Novenco Car Park Systems

Technical Description October 2006

1

Cars have become a natural part of everyday life.Despite widespread public transport systems,most people nowadays own a car. Parking facili-ties are therefore in great demand, particularly incities and large towns. Conventional, open-air carparks take up far too much space, while people toan increasing degree prefer parks and open spac-es in their cities and towns.

In other situations, climate conditions or a desireto prevent parked cars from being vandalised ne-cessitate closed parking facilities. To meet theserequirements, more and more multi-storey carparks are being built, both below and aboveground level.

However, car exhaust contains several hazardousgases, carbon monoxide (CO) and benzeneamong others, and these must be extracted fromcar parks for health reasons.

For many years, Novenco has supplied fans forroad tunnels, and their design and further devel-opment have often taken place in close coopera-tion with the authorities. Since 1993/94, we haveput this experience to use in multi-storey carparks.

Road tunnel ventilation is often based on jet tech-nology, and the fans used are of jet type. Novencohas adapted the design of their jet fans to suit carparking facilities where, among other things, lowsound emission and minimum height are impor-tant, the latter in consideration of the relativelylow clearance.

Over the years, Novenco has established a uniqueexpertise in car park ventilation. Based on our ex-perience in the densely populated Netherlandsand the large cities of Germany where space is ata premium, Novenco has developed car park ven-tilation systems for CO extraction and smoke con-trol in case of fire. The main purpose of this book-let is to describe the principles of CO ventilation incar parks and to provide a brief description ofsmoke extraction and control.

The systems are characterised by low installationand energy costs. They require no ducts in the carpark and are thus extremely flexible.

Our references include CO and smoke control sys-tems installed in the Netherlands, Germany, Den-mark, Portugal, Sweden, Norway, the UK and Bel-gium.

MU 13734 1006

Preface

2

Air transportVentilation is the transport of air. To transport aira mass must be moved. At 20°C, the density of airis approx. 1.2 kg /m3. Ventilating 10 m3 air there-fore involves moving a mass of 12 kg.

Air can be moved in three ways. The best knownmethod is to transport it through ducting bymeans of a fan that either sucks or pushes the airthrough the duct.

It is also well known that air moves vertically in re-sponse to thermal differentials.

The third method is known as jet ventilation andutilises the fact that a moving body changes ve-locity when it is subjected to a "pushing force". Inphysics, this phenomenon is known as thrust.

On the basis of continuous testing, the use of jetventilation has been optimised and integratedinto car park safety systems.

This booklet provides information on the possibil-ities provided by jet ventilation.

Car park typesBasically, there are two types of car park, open orclosed.

Open car parks include uncovered car parks andthose that are sufficiently open to ensure the ne-cessary ventilation. Several requirements must bemet before a car park is classified as being open.Each country has its own regulations, which may bemore or less stringent. Generally, requirements aremore specific in countries with a longer tradition ofbuilding car parking facilities and thus more expe-rience in their design.

Fig. 1

In Denmark, for example, the following applies tocar parking facilities of more than 2000 m2 (article6(17)(1)(4) of BR 95, the Danish building regula-tions): "A sprinkler system is not required if venti-lation openings with a free area corresponding toat least 5% of the floor area are provided. Theopenings must be evenly distributed and must beincapable of being closed. There must never bemore than 12 m horizontal distance to the nearestopening."

In the Netherlands, all the following require-ments must be met:

1. Natural ventilation must be ensured.2. At least two opposite walls must be provided

with permanent openings that cannot beclosed or blocked.

3. The openings in these outside walls must cov-er at least a third of the total wall area of theparking level in question. When calculatingthe wall area, both outside walls and parti-tioning walls must be included. Alternatively,the area of the ventilation openings must beat least 2.5% of the parking level floor area.

4. The distance between opposite walls mustnot exceed 54 metres.

> 5 m

< 54 m

≤ 1,3 m

A≥ A1

3

> 2,5% A

Natural cross-ventilation

Open car park facility

total

floor

Wall opening

3

5. There must be an open distance of at least 5m from an outside wall with ventilationopening to the nearest building.

6. Partitioning walls must not impede naturalventilation.

7. The lowest parking level must be no deeperthan 1.3 m below ground level.

If just one of these requirements is not met, theparking facility is classified as being a closed carpark and forced ventilation must be used in thesection concerned.

