Heating schedule. The dependence of the coolant temperature on the outside air temperature

Reference temperature water in heating system depends on air temperature. Therefore, the temperature graph for the supply of coolant to the heating system is calculated in accordance with weather conditions. In the article we will talk about the requirements of SNiP for the operation of the heating system for objects for various purposes.

from the article you will learn:

In order to economically and rationally use energy resources in the heating system, the heat supply is tied to the air temperature. The dependence of the water temperature in the pipes and the air outside the window is displayed as a graph. The main task of such calculations is to maintain comfortable conditions for residents in apartments. For this, the air temperature should be about + 20 ... + 22ºС.

The temperature of the coolant in the heating system

The stronger the frost, the faster the living quarters heated from the inside lose heat. To compensate for the increased heat loss, the temperature of the water in the heating system increases.

The calculations use normative indicator temperature. It is calculated according to special technique and included in the governing documents. This figure is based on the average temperature of the 5 coldest days of the year. The calculation is based on the 8 coldest winters over a 50-year period.

Why is the drawing up of a temperature schedule for the supply of coolant to the heating system happening in this way? The main thing here is to be ready for the most severe frosts that happen every few years. Climatic conditions in a particular region can change over several decades. This will be taken into account when recalculating the schedule.

The value of the average daily temperature is also important for calculating the margin of safety of heating systems. By understanding the ultimate load, you can accurately calculate the characteristics necessary pipelines, stop valves and other elements. This saves on the creation of communications. Given the scale of construction for urban heating systems, the amount of savings will be quite large.

The temperature in the apartment directly depends on how much the coolant is heated in the pipes. In addition, other factors also matter here:

• air temperature outside the window;
• wind speed. With strong wind loads, heat losses through doorways and windows increase;
• the quality of sealing joints on the walls, as well as the general condition of the decoration and insulation of the facade.

Building codes change as technology advances. This is reflected, among other things, in the indicators in the graph of the coolant temperature depending on the outside temperature. If the premises retain heat better, then energy resources can be spent less.

Developers in modern conditions more carefully approach the thermal insulation of facades, foundations, basements and roofs. This increases the value of objects. However, along with the growth of construction costs are reduced. The overpayment at the construction stage pays off over time and gives good savings.

The heating of the premises is directly affected not even by how hot the water in the pipes is. The main thing here is the temperature of the heating radiators. It is usually in the range of + 70 ... + 90ºС.

Several factors affect battery heating.

1. Air temperature.

2. Features of the heating system. The indicator indicated in the temperature chart for supplying coolant to the heating system depends on its type. AT single pipe systems heating of water up to + 105ºС is considered normal. Two-pipe heating due to better circulation gives a higher heat transfer. This allows you to reduce the temperature to + 95ºС. Moreover, if at the inlet the water needs to be heated, respectively, to + 105ºС and + 95ºС, then at the outlet its temperature in both cases should be at the level of + 70ºС.

So that the coolant does not boil when heated above + 100ºС, it is supplied to the pipelines under pressure. Theoretically, it can be quite high. This should provide a large supply of heat. However, in practice, not all networks allow water to be supplied under high pressure due to their deterioration. As a result, the temperature drops, and during severe frosts there may be a lack of heat in apartments and other heated premises.

3. The direction of the water supply to the radiators. At top wiring the difference is 2ºС, at the bottom - 3ºС.

4. Type of heaters used. Radiators and convectors differ in the amount of heat they give off, which means that they must work in different temperature conditions. Better performance heat transfer from radiators.

At the same time, the amount of heat released is affected, among other things, by the temperature of the outdoor air. It is she who is the determining factor in the temperature schedule for supplying coolant to the heating system.

When the water temperature is +95ºС, we are talking about the coolant at the entrance to the dwelling. Given the heat loss during transportation, the boiler room should heat it much more.

In order to supply water of the required temperature to the heating pipes in the apartments, a special equipment. It mixes hot water from the boiler room with the one that comes from the return.

Temperature chart for supplying coolant to the heating system

The graph shows what the water temperature should be at the entrance to the dwelling and at the exit from it, depending on the street temperature.

The presented table will help to easily determine the degree of heating of the coolant in the system central heating.

