Contents
In the last few years, a closed heating system has become increasingly popular. Heating equipment is becoming more and more expensive, and you want it to last longer. In systems of a closed type, the possibility of free oxygen getting inside is practically excluded, which prolongs the life of the equipment.
Closed heating system – what is it
As you know, in any heating system of a private house there is an expansion tank. This is a container in which some coolant is removed. This tank is necessary to compensate for thermal expansion in various operating modes. By design, expansion tanks are open and closed, respectively, and heating systems are called open and closed.
In recent years, it is the closed heating circuit that has become increasingly popular. Firstly, it is automated and works without human intervention for a long time. Secondly, any type of coolant can be used in it, including antifreeze (it evaporates from open tanks). Thirdly, the pressure is maintained constant, which allows you to use any household appliances in a private house. There are a few more advantages that relate to wiring and operation:
- There is no direct contact of the coolant with air, therefore, there is no (or almost no) free oxygen, which is a powerful oxidizing agent. This means that the heating elements will not oxidize, which will increase their service life.
- An expansion tank of a closed type is placed anywhere, usually not far from the boiler (wall-mounted gas boilers come immediately with expansion tanks). An open tank should be in the attic, and these are additional pipes, as well as insulation measures so that heat does not “leak” through the roof.
- In a closed system, there are automatic air vents, so there is no airing.
In general, a closed heating system is considered more convenient. Its main drawback is energy dependence. The movement of the coolant is provided by a circulation pump (forced circulation), and it does not work without electricity. Natural circulation in closed systems can be organized, but it is difficult – flow control is required using the thickness of the pipes. This is a rather complicated calculation, because it is often believed that a closed heating system only works with a pump.
To reduce energy dependence and increase the reliability of heating, they install uninterruptible power supplies with batteries and / or small generators that will provide emergency power.
Components and their purpose
In general, a closed heating system consists of a certain set of elements:
- Boiler with safety group. There are two options here. The first is that a safety group is built into the boiler (gas wall-mounted boilers, pellet boilers and some solid fuel gas generators). The second – there is no safety group in the boiler, then it is installed at the outlet in the supply pipeline.
- Pipes, radiators, water floor heating, convectors.
- Circulation pump. Provides the movement of the coolant. It is installed mainly on the return pipeline (here the temperature is lower and there is less possibility of overheating).
- Expansion tank. Compensates for changes in the volume of the coolant, maintaining a stable pressure.
Now more about each element.
Boiler – which one to choose
Since the closed heating system of a private house can work offline, it makes sense to install a heating boiler with automation. In this case, after setting the parameters, you do not need to return to this. All modes are supported without human intervention.
The most convenient gas boilers in this regard. They have the ability to connect a room thermostat. The temperature set on it is maintained with an accuracy of one degree. She fell by a degree, the boiler turned on, heating the house. As soon as the thermostat has tripped (temperature reached), the operation stops. Comfortable, convenient and economical.
In some models, it is possible to connect weather-dependent automation – these are external sensors. According to their testimony, the boiler adjusts the power of the burners. Gas boilers in closed heating systems are good equipment that can provide comfort. The only pity is that gas is not everywhere.
Electric boilers can give a no lesser degree of automation. In addition to traditional units on heating elements, induction and electrode ones appeared not so long ago. They are compact in size and low inertia. Many believe that they are more economical than boilers on heating elements. But even this kind of heating units can not be used everywhere, since power outages in winter are a frequent occurrence in many regions of our country. And to provide electricity to the boiler power. 8-12 kW from the generator is a very difficult task.
Boilers for solid or liquid fuel are more versatile and independent in this regard. An important point: to install a liquid fuel boiler, a separate room is required – this is a requirement of the fire department. Solid fuel boilers can stand in the house, but this is inconvenient, since a lot of debris falls from the fuel during combustion.
