How  the valve works in the AHU systems and HVAC

How the valve works in an AHU and HVAC system

An overview of the functions and usage of the water valves in an Air Handling Units

The role of the valve in the HVAC and their relation with the Air Handling Unit.

HVAC systems are sophisticated circuits composed of different parts, and each of these contributes to the control of environmental conditions. In an AHU system, accessories such as the valves have an important role in the execution of the inputs sent from the controllers and support from other devices such as, for example, the actuators.

What is a Valve in HVAC?

In general, a valve is a tool used to manage and control the direction of a given flow, of a gas or a liquid. Even though its usage is common in different areas and industries, in the HVAC systems, valves are mainly applied to manage the flow of fluid inside the pipes. Their opening and closing motion regulates the flow following the indication of the air handling unit and the AHU controllers. The capacity of opening and modulating the aperture of the pipe at different levels depends on the type of the valve, its specifications and the other devices involved in the task such as the actuators.

Valve types are required for AHU's. What are the different types of valve control?

AHU valves differ for usage and physical characteristics.

The first aspect that shapes the type of valve is how it interacts with the flow:

The Control Valves directs the flow of the fluid following the electrical input of an AHU controller, allowing partial opening of the valve to 60% rather than just fully closed (0%) or fully open (100%).

The Shut-off Valves are used to stop the flow of the fluid when required by adjusting the valve position to fully closed or fully open.

The Change over Valves are capable of diverting the flow into another pipe or direction.

The pattern of the valve is another aspect to consider:

The 2-way valves are designed with two ports.

The Belimo R2025-6P3-S2 is an example of a 2-way valve used in air handling systems.

The Danfoss 065Z0280 Seated Plant Valve is another type of 2-way valve.

The 3-way valves are designed with three ports

The Belimo R3015-4-S1 is a valve with 3 ports usually used in HVAC.

The Danfoss 065B1685 is a different example of 3 ports valve.

The Danfoss 065B1685 is a different example of 3 ports valve.

Additionally, the valves are grouped in different groups:

The Ball valve uses a perforated ball to manage the flow of the fluid.

The Butterfly valves control the fluid by using a rotating disk.

The Globe valves are equipped with a spherical body containing a plug or disc to control the flow of fluid.

Also, the Pressure Independent Control valve, also known as PICV, is a control valve with an automatic flow and an actuator.

Valve size, measurement and selection

Selecting the right valve is a relevant aspect to consider when engineers build or replace parts of an AHU system. Here are the main values to check in a valve:

Pressure Nominal (PN): this refers to pressure class in bars of pressure, the nominal working pressure that a valve is rated to flow .

The Belimo R2025-10-S2 is a control valve with a Pressure Nominal of 40 used in AHU systems

Diameter Nominal (DN): it is the measurement of the diameter.

The Siemens VVF32.25-10 is a two-port valve with a Diameter Nominal of 40.

Flow Rate: this is the amount of fluid per unit time capable of passing through the valve, determining the flow control valve type.

Application: a valve is either Pressure dependent or Pressure independent. In other words, the pressure control valve types are related to the nature of a valve to change the flow rate when there is an internal pressure difference, as it happens in the pressure-dependent (PICV) valves, or not, as in the pressure independent valves. 

What a Control Valve is

In general, a control valve is a specific type of valve that aims to regulate the flow of a fluid and it is managed by a controller. In an AHU system, the controller manipulates values of a fluid such as a temperature and pressure. The AHU valve actuator is the device used by the controller to direct the AHU control valve. The control valve sizing is determined by the values of DN and PN. 

The Siemens VPI46.15L0.2Q is a control valve used in HVAC systems.

The Belimo R3015-1P6-S1 is another electronic control valve used for AHU systems.

What is a control valve used for?

The control valve, in AHU systems, is applied for different processes to manage values such as flow, temperature, pressure.

What is the difference between a valve and a control valve?

The control valve and valve have, in general, the same function: controlling the flow of a fluid. However, the control valve is directed by an air handling unit controller.

What is a temperature control valve?

The temperature control valve is focused on the control of the temperature in a fluid.

What are the main parts of the control valve? What are control valve actuators and positioners?

The valve control system is composed of:

Valve actuator: it is the accessory that physically moves the valve in order to modulate the flow.

Valve positioner: it is the device controlling the valve to reach the expected opening.

Valve body: it is the valve that directly regulates the flow.