Representatives of utilities and resource-supplying organizations measure the water temperature using a thermometer. The 5th and 6th columns indicate the figures for the pipeline through which hot coolant. 7 column - for the return.

The first three columns indicate fever- these are indicators for heat generating organizations. These figures are given without taking into account heat losses that occur during the transportation of the coolant.

The temperature schedule for supplying coolant to the heating system is needed not only by resource-supplying organizations. If the actual temperature differs from the standard one, consumers have reasons to recalculate the cost of the service. In their complaints, they indicate how warm the air in the apartments is. This is the easiest parameter to measure. Inspecting authorities can already track the temperature of the coolant, and if it does not comply with the schedule, force the resource supplying organization to perform its duties.

A reason for complaints appears if the air in the apartment cools below the following values:

• in corner rooms in the daytime - below + 20ºС;
• in the central rooms in the daytime - below + 18ºС;
• in corner rooms at night - below +17ºС;
• in the central rooms at night - below +15ºС.

SNiP

Requirements for the operation of heating systems are fixed in SNiP 41-01-2003. Much attention in this document is given to security issues. In the case of heating, the heated coolant carries a potential hazard, which is why its temperature for residential and public buildings limited. It, as a rule, does not exceed + 95ºС.

If the water in the internal pipelines of the heating system is heated above + 100ºС, then the following safety measures are provided for at such facilities:

• heating pipes are laid in special mines. In the event of a breakthrough, the coolant will remain in these reinforced channels and will not be a source of danger to people;
• pipelines in high-rise buildings have special structural elements or devices that do not allow water to boil.

If the building has heating made of polymer pipes, then the temperature of the coolant should not exceed + 90ºС.

We have already mentioned above that in addition to the temperature schedule for supplying coolant to the heating system, responsible organizations need to monitor how hot the accessible elements of heating devices are. These rules are also given in SNiP. Permissible temperatures vary depending on the purpose of the room.

First of all, everything here is determined by the same security rules. For example, in children's and medical institutions allowable temperatures are minimal. AT in public places and there are usually no special restrictions for them at various production facilities.

Surface of heating radiators general rules should not be heated above +90ºС. If this figure is exceeded, Negative consequences. They consist, first of all, in the burning of paint on batteries, as well as in the combustion of dust in the air. This fills the indoor atmosphere with substances harmful to health. In addition, there may be harm to appearance heating appliances.

Another issue is safety in rooms with hot radiators. As a general rule, it is necessary to protect heating appliances whose surface temperature is above +75ºС. Usually, lattice fences are used for this. They do not interfere with air circulation. At the same time, SNiP provides for mandatory protection of radiators in children's institutions.

In accordance with SNiP, Maximum temperature coolant varies depending on the purpose of the room. It is determined both by the characteristics of the heating of different buildings, and by security considerations. For example, in medical institutions, the permissible water temperature in pipes is the lowest. It is + 85ºС.

The maximum heated coolant (up to +150ºС) can be supplied to the following facilities:

• lobbies;
• heated pedestrian crossings;
• landings;
• technical premises;
• industrial buildings, in which there are no aerosols and dust prone to ignition.

The temperature schedule for supplying coolant to the heating system according to SNiP is used only in the cold season. In the warm season, the document in question normalizes the microclimate parameters only in terms of ventilation and air conditioning.

The temperature chart of the heating system 95 -70 degrees Celsius is the most demanded temperature chart. By and large, we can say with confidence that all central heating systems operate in this mode. The only exceptions are buildings with autonomous heating.

But also in autonomous systems there may be exceptions when using condensing boilers.

When using boilers operating on the condensation principle, the temperature curves of heating tend to be lower.

Application of condensing boilers

For example, when maximum load for a condensing boiler, there will be a mode of 35-15 degrees. This is due to the fact that the boiler extracts heat from the exhaust gases. In a word, with other parameters, for example, the same 90-70, it will not be able to work effectively.

Distinctive properties of condensing boilers are:

• high efficiency;
• profitability;
• optimal efficiency at minimum load;
• quality of materials;
• high price.

You have heard many times that the efficiency of a condensing boiler is about 108%. Indeed, the manual says the same thing.

