Experimental studies of mechanical venting for smoke control in tall office buildings

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Experimental studies of mechanical venting for smoke control in tall

office buildings

Tamura, G. T.; Shaw, C. Y.

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EXPERIMENTAL STUDIES O F MECHANICAL VENTING FOR

SMOKE CONTROL IN T A L L O F F I C E BUILDINGS

by

George T. T a m u r a and Chiau-Y u Shaw

~NEJ.**

R e p r i n t e d f r o m

ASHRAE T r a n s a c t i o n s

Vol. 84, P a r t 1 , 1978

p.

54

-

71

DBR P a p e r No. 827

Division of Building R e s e a r c h

P r i c e

25 cents

OTTAWA

NRCC 17234

Des essais ont gt; faits dans quatre bgtiments de grande hauteur en vue

de dgterminer le taux d'extraction d'air exigg pour produire une diffe'lrence

de pression suffisante sur un gtage en proie 5 un incendie de fason

2

emp6cher

la propagation de la fumge aux autres Ptages.

On a dgtermin; les fuites totales

et individuelles, et on a gtudig l'influence des divers modes de fonctionnement

des rgseaux de traitement d'air dans les bitiments sur les taux d'extraction

exiges. Une m6thode graphique a 6t; mise au point pour le choix d'un venti-

lateur d'extraction convenable, en tenant compte des fuites partant des aires

de planchers et atteignant les gaines d

'gvacuation d'air et du

NO. 2472

EXPERIMENTAL STUDIES OF MECHANICAL

VENTING FOR SMOKE CONTROL IN

TALL OFFICE BUILDINGS

GEORGE T. TAMURA, P.E.

DR. CHIA-YU SHAW, P.E.

Member ASHRAE

ABSTRACT

Tests have been conducted on four tall buildings to determine the rate of air extraction

required to produce enough pressure difference across a fire floor enclosure to prevent smoke

from spreading to other floors. Over-all and component leakage values of the floor enclosures

were determined; and the effect on the required exhaust rates of various modes of operating the

building air-handling systems were investigated.

A graphic method was developed for selecting the correct exhaust fan, taking into account

leakage flow from floor spaces into the exhaust shaft as well as the exhaust flow from the fire

floor.

INTRODUCTION

Venting of a fire compartment helps to remove smoke, toxic gases and heat, thereby assisting

firefighters. Provision for venting can be an essential component of an over-all smoke control

system for multi-story buildings; it helps to protect occupants by inhibiting the spread of

smoke and toxic gases from the floor of origin to other floors.

Venting can be effected by providing openings in either the exterior walls or the roof, or

by using a mechanical exhaust system. Size requirements for roof vents in a single-story

building with large compartments are set out in the current NFPA 204, Guide for Smoke and Heat

Venting, and are based on studies conducted by Thomas and Hink1ey.l As there is little

information available on venting requirements applicable to multi-story buildings, a study was

undertaken at DBR/NRC to develop information to aid the designer of exterior wall venting and

mechanical exhaust systems. This paper deals with the latter method of venting, with emphasis

on the exhaust flow rate requirements for preventing smoke spread within a building.

By venting the fire floor with an exhaust fan, pressures on that floor are reduced below

those of adjacent floors so that the direction of gas flow is from the adjacent spaces to the

fire floor, exiting through the exhaust fan. The required pressure difference across the

enclosure of the fire floor is that necessary to overcome the fire pressures, which on the

average are about 12.5 Pa (0.05 in. of water) and can be as high as 37.5 Pa (0.15 in. of water)

for a short t i ~ n e . ~ , ~

In the event of window breakages that create large openings, venting will

no longer be effective in maintaining favourable pressure differences. Furthermore, if

breakages occur during cold weather and the fire floor is located below the neutral pressure

plane, building stack action can cause adverse pressure differences across the fire floor

enclosure. These will be much greater than the pressure differences caused by a fire, and can

result in the spread of smoke to upper floors. For this reason, venting alone does not

constitute an adequate smoke control system. Additional measures are required (for example, the

pressurized building approach to smoke control)

.4

The present study of mechanical venting for

tall buildings was conducted in this context, assuming that the exterior walls remain intact

and that other measures will assist in coping with smoke migration caused by window breakages.

G.T. Tamura and C.Y. Shaw are Research Officers, Energy and Services Laboratory, Division of

Building Research, National Research Council of Canada, Ottawa, Canada.

Reprinted from ASHRAE TRANSACTIONS, Volume 84, Part 1, pages

54-71,

by permission

of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Copyright 1978.

The exhaust flow rate required to produce a given pressure difference across the fire floor enclosure depends, of course, on the air leakage characteristic of the enclosure. The major components through which air can leak are the exterior walls, floor, ceiling, and walls of elevator, stair and various service shafts. The exhaust flow rate also depends on how the building air-handling systems are operated, together with mechanical smoke exhaust. To develop such information, tests were conducted on four tall office buildings ranging in height from 19 to 27 stories.

