VAV valve systems. VAV systems

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 to use ventilation system with recuperator. 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 overpressure 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 allow a ventilation system with a powerful heater to waste energy in vain? However, traditional ventilation systems work exactly like this: they supply heated air to all rooms where people could be, regardless of whether they actually are there. If we controlled the light in the same way as traditional ventilation, it would burn all over the apartment at once, even at night! Despite the obvious advantage of VAV systems, in Russia, unlike Western Europe they haven't received yet widespread, partly 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. Suppose that in winter the power of the heater will not be enough to heat such an air flow to a 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, the 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 point, the differential pressure sensor, which measures the outlet air pressure air handling unit, fixes 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 based on a Breezart 550 Lux air handling unit with a capacity of 550 m³/h, which is enough to serve an apartment or a small cottage (taking into account the fact that a variable air flow system may have a lower capacity compared to a traditional ventilation system). 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. In all rooms, except for bedrooms, the air is supplied 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 when there is a long 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 a single system controlled via the ModBus bus. Programming of scenarios and control of all modules is carried out from the standard remote control of the ventilation unit. A concentration sensor can be connected to the JL201 module carbon dioxide or 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.

Variable Air Volume - variable air flow

SISTEMAGROUP specialists have implemented more than one project using Systemair VAV ventilation and air conditioning systems, both at the stage of design and installation and modernization of existing systems.

Advantages of VAV - variable flow systems over CAV - constant air flow systems:

Individual comfort in every room- the organization of air supply is carried out on demand from a certain external factor or their sum and priority: temperature t, humidity, CO2, movement.
Energy saving- maximum energy efficiency, allows you to save up to 70% of electricity consumption.
Increases the service life of the equipment
Low level system noise

Let's consider three examples, from the objects we have implemented, of the layout of VAV systems from advanced to simple.

In all three examples, air handling units with recuperation are used. The ventilation system control mode is carried out by maintaining the temperature t of the exhaust air (maintaining the temperature in the room). The ventilation system controller itself sets the supply air temperature t (tmin and tmax).

1. Example

The task set by the Customer is to individually maintain accurate and continuous control of humidity and temperature t in each of the six living quarters: four bedrooms, a hall, a dining room.

In this project, it was required to regulate six zones, the principle of operation of the system was implemented on OPTIMA variable air flow VAV controllers and an optimizer controller.

The air flow in a given VAV system is independent of the pressure in that system.

Variable flow VAV controllers receive a control signal (0/2-10V) from humidity and temperature sensors installed in the premises - Vx m3/h is required.
The moving air stream creates a pressure difference, which is measured using a Pitot tube.
The actual value of the air flow m3/h obtained from the differential pressure sensor is sent to the controller of the variable flow controller
The controller compares the actual air flow m3/h. and the required value, in the presence of deviations, sends a corrective signal to the electric actuator, which regulates the valve section until the required air flow m3 / h. will not be reached
The optimizer controller receives a signal via the MP-bus network from all VAV controllers and corrects the operation of the fans.

Topvex TR_EL - vertical air handling unit with rotary heat exchanger and electric heater
AIAS COMBOX MODULE - controller optimizer VAV variable flow regulators
CO2RT Wall mounting 0-2000 ppm - CO2 level, humidity and temperature transmitters
OPTIMA-R-BLC1 - variable flow controllers
Mitsubishi Electric SUZ-KA_ inverter - condensing unit (KKB)
DXRE - freon cooler
PAC-IF012B-E - KKB controller
Carel compactSteam is an isothermal humidifier.

2. Example

The task set by the Customer is to maintain accurate and continuous control of CO2 concentration and temperature t in two sports halls.

In this project, it was required to regulate two zones, the principle of operation is implemented according to the scheme - The air flow in a given VAV system depends on the static pressure Pa in that system.

Electric actuators of air valves receive a control signal (0/2-10V) from CO2 concentration and temperature sensors installed in sports halls
The air valve, by changing the section, delivers the required air flow m3/h.
The moving air flow creates a differential pressure Pa, which is measured by differential pressure sensors
Differential pressure sensors send a signal to the controller of the air handling unit, which in turn adjusts the operation of the fans depending on the current demand for air flow m3/h.

Equipment installed at the facility:

Topvex FR_HWL - horizontal air handling unit with rotary heat exchanger and water heater
VAV Duct pressure control - differential pressure sensors
Belimo LF 24-SR - electric actuators 0-10V controlled by CO2 level converters
DXRE - freon cooler
PAC-IF013B-E - KKB controller.

