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Pressure applications
in isolated rooms

Controlled conditioned air in isolated rooms

The transmission of pathogens can be prevented by isolating or physically separating one or more persons from other parts of society. People and their surroundings can be protected from patients with infectious diseases or immunocompromised patients from infectious pathogens. In hospitals, special isolation rooms or complete isolation wards are established for this purpose. The main focus of these measures are the doctors and nursing staff, who can break paths of infection by adhering to specific hygiene guidelines.

Isolation rooms are operated with a negative or positive room pressure ratio with regards to their surroundings, i.e. with a slight overpressure or slight negative pressure, depending on the case of use.

The required pressure difference is generated by the difference between the supplied and extracted air. The ventilation concept is therefore based on a combination of volumetric flow and room pressure control that is precisely matched to the respective zone.

The new, modular structure of the VAV-Universal controller product range (now with integrated ∆p sensor) makes it easy to create the ideal combination of controller and damper motorisation for any VAV, duct pressure and room pressure application.

There are three main room pressure applications:

- Simple room pressure control (direct control of the supply air or extract air damper),
- Simultaneous volumetric flow/room pressure control (bypass damper control parallel to the extract air damper) and
- Room pressure and volumetric flow cascade control.

These frequently implemented room pressure applications are explained below using simplified diagrams.

Controlling "not airtight" rooms with moderate leakage rates/overflows

The room pressure controller VRU-M1R-BAC (A, in the extract air in the example) records the air pressure in the room. This is compared with the reference value and the damper is adjusted to the specified room pressure setpoint using an actuator solution ideally suited to the application.

The corresponding VAV unit (supply air) is responsible for the necessary air exchange rate based on the room temperature or air quality.

Controlling rooms with low leakage rate/overflow using a bypass damper

The two VAV units (A, B) control the required air exchange rate. Both units are controlled in parallel based on the room temperature or air quality.

The room pressure controller VRU-M1R-BAC (C) compares the pressure in the room with the defined reference value and then controls the bypass damper to the specified room pressure setpoint. The bypass damper is adequately dimensioned to the room tightness and enables a high level of control accuracy.

The "positive/negative pressure ratio" operating mode can be switched to the current requirements for hospital operation.

Room pressure and volumetric flow cascade control for airtight rooms

Airtight rooms place increased demands on the control system.

Minimal leakages in the room do not allow for the natural compensation of common volumetric flow tolerances.

This places high demands on the control equipment.

The two VAV units (A, B) are responsible for the required air exchange rate and are controlled in parallel based on the room temperature or air quality.

The additional room pressure controller (C, without motorisation) initiates a setpoint shift on the VAV unit (B).

The operating mode "positive/negative pressure ratio" can be switched to the current requirements.

Description of the VAV-Universal controller product range


– Volumetric flow VAV/CAV
– Volumetric flow summation
– Duct pressure
– Room pressure with switchable operating mode "positive/negative pressure ratio"

Actuator solutions

– Rotary actuator
– Fail-safe rotary actuator
– Very fast running rotary actuator
– Very fast running fail-safe rotary actuator


– Conventional control 0...10 V/2...10 V
–  BACnet and Modbus incl. Hybrid Mode, MP-Bus
–  Can be switched using the Belimo Assistant App


– Belimo Assistant App (iOS, Android)
– Wireless tool connection via NFC (Bluetooth)
– PC-based configuration tool available for VAV manufacturers



Reliable room pressure applications require perfectly matched controller/damper combinations. VAV-Universal components are therefore only available from manufacturers of VAV units.

Influence of indoor air quality on our health

People spend approximately 90 percent of their time indoors, and breathe 12,000 litres of air per day. It is therefore important to understand the powerful influence that indoor air quality has on our wellbeing. Belimo shares its deep insights into the effects of indoor humidity, VOC and central air treatment systems and presents valuable suggestions for your health.

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