Hot tap water has long ceased to be a luxury. Today it is one of the mandatory requirements of a normal life. One of the possibilities for organizing hot water supply in a private house is the installation and connection of an indirect heating boiler.
What is an indirect heating boiler and what are they
A water heater or an indirect exchange boiler is a tank with water in which a heat exchanger is located (a coil or, according to the type of water jacket, a cylinder in a cylinder). The heat exchanger is connected to a heating boiler or to any other system in which hot water or other coolant circulates.
Heating is simple: hot water from the boiler passes through the heat exchanger, it heats the walls of the heat exchanger, and they, in turn, transfer heat to the water in the tank. Since the heating does not occur directly, then such a water heater is called “indirect heating”. The heated water is used for household needs as needed.
One of the important details in this design is the magnesium anode. It reduces the intensity of corrosion processes – the tank lasts longer.
Types
There are two types of indirect heating boilers: with built-in control and without. Indirect heating boilers with built-in control are connected to a heating system powered by boilers without control. They have a built-in temperature sensor, their own control that turns on / off the supply of hot water to the coil. When connecting this type of equipment, all that is needed is to connect the heating supply and return to the corresponding inputs, connect the cold water supply and connect the hot water distribution comb to the upper outlet. That’s all, you can fill the tank and start heating it.
Conventional indirect heating boilers work mainly with automated boilers. During installation, it is necessary to install a temperature sensor in a certain place (there is a hole in the body) and connect it to a certain boiler inlet. Next, they make the piping of the indirect heating boiler in accordance with one of the schemes. You can also connect them to non-volatile boilers, but this requires special schemes (see below).
What you need to remember is that the water in the indirect heating boiler can be heated just below the temperature of the coolant circulating in the coil. So if your boiler works in low-temperature mode and produces, say, + 40 ° C, then the maximum temperature of the water in the tank will be just that. You can’t heat it up anymore. To get around this limitation, there are combined water heaters. They have a coil and a built-in heating element. The main heating in this case is due to the coil (indirect heating), and the heating element only brings the temperature to the set one. Also, such systems are good in tandem with solid fuel boilers – the water will be warm even when the fuel has burned out.
What else can be said about the design features? Several heat exchangers are installed in large-volume indirect systems – this reduces the time for heating water. To reduce the time of heating water and for slower cooling of the tank, it is better to choose models with thermal insulation.
Which boilers can be connected to
Boilers of indirect heating can work with any source of hot water. Any hot water boiler is suitable – solid fuel – on wood, coal, briquettes, pellets. It can be connected to any type of gas boiler, electric or oil-fired.
It’s just that, as already mentioned above, there are models with their own control, and then installing and tying them is a simpler task. If the model is simple, it is necessary to think over a system for controlling the temperature and switching the boiler from heating radiators to heating hot water.
Tank shapes and installation methods
The indirect heating boiler can be installed on the floor, it can be hung on the wall. Wall-mounted options have a capacity of no more than 200 liters, and floor options can hold up to 1500 liters. In both cases, there are horizontal and vertical models. When installing the wall-mounted version, the mount is standard – brackets that are mounted on dowels of the appropriate type.
If we talk about the shape, then most often these devices are made in the form of a cylinder. In almost all models, all working outputs (pipes for connection) are brought out at the back. It is easier to connect, and the appearance is better. On the front of the panel there are places for installing a temperature sensor or a thermal relay, in some models it is possible to install a heating element – for additional heating of water in case of a lack of heating power.
When installing the system, it is worth remembering that the system will work effectively only if the boiler capacity is sufficient.
Schemes and connection features
There are two principles for connecting an indirect heating boiler: with and without hot water heating priority. In priority heating, all the heating medium is pumped through the boiler heat exchanger if required. Heating takes a little time. As soon as the temperature reaches the set point (controlled by a sensor, thermostatic valve or thermostat), the entire flow is again directed to the radiators.
In schemes without water heating priority, only some part of the heat carrier flow is directed to the indirect water heater. This leads to the fact that the water is heated for a long time.
When connecting an indirect heating boiler, it is better to choose a scheme with priority – it provides hot water in the required amount. At the same time, heating does not suffer much – it usually takes 20-40 minutes to heat the entire volume of water, and 3-8 minutes to maintain the temperature at a flow rate. During such a time, no house can cool down enough to feel it. But this is provided that the power of the boiler is comparable to the power of the boiler. Ideally, the boiler is more productive, with a margin of 25-30%.
General rules
To ensure the normal operation of all appliances connected to the hot water manifold, an expansion tank for hot water (not for heating) is installed at the outlet of the boiler. Its volume is 10% of the volume of the tank. It is necessary to neutralize thermal expansion.