But how can this be, because we are still with school desk taught that more than 100% does not happen.

1. The thing is that when calculating the efficiency of conventional boilers, exactly 100% is taken as a maximum.
   But ordinary ones simply throw flue gases into the atmosphere, and condensing ones utilize part of the outgoing heat. The latter will go to heating in the future.
2. The heat that will be utilized and used in the second round and added to the efficiency of the boiler. Typically, a condensing boiler utilizes up to 15% of flue gases, this figure is adjusted to the efficiency of the boiler (approximately 93%). The result is a number of 108%.
3. Undoubtedly, heat recovery is a necessary thing, but the boiler itself costs a lot of money for such work..
   The high price of the boiler due to stainless heat exchange equipment, which utilizes heat in the last path of the chimney.
4. If instead of such stainless equipment we put ordinary iron equipment, then it will become unusable after a very short span time . Since the moisture contained in the flue gases has aggressive properties.
5. The main feature of condensing boilers is that they achieve maximum efficiency with minimum loads.
   Conventional boilers (), on the contrary, reach the peak of economy at maximum load.
6. The beauty of it useful property is that during the entire heating period, the load on heating is not always maximum.
   On the strength of 5-6 days, an ordinary boiler works at maximum. Therefore, a conventional boiler cannot match the performance of a condensing boiler, which has maximum performance at minimum loads.

You can see a photo of such a boiler a little higher, and a video with its operation can be easily found on the Internet.

conventional heating system

It is safe to say that the heating temperature schedule of 95 - 70 is the most in demand.

This is explained by the fact that all houses that receive heat from central heat sources are designed to work in this mode. And we have more than 90% of such houses.

The principle of operation of such heat production occurs in several stages:

• heat source (district boiler house), produces water heating;
• heated water, through the main and distribution networks moves towards consumers;
• in the home of consumers, most often in the basement, through elevator unit hot water is mixed with water from the heating system, the so-called return, the temperature of which is not more than 70 degrees, and then heated to a temperature of 95 degrees;
• further heated water (the one that is 95 degrees) passes through the heaters of the heating system, heats the premises and again returns to the elevator.

Advice. If you have a cooperative house or a society of co-owners of houses, then you can set up the elevator with your own hands, but this requires you to strictly follow the instructions and correctly calculate the throttle washer.

Poor heating system

Very often we hear that people's heating does not work well and their rooms are cold.

There can be many reasons for this, the most common are:

• schedule temperature system heating is not observed, the elevator may be incorrectly calculated;
• the house heating system is heavily polluted, which greatly impairs the passage of water through the risers;
• fuzzy heating radiators;
• unauthorized change of the heating system;
• poor thermal insulation of walls and windows.

A common mistake is an incorrectly dimensioned elevator nozzle. As a result, the function of mixing water and the operation of the entire elevator as a whole is disrupted.

This could happen for several reasons:

• negligence and lack of training of operating personnel;
• incorrectly performed calculations in the technical department.

During the many years of operation of heating systems, people rarely think about the need to clean their heating systems. By and large, this applies to buildings that were built during the Soviet Union.

All heating systems must be hydropneumatic flushing in front of everyone heating season. But this is observed only on paper, since ZhEKs and other organizations carry out these works only on paper.

As a result, the walls of the risers become clogged, and the latter become smaller in diameter, which violates the hydraulics of the entire heating system as a whole. The amount of transmitted heat decreases, that is, someone simply does not have enough of it.

You can do hydropneumatic purge with your own hands, it is enough to have a compressor and a desire.

The same applies to cleaning radiators. Over many years of operation, radiators inside accumulate a lot of dirt, silt and other defects. Periodically, at least once every three years, they need to be disconnected and washed.

Dirty radiators greatly impair the heat output in your room.

The most common moment is an unauthorized change and redevelopment of heating systems. When replacing old metal pipes with metal-plastic ones, diameters are not observed. And sometimes various bends are added, which increases local resistance and worsens the quality of heating.

Very often, with such unauthorized reconstruction, the number of radiator sections also changes. And really, why not give yourself more sections? But in the end, your housemate, who lives after you, will receive less of the heat he needs for heating. And the last neighbor, who will receive less heat the most, will suffer the most.

