Heating network design

Recommendation points

• Briefly about heating networks
• Types of heating networks
• 2-pipe
• 3-pipe
• 4 pipe
• Other
• Existing methods of laying heating mains
• Aboveground
• Underground
• The main elements of the heating network
• Design
• Rules for choosing a designer
• Design stages
• Drawing up a design contract

Are you faced with the question of connecting to district heating networks? This article is for you: what types of heating networks are, what this communication consists of, which organizations and why are most suitable for project development and what can sometimes be saved on, read right now.

Briefly about heating networks

Many people imagine what a heating network is, but for a more accessible narration, a few common truths should be recalled.

Firstly, the heating system does not supply hot water directly to the batteries. The temperature of the coolant in the main pipeline on the coldest days can reach 150 degrees and its direct presence in the heating radiator is fraught with burns and is dangerous to human health.

Secondly, in most cases the coolant from the network should not enter the building’s hot water supply system. This is called a closed DHW system. To satisfy the needs of the bathroom and kitchen, drinking water (from the water supply) is used. It was decontaminated, and the coolant only provides heating to a certain temperature of 50-60 degrees by means of a contactless heat exchanger. The use of network water from heat pipelines in the hot water supply system is wasteful to say the least. A heat carrier is prepared at a heat supply source (boiler room, CHP) by chemical water treatment. Due to the fact that the temperature of this water is often higher than the boiling point, hardness salts that cause scale are necessarily removed from it. The formation of any deposits on the pipeline nodes can damage the equipment. The tap water is not heated to such an extent and, therefore, expensive demineralization does not pass. This circumstance influenced the fact that open hot water systems, with direct water intake, are practically not used anywhere..

Types of heating networks

Consider the types of laying heating networks by the number of pipelines laid alongside.

2-pipe

Such a network includes two lines: supply and return. Preparation of the final product (lowering the temperature of the heating medium for heating, heating of drinking water) takes place directly in the heat-supplied building.

3-pipe

This type of laying of heating networks is used quite rarely and only for buildings where interruptions in heat are not acceptable, for example, hospitals or kindergartens with a constant stay of children. In this case, a third line is added: the supply pipeline reserve. The unpopularity of this method of backup is its high cost and impracticality. The laying of an extra pipe is easily replaced by a permanently installed modular boiler room and the classic 3-pipe version is practically not found today.

4 pipe

The type of laying, when the consumer is supplied with both the coolant and hot water of the water supply system. This is possible if the building is connected to the distribution (intra-quarter) networks after the central heating point, in which drinking water is heated. The first two lines, as in the case of a 2-pipe laying, are the supply and return of the coolant, the third is the supply of hot drinking water, the fourth is its return. If we focus on diameters, then 1 and 2 pipes will be the same, the 3rd may differ from them (depending on the flow rate), and the 4th is always less than the 3rd.

Other

There are other types of laying in the operated networks, but they are no longer connected with functionality, but with design flaws or unforeseen additional development of the area. So, if the loads are incorrectly determined, the proposed diameter can be significantly underestimated and in the early stages of operation it becomes necessary to increase the throughput. In order not to rebuild the entire network, another pipeline of larger diameter is reported. In this case, the feed goes along one line, and the return goes along two lines, or vice versa..

When constructing a heating network to an ordinary building (not a hospital, etc.), either a 2-pipe or 4-pipe option is used. It only depends on which networks you were given the tie-in point on.

Existing methods of laying heating mains

Aboveground

The most profitable way in terms of operation. All defects are visible even to a non-specialist, no additional control systems are required. There is also a drawback: it can rarely be used outside the industrial zone – it spoils the architectural appearance of the city.

Underground

This type of gasket can be divided into three more types:

1. Duct (heating system fits into the tray).

Pros: protection from external influences (for example, from damage by an excavator bucket), safety (if pipes burst, the soil will not be washed out and its failures are excluded).