TEST PROCEDURE

The mechanical venting tests were conducted on buildings designated A, B, C, and D, and described in Table 1. A 23.5-m3/s (50,000-cfm) fan equipped with variable-pitch blades and mounted on a trailer was used to extract air from the test floor, always either the 4th or 5th floor. The inlet side of the fan was connected to one of the stairshafts (stairshaft No. 1) by means of a number of 0.914-m (3-ft) diameter aluminum ducts (Fig. 1). The stairshaft served as part of the exhaust system simply by opening the stair door on the test floor. To minimize extraneous leakage flow into the exhaust system, all other doors of this stairshaft were sealed with tape as well as

all

joints in the aluminum ductwork. Total pressure averaging tubes and static pressure taps were installed in the aluminum ductwork for measuring the rate of air exhaust. These were calibrated with pitot traverses, which indicated that the accuracy of the flow measurement was within 5%.

An

orifice plate was inserted in the ductwork to measure flow rates less than 4.7 m3/s (10,000 cfm)

.

Tests were conducted during mild weather, with outside temperatures ranging between 18 and 24OC (64 and 7S°F). The central air-handling systems of the buildings were put into one of the following modes of operation to simulate their possible role as part of a smoke control system:

1. all building air-handling systems shut down,

2. all building air-handling systems shut down, with the inlet openings of the return air systems on the test floor sealed,

3. all building air-handling systems operating,

4. all building air-handling systems operating, with inlet openings of the return air systems on the test floor sealed.

The significance of each of these modes of operation will be discussed later.

With the building air-handling systems operating in the required mode, the exhaust flow rate was adjusted to achieve pressure differences across the test floor enclosure of about 12.5(0.05), 25 (0. lo), 37.5 (0.15) and 50 (0.20) Pa (in. of water)

.

Pressure differences were measured across the stair door, elevator doors, and the floor and ceiling constructions on the test floor; and across the doors of the stairshaft serving as an exhaust shaft on several other floors. A diaphragm-type pr.essure transducer with silicon piezo-resistive gauge (static error band of 5% full-scale output) was used. The exhaust air flow rate at the inlet ductwork of the exhaust fan was also measured, as were air velocities (using a hot wire anemometer) at 12 locations in the stair door opening on the test floor. The door to stairshaft No. 2 on the test floor was opened, and the air flow velocities were measured with pressure differences across the test floor enclosure of 25 and 50 Pa (0.10 and 0.20 in. of water). This was repeated with the stair door on the ground floor (of stairshaft No. 2) also open.

The air tightness values of the exterior walls, and stair and elevator shafts of Buildings A, B, C and D have already been r e p ~ r t e d . ~ , ~ To determine the air tightness value of the floor construction, tests were conducted on Buildings A, B, and C, using the test arrangement shown in Fig. 1. Air leakage characteristics of the enclosures for two adjacent floors were measured both separately and in combination. When tested in combination, both floors were exhausted at the same time by opening the doors of the stairshaft connected to the exhaust fan. For a given pressure difference across the test floor enclosure, the sum of the exhaust flow rates of the two floors measured individually will be greater than that measured in combination, because the former would have two additional floor constructions for air to leak through. One-half of the difference between the two exhaust flow rates, therefore, represents the leakage rate through one floor construction. As a check on the method, air leakage characteristics of the enclosure of three adjacent floors of Building A were measured separately and in combination.

RESULTS AND DISCUSSION

The rate of leakage from all the floors into stairshaft No. 1, based on air leakage data for the test buildingsY6 was subtracted from the exhaust flow rate measured in the duct leading to the

fan. The exhaust flow r a t e s calculated from a i r v e l o c i t i e s measured a t t h e s t a i r door opening on t h e t e s t f l o o r , using a hot-wire anemometer t r a v e r s e , were about 17% lower than t h e adjusted fan exhaust r a t e s (Fig. 2). On t h e assumption t h a t they a r e more accurate, t h e adjusted fan exhaust r a t e s a r e used i n t h i s paper.

A i r Leakage C h a r a c t e r i s t i c s of Floor Enclosure f o r Various Modes of Air-Handling System Operation A i r leakage values of t h e f l o o r enclosure a r e shown i n Fig. 3 with air-handling systems shut down. The a i r leakage r a t e s ( a i r exhaust r a t e s ) a r e expressed i n a i r changes/hr based on t h e gross f l o o r volume. The a i r exhaust r a t e s required t o produce a pressure d i f f e r e n c e of 25 Pa (0.10 i n . of water) across t h e f l o o r construction v a r i e d from 3.2 t o 6.0 a i r changes/hr. With air-handling systems shut down, t h e branch a i r ducts of t h e supply, r e t u r n , and exhaust systems provided paths f o r a i r t o flow from o t h e r f l o o r s i n t o t h e t e s t f l o o r .