Closed car parks are characterised by:

1. Outside walls that are more than 54 m apart.2. Only a single outside wall with ventilation

openings, or openings that can be blocked.3. Ventilation openings, if any, that do not

meet the requirements on open car parks(see definition on page 3).

4. Underground car parks with no ventilationopenings.

5. A distance of less than 5 m to neighbouringbuildings.

6. A depth of more than 1.3 m below groundlevel.

7. Partitioning walls that impede natural venti-lation.

If just one of these conditions applies, forced ven-tilation must be used.

Conventional ventilation methods in car parksPresently, four different ventilation methods areused in car parking facilities, depending onwhether the car park is open or closed.

Natural ventilation by means of wind and thermalconditions is used in open car parks.

Fan-assisted natural ventilation is similar to theabove, but supplemented with a fresh-air fan orexhaust fan. Such systems may also include ducts(fig. 2) or jet fans.

Conventional ventilation is used in closed carparks. It consists of both fresh-air fans and ex-haust fans in combination with ducts for trans-porting air (fig. 4).

Simple conventional ventilation is used in closedcar parks. Such systems also consist of fresh-airfans and exhaust fans, but no ducts are used.

Fig. 2

Semi-natural ventilation

4

In practice, there are several problems with con-ventional ventilation systems.

For example:

• There is no or insufficient room for inlet and/or exhaust ducts.

• There is no guarantee that the system willprovide sufficient ventilation.

• So-called "dead" corners with little or noventilation may result.

• There is no room for ducts. • Smoke control in case of fire is not consid-

ered during system design.• The possibility of regulating the level of ven-

tilation in response to variable requirementsis not considered.

• Fire protection installations such as fire doorsand fire walls prevent an unobstructed viewof the car park.

Novenco jet ventilation systems can be adapted tocover needs for both CO ventilation and, in spe-cial circumstances, smoke control in case of fire.Considerable energy savings are also possible iflarge facilities are sectioned into independentzones.

Semi-mechanical ventilation

Fig. 3 Fig. 4

Mechanical ventilation

Top view Side view

Air inlet

Air outletConventional system with ducts

5

Principle of jet ventilationIn conventional ventilation systems, all air isdrawn through fans and ducting. This applies toboth the fresh air supplied and the spent air dis-charged. To prevent pressure drop, air velocity iskept as low as possible. However, this means thatducts must be relatively wide, thus requiring con-siderable space.

In jet ventilation, a different approach is taken.Here, a small quantity of air is sucked into a fanand then ejected at high velocity. When this airhits the air in front of the fan, it thrusts it for-wards while at the same time drawing the sur-rounding air along with it. In this way, all the sur-rounding air is set in motion and transported overa distance of 20-40 metres without the use ofducts. The entire car park functions as a duct. Theprinciple behind jet ventilation is the same asused in rockets, where a small quantity of air(combustion products) is forced from the burnerat high velocity, thus thrusting the rocket up-wards.

As the fan is firmly secured, all energy is trans-ferred from the ejected air to the surroundings inthe form of a velocity. The fan stays in place whilethe air is driven forwards.

As a result of entrainment, the quantity of air inmotion will always be considerably greater thanthe quantity of air passing through the fan.

The quantity of air in motion is the same in diffe-rent cross-sections of the facility. Depending onsystem dimensioning, an average velocity of, forexample, 1 m/s can be achieved.

The necessary size and number of jet fans dependon the size and layout of the car park and onwhether the system is primarily to be used for COventilation or also for smoke control.

Fig. 5a

Fig. 5b

Figures 5a and 5b illustrate jet ventilation in prac-tice. Both figures are in longitudinal direction.

Thrust, the force generated by jet fans, is ex-pressed in Newton [N] and is the product of themass flow rate and the change in velocity. It is theunit of measurement for jet fans, in contrast toconventional fans whose output is measured inm3/s or Pa. Jet fans are typically installed beneaththe ceiling (figs 5a and 5b).

