Calculation of heat transfer from heating batteries. How a room is heated by a central heating radiator How the heat from a radiator spreads throughout the room

The issue of choosing a suitable radiator for heating a house or apartment plays an important role. After all, safety, the possibility of saving on energy resources, compliance with interior design, warmth, and therefore a feeling of comfort in the home depend on this. To answer the question for central heating, you first need to establish the technical characteristics and operating features of each type of modern battery.

Choosing a heating radiator must take into account many factors.

When purchasing a radiator, the following aspects are important:

• Operational efficiency, that is, the ability to heat the room.
• Safety and durability.
• Availability in terms of price.

Also, the choice of heating radiators is largely determined by the system in which they will be installed - central or autonomous.

The centralized system used in apartment buildings has the following features:

1. Typically, the operating pressure in this system at supply is around 4-5 kgf/cm 2 and slightly less at the outlet. In private homes, the maximum pressure is only 2 kgf/cm2.
2. In central systems there is a much higher probability of unforeseen circumstances associated with water hammer, the use of coolants with a temperature higher than permissible, etc.

The choice of radiator is also directly influenced by the technical characteristics of the heating system, which are determined by:

• The magnitude of the working pressure.
  The basic rule: the pressure of heating batteries is greater than in the room in which they are installed. Otherwise, a leak will soon appear. The choice of radiator is also directly influenced by the technical characteristics of the heating system, which are determined by:
• The type of heating system is one- or two-pipe.
• Radiator power. The most important quantity that indicates the efficiency of heat transfer from the source to the consumer, that is, how well the radiator heats the house. The power indicator is influenced by the presence of windows and the material from which they are made (wood or plastic), the type of house (panel or brick), the number of external walls, and the area of ​​the room. The required value is determined by multiplying the room area by 100 W and increases by a certain percentage depending on various factors:
  • if there are 2 external walls and 2 windows - by 30%;
  • when windows face north - by 10%.

• Radiator sizes. The dimensions of the device must correspond to the location intended for installation. The optimal distance between the window and the radiator is 10 cm or more, the floor and the radiator is 6 cm. The width of the radiator must exceed 50% of the width of the window under which it is installed.

The main types of radiators have the following characteristics:

Also, do not forget about such nuances as the presence of a thermostat, pipe diameter, window width.

Main types of radiators for central heating, their disadvantages and advantages

Cast iron radiators. The leading type of radiator in terms of popularity for several decades. Only the appearance has changed significantly - there are models that are real designer samples (their cost is appropriate). Good for use in residential and industrial multi-storey buildings.

Advantages:

• high heat transfer;
• strength and durability;
• unpretentiousness and endurance;
• large flow area, allowing you to maintain throughput even with the accumulation of deposits.

Flaws:

• the need for washing 2-3 times a year;
• vulnerability to strong mechanical stress (the battery may crack);
• high price.

Aluminum radiators. Currently very popular among Russians. They consist of sections, the number of which depends on the area of ​​the heated room. It is this type that is characterized by the highest degree of heating, achieved due to the high thermal conductivity of the metal itself and an increase in the thermal conductivity area, thanks to the developed finning system. Based on their design, there are sectional and solid models.

For centralized heating systems, aluminum radiators are not recommended for use. Because in the presence of oxygen in the coolant, this metal oxidizes, and “airing” of the sections occurs due to the release of hydrogen. To avoid this, the device requires regular maintenance and air pumping.

Advantages:

• ease;
• external attractiveness;
• strength and reliability;
• excellent heat dissipation.

Flaws:

• susceptibility to corrosion;
• the need to regularly bleed air from the radiator through the vent valve;
• deformation of aluminum during water hammer;
• solid particles present in coolants contribute to the destruction of the walls of the device from the inside, which reduces the service life of the device (this problem can be solved by equipping the radiator with mud traps and additional filters that require regular cleaning);
• when connecting aluminum pipes to copper pipes, the aluminum quickly deteriorates.

