The air supplied to buildings must meet the specified characteristics. To do this, the air is processed by such methods as filtering, heating, cooling, and increasing the moisture content. Air heating is provided by a heater for supply ventilation. For getting air flow given temperature regime, it is necessary to make a calculation and select a heater.
Types of heaters
Heat exchangers are available in various modifications and for various types coolants. The coolants are often steam or water. Electric heaters are also common.
Water heaters
Hot water heaters are used in round or round supply ventilation systems. rectangular 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 any solid, fibrous or sticky substances.
Steam heaters
Compared to water devices, steam devices are used infrequently, usually in industrial enterprises where steam is produced for technological needs.
Note! Sometimes there is a large-scale consumption of air by supply ventilation, and in this case 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.
To carry out the calculation, the following data is required:
- Volume or mass of supply air to be heated. It can calculate volume flow (cubic m/h) or mass flow (kg/h).
- The initial air temperature, which is equal to the outside air temperature.
- The target temperature to which the supply air must be heated before being supplied to the premises.
- The temperature regime of the coolant, which is used to heat the air.
Instructions for calculation
When calculating the 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:
Af = Lρ / 3600 (ϑρ), here:
- L – supply air flow rate by volume, m³/h;
- ρ – value of the density of external air, kg/m³;
- ϑρ – mass velocity of air masses in the design section, kg/(s m²).
The frontal 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 calculations, the cross-sectional area is too large, you will need to opt for several heaters mounted in parallel to obtain the required area.
The real mass velocity indicator must be calculated taking into account the actual front area of the selected heaters:
Q = 0.278Gc (tп – tн), where:
- Q – amount of heat, W;
- G – mass flow of heated air, kg/h;
- c – value specific heat capacity air mixture is assumed to be 1.005 kJ/kg °C;
- tп – inflow temperature, °С;
- tн – initial air temperature from the street.
Since the fan is installed in the supply ventilation before the heat exchanger, the mass flow G is calculated taking into account the air density outside.
Otherwise, the density is determined by the temperature of the air after it is heated. The calculated amount of heat allows us to calculate the coolant costs in the heater (kg/h) to transfer this heat to the air being passed through:
Gw = Q / cw (tg – t0)
In this formula:
- cw – heat capacity value for water, kJ/kg °C;
- tg – design temperature of water in the supply pipeline, °C;
- t0 – design water temperature in return pipeline, °C.
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 calculation. Having information about the coolant flow rate, you can calculate the speed (m/s) of its movement through the heater pipes:
w = Gw / 3600 ρwAmp, here:
- Amp – cross-sectional area of the heat exchanger tubes, m²;
- ρw – density of water at the average temperature of the coolant in the heater, °C.
Calculation of the average temperature of water circulating through the heater is carried out using the formula:
The speed calculated using the above formula will be valid for a set of heat exchangers connected in series. If parallel piping is performed, 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 reduction will not bring an increase in productivity, but will cause a decrease in 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 accept a coolant movement speed of more than 0.2 m/s.
Heating surface calculation
The heat transfer coefficient for the surface heater is determined using reference books for calculated indicators of the coolant movement speed and the mass air flow rate. 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 – heat transfer coefficient by the heater, W/(m°C);
- tav.t – value of the average coolant temperature, °C;
- tav.v – value of the average temperature of supply air for ventilation, °C;
- the number 1.2 is the required safety factor, taking into account further cooling of the air masses in the air ducts.
The average air temperature is calculated using the formula:
IN the specified option, if the heating surface of one heat exchanger is not enough to warm the air, the number of air 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 = K (tav.t – tav.v) Nfact Ak.
here Nfact is taken with the rounded value Nmp, the remaining parameters are 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 thermal energy transfer coefficient of the heater almost never coincide with the data in the tables, and more often in the direction of decrease;
- The performance of the device decreases with increasing service life of the equipment and the formation of pipe blockages.
However, it is not advisable 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 provide a guarantee on the accuracy of the specified parameters. In this case, the power reserve can be set within 5%. To avoid defrosting, the coolant movement speed should be set at - 0.12 m/s. The heat exchanger piping may include a circulation pump system that maintains a balance of performance. Some heat exchanger models are available with a built-in bypass valve that protects against defrosting.