It is important that jet fans be positioned in themidst of the air they are to set in motion.

In theory, assuming that the surrounding air haszero initial velocity, the thrust generated by a jetfan is equal to the volumetric flow rate times thedensity of air times the outlet velocity.

Jet fans running; side view

Air velocity profile; top view

Jet fans running; top view

Air velocity profile; top view

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Fig. 6

For optimum efficiency, jet fans should be sus-pended completely freely.

In practice, they are installed as close to the cei-ling as possible to provide maximum clearance be-neath the fans. Air tends to adhere to even sur-faces. This phenomenon, known as the Coandaeffect, is of great importance for overall efficien-cy. To compensate for this, Novenco jet fans areequipped with directional grilles that bend the airflow away from neighbouring surfaces.

Overall efficiency is also affected by inlet and out-let conditions. Compensation must be made forobstacles in the vicinity of the fans.

As previously mentioned, nominal thrust equalsmass air flow times the outlet velocity.

The effective thrust is the product of the nominalthrust and a "system efficiency factor", and is al-ways less than the nominal thrust.

Figure 6 illustrates the way in which jet fans canbe installed to provide space-saving ventilation ina car parking facility. Note that, in order to

achieve the greatest possible effective output,there must be at least 0.5 m to the nearest girderon the inlet side and 2.0 m on the outlet side.Girders should be no more than 0.4 m in height.Otherwise, girder height must be compensatedfor, either by suspending the fans beneath theceiling or by increasing the distance to the nearestgirder.

This section provided a brief introduction to thebasic theory of jet ventilation. The following pag-es will describe its use in practice.

No room for ducts

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In car parking facilities, jet fans can be used to re-place ducts for the extraction of both CO and ex-plosive petrol fumes (CH4). The presence of CO ina car park indicates that other hazardous fumes(e.g. benzene) are also present. As a result of this,the German authorities have reduced the limitsfor CO in car parking facilities from 100 ppm to50-60 ppm, depending on the federal state inquestion. Ventilation is activated by sensors in thecar park for monitoring the level of CO and CH4.The necessary number of sensors depends on thelayout of the car park and varies between one per100 m2 to one per 500 m2. CH4 sensors are nor-mally installed close to the ground (approx. 30 cmabove the ground) while CO sensors are installedat head height (approx. 150 cm above theground). If sensors with 4-20 mA output are used,these can be connected to a CTS control system,thus allowing limits to be adjusted.

Fig. 7

Figure 7 illustrates the possible design of a closedsystem consisting of jet fans and an exhaust faninstalled in a shaft. The extraction unit typicallyconsists of a grille, an exhaust fan and, if neces-sary, a sound attenuator. When the set limit is ex-ceeded, the exhaust fan is started first, followedby the jet fans.

In open car parks (see page 4), where no ventila-tion is required, natural ventilation can be assist-ed by jet fans, thus preventing the occurrence of"dead" areas. The same applies to parking facili-ties that only just fail to meet the requirementson open car parks. Here too, requirements can of-ten be met using jet fans alone. In such cases it isoften best to use 100% reversible Novenco fans.These fans are capable of providing the samethrust in either direction so that the direction offlow can be changed to suit wind conditions.

8

Jet ventilation for smoke control With respect to fire control in underground carparks, many conditions, both technical and legis-lative, must be considered.

In Denmark, standards are currently being pre-pared. These will be based on function require-ments rather than systems, but details of theseare as yet unavailable.

Previously, requirements on fire protection werebased on walls, doors, gateways, horizontal divi-sions, and sprinkler systems.

All these delay or stop the spread of fire. Howev-er, when fires occur, most casualties are notcaused by the fire itself but rather by the smoke itproduces.

That is why smoke extraction systems are current-ly required to fulfil various functions. They mustbe capable of:

• Extracting smoke so that people present inthe car park can escape before being over-come by the smoke.

• Controlling smoke so that firefighters canenter the car park, localise the fire and getclose enough to it to be able to extinguish it.

Specific requirements are often set by the localfire authority.

