Pressure Differential System (PDS) costs – overview of solutions

Smoke control systems are, along with education, compartmentation and suppression, one of the key components of fire safety in buildings, allowing smoke and heat to be removed during a fire. Pressure differential systems protect spaces such as lobbies or stairwells from smoke inflow, allowing people to evacuate in safe conditions. How to implement the appropriate pressure differentiation system for a given investment?

Pressure differential system – a complete fire protection solution

Smoke is effectively separated from evacuation zones, which improves visibility and allows for faster evacuation, as well as providing asylum for people with disabilities. Furthermore, firefighters can reach the fire scene quickly and efficiently and take action in a stream of fresh, cool air, making rescue operations more effective and less time-consuming, so there is less risk of damage to the building.

Advantages of positive pressure systems

The most important goal and advantage of pressurisation systems is to ensure the safety of human life, but this dimension also translates into quantifiable benefits. Buildings equipped with such systems often have a higher value and are more attractive to potential buyers or tenants because of the additional safety features, and they may also carry lower insurance premiums.

Pressure differentiation system – is it profitable?

We are aware that investors and owners of newly constructed buildings, as well as those undergoing modernisation, may wonder about the costs of implementing a pressure differential system in their investments. Therefore, we have prepared detailed information that investors must take into account in order to most effectively implement fire ventilation systems in their building.

The costs of implementing a pressure differentiation system

Due to the variety of system configurations, their costs can vary significantly between different building types. Below, we have described what factors influence cost generation.


The cost of implementing a pressurisation system in a stairwell depends largely on the class and height of the building. For low and medium-rise buildings, 1 pressurisation unit is sufficient. The advantage of iSWAY units is that there is no need for a pressure relief damper, thus reducing the cost of the system and making it easier for designers. In tall buildings, where the stack effect negatively affects the pressure distribution, 2 reversible units located at the top and bottom of the building should be used. Depending on the class and height of the building, it is sometimes necessary to use an additional unit (or more) in the middle of the building to cover local pressure drops and airflow criteria.

What needs to be considered:

  • System class – this determines how many doors should be considered open for calculations and what velocity should be achieved on them, and therefore the size of the unit.
  • Building height – the stack effect is the air movement in high vertical spaces due to the temperature difference inside and outside the building. It causes uneven pressure distribution. The higher the building or the greater the temperature difference, the stronger the stack effect. To mitigate it, you can use a Flow System based on reversible fans. Thus, for most low-rise and medium-rise buildings, 1 unit is sufficient, while for high-rise buildings, 2 or 3 are needed, and in the case of particularly tall buildings or with complex architecture, this number and the associated costs may increase.


As standard, one pressure relief unit is required for the lobbies. This unit controls the pressure in only one lobby at a time – on the fire floor. The other floors are disconnected by means of smoke control dampers. Therefore, in addition to the cost of the unit, the cost of the smoke control dampers and pressure sensors must be taken into account in a quantity equal to the floors of the building.

What needs to be considered:

The correct unit selection will depend on the size of the lobby and its leakage (pressure criterion), as well as the class of the system and the size of the door (airflow criterion). The iSWAY, which uses a self-learning adaptive algorithm, adjusts instantly to the changing criterion and can achieve an operating range of 200 to 50000 m3/h without additional space.

The damper and air supply should be sized so that the effective discharge velocity does not exceed 5 m/s. These dampers must be appropriately positioned and integrated with the FAS (Fire Alarm System) to ensure effective operation in fire situations.

Differential pressure sensors monitor the pressure differences in the lobby in relation to the unprotected space, allowing the operation of the pressurisation system to be adjusted in real time. As only one lobby is protected at the time and we need information about the pressure in it, it is necessary to use as many sensors as there are potentially protected lobbies.


To achieve the airflow criterion on the door between the last protected space (e.g. lobby) and the unprotected space, it is necessary to vent the air in the latter. Without this, the unprotected space will quickly pump up from the air supplied by the door, the pressures will equalise and smoke will enter the protected space.

