Stairwell Pressurization Research Articles

Characterization of Stack Effect in High-Rise Buildings Under Winter Conditions, Including the Impact of Stairwell Pressurization

To characterize the magnitude of stack effect within stairwells and elevator shafts, differential pressure measurements were taken in fifteen (15) high-rise buildings in four (4) different cities (Cleveland, Baltimore, Minneapolis, and Philadelphia) during the winter months of January–March, 2013. Test buildings ranged in height from 44 m to 150 m (143 ft–492 ft). Outside temperatures during testing ranged from −12°C to 15°C (10°F–59°F). Based on the differential pressures measured, there was evidence of winter stack effect in all buildings tested. On the lower levels of all buildings, air was observed flowing from the building into the stairwells and elevator hoistways with pressure differential magnitudes ranging from −2.7 Pa to −24.9 Pa, −12.0 Pa average (−0.011 in. w.g. to −0.100 in. w.g., −0.048 in. w.g. average). Similarly, in most buildings (excluding Buildings 6 and 7) air was observed flowing from the stair and elevator hoistways into the building on the upper levels with pressure differential magnitudes ranging from 0.5 Pa to 34.9 Pa, 11.2 Pa average (0.002 in. w.g. to 0.140 in. w.g., 0.045 in. w.g. average). Under winter conditions, the data suggests that large quantities of air can migrate, floor-to-floor, via unprotected elevator shafts. Data further suggests activation of the stairwell pressurization system can increase vertical air movement via unprotected elevator shafts. This behavior is expected to impact the movement of smoke floor-to-floor during a fire, as airflow is indicative of smoke migration. The exterior stack force on the building’s envelope (governed by the building’s height and temperature differential between the building interior and exterior) does not always translate proportionally to shaft-to-building differential pressures (i.e., “stack effect”), as each building is unique. Although a building’s height and outside temperature play important roles in determining vertical airflow movement within a building, height alone was not found to be a good predictor of vertical airflow (or smoke movement) within the building due to stack effect. Other variables, such as architectural layout, architectural leakage, wind effects, and ventilation systems should all be considered. Simplified algebraic calculations (i.e. hand calculations) do not treat the building as a complete system, and do not account for all variables involved. Therefore, simplified algebraic calculations may result in inaccurate shaft-to-building differential pressure predictions. Based on this analysis, unless conservative leakage values are used, the simplified algebraic calculations may underpredict the shaft-to-building differential pressures. Using simplified algebraic calculations may be suitable for preliminary approximations, however, for design purposes a more complex analysis is recommended. The more complex analysis should consider other variables that affect pressure differentials such as changes in architectural layout and envelope leakage from floor-to-floor, HVAC systems, and wind.

가압 계단실의 방연풍속 형성에 대한 수치해석적 분석

In high-rise commercial buildings, the smoke that occurs in case of a fire tends to be spread rapidly to the horizontal and vertical direction due to the structural characteristics of the buildings. In particular, since the smoke spread to evacuation stairwells and elevator shafts results in the toll of lives, Design Guidelines for Smoke Control System of Special Evacuation Stairwell and Lobby of NFSC 501A was proposed in Korea as one of fire safety standards to prevent the penetration of the smoke into the above mentioned areas. Towards this end, the vestibule pressurization method was largely used in the past, but the stairwell pressurization method is introducing in recent years. This study attempted to analyze whether air egress velocity suitable for the standards is secured, targeting the actual buildings designed with stairwell pressurization system through numerical analysis. For this, a real-size model for numerical analysis was made by measuring the floor plan, airflow, pressure and flow area of any floor in a fire, and velocity to prevent smoke backflow was analyzed.

Full Scale Testing of the Effect of Stairwell Pressurization on Pressure Differential and Flow Velocity

A series of full-scale testing was conducted to examine the effect of stairwell pressurization on the pressure differential between the stairwell and the auxiliary room and between the auxiliary room and the residence. Also, flow velocity profiles at open doors were measured. The building tested was a condominium that had twenty floors above the ground and two floors underground. For pressurization of the stairs, a blower was used to supply air into the stairwell at one location underground. Thirteen different cases were tested, and test variables included the number of floors with open doors and the flow rate of the air supply. When the doors on the first floor were open, the pressure differential between the stairwell and the auxiliary room was distributed almost uniformly except for locations near the first floor. When the flow rate was in the range of 180~270 CMM and the doors of one floor were open, the flow velocity could satisfy the requirement of fire safety standards and the stairwell pressure was positive at all levels. However, the minimum pressure requirement (10 Pa) could not always be satisfied. When doors on two floors were open, the flow velocity requirement could be satisfied by increasing the flow rate, but it was found impractical to satisfy the minimum pressure requirement without causing excessive pressure differential in the area near the blower.

