Analysis of design solutions for overpressure systems in accordance with PN-EN 12101-6

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Autor
Rafał Polichnowski
Rafał Polichnowski

Assistant Commercial Director – SMAY Sp z o.o

The PN-EN 12101-6 standard defines six classes of pressure differential systems: A, B, C, D, E and F. A designer working with an expert should establish which class to use in a given building. Depending on the choice, certain system design criteria introduced by the standard must be met.

In this article, we will focus on the class B pressure differential system and the airflow rate criterion, that is the air supplied to a zone engulfed in fire, which is 2 m/s (Figure 1). The airflow rate must be ensured at an open door in a baffle between the zone engulfed in fire and protected space (an entrance hall or a lift foyer).

This criterion can be met by supplying an adequate quantity of air to the stairwell, and then forcing it through an open door to the entrance hall and the zone engulfed in fire, or by first supplying air directly to the entrance hall, and then to the zone engulfed in fire. Before we decide on a place to supply air in order to meet the airflow rate criterion of 2 m/s, we should conduct an architectural building analysis and an airflow dynamics analysis between the place where air is supplied and the place where it is extracted.

Let’s assume that the doorway, for which the airflow rate is measured, has an area of 2 m2. The quantity of air that should be supplied is then 2 m2 × 2 m/s × 3,600 = 14,400 m3/h. It is important to know that the air will only flow from the overpressure zone if the room engulfed in fire has an appropriate exhaust located outside the building. If there is no exhaust, the pressure between the zones will be equalized, resulting in a dynamic migration of smoky air to the protected zone (i.e. the staircase / lift foyer / entrance hall).

Let’s first agree with the architect on a solution to extract hot smoke from the zone engulfed in fire (mechanical or gravitational). The extraction value must be equal or greater than 14,400 m3/h.

Today, we are going to discuss solutions using gravitational extraction of hot smoke from a zone engulfed in fire.

Gravitational exhaust ventilation

When using this solution, we need to ensure the lowest possible calculated airflow resistance as the resistance value directly impacts the entire pressure differential system output. In the class B pressure differential systems, with an airflow rate of 2 m/s at the staircase the door is open not only at the storey engulfed in fire, but also below this storey and at the storey where evacuation from the building takes place (usually the ground floor).

Airflow rate criterion

a) Let’s assume that the entire air is supplied to the staircase (Figure 2). The air flowing at a rate of 14,400 m3/h passes through the doorway between the staircase and entrance hall, and then through the doorway between the entrance hall and the zone engulfed in fire. Subsequently, the air is pushed out of the building through the provided exhaust. Let’s analyse the resistance and system output generated with this airflow criterion.

LEGEND
1. iSWAY air supply unit
2. Damper-controlled double supply louvre system
3. P-MACF remote pressure sensor
4. STW/GA air supply grille with a damper
5. Smoke exhaust window with an actuator – exhaust feature
6. Acoustic silencer

The air flowing through the doorway from one zone to the other at a rate of 2 m/s generates a resistance of 6 Pa (Table 1). We have two doorways. The total resistance equals 12 Pa. Next, let’s assume that the air will be extracted through a smoke exhaust window. It has an area of 2 m2. The total resistance thus amounts to 18 Pa. We can therefore state that all the other openings in the staircase require a resistance of at least 18 Pa so that the air passes through an open door in the direction of the smoke exhaust window.

The biggest opening in the staircase is an open emergency exit door outside the building. Let’s assume that its area is 2 m2. In order to ensure a flow resistance of 18 Pa, the airflow rate must equal 3.5 m/s. It seems that – considering that the air should flow to the staircase at a rate of 2 m/s – we must supply additional 25,200 m3/h (we shall not include any other leaks in the staircase in this analysis). Therefore, the total amount of air required to meet the airflow rate criterion with such a gravitational exhaust is 14,400 m3/h + 25,200 m3/h = 39,600 m3/h.

Airflow rate criterion - 1

Now, we should consider a proper placement of air supply points in the staircase in order not to exceed door opening force at any storey, i.e. 100 N.

ATTENTION!

In case of the pressure difference criterion leaks in the staircase may be significantly lower (Figure 1). The fan must therefore supply extremely different quantities of air depending on the number of open and closed doors. Only devices with valid certificates stating fan working ranges and system response times should be used.

Airflow rate criterion - 2

b) Let’s assume that the entire air is supplied to the entrance hall (Figure 3). The air flowing at a rate of 14,400 m3/h passes through the doorway between the entrance hall and the zone engulfed in fire. Subsequently, the air is pushed out of the building through the provided exhaust. Let’s analyse the resistance and system output generated with this airflow criterion.

Airflow rate criterion - 3

LEGEND

  1. iSWAY air supply unit
  2. Damper-controlled double supply louvre system
  3. P-MACF remote pressure sensor
  4. STW/GA air supply grille with a damper
  5. Smoke exhaust window with an actuator – exhaust feature
  6. TAP rectangular acoustic silencer
  7. KWP-P-E fire ventilation damper with an actuator
  8. STW air supply grille

The air flowing through the doorway from one zone to the other at a rate of 2 m/s generates a resistance of 6 Pa (Table 1). We only have one doorway, so the total resistance is 6 Pa. Next, let’s assume that the air will be extracted through a smoke exhaust window. It has an area of 2 m2.

The total resistance thus amounts to 12 Pa. We can therefore state that all the openings in the staircase require a resistance of at least 12 Pa so that the air passes through an open door in the direction of the smoke exhaust window.

The biggest opening in the staircase is an open emergency exit door outside the building. Let’s assume that its area is 2 m2. In order to ensure a flow resistance of 12 Pa, the airflow rate must equal 2.9 m/s. It seems that – considering that the air should flow to the staircase at a rate of 2 m/s – we must supply 20,880 m3/h (we shall not include any other leaks in the staircase in this analysis). Therefore, the total amount of air required to meet the airflow criterion with such gravitational exhaust ventilation is: 14,400 m3/h + 20,880 m3/h = 35,280 m3/h. Now, we should consider a proper placement of air supply points in the staircase in order not to exceed door opening force at any storey, i.e. 100 N. This also applies to the door in the entrance hall to the zone engulfed in fire. Air is supplied to the entrance hall and staircase by two independent devices.

 

ATTENTION!

In case of the pressure difference criterion leaks in the entrance hall and staircase may be significantly lower (Figure 1). The fan must therefore supply extremely different quantities of air depending on the number of open and closed doors. Only devices with valid certificates stating fan working ranges and system response times should be used.

The above analyses indicate that the choice of a design solution impacts the total quantity of air supplied to protected zones. In accordance with the PN-EN 12101-6 standard additional 15% should be provided due to uncontrollable leaks. Consequently, the number of devices supplying air, electric motor power, power cable cross-section and I&C cabinets may significantly differ. In SMAY’s experience, the choice of a solution significantly impacts the total cost of a pressure differential system.

Safety Way: an innovative differential pressure system – escape routes free from smoke and fire – highest degree of protection.

The Safety Way differential pressure system is a solution designed for multi-storey buildings:

• iSWAY-FC® differential pressure product for smoke and heat control systems;
• Innovative predictive algorithm;
• Anti-Frost system that endures even the most extreme weather conditions;
• 24-hour automatic test of all the components;
• Automatic adaptation to changing service conditions;
• Communication between individual components of the set and continuous tracking of all components (regulators, remote pressure sensors, etc.);
• Continuous measurement of the set value of static differential pressure between the protected and reference zones by the P-MAC(F) sensor.

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