Calorifier calculation: how to calculate the power of a device for heating air for heating

Heaters have high performance, so even very large rooms can be heated with them in a fairly short time. Many models of these devices, working on the basis of different coolants, go on sale.

To choose the best option, you need a calorifer calculation, which you can perform either manually or using the online calculator. We will help you figure out the issue of calculations - in this article we give an example of the calculations that will be needed when choosing the right device for heating air.

And also consider the design features of various types of heaters, the advantages and disadvantages of a heating system using such devices.

Pros and cons of heating with a heater

The home heating system, based on the supply of air warmed up to the set temperature directly into the house, is of particular interest to owners of their own homes.

This design of the heating system consists of the following important components:

• a heater that acts as a heat generator that heats the air;
• channels (ducts) through which heated air masses enter the house;
• a fan that directs well-warmed air throughout the room.

There are many advantages to this type of system. These include high efficiency, and the absence of auxiliary elements for heat transfer in the form of radiators, pipes, and the ability to combine it with the climate system, and low inertia, as a result of which heating of large volumes occurs very quickly.

For many homeowners, the drawback is that the installation of the system is possible only simultaneously with the construction of the house itself and then its further modernization is impossible.

The disadvantage is such a nuance as the mandatory availability of backup power and the need for regular maintenance.

The air heater is easy to install and operate, affordable, but most importantly, it is an effective device for heating the room. In the photo, a water heater mounted in the system

On our site there are more detailed materials on the device for air heating in the house and cottage. We recommend that you familiarize yourself with them:

• DIY air heating: all about air heating systems
• How to arrange air heating of a country house: rules and schemes of construction
• Calculation of air heating: basic principles + calculation example

Classification of heaters

Heaters are included in the design of a heating system for heating air. The following groups of these devices by the type of coolant used: water, electric, steam, fire.

It makes sense to use electrical appliances for rooms with an area of ​​not more than 100 m². For buildings with large areas, a more rational choice would be water heaters, which only function if there is a heat source.

The most popular are steam and water heaters. Both the first and second in shape of the surface are divided into 2 subspecies: ribbed and smooth-tube. Ribbed heaters on the geometry of the ribs are lamellar and spiral-wound.

The performance of air heaters operating on such a coolant as steam is regulated using special valves installed on the inlet pipe

By design, these devices can be one-way, when the coolant in them moves along the tubes, adhering to a constant direction and multi-way, in the covers of which there are partitions, as a result of which the direction of movement of the coolant is constantly changing.

4 models of water and steam heaters, differing in heating surface area, are on sale:

• CM - the smallest with one row of pipes;
• M - small with two rows of pipes;
• WITH - average with pipes in 3 rows;
• B - large, having 4 rows of pipes.

Water heaters during operation withstand large temperature fluctuations - 70-110⁰. For the air heater of this type to work well, the water circulating in the system must be heated to a maximum of 180⁰. In the warm season, the air heater can act as a fan.

Design of different types of heaters

The heating water heater consists of a body made of metal, a heat exchanger placed in it in the form of a series of tubes and a fan.At the end of the unit there are inlet pipes through which it is connected to the boiler or centralized heating system.

Typically, the fan is located on the back of the appliance. Its task is to drive air through the heat exchanger.

After heating, through the grill located on the front of the heater, air flows back into the room.

Most often, the case is made in the form of a rectangle, but there are models designed for ventilation ducts of circular cross section. Two or three-way valves are installed on the supply line to adjust the power of the unit.

The fan blows through the tubes located in the heater case. The heated water from the heating system moves through the tubes, and the fan distributes evenly warm air throughout the room

The heaters differ in the method of installation - they are ceiling and wall. Models of the first type are placed behind the false ceiling, only the grille peeps out of it. Wall mounted appliances are more popular.

View # 1 - smooth tube heaters

Smooth-tube design consists of heating elements in the form of hollow thin tubes with a diameter of 20 to 32 mm, located at a distance of 0.5 cm relative to each other. A coolant circulates through them. The air, washing the heated surfaces of the tubes, is heated by convective heat exchange.

The tubes in the air heater are staggered or corridor. Their ends are welded into the collectors - upper and lower. The coolant enters the junction box through the inlet pipe, then, passing through the pipes and heating them, leaves the outlet pipe in the form of condensate or chilled water.

More stable heat transfer is provided by devices with a checkerboard arrangement of tubes, but the resistance to air flow here is higher. It is necessary to perform the calculation of the power of the unit in order to know the real capabilities of the device.