Steel radiators. A common type in low-rise private construction. Not the best option for centralized heating because:

• usually the operating pressure in the heating system exceeds the permissible limit;
• With water hammer, the service life is significantly reduced and amounts to only a few months.

Advantages:

• attractive design;
• occupying a small space indoors.

Flaws:

• susceptibility to corrosion;
• The average service life, subject to operating rules, is no more than 7 years.

Bimetallic radiators. They combine the advantages of the two previous types of radiators due to a special design - an aluminum shell and a steel core. They are used for any type of heating, but have proven themselves especially well in high-rise buildings with central heating.

Advantages:

• ability to withstand significant loads and hydraulic shocks, strength;
• high heat transfer;
• light weight and well-thought-out shape, contributing to efficient heating of the room.

Flaws:

• high price due to the complexity of the design.

conclusions

So, it is not possible to give an unambiguous answer to the question of which heating radiators are better for central heating, since each specific situation is individual and the choice depends on the characteristics of living conditions and the price range. But in general, expert opinions boil down to the following:

1. Due to the unpredictability of central heating, those that combine mechanical strength, high heat transfer and aesthetic appearance are considered the best today. The main disadvantage is the high cost.
2. Cast iron radiators also deserve attention, but require more care.
3. It is better to avoid steel and aluminum radiators in houses with central heating, due to the characteristics of these metals - susceptibility to corrosion, interaction with other metals, etc.

", where we briefly touched on the topic of organizing heating in the house. Today, in the article " Heating the house - for residents!"Let's expand and deepen the topic.

Heating the house - for residents! What is meant? And the fact is that when you are planning to install a new heating system (or replace an old one), it is best to focus on what you need. In order to avoid being the proud owner of an inefficient heating system, you need to take into account that when choosing for yourself, you need to take into account a number of its characteristics:

1. Heating at home should be more reliable in terms of operation and, as a consequence, more durable in terms of service life. Durability is very important, since the heating system is a complex branched network of pipes integrated into the body of the building and is its integral and integral part. In relation to the heating system, reliability lies in its failure-free operation in the sense of reducing the likelihood of breakdowns and leaks, and high maintainability. Repairing a heating system is a very painful procedure, and a complete replacement of pipes is equivalent to a fire in terms of disaster.
2. The heating system must have stable hydraulic characteristics and thermal stability (the ability to control and predictability of coolant flows in pipes). That is, so that warm water does not suddenly “stagnate” where it is not needed and does not reach where it is needed.
3. She must be more heat capacity and, as a consequence of this, more thermally inertial. That is, you need to have as large a supply of hot coolant (energy) as possible so that in the event of an accident or failure in the heating system, the house remains warm for as long as possible. This is especially true for a brick house.
4. The system must have low hydraulic resistance. The lower it is, the better the system. To do this, the coolant path should be as free as possible from obstacles, such as bends, narrowings, corners, changes in flow direction. There should be fewer different kinds of devices on the way that create obstacles - valves, regulators, and so on. IN ideal In this case, the hydraulic resistance can be so low that the coolant (water) circulates in the heating system itself under the influence of the laws of physics, according to which warmer masses rise upward and colder masses sink down, replacing them. This is exactly how natural circulation heating systems work.
5. It's best for the system to be electrically independent- in order to ensure the viability of the house. This is true when people are not careless and, in addition to a gas or solar boiler, install a solid fuel boiler and have a supply of firewood for the winter. By the way, the Russian word carefree just speaks of people who are so carefree that they don’t even have a stove.
6. The system should, if possible, produce higher quality heat.

What is "higher quality heat"? How can heat even have a quality? Well, here's the thing. Heat is nothing more than the speed of molecular movement. The faster the molecules move, the hotter the body is. The colder the body, the slower the molecules move. Accordingly, absolute zero is when not a single molecule moves.

Accordingly, there are several ways to transfer heat, that is, to accelerate the movement of molecules.

