Case Study

With increasing amounts of road traffic and continual inner-city office developments, the inevitable question of where to create new parking space is ever prevalent. Multi-storey and underground car parks are the logical solution for bustling city centres. However, they have stringent ventilation and fire safety issues which add complexity and considerable expense to the project.

The systems use the reliable Optidrive Eco variable frequency drive from Invertek to provide many installation and operational cost savings. Headroom is also increased by eradicating the need for unsightly ventilation ducts.

The galvanised ducting is replaced with a series of impulse or jet fans which are fixed in strategic locations within the car park. They combine forces with larger extraction fans which are installed in plant rooms away from the public gaze. This powerful fan combination ensures air is changed regularly during normal operation and can remove smoke and fumes quickly should an emergency fire situation occur.

The exact location of the impulse fans are calculated using Computational Fluid Dynamics. This is a software simulation process where each fan is positioned in a computer program to map how and where fumes and smoke flow through the car park during various conditions. This allows the designer to locate the optimum fan positions prior to installation.

Crawford Controls developed a control system using Invertek's Optidrive Eco drives. The system controls fan activation and adjusts set speeds according to the CO levels detected within a period of time. The system also responds to fire or smoke detection with an emergency smoke clearance mode.

Each car park is installed with carbon monoxide detectors and a fire alarm or smoke detection system. When low-levels of CO are detected the fans initiate at low-speed and start agitating the air to dilute the gases and direct airflow toward the larger extract fans. If CO levels do not fall within a given period, a second higher level of detection will increase the fan speed further and so on.

Controlling fan activation and fan speeds in this way means substantial amounts of energy and unnecessary wear and tear can be saved.

On detection of a fire; the system utilises the inverters soft-start function to ramp all the fans up to full speed, while ensuring minimum power and mechanical stress is applied to the system as a whole.

Technical and Commercial Challenges

With as many as 40 Impulse fans within a system it is uneconomical to have one inverter per fan. Fire environments also require controls to be protected for at least 1 hour, so it is difficult to install any control components within the Car Park itself.

All of the fire related controls must be installed away from the car park in a safe area, usually a plant room, with only the actual detection devices in the car park. Unfortunately inverters are not ideally suited to long cable runs and can suffer from capacitance problem particularly when using MICC cable.

With assistance from Invertek Drives, Crawford Controls has been able to overcome the problems both technically and cost effectively by running groups of fans from a single inverter with up to 800m of cable attached in a parallel formation! All control components are mounted at the main panel and in the case of multiple fan inverters, an output choke is fitted to overcome the inherent problems of capacitance in long parallel cable runs.