Air flow control is part of the process of setting up ventilation and air conditioning systems, it is carried out using special air control valves. Regulation of air flow in ventilation systems allows you to provide the required inflow fresh air to each of the serviced premises, and in air conditioning systems - cooling of the premises in accordance with their heat load.
To control the air flow, air valves, iris valves, systems for maintaining a constant air flow (CAV, Constant Air Volume), as well as systems for maintaining a variable air flow (VAV, Variable Air Volume) are used. Let's take a look at these solutions.
Two ways to change the air flow in the duct
In principle, there are only two ways to change the air flow in the duct - change the fan performance or bring the fan to the maximum mode and create additional resistance to the air flow in the network.
The first option requires the connection of fans through frequency converters or step transformers. In this case, the air flow will change immediately in the entire system. Adjust the air supply to one specific room in this way is not possible.
The second option is used to control the air flow in directions - by floors and by rooms. To do this, various adjustment devices are built into the corresponding air ducts, which will be discussed below.
Air shut-off valves, gate valves
The most primitive way to control the air flow is to use air shut-off valves and gates. Strictly speaking, shut-off valves and dampers are not regulators and should not be used for air flow control purposes. However, formally they provide regulation at the level of "0-1": either the duct is open and the air moves, or the duct is closed and the air flow is zero.
The difference between air valves and gate valves lies in their design. The valve, as a rule, is a body, inside of which a rotary damper is provided. If the damper is turned across the axis of the duct, it is blocked; if along the axis of the duct - it is open. At the gate, the damper moves progressively, like a closet door. Blocking the section of the duct, it reduces the air flow to zero, and, opening the section, provides air flow.
In valves and dampers, it is possible to install the damper in intermediate positions, which formally allows you to change the air flow. However, this method is the most inefficient, difficult to control and the most noisy. Indeed, it is almost impossible to catch the desired position of the damper when it is scrolling, and since the design of the dampers does not provide for the function of regulating the air flow, the dampers and dampers are quite noisy in intermediate positions.
Iris valves
Iris dampers are one of the most common solutions for air flow control in rooms. They are round valves with petals arranged along the outer diameter. When adjusted, the petals are displaced towards the axis of the valve, blocking part of the section. This creates an aerodynamically well-circumscribed surface, which helps to reduce the noise level during air flow control.
Iris valves are equipped with a scale with risks, which can be used to monitor the degree of overlap of the valve's open area. Next, the pressure drop across the valve is measured using a differential pressure gauge. The pressure drop determines the actual air flow through the valve.
Constant flow regulators
The next stage in the development of air flow control technologies is the emergence of constant flow controllers. The reason for their appearance is simple. Natural changes in the ventilation network, clogging of the filter, clogging of the external grille, replacement of the fan and other factors lead to a change in air pressure in front of the valve. But the valve was set to some standard pressure drop. How will it work in the new conditions?
If the pressure in front of the valve has decreased, the old valve settings will “transfer” the network, and the air flow into the room will decrease. If the pressure in front of the valve has increased, the old valve settings will “underpressure” the network, and the air flow into the room will increase.
However main task control system is precisely the preservation of the design air flow in all rooms throughout the entire life cycle climate system. This is where solutions for maintaining a constant air flow come to the fore.
The principle of their operation is reduced to an automatic change in the flow area of the valve, depending on external conditions. To do this, the valves are provided with a special membrane, which deforms depending on the pressure at the inlet to the valve and closes the cross section when the pressure increases or releases the cross section when the pressure decreases.
Other constant flow valves use a spring instead of a diaphragm. Increasing pressure upstream of the valve compresses the spring. The compressed spring acts on the flow area regulation mechanism, and the flow area decreases. In this case, the resistance of the valve increases, neutralizing high blood pressure to the valve. If, however, the pressure in front of the valve has decreased (for example, due to clogging of the filter), the spring is unclenched, and the orifice control mechanism increases the orifice.
The considered controllers of constant air flow operate on the basis of natural physical principles without the participation of electronics. There are also electronic systems for maintaining a constant air flow. They measure the actual pressure drop or air velocity and change the valve's orifice area accordingly.
Variable Airflow Systems
Variable airflow systems allow the supply airflow to be varied depending on the actual situation in the room, e.g. depending on the number of people, concentration carbon dioxide, air temperature and other parameters.