An important role is played thermal resistance building envelopes, windows and doors. As statistics show, up to 60% of heat can escape through them.

Elevator node

As we said above, all water-jet elevators are designed to mix water from the supply line of heating networks into the return line of the heating system. Thanks to this process, system circulation and pressure are created.

As for the material used for their manufacture, both cast iron and steel are used.

Consider the principle of operation of the elevator in the photo below.

Through pipe 1, water from heating networks passes through the ejector nozzle and with high speed enters the mixing chamber 3. There, water is mixed with it from the return of the heating system of the building, the latter is supplied through pipe 5.

The resulting water is sent to the heating system supply through diffuser 4.

In order for the elevator to function correctly, it is necessary that its neck be correctly selected. To do this, calculations are made using the formula below:

Where ΔРnas is the design circulation pressure in the heating system, Pa;

Gcm - water consumption in the heating system kg / h.

Note!
True, for such a calculation, you need a building heating scheme.

From a series of articles "What to do if it's cold in the apartment"

What is a temperature chart?

The water temperature in the heating system must be maintained depending on the actual outdoor temperature according to the temperature schedule, which is developed by heat engineers of design and energy supply organizations according to a special methodology for each source of heat supply, taking into account specific local conditions. These schedules should be developed based on the requirement that, in cold period years in living rooms supported optimum temperature*, equal to 20 - 22 ° С.

When calculating the schedule, heat losses (water temperatures) in the area from the heat supply source to residential buildings are taken into account.

Temperature graphs should be drawn up both for the heating network at the outlet of the heat supply source (boiler house, CHPP), and for pipelines after the heating points of residential buildings (groups of houses), i.e. directly at the entrance to the heating system of the house.

Hot water is supplied from heat supply sources to heating networks according to the following temperature charts:*

• from large CHP plants: 150/70°С, 130/70°С or 105/70°С;
• from boiler houses and small CHP plants: 105/70°С or 95/70°С.

*the first digit is the maximum temperature of the direct network water, the second digit is its minimum temperature.

Other temperature schedules may be applied depending on specific local conditions.

So, in Moscow, at the exit from the main sources of heat supply, schedules of 150/70°С, 130/70°С and 105/70°С (maximum/minimum water temperature in the heating system) are used.

Until 1991, such temperature schedules were annually approved by the administrations of cities and other settlements before the autumn-winter heating season, which was regulated by the relevant regulatory and technical documents (NTD).

Subsequently, unfortunately, this norm disappeared from the NTD, everything was given to the owners of boiler houses, thermal power plants, and other factories - steamships, who at the same time did not want to lose profits.

However regulatory requirement on the obligation to draw up temperature schedules for heating restored federal law No. 190-FZ of July 27, 2010 "On heat supply". Here is what is regulated in FZ-190 according to temperature chart(the articles of the Law are arranged by the author in their logical sequence):

“... Article 23. Organization of the development of heat supply systems for settlements, urban districts
…3. Authorized ... bodies [see. Art. 5 and 6 FZ-190] should develop, statement and annual update* * heat supply schemes, which should contain:
…7) Optimal temperature chart…
Article 20 heating period
…5. Check readiness for heating period heat supply organizations... is carried out in order to ... readiness of these organizations to fulfill the heat load schedule, maintaining the temperature schedule approved by the heat supply scheme…
Article 6. Powers of bodies local government settlements, urban districts in the field of heat supply
1. The powers of local self-government bodies of settlements, urban districts for the organization of heat supply in the respective territories include:
…4) fulfillment of requirements, established rules assessing the readiness of settlements, urban districts for the heating period, and readiness control heat supply organizations, heat network organizations, certain categories of consumers for the heating season;
…6) approval of heat supply schemes settlements, urban districts with a population of less than five hundred thousand people ...;
Article 4, paragraph 2. To the powers of the fed. organ isp. authority authorized to implement the state. heating policies include:
11) approval of heat supply schemes for settlements, mountains. districts with a population of five hundred thousand or more ...
Article 29. Final provisions
…3. Approval of heat supply schemes for settlements ... must be carried out before December 31, 2011.”

