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Designing & Implementing Car Park System

Description

Estimating fan quantities

For the purpose of estimating costs, the steps on the following pages may be bypassed. Allow 5N of thrust per 100m²of car park floor area to approximate the number of fans required.

The following steps are sufficient to create an initial ventilation system design. A Computational Fluid Dynamics (CFD) analysis is often required to prove and further refine the design. Fans may need to be re-orientated, or in some cases, added or removed.

A ventilation system can be tailored to suit virtually any car park. Before considering fan locations, the system layout will need to be identified. Refer to the previous section for information relating to system layouts and their suitability for particular car parks.

Step 1 - Assessing Car Park Geometry

First identify the supply and exhaust points in the car park. A system that complements the natural air path and is able to circulate or move air effectively within the car park should be chosen. Certain layout features may assist the effectiveness of a particular layout as shown below:

(a) ‘Natural air path’

Preferred natural air path

Natural air path to be avoided

For ‘Linear Flow Systems’, supply and exhaust points should be spaced across the length of a car park.
‘Circular Mixing Systems’ are more tolerant of closely placed supply and exhaust points, but it is advisable to have a good amount of separation.
Supply air points should include access ramps to outside.
The ventilation system layout should complement the natural air path from supply to exhaust points.

(b) Ceiling features

To make the system more effective, position JetVent Fans in-line with supporting ceiling beams. If this is not possible, the system becomes less effective and more fans may be needed.

Fan’s air movement parallel to beams is most effective

Fan’s air movement perpendicular to beams is less effective

Sufficient vertical clearance ensures maximum flexibility in system design. JetVent Fans may be recessed between ceiling beams to minimise the height of the system.

Sufficient clearance

JetVent vertical clearance -insufficient

Insufficient clearance

(d) Obstructions

If there is no option and the JetVent Fans must blow across ceiling beams, they have to be positioned a sufficient distance away from the obstruction. A horizontal distance eight times (8x) the height of the obstruction is generally sufficient. Nozzles on the JetVent units are specially designed and angled downwards for this purpose.

Obstruction too close

Obstruction out of the way

(e) Clashes with other services

Place mechanical service components, such as sprinklers, signs and pipework out of the JetVent’s discharge pattern area. Examples of these clashes are shown below.

An example of how to avoid clashes with pipe-work

Signs can impede fan throw

Pipework can impede fan throw

Jet fan layout in relation to sprinkler heads

Step 2 - Identify Fan Selection and Spacing

This table shows the maximum and recommended spacings between JetVent Fans for different levels of fan thrust. These spacing distances are guidelines for fans placed in series. When using these spacings, air velocities in most of the ventilated areas should be greater than 1m/s. AFCD analysis will determine whether this is achieved in a particular car park design. In some ideal cases, designs using the maximum distances have been effective.

Fan thrust depends on the operating speed of a particular fan unit and its thrust rating.

JetVent Selection

Step 1

Select the EC JetVent fan model based on their recommended spacing/ coverage and the space needing to be ventilated.

Operating Fan Thrust	Operating Fan Thrust	Recommended Fan Spacing*	Maximum Fan Spacing	Recommended Coverage*
48.2N	50m	60m	1000m²	JIU-CPCEC-HP
36.5N	35m	46m	730m²	JIU-CPCEC-USD
28.4N	30m	40m	560m²	JIU-CPCEC-SD
18.9N	25m	33m	730m²	JIU-CPCEC-LH
23.0N	20m	27m	350m²	JIU-CPCEC-ULH

Step 2

Select Isolator and Smoke Detection Kit

ISOLATOR KIT

HP, USD, SD, LH JetVent Models
Code: JIU-ISOLATORKIT

SMOKE DETECTOR KIT

HP, USD, SD, LH JetVent Models
Code: JIU-SMOKEKIT

ULH JetVent Model
Code: JIU-SMOKEKIT-ULH

*Recommended Spacing & Coverage figures are to be used as a design guide only and are subject to variance with respect to car park usage type, supply/exhaust rates and car park geometry. Final spacing will be confirmed via CFD analysis.

After a preliminary fan layout is completed using the spacing distances above, the layout may be checked for total installed thrust. Successful designs typically have approximately 5N of thrust per 100m2 of car park floor area. This thrust ratio also works well for estimating purposes.