Regulators of this type are motorized valves, the operation of which is determined by the controller, which receives information from sensors located in the room. The regulation of air flow in ventilation and air conditioning systems is carried out according to different sensors.
For ventilation, it is important to provide the required amount of fresh air in the room. At the same time, carbon dioxide concentration sensors are activated. The task of the air conditioning system is to maintain the set temperature in the room, therefore, temperature sensors are used.
In both systems, motion sensors or sensors for determining the number of people in the room can also be used. But the meaning of their installation should be discussed separately.
Certainly than more people indoors, the more fresh air should be supplied to it. But still, the primary task of the ventilation system is not to ensure the flow of air "by people", but to create a comfortable environment, which in turn is determined by the concentration of carbon dioxide. With a high concentration of carbon dioxide, ventilation must operate in a more powerful mode, even if there is only one person in the room. Similarly, the main sign of the operation of the air conditioning system is the temperature of the air, and not the number of people.
However, occupancy sensors make it possible to determine whether a given room needs to be serviced at all. this moment. In addition, the automation system can “understand” that “it’s time for the night”, and it is unlikely that anyone will work in the office in question, which means that it makes no sense to spend resources on its air conditioning. Thus, in systems with variable air flow, different sensors can perform different functions - to form a regulatory influence and to understand the need for the operation of the system as such.
The most advanced systems with variable air flow allow, based on several controllers, to generate a signal to control the fan. For example, in one period of time, almost all regulators are open, the fan operates in the mode high performance. At another point in time, some of the regulators lowered the air flow. The fan can operate in a more economical mode. At the third moment of time, people changed their location, moving from one room to another. The regulators have worked out the situation, but the total air flow has not changed much, therefore, the fan will continue to operate in the same economy mode. Finally, it is possible that almost all regulators are closed. In this case, the fan reduces speed to a minimum or turns off.
This approach allows you to avoid constant manual reconfiguration of the ventilation system, significantly increase its energy efficiency, increase the service life of equipment, accumulate statistics on the climatic regime of the building and its changes throughout the year and during the day, depending on various factors - the number of people, outdoor temperature, weather phenomena.
Yury Khomutsky, technical editor of the journal "Climate World">
Variable air flow controllers KPRK for air ducts round section designed to maintain the set air flow rate in ventilation systems with variable air flow (VAV) or constant air flow (CAV). In VAV mode, the air flow setpoint can be changed using a signal from an external sensor, controller or dispatch system; in CAV mode, the regulators maintain the set air flow
The main components of flow regulators are air valve, a special pressure receiver (probe) for measuring air flow and an electric drive with a built-in controller and pressure sensor. The difference between the total and static pressures at the measuring probe depends on the air flow through the regulator. The current differential pressure is measured by a pressure sensor built into the actuator. The electric actuator under the control of the built-in controller opens or closes the air valve, maintaining the air flow through the regulator at a given level.
KRPK regulators can operate in several modes depending on the connection scheme and settings. Air flow rates in m3/h are programmed at the factory. If necessary, the settings can be changed using a smartphone (with NFC support), a programmer, a computer or a supervisory system via MP-bus, Modbus, LonWorks or KNX protocol.
Regulators are available in twelve versions:
- KRPK…B1 – basic model with MP-bus and NFC support;
- KRPK…BM1 – controller with Modbus support;
- KRPK…VL1 – regulator with LonWorks support;
- KPRK…BK1 – controller with KNX support;
- KPRK-I…B1 – controller in a heat/sound insulated housing with MP-bus and NFC support;
- KPRK-I…BM1 – controller in a heat/sound insulated housing with Modbus support;
- KPRK-I…VL1 – controller in a heat/sound insulated housing with LonWorks support;
- KPRK-I…BK1 – controller in heat/sound insulated housing with KNX support;
- KPRK-Sh…B1 – controller in a heat/sound insulated housing and a silencer with MP-bus and NFC support;
- KPRK-Sh…BM1 – controller in a heat/sound insulated housing and a noise suppressor with Modbus support;
- KRPK-Sh…VL1 – regulator in a heat/sound insulated housing and a noise suppressor with LonWorks support;
- KPRK-Sh…BK1 is a controller in a heat/sound insulated housing and a noise suppressor with KNX support.