In the case of underground car parks, it is impor-tant to note that there will be no smoke-free lay-er due to the relatively low ceilings (approx. 2.5m). The area surrounding the fire will becomefilled with smoke, which will spread to surround-ing areas (fig. 8C). Figure 8 illustrates this situa-tion in a closed car park. Fresh air is drawn in, andspent air discharged, by means of axial flow fanswhile air is transported across the car park bymeans of jet fans.

Jet fans running; top view, fig. 8a

Jet fans running; side view, fig. 8b

Jet fans not running; side view, fig. 8c

Fig. 8

9

In case of fire, the jet fans are turned off and thefresh-air and exhaust fans are switched to maxi-mum power, corresponding to the necessarysmoke extraction rate. This allows anyone in thecar park to escape. Once the building has beenevacuated or the fire brigade has arrived, the jetfans are turned on, thus forcing air towards theexhaust fan. This provides two benefits:

• Firstly, smoke accumulates in a relatively lim-ited area (figs 8a and 8b), allowing the site ofthe fire to be located and the fire extin-guished.

• Secondly, the temperature in the immediatevicinity of the fire is reduced, allowing fire-fighters to get closer.

• As an additional benefit, damage to thebuilding is minimised as the large quantitiesof air cool the smoke and building surfaces.

It is important to note that, in relation to CO ven-tilation, smoke control requires a many-fold in-crease in the quantity of air taken in and dis-charged. The system must therefore be dimen-sioned for smoke control if this is required.

The use of jet fans for smoke control purposes re-quires that all possible fire scenarios be analysedin detail.

• Where are escape routes located?• How long will it take to evacuate the car

park?• What is the expected output of a fire?

What if more than one car catches fire?• How much smoke is expected, what is the ex-

pected smoke temperature and how will itaffect visibility?

• How long will it take for the fire brigade toarrive?

• What are the action plans in case of fire?• Where can smoke be extracted?• How is a car fire expected to develop?

From the above-mentioned points, it is clear thatthe local fire brigade has an important role, andplanning should therefore be performed in closecooperation with the fire authorities.

Several of the above-mentioned points have beeninvestigated by Novenco in the Netherlands inlarge, full-scale tests of jet fan ventilation. The re-sults of these tests are presented on page 18.

10

As previously mentioned, Novenco has played aleading role in the development of car park ven-tilation systems. The following provides a briefsummary of the benefits to be achieved from us-ing jet ventilation in car parking facilities:

1. Space savingThere is no need for space-consuming ductsin the car park, thus allowing the ceiling tobe lower. This allows a better use of limitedspace in underground car parks and im-proves layout.Jet fans transport and distribute fresh airwithin a "giant duct" – the car park itself.

2. Flexible installationVarious tests have shown that jet fans can beflexibly positioned. Individual fans can bepositioned within a radius of 2 m without af-fecting system efficiency.

3. Complete mixing of airWhen jet ventilation is used, directional"thrusts" of up to 45 m can be achieved.Firstly, this allows complete air mixing andefficient CO dilution. Secondly, it allows airto be directed into "dead" corners wherethere would otherwise be a high risk of COaccumulation. With conventional ventilation systems whereair is extracted through ducts, such pocketsof high CO concentration may easily arise assuction cannot be directional.

4. Improved ventilation of the entire car parkWith a conventional duct-based extractionsystem, a comprehensive network of ducts isrequired if all areas of the car park are to re-ceive sufficient ventilation. Such ducts maycause problems for the design and layout ofunderground car parks.All such problems can be avoided withNovenco jet fans.

5. Energy savingsJet fans can be arranged in groups, control-

led by corresponding groups of CO or CH4sensors. The quantity of air to be moved canthus be regulated in response to require-ments. As this is achieved at relatively low airvelocities, energy is saved. Energy costs cantypically be reduced to approx. 60% whenjet fans are used.In conventional systems, relatively high airvelocities are used in order to reduce ductsize, and this results in large pressure drops.When ventilation is required, the entire sys-tem is started, and energy unnecessarilywasted. This cannot be avoided as all ductsare interconnected.