Note that using higher rated JetVent fans generally makes the system more cost effective than using more lower rated fans. This is due to the requirement of less JetVent fans and hence saving on capital costs, installation costs and running costs. However, to effectively ventilate car parks with low ceiling heights, unusual or irregularly geometries, selecting more fans with smaller thrust ratings may be necessary.

Two 25N fans

One 50N fan

Step 3 - Design Example

For the purpose of estimating costs, the steps below may be bypassed. Allow 5N of thrust per 100m² of car park floor area to approximate the number of fans required.

Fans should be placed in the laneways with the air blowing along them. This is to avoid obstructions such as parked cars and also ensure that the throw pattern of the selected fan is long enough to reach the next JetVent fan.

An example of how fans are sized and placed based on floor area. [Download PDF]

Fan sizing and placement example

JetVent Design parameters;

Based on 5N per 100m² floor area, minimum total fan thrust = car park floor area x 5N/100m²
= 1920m² x 5N/100m²
= 96N
Minimum thrust criteria can be achieved with 4 x JIU-CPCEC-SD fans on preset speed (operating thrust 28.4N), total fan thrust = 28.4N x 4= 113.6N.
Fans are spaced within the 35m spacing recommendation for thrust levels.
Final fan to wall spacing under 40m maximum spacing guide lines for fan thrust. This is because the exhaust point is an area of low pressure, making it likely to enhance the fan throw distance.

ComLink Design Parameters

Aviator controls should be placed in the Mechanical Services Switchboard enclosure. The RS485 ComLink line must start at the controller and then daisy chain to all the JetVent Fans and Drives. The last connection must have an End-of-Line resistor. If the line is greater than 1,000m or includes more than 32 connected devices, then a communications repeater must be added to extend the line. A repeater can also be used where the ComLink line branches off, such as at the beginning of each level in a multi-story car park.

Fantech can provide support for electrical cabling mark-up designs, to help ensure the most efficient ComLink strategy is used.

Placement of CO sensors:
Because the guidelines for positioning CO sensors in AS/NZS1668.2:2012 is based on a ducted system, we propose that the following guidelines be used as a starting point for their placement in a jet fan system.

No part of the enclosure shall be greater than 25 metres from a sampling point. (A 50 metre diameter circle around a CO sensor can show coverage areas).
Additional detectors shall be installed in areas where people may congregate within the car park and are not within separately ventilated areas.
The most practical mounting position for a CO sensor within a car park is the support columns.
CO sensors will be more effective if placed in areas where CO levels are likely to be high. Eg. Placing a CO sensor in front of a fresh air intake is not likely to be effective.

ComLink Design Parameters

Fantech can provide support for electrical cabling mark-up designs, to help ensure the most efficient ComLink strategy is used.

Step 4 - Calculate Supply & Exhaust Rates

Section 4 of AS1668.2:2012 details requirements for ventilating car parks. In particular, sub-sections 4.4.3 and 4.4.4 of the standard outlines calculations of exhaust rates. In any of the two cases below, the exhaust air flow rate for a car park is taken as the greatest of the following calculations:

Calculation of exhaust air flow rates (L/s)

Car parks with more than 40 spaces	Car parks with less than or equal to 40 spaces
a) 2000 x F x T (minimum air quantity for one operating car)	a) 2000
b) 0.85 x P x (100 x n₁+ n₁ x d₁ + n₂ x d₂ ) x E x T	b) 2.5 x A
c) 2.5 x A (minimum air quality based on area of car park)	c) 400 n₁ x P

Supply air flows should range from 75% to 90% of the exhaust air quantity. This is based on the pressurisation of the car park, which should be 12Pa maximum.

Reference information for the calculation of exhaust air flow rates in the table above:
A = the area of the zone or level, in square metres
d₁ = the average driving distance, in metres, within the zone or level under consideration for the exit of a car parked there (see Clause 4.4.4.1)
d₂ = the average driving distance, in metres, within the zone or level under consideration for the exit of a car whose exit route passes through the zone or level under consideration, but excluding any part of the exit route designated as queuing areas and ventilated in accordance with Clause 4.6 (see Clause 4.4.4.1)
E = the staff exposure factor (E)
F = the staff usage factor (F)
n₁ = the number of parking spaces in the zone of level under consideration (see Clause 4.3.2)
n₂ = the number of parking spaces situated in other parts of the car park, having exit routes passing through the zone or level under consideration
P = the parking usage factor (P)
T = the vehicle type factor (T)

If the car park has significant queuing areas for vehicles, refer to section 4.6 in AS1668.2:2012