For the coordinated operation of several variable air flow controllers KPRK and ventilation unit it is recommended to use Optimizer - a regulator that provides a change in the fan speed depending on current need. Up to eight KPRK controllers can be connected to the Optimizer, and several Optimizers can be combined, if necessary, in Master-Slave mode. Variable air flow controllers remain operational and can be operated regardless of their spatial orientation, except when the measuring probe fittings are directed downwards. The direction of air flow must correspond to the arrow on the body of the product. Regulators are made of galvanized steel. Models KPRK-I and KPRK-Sh are made in a heat/sound insulated housing with an insulation thickness of 50 mm; KPRK-Sh is additionally equipped with a 650 mm silencer on the air outlet side. Body nozzles are equipped rubber seals, which ensures the tightness of the connection with the air ducts.
Imagine that you want to install a ventilation system in your apartment. Calculations show that for heating supply air in the cold season, a 4.5 kW heater will be required (it will allow heating the air from -26 ° C to + 18 ° C with a ventilation capacity of 300 m³ / h). Electricity is supplied to the apartment through a 32A automatic machine, so it is easy to calculate that the power of the heater is about 65% of the total power allocated to the apartment. This means that such a ventilation system will not only significantly increase the amount of electricity bills, but also overload the power grid. Obviously, it is not possible to install a heater of such power and its power will have to be reduced. But how to do this without reducing the comfort level of the inhabitants of the apartment?
How to reduce electricity consumption?
Ventilation unit with recuperator.
It needs a network to work.
supply and exhaust ducts.
The first thing that usually comes to mind in such cases is the use of a ventilation system with a heat exchanger. However, such systems are well suited for large cottages, while in apartments there is simply not enough space for them: in addition to the supply air supply network, an exhaust network must be connected to the heat exchanger, doubling the total length of the air ducts. Another disadvantage of recuperation systems is that in order to organize the air overpressure of "dirty" rooms, a significant part of the exhaust flow must be directed to the exhaust ducts of the bathroom and kitchen. And the imbalance of the supply and exhaust flows leads to a significant decrease in the efficiency of recuperation (it is impossible to refuse the air backwater of "dirty" premises, since in this case unpleasant odors will begin to walk around the apartment). In addition, the cost of a recuperative ventilation system can easily exceed twice the cost of a conventional supply system. Is there another inexpensive solution to our problem? Yes, this is a supply VAV system.
VAV system or VAV(Variable Air Volume) system allows you to adjust the air supply in each room independently of each other. With such a system, you can turn off the ventilation in any room in the same way that you used to turn off the lights. Indeed, after all, we do not leave the light on where there is no one - it would be an unreasonable waste of electricity and money. Why let a ventilation system with a powerful heater waste energy in vain? However, traditional ventilation systems do just that: they supply heated air to all rooms where people could be, regardless of whether they actually are there. If we controlled the light in exactly the same way as traditional ventilation- it would burn at once in the whole apartment, even at night! In spite of obvious advantage VAV systems, in Russia, unlike Western Europe, they have not yet become widely used, in part because their creation requires complex automation, which significantly increases the cost of the entire system. However, the rapid reduction in the cost of electronic components, which occurs in recent times, allowed the development of inexpensive turnkey solutions for building VAV systems. But before proceeding to the description of examples of systems with variable air flow, we will understand how they work.