And here is what is said about the temperature graphs of heating in the "Rules and norms for the technical operation of the housing stock" (approved by the Post. Gosstroy of the Russian Federation of September 27, 2003 No. 170):

“…5.2. Central heating
5.2.1. The operation of the central heating system of residential buildings should ensure:
- maintaining the optimum (not below the permissible) air temperature in heated rooms;
- maintaining the temperature of the water entering and returning from the heating system in accordance with the schedule quality regulation water temperature in the heating system (Appendix N 11);
- uniform heating of all heating devices;
5.2.6. The premises of the operating personnel should have:
... e) a graph of the temperature of the supply and return water in the heating network and in the heating system, depending on the outdoor temperature, indicating the working water pressure at the inlet, static and maximum allowable pressure in system;…"

Due to the fact that a heat carrier with a temperature not higher than can be supplied to house heating systems: for two-pipe systems - 95 ° С; for single-pipe - 105 ° С, at heating points (individual house or group for several houses), before water is supplied to houses, hydraulic elevator units are installed in which direct network water having high temperature, mixed with chilled return water returning from the heating system of the house. After mixing in the hydraulic elevator, the water enters the house system with a temperature according to the "house" temperature chart 95/70 or 105/70 ° С.

The following, as an example, shows the temperature graph of the heating system after heating point a residential building for radiators according to the top-down and bottom-up scheme (with outdoor temperature intervals of 2 °C), for a city with an estimated outdoor air temperature of 15 °C (Moscow, Voronezh, Orel):

WATER TEMPERATURE IN DISCHARGE PIPELINES, deg. C

AT DESIGN OUTSIDE AIR TEMPERATURE

Explanations:
1. In gr. 2 and 4 show the values ​​of the water temperature in the supply pipeline of the heating system:
in the numerator - at a calculated water temperature drop of 95 - 70 °C;
in the denominator - with a calculated difference of 105 - 70 °C.
In gr. 3 and 5 show the water temperatures in the return pipeline, which coincide in their values ​​with calculated differences of 95 - 70 and 105 - 70 °C.

Temperature graph of the heating system of a residential building after a heat point

Source: Rules and Regulations technical operation housing stock, adj. 20
(approved by order of the Gosstroy of the Russian Federation of December 26, 1997 No. 17-139).

Since 2003 they have been operating "Rules and norms for the technical operation of the housing stock"(approved by the Post. Gosstroy of the Russian Federation of September 27, 2003 No. 170), adj. eleven.

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 of quality regulation of heat supply according to average daily temperature outside air. I want to warn those who, on the basis of these figures, will try to sort things out with housing departments or heating networks: heating schedules for each individual locality are different (I wrote about this in an article). Thermal networks in Ufa (Bashkiria) operate according to this schedule.

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 network work 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.

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 work colleague 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.

All. 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.

Build for closed system heat supply schedule of central quality regulation of heat supply for the combined load of heating and hot water supply (increased or adjusted temperature schedule).

Take the estimated temperature of the network water in the supply line t 1 = 130 0 С in the return line t 2 = 70 0 С, after the elevator t 3 = 95 0 С. indoors tv = 18 0 C. Estimated heat flows accept the same. Temperature hot water in hot water supply systems tgv = 60 0 C, temperature cold water t c \u003d 5 0 C. Balance coefficient for the load of hot water supply a b \u003d 1.2. The scheme for switching on water heaters of hot water supply systems is two-stage sequential.

Decision. Let us preliminarily perform the calculation and construction of a heating and household temperature graph with the temperature of the network water in the supply pipeline for the break point = 70 0 C. The values ​​of the temperatures of the network water for heating systems t 01 ; t 02 ; t 03 will be determined using the calculated dependencies (13), (14), (15) for outdoor air temperatures t n = +8; 0; -ten; -23; -31 0 С

Let us determine, using formulas (16),(17),(18), the values ​​of the quantities

For t n = +8 0С values t 01, t 02 ,t 03 respectively will be:

Calculations of network water temperatures are performed similarly for other values t n. Using the calculated data and taking minimum temperature network water in the supply pipeline \u003d 70 0 С, we will build a heating and household temperature graph (see Fig. 4). The breaking point of the temperature graph will correspond to the network water temperature = 70 0 С, = 44.9 0 С, = 55.3 0 С, outdoor air temperature = -2.5 0 С. in table 4. Next, we proceed to the calculation of the elevated temperature graph. Given the value of subheating D t n \u003d 7 0 С, we determine the temperature of the heated tap water after the water heater of the first stage