There are certain requirements for air - there should be no fibers, suspended particles, sticky substances. Permissible dust content is less than 0.5 mg / mᶾ. The inlet temperature is at least 20⁰.

One-way and 3-way heaters. 1 - inlet pipe through which the coolant enters, 2 - distribution box, 3 - pipe, 4 - outlet pipe, 5 - partition

Thermotechnical characteristics of smooth-tube heaters are not very high. Their use is advisable when significant air flow and its heating to a high temperature are not required.

View # 2 - finned air heaters

Pipes of ribbed devices have a finned surface, therefore, the heat transfer from them is greater. With a smaller number of pipes, their thermal performance is higher than that of smooth-tube air heaters.

The composition of plate heaters includes tubes with plates mounted on them - rectangular or round.

The first type of plates are mounted on a group of pipes. The coolant passes into the junction box of the device through the fitting, heats the air passing at a considerable speed through the channels of small diameter, and then leaves the collection box through the fitting.

Heaters of this type are compact, easy to maintain and install.

Single-pass plate devices are designated: KFB, KFS, KVB, STD3009V, KZPP, K4PP, and multi-way - KVB, K4VP, KZVP, KVS, KMS, STDZOYUG, KMB. The middle model is designated KFS, and the large - KSE.

A steel corrugated tape 1 cm wide and 0.4 mm thick is wound on the tubes of these heaters. The heat carrier for them can be both steam and water.

Water heaters can not be connected with metal-plastic or polymer pipes. they are not designed for high heat carrier temperature. Need steel pipes and better galvanized to eliminate corrosion

The first is equipped with three rows of tubes, and the second four. The middle model's plates have a thickness of 0.5 mm and dimensions of 11.7 x 13.6 cm.Plates of a large model of the same thickness and width are distinguished by a longer length - 17.5 cm.

The plates are at a distance of 0.5 cm from each other and have a zigzag arrangement, whereas in the middle-view models, the plates are arranged according to the corridor principle.

Air heaters with the marking STD have 5 numbers (5, 7, 8, 9, 14). Steam is the heat carrier in the STD4009B air heaters, and water is the heat carrier in the STD3010G. Installation of the first is performed with the vertical orientation of the tubes, the second - with the horizontal.

View # 3 - bimetal fin heaters with fins

In heating systems with air heating, models of bimetallic heaters KP3-SK, KP4-SK, KSk - 3 and 4 are often used with a special type of fins - spiral-rolling. The heat carrier for KP3-SK, KP4-SK air heaters is hot water with a maximum pressure of 1.2 MPa and a maximum temperature of 180⁰.

For the other two air heaters to work, steam is required with the same working pressure as for the first, but with a slightly higher temperature - 190⁰. Manufacturers are required to carry out acceptance tests. Test devices and for tightness.

The heat exchanger of the KSK air heater consists of tubes made of steel and having aluminum fins. Connect their tube sheets

There are 2 lines of bimetallic heaters - KSK3, KPZ, with 3 rows of tubes, belong to the middle, and KSK4, KP4 with 4 rows of tubes - to large models. The components of these devices are bimetallic heat exchange elements, side shields, tube grilles, covers with partitions.

The heat exchange element consists of 2 tubes - an inner diameter of 1.6 cm, made of steel and aluminum outer with fins mounted on it. The transverse interval between the heat transfer tubes is 4.15 cm and the longitudinal is 3.6 cm.

Rules for calculation and selection of a suitable unit

In designing a heating system with one or a group of heaters, as well as in performing calculations, a number of rules should be observed. Let's consider them in more detail in the photo selection below.

Calculation of water heater

To calculate the power of a water or steam heater, the following initial parameters are needed:

1. System performance or in other words - the amount of air distilled per hour. The unit of measurement of volumetric flow rate is mᶾ / h, mass kg / h. The symbol is L.
2. Initial or external temperature - tul.
3. The final air temperature is tcon.
4. Density and heat capacity of air at a certain temperature - the data is taken from the tables.

First, the cross-sectional area is calculated from the front of the air-heating device. Having learned this value, get the preliminary dimensions of the unit with a margin.

For the calculation using the formula:

AF = Lρ / 3600 (ϑρ),

Where L - air volumetric flow rate or capacity in m³ / h, ρ - outside air density measured in kg / m³ ϑρ - mass air velocity in the calculated section, measured in kg / (cm²).