Calculation features for steam heaters
If the coolant is steam, the selection and calculation of the heater is carried out in the same way, but the coolant flow rate when heating the air is calculated as follows:
In this formula, the parameter r (kJ/kg) – specific heat, released during condensation of water vapor. The speed of movement of water vapor in the heater tubes is not calculated.
Strapping methods
The tying knot is a special reinforcement cage to regulate the flow of hot water. Tying is carried out using 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.
Installation of the piping unit is necessary, as it makes it possible to control the performance of the heater and protects it from freezing.
Selecting an electric heater
If it is decided to use an electric heater in the supply ventilation system, then the device is selected based on the required air flow, as well as its inlet and outlet temperatures. If the manufacturer of the electric heater specifies 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 volume of air flow allowed by the factory. Ignoring this requirement leads to damage to the heating elements of the electric heater. If the proposed acquisition involves such operating mode, you need to use step control of the heating elements. The power reserve for the electric heater is up to 10%.
For indoors small area It is better to opt for electric heaters, since they are not difficult to operate and easy to install. For large buildings best choice There will be installation of water heaters, since in comparison with electric heaters they are more economical.
To solve air exchange issues in private homes and industrial buildings Along with fans, devices are used that heat or cool air that comes from the street. This helps improve the characteristics of the indoor microclimate and increase the level of comfort.
One of the economical and available devices is a water heater for fresh air ventilation, more familiar to residents of the northern regions. From our material you will learn about the principles of operation and design features equipment of this type. We will also talk in detail about several popular models of air heaters for ventilation.
Let us immediately note that devices used to heat air in ventilation and air heating systems can operate not only on water.
There are four types of heaters, differing in the method of heating the coolant:
- fire;
- water;
- steam;
- electric.
Water ones are the most popular due to their budget cost and minimum costs for service. The only difficulty concerns installation, which requires connecting water supply pipes.
Image gallery
For this reason, it is impossible to install the device in city apartments, but in large buildings (for example, in warehouses, garages, establishments Catering) system with correct strapping The heater is quite effective.
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 install and maintain steam pipelines, their use for private housing is impractical.
If you need quick installation, uncomplicated by connecting communications, use models of electric heaters for. A protected power supply point is sufficient for their operation. There is no coolant as such at all. Like any electrical appliances, they are unprofitable material point vision.
Water heating equipment used in ventilation systems is the most economical and productive option, capable of quickly heating a large space at minimal cost.
Operating principle and design features
Universal devices operating on water are installed in places with a well-established heat supply system. Simple but quite effective design solution allows you to heat air in the range from + 70 ° C to + 100 ° C and is relevant for hangars, gyms, supermarkets, greenhouses, warehouses, large pavilions - that is, large premises that require additional heating.
An example of using a VOLCANO air heater in a greenhouse. Heating is carried out through distribution warm air(water temperature – +90º C) using a fan and adjustable blinds
If you have ever used a household heat heater, you will easily understand the principle of operation of a water device. It also heats the air, but the role of an electric coil enclosed in a small housing is played by a set 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 ° C to + 180 ° C), from the heating pipes it enters a heat exchanger consisting of small aluminum, steel, bimetallic or copper tubes;
- the 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 - towards the device.
There is no need to specially heat the water, since it is part heating system, so there are 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 units are connected in a rigid way, in versions 2 and 4 - using flexible metal hoses.
Adjusting the heating process
To regulate the thermal power of air heating devices, mixing units with are used. Thanks to the mixing principle, you can significantly reduce the cost of heating a 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 discharged from the heat exchanger.
The installation increases the efficiency of the system. It is preferable to install it at the outlet, since the chilled water (or Alternative option– glycol solution) extends the life of the device.
There are several important operating conditions for mixing equipment:
- maximum proximity to the heater;
- accessibility for maintenance;
- filtered coolant without chemical inclusions;
- the air temperature in the room is above 0 °C.
Technical characteristics of devices may vary, but on average the recommended coolant temperature is from + 2 °C to + 150 °C. To regularly monitor the indicators, it is recommended to install two thermomanometers near the heat exchanger.