The illustration shows a VAV system with a maximum capacity of 300 m³/h serving two areas: a living room and a bedroom. In the first figure, air supply is provided to both zones: 200 m³/h to the living room and 100 m³/h to the bedroom. Let us assume that in winter the power of the heater will not be enough to heat such an air flow to comfortable temperature. If we had used a conventional ventilation system, we would have had to reduce the overall performance, but then it would have become stuffy in both rooms. However, we have a VAV system installed, so during the day we can only supply air to the living room, and at night only to the bedroom (as in the second picture). To do this, valves that regulate the volume of air supplied to the premises are equipped with electric drives that allow you to open and close the valve dampers using conventional switches. Thus, by pressing the switch, the user turns off the ventilation in the living room before going to bed, where there is no one at night. At this moment, the differential pressure sensor, which measures the air pressure at the outlet of the air handling unit, detects an increase in the measured parameter (when the valve is closed, the resistance of the air supply network increases, leading to an increase in air pressure in the air duct). This information is transmitted to the air handling unit, which automatically reduces the fan performance just enough to keep the pressure at the measuring point unchanged. If the pressure in the duct remains constant, then the air flow through the valve in the bedroom will not change, and will still be 100 m³ / h. The overall performance of the system will decrease and will also be equal to 100 m³ / h, that is, the energy consumed by the ventilation system at night will decrease by 3 times without sacrificing people's comfort! If you turn on the air supply alternately: during the day in the living room, and at night in the bedroom, then the maximum power of the heater can be reduced by a third, and the average energy consumed by half. The most interesting thing is that the cost of such a VAV system exceeds the cost of a conventional ventilation system by only 10-15%, that is, this overpayment will be quickly compensated by lowering the amount of electricity bills.
A short video presentation will help you better understand the principle of the VAV system:
Now, having dealt with the principle of operation of the VAV system, let's see how you can assemble such a system based on the equipment available on the market. As a basis, we will take the Russian VAV-compatible Breezart air handling units, which allow you to create VAV systems serving from 2 to 20 zones with centralized control from the remote control, timer or CO 2 sensor.
VAV system with 2-position control
This VAV system is assembled on the basis of the Breezart 550 Lux air handling unit with a capacity of 550 m³/h, which is enough to service an apartment or small cottage(bearing in mind that a system with a variable air flow may have a lower capacity compared to traditional system ventilation). This model, like all other Breezart units, can be used to create a VAV system. In addition, we need a set VAV-DP, which includes a JL201DPR sensor that measures duct pressure near the branch point.
VAV-system for two zones with 2-position control
The ventilation system is divided into 2 zones, and the zones can consist of either one room (zone 1) or several (zone 2). This allows the use of such 2-zone systems not only in apartments, but also in cottages or offices. The valves of each zone are controlled independently of each other using conventional switches. Most often, this configuration is used to switch night (air supply to zone 1 only) and day (air supply to zone 2 only) modes with the possibility of supplying air to all rooms, if, for example, guests have come to you.
Compared conventional system(without VAV control) the increase in the cost of basic equipment is approx. 15% , and if we take into account the total cost of all elements of the system, together with installation work, then the increase in value will be almost imperceptible. But even such a simple VAV system allows save about 50% electricity!
In the given example, we used only two controlled zones, but there can be any number of them: the air handling unit simply maintains the set pressure in the air duct, regardless of the configuration of the air supply network and the number of controlled VAV valves. This allows, in case of a lack of funds, to first install the simplest VAV system on two zones, further increasing their number.
So far, we have considered 2-position control systems in which the VAV valve is either 100% open or fully closed. However, in practice, more convenient systems with proportional control, allowing you to smoothly adjust the amount of air supplied. We will now consider an example of such systems.
VAV system with proportional control
VAV system for three zones with proportional control
This system uses a more efficient Breezart 1000 Lux PU at 1000 m³/h, which is used in offices and cottages. The system consists of 3 zones with proportional control. The CB-02 modules are used to control proportional valve actuators. Instead of switches, JLC-100 regulators (outwardly similar to dimmers) are used here. Such a system allows the user to smoothly adjust the air supply in each zone in the range from 0 to 100%.
The composition of the basic equipment of the VAV system (supply unit and automation)
Note that in one VAV system, zones with 2-position and proportional control can be used simultaneously. In addition, control can be made from motion sensors - this will allow air to be supplied to the room only when there is someone in it.
The disadvantage of all the considered options for VAV systems is that the user has to manually adjust the air supply in each zone. If there are many such zones, then it is better to create a system with centralized control.
VAV system with centralized control
Centralized control of the VAV system allows you to enable pre-programmed scenarios by changing the air supply in all zones simultaneously. For example:
- Night mode. Air is supplied only to the bedrooms. In all other rooms, the valves are open at a minimum level to prevent stagnant air.
- day mode. All rooms except bedrooms are supplied with air in full. In the bedrooms, the valves are closed or open at a minimum level.
- Guests. The air flow in the living room has been increased.