PDS strategies for air release paths

There are three different strategies for air release paths, with a fourth one on the way:

a) Passive air release path: AOV

The space can be unsealed by automatically opening vents (e.g. actuated windows). These should be EN12101-2 certified. Due to the negative impact of wind blowing towards the window, a minimum of 2 smoke ventilation windows should be provided on different facades of the building, each sized for the total supply airflow through the door. This solution can be difficult to apply in some building configurations. It is not recommended for open-space areas that may be subdivided for tenants in the future, thereby cutting off the airflow route by walls.

b) Passive air release path: shafts

One solution is to provide shafts of about 1m2 or 2m2 (depending on the class of system). The main cost of this solution is the occupied space that could be used commercially A low-resistance smoke control damper should be provided on each floor to isolate the other floors. With tall buildings, there is a risk of a stack effect in the shaft, which can increase the flow resistance through the air release path. The greater the resistance, the more air we need to bring into the protected space to overcome it in the airflow criterion.

c) Active air release path: mechanical extraction

This system consists of one (or two in the case of duty/standby setup) fan, a smoke control damper on each floor, and additional compensating elements:
• Transfer damper,
• Electronically-controlled transfer,
• Compensation iSWAY ,
• AOV,
• Passive compensation shaft.
Mechanical smoke extraction provides the greatest confidence in the operation of the system, making it independent of weather conditions and most unforeseen scenarios, as well as providing continuous smoke removal (even when the doors are closed). However, the designer must face the additional challenge of providing compensation air while the doors are closed. This involves additional equipment – dampers and shafts – and the need to integrate a control system.

d) Other options

Stay tuned to discover the New Way for the air release path! The SMAY team continues to work on implementing innovations to ensure maximum system flexibility and reduced cost while maintaining the highest level of security. More details soon!

Additional components required for the operation of the pressure differentiation system

Several additional elements are needed for the PDS to function. The first is a control board for the maintenance and fire brigade. For systems up to 6 iSWAYs, we use a TSS-x board (where x is the number of units), while larger systems require a TS-x board together with an MSPU touchscreen panel to check the status of each unit.

Components of the Safety Way system

The iSWAY pressurisation units and pressure sensors should receive fire signals from the FAS, while the smoke control dampers should be controlled according to the relevant scenario included in the control matrix, and their position and the continuity of the supply lines should be monitored. All these functionalities can be achieved directly by an appropriate extension of the FAS, or by using SMAY’s modular distributed control system, CSUP. It can control all components by receiving only information from the FAS in which fire zone a smoke has been detected.

Power sources for the Safety Way system

The pressurisation system should operate during a fire regardless of the state of the primary power supply to the building. A guaranteed power supply, i.e. one with two different power sources and an EN12101-10 certified automatic power switch, should be provided. These may fall within the scope of the electrical design or a certified ZUP power supply from SMAY may be used.

Simple activation of the pressure differential system

If, looking to save money at all the previous stages, you have chosen a system based on a pressure relief damper, this will be the most difficult stage for you, at which all its flaws will come out. The stack effect in high-rise buildings, the influence of the wind dynamically changing the pressures in the building, the calibration of the system to achieve the correct airflow rates, the issue of too much variation between criteria and the risk of oscillation – all these issues are not a problem for the SafetyWay system based on intelligent iSWAY units!

Basic systems

For basic systems, commissioning works on a plug-and-play basis. You switch on the unit and it immediately adjusts the supply air flow to the conditions in the space. If adjustments to the operating programme are required – we can do this remotely by connecting a remote access router by the installer.

Moderately complex systems

For moderately complex systems we offer the assistance of one SMAY employee (measurements on the customer’s side), while for very complex systems we provide full start-up and commissioning.

Pressurisation systems

The pressurisation system should be integrated with other safety systems such as fire detection, alarm, power, control and smoke extraction systems to ensure a coordinated and effective response in the event of a fire.

Implementation of the Safety Way system? It pays off!

The use of the SafetyWay system allows you to generate a number of investment and operational savings.
The experience of our Technical Support team ensures that we can help you carry out the technical design of your system quickly and without problems. We can also search for the optimum solution for a specific building. We provide guidance for the architects, and accurate materials for the mechanical and electrical designer, as well as the contractors, thus reducing coordination time.

Cabling savings

The loop topology, rather than the star, not only guarantees the greatest level of safety by maintaining 2 communication routes, but also massive savings on cabling. In large buildings, we can save kilometres of fire-rated cables!

Shorter commissioning time

In low-rise buildings, there is no need for a pressure relief damper. The system is auto-adaptive, so in addition to adapting dynamically to current conditions, it allows for maximum simplification and reduced commissioning time.

Lower maintenance costs

Every 24 hours, each iSWAY unit performs a self-check, i.e. an operational check of the shut-off damper and fan. This reduces maintenance costs, replaces daily checks, reduces reliance on employee action (the lack of daily reports can be very costly in the event of an insurance investigation) and, above all, drastically reduces the risk of the system being non-functional, as any potential error can be quickly diagnosed and fixed.

The SMAY team is still working on further improvements that will reduce the price of the system, increase its flexibility and, at the same time, ensure the highest level of security.

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