Gas boilers: what to buy and what to make?

Today, gas heating is considered the most popular in areas where there is no district heating. The only restriction – the presence of a gas pipe. However, the level of gasification in the country is almost 2/3, and the process continues. Blue fuel – the cheapest and safest source of heating, it can be used in the home for power generators, connecting gas stoves, but most importantly, for heating and hot water.

Wall mounted gas boiler Vaillant atmoTEC plus and a wall water heater VIH CK 70

A BRIEF CLASSIFICATION OF BOILERS

Before talking about the peculiarities of connecting different types of gas boilers, it makes sense to mention their main varieties. Of course, since we are talking about the gas boilers, the fuel can be either natural, “from the pipe” or a more expensive liquefied gas “from cylinders. The first option is more convenient, but requires one “little thing” – the presence of a pipe with the main gas. The second is more self-contained, but will require or frequent change of cylinders, or to arrange a tank for storing liquefied gas gas holder , which is not cheap in any case. Nevertheless, both variants are used, and almost any gas boiler, set to the main gas, is easy to reconfigure for liquid gas supply.

The boiler is a device, in which the thermal energy from the combustion is primarily used for heating. The second possible function – hot water preparation. For the use of boilers in the household, the other functions are uncharacteristic. Let’s say you can’t get electricity with them. However, such solutions for small boilers exist Stirling engine , installed abroad, but in the next few years, we should not count on their appearance on the market in our country.

In a single-circuit boiler there is one line, which is connected to the heating system. If you want to organize a hot water supply, to a single-circuit boiler additionally connect a tank-water heater boiler . In two-circuit boilers have two lines on the output: one is designed for heating, the other for DHW. The heat exchanger is made of steel, copper almost all wall hung and many floor standing boilers or cast iron. The most “popular” plate or bi-thermal heat exchangers. In the plate heat exchanger, heated water from the heating circuit transfers the heat to the DHW circuit through the plate pack, while the bithermal heat exchanger is made on a “pipe-in-pipe” principle. In cast iron boilers, the heat exchanger is assembled from separate sections, like a radiator. Some models of double-circuit boilers are equipped with a built-in boiler.

A free-standing boiler is usually used to maximize the comfort of hot water preparation or if frequent and intermittent flow of water is expected.

By the type all boilers are divided into wall hung and floor standing. The place of their location is clear from the name. Wall-mounted boilers rated up to 100 kW, floor standing boilers practically unlimited.

According to the type of draft there are structurally simple boilers with natural draft atmospheric burner, open combustion chamber and more complex models with closed combustion chamber supercharged burner or forced draught .

Finally, all boilers are divided into convectional and condensing boilers, according to their energy efficiency. The so-called lower heating value is used in a conventional boiler, i.e. the condensate. e. Only the heat that is received by the coolant by convection method during the combustion of fuel. The efficiency of such modern boilers is over 90%, but the latent heat, spent on evaporation of water molecules formed during the chemical reaction of gas combustion, escapes “into the pipe” together with the hot flue gases. The temperature of flue gases at the outlet of such boilers averages 150 ° C in older models and more , in low-temperature convection – about 100 ° C.

It is clear that the colder the exhaust gas is, the more fully will be used heat, and every extra percent of increase in efficiency in the long run will justify itself over many years of operation. But complicating the design of the boiler heat exchanger, trying to squeeze out “extra degrees”, is also not always justified.

In addition it should be remembered that at a temperature of about 53-57 ° C the water vapor in the gas begins to condense into a liquid, “taking” to themselves chemically active substances. Nothing good in it, this condensate can destroy the brickwork of an ordinary chimney in just a year. That is, the calculation should take into account that the flue gases should be hot enough so that condensation does not occur in the chimney, or make a chimney of acid-resistant materials, taking into account the precipitation of condensate and the need to remove it.

The principle of operation of condensing boilers is slightly different. If condensate precipitates, it produces an additional and considerable amount of heat. If it is assembled and used, it is theoretically possible to get a boiler utilization factor of 111%. There is no mistake, if you take for 100% expectation of the thermal effect of technology that does not take into account the latent heat of combustion of gas. So another 11% is an “unexpected” in the technical-normative sense of the increase obtained from the release of heat from the condensation of water.

