How to calculate the power of the device for heating air

The heater provides and maintains the desired temperature conditions in the room. It is installed in the supply ventilation, air conditioning and heating system, it is capable of heating large areas, since it is characterized by high power and performance. In order for the device to function correctly, it is necessary to calculate the power of the heater before purchasing it.

Air heater classification

Devices operate on different energy sources and are classified according to the type of coolant. Three types are widely used:

• water;
• steam;
• electrical.

The first ones themselves do not heat the air, but only transfer heat to the air flow, since a heat carrier is supplied to the heater. Electrical appliances do not use a coolant, they heat the air thanks to electricity. The main elements in such devices are heating elements.

Aquatic

Water heaters are a budget option. Their price and maintenance costs are low. It is necessary to bring a water supply system to the device, therefore installation requires certain skills. You won't be able to quickly transfer it to another place. The heating medium (water or ethylene glycol) can come from the heating system, hot water supply or a boiler. To adjust the air temperature, it is necessary to take into account the power, the level of heating of the coolant and air mass. Controlled by a thermostat.

When installing water and steam heaters, polymer and metal-plastic pipes must not be used, as they will melt. Galvanized steel pipes are recommended.

In addition to efficiency, the water appliance is different:

• ease of use;
• high efficiency;
• security;
• simple operating principle.

The disadvantage is the limitation on the minimum temperature and dust content of the inlet flow.

It is advisable to install a water device in spacious industrial premises, warehouses, catering establishments, cottages with good ventilation. It quickly warms up large volumes of air.

Steam

In addition to the coolant, steam heaters practically do not differ from water heaters. An insignificant difference is the 2 mm tube wall thickness versus 1.5 mm. The need for additional reinforcement is associated with the high pressure in the steam system. It varies from 0.5 to 1.2 Pa. They use carbon steel and stainless steel.

Steam heaters are also installed in factories, and those where steam is generated during the production process. The maximum steam temperature is 180 ° C.

Electrical

An electric heater does not need to be connected to a line with a coolant, it has small dimensions and weight, therefore, it is easier to install.

The advantages of electrical devices:

• Ease of use;
• mobility;
• compactness.

Disadvantages:

• run on electricity;
• dry the air.

High energy costs make the constant use of this type of appliance unprofitable. They are less powerful than steam and water appliances, therefore they are not suitable for heating rooms with an area of ​​more than 100 m2, but they are optimal for heating apartments.Electrical appliances use three times more energy than water heaters, but their performance is lower. They are often used as temporary heaters.

To adjust the temperature of the air mass at the outlet, it is only necessary to install a temperature sensor.

To save energy, the recuperator should be installed.

Advantages and disadvantages

Water and steam heaters designed for heating industrial premises are extremely profitable, since they do not require additional investments. Financial resources are spent only on the purchase of the device. Their advantages:

• rapid achievement of the desired air temperature;
• easy installation;
• safety;
• reliability;
• the ability to adjust the heating level.

Among the shortcomings are noted:

• use in rooms with a plus air temperature;
• impossibility of using for heating apartments;
• equipment for air traction is required;
• if the supply of coolant is interrupted, the system stops working.

The last point is also true for electric heaters, only for power outages.

Design of heaters of different types

A heater is a heat exchanger that transfers heat carrier energy to an air heating stream and operates on the principle of a hair dryer. Its design includes removable side shields and heat dissipation elements. They can be connected in one or more lines. The built-in fan provides air draft, and the air mass enters the room through the gaps between the elements. When outside air passes through them, heat is transferred to it. The heater is installed in the ventilation duct, therefore the device must correspond to the shaft in size and shape.

Water and steam heaters

Water and steam heaters can be of two types: ribbed and smooth tube. The former, in turn, are divided into two more types: lamellar and spiral-wound. The design can be single-pass or multi-pass. In multi-way devices there are baffles, due to which the direction of flow is changed. The tubes are arranged in 1-4 rows.