1. The first way is thermal conductivity. Characteristic primarily for solids. In a heat source, molecules move quickly; they come into contact with a less rapidly moving layer and begin to “sausage” it—that is, to heat it up. Accordingly, the heated next layer is in direct contact with the third layer, accelerating the movements of molecules already in it - and so on.
2. The second way is convection. Characteristic for liquids and gases. Principle: a heat source heats (that is, accelerates the movement of molecules) a portion of liquid (gas), it changes its properties, becomes lighter and “floats” up. In its place comes unheated cold air (or water), where the molecules move more slowly, and so on, resulting in a circulation of warm and cold masses.
3. The third method of heat transfer is thermal radiation. In this case, the heated body emits electromagnetic waves in the infrared range. These electromagnetic waves “fly” to surrounding objects, and remotely, without direct contact with a heat source, cause the molecules of these objects to move faster. Accordingly, objects surrounding the source heat up. Examples: fire, stove.

It is assumed that the usual heat most often encountered in the case of a heating system - convection - is of low quality. That is, the battery (or heat fan) heats the air, and the air already warms the person. Why is heating the air bad? The fact is that when the air is heated, and the surrounding objects - walls, ceiling, floor, furniture, etc. cold, then in such a room it's uncomfortable to be there. There is a feeling of “non-residential premises”, temporary housing and no space.

Naturally, over time, the air temperature rises so much that the walls, ceiling, floor and furniture heat up, and they begin to radiate heat on their own. And if the air suddenly cools, then the room will have a normal temperature for some time due to the fact that the walls cool down and share their heat. In this case, heat is transferred primarily not by convection, through heated air, but by thermal radiation.

Why is radial heat transfer a better option than convection?

Because a warm person in a room with heated air but cold walls plays a role energy donor- it constantly warms them with its infrared (radiant) heat, just as a fire warms people sitting around it. After all, a person has a body temperature of 36 degrees Celsius, and the stone walls of, for example, an ordinary panel house heat up at best to a temperature of 20 degrees, when the air temperature in the room is 24 degrees Celsius.

Accordingly, the pattern becomes interesting: in order to compensate for the constant loss of infrared (radial) heat, a person is forced to eat more, eat more high-calorie (fatty) foods, drink stronger alcoholic drinks, and have a larger fat layer.

Thus, if we generalize, we can say that

• Heat has a higher quality when it is transmitted radiantly, by emitting infrared waves,
• whereas heat transfer through the diffusion of warm air, convection, is a lower quality type.

Naturally, there is no comrade to taste and color - however personal observations in this area will allow you make your own judgment for high or low heat quality. We are moving on.

Let's compare modern plate radiators and ancient cast iron radiators from the point of view of convection and infrared radiation. Which of them predominantly use which method of heat transfer?

Modern plate radiators are essentially convectors. They give off more than 70% of their heat by convection, have a minimum volume of coolant, are light and elegant. We will supply you with thin pipes, small, compact, but warm (red-hot) elegant convectors. To make it all work, we will install a powerful pump (pumps) and pump these several canisters of coolant - sooner, or later, or never... Having saved on materials - radiators and pipe cross-section once, the owner of such “wealth” dooms himself to constant torment.

On the other hand, cast iron radiators transmit heat primarily in the form of radiation. A cast iron radiator is reliable, durable and unpretentious, has low hydraulic resistance and therefore behaves well in any heating systems, including those with natural coolant circulation. In addition, a cast iron radiator is thermally inertial - it has a large volume of coolant, and thick walls make it more of a radiant device than a convection one.

That is, the transfer of heat when heating a house in the form of thermal radiation is real.