I f t h e r e t u r n a i r system were t o be operated a s a smoke exhaust system, t h e branch r e t u r n a i r ducts would not a c t as leakage openings i n t h e f l o o r enclosure. To r e p r e s e n t t h i s case, t e s t s were conducted with t h e branch r e t u r n a i r ducts on t h e t e s t f l o o r sealed. A s expected, exhaust r a t e s required t o produce a pressure d i f f e r e n c e of 25 Pa (0.10 i n . of water) (Fig. 4) were lower than those i n t h e previous case and varied from 2 . 2 t o 5.0 a i r changes/hr.

Tests conducted with t h e building air-handling systems operating represented supply a i r systems bringing i n only o u t s i d e a i r and r e t u r n a i r systems exhausting 100%. These t e s t s (Fig. 5) indicated t h a t t h e required exhaust r a t e s with a separate exhaust system were about t h e same a s with t h e building air-handling systems shut down (Fig. 3) f o r Buildings A and D but lower f o r Buildings B and C .

The r e s u l t s of t h e t e s t s with t h e building air-handling systems operating and with t h e r e t u r n a i r ducts on t h e t e s t f l o o r sealed a r e shown i n Fig. 6. When t h e exhaust fan was o f f , t h e t e s t f l o o r enclosure was pressurized. The exhaust a i r r a t e s required t o produce zero pressure d i f f e r e n c e across t h e f l o o r enclosure r e p r e s e n t t h e r a t e s of supply a i r t o t h e f l o o r : about

1.4 a i r changes/hr f o r Building A, and 3.5 a i r changes/hr f o r Buildings B , C and D. Building A

i s equipped with a v a r i a b l e air-volume type i n t e r i o r supply a i r system, whereas t h e o t h e r buildings a r e equipped with a constant volume system. This may account f o r p a r t of t h e l a r g e difference i n t h e supply a i r r a t e s .

With equal supply a i r r a t e s t o a l l f l o o r s , a s f o r t h e pressurized building approach t o smoke c o n t r o l , t h e pressure d i f f e r e n c e s across t h e f l o o r construction a r e zero because a l l f l o o r s w i l l be pressurized by t h e same amount. The curves of Fig. 6, t h e r e f o r e , were s h i f t e d t o t h e r i g h t

so t h a t each curve s t a r t e d a t zero pressure d i f f e r e n c e on t h e abscissa a t zero exhaust flow r a t e , a s shown i n Fig. 7. This f i g u r e , i n e f f e c t , shows t h e a i r leakage c h a r a c t e r i s t i c s of t h e f l o o r enclosure with no supply and r e t u r n a i r ducts p e n e t r a t i n g it. The required exhaust flow r a t e s , which varied from 1.3 t o 3.7 a i r changes/hr a t 25 Pa (0.10 i n . of water) pressure d i f f e r e n c e , were found t o be t h e lowest of t h e four cases i n v e s t i g a t e d . I f t h e supply a i r t o t h e f i r e f l o o r were stopped, t h e required exhaust r a t e s would be lower than those shown i n Fig. 7.

In s i z i n g t h e exhaust fan, t h e t o t a l r a t e of a i r leakage from a l l f l o o r s i n t o t h e v e r t i c a l exhaust s h a f t must be added t o t h e exhaust r a t e a t t h e f i r e f l o o r t o determine t h e required fan capacity. Graphical methods f o r determining t h e required fan capacity and t h e t o t a l pressure drop within t h e exhaust s h a f t were developed and a r e given i n Appendix A. A s shown i n t h e example, t h e t o t a l a i r leakage r a t e of t h e exhaust s h a f t can be much g r e a t e r than t h e exhaust r a t e a t t h e f i r e f l o o r .

D i s t r i b u t i o n of Leakage Openings i n Floor Enclosure

Table 2 gives t h e estimated s i z e s of leakage openings i n t h e f l o o r enclosure of t h e t e s t buildings expressed i n terms of equivalent o r i f i c e a r e a based on a i r flow r a t e s a t 25 Pa

(0.10 i n . of water). The t o t a l leakage opening was c a l c u l a t e d , using t h e a i r leakage d a t a given i n Fig. 3, with t h e building air-handling systems shut down. Leakage openings f o r e l e v a t o r s h a f t s , s t a i r s h a f t s , and outside walls were calculated from t h e a i r leakage d a t a f o r t h e t e s t buildings reported i n Ref 5 and 6. The leakage openings f o r t h e f l o o r construction were determined from Fig. 8, which i s based on t h e average leakage value of two f l o o r

constructions. Tests repeated on Building A t o give an average value f o r four f l o o r

constructions r e s u l t e d i n a leakage value s l i g h t l y higher than t h a t given i n Fig. 8. Possible sources of leakage i n t h e f l o o r construction a r e t h e j o i n t s between f l o o r and outside walls and around e l e c t r i c a l conduits and pipes. Another, which was not present i n t h e buildings t e s t e d ,

perimeter induction u n i t s . Leakage a r e a s f o r t h e building air-handling systems were determined from t h e a i r leakage r a t e s , calculated by s u b t r a c t i n g t h e r a t e s given i n Fig. 7 (building a i r - handling systems operating, with t h e r e t u r n a i r ducts sealed) from those given i n Fig. 3

(building air-handling systems shut down). The leakage areas of t h e s h a f t s f o r t h e usual building s e r v i c e s were obtained by summing t h e leakage a r e a s from o t h e r sources and s u b t r a c t i n g them from t h e t o t a l leakage area. Values i n Table 2 can serve as a guide f o r computer modeling i n studying a i r and smoke movement i n buildings.

