In the context of ever-increasing energy prices, the issues of saving energy resources come to the fore in almost all sectors of the national economy. The energy spent on heating the premises of both residential and industrial facilities is no exception.
Building Norms and Rules strictly regulate the parameters of air exchange for all types of premises, while most of the heat energy is removed through the ventilation system along with the exhaust air. Partially offset heat loss allow the so-called heat recuperators, which are part of the supply and exhaust ventilation. Unfortunately, the efficiency of most recovery plants is far from ideal, and heat losses must somehow be replenished to maintain optimal temperature regime.
One of effective ways creating and maintaining optimal microclimatic parameters in the room is an additional supply ventilation system with duct heaters.
Story
Idea duct heater is by no means new. The first duct (fire-air) heater was designed and installed according to the project of Ammosov N.A. in 1835 in St. Petersburg and was used to heat the halls of the Imperial Academy of Arts. In terms of efficiency, one "Ammos" stove was equated to 30 "coils" (prototypes of modern centralized heating). Subsequently, by decree of Emperor Nicholas I, fire-air furnaces were used to heat the Winter Palace (55 large furnaces and 29 small ones). But, despite the high efficiency for that time, the Ammos furnace had significant drawbacks:
- the fire-air heating system emitted a constant hum;
- during thunderstorms drops atmospheric pressure provoked a crack in ventilation ducts;
- the ventilation system, through which hot air was supplied, overheated too much, which negatively affected the interior of the premises, in particular, the paintings on the walls and paintings quickly fell into disrepair.
It was the last drawback that forced us to abandon the use of the prototype of the duct heater. The last Ammos furnace was dismantled in 1912. And although the implementation of the Ammos heater did not justify the hopes placed on it, it is completely from the idea supply ventilation heated air was not abandoned, and today duct heaters and heated supply units are widely used in residential, domestic and industrial premises.
Electric heaters
Electric duct heater is usually designed to work with air in the temperature range from 0 to +30°C at its relative humidity up to 80%. Maximum working temperature air environment at the outlet of the heater is +40°C. The body of the device and the main elements are made of galvanized or of stainless steel. Protection class according to international standard- IP43. At the entrance supply air it is recommended to install mechanical filters in the heater, the air must not contain dust, fibrous substances or grease.
As a rule, electric heaters do not have their own control and automation system, but are connected to common system ventilation control. The program of the ventilation system controller should provide for automatic shutdown of the heater (by timer or air temperature), as well as an emergency stop in case of overheating.
The choice of the duct heater is made according to the power. Simplified, the required power can be calculated by the formula:
P \u003d 0.34 * Q * t
where Q- ventilation capacity, m3/hour;
t- temperature difference at the inlet and outlet of the ventilation duct.
By installing a heat exchanger in the ventilation system, you can save on the power of the heater, which means lower operating costs.
Water heaters
Water heaters are fundamentally different from electric ones and are mainly intended for installation in ventilation systems. rectangular section, although there is the lineup and for round ducts.
The design and principle of operation of the water duct heater are as follows. In a case made of stainless or galvanized steel, the links of a copper hollow “serpentine” and aluminum heat-releasing plates are located in a checkerboard pattern. Heated water or a water-glycol solution circulates inside the copper circuit (if the heater is installed outside the building and there is a risk of it freezing in winter period time). Thermal energy the circulating liquid is transferred to aluminum plates (which are needed to increase the area of heat transfer to the passing air), and they, in turn, warm up the air flows of the supply ventilation.
The use of a water heater (as well as an electric one) implies the presence of an air filter for ventilation in the system. The supply air must not contain abrasive particles, fibrous or sticky substances, chemically aggressive impurities, etc. The operating temperature range is +5…+60°C at 80% humidity. For effective work heater, the pressure in the air ducts of the ventilation system must be at least 1.5 MPa.
As a rule, water heaters do not have their own capacity control system, therefore, in general, control is carried out through one of the following additional external devices:
- a throttle (overflow) valve that regulates the rate of liquid circulation in the coil;
- three-way valve on the principle of "open-closed";
- a mixing unit that allows you to steplessly adjust the ratio of the liquid entering the radiator and returning it.
The air supplied to the buildings must meet the specified characteristics. To do this, the air is processed in such ways as filtering, heating, cooling, increasing the moisture content. Air heating is provided by a heater for supply ventilation. To obtain an air flow of a given temperature regime, it is necessary to make a calculation and selection of a heater.