- Cyclic ventilation(used in case of prolonged absence of people). A small amount of air is supplied to each room in turn - this avoids the appearance of unpleasant odors and closeness, which can create discomfort when people return.
VAV system for three zones with centralized control
For centralized control of valve actuators, JL201 modules are used, which are combined into single system controlled via ModBus. Programming of scenarios and control of all modules is carried out from the standard remote control of the ventilation unit. The JL201 module can be connected to a carbon dioxide concentration sensor or a JLC-100 controller for local (manual) control of actuators.
The composition of the basic equipment of the VAV system (supply unit and automation)
The video describes how to control a VAV system with centralized control for 7 zones from the Breezart 550 Lux air handling unit:
Conclusion
In these three examples, we have shown general principles construction and briefly described the capabilities of modern VAV systems, more detailed information about these systems can be found on the Breezart website.
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The main purposes of this system are to reduce operating costs and compensate for filter contamination.
According to the differential pressure sensor, which is installed on the controller board, the automation recognizes the pressure in the duct and automatically equalizes it by increasing or decreasing the fan speed. supply and exhaust fan while working synchronously.
Filter clogging compensation
During the operation of the ventilation system, the filters inevitably get dirty, the resistance of the ventilation network increases and the volume of air supplied to the premises decreases. VAV system will support constant flow air throughout the life of the filters.
- The VAV system is most relevant in systems with high level air purifiers, where dirty filters lead to a noticeable reduction in the volume of air supplied.
Reduced operating costs
The VAV system can significantly reduce operating costs, this is especially noticeable on supply ventilation systems, which have a high energy consumption. Achieve savings by completely or partially turning off the ventilation of individual rooms.
- Example: you can turn off the living room at night.
At calculation of the ventilation system guided various norms air consumption per person.
Usually, in an apartment or house, all rooms are ventilated at the same time, the air flow for each of the rooms is calculated based on the area and purpose.
What to do if in this moment is there no one in the room?
You can install valves and close them, but then the entire volume of air will be distributed to the remaining rooms, but this will lead to an increase in noise and useless consumption of air, for which the cherished kilowatts were spent to heat.
It is possible to reduce the power of the ventilation unit, but this will also reduce the volume of air supplied to all rooms, and where there are users, there will be “not enough” air.
The best decision, it is to supply air only to those rooms where there are users. And the power of the ventilation unit must be regulated by itself, according to the required air flow.
This is exactly what the VAV ventilation system allows you to do.
VAV systems pay for themselves quite quickly, especially on air handling units, but most importantly, can significantly reduce operating costs.
- Example: Apartment 100m2 with and without VAV system.
The volume of air supplied to the room is regulated by electric valves.
An important condition for the construction of a VAV system is the organization of a minimum supplied air volume. The reason for this condition lies in the inability to control the air flow below a certain minimum level.
This is solved in three ways:
- in a single room, ventilation is organized without the possibility of regulation and with an air exchange volume equal to or greater than the required minimum flow air in the VAV system.
- a minimum amount of air is supplied to all rooms with the valves turned off or closed. In total, this amount must be equal to or greater than the required minimum air flow in the VAV system.
- Together the first and second options.
Control from household switch:
This will require a household switch and a valve with a return spring. Switching on will lead to the full opening of the valve, and ventilation of the room will be carried out in full. When switched off, the return spring closes the valve.
Shutter switch/switch.
- Equipment: One valve and one switch will be required for each serviced area..
- Exploitation: If necessary, the user turns on and off the ventilation of the room with a household switch.
- pros: The simplest and a budget option VAV systems. Household switches always match the design.
- Minuses: User participation in regulation. Low efficiency due to on-off regulation.
- Advice: The switch is recommended to be installed at the entrance to the serviced premises, at +900mm, next to or in the block of light switches.
The minimum required air volume is always supplied to room 1, it cannot be turned off, room 2 can be turned on and off.
The minimum required air volume is distributed to all rooms, since the valves are not completely closed and the minimum amount of air passes through them. The entire room can be turned on and off.
Rotary control:
This will require a rotary regulator and a proportional valve. This valve can be opened by adjusting the volume of supplied air in the range from 0 to 100%, the required degree of opening is set by the regulator.