6. Cost savingsThere is no need to install ducts when jetfans are used in car parking facilities. Inclosed car parks there need only be a fresh-air inlet and spent-air outlet. Pressure drop isthus limited to that occurring in damper,sound attenuator (if any) and shaft. This al-lows smaller motors and fans to be used,thus reducing sound levels.On the other hand, jet ventilation systems re-quire more cabling and larger electrical cab-inets. However, even including these costs,jet ventilation systems are typically 30%cheaper to purchase and install than conven-tional systems.

11

Fire tests at TNO

7. Simple adjustmentDuct-based ventilation systems are often fit-ted with grilles that must be adjusted toachieve the required ventilation.This is not necessary with jet ventilation sys-tems as the fans are equipped with a direc-tional grille that bends the air flow awayfrom walls and ceilings. These grilles are fac-tory-set and seldom require readjustment,although adjustment can easily be per-formed on site if necessary.If there is no need for full ventilation, thequantity of air can be regulated by runningthe jet fans at half speed or by only operat-ing a group of fans at a time.

Smoke control

While there has been no doubt about the benefitsof jet ventilation for CO extraction, there wassome discussion in the Netherlands in the early1990s about the suitability of jet ventilation sys-tems for smoke control. Due to a lack of realistictests, the fire authorities were reluctant to ap-prove jet ventilation systems as an alternative tosprinkler systems, fire doors and fire walls. Theirreluctance was based on two objections:

• Early tests were performed with cold smokeand did not live up to expectations. Cold

smoke has a different density than the hotsmoke produced by a fire. Cold smoke there-fore behaves differently from hot smoke,and the results of tests using cold smoke can-not accurately describe a fire situation.

• It had yet to be proved that jet ventilationcould replace sprinkler systems.

Novenco convinced the Dutch authorities of thenecessity for full-scale tests which, under realisticconditions, could determine whether the systemshould be approved. In June 1998, such tests wereperformed in cooperation with TNO (NetherlandsOrganisation for Applied Scientific Research). Theresults of the tests are summarised on page 18.

The tests consisted of 18 different full-scale firesin a closed car park. The purpose was to testNovenco’s calculation model and to develop mod-els for use in CFD simulation software.

Data and experiences from all the fires were col-lected in a report which has since provided a basisfor the use of jet ventilation for smoke control incar parks.

Today, jet ventilation systems reign supreme inthe Netherlands and have completely oustedsprinkler systems and conventional duct-basedventilation systems.

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Design criteria

Regarding the practical design of jet ventilationsystems, determining the following five factors isof particular importance:

1. CO production2. Ventilation quantity3. Direction of air movement4. Noise levels within and outside the car park5. Ventilation and extinguishing strategy in

case of fire

Re 1: CO production

Several factors affect the amount of CO pro-duced. More modern cars produce less pollutionthan older models as a result of improved com-bustion and the use of catalytic converters. Coldengines produce more CO than hot engines.Speed also affects CO production. All these fac-tors must be taken into account when designingventilation systems. They also explain why COproduction values differ from country to country.Some countries have relatively many old carswhile in other countries, a greater proportion ofthe cars are new.

There are no standardised regulations in the Nor-dic countries, but a model for calculating the re-quired air quantity for CO ventilation is normallyused. The model calculates a necessary ventilationflow on the basis of the number of parking spac-es, the distance travelled to reach them and thenumber of cars arriving and leaving per hour. Theinput data on CO production does not differenti-ate between cold and hot starts. Nor does it takeinto account the acceptable CO concentrationwithin the car park, the CO concentration of theair outside the car park, or whether the car parkis part of a shopping centre or housing complex.

Since catalytic converters were introduced, theproduction of CO by cars has fallen dramatically inrelation to other combustion products. In Germa-

ny, this has meant that CO is now considered as anindicator for other hazardous gases, includingNOx and benzole. As a result, permissible CO lim-its have been reduced from 120 ppm to 50-60ppm which, with certain modifications, apply inthe individual federal states. The specified limit isan average value for a 30-minute period.

If the fresh-air intake is from a street with heavytraffic, the CO concentration of the intake airshould be set to 5 ppm, while in suburban areaswith light traffic, the CO concentration can be as-sumed to be zero.