3. Example

The task set by the Customer is to maintain accurate and continuous temperature control t in the office space.

In this project, it was required to ensure the temperature of a single office space(call centre). The principle of operation of the system is implemented according to the scheme of the Corrigo ventilation system controlled directly by the controller. The settings of the Corrigo controller allow you to change the airflow m3/h. depending on the temperature deviation t in the room.

Equipment installed at the facility:

Topvex FC_EL - suspended air handling unit with heat exchanger and electric heater
DXRE - freon cooler
Mitsubishi Electric PUHZ-ZRP_YKA inverter - condensing unit (KKB)
PAC-IF013B-E - KKB controller

Variable Air Volume - variable air flow

SISTEMAGROUP specialists have implemented more than one project using VAV ventilation and air conditioning systems both at the stage of design and installation and modernization of existing systems.

Advantages of VAV - variable flow systems over CAV - constant air flow systems:

Individual comfort in every room- the organization of air supply is carried out on demand from a certain external factor or their sum and priority: temperature t, humidity, CO2, movement.
Energy saving- maximum energy efficiency, allows you to save up to 70% of electricity consumption.
Increases the service life of the equipment
Low noise system operation

Let's consider three examples, from the objects we have implemented, of the layout of VAV systems from advanced to simple.

1. Example

The task set by the Customer is to individually maintain accurate and continuous control of humidity and temperature t in each of the six living quarters: four bedrooms, a hall, a dining room.

In this project, it was required to regulate six zones, the principle of operation of the system was implemented on OPTIMA variable air flow VAV controllers and an optimizer controller.

The air flow in a given VAV system is independent of the pressure in that system.

Variable flow VAV controllers receive a control signal (0/2-10V) from humidity and temperature sensors installed in the premises - Vx m3/h is required.
The moving air stream creates a pressure difference, which is measured using a Pitot tube.
The actual value of the air flow m3/h obtained from the differential pressure sensor is sent to the controller of the variable flow controller
The controller compares the actual air flow m3/h. and the required value, in the presence of deviations, sends a corrective signal to the electric actuator, which regulates the valve section until the required air flow m3 / h. will not be reached
The optimizer controller receives a signal via the MP-bus network from all VAV controllers and corrects the operation of the fans.

Topvex TR_EL - vertical air handling unit with rotary heat exchanger and electric heater
AIAS COMBOX MODULE - controller optimizer VAV variable flow regulators
CO2RT Wall mounting 0-2000 ppm - CO2 level, humidity and temperature transmitters
OPTIMA-R-BLC1 - variable flow controllers
Mitsubishi Electric SUZ-KA_ inverter - condensing unit (KKB)
DXRE - freon cooler
PAC-IF012B-E - KKB controller
Carel compactSteam is an isothermal humidifier.

2. Example

The task set by the Customer is to maintain accurate and continuous control of CO2 concentration and temperature t in two sports halls.

In this project, it was required to regulate two zones, the principle of operation was implemented according to the scheme - The air flow in this VAV system depends on the static pressure Pa in this system.

Electric actuators of air valves receive a control signal (0/2-10V) from CO2 concentration and temperature sensors installed in sports halls
The air valve, by changing the section, delivers the required air flow m3/h.
The moving air flow creates a differential pressure Pa, which is measured by differential pressure sensors
Differential pressure sensors send a signal to the controller of the air handling unit, which in turn adjusts the operation of the fans depending on the current demand for air flow m3/h.

Equipment installed at the facility:

Topvex FR_HWL - horizontal air handling unit with rotary heat exchanger and water heater
VAV Duct pressure control - differential pressure sensors
Belimo LF 24-SR - electric actuators 0-10V controlled by CO2 level converters
DXRE - freon cooler
PAC-IF013B-E - KKB controller.

3. Example

The task set by the Customer is to maintain accurate and continuous temperature control t in the office space.

In this project, it was required to ensure the temperature of a single office space (call center). The principle of operation of the system is implemented according to the scheme of the Corrigo ventilation system controlled directly by the controller. The settings of the Corrigo controller allow you to change the airflow m3/h. depending on the temperature deviation t in the room.

Equipment installed at the facility:

Topvex FC_EL - suspended air handling unit with heat exchanger and electric heater
DXRE - freon cooler
Mitsubishi Electric PUHZ-ZRP_YKA inverter - condensing unit (KKB)
PAC-IF013B-E - KKB controller