Having received this parameter, for further calculations take the typical size of the heater, the closest in size. With a large total value of the area, several identical units are installed in parallel, the area of ​​which in total is equal to the obtained value.

Heaters are not only heat exchangers, but also cold water air coolers, which are much less popular

To determine the required power for heating a specific volume of air, you need to find out the total consumption of heated air in kg per 1 hour according to the formula:

G = L x p,

Where R - air density at medium temperature. It is determined by summing the temperatures at the inlet and outlet of the unit, then divided by 2. The density indicators are taken from the table.

From this table, you can take data on the density and specific heat of air at a certain temperature to calculate the power of the device

Now you can calculate the heat consumption for heating the air for which the following formula is used:

Q (W) = G x c x (t con. - t beg.),

Where G - mass air flow in kg / h. When calculating, the specific heat of the air measured in J / (kg x K) is also taken into account. It depends on the temperature of the incoming air, and its values ​​are in the table above. The temperature at the inlet and outlet of the device is indicated t beg. and t con. respectively.

Suppose you need to choose a heater with a capacity of 10,000 mᶾ / h so that it heats the air to 20⁰ at an outside temperature of -30⁰. The coolant is water having a temperature at the inlet to the unit of 95⁰ and 50⁰ at the outlet.

Mass flow rate: G = 10,000 mᶾ / h. х 1,318 kg / mᶾ = 13,180 kg / h.

Density Value: ρ = (-30 + 20) = -10, dividing this result in half received -5. From the table, the density corresponding to the average temperature was chosen.

Substituting the result in the formula, get the heat consumption: Q = 13 180/3600 x 1013 x 20 - (-30) = 185 435 W. Here 1013 is the specific heat selected from the table at a temperature of –30⁰ in J / (kg x K). To the calculated value of the power of the heater add from 10 to 15% of the reserve.

The reason is that tabular parameters often differ from the real ones in the direction of reduction, and the thermal performance of the unit, due to clogging of the tubes, decreases with time. Exceeding the margin is undesirable.

With a significant increase in the heating surface, hypothermia can occur, and even thawing in large frosts.

In the steam heater, the coolant is supplied from above, and the water resulting from the condensation of the exhaust steam is discharged from below. In the photo - a diagram of the strapping of a steam heater

The power of steam heaters is calculated in the same way as water heaters. Only the coolant calculation formula differs:

G = q / r,

Where r - specific heat released during steam condensation, measured in kJ / kg.

Calculation of an electric heater

Manufacturers in the catalogs of electric heaters often indicate the installed power and air flow, which greatly simplifies the choice. The main thing is that the parameters should not be smaller than those indicated in the passport otherwise it will quickly fail.

The design of the air heater includes several special electric heating elements, the area of ​​which is increased due to the mounting of fins on them.

Power devices can be very large, sometimes it is hundreds of kilowatts. Up to 3.5 kW, the air heater can be powered from a 220 V outlet, and with a voltage above this, it is necessary to connect the hotel cable directly to the shield. If there is a need to use a heater with a power above 7 kW, a power supply of 380 V.

These devices have small dimensions and weight, they are completely autonomous, they do not need the presence of centralized hot water or steam.

A significant minus is the low power insufficient to apply them over large areas.The second drawback is the high energy consumption.

From the calculation of the heater, it follows that the result of using the device is a tangible saving of energy resources. Sometimes this unit is combined with a recuperator and then air intake does not take place outside, but from the premises

To find out what current the heater uses, you can use the formula:

I = P / U,

Where P - power U - supply voltage.

With a single-phase connection, the heater U is taken equal to 220 V. With a 3-phase - 660 V.

The temperature to which a heater of a certain power heats the air mass is determined by the formula:

T = 2.98 x P / L,

Where L - system performance. The optimal values ​​of the air heater power for the house are from 1 to 5 kW, and for offices - from 5 to 50 kW.

Conclusions and useful video on the topic

What air density to take in the calculation is described in this video:

Video about how the heater works in the heating system:

When choosing a certain type of heater, you should proceed from considerations of expediency and operational characteristics of the house.

For small areas, an electric heater will be a good purchase, and for heating a large house, it is better to choose another option. In any case, do not do without preliminary calculation.

Are you well versed in choosing and calculating a heater? Perhaps you want to share useful recommendations on choosing an air heater or point out an error or inaccuracy in the calculations in the material discussed above? Leave your comment under this article - your opinion may be useful to people who choose the right air heater for their home.