Let's take into account a few more nuances. Yes, according to the laws of physics It is correct to paint radiators not white, but black. The blacker the device, the more heat it emits (and absorbs). It’s not for nothing that artists divide colors into warm and cold; people feel this property of color intuitively. In hot countries they wear white clothes, prefer white cars and whitewash their houses to reduce heat. When repainting it matte black, the radiant heat transfer of a white radiator increases by about 20%. Here is an example of a black battery in the interior:

Another interesting detail. Radiators (both convection and cast iron) are made ribbed to increase the area of ​​heat transfer. That is, if we take it in theory, the more fins, the better, the more thermal radiation is transmitted from the radiator. In practice, this does not happen because the ribs “look” at each other and irradiate each other, rather than the occupants, with thermal radiation. You can increase the radiation from radiators if you install not 10 sections in a row, but the same number - but at some distance from each other. Better yet, separate them from each other and from the wall with foil. The foil reflects thermal radiation and transfers it to a greater extent not to the radiator, but to the inhabitants of the house.

Another interesting way to increase the radiant efficiency of radiators is to insulate them “at the back” and cover them with bricks at the front. Radiators will heat the brick, will not give off heat to the outside due to insulation, and the already heated brick will give off radiant heat to the people in the room. In fact, this solution has been known for quite a long time, and was used primarily in kindergartens - at the same time it protected children from hot radiators.

It is important to consider that heating a house due to thermal radiation is really only relevant when the house is really WELL insulated, otherwise the heat loss will be much greater than if the convection method is used for heating. It is also important that the sources of radiant heat should primarily be the floor and ceiling, while the walls (to reduce heat loss) should be heated minimally so as not to cause discomfort (up to about 22-24 degrees Celsius).

Conclusion: home heating should be created for the residents, and it is better to use thermal radiation for heating primarily.

Based on materials from http://zhiva-hata.rf/info/page/239

Heating the house - for residents!

The funny thing about radiators is that they aren't really radiators at all. The fact is that the term “radiator” is a little inappropriate for a device that heats a room. The word radiator comes from the English word “radiate”, which translates as to radiate. But radiators don't actually emit heat; they heat the room through convection.

So what is it then?

Regardless of the material of the radiators and their design, the vast majority of radiators radiate about 80% of the heat produced by convection, leaving only 20% for thermal radiation. Don't worry, there's nothing wrong with this ratio. Some experts mistakenly believe that this ratio is 50/50.

Radiators were invented by Russian businessman San Galli, although some people still dispute his invention.

He called them "hot boxes", which is a fairly accurate description of the radiator. A warm box that moves air around itself and raises the temperature in the room.

In the USA they are called heaters. It is worth noting that Americans use a more precise term derived from the word “heaters”. After all, this is exactly what radiators do - they heat and release heat.

A scientist will refer to heat as thermal energy that can move through space by conduction, convection, or radiation. Your home installed on the wall under the window heats the cold air above it, and with the help of the slightest drafts from the window, convection currents move heat around the room.

How does a heating radiator heat a room?

Convection currents are created when the air above the radiator is heated, then cooled, and then heated again. This process occurs continuously as long as you have the heating on. In this way, radiators move heat around the room, making the house warm and cozy. To put it scientifically, heat is created by converting potential energy into kinetic energy.

When a radiator heats the air, it causes the atoms to vibrate at a high frequency. The atoms continue to vibrate faster and faster, resulting in the creation of thermal energy. This process is known as convection.

No matter how Strangely, the term “radiator” suits floor heating much better. Because this system actually radiates heat throughout the entire room. More than half of the heat created is produced through radiation.

Get the most out of your radiator

Given that the radiator works to create those wonderful convection currents while you're watching football, it's worth making sure the heat stays inside the house. This will save energy, money and heat. Thermal energy, like Houdini, loves to disappear unnoticed.

It can escape through the roof, windows, walls and any small gap invisible to the human eye. Are your poor (or hot boxes ☺) working so hard and you're letting the heat escape your home? Do not do that!

Install attic insulation, insulate wall cavities and make sure windows are in good condition. This will keep the atoms indoors and prevent them from escaping outside, taking with them precious degrees of heat.