Types of heaters
Heat exchangers are available in various modifications and for various types coolants. The heat carriers are often steam or water. Electric heaters are also common.
Water heaters
Hot water heaters are used in supply ventilation systems of round or rectangular cross section and are mounted in ventilation ducts. Water heaters can be two- or three-row. The air passing through the water heat exchanger must not contain solid, fibrous or sticky substances.
Steam heaters
Compared to water devices, steam devices are used infrequently - usually in industrial enterprises where there is steam production for technological needs.
Note! Sometimes there is a large-scale consumption of air by supply ventilation, and at the same time, the installation of a heat exchanger with a significant flow area is not possible. In such cases, a whole series of smaller devices is installed.
The following information is required for the calculation:
- The volume or mass of supply air to be heated. Can calculate volume flow (cbm/h) or mass flow (kg/h).
- The initial air temperature, which is equal to the air temperature outside.
- The target temperature to which the supply air must be heated before it is supplied to the premises.
- The temperature regime of the coolant, which is used to heat the air.
Instruction for calculation
When calculating the air heater used for supply ventilation, it is necessary to calculate the heating surface area and the required power. You need to start by calculating the cross-sectional area of the heat exchanger along the front:
Aph = Lρ / 3600 (ϑρ), here:
- L – supply air consumption by volume, m³/h;
- ρ is the value of the density of the outside air, kg/m³;
- ϑρ is the mass velocity of air masses in the design section, kg/(s m²).
The front cross-section indicator is necessary for awareness of the size of the heat exchanger. Next, you need to use the nearest larger device for the calculation. If, according to the calculations, the cross-sectional area is too large, it will be necessary to stop the choice on several parallel-mounted heaters in order to obtain the required area.
The indicator of the real mass velocity must be calculated, taking into account the real area along the front of the selected heaters:
Q = 0.278Gc (tp – tn), where:
- Q is the amount of heat, W;
- G is the mass flow rate of heated air, kg/h;
- c - value specific heat air mixture is taken equal to 1.005 kJ/kg °C;
- tp – inflow temperature, °C;
- tn - initial air temperature from the street.
Since the installation of the fan in the supply ventilation is carried out before the heat exchanger, the mass flow G is calculated taking into account the density of the air outside.
Otherwise, the density is determined by the temperature of the air after it is heated. The calculated amount of heat allows you to calculate the cost of the coolant in the heater (kg / h) for the transfer of this heat to the passed air:
Gw = Q / cw (tg - t0)
In this formula:
- cw is the value of heat capacity for water, kJ/kg °C;
- tg is the design water temperature in the supply pipeline, °С;
- t0 is the calculated water temperature in return pipeline, °С.
The specific heat capacity of water is a reference indicator. The temperature characteristics of the coolant used for calculations are taken based on real indicators under existing conditions. If there is a boiler room or connection to a central heating network, the characteristics of their coolants will be needed for the calculation. Having information about the flow rate of the coolant, it is possible to calculate the speed (m/s) of its movement through the heater pipes:
w = Gw / 3600 ρwAmp, here:
- Amp is the cross-sectional area of the heat exchanger tubes, m²;
- ρw is the density of water at the average temperature of the coolant in the heater, °C.
The calculation of the average temperature of the water circulating through the heater is carried out according to the formula:
The speed calculated according to the above formula will be valid for a set of series-connected heat exchangers. If parallel piping is made, the cross-sectional area of the pipes will more than double. In turn, this will cause a decrease in the speed of movement of the coolant. Such a decrease will not bring an increase in productivity, but will cause a decrease in the temperature in the return pipeline. In order not to encounter an excessive increase in the hydraulic resistance of the heat exchanger, it is not necessary to take the coolant movement speed to be more than 0.2 m/s.
Calculation of the heating surface
The heat transfer coefficient for the surface heater is determined according to the reference books for the calculated indicators of the speed of the coolant and the mass flow rate of air. Next, the heating surface area (sq. m) of the heat exchanger is determined using the formula:
Amp = 1.2Q / K (tav.t - tav.v), where:
- K is the coefficient of heat transfer by the heater, W/(m°C);
- tav.t is the value of the average coolant temperature, °C;
- tav.v - the value of the average temperature of the supply air for ventilation, ° С;
- the number 1.2 - the required safety factor, takes into account the further cooling of the air masses in the air ducts.
