The main types of heat exchangers in the furnace and its installation methods

Despite the widespread use of modern heating boilers, traditional stoves do not lose their relevance. However, their effectiveness sometimes leaves much to be desired. Installing a heat exchanger for the oven will make it truly versatile. Not only the ambient air will be warmed up, but also the coolant circulating through the system. Buying a new full-fledged boiler is not always advisable. Especially if the zealous owner has the desire, opportunity and guidance for action.

The principle of operation and function of the heat exchanger

A liquid heat exchanger is a container, part of a furnace structure, equipped for connection to a pipeline. The tank heats up, in contact with the combustion products, and transfers this energy to the water. Water, moving through the system, gives off heat to heating devices - radiators, from which the air is heated convectionally. The heating of the container can be direct or indirect, and the circulation of the coolant can be natural or forced.

Heat carrier

Antifreezes based on ethylene glycol, propylene glycol, alcohol or oil are often used instead of water. Their main advantage is their low freezing point, ranging from -30 to -70 ° C. The exact numbers depend on the chemical composition and concentration of the liquid. The use of such chemistry has a number of advantages:

• protection of system elements from damage due to defrosting;
• anti-corrosion protection due to appropriate additives;
• absence of abrasives, salts and other impurities that destroy (clog) the pipeline or fittings.

Some heat exchangers, for example, for a bath, serve not only heating appliances, but also a shower or a separate tank. Therefore, water is used here. In order to avoid defrosting, the device is designed so that the filling of water does not take much time. If the bathhouse or sauna is heated often, and the enclosing structures are insulated with high quality, the problem is removed.

Propylene glycol is expensive, alcohol and oil are fire hazardous, and ethylene glycol is a highly toxic heat carrier.

Heat exchanger functions

The function of the heat exchange tank, as part of the furnace structure, is to receive and transfer heat to the coolant from the combustion products. But as an element of a wider system (heating, water supply), it solves several problems.

• Distribute heat evenly and economically throughout the heated rooms.
• Provide the house (cottage, cottage, bathhouse, apartment, etc.) with hot water.
• Accumulate heat energy for use when the stove is not working.

A heat accumulator connected to a heat exchanger for a wood-burning stove stores energy due to the heat capacity of the storage agent. Therefore, it can be made by insulating any container. A barrel doused with polyurethane foam and partially filled with rubble or sand is already a heat accumulator. If equipped with four connections and correctly connected, the unit will become a functional element of the system.

Cooling down by 1 ° C, water heats 1 m3 of still ambient air by 4 ° C. This is the reason for the successful use of water heat accumulators.

Types of heat exchangers

A simple device can be effective in different ways - depending on the type. The classification is carried out according to several criteria.Different models of factory or homemade heat exchangers, for example, in a bath, differ:

• design,
• installation site,
• material.

These factors affect each other and on the characteristics of the heat exchange unit as a whole: its cost, efficiency, productivity, system volume, installation complexity, etc.

Design

Design differences largely depend on the purpose of the product. For example, heating water for washing involves a substantial volume and intense heat transfer. And use only for heating requires a gradual transfer of heat to the coolant.

• The coil is a pipe bent at different angles. Warms up quickly, but often does not have enough volume. Suitable for installation in a wood-burning firebox, behind a firebox, in a heater, on a chimney (if the coil is spiral).
• The register is an analogue of a pipe radiator, perhaps the most popular, versatile, energy efficient. Typically, these are several large diameter pipes connected by thin tubes. The choice of a specific form and place of installation is limited by the imagination of the author, as well as by the general scheme.
• Diplomat - one or more interconnected containers with nozzles. This is a common model, easy to assemble and install. A stove for a bath with a heat exchanger of this type will provide heat, heat, hot water. Disadvantages - a significant volume reduces the heating rate, limits the choice of a place for installation. The primitive form does not contribute to full-fledged heat transfer, interfering with the heating of parts of the stove itself. Therefore, it is well suited only for installation inside the heater (if we are talking about a sauna), behind it or behind the firebox.
• The water jacket is a casing installed on the parts of the heat generator heated from the inside. Often this is a cylinder with nozzles, put on the chimney. Difficult for handicraft assembly, prone to leaks, but does not require disassembling the stove for installation and is quite effective.