How a heating radiator heats a room was last modified: April 10th, 2017 by Jennifer Thompson

When the room is cold when the central heating radiators are running, many people turn on additional heating devices, but rarely does anyone think about how to increase heat transfer from central heating radiators. If turning on heaters is a temporary and very expensive measure, then increasing the efficiency of batteries is a long-term solution to the problem of a cold room, which often does not require the investment of additional funds. This article will provide simple and complex ways to effectively increase the heat transfer of batteries.

What affects the efficiency of central heating radiators?

1. Coolant temperature in the system;
2. Coolant movement speed;
3. Type of connection to the heating system;
4. The material from which the radiator is made;
5. Heat transfer area and number of radiator sections.

Other factors that appear during the operation of radiators also play an important role. For example, the heat dissipation of batteries will decrease if:

• Apply many layers of paint;
• Do not wipe off dust;
• Do not periodically bleed air from radiators;
• The internal cavity, filters and pipes are clogged;
• The radiator is covered with a decorative screen, curtains, furniture, etc.

In general, impaired air convection (last point) is one of the main conditions for poor heat transfer of central heating radiators. All efforts must first be directed towards eliminating this problem.

Simple ways to increase heat transfer from radiators

. The batteries transfer heat to the air, which, when heated, rises, and then, when cooled, falls down. This is how air circulates, and the room becomes as warm as the heat transfer of the battery and the air flow speed allow. Therefore, in order to increase the temperature inside the room, first of all, you need to ensure good air circulation. To do this, you should free up the space around the battery as much as possible: remove the protective screen, raise the curtains, move the furniture, and so on.

Speed ​​up air circulation with a fan. The faster the air moves, the more thermal energy it can take from the battery. On the coldest days, you can turn on the fan, directing it to the center of the radiator to cover as much area as possible. To ensure the autonomy of such a system and ensure its quiet operation, computer fans can be placed. They are quiet, low-power, and when placed directly under the battery, they do not disrupt the natural direction of air movement in the room. The fans will allow you to raise the temperature in the room by 3-10 degrees, and their low consumption makes it possible to blow on the battery all winter long without significantly damaging your wallet. Calculate for yourself: the power of ordinary fans is about 40 Watts, computer fans – no more than 5. Total consumption: 40 * 24 (hours) * 30 (days) = 29 Kilowatts = about 95 rubles per month. In the case of computers, it’s even less – about 23 rubles/month. when connecting 2 at once.

Installing a heat-reflecting screen. Heat from the radiator emanates in all directions, and in order not to heat the walls, but to direct thermal energy into the room, you need to install a heat-reflecting screen behind the radiator. For these purposes, you can use foil-isolon (foam base with foil on one side), gluing it to the cleaned wall behind the battery with any suitable means (tile adhesive, universal glue 88, silicone, etc.). Ideally, the area of ​​the heat-reflecting screen should be larger than the area of ​​the battery.

If the battery at the top is cold you need to bleed the air. To do this, you need to unscrew the regular or “Mayevsky” tap at the top of the battery.

It will not be superfluous to keep a container or towel under the valve, because as soon as the air comes out, water will flow in a thin stream. Once this happens, the valve can be closed. The procedure should be repeated for each battery in the house.

Complex ways to increase heat transfer from radiators

If the previous methods did not help, or their use causes significant discomfort, you can solve the problem in one of the drastic ways:

• Replace heating radiators (a table of thermal conductivity and thermal power of radiators will be given below);
• Increase the number of battery sections (more battery area - warmer room);
• Clean the internal cavity of the radiator from dirt, corrosion, and scale;
• Change the type of connection (optimal - straight diagonal or straight one-sided);

All this work must be carried out with the heating system turned off, which in most cases is difficult during the heating season. However, the situation will be significantly simplified if shut-off valves are installed at the inlet and outlet, allowing each radiator to be disconnected from the heat supply network individually.

Table No. 1: Thermal conductivity coefficient of metals

Table No. 2: Thermal power of radiators

The best option is bimetallic radiators, which are not demanding on the quality of water in the heating system and at the same time have high thermal power. This was achieved through a combination of steel (inside) and aluminum (outside), as well as thanks to modern technologies, which made it possible to achieve a large heat transfer area with relatively oversized sections.

