Formulas and methods for calculating water consumption for a heating boiler

2017-06-01 Evgeny Fomenko

Calculation of the amount of coolant

The amount of coolant must be such that the power of the unit is sufficient for heating. If the volume is exceeded, this will lead to insufficient heating, the boiler will work constantly, which will lead to its premature wear and high gas consumption.

The internal volume of pipes of different diameters

The dependence of the maximum flow rate on the power is calculated as the boiler power in kilowatts multiplied by a factor of 13.5 kilowatts per liter. The following formula is used to calculate the water flow for the boiler: V coolant = V boiler + V radiators + V expansion tank + V pipes.

The volume of the boiler depends on the power of your unit, the numbers are given in the instructions. The volume of the expansion tank is also given in the instructions, ideally it should be approximately two power from the unit's power value. So for example, if the power is 10 kW, then the expansion tank occupies a volume of 20 liters.

The volume of radiators depends on the material from which they are made. For example, one section of aluminum batteries occupies a volume of 0.44 liters, from bimetal - 0.35 liters, cast iron of a new sample - 1 liter, old sample - 1.4 liters. Counting the number of sections, get the volume of radiators.

The volume of a pipe 1 m long and 15 mm in diameter is 0.176 l, 20 mm in diameter is 0.3 l, and 25 mm in diameter is 0.485 l. Multiplying by the length of the pipes, we get the total volume occupied by the coolant in the pipes.

Adding all the data obtained, we can calculate the total volume of liquid. The most popular models for household needs are Wolf, Vaillant, Bayxi, and industrial models include: DKVR 10 13, KVGM 10, PTVM 30M. The volume of feed water for them is calculated by specialists.

Water is the most common coolant

Water and antifreeze are used as a heat carrier in boilers.

Water is used much more often for the following reasons:

• water is the most cheap coolant;
• has a high heat capacity- the ability to give off heat. Heated to 90 degrees and cooled to 70 degrees in heating radiators, water gives off 20 kcal of heat to the surrounding air per 1 kg of its own weight;
• environmentally friendly, safe for human health and the environment in case of leakage;
• easy to add volume in case of leaks, it is simply added to the expansion tank.
• leak is easily fixed by sealing the leak.

At the same time, there are disadvantages caused by the content of salts and oxygen in the water, which contribute to the formation of scale on the walls of the internal parts of the boiler. Scale reduces the flow of water through the coolant and heat transfer.

Therefore, it is best to use distilled or rain water. Before pouring, thoroughly flush the entire heating system, regardless of whether it is old or new.

Choosing a circulation pump

The circulation pump serves to maintain the optimum water pressure for heating.

heating pump

To choose the right one, you need to consider the following parameters:

• performance, is calculated at the minimum flow rate;
• pump working pressure;
• heated area, type and temperature of the heat carrier, room temperature, pipe size;
• pump dimensions, noise level.

Pumps are divided into 2 types according to the type of rotor - "dry" and "wet". The "dry" rotor is not in contact with the coolant, it is protected from it by a seal. Such pumps have a high efficiency, up to 86%, but are quite noisy in operation, they are more often used in enterprises or in large boiler houses.

In wet type pumps, the rotor is in direct contact with the coolant, it is more silent. Such a device is equipped with speed switches. Durable in operation, but have a low efficiency - up to 66%. Widely used in domestic heating systems.

To select the parameters of the circulation pump, the formula is used: Q \u003d N / (t 2- t 1),

where Q is the pump performance;

N is the power of your boiler;

t 2 - temperature of the supply fluid;

t 2 - return temperature.

Heating pump installation diagram

The temperature of the supply fluid is usually in the range of 90-95 degrees, the return temperature is 50-75 degrees.

One of the most popular pumps is the GRUNDFOS pump. Using the example of the GRUNDFOS UPS 25-4 model, we will describe what the marking means. The number 4 indicates the amount of rise of the coolant to the heating circuit, 4 meters or a pressure of 0.4 atmospheres.

The numbers 25 are the diameter of the connected pipes or adapters. When replacing or installing a pump, always refer to the diameter of your pipes. The amount of water in the heating circuit depends on the diameter of the pipes, therefore, with a larger diameter, there must be a more powerful pump.

If you are using antifreeze as a fluid, and it is more viscous, you will need a large pump.

Water for domestic needs - calculation of the capacity of the DHW circuit

In gas double-circuit boilers, hot water is heated in a flow way. The time of water flow through the heat exchanger is insignificant, so the power of the unit must be such that it has time to heat it.

The minimum power of such a unit should be at least 18 kW. To reduce it, a storage tank is used, in which the heated water maintains its temperature for some time and allows you to use hot water immediately after opening the tap.

DHW circuit example

When using a single-circuit boiler in conjunction with a boiler to produce hot water, the capacity of the boiler should be 80 liters in order to be able to use it comfortably and reduce the fuel consumption of the boiler.

Ways to save heat and hot water

To save money, you should well insulate the room, windows, doors, walls. Reducing the number of windows will also reduce heat loss. Timely cleaning of your boiler blocks will also help to significantly reduce fuel consumption.

Reducing the heating temperature of both heating water and domestic hot water by a small amount will also save you money.