The choice of the model is usually related not so much to efficiency and price as to the complexity of the installation. For example, some modifications of water "jackets", "coils" and "diplomats" are mounted without disassembling the stove. The maximum is the modernization of a part of the pipe or replacement of the cast-iron stove (for cooking) with a "diplomat".

Heat transfer registers are generally preferred over other devices. However, they are installed only during the construction of a new stove or a serious alteration of the old one.

Material

When designing a stove or fireplace with some kind of heat exchanger, the engineer (or stove-maker) takes into account the parameters of the materials. The required properties are fire resistance, elasticity, corrosion resistance, heat capacity, thermal conductivity. Only metals have these characteristics.

• Steel is excellent in all respects, except for corrosion resistance. However, if the coolant is always filled, it will not rust.
• Stainless steel has no disadvantages other than the high cost and difficulty of welding. Galvanized steel is almost never used due to toxic emissions associated with high temperatures.
• Cast iron, the disadvantages of which are the complexity of welding and a high probability of cracking (due to sudden temperature changes with uneven heating).
• Copper, which is good for everyone, except for the high price and soldering of parts. Solder "does not hold" strong heat if the water is drained, therefore the use of copper is limited.

The choice is usually related to the availability or availability of the material. Often there are bath stoves with a cast-iron heat exchanger, which is a modified battery. The revision consists in welding the joints of the sections and plugs in the extra holes. Thus, a heat exchange register is obtained that has all the necessary properties. Its disadvantage is its cumbersomeness, which limits the choice of location.

DIY making

Making a decision on self-production, as a rule, indicates the presence of some kind of tool and skills to work with it.Ideally, a full-fledged workshop with a vice, welding (of two types), a workbench, an anvil, etc. is needed. If the equipment leaves much to be desired, it is possible to assemble the simplest modification - a copper spiral coil.

Pros of this option:

• Copper is relatively easy to bend and solder.
• The coil does not contain compounds subject to strong heat.
• The spiral shape is simple, versatile, and does not require sophisticated equipment.
• The installation of such a heat exchanger does not require serious modernization of the furnace structure.

A sauna stove with such a heat exchanger will cope with everything that can be expected from it: it will ensure the operation of 2 - 3 heating radiators, and heat the water in a small tank. The heater is, nevertheless, responsible for the microclimate in the steam room.

Consumables

Of the special tools for working with copper, only a gas burner is needed. A professional will need a pipe cutter, a beveller, and a metal brush of the right size. However, all this is replaced by a grinder, a file (rasp), a soft abrasive sponge. You will also need a minimum of consumables:

• annealed copper pipe in a coil d32, length 3.5 - 4.5 m (depending on the d of the chimney);
• transitional water sockets (thread-soldering) d32 * 1.25 "- 2 pcs;
• common low temperature and hard copper solder for medium temperature brazing (650 - 750 ° C);
• gumboil paste;
• soft abrasive sponge;
• propane-butane gas for medium-temperature soldering - 1 cylinder (0.5 l);
• washed sifted fine sand - 5 - 6 kg;
• pipeline, taps, valves "Mayevsky", radiators.

A "pipe bender" is required - an even round log. With its help, the heat exchanger for the sauna stove will take the form of a spiral coil. The length of the log is at least 1 m, and the diameter is equal to the dimensions of the chimney at the exit from the stove. As a rule, the parameter depends on the size of the firebox and is not less than 10 cm.

The log should be firmly secured by fixing it with powerful self-tapping screws / dowels between two trees or walls.

