Car Park Ventilation Tips and Advice

"Cheap is not always cheerful"

In recent surveys of car park ventilation systems, some alarming shortcomings have been brought to light, particularly regarding the application of jet fan systems. There are a range of inadequacies ranging from basic poor design where substantial areas of the car park are devoid of ventilation by schemes originally designed to ventilate and control smoke but in reality are incapable of achieving this objective.

Jet fan systems have been around for several years and with over 95% of new installations being jet fan systems, people feel that it cannot be overly difficult to design these systems themselves and simply purchase the fans. Even systems designed and installed by some so called specialists however have revealed substantial shortcomings.

Simple misunderstanding of regulations and lack of knowledge of fan installations help explain how many of these problems arise. A recent investigation on one installation revealed two axial main extract fans installed in parallel, discharging into a common plenum. Whilst this was correct, they were also installed without non-return dampers fitted to the fans. This would mean should one of the installed fans fail, there would not only be a loss of performance in that fan but also a substantial reduction in the overall performance of the second fan caused by air short-circuiting through the failed fan.

There have been scenarios where the fire strategy has been accidently or purposely disregarded. Another example was an installation where the fire strategy required an advanced smoke control systems which could ensure that access to lobbies were kept free from smoke contamination in the occurrence of a fire in the car park. The reality was far from the requirements, with the most basic of smoke clearance systems being installed, no meeting the requirements at all. The most worrying aspect of this case is that between the consulting engineer, the building control officer and the client, none picked up on this and instead only recently was it identified by a fire officer and thus we were called in.

Why does this occur? The main motive is cost and the "design & build" culture in which the original objectives created by the architect, consulting engineer and fire engineer become lost, disregarded or forgotten against the background of Value Engineering.

This is not to say there is anything wrong with Value Engineering if the original objectives and strategy are met; however these can be easily forgotten and conveniently ignored when the contractor, encouraged and guided by a fervent pseudo-specialist who promises wonderful cost savings. When told by a specialist that the system will be “fully code compliant” and will meet all building regulations, it becomes very plausible and it may very well be the case. Conversely what has been overlooked is the initial enhanced design specification that was agreed at the opening design stage and against which relaxations were granted by building control on the requirement for sprinklers and the ventilation of access lobbies.

This can result in a range of problems. It could be several months later that the error may be identified. This leads to an expensive process of correcting the mistake, therefore rendering the once wonderful savings pointless as the initial savings become a drop in the ocean compared to costs of correction. Most importantly, not only could the handover of the building be delayed but if these shortcomings are not ultimately identified, the occupants and residents of the building could be put at considerable risk.

So how can we prevent this in the future? Through a fundamental understanding of how the original system design was developed and why. If apparent savings offered by alternative suppliers of specialists systems appear too good to be true, then the chances are they are and discussions with the companies involved in developing the original design should always be consulted in order to gain a full appreciation of the design requirements and objectives that must be obtained.

Richard Brooks

Richard Brooks is General Manager of the Advanced Smoke Group with over 35 years experience in the smoke control industry. He was Chairman of the Smoke Control Association 2002 – 2004; Chairman of the Association’s working group on the guide to the Ventilation of Loading Bays, Service Yards and Coach Parks; a member of the British Standards Institute Fire Engineering Group (FSH25) and a member of the BSI working group, drafting BS7346: Part 7: 2006 for Car Park Ventilation.

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Maximising the Efficiency of Car Park Ventilation Systems

Whilst a number of car park ventilation companies nowadays install CO monitoring as a standard feature, little consideration appears to be given to fully exploiting the true potential of environmental monitoring and, consequently, many car parks are still the source of high energy costs.

1. System design criteria – day to day operation and smoke extract

All car park ventilation systems are required to be designed to meet the performance requirements of the current building regulations. The relevant regulations and standards relating to car park ventilation are as follows:

Approved Document F1 – This document sets out the minimum requirements for the day to day ventilation of naturally and mechanically ventilated car parks. It specified the maximum permissible carbon monoxide levels of 30ppm averaged over 8 hours, with levels not exceeding 90ppm for 15 minutes.

With the introduction of carbon monoxide (CO) monitoring within car parks during the last 10 years, car park environmental control has become far more efficient, enabling the ventilation rate to be accurately linked to the level of vehicle exhaust pollution within the car park.

Approved Document B3 – Covers the provision of natural ventilation under fire conditions for “open sided” car parks and mechanical ventilation for those car parks which are “not open sided”.

Naturally ventilated car parks require a minimum 2.5% of the net floor area of the car park in openings linked directly to atmosphere with at least 50% of the opening being split between

two opposing walls. The minimum airflow rate for a mechanically ventilated car park is 10 air changes per hour under fire conditions.

BS7346: Part 7: 2006 – Specifies the requirements for one of three design options,

1. smoke clearance
2. aid to fire fighting and
3. means of escape

The document further sets out standards for controls and powers supplies, the criteria for CFD modelling and for commissioning of systems.

2. Maximum Efficiency System Control

Whilst it is, of course essential to design for a fire condition, most car park ventilation systems are ever employed within a fire scenario. Most car park ventilation system currently installed are notoriously inefficient, simply working on the basis of providing 6 air changes per hour for day to day ventilation or 10 air changes per hour for a fire condition.

Even when the car park ventilation “specialist” designs for a variable rate of ventilation, it is only the main extract fans that are actually controlled, most or all of the jet fans are activated in a day to day ventilation condition with no variation in speed to the jet fans.

Advanced Smoke Group now install the ASG “MAX-EFF” car park ventilation system as standard, employing an addressable CO monitoring system which enables the activation and speed control of not only the main extract fans, but also the impulse fans, thereby maximising the energy saving applied to the system.

In larger car parks, control of the jet fan activation and speed will significantly reduce the power taken by the fans and make corresponding saving in operating costs.

3. Smoke Control

Obviously, it is vitally important to remember that the system may be required to operate in a fire condition, consequently, in order to comply with the latest guidance on the use of smoke extract fans linked to frequency inverters the control of the system must take account of the need to “link out” all protection normally afforded to the fan motor under day to day operation.

The Author

Richard Brooks is the General Manager at Advanced Smoke Group with 30 years experience in the smoke control industry and specialising in car park ventilation for 11 years.

Chairman of the Smoke Control Association 2002-2004 and chairman of the Association's working group on the guide to the ventilation of Loading Bays, Service yards and Coach Parks.

Member of the British Standards Institute Fire Engineering Group (FSH25) and member of the BSI working group drafting BS7346: Part 7: 2006 for car park ventilation