Sample 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
Adjustment three way valve carried out using a drive and a controller. Measuring instruments allow you to set the required temperature and change the pressure as accurately as possible.
Installation and connection features
A team of specialists is invited to install air heaters in production workshops or other industrial facilities. You can connect household devices yourself if you strictly follow the instructions and have the skills to work with electrical and heating appliances.
For those who have equipped their home with their own hands, installing 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 concrete are considered the strongest brick walls, moderately suitable - wooden, the weakest - plasterboard.
First of all, a metal frame is attached - a bracket with holes for fixing the body. Some manufacturers call the frame a mounting bracket.
Installation location duct heater for supply ventilation in the air exchange system. If there is a possibility of the temperature falling below normal, it is necessary to install a frost protection thermostat
Suspend the heater body and alternately connect the pipes with the kit shut-off valves or a mixing unit, which can be partially installed before installing the device.
Tapping into the heating system is carried out in two ways: by using connection fittings(couplings with gaskets) or welding 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, the load on the pipes should be avoided. To ensure the insulation of the system and prevent leaks, the joints are treated with sealant.
If a water heater is installed on a permanent basis, it is connected with rigid pipes. If you plan to transfer or shift, it is better to use a flexible liner
Before the testing process, it is necessary to remove air from the channels, check the operation of valves and blind guides.
Operating rules and repair possibilities
To ensure that the equipment works flawlessly and fully performs its functions, the following rules should be taken into account:
- monitor the air composition in the room (compliance requirements can be found in GOST 12.1.005-88);
- carry out installation strictly according to the instructions and based on the manufacturer’s recommendations;
- do not increase the coolant temperature above + 190 °C;
- comply with pressure standards - about 1.2 MPa;
- after cooling the room, heat up gradually, at 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 must be IP66 or higher.
We do not recommend making repairs yourself, since one breakdown most often leads to the next, and in the end you will simply have to replace some parts. It's better to contact service center and entrust the work to professionals. In addition, you should not ignore before purchasing, otherwise there is a chance of wasting money.
Brief overview of modern models
To get an impression of the brands and models of water heaters, let’s look at several devices from different manufacturers.
No. 1 – KSK air heaters
Heaters KSK-3, produced at the company T.S.T.
Model range of water heaters KSK domestic production includes 2/3/4-row units that vary in performance and size
Specifications:
- coolant temperature at the inlet (outlet) – +150 °C (+70 °C);
- inlet air temperature – from -20 °C;
- operating pressure– 1.2 MPa;
- maximum temperature – +190 °C;
- service life – 11 years;
- working resource – 13,200 hours.
External parts are made of carbon steel, heating elements– made of aluminum.
No. 2 – Volcano fan heaters
Water fan heater Volcano mini is a compact device from the Polish brand Volcano, it is practical and ergonomic design. The air flow direction is adjusted using controlled blinds.
One Volcano mini fan heater is capable of generating as much heat as a dozen ordinary ones. bimetallic radiators, composed of ten sections
Specifications:
- power within the range - 3-20 kW;
- maximum productivity – 2000 m³/h;
- heat exchanger type – double 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 for heating air in household and production premises using water coolant.
No. 3 – Galletti AREO air heaters
Galletti AREO heater made in Italy.
Galletti AREO water heaters are capable of both heating the premises being treated and cooling the space in hot weather
Models are equipped with a fan, 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;
- working 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 heaters and water air 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
Review of the Volcano brand water heater:
Details about the technical characteristics of the Ballu BHP-W-60 model:
Simple design and affordable self-execution installation - reasons why water heaters are chosen. Right choice The device and proper installation of the piping will increase the efficiency of ventilation and improve the heating system of industrial and residential premises.
Do you have any questions about the topic of this article? Or maybe you found some shortcomings in our material or want to supplement it with interesting information? Please write your comments in the block below.
Expert opinion
Heating and ventilation engineer RSV
Fedorov Maxim Olegovich
Water heaters (over modern name- water air heaters) are a unit consisting of a fan and a heat exchanger that uses hot (superheated) water as a coolant. They are used for efficient and economical heating of premises 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 rooms of these categories.
All available types of heating devices for ventilation are inferior or, at best, come close in their technical characteristics to water appliances.