The average air temperature is calculated by the formula:
AT specified option if the heating surface of one heat exchanger is not enough to heat the air, the number of heaters of one type must be calculated as follows:
Nmp = Amp / Ak, here Ak
The final result is the value obtained using the formula rounded up.
Qfact \u003d K (tav.t - tav.v) Nfact Ak.
here Nfact is taken with the rounded value Nmp, the other parameters are the same as in the previous formulas.
It will be necessary to take into account the additional power reserve of the heat exchanger - 12-15%. There are explanations for this approach:
- the true indicators of the heat transfer coefficient of the heater almost never coincide with the data in the tables, and more often in the downward direction;
- the performance of the device decreases with the increase in the life of the equipment and the formation of blockages in the pipes.
However, it is not desirable to exceed the power reserve, since a significant expansion of the heated surface leads to their excessive cooling, and during low temperatures air - to defrosting. Some manufacturers guarantee the accuracy of the specified parameters.. In this case, the power reserve can be set within 5%. In order not to encounter defrosting, the speed of movement of the coolant should be set at - 0.12 m/s. The piping of the heat exchanger may include a circulation pump system that maintains a balance of performance. Some models of heat exchangers are available with a built-in bypass valve to protect against defrosting.
Features of the calculation for steam heaters
If the heat carrier is steam, the heater is selected and calculated in the same way, but the heat carrier flow rate during air heating is calculated as follows:
In this formula, the parameter r (kJ / kg) - specific heat released during the condensation of water vapor. The speed of movement of water vapor in the tubes of the heater is not calculated.
Strapping methods
The binding knot is a special reinforcing cage to regulate the flow of hot water. Binding is carried out by one of two methods:
- two-way valves - networks where the return flow of water is not controlled;
- three-way valves - when using a boiler or boiler room.
The installation of the piping unit is necessary, as it makes it possible to control the performance of the heater and protects it from freezing.
Choosing an electric heater
If it is decided to use an electric heater in the supply ventilation system, then the device is selected according to the required air flow, as well as its inlet and outlet temperatures. If the manufacturer of the electric heater prescribes in the documentation the consumption of air and electrical power- the choice of equipment is simple. However, here it is necessary to maintain the minimum amount of air inflow allowed by the plant. Ignoring this requirement leads to damage to the heating elements of the electric heater. If the proposed acquisition includes such operating mode, it is necessary to use stepwise regulation of heating elements. The size of the power reserve for the electric heater is up to 10%.
For premises small area it is better to opt for electric heaters, since they are not difficult to operate and easy to install. For large buildings the best choice there will be the installation of water heaters, since they are more economical in comparison with electric heaters.
Expert opinion
Heating and ventilation engineer RSV
Fedorov Maxim Olegovich
Water heaters (over modern name- water air heaters) are a unit of a fan and a heat exchanger that uses hot (superheated) water as a coolant. They are used for efficient and economical space heating in industrial, public and administrative buildings. The efficiency, economy and high degree of safety of water heaters have made them the main method of heating in these categories of premises.
All available types of heating devices for ventilation are inferior or, at best, approaching in their technical characteristics to water appliances.
The main area of use for heaters is buildings or rooms in which, for various reasons, it is not possible to install radiators. For example, with large volumes of premises, radiators simply cannot cope, but, on the contrary, will be the most efficient. Most rational arrangement of water heaters is the supply ventilation line, since it is impractical to heat the output stream.
In addition to heating, active supply air heating is applied used to save the already existing heat in the room. If a fresh jet is transported along a long line of air ducts, then condensate will accumulate on them without air heating, which will create a lot of operational problems. To solve all these issues, water heaters are used.
Water air heater: principle of operation and design
The most common type are . They have replaced plate structures, which are less successful in maintenance and require periodic maintenance in a rather laborious form.
Heater
The main element of the heater is a steel tube, on the outer surface which is coated with aluminum fins. These fins serve as a heat-releasing surface, the total area of which is quite large. At the same time, full outside diameter tubes (including fins) is 37 mm, and the tube itself is 16 mm, so the depth of the fins is relatively small and does not cause the danger of filling with dirt, dust or other foreign materials that reduce heat transfer. The distance between the fins is 2.8 mm, which allows you to keep warm even with intense airflow, making the device highly efficient.
To solve the problems of air exchange in private houses and industrial buildings along with fans, devices are used that heat or cool the air that comes from the street. This helps to improve the characteristics of the microclimate inside the room, increase the level of comfort.