An engine produces more CO when it is cold thanwhen it is warm. VDI, the German Association ofEngineers, recommends the following engineemission values:

Hot engine: 0.008·s [g]Cold engine, s<80 m: 7. 6 [g]Cold engine, 80 m<s<500 m 0.89·s0.49 [g]

where s is the distance driven inside the car park.

Re 2: Ventilation quantity

The following calculations are in accordance withthe German standard VDI 2053 Jan 2002.

Formula for determining the quantity of CO, qCO:

qCO= P×e [m3/h] ρCO

where

P = the percentage of parking spaces vacatedor occupied per hour

e = emission valueρCO = density of CO = ρCO 1.16 kg/m3 at 20°C

Note that qCO is calculated for all cars in motion,i.e. cars that start and leave, and cars that arriveand are therefore hot. It is thus a calculation ofqCO.

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Formula for calculating the necessary ventilationquantity, Q:

COperm = the permissible CO concentration inppm. There are no standards for COperm in Den-mark, but VDI 2053 provides recommended limits.

COout = the CO concentration of the outside air inppm. There are no standards for COout in Den-mark, but VDI 2053 provides recommended limits.

fg = a system factor, varying from 1.0 to 1.5fg = 1.0 for jet systemsfg = 1.25-1.5 for duct-based systems

ΣqCO = (qCO × n1 + qCO × n2 + ·····+ qCO × nn)

n1 = the number of parking spaces to be venti-lated in the level/section under considera-tion

n2 ··· nn = the number of parking spaces in other sections accessed through n1

s1 = the average distance driven in n1s2 = the average distance driven in n1 by cars en-

tering/leaving n2

As previously mentioned, P is the percentage ofall parking spaces that are vacated/occupied perhour. It is also known as the parking frequency.

P varies greatly, depending on the location of thecar park. With certain reservations, the followingP-values may be used:

Housing complexes 20-60%Shopping centres 70-150%Office blocks 50-70%Sports centres 100%Theatres 100%

With regard to housing complexes, the parking pat-tern must be determined. Is there a steady stream oftraffic throughout the day, or do all cars leave at thesame time in the morning and return together inthe evening? The parking pattern may thus result in

considerable fluctuation in the quantity of fresh airrequired to ventilate the car park, and P must there-fore often be evaluated from case to case.

Note that parking frequency is based on the totalnumber of entries and departures per hour.

If 25% of the parking spaces are vacated per hourand 25% become occupied, the parking frequen-cy is 50%. In this case, CO production must be cal-culated for both cold and hot engines.

An example of calculating ventilation re-quirements

Consider a two-storey car park (levels 1 and 2)with the following characteristics:

Morning traffic

Type: Housing complex parking facility

fg = 1.25 (well designed duct-based parking facili-ty, i.e. optimum design with respect to ducts)

P = 60% (per hour)n1 = 174 spacesn2 = 106 spaces

The total average distance driven (S) is calculatedas half the distance travelled (sn) plus a distancefor parking manoeuvres (sman) plus the length ofthe entry/exit ramp (srmp).

Sn = (sman + ½ × sn + srmp)s1 = 134 ms2 = 156 msman = 10 msentry = 40 msexit = 40 m

Note that the distance driven within the car parkcan only be calculated correctly from drawingscontaining the routes taken. On the basis of theabove data, the total average distance driven (S)for the two levels can be calculated as follows:

S1 = (10+134/2+40) = 117 mS2 = (10+156/2+40) = 128 m

Q qco∑ fg×

COperm COout–----------------------------------------------[m3/h]=

ramps⎫⎬⎭

14

As the traffic under consideration is morning traf-fic with cold engines (see pages 12 and 13):

qCO1 = P×e [m3/h]ρCO

= 0.6×0.89×1170.49/(1.16×103)=0.0048 m3/h/car

qCO2 = P×e [m3/h]ρCO

= 0.6×0.89×1280.49/(1.16×103)=0.0050 m3/h/car

In this example, COperm is assumed to be 50 ppmand COout to be 0 ppm.