The heater, working on water, consists of a metal, often rectangular frame, inside which there are rows of tubes and a fan. Connection is made to the boiler or the central heating center using the outlet pipes. The fan is located on the inside and blows air into the heat exchanger. 2 or 3-way valves are used to control power and outlet air temperature. The devices are installed on the ceiling or on the wall.

There are three types of water and steam heaters.

Smooth pipe... The structure consists of hollow tubes (2 to 3.2 cm in diameter) spaced at small intervals (about 0.5 cm). They can be made of steel, copper, aluminum. The ends of the tubes are in communication with the manifold. Heated coolant enters the inlet openings, condensate or cooled water enters the outlet. Smooth tube models are less efficient than others.

Features of use:

• the minimum temperature of the inlet stream is –20 ° C;
• requirements for air purity - no more than 0.5 mg / m3 in terms of dust content.

Ribbed... Due to the finned elements, the heat transfer area increases, therefore, all other things being equal, finned air heaters are more efficient than smooth-tube ones. Plate models are distinguished by the fact that plates are mounted on the tubes, which further increase the heat transfer surface area. Steel corrugated tape is wound in winding ones.

Bimetallic with ribbing... The greatest efficiency is achieved through the use of two metals: copper and aluminum. Headers and pipes are made of copper, and fins are made of aluminum. Moreover, a special type of ribbing is performed - spiral-rolling.

In electrical appliances, air is heated due to its contact with hot plates or spirals. Heating elements are made of refractory metals.

Calculation of the power of the heater

For the correct calculation of the air heater, it is necessary to determine the initial data: performance, air density, street and desired room temperature. The latter indicators are extremely important, since the amount of heat spent on heating 1 m3 of air depends on them. Some of the data can be found from special tables.

Water appliance

To calculate the cross-sectional area of ​​a water heater, use the formula Af = L × ρ_st/ 3600 (ϑρ)... Values ​​used:

• L - productivity, which is expressed in m3 / h or kg / h;
• p_st - outdoor air density according to the table;
• ϑρ Is the mass velocity of air in the section.

Having received the result, one air heater of a standard size or several devices are selected for the ventilation system so that the area or the sum of the areas is equal to or slightly larger than the calculated value.

Mass air flow in kg / h is calculated by the formula G = L × p_Wed:

• p_Wed- air density at average temperature.

pav calculated by the formula (t_st+ t_con)/2:

• t_st - outdoor air temperature in the coldest five-day period of the year;
• t_con - desired room temperature.

Then, for the average, the density is determined according to the table.

Calculate the heat consumption for heating the air according to the formula:Q (W) = G × c × (t_con–T_st)

For example, the data will be calculated if it is known:

• L - 10,000 m3 / h (capacity is indicated in the documentation);
• t_con - 21 ° C;
• t_st - –25 ° C.

pav = (- 25 ° C + 21 ° C) / 2 = –2 ° C

The density of air at this temperature is 1.303.

The mass flow rate of the air mass is G = 10000 m3 / h × 1.303 kg / m3 = 13030 kg / h

From here Q = 13030/3600 × 1011 × (21 - (- 25)) = 168325 W.

It is necessary to add 10-15% to this value for the power reserve.

Steam heater

The power of the steam heater is determined in the same way, only for calculation G use the formula G = Q / r. r - specific heat generated during steam condensation in kJ / kg.

Electric heater

For electrical appliances, most of the necessary data is usually indicated by the manufacturer, which greatly simplifies the calculation of air heating and the choice of a heater. Despite the relatively low thermal power, the electric heating system consumes a lot of electricity, so it often has to be connected to the panel with a separate cable. Heaters with a power of more than 7 kW are powered from a 380 V network.

The consumed current is calculated by the formulaI = P / UwhereP - power, and U - tension. Value U depends on the characteristics of the connection. If the connection is single-phase, U = 220Vif three-phase, U = 660V.

The heating temperature is calculated by the formulaT = 2.98 × P / Lwhere L - as in other calculations, system performance.

For heating small areas, it is recommended to purchase an electric heater, it is more convenient and does not require complex installation. If the heating area is more than 100 m2, it is more profitable to use a water or steam device. In any case, in order to correctly select the heater, it is necessary to make preliminary calculations.