Modern solid fuel boilers, although they remain intermittent equipment (they warm up during combustion, cool down when the bookmark burns out), they also have automation that allows you to maintain the set temperature in the system by adjusting the intensity of combustion. Although the degree of automation is not as high as that of gas or electric boilers, it is.
Boilers on pellets are not very common in our camp. In fact, this is also solid fuel, but boilers of this type operate continuously. Pellets are automatically fed into the firebox (until the stock in the burker is finished). With good fuel quality, ash cleaning is required once every few weeks, and all operating parameters are controlled by automation. Only its high price hinders the distribution of this equipment: the manufacturers are mainly European, and their prices are corresponding.
A little about the calculation of boiler power for closed-type heating systems. It is determined according to the general principle: per 10 sq. meters of area with normal insulation take 1 kW of boiler power. Only take “back to back” is not advised. Firstly, there are abnormally cold periods during which you may not have enough rated power. Secondly, work at the power limit leads to rapid wear of the equipment. Therefore, it is desirable to take the boiler power for the system with a margin of 30-50%.
Security group
A safety group is placed on the supply pipeline at the outlet of the boiler. It should control its operation and system parameters. It consists of a pressure gauge, an automatic air vent and a safety valve.
The manometer makes it possible to control the pressure in the system. According to the recommendations, it should be in the range of 1,5-3 Bar (in one-story houses it is 1,5-2 Bar, in two-story houses – up to 3 Bar). In case of deviation from these parameters, appropriate measures must be taken. If the pressure has dropped below normal, it is necessary to check if there are any leaks, and then add a certain amount of coolant to the system. At elevated pressure, everything is somewhat more complicated: it is necessary to check in what mode the boiler is operating, whether it has overheated the coolant. The operation of the circulation pump, the correct operation of the pressure gauge and the safety valve are also checked. It is he who should dump the excess coolant when the threshold pressure value is exceeded. A pipe / hose is connected to the free branch pipe of the safety valve, which is led into the sewer or drainage system. Here it is better to do it in such a way that it is possible to control whether the valve works – with frequent discharge of water, it is necessary to look for the causes and eliminate them.
The third element of the group is an automatic air vent. Through it, the air that has entered the system is removed. A very convenient device that allows you to get rid of the problem of air jams in the system.
Security groups are sold assembled (pictured above), or you can buy all the devices separately and connect them using the same pipes that were used to wire the system.
Expansion tank for closed heating system
The expansion tank for is designed to compensate for changes in the volume of the coolant depending on temperature. In closed heating systems, this is a sealed container, divided by an elastic membrane into two parts. In the upper part there is air or an inert gas (in expensive models). While the coolant temperature is low, the tank remains empty, the membrane is straightened (picture on the right in the figure).
When heated, the coolant increases in volume, its excess rises into the tank, pushing the membrane and compressing the gas pumped into the upper part (in the picture on the left). On the pressure gauge, this is displayed as an increase in pressure and can serve as a signal to reduce the intensity of combustion. Some models have a relief valve that releases excess air/gas when a pressure threshold is reached.
As the coolant cools, the pressure in the upper part of the tank squeezes the coolant out of the tank into the system, the pressure gauge returns to normal. That’s the whole principle of operation of the expansion tank of the membrane type. By the way, there are two types of membranes – dish-shaped and pear-shaped. The shape of the membrane does not affect the principle of operation.
Volume calculation
According to generally accepted standards, the volume of the expansion tank should be 10% of the total volume of the coolant. This means that you must calculate how much water will fit in the pipes and radiators of your system (it is in the technical data of the radiators, but the volume of pipes can be calculated). 1/10 of this figure will be the volume of the required expansion tank. But this figure is valid only if the coolant is water. If an antifreeze liquid is used, the tank size is increased by 50% of the calculated volume.
Here is an example of calculating the volume of a membrane tank for a closed heating system:
- the volume of the heating system is 28 liters;
- expansion tank size for a system filled with water 2,8 liters;
- the size of the membrane tank for a system with antifreeze liquid is 2,8 + 0,5 * 2,8 = 4,2 liters.