Also, shut-off valves (ball valves) are installed in each branch of the connection. They are needed so that each device can be used – a three-way valve, a circulation pump, etc. – if necessary, disconnect and service.
Check valves are usually also installed on the supply pipelines. They are necessary to exclude the possibility of backflow. In this case, the connection of an indirect heating boiler will be safe and easy to maintain.
Installation next to the boiler in a forced circulation system (with 3-way valve)
If a circulation pump is already installed in the system, and it is installed on the supply, and a forced heating boiler can be placed next to the boiler, it is better to organize a separate circuit that comes from the heating boiler. This connection of an indirect heating boiler is implemented with most wall-mounted gas or other boilers that have a circulation pump on the supply pipe. With this connection scheme, it turns out that the water heater and the heating system are connected in parallel.
With this piping method, a three-way valve is installed after the circulation pump, controlled by a temperature sensor (installed on the boiler). One of the outlets of the three-way valve is connected to the boiler pipe to connect the heating. A tee cuts into the return pipeline before entering the boiler, a branch pipe is connected to it to drain water from the heat exchanger. Actually, the tie-in to the heating system is completed.
The way this circuit works is:
- When information is received from the sensor that the water temperature is below the set one, the three-way valve switches the coolant to the boiler. The heating system is turned off.
- The entire flow of the coolant goes through the heat exchanger, the water in the tank is heated.
- The water heats up enough, the three-way valve redirects the coolant to the heating system.
As you can see, the scheme is simple, its operation is also clear.
Scheme with two circulation pumps
When installing a water heater in the system with a circulation pump, but not next to it, but at some distance, it is better to install a circulation pump in the circuit on the water heater. The connection of an indirect heating boiler for this case is shown in the diagram below.
The circulation pump can be installed either on the supply pipe or on the return. In this scheme, there is no three-way valve; the circuit is connected through conventional tees. Switching the flow of the coolant is carried out by turning on / off the pumps, and it is controlled by a temperature sensor, which has two pairs of contacts.
If the water in the tank is colder than the one set on the sensor, the power circuit of the circulation pump in the boiler circuit is turned on. When a predetermined degree of heating is reached, the contacts of the pump are closed, which drives the coolant into the heating system.
Scheme for a non-volatile boiler
In a scheme with a non-volatile boiler, in order to ensure the priority of the boiler, it is desirable that it be higher than the radiators. That is, in this case, it is desirable to install wall models. Ideally, the bottom of the indirect water heater is above the boiler and radiators. But such an arrangement is not always possible.
The schemes will also work with the floor location of the boiler, but the water will heat up more slowly and in the lower part it will not be hot enough. Its temperature will be comparable to the degree of heating of the return pipeline, that is, the supply of hot water will be less.
With non-volatile heating, the movement of the coolant occurs due to the force of gravity. In principle, it is possible to connect an indirect heating boiler according to the traditional scheme – with a circulation pump in the circuit for heating it. Just in this case, when the electricity is off, there will be no hot water. If this turn doesn’t suit you, there are several schemes that will work with gravity systems.
When implementing this scheme, the circuit that goes to the water heater is made with a pipe with a diameter of 1 step larger than the heating one. This is what gives priority.
In this scheme, after a branch to the heating system, a thermostatic head with an attached sensor is installed. It runs on batteries and does not require external power. The desired water heating temperature is set on the thermostatic head regulator (not higher than the temperature at the boiler supply). While the water in the tank is cold, the thermostat opens the supply to the boiler, the coolant flow goes mainly to the boiler. When heated to the required degree, the coolant is redirected to the heating branch.
With coolant recirculation
If there is a water heated towel rail in the system, constant circulation of water through it is necessary. Otherwise, it won’t work. All consumers can be connected to the recirculation loop. In this case, hot water will constantly chase in a circle with a pump. In this case, by opening the water at any time you will immediately receive hot water – you will not have to wait until cold water drains from the pipes. This is a positive thing.
The negative is that by connecting the recirculation, we increase the cost of heating water in the boiler. Why? Because running along the ring, the water cools down, therefore the boiler will be more often connected to water heating and spend more fuel on it.
The second drawback is that recirculation stimulates the mixing of water layers. During normal operation, the hottest water is at the top, from where it is fed into the DHW circuit. With stirring, the total supply water temperature drops (at the same settings). However, for a heated towel rail, this is perhaps the only way out.
How to implement the connection of an indirect heating boiler with recirculation? There are several ways. The first is to find special indirects with built-in recirculation. Very convenient – the heated towel rail (or the entire loop) is simply connected to the corresponding pipes. But the price of such options for water heaters is almost twice as much as the price of a conventional tank of the same volume.
The second option is to use models that do not have an input for connecting a recirculation circuit, but connect it using tees.