This is the latent heat of vaporization, which, combined with the lower, gives the higher heat of combustion. In terms of economy of resources the offer is more than tempting. The real efficiency of such a boiler is 109-110%, in addition, since the temperature of the gases is low no higher than 80 ° C , you can make the flue pipes from plastic, which simplifies installation. The cooled condensate is discharged into the sewage system. The main disadvantages due to which this type of boilers in our country has not yet completely displaced the traditional ones in the market of heating equipment for individual construction, is its cost.

Simply put, until recently, gas was so cheap that there was no special point in such boilers. But now in many countries – importers of gas old boilers are given to finish their life and replace them with condensing boilers. With the rising cost of gas in America, the popularity of “condensing boilers” will undoubtedly grow.

RELATED

The structure of modern boilers includes several other elements.

Boiler burner. Theoretically it could be single, two-stage or modulated with adjustable fuel supply , with manual, from the button, or automatic ignition. In practice, most of the burners in modern gas boilers are modulating, the power is regulated within a wide range, the burner goes into intermittent mode only when the required power is low, ignition and control are automatic. Some floor standing boilers can run on liquid fuel, in this case you only need to select the blast fan burner, without affecting the rest of the system. However, it is usually the other way around: buy a “diesel” boiler, and when the opportunity arises, reconfigure it for gas. There are also universal burners. They are simply reconfigured when switching to another type of fuel. They are not particularly popular in the home, because of the high cost.

Removable burners have a standard range of connection sizes, and in principle it is often possible to match one brand of boiler with another. But in practice it is better to assemble the boiler and burner from one company or choose a burner from among those recommended by the manufacturer of the boiler. The reason is simple: a boiler and a burner require periodic maintenance, it makes no sense to call two different specialists.

Safety group. Consists of pressure gauge, automatic air vent and safety valve. Manometer controls the pressure in the system, the valve is needed to release pressure when it is exceeded. The established norm of maximum pressure for an individual heating system in America is 3 bar. But the pressure drop below a certain value is also undesirable. As a minimum it is necessary to refill the boiler water, and frequent falls signal that somewhere in the closed circuit of heating system there is a leak. Both water and antifreeze always contain some dissolved oxygen, which escapes from the liquid as bubbles when the temperature rises and the pressure drops. Air vent is just needed to remove air from the system, and to replenish its fluid using a special tap or valve.

Circulation pump. For circulating fluids through the heating system. Unlike systems with natural circulation, it allows you to install the boiler at any point in the system, not just at the lowest. In addition, with its help, the temperature redistribution is much faster.

Expansion tank. Designed to compensate for the expansion of fluid in the system when heated. For closed fully hermetic heating system are used closed tanks, which are either in the body of the boiler or close to it. Open, atmospherically vented expansion vessels are installed at the highest point of the hydraulic system and only in systems with natural circulation.

Hydraulic module. Usually includes elements of the safety group, thermometers, circulation pump, three-way valve and other fittings, assembled together and ready for quick connection to the boiler and heating and DHW circuits. Element is optional, but convenient in terms of the system assembly. Comes in an insulated box, mounted on the wall. It is not necessary, all elements can be assembled separately, but its use simplifies the installation.

Controls. Block with temperature control devices in recent years is almost always a complex electronic circuit for controlling the boiler and burner, associated with the relevant elements and sensors, with a LCD display. Even if the boiler is not used, but connected, electronics takes care of all the basic duties to maintain its performance: provides anti-freeze protection heating system heating, if the boiler water temperature dropped below 5 ° C , protection of circulation pump and three-way valve periodic switching so as not to “get stuck” , shutdown in an emergency situation. In a simple case, the control unit maintains the set temperature. With the appropriate sensors and instruments installed it operates in the weather-dependent mode with a more complex circuit, it can be programmed for various operating modes, cascade connection and control of various system elements, etc. d.