One of the economical and available devices is a water heater for supply ventilation, more familiar to residents of the northern regions. From our material you will learn about the principles of work and design features this type of equipment. We will also talk in detail about several popular models of air heaters for ventilation.
We note right away that the devices used to heat air in ventilation and air heating systems can work not only on water.
There are four types of heaters that differ in the way the coolant is heated:
- fire;
- water;
- steam;
- electrical.
Water are the most popular due to the budget cost and minimal cost for service. The only difficulty concerns the installation, in which it is required to bring water supply pipes.
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For this reason, it is impossible to install the device in urban apartments, but in large buildings (for example, in warehouses, garages, establishments Catering) system with correct strapping heater is quite efficient.
Installation for heating air in large areas, consisting of a water heater and a radial fan. Serves to create thermal curtains and air ventilation in office buildings, shops, workshops
A distinctive feature of steam appliances is the high speed of reaching the required temperature. They are relevant for industrial enterprises, where it is easy to ensure the installation and maintenance of steam pipelines, their use is impractical for private housing.
If you need a quick installation, not complicated by the supply of communications, use models of electric heaters for. A protected power point is sufficient for their operation. There is no coolant as such at all,. Like any electrical appliances, they are disadvantageous with material point vision.
Water heating equipment used in ventilation systems is the most economical and productive option that can quickly heat a large space at minimal cost.
Principle of operation and design features
Universal water-powered devices are installed in places with a well-established heat supply system. Simple but quite effective design decision allows you to heat the air in the range from + 70 ° C to + 100 ° C and is relevant for hangars, gyms, supermarkets, greenhouses, warehouses, large pavilions - that is, large rooms that require additional heating.
An example of using a VOLCANO air heater in a greenhouse. Heating is provided by distribution warm air(water temperature - +90º C) with a fan and adjustable shutters
If you have ever used a household thermal heater, you will easily understand the principle of operation of a water device. It also heats the air, but the kit plays the role of an electric spiral enclosed in a small case. metal pipes ok, through which the heated coolant circulates.
The heating process is as follows:
- hot water heated to desired temperature(on average from + 80 ° С to + 180 ° С), from the heating pipes it enters the heat exchanger, consisting of small aluminum, steel, bimetallic or copper tubes;
- tubes heat the air passing through the device;
- the built-in fan distributes heated air throughout the room and stimulates its movement in the opposite direction - to the device.
It is not necessary to specially heat up the water, since it is part of the heating system and therefore significant cost savings.
The designations for the four presented piping schemes are common: 1 - ball valve; 2 - filter; 3 - three-way valve; 4 – circulation pump; 5 - check valve; 6 - thermomanometer
In versions 1 and 3, the nodes are connected in a rigid way, in versions 2 and 4 - using flexible metal hoses.
Adjustment of the heating process
To control the thermal power of air heaters, mixing units with are used. Thanks to the mixing principle, you can significantly reduce the cost of heating the room.
The three-way valve allows you to reduce the temperature of the coolant by mixing in hot water, entering the heater, a certain amount of cooled liquid released from the heat exchanger.
Installation increases the efficiency of the system. It is preferable to mount it at the outlet, as the chilled water (or Alternative option– glycol solution) prolongs the life of the device.
There are several important conditions for the operation of mixing equipment:
- maximum proximity to the heater;
- availability for maintenance;
- filtered, without chemical inclusions coolant;
- the air temperature in the room is above 0 °C.
The technical characteristics of the devices may vary, but on average the recommended coolant temperature is from + 2 °С to + 150 °С. For regular monitoring of performance, it is recommended to mount two thermomanometers near the heat exchanger.
A sample of a mixing unit for a water heater. In fact, this is one of the strapping options with the ability to adjust the temperature and control its change.
The adjustment of the three-way valve is carried out with the help of an actuator and a controller. Measuring instruments allow you to set the required temperature and change the pressure as accurately as possible.
Features of installation and connection
A team of specialists is invited to install heaters in production workshops or at other industrial facilities. Household devices can be connected independently if you clearly follow the instructions and have the skills to work with electrical and heating appliances.
For those who have equipped the house with their own hands, the installation of an air heating unit will seem like child's play.
Household models are small in volume and relatively light in weight, but before hanging them on a wall (or ceiling), you should check the strength of the base. Concrete and brick walls, moderately suitable - wooden, the weakest - drywall.
First of all, a metal frame is fixed - a bracket with holes for fixing the case. For some manufacturers, the frame is called the mounting console.
