Paper 4
The Influence of Air Circulation,
Jet Discharge Momentum Flux and Nozzle Design Parameters on the Tightness
of an
Upwards Blowing Air Curtain
Aki Valkeapää1 and Kai Sirén2
1Mikkeli University of Applied Sciences, Patteristonkatu 3,
FI-50190 Mikkeli, Finland
2Laboratory of Heating, Ventilating and Air Conditioning,
Helsinki University of Technology, Sähkömiehentie 4. FI-02150 Espoo,
Finland
Abstract
Air curtains are used to eliminate airflows through doorways (doorway
tightness). In this paper the impacts of air circulation, jet discharge
momentum flux and nozzle design parameters on the tightness of an upwards
blowing air curtain are presented. The tightness values were measured
using a tracer gas decay method in the laboratory hall. Measurements were
undertaken for two nozzle widths, 30 mm and 120 mm, and for two different
discharge angles, 10° and 30°. According to the study, the upper limit
for the tightness of the upwards blowing air curtain is 80%. The
difference in tightness between a recirculated and non-circulated air
curtain is significant, being 20%. The selection of the jet design
parameters can be undertaken fairly freely as long as the force balance at
the doorway is valid. When the jet discharge momentum is optimal, the
effect of the nozzle width, discharge angle and discharge velocity on the
tightness of the air curtain is small. To keep the tightness level of the
air curtain high enough, regardless of outdoor temperature fluctuation, a
jet velocity controlling system is recommended. In the typical outdoor
temperature range for Finland
(-30°C to +10°C), the lack of a jet velocity controlling system reduces
the tightness of the air curtain by
20 to 60% depending on the nozzle width and discharge angle. When
selecting the jet design parameters by the moment of momentum principle in
a relatively tight building (n50-value < 4.2 1/h), it is recommended to
use a value of 0.6 - 0.7 times the doorway height for the stack neutral
pressure height in order to achieve an airtight air curtain and to avoid
the breakthrough phenomenon.
Key words: air curtain, tightness, air leakage rate, neutral pressure
level, air circulation, jet.
References
ASHRAE: (1985) "ASHRAE Handbook - Fundamentals", Chapter 22.
Costa JJ, Oliveira LA and Silva MCG: (2006) "Energy savings by
aerodynamic sealing with a downward-blowing plane air curtain- A numerical
approach", Energy and Buildings, 38, pp1182-1193.
Downing CC and Meffert WA: (1993) "Effectiveness of cold -storage
door infiltration protective devices", ASHRAE Transactions, 99,
pp356-366.
EN 13829: (2000) "Thermal performance of buildings - Determination
of air permeability of buildings, Fan pressurization method, ISO 9972:
modified 1996", European Committee for Standardization, 23p.
Foster AM, Swain MJ, Barret R, Adago PD and James SJ: (2006)
"Effectiveness and optimum jet velocity for a plane jet air curtain
used to restrict cold room infiltration". International Journal of
Refrigeration, 29, pp692-699.
Hayes FC and Stoecker WF: (1969) "Design Data For Air
Curtains", ASHRAE Transactions 2121, pp168-180.
Howell RH, Van NQ and Smith SE: (1976) "Heat and moisture transfer
through turbulent recirculated plane air curtains", ASHRAE
Transactions 2414, pp191-205.
Longdill GR and Wyborn LG: (1980) "Performance of air curtains in
single storey cold stores", Progress in Refrigeration Science and
Technology, Proceedings of XVth International Congress of refrigeration,
Venice, IV, p77-85.
Siren K: (2003) "Technical dimensioning of a vertically
upwards-blowing air curtain, Part I", Energy and Buildings, 35,
pp681-695.
Takahashi K and Minoru I: (1963) "Some measurements on air curtain
efficiency for cold rooms", Proceedings of the 11th International
Congress of Refrigeration, Munich, pp1035-1039.
Van NQ and Howell RH: (1976) "Influence of initial turbulence
intensity on the development of a plane air curtain jet", ASHRAE
Transactions 2396, pp208-228.
Valkeapää A, Hejazi-Hashemi S and Siren K: (2000) "Experimental
study on upwards blowing air curtain jet", 6th International
Symposium on Ventilation for Contaminant Control, Ventilation 2000,
Helsinki, Finland.
Valkeapää A and Anttonen H: (2004) "Draught Caused by Large
Doorways in Industrial Premises. The International Journal of Ventilation,
3, (1), pp41-51.
|
Contents
Paper
1
Measurement of Ventilation Airflow Rates of 39 Houses by Three Different
Methods
Paper
2
Moisture and Condensation in Residential Buildings in a Relatively Dry
Region
Paper
3
The Measurement of Air Supply Volumes and Velocities in Cleanrooms
Paper
4
The Influence of Air Circulation, Jet Discharge Momentum Flux and Nozzle
Design Parameters on the Tightness of an Upwards Blowing Air Curtain
Paper
5
Experimental Study of Non-Isothermal Diverging Swirling and Non-Swirling
Annular Jets with Central Aspiration
Paper
6
Studying the Effect of Indoor Sources and Ventilation on the
Concentrations of Particulates in Dining Halls
Paper
7
Simulation of Atrium Smoke Filling by Computational Fluid Dynamics
Paper
8
Fire and Smoke Management in a Uni-Directional Road Tunnel for a Congested
Traffic Condition
|