Effect of Opening a S t a i r Door on a Mechanically Vented Floor

Values of exhaust flow r a t e s and t h e concommitant pressure d i f f e r e n c e s across t h e f l o o r construction and walls of e l e v a t o r and s t a i r s h a f t s a r e given i n Table 3 f o r t h e case with t h e doors of s t a i r s h a f t No. 2 closed. They a r e compared with flow r a t e s f o r t h e s t a i r door on t h e t e s t f l o o r open and f o r t h e s t a i r doors on both t e s t and ground f l o o r s open. Exhaust flow r a t e s were adjusted t o give a pressure d i f f e r e n c e across t h e f l o o r construction of 25 Pa (0.10 i n . of water) and 50 Pa (0.20 i n . of water) with t h e s t a i r door closed and with t h e building a i r - handling systems shut down. A l l s t a i r doors measured 0.914 m ( 3 f t ) by 2.13 m ( 7 f t ) . When open, each was held i n t h e maximum open p o s i t i o n . The a i r v e l o c i t i e s and flow r a t e s a t t h e s t a i r door opening i n Table 2 were determined from a i r v e l o c i t i e s measured with a hot-wire anemometer t r a v e r s e , and a s previously indicated ( ~ i g . 2) a r e probably lower than t h e a c t u a l values.

This s e r i e s of t e s t s was designed t o evaluate t h e performance of venting systems when

f i r e f i g h t e r s open s t a i r doors t o gain access t o t h e f i r e f l o o r . With t h e s t a i r door open on t h e vented f l o o r , t h e pressure d i f f e r e n c e s across t h e f l o o r enclosure were reduced by about SO%, and when t h e s t a i r door on t h e ground f l o o r a l s o was opened, a f u r t h e r s i g n i f i c a n t reduction

occurred i n t h e pressure d i f f e r e n c e s , except f o r Building D which had a closed door i n s i d e t h e s t a i r s h a f t between t h e ground f l o o r and t h e f l o o r above. The a i r flow r a t e s through t h e open s t a i r door on t h e vented f l o o r were 20 t o 42% of t h e exhaust flow r a t e s , and these increased t o 44 t o 78% when t h e ground f l o o r s t a i r door a l s o was opened, except f o r Building D where flow r a t e increased by only a small amount.

CONCLUSION

The exhaust r a t e required t o produce a given pressure d i f f e r e n c e across a f l o o r enclosure depends on t h e a i r leakage c h a r a c t e r i s t i c of t h e enclosure and t h e operational mode of t h e building air-handling systems. The o v e r - a l l and component a i r leakage values of t h e f l o o r enclosures were determined and a r e given i n Table 3. The required exhaust r a t e s f o r t h e four modes of building air-handling system operation a r e given i n Fig. 3, 4, 5 and 7. The case with t h e building air-handling systems shut down required t h e highest exhaust r a t e s . They were lower with t h e supply a i r systems shut down and with t h e r e t u r n a i r systems e i t h e r a c t i n g a s an

exhaust system serving only t h e f i r e f l o o r o r shut down and dampered on a l l f l o o r s . With t h e supply a i r system supplying 100% outside a i r and t h e r e t u r n a i r s y s t e m s e x h a u s t i n g from a l l f l o o r s t o o u t s i d e , t h e required exhaust r a t e s f o r a separate exhaust system were equal t o o r lower than with t h e building air-handling systems shut down. The lowest required exhaust r a t e s were

obtained with t h e supply a i r systems supplying 100% outside a i r t o a l l f l o o r s and with t h e r e t u r n a i r systems e i t h e r shut down and dampered o r serving a s a f i r e f l o o r exhaust system. For t h i s case, t h e required exhaust r a t e s would be lower s t i l l i f t h e supply a i r t o t h e f i r e f l o o r were stopped.

Based on t h e t e s t r e s u l t s of four b u i l d i n g s , an exhaust r a t e a t t h e f i r e f l o o r of about 6.0 a i r changes/hr f o r most t a l l o f f i c e buildings w i l l probably produce pressure d i f f e r e n c e s across t h e f i r e f l o o r enclosure s u f f i c i e n t t o prevent smoke migration as a r e s u l t of f i r e pressures. In determining t h e s i z e of t h e exhaust fan, t h e designer must take i n t o account t h e leakage flow i n t o t h e exhaust s h a f t . I t can be s u b s t a n t i a l f o r an exhaust system serving many s t o r i e s

(Appendix A)

.