Cons: the cost of installation is quite high, with poor waterproofing, the channel is filled with ground or rain water, which negatively affects the durability of metal pipes.

2. Channelless (the pipeline is laid directly into the ground).

Pros: Relatively low cost, ease of installation.

Cons: if a pipeline ruptures, there is a danger of soil erosion, it is difficult to determine the location of the rupture.

3. In sleeves.

Used to neutralize vertical pipe loads. This is mainly necessary when crossing roads at an angle. It is a heating network pipeline laid inside a pipe of a larger diameter.

The choice of the laying method depends on the terrain through which the pipeline passes. The channelless option is optimal in terms of cost and labor costs, but it cannot be applied everywhere. If a section of the heating network is located under the road (does not cross it, but runs parallel under the carriageway), duct laying is used. For ease of use, the location of the network under the driveways should be used only in the absence of other options, since if a defect is found, it will be necessary to open the asphalt, stop or restrict movement along the street. There are places where a channel device is used to enhance security. This is mandatory when laying a network across hospitals, schools, kindergartens, etc..

The main elements of the heating network

The heating network, to which variety it does not belong, is essentially a set of elements assembled into a long pipeline. They are produced by the industry in finished form, and the construction of communication comes down to laying and connecting parts to each other..

The pipe is the basic building block in this constructor. Depending on the diameter, they are produced in lengths of 6 and 12 meters, but on order at the manufacturer’s plant, you can purchase any footage. It is recommended to adhere, oddly enough, to standard sizes – factory cutting will cost an order of magnitude more.

For the most part, steel pipes covered with a layer of insulation are used for heating systems. Non-metallic analogs are rarely used and only on networks with a very low temperature graph. This is possible after central heating points or when the source of heat supply is a low-power water-heating boiler house, and even then not always.

For the heating network, it is necessary to use exclusively new pipes; the reuse of used parts leads to a significant reduction in the service life. These savings in materials lead to significant costs for subsequent repairs and fairly early renovation. It is undesirable to use any type of pipe laying with a spiral welded seam for heating mains. Such a pipeline is very laborious to repair and reduces the speed of emergency elimination of ruptures..

90 degree elbow

In addition to ordinary straight pipes, the industry also produces shaped parts for them. Depending on the selected type of pipeline, they can vary in quantity and purpose. In all versions, bends (pipe turns at an angle of 90, 75, 60, 45, 30 and 15 degrees), tees (branches from the main pipe, a pipe of the same or smaller diameter welded into it) and transitions (changing the diameter of the pipeline) are required. The rest, for example, the end elements of the operational remote control system, are released as needed..

Branch from the main network

An equally important element in the construction of a heating main is shut-off valves. This device blocks the flow of the coolant, both to the consumer and from him. The absence of shut-off valves on the subscriber’s network is unacceptable, since in case of an accident on the site, not only one building will have to be turned off, but the entire neighboring area.

For the air laying of the pipeline, it is necessary to provide measures that exclude any possibility of unauthorized access to the control parts of the valves. In case of accidental or intentional closure or limitation of the throughput of the return pipeline, an unacceptable pressure will be created, the result of which will be not only a rupture of the heating network pipes, but also the heating elements of the building. Most dependent on battery pressure. Moreover, new design solutions for radiators are torn apart much earlier than their Soviet cast-iron counterparts. It is not difficult to imagine the consequences of a burst battery – rooms filled with boiling water require quite decent sums for repairs. To exclude the possibility of controlling the valves by unauthorized people, you can provide boxes with locks that close the controls with a key, or removable steering wheels.

In case of underground laying of pipelines to the valves, on the contrary, it is necessary to provide for the access of service personnel. For this, thermal chambers are being built. Descending into them, workers can perform the necessary manipulations.

With channelless laying of pre-insulated pipes, the fittings look different from their standard appearance. Instead of a steering wheel, the ball valve has a long stem, at the end of which a control element is located. Closing / opening occurs with a T-shaped key. It is supplied by the manufacturer, complete with the basic order for pipes and fittings. To organize access, this rod is placed in a concrete well and closed with a hatch.