The main area of use of air heaters is buildings or premises in which, for various reasons, it is not possible to install radiators. For example, for large rooms, radiators simply will not cope, but, on the contrary, will be the most effective. Most rational arrangement water heaters is the supply ventilation line, since it is impractical to heat the exhaust flow.
In addition to heating, active heating of the supply jet is used, used to retain existing heat in a room. If a fresh stream is transported through a long line of air ducts, then condensation will accumulate on them without heating the air, which will create a lot of operational problems. To solve all these issues, water air heaters are used.
Water air heater: operating principle and design
The most common type are . They replaced plate structures, which were less easy to maintain and required periodic maintenance in a rather labor-intensive manner.
Heater
The main element of the heater is a steel tube, on outer surface which is coated with aluminum fins. These fins serve as a heat-transfer surface, the total area of which is quite large. At the same time, complete outside diameter The tubes (including fins) are 37 mm, and the tube itself is 16 mm, so the depth of the fins is relatively small and does not pose the risk 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 retain heat even with intense airflow, making the device highly efficient.
In the context of constantly rising energy prices, issues of energy conservation come to the forefront in almost all sectors of the national economy. The energy spent on heating premises, both residential and industrial, is no exception.
Building Codes and Rules strictly regulate air exchange parameters for all types of premises, while most of the thermal energy is removed through the ventilation system along with the exhaust air. Partially compensate heat losses allow so-called heat recuperators, which are part of the supply and exhaust ventilation. Unfortunately, the efficiency of most heat recovery units is far from ideal, and heat losses must be somehow replenished to maintain optimal temperature conditions.
One of effective ways creating and maintaining optimal microclimatic parameters in the room is an additional supply unit ventilation system duct heaters.
Story
The idea of a duct heater is by no means new. The first duct (fire-air) heater was created and installed according to the design of N.A. Ammosov. 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 equivalent to 30 “coils” (prototypes of modern centralized heating). Subsequently, by decree of Emperor Nicholas I, fire-air stoves were used to heat the Winter Palace (55 large stoves and 29 small ones). But, despite its high efficiency for that time, the Ammosov furnace had significant disadvantages:
- the fire-air heating system made a constant hum;
- changes during thunderstorms atmospheric pressure provoked a crackling sound in the ventilation ducts;
- the ventilation system, through which hot air was supplied, overheated, which negatively affected the interior of the premises, in particular, the paintings on the walls and paintings quickly became unusable.
It was the latter drawback that forced us to abandon the use of the prototype of the duct heater. The last Ammosov furnace was dismantled in 1912. And although the implementation of the Ammosov heater did not live up to the hopes placed on it, the idea of supply ventilation with air heating was not completely abandoned, and today duct heaters and heated supply units are widely used in residential, domestic and industrial premises.
Electric heaters
An electric duct heater is usually designed to operate with air in the temperature range from 0 to +30°C with a relative humidity of up to 80%. Maximum working temperature air environment at the heater outlet is +40°C. The device body and main elements are made of galvanized or of stainless steel. Protection class according to international standard- IP43. It is recommended to install mechanical filters at the supply air inlet to the heater; the air should 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 supply ventilation control. The ventilation system controller program should provide for automatic shutdown of the heater (based on a timer or air temperature), as well as an emergency stop in case of overheating.
The duct heater is selected based on power. Simplified, the required power can be calculated using the formula:
P = 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 recuperator in the ventilation system, you can save on heater power, and therefore reduce operating costs.
Water heaters
Water heaters are fundamentally different from electric ones and are mainly intended for installation in rectangular ventilation systems, although there is the lineup and for round air ducts.
The design and operating principle of a water duct heater are as follows. In a housing made of stainless or galvanized steel, links of a copper hollow “coil” and aluminum heat-dissipating 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 freezing in winter period time). Thermal energy The circulating fluid 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 in the system for ventilation. 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% air humidity. For efficient 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 performance control system, so control is mainly carried out through one of the following additional external devices:
- a throttle (transfer) valve that regulates the speed of liquid circulation in the coil;
- three-way valve based on the “open-closed” principle;
- a mixing unit that allows you to continuously regulate the ratio of the liquid entering the radiator and the liquid being returned.