Opening t h e s t a i r door on t h e f i r e f l o o r during f i r e f i g h t i n g

w i l l

cause a s u b s t a n t i a l

reduction i n t h e pressure d i f f e r e n c e s across t h e f l o o r enclosure produced by t h e exhaust system. This, however, i s accompanied by a s u b s t a n t i a l inflow of a i r from t h e s t a i r s h a f t t h a t w i l l a s s i s t f i r e f i g h t e r s attempting t o gain access t o t h e f i r e f l o o r .

REFERENCES 1

Thomas, P.H. and P.L. Hinkley, Design of Roof Venting Systems for Single-Story Buildings, Fire Research Technical Paper No. 10, Ministry of Technology, Industrial and Fire Offices

Committee, Joint Fire Research Organization, Her Majesty's Stationary Office, London, 1964. De Cicco, P.R., R.J. Cresci and W.H. Correale, Report of Fire Tests, Analysis and Evaluation of Stair Pressurization and Exhaust in High-Rise Office Buildings Performed for the New York City Fire Department. Center for Urban Environmental Studies, Polytechnic Institute of Brooklyn, September 1972.

Butcher, E.G., P.J. Fardell and J. Clark, Pressurization as a Means of Controlling the Movement of Smoke and Toxic Gases on Escape Routes. JFRO Symposium No. 4, Movement of Smoke

in Escape Routes in Buildings, Paper 5, Watford, 1969.

Tamura, G.T. and J.H. McGuire, The Pressurized Building Method of Controlling Smoke in High-Rise Buildings, National Research Council of Canada, Division of Building Research, NRCC 13365, September 1973.

Tamura, G.T. and C.Y. Shaw, Studies on Exterior Wall Air Tightness and Air Infiltration of Tall Buildings, ASHRAE TRANSACTIONS, Vol. 82, Part I, p 122, 1976.

Tamura, G.T. and C.Y. Shaw, Air Leakage Data for the Design of Elevator and Stair Shaft Pressurization Systems, ASHRAE TRANSACTIONS, Vol. 82, Part 11, p 179-190, 1976.

ACKNOWLEDGEMENTS

The authors are indebted to the Department of Public Works for their co-operation in making this study possible, and wish to acknowledge the assistance of R.G. Evans in the field tests and processing of test results. This paper is a contribution from the Division of Building Research, National Research Council of Canada, and is published with the approval of the Director of the Division.

TABLE 1

Description of Test Buildings

Building

No.

of

Typical Floors

F l o o r Plan, m x m ft x

fr

Floor Height, m

Floor Volume, m5

No. of S t a i r s h a f t s No. of Elevator Shafts

Serving Each Floor 2 2-car s h a f t s 2 2-car s h a f t s 2 2-car s h a f t s 2- and 3-car s h a f t s

Window Type Openable sealed

double glazing (key locked) Fixed sealed double glazing Fixed sealed double glazing Fixed s e a l e d double glazing

Exterior Wall Precast

concrete panel

Precast

concrete panel

Metal panel Precast

concrete panel

Floor Construction Reinforced

concrete s l a b Reinforced concrete s l a b Reinforced concrete s l a b Reinforced concrete slab

HVAC System Central perimeter

induction u n i t v a r i a b l e volume i n t e r i o r supply Central perimeter induction u n i t constant volume i n t e r i o r supply

Central

perimeter induction u n i t constant volume i n t e r i o r supply Central perimeter induction u n i t constant volume i n t e r i o r supply

TABLE 2

Building

Estimated Size of Leakage Openings in Test Floor Enclosure (Air-Handling Systems Shut Down)

2 2

Leakage Openings in Terms of Equivalent Orifice Area, m (ft )

2 Elevator Shafts 2 Stair Shafts Outside Walls 2 Floor Constructions Air-Handling Systems Service Shafts Total

TABLE

3

Results of Floor Mechanical Venting Test at 25 and 50 Pa Pressure Differences

(Building Air-Handling Systems Shut Down)

Test

Building

Pressure Differences, Pa

Exhaust Flow Rate, m3/s

AP Floor Construction,

Pa

AP Elevator Shaft, Pa

AP Stair Shaft No. 2, Pa

Door of Stair Shaft No. 2 Open on Test Floor

Q

Exhaust Flow Rate,

m3/s

AP Floor Construction, Pa

AP Elevator Shaft, Pa

Average Air Velocity through Open Stair Door, m/s

Air

Flow

Rate through

Open Stair Door, m3/s

Doors of Stair Shaft No. 2

Open on Test and Ground Floors

Exhaust Flow Rate,

m3/s

AP Floor Construction, Pa

AP Elevator Shaft, Pa

Average Air Velocity through Open Stair Door, m/s

Air Flow Rate through Open Stair Door, m3/s

Note:

