Diffuser connection boxes OC

Purpose and Function of a Plenum Box

A plenum box (or diffuser connection box) is the final element in radial MVHR (Mechanical Ventilation with Heat Recovery) systems. It serves as the transition between the flexible duct and the air distribution device (a diffuser or air valve) in the room. The primary role of this component is to condition the airflow: stabilizing it, reducing its velocity, and dampening turbulence to ensure a uniform and quiet supply of air into the occupied space.

The use of galvanized steel for diffuser connection boxes is a professional standard dictated by requirements for strength and fire safety. Unlike plastic alternatives, a steel body has high mechanical rigidity, which is a critical condition for concealed installation in a concrete screed or walls. It does not deform under load, ensuring the system's airtightness is maintained for decades. Furthermore, steel is a non-combustible material, which simplifies compliance with building codes and enhances the overall safety of the property.

The Role of a Plenum Box in Ensuring System Efficiency

The performance parameters of the entire heat recovery system, its energy consumption, and the acoustic comfort in the rooms directly depend on the technical characteristics of the plenum boxes. Galvanized steel components designed to modern standards perform four key functions:

• Ensuring Energy Efficiency: Class D airtightness plenum boxes guarantee maximum air impermeability of the connections. This eliminates air leaks and prevents the intake of dust and contaminants from building structures. As a result, the heat recovery unit's fan operates at its nominal mode, consuming minimal energy (low SFP), which ensures the system complies with the EU's ErP directive.
• Maintaining Acoustic Comfort: Due to its volume, the plenum box acts as an expansion chamber, which dampens the aerodynamic noise generated as air passes through the balancing damper. This is a critical factor in meeting regulatory requirements for noise levels in residential spaces.
• Enabling Precise Balancing: The design of the boxes provides for the standard installation of regulating dampers. This allows engineers during the commissioning phase to perform precise hydraulic balancing—setting the design airflow for each room individually.
• Durability and Fire Safety: The use of galvanized steel provides high mechanical strength, which is necessary for safe installation within concrete floor screeds or walls. Unlike polymer alternatives, steel is non-combustible and does not deform under load, ensuring long-term durability and safety.

Explanation of Airtightness Classes (EN 12237 standard)

The airtightness class is a key indicator that defines the quality of the entire ductwork system. It specifies the volume of air lost due to leaks in the connections. The standard establishes four main classes:

• Class A: A basic level with high permissible leakage. It is not used in modern energy-efficient buildings.
• Class B: An improved class, formerly the standard for general ventilation. It is insufficient for heat recovery systems due to significant losses.
• Class C: A high class of airtightness. It is considered the mandatory minimum for quality ventilation systems aiming to meet energy efficiency standards.
• Class D: The highest possible class, with maximum airtightness. Air leakage is practically reduced to zero. This is the "gold standard" for passive and nearly zero-energy buildings (NZEB), guaranteeing that no energy spent on air treatment is wasted.

Key Technical Solutions

High performance is achieved through the following design features:

Technical Comparison of Different Plenum Box Types

Plenum Box Types and Their Application

Galvanized steel plenum boxes are manufactured in various configurations to solve specific engineering tasks related to airflow volume and installation conditions. Choosing the correct model directly impacts the system's efficiency and acoustic characteristics.

Main selection criteria:

1. By Number of Connected Ducts (Capacity)

The number of spigots for connecting flexible ducts (ø75 or ø90 mm) determines the maximum air volume the plenum box can handle without increasing flow velocity and noise.

• With 1 spigot: A standard solution for small rooms such as bedrooms, offices, or closets, with a design airflow of up to 30 m³/h.
• With 2 spigots: Used in medium-sized rooms, like children's rooms, kitchens, or small living rooms, requiring higher air exchange (30-60 m³/h).
• With 3 spigots: Designed for large spaces, such as spacious living rooms or open-plan offices, where a significant air volume is needed (over 60 m³/h).

2. By Main Outlet Direction (Installation Conditions)

The design of the outlet, which connects to the diffuser, determines the most suitable installation environment for the box.

• Straight Outlet: A vertically oriented spigot is ideal for installation in suspended ceilings with sufficient clearance or in thick floor screeds where there is space for a direct diffuser connection.
• Side Outlet: An outlet located on the side of the main chamber is an excellent solution for height-restricted conditions. Such models are often used in shallow suspended ceilings or screeds, allowing for more compact placement of the box and diffuser.

Plenum Box Selection Criteria

When specifying a ventilation system, four key aspects should be considered when choosing diffuser connection boxes:

• Certified Airtightness Class: Products with a confirmed Class D rating according to the EN 12237 standard should be chosen.
• Presence of Factory Gaskets: Integrated EPDM gaskets on the spigots are a mandatory condition for a durable, airtight connection.
• Body Strength and Material: The galvanized steel construction must be appropriate for the intended installation type (ceiling, wall, or concrete screed).
• Compatibility with Dampers: It is necessary to ensure the design allows for the installation of dampers for subsequent hydraulic balancing of the system.

Choosing a quality plenum box with the right characteristics is half the battle. The other half is proper installation, which will allow all the component's built-in advantages to be realized and ensure the longevity of the entire system.

Main Steps for Plenum Box Installation

Correct installation is the key to preserving all the technical advantages of the component. The installation process includes the following steps:

• Connecting Flexible Ducts: The duct is inserted into the plenum box spigot until the locking mechanism clicks. The factory EPDM gasket ensures a completely airtight seal without the need for additional tapes or sealants.
• Securing the Body: The plenum box is securely fastened to the supporting structure (concrete base, suspended ceiling profiles, or wall frame). It is important to precisely align the outlet opening with the future location of the diffuser.
• Installing the Regulating Damper: If individual flow adjustment is required for the room, a regulating damper is installed in its designated housing inside the box. This is done before the final finishing of the ceiling or walls.
• Connecting to the Diffuser: After finishing work (plastering, painting) is complete, the diffuser's adapter is installed into the plenum box outlet, completing the assembly of the unit.

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