Shut-off valves with gear

On pipelines of small diameter, you can save on reinforced concrete rings and hatches. Instead of reinforced concrete, the rods can be placed in metal rugs. They look like a pipe with a lid attached to the top, mounted on a small concrete pad and buried in the ground. Quite often, designers on small pipe diameters propose to place both reinforcement rods (supply and return pipelines) in one reinforced concrete well with a diameter of 1 to 1.5 meters. This solution looks good on paper, but in practice, such an arrangement often leads to the impossibility of valve control. This is due to the fact that both rods are not always located directly under the hatch, therefore, it is not possible to install the key vertically on the control element. Fittings for pipelines of medium and larger diameter are equipped with a gearbox or an electric drive, it will not work to place it in the carpet, in the first case it will be a reinforced concrete well, and in the second – an electrified thermal chamber.

Set carpet

The next element of the heating network is a compensator. In the simplest case, this is pipe laying in the form of the letter P or Z and any turn of the route. In more complex versions, lens, stuffing box and other compensating devices are used. The need to use these elements is caused by the susceptibility of metals to significant thermal expansion. In simple words, the pipe under the influence of high temperatures increases its length and in order to prevent it from bursting as a result of excessive load, at certain intervals special devices or angles of rotation of the route are provided – they remove the stress caused by the expansion of the metal.

U-shaped expansion joint

For the construction of subscriber networks, it is recommended to use only simple track turn angles as compensators. More complex devices, firstly, cost a lot, and secondly, they require annual maintenance..

For channelless laying of pipelines, in addition to the angle of rotation itself, a small space is also provided for its operation. This is achieved by placing expansion mats at the bend in the net. The absence of a soft section will lead to the fact that at the time of expansion, the pipe will be pinched in the ground and simply burst.

U-shaped expansion joint with laid mats

Drainage is also an important part of the thermal communication designer. This device is a branch from the main pipeline with fittings, which descends into a concrete well. If it is necessary to empty the heating system, the taps are opened and the coolant is discarded. This element of the heating main is installed at all lower points of the pipeline.

Drainage well

The discharged water is pumped out of the well using special equipment. If there is an opportunity and the appropriate permission has been obtained, then it is possible to connect the waste well to the networks of household or storm sewers. In this case, no special equipment is required for operation..

In small sections of networks, up to several tens of meters, it is allowed not to install drainage. During repairs, the excess coolant can be dumped by the old-fashioned method – to cut the pipe. However, with such an emptying, the water should significantly reduce its temperature due to the danger of burns to personnel and the timing of the completion of the repair is slightly delayed.

Another structural element, without which the normal functioning of the pipeline is impossible, is an air vent. It is a branch of the heating network, directed straight up, at the end of which there is a ball valve. This device serves to release the air from the pipeline. Without removing gas plugs, normal filling of pipes with a coolant is impossible. This element is installed at all upper points of the heating network. In no case should you refuse to use it – no other method of removing air from pipes has yet been invented.

Tees with air vent ball valve

When arranging an air vent, in addition to functional ideas, one should also be guided by the principles of personnel safety. There is a risk of burns when venting. The air outlet tube must be directed to the side or downward.

Design

The designer’s work when creating a heating network is not based on templates. Each time, new calculations are carried out, equipment is selected. The project cannot be reused. For these reasons, the cost of such work is always quite high. However, price should not be the main criterion when choosing a designer. The most expensive is not always the best, and vice versa. In some cases, the excessive cost is caused not by the laboriousness of the process, but by the desire to increase one’s worth. Experience in the development of such projects is also a significant plus in the selection of an organization. True, there are times when a company has gained a status and completely changed its specialists: it abandoned the experienced and expensive in favor of the young and ambitious. It would be nice to clarify this point even before the conclusion of the contract.