Above

readings apply to test floor

1 m/s =

196.8 ft/min

1 m3/s = 2119 cfm

S T A I R S H A F T NO. 2 S T A I R S H A F T NO. 1 ( S T A I R DOORS S E A L E D

I

E L E V A T O R

I

W I T H T A P E ) S H A F T T E S T F L O O R E X H A U S T

-

L O C A T I O N O F P R E S S U R E D I F F E R E N C E MEASUREMENT F i g . 1 A r r a n g e m e n t f o r m e c h a n i c a l v e n t i n g t e s t s E X H A U S T F L O W R A T E A T F A N I N L E T D U C T , 1 0 0 0 C F M F A N 1 4 1 . E X H A U S T F L O W R A T E A T F A N I N L E T _{D U C T D E T E R M I N E D F R O M V E L O C I T Y}

I

PRESSURE A V E R A G I N G TUBE R E A D I N G S A N D C O R R E C T E D F O R S T A I R S H A F T W A L L L E A K A G E S .

-

_{2 .} E X H A U S T F L O W R A T E A T S T A I R

-

25 D O O R O P E N I N G DETERMINE^ F R O M 1 2 - P O I N T A I R V E L O C I T Y R E A D I N G S T A K E N W I T H A

-

H O T W I R E A N E M O M E T E R .

/

t

-

_{1 0} E X H A U S T F L O W R A T E A T F A N I N L E T D U C T , 3 m I s F i g . 2 C o m p a r i s o n o f e x h a u s t f l o w _{r a t e s m e a s u r e d a t s t a i r} d o o r o p e n i n g a n d f a n i n l e t d u c t

PRESSURE DIFRRENCE ACROSS FLOOR CONSTRUCTION OF TEST FLOOR. in. OF WATER

8

-

-1 B U I L D I N G 0 B U I L D I N G C AIR C H A N G E h r BASED O N

-

GROSS V O L U M E O F T E S T FLOOR P R E S S U R E D I F F E R E N C E A C R O S S F L O O R C O N S T R U C T I O N O F T E S T F L O O R . P a

PRESSURE DIFRRENCE ACROSS FLOOR CONSTRUCTION OF TEST FLOOR, in. OF WATER

l o O

0. 05 _I 0. 10 _I 0 . 1 5 _I 0. 20 _I 0. 25 _I 0. 30 8

-

_{B U I L D I N G D}

-

P R E S S U R E D I F F E R E N C E A C R O S S F L O O R C O N S T R U C T I O N O F T E S T F L O O R , P a F i g . 3 A i r l e a k a g e c h a r a c t e r i s t i c s F i g . 4 A i r l e a k a g e c h a r a c t e r i s t i c s o f f l o o r e n c l o s u r e

-

b u i l d i n g a i r - o f f l o o r e n c l o s u r e

-

b u i l d i n g a i r - h a n d l i n g s y s terns s h u t d o w n h a n d l i n g s y s t e m s s h u t d o w n , r e t u r n a i r d u c t s o n t e s t f l o o r s e a l e d

PRESSURE DIFFERENCE ACROSS FLOOR CONSTRUCT I O N OF TEST FLOOR, in. OF WATER

I I I I I

-

-

-

B U I L D I N G C B U I L D I N G B P R E S S U R E D I F F E R E N C E A C R O S S F L O O R C O N S T R U C T I O N O F T E S l F L O O R , P a F i g . 5 A i r l e a k a g e c h a r a c t e r i s t i c s o f f l o o r e n c l o s u r e

-

b u i l d i n g a i r - h a n d l i n g s y s terns o p e r a t i n g 10

P R E S S U R E D l F F E R E N C E A C R O S S F L O O R C O N S T R U C T I O N O F T E S T F L O O R , i n . O F W A T E R P R E S S U R E D I F F E R E N C E A C R O S S F L O O R C O N S T R U C T I O N O F T E S T F L O O R , P a

-0.30

-0.20

-0.10

0

0.10

0. 20

0. 30

F i g . 6 A i r l e a k a g e c h a r a c t e r i s t i c s o f f l o o r e n c l o s u r e

-

b u i l d i n g a i r h a n d l i n g s y s t e m s o p e r a t i n g , r e t u r n a i r d u c t s o n t e s t f l o o r s e a l e d

10

6 4

PRESSURE DIFFERENCE ACROSS FLOOR CONSTRUCTION OF TEST FLOOR, in. OF WATER

I 1 I T B U I L D I N G D 8'L 3

-

-

_{B U I L D I N G B} B U I L D I N G C

*

-I

B U I L D I N G A *dH / / L I I &.A *' I I I I A I L * 1 1 1 1

-

15

-50

-

25

0

2 5

5

0

75 P R E S S U R E D I F F E R E N C E A C R O S S F L O O R C O N S T R U C T I O N O F T E S T F L O O R , P a

PRESSURE OIFRRENCE ACROSS FLOOR, in. OF WATER

P R E S S U R E D I F F E R E N C E A C R O S S F L O O R , P a F i g . 8 A i r l e a k a g e c h a r a c t e r - i s t i c o f f l o o r c o n s t r u c t i o n F i g . 7 A i r l e a k a g e c h a r a c t e r i s t i c s o f f l o o r e n c l o s u r e

