Heaters have high performance, so even very large rooms can be heated with their help in a fairly short time. Many models of these devices based on different coolants are on sale.
To choose the best option, you need to calculate a heater, which you can perform either manually or using the online calculator. We will help you deal with the issue of calculations - in this article we give an example of the calculations that will be needed when choosing a suitable 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.
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Air heating equipment
Air conditioning system with air heater
Air heating with air heater
Fast heating of large areas
For many homeowners, the disadvantage is that the installation of the system is only possible simultaneously with the construction of the house itself and then its further modernization is impossible.
A minus is such a nuance as the mandatory availability of backup power and the need for regular maintenance.
The heater is easy to install and operate, affordable, but most importantly, it is an effective device for heating the room. Pictured is 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 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 when there is a heat source.
The most popular 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 according to the geometry of the ribs are lamellar and spiral-wound.
The performance of 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;
- FROM - average with pipes in 3 rows;
- B - large, with 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.
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Water heater in the production room
Steam heater on a glazed terrace
Compact electric air heater
Spiral-wound steam model
Design of different types of heaters
The heating water heater consists of a housing 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, the air flows back into the room.
Most often, the case is made in the shape 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 body. 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 peeks out of it. Wall mounted appliances are more popular.
View # 1 - smooth tube heaters
The 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. Air, washing the heated surfaces of the tubes, heats up due to 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 carry out 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 coolant enters, 2 - distribution box, 3 - pipe, 4 - outlet pipe, 5 - partition
The thermal 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 onto 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. Medium model plates have a thickness of 0.5 mm and dimensions 11.7 x 13.6 cm. Plates of a large model of the same thickness and width have a longer length - 17.5 cm.
The plates are located 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.
STD heaters have 5 numbers (5, 7, 8, 9, 14). Steam is the heat carrier in the STD4009B 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 - finned bimetal heaters
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 KSK air heater heat exchanger consists of tubes made of steel and having aluminum fins. Connect their tube sheets
There are 2 lines of bimetallic heaters - KSK3, KPZ, which have 3 rows of tubes, are medium, and KSK4, KP4 with 4 rows of tubes are 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.
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Parallel connection of a group of heaters
Cold air heaters
Instrument control valves
Finned Steam Air Heater
Calculation of water heater
To calculate the power of a water or steam heater, the following initial parameters are needed:
- System performance or in other words - the amount of air distilled per hour. The unit of measurement of volumetric flow is mᶾ / h, mass kg / h. The symbol is L.
- Initial or external temperature - tul.
- The final air temperature is tcon.
- Density and heat capacity of air at a certain temperature - 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 - air density outside 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.
Not only heat exchangers are called heaters, but 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 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 unit inlet 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 are not smaller than those specified 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.
The power of 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 air 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.
Video about how the heater works in the heating system:
Choosing a certain type of heater, it is necessary to 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.