In addition to gas boilers with two heat exchangers, other variants of internal design of heating devices are also produced. One of them is the combination of devices responsible for heating the living space and hot water supply into a more complex configuration. To choose a boiler for your needs, you need to study the properties of a bithermal heat exchanger, the advantages and limitations to its use.
Bithermic heat exchanger design
The device is also called a "pipe within a pipe". This is due to the fact that the bithermal heat exchanger is sharpened for the implementation of two purposes with one element. In the inner tube, water for domestic needs is heated, and in the outer tube, for heating. This heat exchanger is based on a copper tube of a specific design. In section, its core contour is diamond-shaped. It is soldered to the inside of the main tube. This makes it possible to combine the mechanisms responsible for heating and heating water: for one, the outer space is used, for the other, the core. The outer tube is also equipped with plates that create more contact with the combustion products. This improves heat transfer.
Region division is used instead of a set of hollow tubes. Water intended for one purpose and for another circulates within their zones. No mixing takes place. Like other types of devices, plate fins are used here to increase heat transfer. Other characteristics of the structure are already associated with the method of integrating the heat exchanger into the unit. Since in gas boilers, heating is carried out using a burner, the body is equipped with additional protective mechanisms. A safety unit is also mounted to prevent the short circuit of the electric current.
Advantages and disadvantages
The peculiarities of the "pipe-in-pipe" design seriously affect the functioning of the serviced unit.
The advantages of the device include:
- High efficiency and speed of liquid heating. Using a burner flame saves energy and gas costs.
- Simplicity of design, rationality of the layout, no need for a secondary exchanger and triple valve.
- Low probability of failure due to the fact that there are not many parts.
However, such a heat exchanger also has disadvantages. The main one is a high demand for water quality. You should not choose a unit with such a model if the water in the region is of poor quality and with a large percentage of salts: in this device they are deposited much more actively than in a separate one, and its maintainability is lower. If a mechanism is out of order, it is often easier to replace it than to repair it. To minimize the likelihood of such an incident, it is recommended to purchase water softening filters. Also, do not put the boiler in the "boiling" mode from below.
Comparison with a separate heat exchanger
The split device is much easier to repair. If a depressurization occurs, you can eliminate it yourself using a soldering iron. In combination with simplicity in water quality, this is the main advantage of these devices.However, heating is not as fast as when using a pipe-in-pipe coaxial exchanger.
The disadvantages of the separate device are its large size, the need for a crane with three strokes, a large number of parts, which increases the likelihood of breakage. Lightweight and compact bithermic exchangers are often used in wall-hung boilers. Separate ones are usually used in floor-standing units, which often require placement in a separate room.
The principle of operation of the bithermic heat exchanger
The operating modes for home heating and hot water preparation are different. In the first case, the coolant heats up during fuel combustion and then moves along the circuit. The provision of water supply is implemented as a secondary option. The carrier is heated in the same way, the heat is given to the containers allocated for liquid for household needs. In this case, water does not have to move along the contour, it is in the tank.
Most boilers with such a heat exchanger are capable of serving only one circuit at a time. Parallel circulation of the heating medium for heating and water heating does not occur in this case. When the tap is closed, only the liquid that belongs to the dwelling heating system moves through the exchanger. By opening the hot water supply, the consumer suspends heating for the heating system for the duration of the intake. Serving the two tasks in turn helps to focus more on the heat supplied by the burner.
Operating conditions
It is worth purchasing a boiler with such a heat exchanger only if you are confident in a sufficiently good quality of water used as a heat carrier. It is imperative to install a system of filters and softeners, because the device has low maintainability. This simple step should not be neglected in order to minimize the likelihood of the need to go to the workshop. The documentation supplied with the boiler indicates the requirements for the heating medium. It is necessary to check that the water in the area corresponds to them.
If the exchanger fails, you must contact the service center. In practice, it sometimes turns out that repairmen take up work with such devices reluctantly and without guarantees, and as a result they have to buy a new one.
The structure is easily clogged with soot, limescale accumulates on it. This reduces the efficiency - one of its main advantages over separate options. It is advisable to periodically (every 2 years) clean the exchanger with a pressure pump. Before carrying out it, you need to consult the technical center regarding the composition of the solution and the technology of the procedure. Errors in this matter easily lead to depressurization; in such an incident, the heat exchanger needs to be replaced. It is good if there is an opportunity to invite a master to your home - this will allow you to get expert advice without dismantling the boiler.
Aggressive cleaning agents are used only as a last resort if milder ones do not work.
Comparison with a separate heat exchanger
If the quality of water meets the requirements and the use of filtration and softening, the bithermal exchanger will give good efficiency and quickly heat the liquid. It is also advisable to provide him with preventive washing every two years, but without the consultation of the master and knowledge of the intricacies of the technology, you should not undertake this. In terms of maintainability, the device loses much to a separate one: the latter is easily repaired even at home, and if the operating conditions are not observed, the coaxial exchanger often has to be replaced with a new one.
The operation of the boiler depends on the design of the exchange mechanism and on its material. Copper, from which bithermic products are usually made, has a high heat capacity, which makes it possible to make compact units suitable for wall mounting or placement in the kitchen.Exchangers are also available in aluminum and steel. In separate designs, stainless steel is often used. Its heat capacity is lower than that of copper, it is susceptible to corrosion and requires large volumes of coolant. Durable cast iron exchangers have been widely available in the market in the past and have now been supplanted by lighter weight options.
Bithermal heat exchangers have a high efficiency, their design allows you to design more compact and lightweight boilers. The disadvantage of such devices is the susceptibility to overgrowing of the walls with lime deposits.