Let us determine by formula (19) the balance load of hot water supply

Using formula (20), we determine the total temperature difference of network water d in both stages of water heaters

Let us determine by formula (21) the temperature difference of the network water in the water heater of the first stage for the range of outdoor air temperatures from t n \u003d +8 0 C to t" n \u003d -2.5 0 C

Let us determine for the specified range of outdoor air temperatures the temperature difference of network water in the second stage of the water heater

Using formulas (22) and (25), we determine the values ​​of the quantities d 2 and d 1 for outdoor temperature range t n from t" n \u003d -2.5 0 C to t 0 \u003d -31 0 C. So, for t n \u003d -10 0 C, these values ​​\u200b\u200bwill be:

Similarly, we will calculate the quantities d 2 and d 1 for values t n \u003d -23 0 C and tн = –31 0 С. The temperature of the network water and in the supply and return pipelines for the increased temperature graph will be determined by formulas (24) and (26).

Yes, for t n \u003d +8 0 C and t n \u003d -2.5 0 C, these values ​​will be

for t n \u003d -10 0 C

Similarly, we perform calculations for the values t n \u003d -23 0 С and -31 0 С. The obtained values ​​of the quantities d 2, d 1, , we summarize in table 4.

To plot the temperature of network water in the return pipeline after the heaters of ventilation systems in the range of outdoor air temperatures t n \u003d +8 ¸ -2.5 0 С use formula (32)

Let's define the value t 2v for t n \u003d +8 0 C. We first set the value to 0 C. We determine the temperature differences in the heater and, accordingly, for t n \u003d +8 0 C and t n \u003d -2.5 0 C

Calculate the left and right sides of the equation

Left side

Right part

Insofar as numerical values the right and left parts of the equation are close in value (within 3%), we will take the value as final.

For ventilation systems with air recirculation, we determine, using formula (34), the temperature of the network water after the heaters t 2v for t n = t nro = -31 0 C.

Here the values ​​of D t ; t ; t correspond t n = t v \u003d -23 0 С. Since this expression is solved by the selection method, we first set the value t 2v = 51 0 C. Let us determine the values ​​of D t to and D t

Since the left side of the expression is close in value to the right (0.99"1), the previously accepted value t 2v = 51 0 С will be considered final. Using the data in Table 4, we will build a heating and domestic and increased temperature control graphs (see Fig. 4).

Table 4 - Calculation of temperature control curves for a closed heat supply system.

Fig.4. Temperature control charts for a closed heat supply system (¾ heating and household; --- elevated)

Build for open system heat supply of the adjusted (increased) schedule of the central quality regulation. Accept the balance coefficient a b = 1.1. Take the minimum temperature of the network water in the supply pipeline for the break point of the temperature graph 0 C. Take the rest of the initial data from the previous part.

Decision. First, we build temperature graphs , , , using calculations using formulas (13); (fourteen); (fifteen). Next, we will build a heating and household graph, the break point of which corresponds to the temperature values ​​of the network water 0 С; 0C; 0 C, and outdoor temperature 0 C. Next, we proceed to calculate the adjusted schedule. Determine the balance load of hot water supply

Let us determine the ratio of the balance load for hot water supply to the calculated load for heating

For a range of outdoor temperatures t n \u003d +8 0 С; -10 0 С; -25 0 С; -31 0 C, we determine the relative heat consumption for heating according to the formula (29)`; For example for t n \u003d -10 will be:

Then, taking the values ​​known from the previous part t c; t h q; Dt define, using formula (30), for each value t n relative costs of network water for heating.

For example, for t n \u003d -10 0 C will be:

Let's do the calculations for other values ​​in the same way. t n.

Supply water temperatures t 1p and reverse t 2n pipelines for the adjusted schedule will be determined by formulas (27) and (28).