Valve and actuator: how they work together

The actuator valve function an AHU can be actioned in different ways depending on the technology. The classic valves are managed through a handle that helps the user to manually open or close the valve. 

Nowadays, the AHU actuator valves can be controlled automatically, without any manual task to run, by using an actuator device. These actuators receive the input from the AHU controller which determines how to regulate the passage of the flow, and apply pressure with their torque to action the valve. Actuators and valves are required to be compatible to be used together.

How a control valve works and the flow control working principle

The control valve types, in air handling unit systems, are part of a wider process where more devices take part in the cycle. The function of the control valve is then the result of a process.

Usually, it is the controller, after receiving the values from the sensors related to the environmental conditions, who sends an electrical signal or input to the actuator. 

The actuator applies specific pressure to the ahu control valve, the valve body, in order to manipulate the flow of the fluid in a pipe. 

The valve positioner makes sure that the degree of opening in the valve is requested by the controller.

What a shut-off valve is and how it works

A shut off valve is used to block a compressed fluid in an HVAC and ventilation system. This type of valve, through its motion, is able to either completely shut the passage of the fluid or fully open and let the fluid pass through without any obstacle.

What a changeover valve is and its function

In ventilation and HVAC systems, the changeover valves have the ability to switch the flow of a fluid from one pipeline to another.

The Belimo  R3040-BL4 is a change-over valve with a Pressure Nominal of 40.

What a ball valve is and how it works 

As suggested in the name, this shut off valve is characterized by its spherical shape. In an AHU system, the fluid, indeed, is controlled by a perforated ball whose position opens or closes the passage. 

When the hollow of the ball is aligned with the flow inlet, the valve is open and let the fluid pass through. When the hollow is pivoted 90 degrees by the motion of the valve, the fluid is blocked. Does a ball valve reduce water pressure and Can you use a ball valve to control flow? This specific type of valve works on flow only and not on pressure and hence is considered to be ‘Pressure Dependent’.

The Belimo R6015RP63-B1 is a Ball valve with a Pressure Nominal of 6.

All the advantages of a ball valve

A ball valves are widely used in the HVAC industry as they have many upsides:

The price and cost is generally low and competitive

The risk of leaks is extremely limited.

The motion of the ball is quick.

The physical dimensions make this valve easy to handle and install as they are small and lightweight.

The range of the ball valve is wide and this increases the flexibility of the tool.

Characterised valve

The main peculiarity of this type of valve is the characterising disc used to control the flows in air handling and ventilation system. It is an internal spherical shape that reduces the oscillation and its opening range ensures a high level of control. Also, it is a type of valve that requires a low level of energy to be actioned.

The Belimo R3020-1-1P6-B2 is a characterised valve with six ways.

Globe Valve

Globe valves and globe control valves are used in air handling systems to manage the flow of a fluid in a pipeline. They take their name from their spherical shape, and they are composed of different parts as follows:

A movable plug or disc

A ring seat

Spherical body

The Siemens VVG41.11 is a Globe Valve used in heating, ventilating and air conditioning systems.

What is the difference between ball valves and globe valves?

Ball valves and globe valves, in AHU systems, differ in their capacity to modulate the flow of a fluid. The Ball valves are able to either fully open or close a pipe by rotating a circle shaped opening. The globe valve, instead, has the ability to regulate the opening at different levels by applying a downward motion which pushes a pin/plug down in order to limit the flow.

Butterfly valves

The butterfly valves are an open/closed type used in HVAC systems and have the ability to isolate or control at different levels the flow of a fluid. Butterfly valves use a rotating disk to manage the closing of the flow.

The Belimo D6450NL is a butterfly valve with two ports.

Pressure Independent Control Valve

The PICV, in HVAC, is a type of valve able to modulate the rate of the flow at different levels of pressure conditions of the HVAC system where it is installed. The PICV valve operation is then not influenced by the pressure.

The Danfoss 003Z0771 is an example of a PICV pressure-independent control valve. For the majority of chilled and chilled water applications, it offers a high-quality, economical solution.

The Siemens VPF43.100F90 is a PICV, a pressure independent control valve used in heating, ventilating and air conditioning systems, district heating, as a control valve.

Conclusion

In this article, we have given an overview of what a valve is used for, how it works and the applications in an HVAC system and AHU unit. All the types of valves mentioned are available here in their specific category with the related spares, the main brands in stock are Belimo and Siemens.

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