Rules for choosing a designer

1. Cost. It should be in the middle range. Extremes are not appropriate.
2. Experience. To determine the experience, the easiest way is to ask for the phones of customers for whom the organization has already carried out similar projects and not be too lazy to call several numbers. If everything was “at the level”, then you will receive the necessary recommendations, if “not very” or “more or less” – you can safely continue your search further.
3. Experienced staff.
4. Specialization. You should avoid organizations that, despite the small staff of employees, are ready to make a house with a pipe and a path to it. The lack of specialists leads to the fact that the same person can develop several sections at once, if not all. The quality of such work leaves much to be desired. The best option would be a narrowly focused organization with a bias in communications or energy construction. Large civil engineering institutions are also not a bad option..
5. Stability. One-day firms should be avoided, no matter how tempting their offer may be. It is good if there is an opportunity to contact the institutes that were created on the basis of the old Soviet research institutes. Usually they support the brand, and the employees in these places often work all their lives and have already “eaten the dog” on such projects.

The design process begins long before the designer picks up a pencil (in the modern version, before he sat down in front of the computer). This work consists of several sequential processes.

Design stages

1. Collection of raw data.

This part of the work can be entrusted either to the designer or to be performed independently by the customer. It is not expensive, but it takes some time to visit a certain number of organizations, write letters, applications and receive answers to them. You should not be engaged in the collection of initial data for the design on your own only if you cannot explain what exactly you want to do.

2. Engineering survey.

The stage is quite difficult and cannot be done on your own. Some design organizations do this work themselves, some give it to subcontractors. If the designer works according to the second option, it makes sense to choose a subcontractor yourself. So the cost can be slightly reduced.

3. The design process itself.

Performed by the designer, controlled by the customer at any stage.

4. Project approval.

The developed documentation must be checked by the customer. After that, the designer coordinates it with third-party organizations. Sometimes, to speed up the process, it is enough to participate in this process. If the customer travels together with the developer as agreed, firstly there is no way to delay the project, and secondly, there is a chance to see all the shortcomings with your own eyes. If there are any controversial issues, it will be possible to control them even at the construction stage..

Many organizations that develop project documentation offer alternative options for its type. Gaining popularity 3D-design, color design of drawings. All of these decorating elements are purely commercial in nature: they add to the design cost and do not in any way raise the quality of the project itself. Builders will perform the work in the same way for any type of design and estimate documentation.

Drawing up a design contract

In addition to what has already been said, it is necessary to add a few words about the design contract itself. A lot depends on the points written in it. It is not always necessary to blindly agree to the form proposed by the designer. Quite often, only the interests of the project developer are taken into account there.

The design contract must contain:

• full names of the parties
• cost
• period of execution
• subject of a contract

These points should be clearly spelled out. If the date is at least a month and a year, and not after a certain number of days or months from the beginning of the design or from the beginning of the contract. Specifying such a wording will put you in an awkward position if you suddenly have to prove something in court. You should also pay special attention to the name of the subject of the contract. It should not sound like a project and a point, but as “the implementation of design work on the heat supply of such and such a building” or “design of a heat network from a certain place to a certain place”.

It is useful to prescribe some points of fines in the contract. For example, a delay in the design period entails the payment by the designer of 0.5% of the contract amount in favor of the customer. It is useful to write down the number of project copies in the contract. The optimal amount is 5 pieces. 1 for yourself, 1 more for technical supervision and 3 for builders.

Full payment for work should be made only after 100% readiness and signing of the acceptance certificate (certificate of completion). When drawing up this document, it is imperative to check the name of the project, it must be identical to that specified in the contract. If the records do not match even by one comma or letter, you run the risk of not proving payment specifically under this agreement in the event of a dispute.

The next part of the article is devoted to construction issues. She will shed light on such moments as: the specifics of the selection of a contractor and the conclusion of a contract for the performance of construction work, give an example of the correct installation sequence and tell you what to do when the pipeline is already laid in order to avoid negative consequences during operation.