-

b u i l d i n g a i r - h a n d l i n g s y s t e m s o p e r a t i n g r e t u r n a i r d u c t s s e a l e d ( m o d i f i e d )

APPENDIX A

SIZING OF EXHAUST FAN

I n s e l e c t i n g an exhaust fan f o r venting t h e f i r e f l o o r

t o

t h e e x t e r i o r v i a a v e r t i c a l s h a f t , one must know t h e t o t a l exhaust a i r r a t e and t h e t o t a l pressure l o s s of t h e exhaust system. The t o t a l exhaust a i r r a t e i s t h e sum of t h e required exhaust a i r r a t e a t t h e f i r e f l o o r and t h e a i r leakage r a t e s through dampers and walls of t h e exhaust s h a f t . The t o t a l pressure l o s s i s t h e

sum

of t h e pressure l o s s across t h e f i r e f l o o r vent, t h e f r i c t i o n pressure l o s s i n s i d e t h e s h a f t and t h e momentum pressure l o s s caused by t h e leakage flow.

Equations f o r c a l c u l a t i n g t h e t o t a l exhaust a i r r a t e and pressure l o s s were derived by t h e authors i n a previous paper,A1 now rearranged a s follows:

where

Pv = Pressure l o s s across f l o o r vent of a venting s h a f t

K = C o e f f i c i e n t = 1.8 +

[:I2

p = A i r d e n s i t y

Qv = Required exhaust a i r r a t e a t t h e f i r e f l o o r

Av = Area of f l o o r vent

PT = Total pressure l o s s of t h e exhaust s h a f t

f-

= F r i c t i o n f a c t o r (0.025)

L = Height of s h a f t

As = Cross-sectional a r e a of exhaust s h a f t

Ds = Equivalent diameter of s h a f t [Ds =

-

4As

S

where S i s t h e perimeter of s h a f t

1

Qt = Total exhaust a i r r a t e

4s

= Leakage a r e a i n s h a f t wall p e r story/Av (see Table Al) $d = Leakage a r e a of damper p e r story/Av (see Table Al)

4

=

4 , + 4 ,

N = Number of s t o r i e s

These equations were solved using the iterative technique and a digital computer. The results are shown in Fig. A1 to A3.

Example: Estimate the total exhaust air rate and the total pressure loss of a mechanically vented smoke shaft for the following design conditions:

Dimensions of fire floor: 30 m by 50 m by 3 m

Total number of floors: 2 0

Size of smoke shaft: 2 m b y 3 m

Size of floor vent: 1.2 m by 2 m

Leakage value per story

(g

s + 'd) 0.0825 (0.0375 for unplastered masonry wall and

0.045 for multi-blade fire damper) Air exhaust rate at fire floor: 6 air changes/hr.

Solution: (a)

Q,,

Volume of the fire floor = 30 x 50 x 3 = 4500 m 3

3 3

Qv = 6 x 4500 = 27000 m /hr = 7.5 m /s (b) Pv

From Fig. Al, for \/Av = 3.13 and AV/As = 0.4, we have Pv = 11.72 Pa

(c)

QT

= 25 L/Ds =

-

2.4 N+ = 20 x 0.0825 = 1.65

From Fig. A2(b), for Ng = 1.65, Av/As = 0.4 and L/Ds = 25, we have

-

Qt

-

-

3.3

Q,,

3

Q,,

= 7.5 m /s 3

Q

= 3.3 x 7.5 = 24.75 m /s T

QT

From Fig. A3, f o r

-

= 3.3 and NI$ = 1.65, we have

%

3

The exhaust fan should be s e l e c t e d on t h e b a s i s of a t o t a l flow r a t e of 24.75 m /s

and

a t o t a l pressure l o s s i n t h e exhaust s h a f t of 38.0 Pa.

REFERENCE

A l . Tamura, G.T. and C.Y. Shaw, Basis f o r t h e Design of Smoke Shafts, F i r e Technology, Vol. 9, No. 3, pp. 209-222, August 1973.