The necessary ventilation quantity (Q) can then becalculated as:

Q = (qCO1×n1+ qCO2× n2)×fg

COperm-COout

Q = (0.0048×174-0.005×106)×1.25

(50-0)×10-6

Q = 34,130 m3/h

Had the parking pattern been different, for ex-ample more evenly distributed throughout theday, the parking frequency, P, could have beenhalved to 30%. This would also halve the neces-sary ventilation air quantity, i.e. to approx. 17,000m3/h.

Evening trafficThe necessary ventilation quantity in the eveningwhen the cars return can similarly be calculated asfollows:

qCO1 = 0.6×0.008×117/(1.16×103)=0.00048 m3/h/carqCO2 = 0.6×0.008×128/(1.16×103)=0.00053 m3/h/car

Q = (0.00048×174-0.00053×106)×1.25

(50-0)×10-6

Q = 2,800 m3/h

It is extremely important that the correct assump-tions be used when designing car park facilities.Such information is only available from the carpark owner and the consulting engineer as theyknow the assumptions made for the project.

Please note that the calculations in the above ex-ample are only applicable to CO ventilation andmust not be used for smoke extraction or controlin case of fire. Significantly greater ventilationquantities are required for smoke control pur-poses and the technical installations used mustmeet special requirements on heat resistance.

Re 3 Direction of air movement

The greatest possible distance between fresh airintake and spent-air discharge must be ensured.Usually, the access ramp is used as the fresh-air in-take, while an exhaust fan is installed in the oppo-site corner.

Re 4 Noise levels within and outside the car park

It is important that requirements on noise levelswithin and outside the car park and the most ex-pedient location for the exhaust system be consid-ered early in the project planning phase. Usually,it will be necessary to use sound attenuators, andspace must be set aside for these and for a shaft.

Re 5 Ventilation and extinguishing strategy in case of fire

If the system is to be used for smoke control, it isimportant that the local fire authority be involvedat an early stage so that the most suitable strate-gy can be determined.

15

General aspects of car park layoutWhen dimensioning an underground car park, itis important to consider the location of air inletsand outlets. In most cases, it will be necessary toinstall an exhaust fan that can discharge the pol-luted air via a ventilation shaft. Out of considera-tion for the surroundings, unsuitable shaft loca-tions must also be determined. It may be possibleto disguise the shaft so that it blends with the sur-roundings, e.g. as an advertising pillar at a shop-ping centre.

When dimensioning the exhaust fan, the pres-sure drop through the entire system from thefresh-air intake to the discharge outlet must betaken into account. Usually, it is best to transportair through the discharge system by means ofsuction rather than pressure as this preventsspent air unintentionally spreading to otherparts of the building. Fans are used to distributeair within the car park and to ensure that "dead"areas do not occur.

Axial flow fans

In most car parks, clearance is limited to approx.2.4-2.5 m. It is therefore important to ensure thatfans are installed where there is no risk of colli-sion.

Alternatively, the clearance required by the con-sulting engineer must be taken into accountwhen choosing fan size and/or location.

It is important to note whether the car park hasvisible girders as these may affect fan efficiency.There must be a free distance to the nearest gir-der/wall of at least 0.5 m on the inlet side and 2.0m on the outlet side. If girder height is greaterthan 0.4 m, it may be necessary to lower the fans.Ceilings without girders provide ideal conditionsfor the ventilation system and make the car parkaesthetically pleasing.

16

Car park

Car parks have many noise sources – the most im-portant being the cars themselves. The noiseemitted by cars in motion is often about 75-80dB(A). There may also be technical installations inthe car park that contribute to the overall noiselevel. Exhaust fans are also a source of noise.

Depending on size and speed, the noise emittedby jet fans varies between 45-66 dB(A) per fan.Such fans are therefore insignificant noise sourcesin comparison with other sources within the carpark.

As standard, jet fans are supplied with dual-speedmotors.

They are usually dimensioned to run at half speedmost of the time and their noise emission will thus

seldom be a problem. In extreme situations, thefans can be switched to full speed.

If the system includes an exhaust fan, the noiseemitted by the fan must comply with applicablebuilding regulations. There may be differences inthe permissible noise level depending on location(industrial site or housing complex). Similarly, thetime of day may affect the permissible noise levelclose to property boundaries or the windows ofhousing complexes.