Assembly Algorithm

The hardest part of the assembly is the spiraling. To do this, the pipe will have to be bent using a rigidly installed log. Unannealed copper cannot be bent, so you need to buy exactly the one in the bays. The easiest way to install a coil heat exchanger in a brick oven (for heating) is to mount it on a chimney. Algorithm of actions:

1. Plug one end of the pipe securely, for example with a factory sealed plug.
2. Fill the pipe with sand by spilling water, tapping with a hammer, sealing with a ramrod. This can be a reinforced plastic pipe or a plugged rubber hose.
3. When the pipe is full, seal the filler as much as possible, then plug the other end. Try not to "loosen up" the sand.
4. Screw a U-shaped or round clamp to the log, which will hold the pipe tightly. The base "P" is perpendicular to the pipe bender closer to the end, and the location around the circumference does not matter.
5. Insert the end of the coil into the clamp, start slowly winding the pipe around the log.
6. If a hall appears somewhere, it means that in this place the sand is not dense enough. It is advisable to start all over again, but, theoretically, you can try to tap it with a hammer.
7. If d of the chimney is 150, and the length of the bay is 4.5, you should get 8 - 9 turns of the spiral (no more than 35 - 40 cm high), as well as two "tails" 30 - 40 cm each.
8. Cut off the plugs, clean out the sand, rinse the coil.
9. Solder the transitional water sockets to the ends of the spiral.
10. Remove the stove cover or dismantle the slide damper (take out part of the chimney).
11. Put the "coil" on the pipe as close to the stove as possible.
12. Assemble the chimney back, taking into account the necessary sealants, windings (if any).

Now you can install and connect the rest of the heating system, including an open samovar-type expansion tank, pipeline, taps, radiators, air valves.To improve natural circulation, the diameter of the piping should not be much smaller than the dimensions of the coil. Ideally, it will also be copper, of the same diameter.

A probable difficulty is a decrease in draft due to unintended heat removal from the chimney. The solution is to increase the length of the chimney.

Installation options for the heat exchange structure

The installation of a heat exchanger of any kind involves a considerable amount of work, especially if its efficiency is of serious importance. For example, the simplest spiral on the chimney may warm up slightly, and there will be no circulation at all without a pump. Then you have to take measures, up to and including rejection of such a design. In practice, one heat exchanger for a furnace, installed in different places, gives different efficiency. Conventionally, you can make up such a TOP, starting with the most effective variety:

• cast iron or steel U-shaped register in the firebox;
• a water jacket around the firebox or at any of its surfaces;
• U-shaped diplomat in the firebox;
• a diplomat directly above or behind the firebox, with maximum contact;
• water jacket around the heater;
• register, diplomat or serpentine in the stove;
• diplomat or serpentine behind the stove;
• chimney water jacket.

The chimney coil is conventionally the least effective option. However, the simplicity of the device often eliminates the disadvantages. In addition, efficiency is improved in a variety of ways. Among them - the lining of the coil with a thermally insulated casing with filling of voids with sand or installation of the structure directly into the heater.

All names are conditional. For example, such a factory design is not uncommon, when a cubic container is built in above the stove. It can be considered a shirt or a diplomat.

Correct connection

A wood stove or fireplace with any heat exchanger is only part of the system. For its energy efficient operation, the circulation of the coolant remains the key factor. Even when a pump is clearly needed (for example, in a large two- or three-story house), natural circulation is important. Thanks to her, pipes do not burst too quickly due to defrosting, and the water does not boil so easily if the electricity goes out. To improve circulation, it is advisable to adhere to the following rules:

• the higher the run-up of the pipes of the heat exchanger in height, the better;
• the expansion tank is placed as high as possible, next to the stove;
• a pipe goes to the tank from the upper branch pipe;
• the pipe from the expansion tank goes to the lower inlet of the radiator;
• all horizontal sections are made at an angle (not less than 3 mm per 1 m);
• exit from the radiator only on the opposite side or diagonally.

Another important point is the throughput of the pipeline. The higher it is, the better. Therefore, you should not narrow the diameter, build in extra elbows, fittings, and also use rusted inside or plastic pipes.

The heat exchanger is installed at the stage of the furnace assembly. If we are talking about an old design, do not be lazy to disassemble it. In this case, it will be possible to install the most efficient device where it is required. Along the way, a detailed inspection of the masonry, as well as other details, will be carried out. Defects and flaws will be eliminated.