Elevator shaft pressurization for smoke control in tall buildings: The Seattle approach

CONTAM simulations of both commercial and residential tall building models are conducted in order to study recently adopted Seattle code requirements for elevator shaft pressurization systems. In contrast to the International Building Code (IBC) requirements, the Seattle approach specifies across elevator door pressure minimums and maximums on only four “fire floors” (including one above, and two below, the fire floor). This is accomplished using a minimal pressurization of the entire elevator shaft in conjunction with venting of the four fire floors. The present study adresses the feasibility of calibrating such a system to meet the design objectives in tall buildings (system performance during an actual fire event is not considered). The two building models correspond to 37 story buildings with dual elevator and dual stairwell shafts extending the entire height of the building. Each model is calibrated to experimental data. Simulations are conducted for a variety of ambient temperatures and exterior building door positions. Coupled pressurization of the stairwells is also considered. The system requirements are found to be achievable for both elevator only and coupled elevator and stairwell pressurization systems. However, the observed pressure differences do change with changes in the ambient temperature as well as changes in the ground floor exterior door position. It is therefore recommended that such systems should be calibrated for pressure differences intermediate to the prescribed minimum and maximum values to compensate for changes to the system performance. Providing a relief vent to ambient on any recall floor may also be advisable.

On stairwell and elevator shaft pressurization for smoke control in tall buildings

Elevator shaft and stairwell shaft-pressurization systems are studied as means of smoke migration prevention through the stack effect in tall buildings using the CONTAM simulation software. A thirty story building model is considered with exterior leakages calibrated to experimental data for both a residential and a commercial building. Stairwell pressurization is found to be completely feasible in the absence of elevator shaft pressurization. In contrast, coupled elevator shaft-pressurization systems are found to produce prohibitively large pressure differences across both the elevator and stairwell doors if (1) minimum pressure differences must be maintained at both open and closed elevator doors and (2) if the system must function properly when the ground floor exterior building doors are closed. Even in these cases situations arise in which smoke may enter the shaft and be actively distributed throughout the building by the fan system. These differences between stairwell and elevator shaft pressurization are directly attributable to the much larger leakage areas associated with elevator doors. Relatively large flow rates through the open elevator doors act to pressurize the ground floor of the building, indirectly causing large pressure differences across upper floor elevator doors. Furthermore, the results show that there is a strong coupling between the fan speed requirements of the stairwell and elevator shaft-pressurization systems. Fan requirements are also found to be sensitive to the ambient temperature. Effects of the fan location, louvers, vents, the building height, and the number of elevator cars and/or shafts are also addressed.

Mitigation Of Wind Effects On The Performance Of Pressurization Systems In High-rise Buildings

Stairwell pressurization systems should ensure a sufficiently high velocity at open doors between the stairwell and the fire floor without exerting large forces on closed doors in the stairwell. It appears, however, that strong winds may make it difficult, and many times impossible, to fulfill simultaneously these two requirements in tall buildings. A simple model is used for evaluating the possible use of different design parameters, such as the shape and size of the stairwell, the flow resistance of the exit path, the orientation of the exit door, relative to the direction of prevailing strong winds, additional lobbies, pressurization of the elevator shaft, and the type and location of the injection system, for mitigating the effect of winds on the performance of pressurization systems. Several examples are presented and compared. One novel finding is that the use of a helical stairwell configuration, which has a relatively low flow resistance, may drastically reduce adverse wind effects. Results of a 1:10 scale model study of flow in a helical stairwell are presented, which show that its resistance to flow resistance is approximately one quarter of that of convectional type stairwells.

The ASHRAE design manual for smoke control

For many years smoke has been recognized as a major killer in fire situations. In response to this problem, the concept of controlling smoke movement in building fires has developed. The American Society of Heating, Refrigeration, and Air-Conditioning Engineers and the U.S. Veterans Administration have sponsored a design manual for smoke control systems. This paper provides an overview of this manual with emphasis on the principles of smoke control, stairwell pressurization, zone smoke control, computer analysis, and acceptance testing.