By using central heating resources wisely, you can forever save yourself from the need to connect additional heating devices. And, knowing ways to increase the heat transfer of batteries, you can regulate the temperature in the room at your discretion.

The purpose of heating radiators is to transfer heat from their surface, heated from the inside by a hot coolant. It would simply be uneconomical to waste paid kilocalories on heating a cold wall located behind the radiator, or to install a decorative screen-casing that does not allow warm air from the radiator to pass through.

Thermal insulation of heating radiators provides:

• shielding the wall to preserve heat transferred by radiation from the surface of the radiator,
• reliable protection from possible burns and bruises on the hot surface of the radiator, but not interfering with the movement of thermal convective flows to heat the home.

Heat shield on the wall behind the radiator

A hot battery transfers part of the heat from its surface by thermal radiation, which is directed in all directions. Naturally, a considerable share of it “falls over” to the internal cold wall, which is direct heat loss. If the battery is placed in a niche, then a thinner wall contributes to an increase in heat losses, especially in frosty weather. The radiator will heat the street, but not the home. Heat leakage reaches 20%.

To avoid such a situation, it is advisable to place a heat-insulating material with a reflective surface between the heating radiator and the wall, which will provide:

• thermal insulation of the wall to prevent heat transfer due to the difference in temperatures outside and inside the home;
• reflection of the heat emitted by the radiator into the room.

Currently, many modifications of foil insulating screens are being produced. All of them are a combination of a material with good thermal insulating properties, such as polystyrene foam or polyethylene foam, and foil as a means of shielding radiant energy. The foil is capable of reflecting up to 90% of the heat in the emitted range; further heat loss is prevented by thermal insulation.

Polystyrene foam with foil is produced in small rolls, layer thickness 3 mm. The most common reflective insulator is polyethylene foam produced in long rolls with a layer thickness of 4 mm. Its thermal insulation properties make it possible to replace a layer of mineral wool up to 100 mm thick.

The distance between the edge of the radiator section and the plane of the inner wall must be at least 4 mm. At a shorter distance, air circulation around the battery is difficult, which disrupts convective heat transfer and, accordingly, reduces heating efficiency. The material is attached to the wall with a heat-insulating layer. In some cases, the location of the battery does not allow the installation of a heat insulator, then it is enough to try to attach at least aluminum foil to the inner wall. Its shiny surface does an excellent job of reflecting incident thermal radiation. For a brick wall with a standard thickness of 51 cm, a sheet of foil will reduce heat loss by up to 35%.

Screens for radiators

As strange as it may sound to most current consumers of central heating, initially cast iron radiators were covered with decorative casings in order to protect (mainly children and the elderly) from bruises and burns on the surface of the heating sections of the radiator heated to a high temperature. There was enough heat for everyone; central heating coped with heating the few apartments equipped with heating appliances. At the same time, incorrectly made blind protective boxes - screens did not allow the lion's share of the heat from the hot radiator to pass through. But many years of practice have taught us how to even intensify convective air flows to heat a home using screens.

To ensure that the screen does not interfere with the spread of radiant energy from the radiator through its surface, it is recommended to cover no more than 50% of the area of ​​the front design of the screen or casing. This is achieved by perforation or a patterned decorative design. The best heat transfer for the room will be provided by metal screens, the design of which is so simple that it does not require professional skills for installation. They are either hung on the battery or attached to the wall in the simplest ways.

Experts have developed recommendations for the most favorable placement of heating radiators and screens for them. According to the established rules, the optimal height from the bottom edge of the radiator section to the floor is 10 cm. Therefore, the screen should not be installed close to the floor, but also raised above the floor to the same height of 10 cm, so as not to interfere with the upward movement of heated air.

It is important! If the radiator is placed under a window, it is recommended to make holes in the window sill to intensify the air flow.

The efficiency of using screens depending on the location of the battery and screen is shown in the figure.