Yes, for t n \u003d -10 0 C we get

Let's do the calculations t 1p and t 2p and for other values t n. Let us determine using the calculated dependences (32) and (34) the temperature of the network water t 2v after heaters of ventilation systems for t n \u003d +8 0 C and t n \u003d -31 0 С (in the presence of recirculation). With a value tн = +8 0 С t 2v = 23 0 C.

Let's define the values Dt to and Dt to

;

Since the numerical values ​​of the left and right parts of the equation are close, the previously accepted value t 2v = 23 0 C, we will consider it final. Let us also define the values t 2v at t n = t 0 = -31 0 C. Let us preliminarily set the value t 2v = 47 0 C

Let us calculate the values ​​of D t to and

The obtained values ​​of the calculated values ​​are summarized in table 3.5

Table 5 - Calculation of the increased (adjusted) schedule for an open heat supply system.

Using the data in Table 5, we will build a heating and household, as well as an increased graph of the temperature of the network water.

Fig. 5 Heating - domestic ( ) and elevated (----) graphs of network water temperatures for an open heat supply system

Hydraulic calculation main heat pipelines two-pipe water heating network of a closed heat supply system.

Design scheme The heating network from the heat source (HS) to city blocks (CV) is shown in Fig.6. For compensation temperature deformations provide gland compensators. Specific pressure losses along the main line should be taken in the amount of 30-80 Pa / m.

Fig.6. Calculation scheme of the main heat network.

Decision. The calculation is performed for the supply pipeline. We will take the most extended and loaded branch of the heating network from IT to KV 4 (sections 1,2,3) as the main highway and proceed to its calculation. According to the hydraulic calculation tables given in the literature, as well as in Appendix No. 12 study guide, based on the known flow rates of the coolant, focusing on the specific pressure loss R in the range from 30 to 80 Pa / m, we will determine the diameters of pipelines for sections 1, 2, 3 d n xS, mm, actual specific pressure loss R, Pa/m, water velocity V, m/s.

By known diameters on sections of the main highway, we determine the sum of the coefficients of local resistances S x and their equivalent lengths L e. So, in section 1 there is a head valve ( x= 0.5), tee per pass at flow separation ( x= 1.0), Number of expansion joints ( x= 0.3) on the section will be determined depending on the length of the section L and the maximum allowable distance between fixed supports l. According to Appendix No. 17 of the training manual for D y = 600 mm this distance is 160 meters. Therefore, in section 1, 400 m long, three gland expansion joints should be provided. The sum of local resistance coefficients S x in this area will be

S x= 0.5 + 1.0 + 3 × 0.3 = 2.4

According to Appendix No. 14 of the training manual (with To e = 0.0005m) equivalent length l uh for x= 1.0 equals 32.9 m. L e will be

L e = l e × S x= 32.9 × 2.4 = 79 m

L n = L+ L e \u003d 400 + 79 \u003d 479 m

Then we determine the pressure loss DP in section 1

D P= R x L n = 42 × 479 = 20118 Pa

Similarly, we perform the hydraulic calculation of sections 2 and 3 of the main highway (see Table 6 and Table 7).

Next, we proceed to the calculation of the branches. According to the principle of linking the pressure loss D P from the point of division of flows to the end points (CV) for different branches of the system must be equal to each other. Therefore, in the hydraulic calculation of branches, it is necessary to strive to fulfill following conditions:

D P 4+5 = D P 2+3 ; D P 6=D P 5 ; D P 7=D P 3

Based on these conditions, we will find the approximate specific pressure losses for the branches. So, for a branch with sections 4 and 5, we get

Coefficient a, which takes into account the share of pressure losses due to local resistances, is determined by the formula

then Pa/m

Focusing on R= 69 Pa / m we determine the diameters of pipelines, specific pressure losses from the tables of hydraulic calculation R, speed V, pressure loss D R in sections 4 and 5. Similarly, we will calculate the branches 6 and 7, having previously determined the approximate values ​​for them R.

Pa/m

Pa/m

Table 6 - Calculation of equivalent lengths of local resistances

Table 7 - Hydraulic calculation main pipelines

Let us determine the discrepancy between pressure losses in the branches. The discrepancy on the branch with sections 4 and 5 will be:

The discrepancy on branch 6 will be:

The discrepancy on branch 7 will be.