water temperature drops to the set value, the sensor gives a signal, and the on-off controller is triggered, opening a passage for water through the bypass branch using a solenoid valve .

To obtain a uniform temperature field after the heater, which is especially important in air conditioners in which an irrigation chamber is installed immediately after the first heating, it is desirable to significantly reduce the temperature of the water supplied to the heater while simultaneously reducing the temperature difference between the direct and return water. Some increase in the required heating surface of the heaters is compensated by a decrease in the return water temperature.

To reduce the temperature of the water leaving the CHP and reduce heat loss at night, it is advisable to switch the circulation line of the hot water supply system to the pipeline for this time cold water in front of the 1st stage of the water heater. At the same time, the setting of the hot water temperature controller should be reduced from 60 to 50 C. During the day, the circulation line should be connected to the pipeline of heated water before stage II or, more rationally, to the pipeline between sections of stage II of the water heater, the water temperature in which is equal to the accepted water temperature in circulating pipeline (approximately in front of the last three sections in the direction of the heated water), as shown in fig. 3.19. Switching is carried out automatically: the time relay closes valve 5, for example, at 0000, directing the circulation flow to stage I, and through the electro-hydraulic relay, the impulse is switched to the temperature controller from the sensor configured to maintain the hot water temperature of 60 C, to another sensor with a setting of 45 - 50 C. At 6 o'clock the time relay makes reverse switching, at open valve 5 through it will flow circulating water, since the water pressure before stage I is much higher than at the point of inclusion of the pipeline on which the valve is installed. At automatic regulation supply of heat for heating, when the temperature of the water from the heating system is below 40 - 45 C, it is not advisable to switch the circulation pipeline in front of the 1st stage of the water heater at such temperatures. In this regard, a temperature sensor is installed on the return pipeline of the heating system, on the signal of which, when the return water temperature drops below 40 - - 45 C, valve 5 remains open at night.

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Determining the values ​​of the standard temperature of the return network water in off-design mode

Candidate of Technical Sciences, Associate Professor V.I. Ryabtsev, G.A. Ryabtsev, engineer, Kursk GT

Rational use of energy is urgent task for all times. But this is not always possible, especially in off-design and transient processes. And the variables thermal regimes networks are almost completely uncovered in the technical literature.

At present, the heat supply of most cities is carried out with the temperature of the network water in the supply lines, which is lower than the directive schedule of 150°/70° or 130°/70°. Under such conditions, operating personnel are unable to determine standard temperature returned return network water (t n about br). And because of this, conditions are created for the uncontrolled use of heat.

A method is proposed for calculating the temperature of the return network water for variable and off-design thermal regimes based on a 150°/70° schedule, according to which all heat sinks of consumers and buildings are designed. It is clearly shown in the figure, where the 150°/70° graph is transformed as a dependence of not only the water temperature on the supply line (t pr), but also the temperature difference between the supply and return network water (?t) on the outside air temperature

It can be seen from the graph that for each temperature of the incoming network water there corresponds its own standard value (?t H \u003d t pr - t arr), which is also determined by the outside air temperature (t nv). But as noted above, very often in reality t pr does not coincide with the required schedule t nv. Points 1 are the initial conditions - in fact, the temperature of the supply network water and the real frost. These two points along the lower curve correspond to their values?t! and?t2. Both values ​​are not real, because for?t 2 the condition of actual more severe frost is not met, and?t! does not have such high temperature t n. Therefore, the desired value?t H is between them?t 2

heat supply water temperature

T 2 - temperature difference according to the schedule 150°/70° for the actual temperature of the supply network water;

t n b - the temperature of the network water in the heating battery of the consumer, determined according to the schedule 150 ° / 70 ° for the actual value of t cf nv;

t vn - indoor air temperature, taken as + 18 ° С;

tf vn - the actual temperature of the outside air;

tf b - network water temperature in the consumer's battery, determined according to the schedule 150 ° / 70 ° for the actual temperature of the supply network water;

V hv - outdoor air temperature, taken according to

150°/70° curve based on the actual supply water temperature.

Checking the formula showed the practical coincidence of the results.

Thus, it was possible to show for the first time that in any operating mode of the heating network for any water temperature in the supply heat pipeline, there is its own standard temperature of the returned return network water. Comparison with the standard and actual temperature of the return network water is the main lever for a more complete and efficient use of the heat of the network water and the basis for a deep analysis of the network operation mode.

Literature

E.Ya.Sokolov. Heating network. Moscow, 1982

Handbook of heat supply and ventilation. Under. ed. Shchekin. Kyiv, 1996