TABLE A 1

Leakage Area of Exhaust Shaft (I$)

Leakage Area of Exhaust Shaft Wall Wall Construction

Monolithic concrete 6

Masonry wall unplastered 6

Masonry wall p l a s t e r e d 6

Gypsum wallboard on s t e e l studs (assumed)

Leakage Area of Dampered Opening i n Exhaust Shaft Type of F i r e Damper +d Curtain f i r e damper Single-blade f i r e damper Multi-blade f i r e damper

Note: As = cross-sectional a r e a of venting s h a f t

A = a r e a of f i r e f l o o r vent v

+,

= leakage a r e a i n s h a f t wall p e r s t o r y / \

+d = leakage a r e a of damper per story/Av

(Values were determined from t e s t s conducted a t DBR/NRC)

DISCUSSION

CLINTON HEDSTEN, O x f o r d D e v e l o p m e n t , M i n n e a p o l i s , M N : R e g a r d i n g t h e e f f e c t o f h e i g h t o f t h e t e s t f l o o r d u e t o p r e s s u r e d r o p o f s t a i r s h a f t : The f a r t h e r f r o m t h e f a n , t h e h i g h e r t h e AP b e t w e e n f a n a n d t e s t d o o r . G.T. TAMURA, D R . C . Y . SHAW: T h e u s u a l a r r a n g e m e n t f o r m e c h a n i c a l v e n t i n g i s t o l o c a t e t h e f a n a t t h e t o p o f t h e e x h a u s t s h a f t . I n o u r t e s t a r r a n g e m e n t , t h e f a n was l o c a t e d a t g r a d e l e v e l w i t h o n e o f t h e s t a i r s h a f t s s e r v i n g a s a n e x h a u s t s h a f t . T h e p r e s s u r e d r o p i n s i d e t h e s t a i r s h a f t w i l l i n c r e a s e w i t h a n i n c r e a s e i n t h e d i s t a n c e b e t w e e n t h e t e s t f l o o r a n d t h e f a n l o c a t i o n . L i k e w i s e , i n a r e a l s i f u a t i o n , t h e p r e s s u r e d r o p i n s i d e a n e x h a u s t s h a f t w i l l i n c r e a s e w i t h a n i n - c r e a s e i n t h e d i s t a n c e b e t w e e n t h e f i r e f l o o r a n d t h e e x h a u s t f a n . The p r o c e d u r e f o r c a l c u l a t i n g t h e r e q u i r e d f l o w c a p a c i t y a n d p r e s s u r e d r o p g i v e n i n A p p e n d i x A w a s b a s e d o n t h e w o r s t s i t u a t i o n , w i t h t h e f i r e f l o o r a s s u m e d t o b e l o c a t e d o n t h e l o w e s t f l o o r t o b e v e n t e d w i t h t h e e x h a u s t f a n a t t h e t o p o f t h e b u i l d i n g . ELLIOTT E. HILL, J o h n s o n 5 J o h n s o n , C h i c a g o , I L : Can y o u g e n e r a l i z e y o u r t e s t r e s u l t s f o r s i n g l e - s t o r y ( l a r g e , medium, o r s m a l l ) i n d u s t r i a l p l a n t s , " 1 , 5 0 0 , 0 0 0 t o 1 0 0 , 0 0 0 f t 2 ?

G.T. TAMURA, D R . C . Y . SHAW: The t e s t r e s u l t s c a n n o t b e u s e d f o r s u c h b u i l d i n g s a s t h e d a t a w e r e o b t a i n e d f o r c o m p a r t m e n t e d b u i l d i n g s , w i t h t h e o b j e c t o f p r e - v e n t i n g s m o k e g e n e r a t e d i n t h e f i r e f l o o r f r o m m i g r a t i n g i n t o o t h e r f l o o r s v i a t h e v e r t i c a l . s h a f t s s u c h a s e l e v a t o r a n d s t a i r s h a f t s ; t h e v e n t i n g r a t e f o r a d e s i r e d s u c t i o n p r e s s u r e o n t h e f i r e f l o o r d e p e n d s o n t h e a i r l e a k a g e c h a r a c - t e r i s t i c s o f t h e f l o o r e n c l o s u r e . I t i s l i k e l y t h a t a d i f f e r e n t a p p r o a c h i s r e q u i r e d i n d e t e r m i n i n g t h e v e n t i n g r a t e f o r i n d u s t r i a l - t y p e b u i l d i n g s . A s f o r r o o f v e n t s , t h e a p p r o a c h may b e t o s i z e t h e f a n t o m i n i m i z e t h e b u i l d u p o f s m o k e l a y e r u n d e r n e a t h t h e r o o f . E.E. HILL: A r e t h e r e a n y p l a n s t o t e s t i n d u s t r i a l - t y p e b u i l d i n g s w i t h s a w t o o t h , h i g h / l o w b a y , f l a t r o o f , r o o f s , o r b r i c k , w o o d , b u t l e r e n c l o s u r e w a l l s ? G.T. TAMURA, D R . C . Y . SHAW: We r e c o g n i z e t h e n e e d t o d e v e l o p t e s t d a t a f o r i n d u s t r i a l - t y p e b u i l d i n g s . H o w e v e r , we a r e n o t p l a n n i n g t o c o n d u c t s u c h t e s t s a t t h i s t i m e .

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