Rotary regulator 0-10V
- Equipment: one 0…10V control valve and one 0…10V regulator will be required for each serviced room.
- Exploitation: If necessary, the user selects required level room ventilation on the controller.
- pros: More precise regulation of the amount of air supplied.
- Minuses: User participation in regulation. Appearance regulators are not always suitable in design.
- Advice: The regulator is recommended to be installed at the entrance to the serviced premises, at the level of +1500mm, above the block of light switches.
The minimum required air volume is always supplied to room 1, it cannot be turned off, room 2 can be turned on and off. In room No. 2, you can smoothly adjust the volume of air supplied.
Small opening (valve 25% open) Medium opening (valve 65% open)
The minimum required air volume is distributed to all rooms, since the valves are not completely closed and the minimum amount of air passes through them. The entire room can be turned on and off. In each room, you can smoothly adjust the amount of air supplied.
Presence sensor control:
This will require a presence detector and a spring return valve. When registering in the user's room, the presence sensor opens the valve and ventilation of the room is carried out in full. In the absence of users, the return spring closes the valve.
Motion Sensor
- Equipment: one valve and one occupancy sensor will be required per serviced space.
- Exploitation: The user enters the room - room ventilation starts.
- pros: The user does not participate in the regulation of ventilation zones. It is impossible to forget to turn on or turn off the ventilation of the room. Many occupancy sensor options.
- Minuses: Low efficiency due to on-off regulation. The appearance of presence sensors is not always suitable for design.
- Advice: Use high-quality presence sensors with a built-in time relay for the correct operation of the VAV system.
The minimum required air volume is always supplied to room 1 and cannot be turned off. When registering a user, ventilation of room No. 2 starts
The minimum required air volume is distributed to all rooms, since the valves are not completely closed and the minimum amount of air passes through them. When a user registers in any of the rooms, the ventilation of this room starts.
Control by CO2 sensor:
This requires a CO2 sensor with a 0...10V signal and a proportional valve with a 0...10V control.
When registering an excess of the CO2 level in the room, the sensor starts to open the valve in accordance with the registered CO2 level.
When the CO2 level drops, the sensor starts to close the valve, while the valve can close both completely and to a position at which the required minimum flow will be maintained.
Wall or duct CO2 sensor
- Example: one proportional valve with 0…10V control and one CO2 sensor with 0…10V signal will be required for each served room.
- Exploitation: The user enters the room, and if the CO2 level is exceeded, the ventilation of the room starts.
- pros: The most energy efficient option. The user does not participate in the regulation of ventilation zones. It is impossible to forget to turn on or turn off the ventilation of the room. The system starts ventilation of the room only when it is really needed. The system regulates the volume of air supplied to the room as precisely as possible..
- Minuses: The appearance of CO2 sensors does not always match the design.
- Advice: Use high-quality CO2 sensors for correct operation. The CO2 duct sensor can be used in supply and exhaust systems ventilation, if both supply and exhaust are present in the manned room.
The main reason why room ventilation is required is an excess of CO2 levels.
In the process of life, a person exhales a significant amount of air with a high level of CO2, and being in an unventilated room, the level of CO2 in the air inevitably grows, and this is the determining factor when they say that there is “not enough air”.
It is best to supply air to the room precisely when the CO2 level exceeds the value of 600-800 ppm.
Focusing on this air quality parameter, you can create most energy efficient system ventilation.
The minimum required air volume is distributed to all rooms, since the valves are not completely closed and the minimum amount of air passes through them. When an increase in the CO2 content is detected in any of the rooms, the ventilation of this room starts. The degree of opening and the amount of air supplied depends on the level of excess CO2 content.
Management of the "Smart Home" system:
This will require a system Smart House» and any kind of valves. Any type of sensors can be connected to the Smart Home system.
Air distribution control can be either through sensors using the control program, or by the user from the central control panel or application from the phone.
smart home panel
- Example: The system works according to the CO2 sensor, periodically ventilates the premises, even in the absence of users. The user can forcibly turn on ventilation in any room, as well as set the amount of air supplied.
- Exploitation: Any control options are supported.
- pros: The most energy efficient option. Possibility of accurate programming of the week timer.
- Minuses: Price.
- Advice: Installed and configured by qualified professionals.