When buying, choose the nearest larger volume. Do not take less – it is better to have a small supply.
What to look for when buying
The stores have red and blue tanks. Red tanks are suitable for heating. Blue ones are structurally the same, only they are designed for cold water and do not tolerate high temperatures.
What else to pay attention to? There are two types of tanks – with a replaceable membrane (they are also called flanged) and with an irreplaceable one. The second option is cheaper, and significantly, but if the membrane is damaged, you will have to buy the whole thing. In flanged models, only the membrane is bought.
Place for installation of expansion tank of membrane type
Usually they put an expansion tank on the return pipe in front of the circulation pump (when viewed in the direction of the coolant). A tee is installed in the pipeline, a small piece of pipe is connected to one of its parts, and an expander is connected to it through the fittings. It is better to place it at some distance from the pump so that pressure drops are not created. An important point is that the piping section of the membrane tank must be straight.
After the tee put a ball valve. It is necessary to be able to remove the tank without draining the heat carrier. It is more convenient to connect the container itself with the help of an American (flare nut). This again facilitates assembly/dismantling.
Please note that some boilers have an expansion tank. If its volume is sufficient, the installation of a second one is not required.
Empty device weighs not so much, but filled with water has a solid mass. Therefore, it is necessary to provide a method of fixing on the wall or additional supports.
Circulation pump
The circulation pump ensures the operability of a closed heating system. Its power depends on many factors: the material and diameter of the pipes, the number and type of radiators, the presence of shut-off and thermostatic valves, the length of the pipes, the operating mode of the equipment, etc. In order not to go into the intricacies of calculating power, the circulation pump can be selected from the table. Choose the nearest higher value according to the heated area or the planned thermal power of the system, in the corresponding line in the first columns find the required characteristics.
In the second column we find the power (how much coolant it is able to pump per hour), in the third – the pressure (system resistance) that it is able to overcome.
When choosing a circulation pump in a store, it is advisable not to save. The entire system depends on its performance. Therefore, it is better not to save and choose a trusted manufacturer. If you decide to buy unknown equipment, you need to somehow check it for noise levels. This indicator is especially critical if the heating unit is installed in a residential area.
Strapping scheme
As mentioned earlier, circulation pumps are installed mainly on the return pipeline. Previously, this requirement was mandatory, today it is only a wish. The materials that are used in the production can withstand temperatures up to 90 ° C, but it’s still better not to risk it.
In systems that can also operate with natural circulation, it is necessary to provide during installation the possibility to remove or replace the pump without the need to drain the coolant, as well as to be able to work without a pump. To do this, a bypass is installed – a bypass through which the coolant can flow if necessary. The installation diagram of the circulation pump in this case is in the photo below.
In closed systems with forced circulation, a bypass is not needed – it is inoperative without a pump. But two ball valves on both sides and an inlet filter are needed. Ball valves make it possible, if necessary, to remove the device for maintenance, repair or replacement. The dirt filter prevents clogging. Sometimes, as an additional element of reliability, a check valve is also placed between the filter and the ball valve, which will prevent the coolant from moving in the opposite direction.
How to fill a closed heating system
At the lowest point of the system, as a rule, on the return pipeline, an additional tap is installed to supply / drain the system. In the simplest case, this is a tee installed in the pipeline, to which a ball valve is connected through a small section of the pipe.
In this case, when draining the system, it will be necessary to substitute some kind of container or connect a hose. When filling the coolant, a hand pump hose is connected to the ball valve. This simple device can be rented at plumbing stores.
There is a second option – when the coolant is just tap water. In this case, the water supply is connected either to a special boiler inlet (in wall-mounted gas boilers), or to a ball valve similarly installed on the return. But in this case, another point is needed to drain the system. In a two-pipe system, this may be one of the last in the radiator branch, to the lower free entrance of which a drain ball valve is installed. Another option is shown in the following diagram. It shows a single-pipe closed-type heating system.