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