Hydraulic calculation of heating systems. Heating in a private house

A modern heating system is a demonstration of a completely new approach to its regulation. To date, this is not a preliminary adjustment before starting the system with the relief of the subsequent hydraulic mode of operation. Modern heating in a private house in the process of work has a constantly changing thermal regime. What requires the equipment is not only to track changes in the heating of the room, but also to respond to them correctly.

Conditions for effective operation of the system

There are some points, compliance with which will ensure a high-quality and efficient operation of the heating system:

• The supply of heat-transfer agent to heating appliances should be made in the quantities that will ensure the heat balance of the room, subject to the constantly changing outside temperature and depending on the temperature regime of the premises determined by its owner.
• Reducing costs, including energy, to overcome the hydraulic resistance.
• Reduction of material costs when installing a heating system, which also depends on the diameter of the pipelines being laid.
• Low noise level, stability and reliability of heating devices.

How to calculate the heating system correctly

To calculate the heating in a private house, you need to know the amount of heat you need. For this purpose, the heat losses of the entire house are calculated in the warm and cold season. This includes heat loss through window, doorways, enclosing structures , etc. These are rather laborious calculations. It is generally accepted that on average the heat source should produce 10 kW per 100 m ^{2 of} heated area.

The heating system is understood as the interrelationship between a set of devices: pipelines, pumps, shut-off and regulating equipment, control and automation means for transferring heat from the source directly to the room.

Types of heating boilers

Before making a hydraulic calculation of heating systems, it is necessary to select the correct boiler (heat source). There are the following types of boilers: electric, gas, solid fuel, combined and others. The choice in most cases depends on the fuel prevailing in the area of residence.

Electric boiler

Due to problems with power connections and a fairly high price for electricity, this equipment has not found its wide distribution.

Boiler gas

To install such a boiler, previously required a special separate room (boiler room). At present, this applies only to equipment with an open combustion chamber. A similar option is most common in places with gasification.

Solid fuel boiler

With relative availability of fuel, this equipment is not very popular. There are some inconveniences during its operation. Within a day, it is necessary to make several times a furnace. In addition, the heat transfer regime has a cyclic character. The use of these boilers is facilitated (reducing the number of furnaces) by using a thermal cylinder or a fuel with a high combustion temperature, due to which the burning time is increased due to the controlled air supply. This can also be done by means of water heat accumulators, to which central heating is connected.

Required parameters for power calculation

• _Wd is the specific power of the heat source (boiler) per building area of 10 m ² , taking into account the climatic conditions of the region.
• S is the area of the heated room.

Also there are generally accepted values of specific power, which depend on the climatic zone:

• W _ud = 0.7-0.9 for the Southern region.
• W _ud = 1.2-1.5 for the Central District.
• W _ud = 1,5-2,0 - for the Northern region.

Formula for boiler output

Before proceeding to such a responsible event as the hydraulic calculation of heating systems, you need to determine the power of the heat source by the following formula:

W _cat = S × W _ud / 10.

For convenience of calculation, we take the average value of _Wd per 1 kW, so we get that 10 kW should account for 100 m ^{2 of} heated area. As a result, the installation scheme of the heating system will depend on the area of the house.

In other cases, forced circulation of the coolant is used by means of circulation pumps.

Two-pipe system

This is a classic version of the heating system, which has proved itself in the best way for a long time of operation. Hydraulic calculation of the two-pipe heating system will be considered below. Why is it called that? The thing is that the basis of engineering design was the installation of several pipelines through the floors of the building. A heating device was connected to one riser with hot water on all the floors, and chilled water from the heating device flowed into the pipeline laid by the side.

As a result, the coolant that had not yet cooled down from the first device entered the device, which was located a floor below, and the circulating liquid had the same temperature as in the first one. Thus, the temperature of the coolant in the first and last pipelines was identical - this means that heat transfer was the same.

Two-pipe heating system - advantages

Central heating in a private house with a two-pipe system has the following advantages:

• On each heated floor, uniform heating of all appliances is ensured.
• Compared with the one-pipe system, it is possible to heat a lot more rooms.
• Regulation of temperature in each room.

Calculation and graphic activities

Performing a complex hydraulic calculation of heating systems, first of all, it is necessary to produce a number of preliminary activities:

1. The heat balance of the heated structure is determined.
2. The type of heating devices is selected, after which they are arranged schematically on the floor plan.
3. Further, a decision is taken to locate all heating units, type and materials of pipelines, regulating and locking devices.
4. To make a hydraulic calculation of heating systems, it will be necessary to draw a schematic diagram in axonometry indicating the design loads and lengths of sections.
5. The main ring is defined as a closed segment that includes serially located sections of pipelines having the maximum flow of the heat carrier from the heat source to the most remote heating device.

For the design section, one that has a constant coolant flow and the same cross section is adopted.

Example of hydraulic calculation of a heating system

On the calculated segment, the heat load is equal to the heat flux that must be transmitted on the supply line, and on the reverse side already transmitted the circulating liquid that passed through this section.

The flow rate of the heat carrier G _{i - j} , kg / h is calculated by the following formula:

G _{i - j} = 0.86 × Q _{i - j} / (t ₂ -t ₀ ), where

G _{i - j} is the amount of heat in the calculated interval ij;

T ₂ -t ₀ are the calculated temperatures of hot and cold liquids, respectively.

How to choose the diameter of pipelines

To reduce the cost of overcoming resistance during the movement of circulating fluid, the diameters of the pipelines should be located within the minimum velocity of the heat carrier, which is required to remove air bubbles that contribute to the appearance of air plugs. To reduce them, the diameter of the pipelines is reduced to a minimum value, which does not lead to hydraulic noise in the valve and pipes of the system.

All production pipelines are divided into polymer and metal. The first are more durable, the latter - mechanically more durable. Which pipes to use in the heating system depends on its individual characteristics.

Hydraulic calculation of the heating system - program

Considering the amount of work to be done at the design stage, you can use specialized software.

Using the initial data, the program performs automatic selection of pipelines of the required diameter, pre-adjusts the regulating and balancing valves, thermostatic valves and automatic regulators in the heating system. Also, the program can independently estimate the size of the heating appliances required.