Noise emission

17

Fire tests at TNO

It was mentioned in the preface that the mainpurpose of this booklet was to describe CO venti-lation. To underline the difference between COventilation and smoke control, the following con-tains a brief summary of the results of fire testsperformed in the Netherlands.

Novenco participated in a comprehensive seriesof tests in Amsterdam designed to create basicdata for use in simulation models of fire out-breaks in car parks. The following authorities par-ticipated in the tests:

• TNO (Netherlands Organisation for AppliedScientific Research)

• Netherlands Ministry of Finance• Amsterdam Fire Brigade• Buildings Department• Amsterdam Parking Administration

Besides evaluating technical requirements, thetests were designed to investigate the efficiencyof the Novenco system for smoke control and ex-traction.

Novenco supplied and installed fans in the carpark while TNO was responsible for recording da-ta, e.g. the temperature of the smoke, air andconcrete.

Cars were set alight at three different points inthe car park and in each case, data was recorded

for the way in which the fire developed, visibility,smoke production and the length of time takenfor the fire to spread to neighbouring cars.

In addition to investigating the Novenco system,tests were also performed with a conventionallydimensioned duct-based system.

Altogether, data was collected from 18 separatefires with up to three cars being set alight simul-taneously. The tests thus provided valuableknowledge on necessary system dimensions andthe way in which car park fires behave.

80 m

35 m

Various parkedcars

Various parkedcars

Various parkedcars

Place of fire Visibility measurement

Temperature measurement smoke/air

Temperature measurement in concrete

Radiationmeasurement

Fire protection

18

The conclusions of the tests are as follows:

• Conventional duct-based ventilation systemsare unsuitable for smoke control purposes,even with air change rates of 8 times perhour. The entire area quickly becomes filledwith smoke and locating the fire is difficult.

• For smoke control, the exhaust fans musthave a capacity of at least 250,000-400,000m3/hour, depending on fire size and car parklayout.

• While the car park is being evacuated, the jetfans must be switched off as they otherwiseincrease the mixing of air and smoke.

• If the jet fans and exhaust fans are run at fullspeed after evacuation is complete, thespread of smoke can be kept within a limitedarea. The fire also remains visible at all times.

• This allows fire development to be observedduring the entire extinguishing process, thusproviding improved safety for the firefight-ers and faster fire extinction.

• Such powerful ventilation also keeps thetemperature down, thus minimising damageto the building.

• Sprinklers are not necessary. Water damagecan thus be minimised and there is no risk ofpetrol from leaking petrol tanks beingspread via water from a sprinkler system.

• Tests with cold smoke are not representativeof fire situations.

• The quantity of air to be extracted also de-pends on car park layout.

• Car parks can be emptied of smoke up to fivetimes faster than conventional duct-basedsystems with air change rates of 10 times perhour.

• Jet ventilation allows unconscious casualtiesto be located and given treatment morequickly.

Novenco has video recordings showing the differ-ence in smoke control between jet ventilation sys-tems and conventional systems.

ConclusionClosed car parking facilities are ventilated moreefficiently by Novenco jet fans than by conven-tional duct-based systems.

In comparison with conventional systems, spacecan be saved, and installation and running costsreduced.

Thanks to the design of the jet fans, most currentrequirements on sound emission can be met.

Large differences exist in ventilation require-ments for CO ventilation and smoke control, par-ticularly in small car parks.

Novenco develops and manufactures

ventilation and fi re fi ghting systems that

are marketed and distributed world-wide

through subsidiaries and agents.

The company was founded in Denmark

1947 and has become one of the

world-leading suppliers.

Novenco symbolises quality and environ-

mentally friendly products. The company

is certifi ed according to ISO 9001 and

ISO 14001.

The headquarters of Novenco is located

in Naestved, Denmark.

Novenco, Hi-Pres and XFlow are

registered trademarks of Novenco.

Read more about Novenco on the

Internet.

Novenco A/S · Industrivej 22 · DK-4700 Naestved · Denmark · Tel. +45 70 12 42 22 · Fax +45 55 75 65 50

www.novenco.biz

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