Place of installation duct heater for supply ventilation in the air exchange system. If it is possible for the temperature to drop below normal, a frost protection thermostat must be installed.
Suspend the body of the heater and alternately connect the pipes with the kit stop valves or mixing unit, which can be partially installed even before the installation of the device.
Insertion into the heating system is carried out in two ways: through the use connection fittings(couplings with gaskets) or welding of metal pipes. The second method is considered the most reliable, but it is not possible with a flexible connection.
One of the weakest areas is the heat exchanger pipes, which need to be ensured stability. If there is a risk of changing the position of the device, it is better to replace rigid tubes with flexible elements. In any case, stress on the nozzles should be excluded. To ensure the isolation of the system and prevent leaks, the joints are treated with a sealant.
If the water heater is installed on a permanent basis, it is connected with rigid pipes. If transfer or displacement is planned, it is better to use a flexible eyeliner
Before the testing process, it is necessary to remove air from the channels, check the operation of the valves and louvers.
Rules of operation and the possibility of repair
In order for the equipment to work flawlessly and fully perform its functions, the following rules should be observed:
- monitor the composition of the air in the room (compliance requirements can be found in GOST 12.1.005-88);
- to carry out installation strictly according to the instructions and based on the recommendations of the manufacturer;
- do not raise the coolant temperature above + 190 °С;
- comply with pressure standards - about 1.2 MPa;
- after cooling the room, heat up smoothly, by about 30 ° C per hour;
- make sure that the air temperature does not fall below 0 ° C, otherwise the heat exchanger tubes will burst.
If the heater is installed in a room with high humidity, the degree of dust and moisture protection should be IP66 or higher.
We do not recommend making repairs on your own, since one breakdown most often leads to the next, but in the end you just have to replace some parts. Better to contact service center and entrust the work to professionals. In addition, you should not ignore before buying, otherwise there is a chance to waste money.
Brief overview of modern models
To get an idea of the brands and models of water heaters, consider several devices from different manufacturers.
No. 1 - heaters KSK
Heaters KSK-3, produced at the enterprise CJSC T.S.T.
Model range of KSK water heaters domestic production includes 2/3/4 row devices differing in performance and dimensions
Specifications:
- coolant temperature at the inlet (outlet) - +150 °С (+70 °С);
- air temperature at the inlet - from -20 °С;
- operating pressure- 1.2 MPa;
- maximum temperature - +190 ° С;
- service life - 11 years;
- working resource - 13 200 hours.
The outer parts are made of carbon steel, heating elements- from aluminium.
No. 2 - Volcano fan heaters
Water fan heater Volcano mini is a compact device of the Polish brand Volcano, which is distinguished by its practicality and ergonomic design. Adjustment of the direction of the air flow is carried out using controlled shutters.
One Volcano mini fan heater is capable of producing as much heat as a dozen conventional ones. bimetallic radiators made up of ten sections
Specifications:
- power within the limits - 3-20 kW;
- maximum productivity - 2000 m³ / h;
- type of heat exchanger - two-row;
- protection class - IP 44;
- maximum coolant temperature - 120 °C;
- maximum working pressure - 1.6 MPa;
- internal volume of the heat exchanger - 1.12 l;
- guide blinds.
Volcano water fan heaters are designed to heat the air in domestic and industrial premises with water coolant.
No. 3 - Galletti AREO heaters
Italian-made Galletti AREO heater.
Water heaters of the Galletti AREO brand are able to work both for heating the processed premises and for cooling the space in hot weather
Models are equipped with a fan, a copper-aluminum heat exchanger and drainage tray.
Specifications:
- power in heating mode - from 8 kW to 130 kW;
- power in cooling mode - from 3 kW to 40 kW;
- water temperature – + 7°C +95°C;
- air temperature – from 10°C to + 40°C;
- operating pressure - 10 bar;
- number of fan speeds - 2/3;
- Class electrical safety– IP 55;
- motor protection.
In addition to the devices of the listed brands, on the market of air heaters and water heaters, you can find models of the following brands: Teplomash, 2VV, Fraccaro, Yahtec, Tecnoclima, Kroll, Pakole, Innovent, Remko, Zilon.
Conclusions and useful video on the topic
Overview of the Volkano brand water heater:
Details about technical specifications Ballu BHP-W-60 models:
Simple design and affordable self-fulfillment installation - the reasons why water-type heaters are chosen. Right choice the device and competent installation of the strapping will increase the efficiency of ventilation and improve the heating system of industrial and residential premises.
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